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Apollo 15

Solo Orbital Operations - 3

Corrected Transcript and Commentary Copyright © 1999-2008 by W. David Woods and Frank O'Brien. All rights reserved.
Last updated 2008-09-03
[This section primarily covers August 1, 1971, the seventh day of the Apollo 15 mission.]

[The last communication with Al Worden and Mission Control in Houston, Texas, was at 134:04:04, although Al's 7 hour rest period began 45 minutes earlier.]

[Endeavour is orbiting the Moon once every two hours and is flying with the SPS (Service Propulsion System) engine facing the direction of travel. This allows the inlet of the Mass Spectrometer to face into any lunar atmosphere and gather its constituent molecules. Other instruments operating during the rest period are the Gamma-ray Spectrometer, the Alpha Particle Spectrometer and the adjacent X-ray Spectrometer]

[The plane of the spacecraft's orbit is inclined 26° to the lunar equator because Endeavour was delivering the Lunar Module to a site at that latitude. Strictly speaking, since the orbit is retrograde, that is, opposite the direction the Moon is rotating, we should say that the orbit's inclination is 180 - 26 = 154°. 38 hours ago, Al carried out the circularisation maneuver which essentially defined his present orbit. Since that time, the Moon has rotated just over 21° underneath the plane of Endeavour's orbit and is taking Al over fresh territory. In the same period, the terminator has moved through 19½°, revealing much of the centre of Mare Imbrium for the first time.]

[CSM Flight Plan pages 3-191, 3-193, 3-195, 3-197, 3-199 and current page, 3-201.]

[The Flight plan defines the end of the rest period as 140:30 and that is exactly when CapCom Karl Henize sends the wake-up call.]

140:30:19 Henize: Alfredo, it's looking like wake-up time. [No answer.]

140:31:11 Henize: Good morning, Al. They tell me you're sleeping very well right now; I'm sorry to wake you up. [No answer.]

140:32:08 Henize: Good morning, Al. On the planet Earth, August the first is creeping in upon us, and your bleary eyed Flight - CapCom down here is standing by at your service. [Long pause.]

140:33:25 Worden: Hello, Houston. Endeavour.

140:33:28 Henize: Hello, Endeavour. Good morning. How are you doing?

140:33:35 Worden: Well, other than being rudely awakened, I'm doing fine, Karl.

140:33:39 Henize: Hey, I'm sorry that I have to do that, Al. Sounded like you were sleeping good. Hey, as the first step, can you give us High Gain [Antenna], Auto, and give us Accept for a state vector?

140:33:55 Worden: Okay, Karl. You've got them both.

[Less than four minutes after his wake up call and Mission Control already have Al busy. This morning, first tasks from the Flight Plan are to complete his post sleep checklist while Mission Control uplinks a new state vector into the guidance system. Al sets the computer to receive it. The consumables will be checked and Al will write down some Flight Plan updates and up coming photographic tasks.]
140:33:58 Henize: Thank you. And we've got about ten minutes until LOS at the present time. When you've got a pencil and a paper, I'll give you a short Flight Plan update and a camera PAD.
[Flight Plan updates are usually one of the first things Mission Control deals with in the morning as the overnight team has had plenty of time to think about what needs to be done.]

[The term PAD, used quite liberally throughout the Apollo missions, stands for Pre-Advisory Data and simply refers to any information which the crew will need for a particular operation, whether it be taking photographs of some interesting feature or igniting the SPS engine for a return to Earth.]

140:34:37 Worden: Okay, Karl. Go ahead. I'm ready to copy.

140:34:42 Henize: Okay. On the Flight Plan update at 141:03, they simply want you to add the report on the Gamma-ray and Mass Spec boom Delta-T's. And at 141:04 there is a "Laser Altimeter, On," which should be transferred down to 141:15. Those numbers come through okay?

140:35:30 Worden: Roger, Karl. I got you. At 141:03 you want me to report the Delta-T's on the retract for the boom; and move the "Laser Altimeter, On" to 141:15.

[Just before Al's rest period, at 130:28:01, Mission Control reported that the Laser Altimeter was showing signs of failing and it was switched off early. They may want to delay powering it up until nearer the time the Mapping Camera comes on to preserve its life.]

[Also, Mission Control want Al to report to them the times he measures for the retraction of the two booms which carry the Gamma-ray and Mass Spectrometers rather than just record them on his paperwork.]

140:35:43 Henize: Roger. And, over at 141:55, I guess we're having a look at photo target 25, and there is a friendly little note that goes with this. It says to be performed only if the CMP feels it won't interfere with his eat period. So, this is your choice. Do you want some numbers?

140:36:09 Worden: Roger. Let's have them.

140:36:11 Henize: Okay. Camera configuration. CM/EL/250/CEX, f/5.6, 1/250, infinity; 15 frames. And at 142:04, the actual [time to] execute [the photography]: photo target 25; A12, A13-P25. And, it says CM with window 3, with the same - with the same camera configuration: f/5.6, 1/250th at infinity; and 15 frames at 10 second intervals. Right. And this is magazine Q, pardon me. So much for the short Flight Plan update. Did the photo target 25 stuff come through okay?

140:37:38 Worden: I think I got most of it. But let me read it back to you just in case. Okay, at 141:55, that would be: set up cameras for photo target 25, at CM/EL/250/CEX, f/5.6, 1/250 at infinity, 15 frames; and then at 142:04 at A12, A13, photo target 25. CM, 3; and the settings going to be for 15 frames at 20 seconds from Mag Q.

140:38:18 Henize: Okay, everything's right except 15 frames at 10 second intervals - one zero.

140:38:28 Worden: Ah, so. Okay, 15 frames at 10 seconds.

[The photography shorthand should have said 'CM3' to indicate that window 3, the hatch window, is to be used and Karl Henize corrected himself. The shorthand decoded means use the Hasselblad EL camera with a 250-mm lens and daylight colour Ektachrome film through window 3 of the Command Module. Exposure should be 1/250th of a second with a lens aperture of f/5.6, and the subject is photo target number 25.]
140:38:31 Henize: That's right. And the computer is yours.
[Mission Control has finished uploading a revised state vector into the computer and so Al can begin using it again.]
140:38:36 Henize: Okay. The only other important thing on this front side pass is to get up the camera PAD to you. That's about the same page there...

140:38:53 Worden: All right, go ahead.

140:38:54 Henize: ...okay. The Mapping Camera Photo PAD starts 141:17:26; [and stops] 144:09:30. And right down below is the Pan Camera PAD, [starts] 141:46:11; [stops] 142:01:31. And as a part of this, just across the page there, at 141:45, we would like to move down that statement, "Mapping Camera Image Motion, Increase;" move that down to 57 - 141:57. And that's all.

140:39:50 Worden: Roger. Understand. The Mapping Camera photo PAD is, 141:17:26; 144:09:30. The Pan Camera photo PAD is 141:46:11; 142:01:31. And move the "Mapping Camera Motion Increase to talkback, barber pole" from 141:45 to 141:57.

140:40:18 Henize: That's excellent. I - I also have science report, which you can probably pick up on the next rev, and consumables report. And I guess we would like a status report from you. We could either do that now or early in the next rev. How do you feel about it?

140:40:49 Worden: Oh, I can give you the status report now, I think, Karl. Stand by one. [Pause.]

140:41:08 Worden: Okay, Karl, I guess - crew status report: Got 6 hours sleep all in one period, and very good night's sleep, I might add; and my PR - no medication, and my PRD [Personal Radiation Dosimeter] is 23149.

140:41:37 Henize: Roger. 23149.

140:41:46 Worden: And standby for the consumables. [Long pause.]

140:42:06 Henize: What was that comment on consumables? Would you like to copy them now?

140:42:14 Worden: Roger, Karl. Might as well get them now.

140:42:16 Henize: Okay. The time is 140 hours; RCS total is, 61 [percent]; quad A, 61; [B] 61; [C] 59; [D] 61; H2 tanks, 70, 70, 48; O2 tanks, 75, 78, 60.

140:42:47 Worden: Roger, Karl. 140:00, RCS total 61, it'd be 61; 61; 59; 61; H2 tanks, 70, 70, 48; O2 tanks, 75, 78, 60.

140:43:07 Henize: That's correct. We - and, they say that they would like to have you do the configuring of the DSE that comes up there at 141:35. And if you can listen for another minute I've got an EECOM status if you'd like.

140:43:39 Worden: Roger. Go ahead. I'll be doing a P52.

[As on every far-side pass, the DSE (Data Storage Equipment) records spacecraft telemetry and SIM bay science data for subsequent replay to the ground on the following front side pass. Normally, the commands to operate the recorder come from Mission Control but here they are asking Al to set it up for them prior to LOS. The P52 platform realignment is, as usual, using option 3, based on the orientation of the landing site. Before starting it, Al places the CMC Mode switch to "Free" to stop the RCS (Reaction Control System) unexpectedly moving the spacecraft.]
140:43:41 Henize: Go ahead on that and the report is mostly nominal on everything. It says that the fuel cells are nominal. The spacecraft average current has read about 80 amps. Cryo purity is good, judging from the very little effect of the fuel cell purges. The battery charges all have been nominal. The cryo quantities are above the nominal Flight Plan level, and the ECS system operation has been normal. And that takes care of the EECOM report.

140:44:16 Worden: Well, that certainly sounds very good, Karl. [Long pause.]

[Based on spacecraft voltage on the main supply buses of 28 volts, the average power consumption, given by P = V × A, is 28 × 80 = 2.24 kilowatts.]
140:44:34 Henize: Okay, Al, we're going to have LOS in about a minute and all the systems down here look Go.

140:44:44 Worden: Roger, Karl.

[Very long comm break.]
140:47:10 Worden (onboard): And, Houston, if you're...

[Al has much to do before mealtime, both during this far-side pass and the subsequent near-side pass. With the CMC Mode switch set to "Auto" and the spacecraft's attitude under RCS control again, he rolls clockwise 40° This roll is done prior to turning the spacecraft around so as to avoid the guidance system getting into the gimbal lock condition.]

[CSM Flight Plan page 3-203.]

[As Endeavour approaches the transition from lunar night to day, Al prepares for a period of photography using the cameras in the SIM bay and his Hasselblad. The spacecraft's attitude is changed to point the sharp end of the Command Module in the direction of travel by changing the omicron value in Noun 78 to 180°. The SIM bay will still be aimed at the Moon before and after this maneuver. The Mass Spectrometer comes off while the Laser Altimeter comes on and the booms are retracted. Al will be monitoring the times taken for the booms to retract in view of problems he has already had with the Mass Spectrometer's boom. Endeavour begins its 33rd revolution around the Moon at about 141:08. Soon after, as the spacecraft enters the sunlight, he will narrow the limits of the spacecraft's attitude drift to a half degree deadband and commence Mapping Camera photography. Mission Control will soon find that this narrow deadband is causing the thrusters to fire more than expected and will talk to Al about this at 142:10:03.]

141:37:46 Henize: Endeavour, this is Houston. How do you read?

141:37:52 Worden: Houston, Endeavour. Read you loud and clear.

141:37:57 Henize: Very good. [Long pause.]

141:38:34 Worden: And, Karl, Endeavour. I've got a message for our friends this morning.

141:38:39 Henize: Go ahead, Endeavour.

141:38:43 Worden: Okay. If the King is there: Mar-hah-bah al el-arde in-Endeavour ee-lay-kum sa-lam.

141:38:54 Henize: Beautiful. If he's not down there listening, I'll make sure it gets relayed to him, if I can remember.

[Al's message is intended for Farouk El-Baz, an Egyptian who, by way of Bellcomm, Inc., a think-tank hired by NASA, had come into the site selection process and, for the later Apollo flights, was pivotal in training the CM pilots to become observers of lunar geology from orbit. El-Baz had sifted through all the Lunar Orbiter imagery taken in 1966 - 67, and classified every feature he saw, in the process becoming an expert on lunar landforms. Through his teaching, he passed on his enthusiasm to the astronauts who nicknamed him 'the King'. Al's message, which is Arabic, translates as "Hello Earth, Greetings from Endeavour." and is one of the nine versions phonetically written down on a piece of paper for Al by El-Baz. This greeting became the title of a book of poetry which Al wrote after the mission.]
141:39:10 Worden: Okay. And I got some gyro torquing angles for you.

141:39:13 Henize: We're ready to copy.

141:39:17 Worden: Okay. Stars used were 01 and 36; Noun 05 was plus four balls 1; Noun 93 was minus 00.004, minus 00.050, plus 00.041. They were torqued at 140:49:00.

[To translate the torquing data: Stars 01 (Alpheratz, the brightest star in Andromeda) and 36 (Vega, Lyra's most prominent star) were used to realign the platform. Al's accuracy in measuring the angle between the two stars, a good guide to the accuracy of his sightings, was 0.01° and each of the gimbals, X, Y and Z were moved, or torqued, by -0.004°, -0.05° and +0.041° respectively.]
141:39:57 Henize: Roger, Al. That all came through loud and clear. And you're coming up in a few minutes - in a few seconds to a Gamma-ray Gain Step operation.

141:40:10 Worden: Roger. And then I'll get back with you on the Delta-T [for the boom retraction].

[This is the start of a ten minute period when a system within the Gamma-ray Spectrometer for discriminating between genuine gamma-ray and other cosmic-ray events is switched off for calibration purposes.]
141:40:13 Henize: Roger. [Pause.]

141:40:21 Worden: Okay. The shield is off and the Delta-Ts, the Mapping Camera extension was 3 plus 50; the Gamma-ray retracts was 3 plus 12; and unfortunately the Mass Spectrometer boom, when I go to Retract, even now, I get a barber pole. It never did go gray.

141:40:56 Henize: We copy, and we're sorry to hear that.

141:41:02 Worden: Although, I'm not so sure but what part of our problem is not in the talkback indicator itself. After 3 - well, 3 to 4 minutes, I was watching the talkback and saw no change, so I went to Extend and noticed that the talkback jumped about half position in the window. So apparently what's happening is that the talkback is - is not triggering before gray. It's going about half way. There's about a half a barber pole in the window and, if I go to Extension, I get full barber pole. So that may indicate that it's just a talkback problem.

141:41:48 Henize: Roger. We copy.

141:41:58 Worden: I don't know whether you understand all that or not. But...

141:42:02 Henize: I'm not sure...

141:42:03 Worden: ...I sort of feel like maybe there's a talkback problem.

141:42:07 Henize: Right. Incidentally, how many times did you cycle the switch on the deploy retract.

141:42:16 Worden: Oh, I guess I probably cycled it 3 or 4 times.

141:42:20 Henize: Okay. I guess the reason I asked is I think we have a suspicion there that we have the - that cable not coiling correctly and recycling may - feed the coils correctly and solve the problem.

141:42:46 Worden: Okay. I'll go ahead and deploy and retract it. I'll cycle it a - a few times here and see if I can get [it] to come in. [Long pause.]

[Worden, from the 1971 Technical Debrief - "At the first part of the lunar orbit activities, the Mass Spectrometer was deployed and retracted almost as I had anticipated, knowing the approximate times the boom should take to deploy and retract. Those times came out very close. Only along towards the end of the lunar-orbit activities did I start to see those times varying. In fact, at one point, the Mass Spectrometer failed to retract. I never did get a gray indication. I turned it off, turned the retract mechanism off, and extended and retracted the Mass Spectrometer in short bursts, cycling it until I got a gray indication. This meant that the Mass Spectrometer was very close to being fully retracted, but yet something was holding it from the final retraction. Looking in the Flight Plan, I noticed that the first time I saw a problem with the Mass Spectrometer boom was at approximately 119 hours and 20 minutes in the flight, when I got no retract on the Mass Spec boom. At that time, I had retracted the boom and waited approximately 2½ minutes and then started watching the talkback, expecting it to go gray so that I could turn the switch off. Instead of going gray, it went to a half barber pole; the gray shutter in the talkback dropped about halfway, and it stayed there. I cycled it to extend three or four times, maybe bursts of 5 or 6 seconds, and then to retract. And after about the third cycle, the talk-back went gray, indicating that it had fully retracted. I ought to clarify the operation of the talkback. On all the extensions, the talkback was full barber pole until the boom was extended, at which time it went gray. On the retraction, it was full barber pole until the nominal time for full retraction had elapsed, at which time the talkback went to half barber pole. That was the only time, on that last bit of the retraction, when there was anything unusual about the operation of the talkback."]

[Henize, from the 1971 Technical Debrief - "Did you ever notice a half barber pole in later retractions? We never heard anything more about it."]

[Worden, from the 1971 Technical Debrief - "Yes. On each succeeding retraction, after that first one, the Mass Spec boom operated exactly the same way. I always got the half barber pole. After 4 or 5 cycles, for a considerable amount of time at least, I could always get the gray indication. Along towards the end, it finally got to the point where I never could get full retraction on the Mass Spec boom. In fact, during the EVA, we had cycled the boom to extend and retract on the short cycles several times. I never could get a gray, and when I looked at it during the EVA, the cover was tilted about 30 degrees on the hinge, and the guide pins in the Mass Spec were just barely coming through the guide slots. It was on the guide rails, but the pins weren't fully extended through the guide slots."]

[From the 1971 Mission Report, - "The Mass Spectrometer boom did not fully retract on five of twelve occasions. Data analysis, supported by the crew debriefing, indicates that the boom probably retracted to within about 1 inch of full retraction. Cold soaking of the deployed boom and/or cable harness preceded each anomalous retraction. In each case, the boom retracted fully after warmup."]

[From the 1971 Mission Report, - "The deploy/retract talkback indicator is normally gray when off, when the boom is fully retracted, or when it is fully extended. The indicator is barber pole when the boom is extending or retracting, and will show half barber pole if the drive motor stalls. The crew noted this last condition on the incomplete retractions."]

[From the 1971 Mission Report, - "An inflight test of the Apollo 15 boom indicated that the problem was a function of temperature. Testing and examination of the Apollo 16 spacecraft showed that the failure was possibly caused by pinching of the cable harness during the last several inches of boom retraction. The cable could have been pinched between the bell housing and rear H-frame bearing, or a cable harness loop was jammed by a boom alignment finger against the bell housing."]

[From the 1971 Mission Report, - "The Mass Spectrometer boom mechanism was qualified by similarity to the Gamma-ray boom mechanism. There are significant differences between the two designs and they are:

  1. When extended, the Mass Spectrometer boom is 1 foot 10 inches shorter than the Gamma-ray Spectrometer boom.
  2. The Mass Spectrometer cable harness contains 6 more wires and, therefore, is larger in cross section than the Gamma-ray Spectrometer cable. In addition, the harness coil diameter on the Mass Spectrometer is ½ inch larger (6.7 inches compared to 6.2 inches).
  3. The Mass Spectrometer cable harness terminates with an in-line connector; whereas, the Gamma-ray Spectrometer harness terminates with a 90 degree connector.
  4. The Mass Spectrometer rear H-frame bearings retract past the lip of the bell housing; whereas, the retracted bearing position for the Gamma-ray experiment boom is even with the bell housing lip. Therefore, the lip on the sides of the Mass Spectrometer bell housing is relieved about ½ inch for bearing clearance."]
[From the 1971 Mission Report, - "The differences between the two configurations are now considered to be significant enough to have required separate testing for the Mass Spectrometer boom assembly. Accordingly, a delta qualification test will be instituted and a thermal vacuum environmental acceptance test will be performed on each flight unit."]
141:43:26 Henize: Endeavour, a time hack is coming up very shortly on the Pan Camera.

141:43:35 Worden: Roger.

[Comm break.]

[This is the modified T-start time read up to Al at 140:38:54. The Panoramic Camera will operate for about 15 minutes. During this time, the only instrument in the SIM bay not operating is the Mass Spectrometer.]

141:45:41 Henize: Okay. We have 30 seconds before Pan Camera Mode goes to Operate.

141:45:50 Worden: Roger, Karl. Right with you. [Long pause.]

141:46:25 Henize: Al, we'd like to have High Gain Antenna, Auto, now.

141:46:32 Worden: Auto.

[Comm break.]

[Included in the current Mapping Camera pass is this image, AS15-1113M, which has the future Apollo 17 landing site near the centre.

Mapping Camera image, AS15-1113M, of Littrow crater and the Taurus Mountains including the Apollo 17 landing site.

Mare Tranquillitatis is to the south and Mare Serenitatis to the west. The distinctive dark mantling of the low-lying ground around Clerke which also covers the floor of the Taurus-Littrow valley is well shown. The area is also being photographed by the Panoramic Camera and is seen in two images kindly scanned and donated by journal contributor Robin Wheeler. In frame AS15-9557P, Littrow crater is seen in the top third. Just above the centre of the image is the distinctive dark-floored valley that will become the Apollo 17 landing site. At the bottom of the image, the eastern rim of crater Beketov is just visible. The 8.4-km Beketov is better seen in frame AS15-9554P along with Jansen C. In the centre, occupying an adjacent dark-floored valley to the Apollo 17 site is the crater Ching-te, 3.7 km in diameter. The western rim of Littrow is visible near the top of this image.]

141:48:15 Henize: Al, if you're not too busy now, I could send you up a science report. And I can cue on that Gamma-ray Gain Step.

141:48:26 Worden: Okay. Go ahead.

141:48:29 Henize: Righto. Here we go. On X-ray Spectrometer, words by Izzy Adler, say the general health of the X-ray experiment is excellent.

[Isidore Adler is the Principal Investigator for the X-ray Fluorescence Spectrometer experiment.]
Henize (continued): And a large amount of useful data is being received. The number 1 channel for the number 1 X-ray detector tends to be a little noisy, but on the whole, this is no great consequence. On the whole, the data is very pleasing. We have high hopes of soon being able to produce a compositional map, along the ground track, for all - for aluminum, magnesium, and silicon. And I just heard some words, that come Monday, I guess that's tomorrow, they begin to hope to produce some crude maps as to how these things are changing with position on the surface.

[One of the interesting parameters which can be determined from the X-ray data is the ratio of Aluminium to Silicon in the surface below. These are both major constituents of moonrocks and the results from the X-ray experiment will be important in understanding the large-scale make up of the Moon.]
Henize (continued): Gamma-ray Spectrometer. Analysis of last night's long run of data - last night was about 24 hours ago - indicate the number of definite features corresponding to expected energy for natural radioactivity of potassium, thorium, and uranium - and uranium. And to some cosmic ray excited elements. Okay, I guess it's about time for us to run that Gamma-ray Gain Step to Shield On [center] and start a - start up the charge on battery A. Maybe I should slow up a second and let you start the charge.

[The ten minute period for having the Gain Step Shield off are up and the Flight Plan also calls for battery A to be charged.]

[The CM batteries are brought online during periods of heavy electrical demand. They are subsequently and regularly recharged from the spare capacity of the fuel cells when the spacecraft's needs are light.]

141:50:04 Worden: Okay, Karl, go ahead. It's on.

141:50:14 Henize: Okay. One more comment on the Gamma-ray Spectrometer, It says that regional differences have been observed in the quick look data. But details will require computer analysis for confirmation. So they're beginning to see some point-to-point differences there also.

[The investigators for the Gamma-ray Spectrometer are beginning to see reproducibility of the count-rate from this instrument.]
Henize (continued): On the Alpha Particle Spectrometer, we say the Alpha Particle Spectrometer has continued to operate satisfactorily, for the most part. One of the ten detectors does show, at certain times, an increased number of counts that are probably detector noise. The internal calibration sources indicate that the gain of the instrument is stable. And - yesterday we heard words to the effect that some radon was being detected, but they're being cautious about saying anything very definite yet - about, exactly what is coming out.
[Even the Preliminary Science Report, produced in the year following Apollo 15, is vague about the results from the Alpha Particle Spectrometer.]
Henize (continued): Mass Spectrometer: It says that Mass Spectrometer data from the first two periods of operation indicates several constituents which may be native to the lunar atmosphere. In particular, I think we have definite confirmation of - native argon; both mass 40 and mass 36. And the reason that we feel reasonably positive about this, is that there is a jump by a factor of three from the night side to the daylight side, as you would expect for a residual atmosphere, about the Moon. And, there is a final caution here saying identification of argon as a native gas is tentative pending positive determination of contamination levels during the plus-X data collection period. So, we've still got a contaminate - we've - we've still got to calibrate their instrument before they will be completely sure of this data.
[The Mass Spectrometer has an inlet on one side of the unit. When this faces the direction of travel (minus-X data collection period), any molecules native to the rarefied lunar atmosphere are rammed into the instrument along with molecules emitted by the spacecraft. The plus-X data collection period has the inlet being shielded by the instrument itself and the detector should only detect molecules from the spacecraft. This simple technique should discriminate between the lunar atmosphere, if it exists at 110 km height, and contamination from the CSM.]
Henize (continued): Photo - photo report says the Mapping Camera operation is nominal and the Laser data - Laser data up till now has been very good. I understand that the Laser is beginning to drop an occasional pulse that gives them some concern, so that we'll probably not be using the - the Laser as extensively as we have in the Flight Plan. There'll be some cut back, I think, to conserve it's health and energy. Although, the data we're getting is still very good. Data from revs - this is going back to the Pan Camera - Data from revs 15 and 16 indicate that we're still getting, as we said before, about 80-percent of the photographs good. And we have some estimates here the - of - of what we expect the quality to be on the bad frames; whereas on the good frames we're expecting a resolution on the order of two meters. The bad frames, or the smeared frames, will be giving us about a resolution of 6 meters, about three times degradation of about three in the - in the resolution there. Still be useful data. It says there's no final resolution yet of the problem with the V over H sensor. Because of the V over H malfunction, photos of the landing site on rev 16 were - were not the best, and we may attempt running the camera in Stereo Self Test Mode on rev 50 over the landing site. And on the V over H sensor, Al. One of the possible reasons for that malfunction is the poss - is the - is the possibility of a piece of Mylar, or something, flapping in front of the light sensing aperture; and, when we rendezvous, we may have a chance to inspect that and see if that would be the source of our problem. I don't know what we could do about it, but at least it would be nice to understand it.

141:54:47 Worden: Roger, Karl. We can check that out, and - if we don't see anything there, we can check it out during the EVA.

141:54:56 Henize: Very good. Good idea. On the...

141:55:01 Worden: And, the Mass Spectrometer is now fully retracted. Talkback is gray.

141:55:08 Henize: Wonderful. Just recycling it a couple of times, and it finally came in; is that what happened?

141:55:16 Worden: Well, it took - I guess probably a half a dozen re - just recycles, jogging it out, then pulling it back in again and that may be - that may be the problem. Maybe that cable is kinking some way or other.

141:55:30 Henize: Okay. Real glad to hear you got that gray talkback.

[Subsequent analysis shows that Al's diagnosis of the boom retraction problem is correct, compounded by extreme low temperatures.]
141:55:41 Henize: Incidentally, the boys on the surface just about took a shower bath this morning. They had a small water leak in the conveyor that let loose a couple of gallons of water. It was a major perturbation, although they've got it cleaned up pretty well. And they're running about an hour, to an hour and a half behind their time line on the second EVA. They haven't got out yet.

[Readers should read the Apollo 15 Lunar Surface Journal at 138:04:15 for more details of the LM water leak. This is second time the crew of this mission have had to deal with leakages from their spacecrafts' water systems.]
141:56:07 Worden: Roger. Understand.

141:56:45 Henize: Okay, Al. We have about 10 seconds before we give an Image Motion Increase for the Mapping Camera.

[Long comm break.]

[CSM Flight Plan page 3-205.]

142:00:59 Henize: Endeavour, this is Houston. You have 30 seconds until Pan Camera Mode goes to Standby.

142:01:09 Worden: Roger, Karl. Right with you.

[Comm break.]
142:03:23 Henize: Al, we're still waiting for a cue on the lens stow, and in the meantime, photo target 25 is roaring down on us.

142:03:34 Worden: Roger... [PAO transcript adds "Got it in sight."] [Long pause.]

[Photo target 25 is the Caucasus Mountains which extend between Mare Serenitatis and Mare Imbrium north of the point where the two meet. The peaks of this range rise 6 km above the surrounding maria. Endeavour's ground track passes well south of them so four images taken by Al, AS15-96-13003 to 13006, are very oblique views of the very southern promontory. AS15-96-13004 is a good example.]
142:04:02 Henize: Endeavour, Houston. We can go Pan Camera Power, Off.

142:04:12 Worden: Roger. Power Off.

[Long comm break.]

[By the Flight Plan, Al should be beginning his meal break, though instead, he is working on the photography he had agreed to do at Mission Control's request at 140:36:09. The next three images he takes look a little south of the Caucasus at the land forms on the other side of the strait between the two maria, at the end of the Apennines. AS15-96-13008 shows one of the rilles near the Fresnel Promontory, AS15-96-13009 is of the Autolycus Gamma Prominence, an isolated outcrop of hills between Autolycus and the Apennine shore of Mare Imbrium.]

[Next, Al takes two excellent images of the Hadley landing site, AS15-96-13010 and 13011, before moving on to a sequence of five images, AS15-96-13012 to 12016, across the 39-km crater Autolycus. This is the smallest of the triangle of craters well known to even the most casual of moon watchers by being sited in Mare Imbrium in a position which has good lighting just when many evening observers are having a look at a first quarter Moon. Autolycus, with its heavily slumped walls and little rim crater, is on the small side of the threshold where an impact generates a central peak. Aristillus, on the other hand, is on the other side of that threshold. 50 km to the north and 55 km in diameter, it displays a well developed triple central peak.]

142:09:49 Henize: Endeavour, this is Houston. When you get the camera stowed, I have one more small item, and then we'll give you some time to get out some food.

142:10:00 Worden: Okay, it's stowed. Go ahead.

142:10:03 Henize: Okay, Al - we're finding out that the - tight deadband in P20 is using a little more RCS propellant than we'd anticipated. Nothing's critical yet, but we would like to take - some preventive measures here. And we suggest that you go into the DAP - and load in a CSM weight of 30000, thirty thousand. And before you erase the current LM weight recorded [corrects himself] the current CSM weight, record it for future use. We think that'll cut down the thruster firing a bit.

142:10:46 Worden: Okay, understand. Roger. You want me to go back and reload the DAP with a CSM weight of 30 000 and record the current weight that's in there for future use.

142:10:58 Henize: That's correct.

[Long comm break.]

[In its current setup, the Stabilization and Control System (SCS), via the Digital Auto Pilot (DAP) routines, is trying to maintain Endeavour's attitude within narrow limits (the "deadband"). The current deadband value of ±0.5° was set into Noun 79 during the last far-side pass. It doesn't take long for the spacecraft to drift to these limits causing the RCS thrusters to fire appropriately to restore the attitude within the deadband. The thrusters should not fire for so long that they cause the spacecraft to move into and through to the other side of the deadband too quickly, where more thruster firing would be needed. The DAP calculates firing durations based on the spacecraft's mass. By loading a lower-than-real figure into Noun 47, the controllers are hoping that they can fool the DAP into thinking that it has a lighter CSM to rotate than is really the case and therefore cause the thrusters to fire for a shorter period.]

[Scott, from the 1971 Technical Debrief - "[To Worden] In the orbital operations, you never got close to the red line [quantities], did you?"]

[Dave is referring to a line on a hypothetical graph of RCS usage against time. They must not go beyond the red line or they jeopardise the mission.]

[Worden, from the 1971 Technical Debrief - "The last number I recall hearing was 15 percent above the red line on one quad. There was some concern about the second day of lunar orbit operation [actually the third] that we were expending fuel more rapidly than we should have been. They called up a weight change for the CSM to try and take the DAP into firing fewer times, to conserve some of that fuel. That didn't work. So we went back to the actual weight and nothing else was said. We never compromised any of the operation and we ended up not even close to the red line. I never did hear a number after the 15 percent, but I assume that we were comfortably above it."]

142:16:15 Henize: Endeavour, a news bulletin from the surface says that they are now depressing the cabin; and there is no need for you to acknowledge. Keep eating.

142:16:28 Worden: Roger, Houston. Understand that, and - one point from here, Karl, - I'm over the spot in Imbrium, I think, close to where you and Whitaker drew from, or figured out, some lava flows coming out of where the wrinkle ridge is, and at this low Sun angle, I can very clearly see some lava flows coming out of what appears to be a ridge, extending in both directions from the ridge. And I wasn't set up this time to take a picture of it, but it might be interesting on the next pass if we could get a - if we could get a PAD to take a picture of that.

[In the 1950s, Ewen Whitaker helped begin work on a series of high quality atlases of the Moon based on telescopic imagery. A self taught Englishman, he continued to study lunar imagery throughout Lunar Orbiter and Apollo periods, having an important influence on Apollo site selection and lunar science. He is credited with tracking down the exact position of the Surveyor 3 unmanned lander on Lunar Orbiter photographs by comparing landmarks on the lander's own photographs with those from Lunar Orbiter 3, thereby giving Apollo 12 a target to aim for. In retirement, he wrote (and to some extent illustrated) a lovely book that reflects his deep interest in lunar mapping, Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature.]

[As Endeavour enters lunar night, Al is due to deploy the Gamma-ray boom about now, retracting it again just prior to reaching sunlight again.]

142:17:14 Henize: Very interesting. Which window are you looking out?

142:17:19 Worden: I'm looking out window 3.

[Window 3 is the central of the Command Module's 5 windows and is mounted in the spacecraft's main hatch.]

[With the spacecraft travelling "sharp-end-forward", and the SIM bay facing the surface, window 3 must be looking towards the North.]

142:17:24 Henize: Window 3; that sounds like it's down to the south of you, then.

142:17:27 Worden: Just slightly north of groundtrack.

142:17:31 Henize: Very good.

142:17:32 Worden: That's right. Just down in the south, just a little.

142:17:34 Henize: Thank you. Sounds like an interesting observation, and I'm sure the guys down below will be sending you up more work to do as a result. Be careful there, now.

[Long comm break.]

[At 145:45:52, Houston will pass up instructions to photograph these lava flows at 148:00.]

[The wrinkle ridge Al is referring to is now known as Dorsum Zirkel which runs northwest from the crater Lambert to Dorsum Heim. Ferdinand Zirkel, 1838-1912 was a German geologist and Albert Heim, 1849-1937 was a Swiss geophysicist.]

[Worden, from the 1971 Visual Observation Debrief - "On the western edge of Imbrium and in [Oceanus] Procellarum, you can see the flow fronts by the difference in color."]

[Farouk El-Baz, from the 1971 Visual Observation Debrief - "Before you see the flow scarp?"]

[Worden, from the 1971 Visual Observation Debrief - "Yes, because the color is distinct and different from the flow that was underneath it. ... After you look at one area and you see 10 or 15 flows that are all overlapping and joining in that area, the picture gets a little bit confused. But that's why I say that I get the impression that there are just hundreds of flows that filled up the basin. They all look like, for example, you'd take a pail of water and sluice it out into a skating rink and let it freeze in place; then, if you do that 15 times around the same area, you would get this overlapping mixed up ice."]

[El-Baz, from the 1971 Visual Observation Debrief - "You're talking about Procellarum?"]

[Worden, from the 1971 Visual Observation Debrief - "Yes. [In Imbrium] there were a lot more than two flows. In fact, I don't recall seeing any place where it looked like there was just one big flow. All the flows were very thin and appeared as if they came out and froze in place."]

142:25:37 Henize: As I look at the map, Al, it looks to me like you're going smack over Tsiolkovsky every rev now. How is it looking to you?

142:25:48 Worden: That's just about right, Karl. Coming right over the middle of it.

142:25:52 Henize: That must be a beautiful sight. Hey, I was sort of fascinated by the fact that, on your first couple of revs, you noted that you could really see the peaks sticking up - the central peak before you could see the rim. Is that really true?

[CapCom Karl Henize is referring to the third orbit when Apollo 15 emerged from behind the Moon. This was immediately after the burn which lowered their pericynthion to only 17 km. At 083:16:41, Dave Scott enthused about how their falling altitude and the Moon's curvature made Tsiolkovsky's central peak appear before the rim.]
142:26:09 Worden: Well, that's not really true, because - it's - it's so hilly and - and ridgy down in that particular area that you just don't see the rim. And Tsiolkovsky is big enough so that you get some, at least optical, impressions of the central peak being higher than the ridges. But I think it's just because the - the basin is - is big enough, is far enough across, that you're - as you're looking from one rim to the other, the curvature kinda gets to you and - and makes the central peak appear higher than it is. But it is a very, very high central peak; it's a - it's a very large mass.

Real Video file (357K)

[Part of Al's description is included in the above Real Video file, taken from NASA's post-mission documentary.]

[Worden, from the 1971 Visual Observation Debrief - "Tsiolkovsky is different. You've got a good feeling for the depth there, probably not as great as the laser shows it to be, but that's just optical. That big scarp over on the west side gives it depth. But that's just because you look at one scarp. If Tsiolkovsky did not have the central peak and if it didn't have that big scarp on the other rim, you might be fooled with the depth. It's kind of the total picture that you see. That central peak is a monster."]

[El-Baz, from the 1971 Visual Observation Debrief - "It really did look huge, and you saw the central peak before you saw the rim?"]

[Worden, from the 1971 Visual Observation Debrief - "Oh, yes. You look over the horizon, and you don't see the [near] rim until you see the central peak. Then, once you see the central peak, you realize that there's a rim there. In other words, you realize that the central peak is sitting off by itself. I guess you're up over the rim enough so that you can see down into the central peak. But the surrounding terrain looks so much alike that you don't have a feeling for the fact that there is a rim there. But that central peak sure does show up."]

Worden (continued): And, as a matter of fact - on the last couple of revs, I've been watching the central peak, and I'm pretty sure that I can see some layering - in - in the central peak there and - there should be some pictures of it. I got some pictures looking down on it. But it looks like a big slab that's been stuck up on edge.

142:27:11 Henize: Hey, that would be great to get pictures of that. I don't know when you were scheduled to look at that - that landslide on the northwest corner of it, but are you seeing anything of that area?

[Al will take 6 photographs of Tsiolkovsky with the 250-mm telephoto lens during his next far-side pass, perhaps prompted by this conversation. AS15-96-13017 to 13019 are three spectacular images of the central peak which can be composited to show the entire structure. 13020 and 13021 show examples of the landslides around Tsiolkovsky's rim. One other shot, AS15-96-13022 shows the "sculpture" beyond the south rim where the flying ejecta from the impact event carved furrows in the surface.]
142:27:28 Worden: Absolutely, I look at it every time I go by and there's just - there's no question in my mind at all that it is a - that it is a - rock avalanche. It - it does have some interesting qualities about it, though. And it's a little bit hard for me to decipher right now, but it seems like the density of crater impacts in that slide is - is greater than in the surrounding terrain, even though the slide had to be emplaced on top of the surrounding terrain. Maybe it's just that the craters are - are fresher in that - fresher looking in that particular material. But no question about the lineaments being parallel to the direction of the travel of the flow in the low peak plateaus and - all the - all the characteristics that I've seen of a rock avalanche.

[Al's point about the density of craters on the rock slide compared to the surrounding terrain is important because it is assumed that a greater numbers of craters on a terrain indicates older age. Planetary scientists believe that although there are short term variations in the numbers and sizes of meteoroid impacts, over very long time scales the flux has been essentially constant for the past three billion years.]
142:28:20 Henize: Roger. That sounds interesting.

142:28:33 Worden: Just want to add one other comment to that. So far, I haven't been able to locate the other one.

142:28:43 Henize: Say again on that, Al?

142:28:49 Worden: So far, I haven't been able to locate Al-Biruni.

142:28:53 Henize: Roger. Okay. [Long pause.]

142:29:43 Henize: Al, Alvin heard that, and he feels crushed.

142:29:52 Worden: Well, tell him not to worry. I'm sure it's there and I'll - I've just got to get a little bit further south around the edge of the crater.

142:29:59 Henize: Okay. Hey, when you can get the Flight Plan and a pencil, I've got a - a few more updates to finish up on this rev.

142:30:16 Worden: Okay, go ahead.

142:30:18 Henize: Okey-doke, let's go over to 143 hours. And, at 143:09, we want to add...

142:30:27 Worden: Say, Houston, Endeavour. Go ahead with your up-dates, Karl.

142:30:30 Henize: Roger. At 143:09, we would like to add "Laser Altimeter, Off"; at 143:12, in that P20 there, we would like you to do a "Verb 25" instead of a "Verb 24"; and we would like to add, in addition to your two angles there, we would like to add "Omicron plus 161.00." Did that come through?

142:31:08 Worden: Roger. Understand, we're going to do - Omicron - add omicron to that - load of plus 161.00.

[The time given to switch off the Laser Altimeter, 143:12, coincides with the time the spacecraft is due to be maneuvered into an attitude for taking backward looking oblique photographs with the Mapping Camera. This sequence of images are AS15-1309M to 1428M. In this attitude, the science instruments in the SIM bay will not be pointing straight down and the data from the Laser Altimeter will be less useful. By switching it off, they hope to save the ailing instrument for later.]
142:31:16 Henize: Roger. And we're going to do the same trick over on 144 hours and 26 minutes. We want add, again, to that load, we want to add "Omicron plus 180.00."

142:31:42 Worden: Understand. At 144:26, you want to add a "Verb 25, Noun 78" - "Omicron plus 180.00."

[This double change of omicron values may be due to the error discovered at 126:46:10 when the omicron value for a P20 maneuver was found to give an incorrect attitude. Mission Control have checked the Flight Plan to ensure that nowhere else is there a wrongly defined P20.]
142:31:52 Henize: That's correct. Next change is over on 146:13. And over there we have a "Laser Altimeter, Off," which had already been put off before so you can delete "Laser Altimeter, Off."

142:32:14 Worden: Roger. Delete "Laser Altimeter, Off."

142:32:19 Henize: And then, if we go over to 151 hours. At 151 hours and 10 minutes, we would like to change the Pan Camera operation there, and we would like to say "Stereo Exposure, Normal." And at 151:15, we would like to delete the "Pan Camera Exposure, Normal."

142:32:59 Worden: Okay, I understand. At 151:10 you want that to read "Stereo Exposure, Normal;" and at 151:15, delete that line.

142:33:08 Henize: That's correct, and that's the end of the update.

142:33:14 Worden: Okay.

[Comm break.]
142:35:29 Henize: Endeavour, this is Houston. They have some data on that new DAP configuration, with the new weights. I guess we're not sure we want to stick with it, and at this time we'd like you to go back to the normal DAP load with the weight.

142:35:47 Worden: Okay, Karl. Understand you want me to go back to normal DAP load and normal weight.

[Twenty five minutes ago, Mission Control asked Al to change the computer's knowledge of the mass of the spacecraft. This was to try and reduce the thruster firings made by the DAP in its attempt to keep the desired attitude. The strategy is not improving matters as they hoped. Note that this is not resulting in a heavy usage in propellant. However, it is in the nature of the entire system to try and wring every last ounce of performance from critical systems such as the RCS in case an emergency demands all the reserves available to get the crew out of a situation. This mentality was nicely observed in the movie film Apollo 13 when the Ken Mattingly character asks to repeat a docking simulation. Though the crew are under pressure to move on, he feels he can do it with a little less fuel.]
142:35:52 Henize: Roger. And, I was so busy talking, I forgot to cue you on [extending] the Gamma-ray boom [19 minutes ago]. I trust you have started - you got that out yet, or did I talk you out of thinking about it.

142:36:05 Worden: Negative. It's out.

142:36:07 Henize: Very good. Thank you.

142:36:12 Henize: Did you record an extension time on that?

142:36:19 Worden: No. I didn't get that, Karl.

142:36:21 Henize: That's okay.

[Long comm break.]
142:45:07 Henize: Endeavour, this is Houston. All your systems look Go as you go around the corner. And see you on the other side.

142:45:16 Worden: Okay, Karl. See you on the other side.

[Very long comm break.]

[Endeavour has disappeared from radio contact with Earth towards the end of its 33rd revolution. Rev. 34 will begin at about 143:06. Currently, all SIM bay instruments are operating except the Mass Spectrometer and, interestingly, the Mapping Camera is also operating right across lunar night. At first, this appears pointless without light to make a photograph. However, the Mapping Camera consists of two cameras, the Metric and the Stellar Cameras, exposing onto a single roll of film. These are operated in conjunction with the Laser Altimeter, the readings from which are also imprinted on this camera's film and which are required to provide contextual information for the other instruments, even over darkened lunar territory. As part of taking a measurement of height, the precise attitude of the spacecraft must be found so that if the laser pulse does not strike the surface exactly vertical, analysts can compensate. The Stellar Camera's images of stars taken at the same time as the laser pulse calibrates the laser's direction.]

[CSM Flight Plan page 3-207.]

[Al is still within his meal period which is due to end at 143:01. Just before Endeavour reaches sunlight again, Al retracts the Gamma-ray boom. He then uses P20, option 5, to make the SIM bay look back 25° from the vertical for a series of backward oblique photographs the Mapping Camera will take throughout the coming daylight pass.]

[Tsiolkovsky, with its dark, mare-like interior and spectacular central peak, is the target for visual observation by Al; specifically its northwest rim. Compared to when they first encountered this striking 198-km crater, its shadows have lengthened considerably and much more texture can be discerned. As well noting how the crater looks for his description, Al takes the six photographs using the telephoto lens.]

[These visual observations have been the subject of considerable training from Farouk El-Baz on the art of geologic description and the correct use of terminology to impart maximum information to geologists on Earth. One of the main justifications for this effort is the understanding that the well-trained human eye can discern far more subtlety than the best photograph. 27 years after the event, the lovingly crafted TV mini-series From the Earth to the Moon, made by actor Tom Hanks for HBO, set aside some time to convey the dedication which went into transforming a bunch of test pilots into very competent geologists with one episode given over to the tale of Apollo 15, its preparation and success in wresting quality science from the Moon. Although a substantial team from NASA and the USGS (U.S. Geological Survey) were involved in 15's geology training, the episode titled Mr Galileo Was Right focused on the role of Professor Lee Silver in turning Dave Scott and Jim Irwin into expert field geologists. It also showed how El-Baz went about his task of making Al Worden into a highly competent aerial observer of the Moon's landforms. While Lee Silver led Dave and Jim on foot through geologically fascinating sites, where they practised the skills they would need for EVA, Al and Farouk took to aircraft and flew over landscapes which it was felt would provide relevant experience and knowledge for his sojourn around the Moon.]

143:31:45 Henize: Endeavour, this is Houston, how do you read?

143:31:54 Worden: Hello, Houston. Endeavour reads you loud and clear.

143:31:58 Henize: Reading you loud and clear likewise.

143:32:42 Henize: Al, if you have time to listen, I have some news bulletins down here; and, somewhere in the middle, I will break in for the High Gain Antenna, Auto.

143:32:46 Worden: Okay, Karl. Go ahead.

143:32:48 Henize: Right. This is the morning national and world news - the world being, of course, the planet Earth. President Nixon, yesterday, declared his administration is determined to revitalize the American country...

143:33:13 Worden: [Garbled]

143:33:15 Henize: Go ahead. I missed that one; Al, say again.

143:33:20 Worden: That's your world right now.

143:33:23 Henize: That's right; that's our world.

143:33:26 Worden: Our world's up here right now, Karl.

143:33:29 Henize: [Laughter] I - I'll give you some news bulletins on that at the end. Things are coming along good in the EVA. Okay. President Nixon was what - he was at ceremonies dedicating a dam in Iowa, and he said the economic potential of rural areas must be developed, quote, "so that the people who live there can be first-class citizens enjoying a first-class way of life." Unquote. In the labor area, about 4,000 Houston area steel workers are expected to be off the job today in a nationwide strike against nine major steel companies. That's beginning to loom as a pretty big factor in [the] economic world down here. Senator Mansfield said Saturday chances are good that the senate will reach an agreement to stop talking and speed up a vote on a bill to rescue Lockheed Aircraft Corporation. The President of Pakistan has accused neighboring India of continued artillery strikes across the border and said, quote, "We are very near to war with India;" a very sad note there. And Senator Edward Kennedy and Senator Edmond Muskie are tied for the top spot in the latest Democratic standings according to the Gallup Poll. I'm sure you'll be fascinated. And in the world of sports, in football, the Houston Oilers lost their first exhibition game to Los Angeles, 17 to 6. In baseball, the Astros won for a change, and beat the Expos 6 to 4; and in golf, Jack Nicklaus and Arnie Palmer shot a total of 64 to take a 4 stroke lead in the PGA National Team Championship in Ligonier, Pennsylvania. Okay, and we are ready for High Gain [Antenna, HGA], Auto, Al.

[Once the HGA has reacquired the Earth after AOS (Acquisition Of Signal), it is always switched to Auto. This may be to inhibit the antenna from returning to the preset position settings in case of a temporary break in the link with Earth.]
143:35:46 Henize: Up on your planet, the latest word is that the Rover is still functioning - functioning brilliantly, and the fellows are well into EVA number 2 and just recently passed Crescent Crater and Dune Crater - well on their way to exploring the Front at Hadley Delta.

143:36:12 Worden: Sounds great.

143:36:14 Henize: Yep. Everything's going great, both in orbit and on the surface. Everybody is very pleased.

143:36:31 Worden: Okay, Karl. If you're through with the news, let me give you some words on Tsiolkovsky.

143:36:37 Henize: Great, we're listening.

143:36:46 Worden: Okay, I'll take the items one at a time as they come. First off, the central peak. The central peak is - is a very large - spur peak on the - on the south and east sides, getting blocky on the north side; and there's what appears to be some layering visible on the - on the south and west exposed scarp of the peak, dipping to the north about 30 degrees.

[Worden, from the 1971 Visual Observation Debrief - "There appeared to be, from my vantage point, distinct layering that was fairly uniform and horizontal. In other words, the layers weren't rotated with respect to the shape of the peak. It appeared as if the feature had been raised up and the layering remained horizontal."]
143:37:28 Henize: You're coming through loud and clear.

143:37:30 Worden: The - Okay. The light material - the light colored flow material - around the edges of the - of the basin - texture appear to be nothing more than just simple mass wasting off of the edges - or off the - of the rims around the basin. The rims themselves are quite - cut with the mass wasting in a - oh, I'd say an extent of about 330 degrees on the north, east, and south sides. Now, on the west side, the rim there is a very, very, large, clean scarp; and when I say clean, it goes almost from the basin floor to the - to the rim itself in one large chunk. And that scarp appears to define the limits of a couple of fault zones that go through that rim of Tsiolkovsky. It was kind - it - I couldn't trace the fault zone beyond Tsiolkovsky from the vantage point I had very well, but they're very distinct in the wall itself. And one fault zone coincides, or - occurs in the same location as the southernmost edge of what appears to be a rock glacier extending northwest into Fermi. Now, that rock glacier has all the flow bending and the loping toes characteristic of what we consider a rock slide; however, one - one feature about that slide that I mentioned before is that it has what looks like fairly fresh crater impacts on the slide itself and seems to have more impacts - in other words, a higher density of craters than the - than the - surrounding floor of Fermi, although Fermi looks - the floor looks much older - its much smoother, more like a Cayley formation.

[One of the often reproduced frames from the metric section of the Mapping Camera, AS15-0757M, is a stunning oblique view over Tsiolkovsky looking towards the west. The extent of the mass wasting from the rim onto the interior of the crater is evident including its absence from a small portion of the west rim, the clean scarp which Al speaks about. During revolution 15, Al took AS15-97-13161 which is a beautiful view of this scarp, and AS15-96-13021 shows a rock avalanche down the crater wall just south of the clean scarp.]

[Tsiolkovsky slightly overlaps the older and much more degraded 210-km crater, Fermi, on its western edge. Enrico Fermi, 1901-1954, was an Italian born nuclear physicist. Al is comparing the ancient floor of Fermi to the Cayley formation, a distinctive plains area which is smooth and light coloured and which lies southeast of Mare Imbrium. It was believed to be volcanic in origin but later interpretations view it is being a huge deposit of ejecta from the impact which created the Imbrium basin.]

143:40:00 Henize: Roger, Al; we're copying.

143:40:01 Worden: Looking - Okay. Looking more to the south, I see no evidence of another rock slide to the south. The pictures might indicate - might hint at some kind of a rock slide there, but it appears that it's - that its more ejecta now. The picture [in the landmark book] doesn't clearly show the ejecta from Tsiolkovsky, but the ejecta pattern and the flow - the flow lines are - at least observable around most of Tsiolkovsky, and the ones that we see on the south and west side of Tsiolkovsky seem to be more ejecta than anything else. I couldn't see any distinct unit there that could have been a flow, such as the one in the northwest corner. And it - it appears that what lineaments there are in that particular part of the - of the ejecta are merely e - ejecta patterns.

[AS15-96-13022 displays these lineaments clearly.]
Worden (continued): Looking into Waterman, there is a small flow that goes into Waterman, but it doesn't come from Tsiolkovsky itself, and I couldn't locate the source of the flow, but it seemed to just come down the side of Waterman and out into the basin. I do have some pictures of it; maybe we can tell from the pictures. But the - what looks like on the picture as you're looking at - at the picture in the landmark book, looking at the V-1A, Victor one Able, it looks like there's a - there's a - maybe a breach in the wall of Tsiolkovsky, between Tsiolkovsky and Waterman, possibly allowing some flow into Waterman. Well, visually that - that particular breach in the wall doesn't - doesn't show up. The terrain there is much more level than it would appear in the photo, and there is, definitely, elevation relief between Waterman and Tsiolkovsky. The flow does come from the direction - on the north side of Waterman toward Tsiolkovsky, and I guess my impression would be that it - that that flow came down the side of Waterman possibly out of some fracture or fault concentric to Tsiolkovsky, but outside the basic rim itself.

143:42:37 Henize: Roger, Al. [Long pause.]

[Waterman is a 70-km eroded crater on the southern side of Tsiolkovsky.]
143:42:51 Worden: One other comment, I guess. And that is, on the crater pair, just north of Tsiolkovsky - there - the - the smaller of the craters on the west side apparently was - was an original crater, with an impact occurring alongside it. Now, that's a - that appears like mass wasting or some kind of a rock avalanche into the westernmost crater - into the smaller of the two craters, and the - the rim of the easternmost crater - I'm sorry - reverse those directions; I'm looking at it upside down. The smaller crater is - is on the eastern side, has - has what looks like a rock slide in it. The larger crater on the west side has a fairly intact rim, being faulted in a couple of places where it crosses the rim of the crater to the west. But that rim is fairly intact. The rim that was apparently moved or obliterated by the most recent impact was the rim of the smaller crater to the west, and that's where all the rock debris is - has fallen into the crater on the west.
[At 107:55, Al took 6 frames, AS15-94-12745 to 12751, of this pair of craters which show the slumping of the wall between them.]
143:47:13 Henize: Very interesting.

143:47:23 Worden: Okay, now, we go on to Picard.

[Comm break.]

[Picard is scheduled to be Al's next target for visual observation and is the most prominent of the craters within Mare Crisium at 23 km diameter. He will photograph it after three more orbits and these two shots are AS15-94-12832 and 12833. Note that the Sun is nearly overhead Mare Crisium and Al will therefore discuss colour and albedo differences as the lack of shadow deprives him of much of a sense of depth.]

143:49:15 Worden: Houston, Endeavour.

143:49:20 Henize: Endeavour, go ahead.

143:49:24 Worden: Okay, Houston. Endeavour's coming up over Picard, and I thought I'd just go ahead and talk while we're going over Picard. First, talking about the color variations, Picard is a slightly different color than the rest of (the) mare basin. It's - I guess what I would consider Crisium - a light brownish gray. Picard, itself, is - is - is more of a brown tone, and it has a darker halo around it. I can see some of the brown - material just on the outside of the rim; and outside of that is some darker material that gradually turns into the gray of Mare Crisium. Inside Picard, I can see - well, let's see now, let's count them - 1, 2, 3, 4, 5, 6, six distinct rings that go around the inside of Picard. And the - and the walls in Picard are very shallow. It looks like a very shallow, almost like a - a dish - kind of basin, and gently from the edges on in toward the center, and, as I say, I can count - five or six rings inside, that are all concentric with the center of the basin. And I can see some definite layering in - in the - particularly in the upper boundary of the rim.

[Al's description of Picard appends his earlier comm at 128:07:19.]

[El-Baz, from the 1971 Visual Observation Debrief - "Was there anything specific about the color of Picard?"]

[Worden, from the 1971 Visual Observation Debrief - "Yes, there was. The mare surface itself is darker - I have to subtract mentally the ejecta from Proclus. The mare surface itself is almost a gunpowder color. ... It's almost black, but then you get fooled because you've got this very light ejecta - very thin ejecta - that is laid down over the mare surface, so that when you're looking at it from some distance away, it doesn't look nearly as black. A lot of that white comes through. The best way I can describe Picard is alternating layers of cream and brown."]

[El-Baz, from the 1971 Visual Observation Debrief - "So it was quite different then?"]

[Worden, from the 1971 Visual Observation Debrief - "Quite different from the surface, yes."]

[El-Baz, from the 1971 Visual Observation Debrief - "And that goes for the whole crater or the interior only?"]

[Worden, from the 1971 Visual Observation Debrief - "The interior is about the only thing you see of the crater. Once you get to the rim, that part from there on out looks pretty much like the rest of the surface. The interior was so distinctively different that that was the thing we looked at. Our eyes just kind of went to the interior, because it was so different. It was kind of a dark brown- and cream-colored alternating layers on the sides of Picard and Peirce. In fact, the interior of a lot of the craters we saw had distinct layering. They had a brown color and not the black color that you see on the surface. ... In the craters in the upland material, there was an absence of layering that I could see, but in almost all the mare-type craters - or the mare-located craters - there was that kind of layering."]

[Al also discusses the appearance of the rays from Proclus over Mare Crisium.]

[Worden, from the 1971 Visual Observation Debrief - "It's very strange the way the ejecta from, particularly, Proclus crosses Crisium. It's almost like flying above a haze layer and looking down through the haze layer at the surface. I don't know whether you've ever had the opportunity to do that or not, but that ejecta from that crater doesn't look like it's resting on the top of Crisium. It looks like it's suspended over it. It gives a very filmy, very gauzy appearance to the whole thing."]

[El-Baz, from the 1971 Visual Observation Debrief - "It must be very thin."]

[Worden, from the 1971 Visual Observation Debrief - "Yes. And I guess the reason it looks like it's just draped or suspended over it is that almost any way you look at it, if it goes through a crater or it goes through a ripple ridge or it goes through any topographic feature, it doesn't make any difference from what angle you view it; those lines - the ejecta pattern - are straight."]

[El-Baz, from the 1971 Visual Observation Debrief - "Okay; now when the ray goes through a topographic prominence or a negative depression of some sort, do you still see the ray through that?"]

[Worden, from the 1971 Visual Observation Debrief - "Yes."]

[El-Baz, from the 1971 Visual Observation Debrief - "Through the crater on top of the ridge?"]

[Worden, from the 1971 Visual Observation Debrief - "As a matter of fact, the areas where you don't see the ray seem to be independent of topographic features. There would be some areas where you wouldn't see any rays from Proclus. I guess the reason for that is that they might have been covered up by material from another crater that was a different color. So, you get rather vague, obscure patterns on the ground where the ray patterns cross, and you don't see the ray from Proclus. But it didn't seem to be tied into topographic features. It seemed to be more a function of just overlapping rays or ray patterns built on top of each other. But that's about all you can see in Crisium. It's like looking at a star field and trying to pick out some familiar stars. At first, all you see are stars; then, you have to orient yourself by picking out a star that you know; and then you pick out the other stars around it. This is almost the same thing. When you first look at Crisium, all you see is the ray pattern. You don't see any features at all; you just see the ray pattern. And then you start picking out some craters or some features that you know. From there, of course, you can see through the ray pattern and it doesn't distract you anymore. Then, you can pick up all these other things. That ray pattern is really prominent. And of course, it looked to me like 90 percent, of it was from Proclus. That's really a ray pattern that just covered everything."]

[El-Baz, from the 1971 Visual Observation Debrief - "Some of the ridges are over 100 meters high, so the ray material cannot be traveling close to the surface. Remember our discussion of how high the ray material would fly and the theory of it cutting right across the surface? If it did, it could not possibly cover the ridge and go right through it. Oh, yes. If it does, it's got to be sticking close to the ground the whole way, and that's just not the case, Yes, it's a very continuous ray pattern, as far as the topography is concerned."]

[There is further discussion of Picard at 149:57:24 including further debriefing with Farouk El-Baz.]

Worden (continued): Now, as opposed to - to - oh, let's - let's say Lick - Lick is - Lick looks like its almost completely obscured - feature now. It - it looks very much like a - collapse. All I can see is a little bit of a - of a ring, a color variation, with some positive relief. And then, inside the crater looks very much like outside - crater, as far as the color and the texture is concerned. However, it does appear to slope gently in towards the center. Lick looks to me like a very large collapse feature, with the same kind of material both inside and outside the basin.

143:52:09 Henize: Roger; we're - we're copying loud and clear.

[Unlike the prominent, fresh nature of Picard, Lick is a flooded crater named after the philanthropist James Lick, 1796-1876, who financed the Lick Observatory in California. Lick is flooded in the sense that the lava material which filled Mare Crisium 3.3 billion years ago, also filled the 31-km crater that was the fresh basin of Lick, sited at the edge of the Crisium basin. After the lava's stopped filling Crisium, Picard was blasted into the smooth mare surface to the north and east of Lick. The dating of mare lavas returned by Apollo, and in the case of Mare Crisium, by the returned samples from Luna 24, allow the relative dating of many features associated with the mare. In this case, we can see that Picard is younger than 3.3 billion years while Lick is older. Also, Lick must have been formed between the impact which formed the Crisium basin and the period when the lavas filled that basin. Although we do not have a date for the Crisium impact, we can see that the dates for the creation of Lick and Picard have been constrained.]
143:52:09 Worden: And, I make the same comment about Yerkes.
[Yerkes is another lava flooded crater, 36 km diameter, on the margins of Crisium and like Lick, is named after a benefactor of a great observatory. In 1897, Charles Yerkes, 1837-1905, financed the construction of what is still the largest refracting telescope in the world at 1.01 metres. This extraordinary instrument is still in regular use over one hundred years after it was built.]

[Although not scheduled to do so, Al is taking an additional opportunity to view the spectacular crater, Proclus, and its distinctive asymmetrical ray pattern. His first extensive description of the crater was at 128:07:19.]

Worden (continued): And I'm on beyond them now; I'm looking at Proclus now. And - may as well comment on Proclus while I'm here. Remember yesterday, we were talking about variations in the crater wall to - that - well, don't exactly know how to describe it, but there - there is a tremendous variation in the wall, which does line up with ejecta pattern. If - there's almost a straight wall on the side of Proclus that is minus an ejecta pattern. And then there is some breakthrough directly in the middle of that - of that wall, which makes Proclus looks like it's almost a circular crater. However, the - the truth is that Proclus looks like a - an elongate crater with - with one wall steeping [sic] - dipping quite steeply into the crater, and that wall is oriented perpendicular to a line bisecting the excluded zone dipping into the crater, and then right - right at the middle of that portion, it looks like there was a - a small - well, a small piece of that wall was - was also ejected, but it - it was only at the top part of that - of that fault scarp. And so, if you look at it from the right angle, you can see almost a flat plate, which looks like it's cut right into Proclus, and to the - to the north and west of that flat plate is the crater Proclus, and to the south and east is a small chunk out of the top of it that coincides with the - the - the central part of the excluded zone.

143:54:49 Henize: Roger, Al; we copy.

143:54:54 Worden: Hope you could understand all that, Karl. I had to talk fast and formulate as I went.

143:55:00 Henize: Roger, it came through loud and clear, and I think it was quite understandable. Very good.

143:55:15 Worden: Okay; I'm drawing a couple of little pictures of it to show you when I get back.

[The following three images from the Mapping Camera are a sequence from the current backward-looking sequence as they pass over the future Apollo 17 landing site.

Mapping Camera image, AS15-1399M, of Maraldi crater and Sinus Amoris.

This image, AS15-1399M, shows the Sinus Amoris region just east of the Taurus-Littrow valley. The craters marked 'D' and 'E' are large, flooded craters which, especially in the case of 'D', are almost completely inundated by the basalt of Mare Tranquillitatis.

Image AS15-1403M is similar to many shown in this journal as it concentrates on the Taurus-Littrow valley where Apollo 17 will land.

Mapping Camera image, AS15-1403M, of the Taurus Mountains including the Apollo 17 landing site.

The transition between the light and dark surface of Mare Serenitatis is very clear. Skipping another frame, we move on to image AS15-1405M and further out across Mare Serenitatis.

Mapping Camera image, AS15-1405M, of the southwestern boundary of Mare Serenitatis.

Again, note the contrast between the Taurus-Littrow region and the bulk of Mare Serenitatis. Also, there is a fainter transition on a larger scale that runs around the edge of the mare which can be running down the image between Borel and Clerke and northwest of Rimae Plinius.]

143:55:21 Henize: Okay, Al; we have Earthshine photography coming up in about 15 minutes. I'd better give you a PAD on it, and I also have another PAD for later photography on that page - or on the following page.

143:55:35 Worden: Okay. Okay, Karl. Stand by one.

[Comm break.]

[By the Flight Plan, the Earthshine photography is to consist of 20 frames through window 3, the central hatch window of the Command Module, using very high speed black & white film in the 35-mm Nikon camera. The Nikon will have its 55-mm lens open at f/1.2 and at the beginning of the procedure, the camera is set to a shutter speed of 1/500th of a second. The time that Henize is about to be give is not the time that the photography begins, it is the time that Al will reset and restart the mission timer. The timer will then be used to sequence events during photography, as follows: As soon as he has reset the timer, Al will cover the lens, take one blank frame, wind on and then set the shutter speed to 1/125. At 4 minutes on the timer, he will take 4 frames at 30 second intervals and then change the shutter to 1/15. When the timer reaches 6 minutes, he takes another 4 frames at 30 second intervals and sets the shutter to 1/8th of a second. These 8 frames are taken as Endeavour crosses the terminator but while the spacecraft itself is still in sunlight. Beginning at 8 minutes on the timer, Al takes 10 frames, again at 30 second intervals while Endeavour passes into near darkness, where the Moon below is lit only by the reflecting Earth.]

[Observers on Earth can see the same effect, often, though erroneously called the 'Ashen Light', when the Moon is nearly new. While the Sun illuminates only a thin crescent, a nearly full Earth illuminates the dark hemisphere of the Moon which becomes quite discernible with the naked eye. Some cutely describe this effect as the Old Moon in the arms of the New. More accurately, the Ashen Light refers to a similar effect seen on the planet Venus by some Earthbound observers though, in this case, it is uncertain what mechanism is responsible.]

143:57:10 Worden: Okay, Houston. Go ahead with the Earthshine PADs.

143:57:13 Henize: Roger. Earthshine PAD at about 144 hours and 5 minutes in your Flight Plan; the number is 144:10:32.

143:57:29 Worden: Understand 144:10:32.

143:57:32 Henize: Roger; and on the next page, a Map Camera photo PAD; take it?

143:57:40 Worden: Go.

143:57:41 Henize: Start, 145:14:16; stop, 146:13:56. [Long pause.]

143:58:19 Henize: The - did the Map Camera photo PAD...

143:58:21 Worden: Okay, I have my Mapping Camera photo PAD.

143:58:23 Henize: Roger.

143:58:26 Worden: Negative; you - you were cut out.

143:58:28 Henize: Oh, Roger. Mapping Camera photo PAD. Start, 145:14:16; stop, 146:13:56.

143:58:42 Worden: Understand. T-start, 145:14:16; T-stop, 146:13:56.

143:58:52 Henize: That's correct.

[Very long comm break.]

[CSM Flight Plan page 3-209.]

[The current run of the Mapping Camera, taking backward looking oblique shots of the lunar surface, is about to come to an end. The next run, which CapCom Karl Henize has just read up to Al, will also take oblique photographs, this time with the spacecraft rotated to make the Mapping Camera look north 40° from the vertical. This sequence runs from AS15-1430M to 1559M.]

144:09:07 Henize: Al, we've got 30 seconds until the Mapping Camera comes off. And then, 1 minute later, we start revving up for the Earthshine photos.

144:09:19 Worden: Roger, Karl.

[Long comm break.]
144:14:11 Henize: Okay, we start Earthshine photos in about 20 seconds.

144:14:29 Worden: Roger, Karl; understand. And, listen, since I got all the lights turned out here, how about stepping me through the Earthshine photos.

[Worden, from the 1971 Technical Debrief - "I did find that I got into a mode of operation where the ground would give me 30-second warnings on something which was in the Flight Plan. That meant I knew the sequence of things coming in the Flight Plan, but I got a reminder from the ground. If there was a 10-minute period before the next item had to be done, then I could completely forget about the sequencing in the Flight Plan. The ground would give me a 30-second warning, and that would be a cue to me to go back to the Flight Plan and do that function. I found that very useful."]
144:14:41 Henize: Roger. Okay, we're plus 4 minutes right now [on the mission timer] in 6 seconds [time]. 4 frames at 30 second intervals. [Long pause.]

144:15:17 Worden: And, Karl, I hope these all turn out, because this is the - the area on the last rev that I commented on all the lava flows, and we're right over now taking pictures.

144:15:27 Henize: Very good. [Long pause.]

144:16:07 Henize: Okay, after your fourth frame, you're going to change the shutter to 1/15th of a second. And - and then take four more frames at 30 second intervals.

144:16:17 Worden: Okay, 1/15th. [Long pause.]

144:16:34 Henize: I'm sorry; I could have been counting time for you, too. We're coming up to plus 6 minutes, which should be about the 4th frame at the old setting. We'll mark on 6 minutes.

144:16:47 Worden: Okay, got it.

144:16:49 Henize: And I'll call out times for you now, too. We go to 1/15th of a second.

144:16:55 Worden: Okay, I just took one frame at 1/15th.

144:16:58 Henize: Excellent. [Long pause.]

144:17:22 Henize: [It is now] Plus 30 seconds after your first picture.

144:17:54 Henize: Take number 3.

144:18:24 Henize: Take number 4, and change shutter setting to 1/8th.

144:18:34 Worden: Roger; 1/8th.

144:18:41 Henize: Now we're going to take 10 frames at 30 second intervals. Give me a mark on your first one.

144:18:48 Worden: Okay.

144:18:49 Worden: Mark. [Long pause.]

144:19:23 Henize: Time for number 2.

144:19:28 Worden: On. [Long pause.]

144:19:53 Henize: Take 3. [Long pause.]

144:20:23 Henize: Take 4. [Long pause.]

144:20:52 Henize: Take number 5. [Long pause.]

144:21:22 Henize: Take number 6. [Long pause.]

144:21:52 Henize: Take 7.

144:21:57 Worden: Roger; take 7, and I just went past the spacecraft terminator.

144:22:07 Henize: Say again? Roger; we copy.

144:22:13 Worden: Okay, I just went by spacecraft terminator.

144:22:17 Henize: Roger; we copy.

[By "spacecraft terminator", Al is referring to the passage of the spacecraft into the Moon's shadow, an event which happens about 6 minutes after it crosses over the lunar terminator.]
144:22:22 Henize: Take 8. [Long pause.]

144:22:52 Henize: Take number 9. [Long pause.]

144:23:22 Henize: Take number 10. Change the shutter to 1/500th, cover the lens, and cycle one frame.

144:23:40 Worden: Okay; thank you.

[Comm break.]
144:25:20 Henize: Okay, Al, in case you don't have your Flight Plan handy, we need to start a "P20 plus-X Forward" in a couple of minutes, and that will be followed by deploy of the Gamma-ray boom.

144:25:39 Worden: Roger; Karl. I'm with it.

[Comm break.]

[All through this daylight pass, the CSM has been flying nose forward and down as the Mapping Camera has been taking backward looking oblique photographs. Values given to P20 to control this attitude are to be changed to make the SIM bay point directly below the spacecraft with the Command Module's apex facing the direction of travel. The first two values define a vector leading from Endeavour at right angles to the SIM bay. P20 has already been told to point this vector towards the centre of the Moon. The third value, omicron, defines the attitude of the spacecraft around this vector with a value of 180° pointing the sharp end forward. Note that, with respect to the stars, the spacecraft rotates once every two hours to match the orbital period, a so-called "orb rate" maneuver.]

144:28:43 Henize: Al, are we in time to get a mark from you when you start the Gamma-ray boom [going] out?

144:28:51 Worden: Roger. I'm ready now. Gamma-ray boom going out.

144:28:56 Worden: Now.

144:28:57 Henize: Thank you.

[Comm break.]
144:30:03 Henize: Hey, time for exercise, Al. [Long pause.]

144:30:18 Worden: Yeah, I guess that's right, Karl.

[Comm break.]

[Al's exercise period is scheduled to extend from 144:30 to 145:00.]

144:31:41 Worden: Okay, Karl.

144:31:42 Worden: Mark; on the Gamma-ray boom.

144:31:45 Henize: Thank you.

[Comm break.]
144:34:13 Henize: Al, you may be interested to know that the Rover boys are up on the slopes of Hadley Delta now. They got themselves up to - to an area where there is considerable angle on the hillside, I'd guess 20, maybe almost 30 degrees. And it's still very fine soil, which acts a lot like snow. And you should have saw Dave about 5 minutes ago; took a beautiful spill in it.

144:34:42 Worden: Tell them to be careful.

144:34:45 Henize: Roger.

[Long comm break.]
144:41:52 Henize: Al, as you go around the corner, all your systems are looking good.

144:42:00 Worden: Roger, Karl.

144:42:03 Henize: See you on the other side.

144:42:08 Worden: Okay.

[Very long comm break.]

[Having restored the spacecraft to the plus-X forward SIM bay attitude, the instruments commence returning full quality data. Meanwhile, as Endeavour passes over the night side of the Moon, Al takes his exercise. The CSM begins revolution number 35 at about 145:01 and comes back into sunlight soon after. Al maneuvers the spacecraft into an attitude which has the SIM bay looking 40° north from the vertical for more oblique Mapping Camera photography. Once again quality of the data from the science instruments is degraded as they are not pointing directly down. The Mapping Camera will be operated throughout this daylit pass.]

[CSM Flight Plan page 3-211.]

145:29:44 Henize: Endeavour, this is Houston. How do you read?

145:29:50 Worden: Hello, Houston; Endeavour. Reading you loud and clear.

145:29:56 Henize: Same here. How goes it up there?

145:30:01 Fine, Karl. And I got a couple of comments on Tsiolkovsky, in addition to what I said last rev.

145:30:09 Henize: Go ahead, we're ready to copy.

145:30:14 Worden: Okay, talk - discussing the - the flow in crater Waterman, south of Tsiolkovsky, I guess what I said before still applies. The - what looks like on a map is the channel between Waterman and Tsiolkovsky is, in fact, too high for anything to flow between the two. There's - there's definitely some elevation there. However, looking at it this time, it's pretty plain that that channel - or gully, or whatever you call the breach in - in Tsiolkovsky's wall there between Waterman and Tsiolkovsky is caused by a graben-like fault system. There are two faults that run through there, and they run almost north and south right towards the central peaks, diverging - the one - the one on the west side, is slightly - is angled slightly to the northwest, but the other one goes almost directly north. And the source of the lava flow in Waterman appears to be high in the - in the wall of Waterman, on the north edge, right where the fault zone crosses the - the rim of Waterman.

145:31:30 Henize: Roger, Al. We copy.

145:31:35 Worden: Okay, now there are a couple of other small - small craters around Tsiolkovsky. Particularly, one on the north side, on the northeast corner, the first large crater that you see there, has a very distinctive lava flow or some kind of flow down in the crater. And that flow also originates up in the corner or up in the - in the high towards the rim of that particular crater, where there's some contact between the - the Tsiolkovsky rim and the rim of that small crater.

145:32:26 Henize: Roger.

145:32:31 Worden: Now again, I saw no evidence of - of any kind of a rock slide to the south of Tsiolkovsky, but the one on the west there is, looks - you know every time I go over it - it certainly confirms my opinion that that's a rock slide. The lineaments, the way the - the thing ended, the lobate - the lobate tongues on it and everything. It's interesting that the rim of Tsiolkovsky, on the west side there, is - different from - across that fault zone - is quite different from [what] it is around the rest of the crater, maybe suggesting that that [is] the source of the flow. The rim seems to be not as sharply defined; it's lower and appears to be out from the edge of the basin more than the rest of the - of the boundary or the rest of the ejecta pattern around Tsiolkovsky, and there, where that very steep, almost smooth scarp is, on the west of Tsiolkovsky, seems to be the - the point at which it starts.

[Al's extensive descriptions are being carefully listened to by the geologists in one of the backrooms at Mission Control, Houston. Any requirement to feedback information or queries to any of the crews, whether on the surface or in orbit, is always via the backup crew. Since Al's backup CMP is Vance Brand, it is he who fulfils this role for the orbital mission, and being an astronaut himself, he may elect to speak to Al directly rather than via the CapCom. Except for very special occasions, like when the President of the United States spoke to the Apollo 11 surface crew, or when Lee Silver, the crew's esteemed professor, is granted a conversation with Dave, Jim and Al just before Endeavour returns to Earth, only other astronauts are permitted to speak over the air/ground link.]
145:33:48 Brand: Al, Vance here. You have any comments on the rim of the north, northwest side, where you, [cough] it appears the rim might have slipped or - or you have a - a fault which shows the displacement?

145:34:07 Worden: Oh, yes, Vance, very definitely. There are a couple of fault zones, through there, and you can - you can see the displacement quite clearly from the air. The one, the fault zone between Waterman and Tsiolkovsky, is a - is a lot more subtle, but I - but I'm quite sure that, that's what's going on there. But the one on the west side is - is very clear. That - that's true.

145:34:29 Brand: Al, we'd like to have High Gain, Auto.

145:34:37 Worden: And, Vance, another comment about that. You got High Gain, Auto, by the way. Another comment about that, where that fault zone appears on the west side, there's much less mass wasting into the interbasin of Tsiolkovsky, than there is around the rest of the - of the crater. Most of that mass wasting seems to taken place outside the crater.

145:35:00 Brand: That's an interesting observation.

[Comm break.]
145:36:09 Henize: Al, Vance and I called up to your apartment a little while ago. Your folks are there. And I guess, as you know, they've got a squawk box look - listening in...

145:36:19 Worden: Oh, great.

145:36:20 Henize: ...listening on our loop with great interest. Except when you go behind the Moon, then they - then they watch the other show that's taking place on the surface. They said to say "Hello." And, they sound like they're having a good time up there.

145:36:36 Worden: Very good. Very good. Hello, folks.

[Long comm break.]

[Throughout the early American space program, it was customary for NASA to supply close relatives of the astronauts with a small loudspeaker, or 'squawk box' to let them listen in to the air-ground communication. The movie Apollo 13 has a scene in Marilyn Lovell's home when she allows herself to break down in private while the squawk box beside her hisses with anonymous static.]

145:40:19 Henize: Al, in 30 seconds we're coming up to a Pan Camera operation Mode, Standby; Power, On.

145:40:28 Worden: Roger.

[Long comm break.]
145:45:36 Henize: Al, while we're waiting for that Pan Camera off cue, I've got a couple of photo PADs - a couple of Flight Plan updates here for you, if you can copy them.

145:45:51 Worden: Okay, Karl; go ahead.

145:45:52 Henize: Okay. 148 hours and 0 minutes, they would like to have you get some good shots on those lava flows you saw over in Imbrium. And the recommendations that we have are as follows: CM3, EL, 250 mm lens, CEX, f5.6, 1/125, infinity, 5 frames at 10 second intervals. Recommend convergent photos starting at TCA minus 30 seconds. The aim point is up to you. Magazine Q, and record frame number. And then on the same page, 148 hours and 18 minutes, we don't need to do that P52 there, because the platform looks very good.

[At 142:16:28, Al had mentioned to Mission Control about seeing evidence of lava flows appearing to come from a ridge on Mare Imbrium and requested that a PAD be read up for some photography of it. This photography is to be taken out window 3, the central, hatch window, using the Hasselblad with a 250 mm lens onto colour daylight film using magazine Q. Mission Control also ask that he takes photographs of the same spot at 10 second intervals, allowing the motion of the spacecraft to change the viewpoint by about 16 km with each image. This will allow the use of stereoscopic techniques to help determine height differences across the landform in question.]
145:47:15 Worden: Okay, Karl. Understand photos of the lava flows in Imbrium that we noted on the last rev, that'd be CM3/EL/250, CEX, f5.6, 1/125, infinity, 5 frames in 10 seconds, use magazine Q, and try and get convergent stereo starting at TCA minus 30.

145:47:38 Henize: That's correct.

145:47:42 Worden: And, also, delete the P52.

145:47:44 Henize: Roger. [Long pause.]

145:48:01 Worden: Karl, while we're going over Crisium here. Looking down at Picard, at Peirce and at Lick, I noticed that all of those craters, that's - that's Lick Delta by the way, Lick Delta, Picard, and Peirce, all look like - they're - they're all about the same. They all have the same ring structure, all have the same low rims. The rims are - are - are what look like very shallow [elevation] compared to the rims on the other craters I've seen around. And, also, they all have a slightly darker halo effect around the - the entire crater. But the - the color difference is very subtle.

145:48:48 Henize: Roger, Al. As I look on the map here, they look like they might have been old craters flooded by the mare. Is that - does that seem feasible to you as you look at them?

[Lick Delta, a 14-km crater, is now known as Greaves, after William Greaves, 1897-1955, a former Astronomer Royal for Scotland. CapCom Karl Henize may be confused by the hearing the name 'Lick' which is a flooded crater on the margins of Mare Crisium. Picard, Peirce and Lick Delta (now Greaves) are all plainly the results of impacts which excavated the lava plains of Mare Crisium and exposed layering within the mare structure.]
145:49:00 Worden: No, it doesn't to me, Karl. They're a quite different texture inside, and you can see the ring structure clear down to the bottom of the crater. So I would say that they were - they were - they were not flooded craters.

145:49:11 Henize: Roger. Okay. [Long pause.]

[Soon, Al is scheduled to make some visual observations of the Littrow area. After his comments on previous orbits, Littrow is generating increasing interest among the geologists in the backroom.]
145:49:52 Henize: Hey, Al. Relevant to your observations coming up on Littrow here, Farouk [El-Baz] has asked whether the comments that you made previously about Littrow, seeing a - a mantling of dark material everywhere with a few puddles in the valleys, whether that same comment would - pertain to Sulpic - Sulpicia - yes...

145:50:15 Speaker (in Mission Control): Sulpicius Gallus?

145:50:16 Henize: ...Sulpicius Gallus. Or do you...

145:50:18 Worden: ...yes, Okay. Sulpicius Gallus. Certainly, Karl.

145:50:21 Henize: Right. Do they - do they look like very similar areas, or are there some contrasts there?

[The roughly circular Mare Serenitatis has two major areas of dark mantling around its shore, the Littrow area in the east and the Sulpicius Gallus area to the southwest.]
145:50:28 Worden: Okay. I'll let you know when I get there. Unfortunately, I think I'm not - I think I'm going to be out of attitude to take a look at Sulpicius Gallus.

145:50:35 Henize: Okay. That's for future reference then.

145:50:40 Worden: Yes, okay. But I'll - if - if I can see across Serenitatis there, I'll - I'll give you a hack on that.

145:51:05 Henize: Okay. I guess I should keep quiet a while and let you look at Littrow coming up in about a minute. [Long pause.]

145:51:55 Henize: Al, we can have Pan Camera Power, Off now.

145:52:01 Worden: Okay. Pan Camera Power, Off.

[Long comm break.]
145:57:05 Worden: Houston, Endeavour.

145:57:07 Henize: Go ahead, Endeavour.

145:57:12 Worden: Okay. Karl, I can give you at least a partial answer on that question. The - the coloration that seems to be continuous from Littrow all the way around through Sulpicius Gallus is the middle color. It's slightly darker than the rest of the mare basin [means surface] itself and not quite as dark as some isolated or localized areas within the Littrow area.

[Al has come up with a rudimentary classification of the shades of grey seen in the lowland areas in and around Mare Serenitatis.

Mare Serenitatis seen from over Moon's north pole.

This photograph was taken by the Jupiter-bound probe, Galileo, during its gravity assist flyby of the Earth-Moon system on December 7 and 8, 1992. The spacecraft flew over the Moon's north pole and this image shows Mare Serenitatis as seen from this northerly perspective. Note how the bulk of the mare is lighter than the margins. This dark margin is what Al refers to as "the middle color." The darker, localised areas are visible to the bottom right of the picture. Another dark area around Sulpicius Gallus is visible by following the shore of Mare Serenitatis around to the ten o'clock position on this photograph.]

Worden (continued): Now, those - those localized areas in the Littrow area were the areas in which I saw what appeared to be some ver - rather prominent, distinctive cinder cones, with their own respective dark halo. And it seemed to be the same darkness as the rest of the material in local areas within the Littrow area. In other words, there are - there are three variations of color. There are three tones of color in the Littrow area. The darker tones are associated with - the - with the lowland areas, like the valleys and like - down on just the edge of the mare surface. Then there's a lighter tone, which seems to be associated all the way around the - the - the ring or the rim of Serenitatis from Littrow all the way around through Sulpicius Gallus. And I don't see any other colors around Sulpicius Gallus, except that one. And they seem to encompass the area between the first wrinkle ridge and - and the contact between the mare basin [means surface] and the front there. Sort of like between the archuan [means arcuate] rilles and the first set of wrinkle ridges in the Serenitatis basin [means surface].

[Once again, Al describes the appearance of apparent cinder cones within the area of dark mantling near the crater Littrow. This observation, along with those at 079:23:46, 122:18:17 and 128:12:46, is enough to sway mission scientists and planners towards sending Apollo 17 to the valley of Taurus-Littrow in seventeen months time.]

[Al appears to be making a common error by confusing the terms 'mare' and 'basin.' To clarify, when a large body, perhaps tens of kilometres across, impacts the lunar surface, it creates an enormous depression in the Moon's figure. This depression is referred to as a basin. About 4 billion years ago, the Moon sustained a number of such impacts, a period often referred to as the Great Bombardment. Later, lava from the Moon's interior welled up through fissures in the basins to fill them. These huge areas of solidified lava, or basalt, are termed the maria and it would be correct to describe a mare as something which fills a basin. For most of the Moon's maria, the only portion of the basin we can see is the rim. An exception to this is Mare Orientale, which contains far less basalt than most of the other maria. Orientale displays many of the spectacular features of a large impact basin including the radial "sculpture" and multiple rings. In the above description by Al Worden, he is clearly making comparisons within the surface of the Serenitatis mare and not of the basin.]

[Journal contributor Robin Wheeler has kindly supplied images from his collection of Apollo SIM camera photography. Here, we include a sequence of the 33 north-facing views taken by the Mapping Camera during this pass as the spacecraft moves across Mare Serenitatis, Mare Imbrium and past the terminator. All the images are available via links but only every second one will have a guide image included.

Mapping Camera image, AS15-1524M, of the western boundary of Mare Serenitatis.

Mapping Camera frame AS15-1524M looks north along the dark-toned eastern shore of Mare Imbrium with Posidonius in the distance. 1525M brings the small crater, Very, into the centre of the frame.

Mapping Camera image, AS15-1526M, looking across the central expanse of Mare Serenitatis.

1526M has the 7.6-km crater Sarabhai in view. Note the very long, light-coloured streak that runs across the mare to its northeastern shore. 1527M has this streak nearly beneath the camera. If this streak is viewed in the context of this full Moon image, kindly donated by astrophotographer Rob Gendler, the streak appears to be part of the huge ray system emanating from Tycho, over 4,000 km to the south. Tycho's rays dominate the Moon's near side. The streak is also coincident with the crater Bessel, the largest crater well within the margin of Mare Serenitatis though it is only 16 km in diameter.]

Worden (continued): And then, As I'm looking at - right now, sorry I interrupted myself there. But looking right now at Bessel, and Bessel has some very distinct layering. In - in fact, Bessel looks like some craters, some volcanic type craters we've seen on Earth, where, to get alternate lava flows and sedimentary kind of rocks, then the lava flows stick out in the edge of the wall. In Bessel, about a third of the way down, there is a very distinct ledge that can - that can be seen all the way around Bessel. The rest of the - of the crater wall appears fairly smooth; but about a third of the way down is a - is a ledge.
[Rather surprisingly, there are no good photographs of Bessel in the Apollo 15 Hasselblad collection.]

[The Mapping Camera continues imaging the expanse of Mare Serenitatis.

Mapping Camera image, AS15-1528M, looking across the west-central expanse of Mare Serenitatis.

This continues on 1529M.

Mapping Camera image, AS15-1530M, looking across the west-central expanse of Mare Serenitatis including Linné.

On 1530M above, and 1531M the tiny yet highly visible crater Linné comes into view.]

[CSM Flight Plan page 3-213.]

[Al is due to change LiOH canister 12 for number 10 in the B receptacle. 10 will be stowed in compartment A9.]

146:00:15 Henize: Roger, Al, you're...

146:00:16 Worden: And that ledge looks like it's caused by a - a harder material.

146:00:21 Henize: Roger. You're coming through loud and clear. [Long pause.]

146:00:43 Henize: Do any of the other craters around that area, around Bessel, show the same sort of interior ledge like that?

146:01:06 Worden: Well, unfortunately, Bessel is the only one of that magnitude around - around that particular area. And I don't see any other craters that appear to go down below - whose depth appears to go down below the depth of the rim in Bessel.

146:01:15 Henize: Right. I - the only two I see possible here are Bessel E and Sulpicius Gallus; and I guess they might not go that deep even so. [Long pause.]

[Bessel E is another crater which has since been renamed by the International Astronomical Union (IAU) as Bobillier after a 19th century French geometer. It is 6.5 km in diameter. The Mapping Camera looks north across the western shoreline of Mare Serenitatis.

Mapping Camera image, AS15-1532M, looking across the western shoreline of Mare Serenitatis including Linné.

At the lower centre of this image, the irregular depression, Krishna, is visible. In 1533M, the Montes Caucasus range come into view.

Mapping Camera image, AS15-1534M, looking across the western shoreline of Mare Serenitatis including Linné.

By 1534M above and 1535M, we are looking at the mountain ranges that separate the two great maria. The Caucasus range is to the top of the image, the Apennine range to the bottom.

Mapping Camera image, AS15-1536M, of the divide between Mare Imbrium and Mare Serenitatis.

This division is very apparent in 1536M above. The landing site in the foreground is seen in beautiful context with the maria, the mountains and the great craters, Aristillus and Autolycus. 1537M continues the pass.

Mapping Camera image, AS15-1538M, of the eastern shore of Mare Imbrium and Palus Putredinus, including landing site.

This is 1538M which put the landing site in context with Palus Putredinus. Note the graben-type rilles, Rimae Fresnel, between the landing site and Autolycus. These are likely expansion features and have a very different morphology from the sinuous Rima Hadley. The large, flooded crater Archimedes starts coming into view in 1539M.

Mapping Camera image, AS15-1540M, showing Archimedes, Aristillus and Autolycus.

In 1540M above, the triumvirate of craters, Archimedes, Aristillus and Autolycus, that rule the eastern half of Mare Imbrium are all seen. In 1541M, the remains of the Archimedes ejecta blanket, Montes Archimedes, comes into the foreground.]

146:01:51 Henize: Hey, Al, have you ever looked at Autolycus and Aristillus with the thought in mind of determining which overlaps the other; which is the younger?

146:02:08 Worden: No, I haven't yet, Karl. Maybe this is a good time to do it.

[Very long comm break.]

[Al does not make any mention of seeing Autolycus or Aristillus during the rest of this pass. The Mapping Camera continues taking oblique images looking north of the spacecraft's position as the spacecraft moves towards lunar sunrise.

Mapping Camera image, AS15-1542M, showing Archimedes, Aristillus and Autolycus.

This image, AS15-1542M, is an excellent shot of Archimedes and the Apennine Bench Formation which includes Montes Archimedes. Beyond Archimedes is Montes Spitzbergen. 1543M moves the view out over Mare Imbrium.

Mapping Camera image, AS15-1544M, showing east-central Mare Imbrium.

This image, 1544M, is of the area west of Archimedes. Note the pair of craters Feuillée and Beer, and the string of craters strung out east of Beer, also well shown in 1545M. Frame 1546M takes us over the featureless expanse of the Imbrium basalt flows, peppered with the smaller craters. Many of those craters are secondary impacts from the formation of the mare's large crater. Coming into view in 1547M is one of these, Timocharis, which is more visible in 1548M

Mapping Camera image, AS15-1548M, and showing east-central Mare Imbrium.

Note the strings of small craters around the main structure at one to two crater-diameters distance. These are all secondary impacts from the ejecta that was thrown out by the primary impact that formed Timocharis. Our vicarious flight across the Moon continues with 1549M, 1550M and 1551M.

Mapping Camera image, AS15-1552M, of central Mare Imbrium.

The above image has the terminator approaching from the left as we look north of Lambert over the wrinkle ridges and small craters of the mare. In 1553M, a particularly dominant wrinkle ridge, Dorsum Zirkel, comes into view. Running northeast from it and slightly darker than the surrounding surface are solidified lava flows and they are part of the terrain which Al will photograph with the Hasselblad during his next pass.

Mapping Camera image, AS15-1554M, Dorsum Zirkel and the lava flows that run around its vicinity.

This image also shows the lobate flows. On the left, Mons La Hire is coming into view. 1555M continues towards the terminator.

Mapping Camera image, AS15-1556M, Dorsum Zirkel and the lava flows that run around its vicinity.

This is the final image in this sequence. In it, the lava flows that Al has identified is well seen in the very low-angle lighting. It runs in a long ribbon from southwest to northeast. Though the flow evidently lies on top of older flows, both are of great antiquity as evidenced by the presence of craters across both.]

146:13:01 Henize: Endeavour, we have the Mapping Camera coming Off in just one minute.

146:13:07 Worden: Roger, Houston.

[Long comm break.]

[Having stopped the Mapping Camera, and as Endeavour moves into lunar night, Al maneuvers the spacecraft to point window 5 of the Command Module towards deep space. As part of this process, he alters the setting in the DAP to give much tighter control of the spacecraft's attitude and therefore the pointing of the Nikon camera. The attitude deadband is reduced from ±5° to ±0.5° and the rate at which the spacecraft is rotated is increased from 0.2° to 0.5° per second.]

[The Nikon camera is loaded with very high speed black and white film, to take calibration images through window 5 for the gegenschein experiment. The gegenschein is a faint patch of light seen on the opposite side of the ecliptic to the Sun. It is thought to be caused by sunlight being reflected back to the observer, preferentially in the direction that the light came from, by tiny particles in the interplanetary medium. In a sense, it is an extension of the zodiacal light which extends along the ecliptic from either side of the Sun. At this stage, the Flight Plan calls for the 55 mm lens to be on the Nikon, at an f/stop of 1.2, focused at infinity and, for the moment, with a shutter speed of 1/500th of a second.]

146:18:12 Henize: Al, I have a couple of comments on the water dump coming up in - 10 or 15 minutes.
[The Flight Plan calls for a urine dump at 146:23.]
146:18:23 Worden: Okay. Go ahead.

146:18:24 Henize: We'd like to dump down to 10 percent. Stop at 10 percent. And they say that the dump will probably take about 8 minutes, so about 6 minutes after you start dumping, keep an eye on it and stop at 10 percent. And also, they'd like for you again to - to make an observation of the particle cloud at sunset and sunrise terminator, if you would, please.

146:18:51 Worden: Okay. Will do. And I understand you just want me to dump down to 10 percent.

146:18:56 Henize: That's correct. And over at 146:33, where you have a "Gamma-ray Gain Step Shield, On, [Center]," we'd like you to take - to make one step increase in - in gain there. That's up momentarily, once.

146:19:20 Worden: And that's at what time?

146:19:23 Henize: That's over at 146:33, where you - they want you to put Shield, On [center]. After you have it on center, take it up once momentarily for one step increase in gain, and then leave it on center.

146:19:46 Worden: Okay; Understand. Gain Step Shield, On and - go one step up, and then leave it Shield, up.

146:19:54 Henize: That's affirmative.

[Comm break.]
146:21:51 Henize: Okay, Endeavour. We're coming up to Gamma-ray Gain Step, Shield, Off in - in about 5 seconds.
[Long comm break.]
146:29:56 Henize: Al, a bulletin from Hadley Rille, says that...

146:30:00 Worden: ...from what?

146:30:04 Henize: Go ahead. [Long pause.]

146:30:29 Henize: Go ahead, Al. We're listening.

146:30:36 Worden: Karl, I didn't call. I'm waiting on you.

146:30:39 Henize: Oh, Roger. A bulletin from Hadley Rille - the crew finished their exploration of the Apennine front. They got over to Spur Crater and actually into Spur Crater, found there a large block of rock, which probably is a really true sample of the Apennine Front and got some good samples there. And, now they're driving back down by the South Complex and they're digging some samples around Dune Crater.

[The block of rock from Spur crater is sample 15415; instantly christened by the media "The Genesis Rock" and probably the most famous sample to come from any of the Apollo missions.

Real Video file (166K)

It had been hoped that this white crystalline rock would be a sample from the original lunar crust. Though it consists of anorthosite, a mineral which floated to the top of the early Moon's magma ocean, this sample was found to be a full half billion years younger than the Moon itself. However, it was from the time before the Great Bombardment and gave useful clues to the early history of the Moon.]

146:31:16 Worden: Very good. Sounds like they're doing quite well down there.

146:31:20 Henize: Yes, indeed.

146:31:25 Worden: I think we're going to give lots of people lots of things to do for a while.

146:31:30 Henize: You said it.

[Comm break.]
146:32:44 Henize: Okay, Al. In about 20 seconds, we have the Gamma-ray operation coming up.

146:32:53 Worden: Roger, Karl. [Pause.]

146:33:07 Worden: Okay. You've got the Gain Step, one step, then it's back at Shield up.

146:33:14 Henize: Very good.

[Long comm break.]

[During this hiatus in communications, Al is allowing the attitude of Endeavour to settle down after the maneuver at 146:18 oriented the windows towards deep space. As he will be taking exposures of three minutes duration, it is necessary for the spacecraft to be as stable as possible. Sloshing of liquids in the tanks, particularly the fuel and oxidizer, are random and significant and even Al's exercising can result in small attitude excursions. Al sets the scale on the FDAI rate meter to 5/1 to show small attitude rates better.]

146:39:56 Henize: Al, this is Houston. All of your systems are looking in great shape as you go around the corner.

146:40:05 Worden: Okay, Karl. And we're looking okay up here. Getting ready to do the gegenschein calibration.

146:40:13 Henize: Very good.

[Very long comm break.]

[From the time when Endeavour goes out of sight of Earth to when it enters sunlight again, there is just under 25 minutes when light from neither the Earth nor the Sun falls on the spacecraft. This is the time when long exposure photography out of the Command Module's window can best be achieved. Once Al has ensured that the spacecraft's attitude has settled and that the CM's light are dimmed, he takes a blank frame, moves the film on and sets the shutter to T (for time exposure). He then makes an exposure of one minute duration out of window 5, another of three minutes duration and finally takes another blank frame after returning the shutter speed to 1/500th of a second. The gegenschein photography proper is due to be carried out at 168:20 but according to the National Space Science Data Center (NSSDC), no useful data was obtained from this experiment due to aiming errors.]

[With the photography out of the way, Al retracts the Mapping Camera, purges the fuel cells, and carries out a water and urine dump. Note that at 146:18:24, he was passed a message to cease the water dump when the tank is 10 percent full. Just before Endeavour re-emerges into sunlight halfway through this far-side pass, it begins its 36th orbit around the Moon and Al will reorient the spacecraft to the forward-pointing SIM bay attitude; instruments facing the Moon and the nose of the CM pointing in the direction of travel. Getting to this attitude is causing Al some problems which he will relate to Mission Control once Endeavour regains communication with Earth. The science instruments are reconfigured by extending the Gamma-ray boom, opening the covers to the X-ray and Alpha Particle experiments and powering up the X-ray Spectrometer. As there is no Mapping or Panoramic Camera activity, the attitude deadband is relaxed to 5°.]

[CSM Flight Plan page 3-215.]

147:29:54 Henize: Endeavour, this is Houston. How do you read?

147:30:00 Worden: Hello, Houston; Endeavour. Loud and clear.

147:30:03 Henize: Good to hear your cheery voice. How is everything up there?

147:30:09 Worden: Yes, just fine. It took us a little longer to lock up that time.

147:30:17 Henize: Yes. A couple of minutes, but it still wasn't bad.

147:30:39 Worden: And, Karl, on the waste water dump, I overshot 10 percent, just a little bit, but I'm reading - I'm reading about 10 percent now.

147:30:48 Henize: How much was that?

147:30:54 Worden: I'm reading 10 percent.

147:30:55 Henize: Roger. Reading 10 percent now. I copy that. [Long pause.]

147:31:26 Henize: Al, we'd like to have High Gain [Antenna], Narrow and Auto.

147:31:50 Worden: Okay, Houston. You got it.

147:31:52 Henize: Very good. Thank you.

147:32:05 Worden: And, one other thing, Karl. The attitude change from the gegenschein calibration attitude to plus-X forward SIM attitude was pretty squarely in the middle of gimbal lock. And I had to do some maneuvering to get around it, using a little extra fuel. You might run that back through with the FAO.

147:32:30 Henize: Roger. We copy. [Long pause.]

[Surprisingly, there are certain attitudes to which the vehicle is never oriented, if possible, with respect to the alignment of the platform. The team at MIT who designed the Apollo guidance system settled on a three-gimbal mounting for the platform, similar to the Polaris missile system and unlike the four gimbals found in the Saturn V Instrument Unit and the Gemini spacecraft. Among the tradeoffs in this decision were a reduced tendency to drift and saving of weight from not having a heavy outer gimbal. However, this arrangement has the unfortunate side effect that, in certain configurations, the assembly loses its ability to keep the platform aligned to the required attitude; this being termed "gimbal lock". Having a fourth gimbal avoids this problem. Great care has to be taken during the flight planning process to ensure that the spacecraft is never orientated to an attitude where gimbal lock can occur. If it does, it is a time consuming procedure to realign the platform, possibly with the loss of important operational work; or worse, near a time critical maneuver where good platform alignment was important and no time is available to correct it.]

[In the Apollo 11 Lunar Surface Journal, Eric Jones accurately comments that "the concept of gimbal lock is not an easy one" and with the help of Journal Contributor Henry Spencer and Neil Armstrong, gives a thorough explanation of the condition. We have taken the opportunity to add diagrams and Eric's text has been amended to accept them.]

[Stripped to the essentials, the inertial platform, which tells the computer how the spacecraft is oriented, is mounted inside a nested set of three gimbals.

Gimbal Lock Figure 1

As shown in figure 1, the outer gimbal (red) is mounted on an axis (No. 1) attached to the spacecraft (shown by the square frame) and the assembly is free to rotate around that axis. The intermediate gimbal (green) is attached to the inside of the outer gimbal at points 90° from the No. 1 axis. This is the No. 2 axis. Similarly, the blue gimbal, which carries the platform, is fixed at points perpendicular to the No. 2 axis. In this diagram, the platform is facing up with a marker tab at one corner. As the spacecraft maneuvers, the gimbals swing in such a way as to keep the platform in the same absolute orientation. For the purposes of this discussion, let us assume that the platform and gimbal system always start in this configuration.

Gimbal Lock Figure 2

Now, let us imagine that the spacecraft does a rotation around the vertical axis as in figure 2. Clearly, the gimbal system will have no trouble keeping the platform properly aligned and, indeed, the three axes will remain mutually perpendicular no matter how large or small a rotation is done.

Gimbal Lock Figure 3

Next, let us go back to the original configuration and consider what happens if the pilot rotates the spacecraft around the inner, No. 3 axis in a clockwise direction. The diagram in figure 3 shows the result. Axis No. 1 is now oriented left-right and axis No. 2 is vertical. However, axis No. 3 has retained its original orientation and, once again, the three axes will remain mutually perpendicular - with the platform in its original orientation - for any arbitrary rotation around the axis No. 3.

Gimbal Lock Figure 4

Finally, let us return to the original configuration and consider what would happen if the pilot did a rotation around the axis No. 2 in such a way that the upper part of axis No. 1 goes back away from us and the lower part comes up towards us. Here, the three axes do not remain mutually perpendicular and, if our pilot were to stop the rotation after 90°, we would find ourselves with a gimbal lock. As is shown in figure 4, the platform is still properly aligned but we also have the No. 1 and No. 3 axes pointing in exactly the same direction. In essence, we now have a two-axis system instead of a three axis system.

Gimbal Lock Figure 5

If, from this configuration, our pilot were to do rotation around an imaginary axis perpendicular to the horizontal plane that contains all three gimbal axes, as in figure 5, then the platform orientation would change and indeed, would rotate in lockstep with the spacecraft. Hence the term, "gimbal lock".]

[O'Brien - "I guess it's safe to say that gimbal lock has been over dramatised by the Apollo 13 movie and all the rest. Obviously it's a serious thing but operationally you always had a procedure that allowed you not have to worry about that."]

[Scott - "No, I don't think so. You have to worry about it. You were always aware of it. 3-axis platform - Gemini had a 4-axis platform."]

[Harland - "Why did they not carry that forward?"]

[Scott - "Because four gimbals give you a lot more drift, a lot more potential failures. Three gimbals are more reliable in a sense and if you stay away from gimbal lock, you don't have to worry about the difference."]

[Harland - "Positive reasons for going to three."]

[Scott - "Oh, yeah. I think three's better. You don't have to fly into gimbal lock. But all this was new when you go into space, because in space, you got a sphere, you know. [Preplanned] trajectories and the REFSMMATs kept us on an orientation that avoided gimbal lock. But you could get into gimbal lock."]

147:32:52 Henize: Al, still a little trouble on the High Gain. Let's go Wide Beam for a second or two and back to Narrow. [Long pause.]
[Just before AOS, Endeavour was placed in the sharp-end-forward SIM bay attitude. One side effect of this is that at AOS, the spacecraft is more or less pointing towards Earth with the HGA at the tail end having to look past the metal hull of the Service Module and it is entirely possible for the antenna to lock onto a reflection from the hull rather than onto Earth. By switching to Wide Beam for a few moments, the reflections are ignored as the antenna locates and locks onto the stronger signal from Earth.]
147:33:57 Henize: Endeavour, let's go back to Reacq.
[Comm break.]

[The Auto mode on the HGA still isn't locking to Earth. In "Reacq" mode, the antenna returns to the dialled-in position if it loses lock. However, the current dialled-in angles were only relevant at AOS and the spacecraft is slowly rotating as it moves around the Moon so Mission Control must send up a revised pair of angles.]

147:35:14 Henize: Al, we'd like to go Pitch, minus 11, Yaw 12, without changing the mode switch.

147:35:25 Worden: Understand; minus 11 and 12.

[Al dials these angles into two controls to the bottom right of panel 2.]
147:35:28 Henize: Affirmative.
[Comm break.]
147:36:48 Henize: Wide - Al, we need to go to Wide for a couple of seconds and then back to Narrow. [Long pause.]

147:37:45 Henize: Endeavour, could we have Wide Beam again for a couple of seconds and then Narrow. [Long pause.]

147:38:37 Henize: Endeavour, this is Houston. How do you read?

147:38:44 Worden: Houston, I'm reading you loud and clear, 5 square.

147:38:48 Henize: Good. Sorry about all of this High Gain switching problem. We're - we'll try to get it squared away - away real quick. I'll let you get back to your parsley soup.

147:39:05 Worden: Okay. I was just getting it out.

147:39:17 Worden: And, Karl, you'll be interested to know I had a very good exercise period this time.

147:39:22 Henize: Very good. Glad to near it.

[Long comm break.]
147:42:46 Henize: We're all squared away on the High Gain now, Al. Thank you.

147:42:53 Worden: Okay, Karl. Was there a problem associated with my gear, or with yours?

147:43:08 Henize: We sus - we suspect that there was some problem about the new attitude, and we were getting some sort of reflection off your skin up there.

147:43:23 Worden: I see. Okay. [Long pause.]

147:44:25 Henize: Endeavour, we'd like to have High Gain [Antenna], Auto.

147:44:36 Worden: Okay. You got Auto.

[Very long comm break.]

[As Al's meal break continues, the gathering of data from the SIM bay is continuing with the Gamma-ray Spectrometer, the X-ray Spectrometer and the Alpha Particle experiment.]

147:55:50 Worden: Houston, Endeavour.

147:55:56 Henize: Endeavour. Go ahead.

147:56:01 Worden: Okay. While I'm trying to get a bite of lunch here, I thought I'd just tell you that after the dump, the same thing happened - the same kind of cloud, the same kind of particles that - that I described yesterday. And they've just about - they've just about dispersed now. Well, you know, Karl, the interesting thing, I guess I hadn't thought about it before, but when you're sitting up here looking at the surface through one window, it's just pitch black out the other windows. So you go from a very bright scene in one window to a black in the other.

147:56:36 Henize: Yes. So, actually out - out the dark window...

147:56:38 Worden: [Garbled]

147:56:39 Henize: Out the dark window, you are still able to see particles?

147:56:42 Worden: Yes, I see particles; there's no cloud now.

147:56:48 Henize: You - you did see...

147:56:49 Worden: You could until just a few minutes ago, and the particles dissipated rather quickly; and now I don't see any particles out that window.

147:56:59 Henize: Roger. We copy.

[Comm break.]

[Al first noticed the particle cloud associated with the spacecraft dumps at 126:34:27, giving experimenters something to think about as it represents contaminant to some of the SIM bay experiments, particularly the Mass Spectrometer, currently not in use.]

147:58:41 Henize: Al, another bulletin from the lunar surface. The fellows have been back at the LM for some time and working again on the ALSEP. And the problems they had with the drill, they're trying to catch up with now. And yesterday they got in one of the heat sensors and then had trouble finding the time to get in the second one. But they did get the second one in today, and I guess now they're going to go after the core - the core drill sample.

147:59:22 Worden: Sounds like they're pretty busy down there, Karl.

147:59:25 Henize: Yes, they are having a good time there, all right.

147:59:33 Worden: Well, good for them. I'm having a hard time keeping my lobster bisque in the bag up here.

147:59:39 Henize: Hey, that sounds like a tough life you've got there. [Long pause.]

[Worden, from the 1971 Technical Debrief - "It takes longer to do things in flight than you'd anticipate. For instance, to eat a meal seems to take me considerably longer than I had thought would be required before flight. Invariably, there were things to do right in the middle of an eat period which took your attention away from that part of the flight and extended the eat period considerably from that shown in the Flight Plan. The same thing was true of the exercise periods. I tried to get the exercise during those periods when it was called out in the Flight Plan, but again, there were things that had to be done almost inevitably during the exercise periods."]

[CSM Flight Plan page 3-217.]

148:00:49 Henize: I just stopped to look at the clock, Al, and I see that the [Imbrium lava] flow photos are coming up on us almost immediately, if you'd like to take them.

148:01:04 Worden: Roger.

[Comm break.]

[Details of this photography task were read up at 145:45:52 based on Al's description of lava flows coming from a ridge at 142:16:28 and his request for a photo PAD to get pictures of it.]

148:02:23 Henize: As I look at the Flight Plan, I had that marked at 148 hours and 0 minutes. They must have given you a 5 minute pad[ding] there. [meaning extra time, not PreAdvisory Data] As I see your position on the Moon, you've got a while before you get there. Is that correct?

148:02:40 Worden: Right, Karl. That's the way it looks to me.

148:02:43 Henize: I have you coming up on Hadley, right - Well, you just passed Hadley, I guess.

148:02:50 Worden: Yes, that's right. I'm just going over Archimedes right now.

148:02:53 Henize: Righto.

[Long comm break.]
148:06:47 Worden: Karl, Endeavour. Just for your information, at present time I'm right over Timocharis, and Lambert's coming up on - the - on the - it's just to the south of me - with Lambert R a very subdued ring just to the - to the south of Lambert. And the photos I want to take are over around the area of Mount La Hire and La Hire Rilles, a little bit west of Lambert.

148:07:20 Henize: We copy that.

[Endeavour is passing over the southern half of Mare Imbrium where, roughly along the spacecraft's track, there is a string of very prominent craters which stand out against the smooth mare surface. First is the great triangle of Aristillus, Autolycus and Archimedes on the eastern side of Imbrium. These are seen well in the Mapping Camera image AS15-1541M. The morphology and situation of these three along with the light-coloured terrain to the south of Archimedes have been crucial to our developing understanding of the Moon's violent history. The sequence of events goes something like this.]

[3.84 billion years ago, a large object struck the Moon excavating an enormous multi-ring basin, 1,100 km across, part of the outer rim of which we now call Montes Apenninus and which Dave and Jim are exploring below. Some time after, light-coloured lava welled up within this basin though now we can only see one plateau of this, the Apennine Bench Formation, a light patch extending from Archimedes to the Apennine Mountains. Another smaller impact formed a crater whose remains are now called Archimedes and we can see the ejecta and secondary impacts from this event overlying the Bench Formation. From 3.3 billion years ago, the dark mare lavas filled the Imbrium basin to form Mare Imbrium, as well as filling the floor of Archimedes. Though the interior of Archimedes was filled, the lavas did not rise high enough to cover the Apennine Bench Formation. This lava-filling episode lasted at least half a billion years and the last vestiges were probably much later. Sometime over a billion years ago, two separate impacts formed the craters Aristillus and Autolycus and the rays from these events are now very faded. To complete the picture, the southern half of Mare Imbrium is overlain with rays from Copernicus to the south. The impact which formed Copernicus has been tentatively dated at just less than 1 billion years ago. It is essentially the last major event to have influenced Mare Imbrium.]

[The other major craters mentioned by Al are: Timocharis, named after a Greek astronomer, 280 B.C.E.; its 33-km diameter walls puncture the mare midway between the eastern and western rim and it has a small crater right in its centre. It is well seen in AS15-1005M taken during rev 27. Lambert is similar to Timocharis though slightly smaller at 30 km and it also sports a small crater in the centre. It was named after Johann Lambert, 1728-1777, a German mathematician and astronomer.]

[Al Worden also mentioned Lambert R, a subdued or ghost crater sited directly south of Lambert which is very difficult to see in all but the most oblique lighting and which is probably the result of a pre-mare crater, like Archimedes, being overwhelmed by the many lava flows that formed Mare Imbrium.]

148:07:21 Worden: And, as a matter of fact, I have - Mount La Hire seems to be in view now and looks like I'm heading right at it.

148:07:33 Henize: Hey, as I look at the map here, it looks like about three - three hills with a crater in the top of each - look like volcanoes here although this map is lousy from that point of view. What do they look like to you?

148:07:51 Worden: Well, I can see a - the - the - they're a chain of hills - ridges, and I can't see much more than that from here right now.

148:08:02 Henize: Roger.

[Comm break.]
148:09:37 Worden: Okay, Karl. If you're following on the map, I'm right south of the intersection of the La Hire Rilles and the wrinkle ridge [Dorsum Zirkel] that runs off to the northwest there, just by Mount La Hire. In fact, I'm directly over Mount La Hire now, and it looks like there's a volcano in - or not a volcano, but a crater, in the top of the western-most hill.

148:10:02 Henize: Roger.

148:10:09 Worden: And I'm starting to take some pictures to the west now.

148:10:13 Henize: We copy.

[Comm break.]

[The area of interest to Al is around Mount La Hire, an isolated massif, 1,500 metres high, about 100 km WNW of Lambert. Al is nearly at the terminator now and can take advantage of the very low angle lighting to see the most subtle of relief in the various lava flows below. Lunar lava is thought to have had a very low viscosity, similar to that of motor oil at room temperature so it ran freely over previous solidified outpourings. The edges of individual lava flows often display recognisable lobate shapes which betray their origin. During the previous pass, the Metric section of the Mapping Camera took some excellent images of the La Hire region of which AS15-1555M is a good example. A particularly clear example of a lobate flow can be seen running bottom-left to top-right between Mons La Hire and the massif to the northwest, then across Dorsum Zirkel.]

[Using the Hasselblad and the 250-mm telephoto lens, Al takes 11 images of this area, AS15-96-13023 to 13033. As these images are taken very near the terminator where the low sun angle accentuates the landscape's subtle relief, the contrast has been stretched to bring out the detail. AS15-96-13024 shows the ends of two fingers of lava flows. Notice how there are more craters between and beyond these flows. Referring back to the Mapping Camera image, AS15-1555M, you can see a closer shot of the flow that runs between the two massifs in photo AS15-96-13029. The smaller massif to the northeast of Mons La Hire is visible to the right with the flow running right across the image. AS15-96-13033 is the last of the sequence and is right on the terminator. The raised rims of the craters are very evident as is a flow scarp running across the image.]

148:11:59 Henize: Al, can you clarify a little more exactly where you're photographing. I see a wrinkle ridge running northwest toward Caroline Herschel from the La Hire Rilles, so this is where I'd guess you're working. Is that correct?

148:12:22 Worden: Negative. That's the large wrinkle ridge running off toward C. Herschel. No, I'm working directly west of La Hire Rilles in that open area out there. Say on a line between Euler and Heis.

[Note that the modern name for the La Hire Rilles is Dorsum Zirkel and Dorsum Heim.]
148:12:40 Henize: Roger. I copy.

148:12:46 Worden: And there's nothing particularly significant that you can see on the map there. It's just that La Hire Rilles seem to be associated with a lot of those flows, and the flows - there are so many of them, and they're so overlapping and intermingling that I just want to get some general pictures of those flows coming out of La Hire.

148:13:07 Henize: Roger. That sounds like a very interesting region, and I see over by Diophantus there, you've got some very prominent rilles at the present time that probably are just on the - on the terminator, aren't they?

148:13:22 Worden: Yes, Karl. I'm - I'm beyond the terminator now.

148:13:48 Henize: Next time you get the Flight Plan in hand, let me give you the T-start for the zodiacal light photography.

148:14:10 Worden: Okay. Go ahead.

148:14:14 Henize: Okay. 148:34:26 is the zodiacal light photo PAD.

148:14:26 Worden: Understand, 148:34:26.

148:14:29 Henize: That's affirmative. [Long pause.]

148:15:17 Henize: Say again, Endeavour.

148:15:23 Worden: Go ahead.

148:15:26 Henize: Disregard, Al. I thought I heard you call, and it was just something else in the background, I guess.

[This is the end of Al's scheduled meal period. With the upcoming P52 alignment deleted from the Flight Plan, Al's next task is to prepare the Nikon camera for photography of the zodiacal light. As before, the camera is loaded with very high speed black and white film and has the 55-mm lens attached. The camera will be mounted in a bracket looking out of window 4, the right-hand, forward-looking rendezvous window. The time given in the PAD passed up to Al just now is the time when he resets the mission timer. He will use it to sequence the taking of 27 frames, some of which have exposures up to 2 minutes.]
148:15:35 Henize: Jim is busy drigging [sic] - digging trenches there by the LM, and he just about dug a hole big enough to - to build a swimming pool in. He did a good job. [Long pause.]

148:16:13 Henize: Can you see as far south as the Carpathian Mountains, Al?

[Just as the southeastern rim of the Imbrium basin is known as Montes Apenninus, another section running west from the most southerly point of the rim is officially named Montes Carpathus.]
148:16:41 Worden: That's negative, Karl. I'm in - I'm - I'm beyond the terminator now in total darkness.

148:16:47 Henize: Right.

148:16:56 Henize: If you - if your orbit ever brings you far enough south to look at those Carpathian Mountains, I should think that would be pretty interesting. I - well, you probably know better than I, I guess, that's probably an overflow of Procellarum into Imbrium there. Probably sort of - well, if that's true, it should have the appearance of the front edge of a lava flow, although it is a tremendous thing.

[Very long comm break.]
148:32:28 Henize: Endeavour, this is Houston. The Rover boys have finished their tasks - most of their tasks with the ALSEP, and they are just now beginning ingress into the LM. Dave managed to get the core drill completely in; and, although he hasn't pulled it out yet, he'll pull it out on the next EVA. The time to set the mission timer, or to set your countdown for the zodiacal light photos is going to be about in one minute. And the word down here is that all of your systems are Go; everything is looking super.

148:33:17 Worden: Roger, Karl. Thank you very much. See you on the other side. And, if you'll check my DSKY, you'll see I got the time count down there too.

[Al's comment about using the DSKY as a counter shows that the condition of the spacecraft is having small repercussions on operations. The popping of the circuit breaker at 033:47 GET, caused by the short circuit in the mission event timer, has deprived Al of his normal timing reference in the LEB. Using his initiative he employs the timing capability of one of the computer's programs, P30, to act as a timer for him. At 153:23:44, he will be informed that this procedure causes a problem that he is currently unaware of.]
148:33:24 Henize: Very good.

148:33:32 Worden: And I'm even managing to finish my lunch. Thank you.

148:33:37 Henize: That is a soft life up there, when you get a chance to finish your lunch.

148:33:45 Worden: You better believe it. Some times it's not so easy.

148:33:52 Henize: I can believe it.

[Very long comm break.]

[The mission timer is begun at 148:34:26 for the zodiacal light photography sequence. At 5 minutes into the count, Al will take his first exposure just after the Earth has disappeared below Endeavour's horizon and neither it nor the Sun can cause glare in the long exposures. In total, 23 frames with exposures ranging from 1/60th of a second to 2 minutes are taken before Endeavour returns to sunlight just after commencing its 37th revolution of the Moon.]

[CSM Flight Plan page 3-219.]

[The final task during this far-side pass is some orbital science photography with the Hasselblad out of window 3. This will be of photo target 9, the crater Meitner, which is just around the eastern limb of the Moon and out of sight of Earth. The shadows are beginning to appear around Tsiolkovsky and AS15-94-12815 is a rather indistinct shot of the north rim of Waterman, a degraded crater just to its south. 12816 and 12817 are two rather dark, overlapping images of the very western rim of Tsiolkovsky, just north of the point where the mare-like interior meets the rim. The Hasselblad Photo Index placed 12818 northwest of Tsiolkovsky but otherwise it is unplaced. AS15-94-12819 is an oblique shot of Lütke and the arcuate feature in its interior. 12820 to 12828 are a overlapping sequence from the northwest rim of Meitner, across the heavily beaten up landscape to the north rim of the large degraded Pasteur. AS15-94-12823 shows the crater Einthoven, with heavily terraced walls and AS15-94-12827 shows a cluster of small craters which obscure the north rim of Pasteur.]

[The final three pictures taken during this far-side pass are AS15-94-12829 to 12831 which show a battered landscape looking towards crater Wyld.]

[In Mission Control, there has been a change of shift and the CapCom position is now filled by Robert Parker.]

149:27:57 Parker: Endeavour, Houston. Over. [No answer.]

149:28:50 Parker: Endeavour, Houston. How do you read? [No answer.]

149:29:20 Parker: Endeavour, Houston. [No answer.]

[Comm break.]
149:31:02 Parker: Endeavour, Houston. How do you read? [No answer.]

149:31:29 Parker: Endeavour, Houston. How do you read? [No answer.]

149:32:14 Parker: Endeavour, Houston. How do you read?

149:32:22 Worden: And Houston. Endeavour loud and clear, and I've got you locked up now.

149:32:26 Parker: Roger. I thought you were trying to tell us something.

149:32:35 Worden: Not trying to tell you a thing, Bobby.

[Comm break.]
149:34:03 Parker: And Al, this is Houston. If you've got a moment, we've got the usual number of little updates to give you.

149:34:14 Worden: Go right ahead, sir. For a change, I'm ready to copy.

149:34:16 Parker: Okay. First of all, we're going to cancel the VHF comm check at 149:37. Your buddies just got into the LM down there, and we don't think they'll be ready, and we won't push them at this time on that.

149:34:32 Worden: Okay. Understand.

149:34:34 Parker: And the second one is, it looks like we'll be delaying your Mapping Camera business at 150:10 in the Flight Plan, and we'll get back to you later on exactly what we'll be doing and when on that. And now if you'll turn to 151 hours, we have a Mapping Camera photo PAD for you.

149:34:58 Worden: Do you mean a Pan Camera photo PAD?

149:35:00 Parker: Negative. It says M - A - P.

149:35:07 Worden: At 151?

149:35:09 Parker: Stand by. [Long pause.]

149:35:30 Parker: Okay, Al, a little explanation. It's a photo PAD I'm due to read you at 150 and 10. You can find the little block there, and it happens that the pass and all that will be taking place on the 151 hour frame. So it's at the 151:10 - 150 and 10 that you'll find the little squares for it.

149:35:50 Worden: Okay. I'm with you. Yes, when you call out a time like that, that's the time I go to the Flight Plan.

149:35:55 Parker: Roger. I thought that's what you should do - but I guess I was wrong. Okay. T-start, 151:09...

149:36:04 Worden: Okay, 150 plus 10?

149:36:06 Parker: Roger. Okay. T-start, 151:09:22; T-stop, 152:09:01. And there's a little note that says at T-start...

149:36:27 Worden: Roger. Understand.

149:36:30 Parker: [Garbled] [Pause.]

[At this stage of the mission, the CSM Flight Plan is laid out with one page to one hour. The delayed start of the Mapping Camera means that the box in which Al enters the T-start time is on the page for the hour commencing 150:00, while the time which is to be entered in the box begins with '151'. CapCom Robert Parker has unintentionally sent Al to the page for 151 where there is a box for the Panoramic Camera. This has caused some confusion.]

[Nine hours ago, Al was given a PAD for the Mapping Camera which had it operating for nearly three hours from 141:17:36. This period included exposures throughout a night time pass which were originally required to gather altitude measurements from the failing Laser Altimeter and associated exposures from the Stellar Camera. The latest update, to delay the Mapping Camera for one hour, is to save the Laser Altimeter.]

149:36:42 Worden: Go ahead with the rest of the PAD, Bob.

149:36:44 Parker: Okay. At T-start, "Mapping Camera Image Motion, Increase, talkback barber pole plus 4". At 151:52:00, "Mapping Camera Image Motion, Increase, talkback barber pole". And then I have a Pan Camera photo PAD, if you're ready to copy that.

149:37:14 Worden: Okay. Let's get this mapping camera straightened out first. T-start is 151:09:22. T-stop, 152:09:01. At T-start, go "Image Motion, Increase, to barber pole plus 4"; at 151:52:00, go "Image Motion, Increase, to barber pole".

149:37:34 Parker: Roger. And this Pan Camera is the one at 151:03 in the Flight Plan.

149:37:43 Worden: Roger. Go.

149:37:45 Parker: Okay. It says T-start, 151:13:13. T-stop, 151:37 to 01. And the next Pan Camera PAD will voiced up [on the] next rev. Over.

149:38:06 Worden: Okay, Bob. Understand. T-start is 151:13:13; T-stop, 151:37:01.

149:38:18 Parker: Roger. Copy. [Long pause.]

149:38:50 Parker: Okay, Al, and another addition is that at 1505 [means 150:05] in the Flight Plan, you'll see some Mapping Camera activities, and you'll find that 150:05.

149:39:09 Worden: Okay, go ahead.

149:39:12 Parker: Roger. And we will move the activities that start with the "Laser Altimeter, On" - that's the third line down in that little block. Move the activities starting with "Laser Altimeter, On", to "Mapping Camera Image Motion, Increase, to [talkback barber pole]/On" which is the last line in that little block. Those will be moved to 151 hours and we will supply you with a T-start later.

149:39:47 Worden: Roger; understand. All items between "Laser Altimeter, On", and "Mapping Camera Image Motion, Increase, to barber pole" should be moved to a GET of 151:00 and you'll supply a start time later.

149:40:01 Parker: Roger.

149:40:13 Parker: And Al, that T-start - turns out I gave to you - is the 151:09:22.

149:40:25 Worden: I see. Convenient, isn't it?

149:40:28 Parker: Well, sort of.

[Very long comm break.]

[Communication has quietened while Al concentrates on photo target number 17, the western side of Mare Crisium. In all he takes 17 images before reaching the terminator, using the Hasselblad fitted with the 80-mm lens. AS15-94-12832 to 12844, 13 images in total, are taken in a sequence as he allows the spacecraft's motion to alter the viewpoint while holding the camera at an essentially constant angle looking out of the hatch window and snapping one frame every 35 seconds. AS15-94-12832 is the first in this sequence and looks directly north over western Mare Crisium. Greaves and Picard are the two fresh craters in the foreground with the flooded craters Lick, and beyond it Yerkes on the very left. Looking across Crisium, the ghostly rays from Proclus spatter the dark mare surface from the source well off to the left of this image. The crew of Apollo 15 earlier mentioned how these rays remind them of flying over mist or haze layers on Earth. As Endeavour continues across to Proclus, Al diverts his viewpoint to get a centred image of this interesting crater, AS15-94-12836. This high resolution scan is presented here by Kipp Teague. Note particularly the area to the west, which is almost devoid of rays, bounded by two prominent rays, and the unusual shape of the crater itself, with the indentation in its western wall. Al has already described Proclus twice in the mission, at 128:07:19 and at 143:52:09. The line of Al's photography roughly follows the northern ray from Proclus to Sinus Amoris (Bay of Love) and three light-coloured craters as seen in AS15-94-12840. In the foreground is Proclus D and beyond are Carmichael and Hill (formerly Macrobius A and B respectively). The sequence ends over the hilly ground to the east of Mare Serenitatis between the dark floored Maraldi and the more distant bowl of Römer.]

[As an extra, Al shoots three more images of the dark mantling around the eastern shore and embayments of Mare Serenitatis. The best of these is AS15-94-12846 in which the transition between the light and dark mare is clearly seen. (12847 is even better in this respect.) Referring back to 12846, a finger of dark material can be seen coming towards the foreground. This is what Gene Cernan will come to call his "beautiful Valley of Taurus-Littrow" when this unusual glen becomes the landing site for Apollo 17 in seventeen months time. Near the centre of the image is the 7-km crater Clerke, named after Agnes Mary Clerke, a British astronomer who lived from 1842 to 1907. Note the tiny ray craters beyond Clerke, one of which includes a ray exclusion phenomena similar to that seen around Proclus.]

[The final shot taken on this pass is as Al passes the terminator and is therefore rather dark. The contrast has been stretched to make it easier to see the subjects. AS15-94-12848 has the Imbrium crater Pytheas in the foreground and beyond Montes Carpathus, the 93-km Copernicus. Pytheus was a Greek navigator, circa 350 B.C.E. who is credited with being the first Greek to link the tides on Earth with the movements of the Moon. The spectacular crater Copernicus, whose bright ray system can be seen by the Earthbound naked eye during full Moon, is rightly named after one of the giants of astronomy, Nicholas Copernicus, 1473-1543, who overturned the Ptolemaic Earth-centred view of the universe by explaining the movements of the planets with a Sun-centred model.]

149:52:57 Parker: Endeavour, Houston. Over.

149:53:02 Worden: Go ahead, Houston; Endeavour.

149:53:04 Parker: Roger. Whenever you got a moment, we've got a few questions the King [Farouk El-Baz] would like to have asked of you concerning your photo activities so far.

149:53:15 Worden: Roger. Go ahead.

149:53:16 Brand: Okay. Hey, Al, Vance here. If you've got a pencil and paper and I'll let you write these things down. Should take about 5 minutes.

[Vance Brand, the backup CMP, is continuing his role as the link between the science backroom and the crew.]
149:53:28 Worden: Okay, just a second. [Long pause.]

149:53:47 Worden: Okay, Vance, go ahead.

149:53:49 Brand: Okay. These are going to all refer to your visual sighting targets, and so the first one is V-1B, Tsiolkovsky. You don't need to pull out the book, just - but I'll reference them to pages in the book. First question - or the first comment is, would you mark area on - in your book - on the central peak where you saw layering and when you get back we can look at it?

[Al's observation of Tsiolkovsky's central peak, and his comments during the post flight debriefing, are at 142:26:09. His observations of the rim and landslides are at 143:36:31.]
149:54:29 Worden: Okay, got that one. Go ahead.

149:54:31 Brand: Okay. You spoke of a crater on the north-east side of Tsiolkovsky's rim, and you said it had a fault line. Could you mark that on your map, also?

149:55:01 Worden: Okay. I think I already have, but I'll double check.

149:55:04 Brand: Okay. Next, referring to the - the rim of Tsiolkovsky, you know, the famous sections that appear to be moved inward and outward. The question - Does it appear to you that the west segment of the wall moved inward, or did the northwest segment move outward?

[Brand is referring to the western section of Tsiolkovsky's rim where it falls in a single plunge to the dark interior.]
149:55:45 Worden: I think it's just the other way around, Vance, I'll - I'll check it again and mark it on the map next time by; but, as I recall, I think the west section looks like it moved westward.

149:55:56 Brand: Okay. Next, and this would be the V-1A, question 2. We'd just like to have you make sure that you take a look at that one.

149:56:20 Worden: Okay. What's the title on V-1A?

149:56:23 Brand: Okay, that's Tsiolkovsky also. Question 2.

149:56:30 Worden: Oh, I see. Yes, okay. Yes.

149:56:33 Brand: Okay, going to V-2. Referring to Picard, you talked about the layering on Picard wall. Do the layers have a uniform thickness and any estimate of how thick the layers are?

149:56:47 Worden: Yes.

149:56:56 Brand: You might speak of the thickness of the layers in terms of the total depth of the crater.

149:57:06 Worden: In terms of the depth of the crater - or in terms of the diameter of the crater?

149:57:11 Brand: Well, either way - [whatever is] most convenient with you.

149:57:24 Worden: Well, okay. That's a - that's a little difficult to do because the layering is - most of the layering is pretty - pretty thin. I would say - maybe 1/20th of the thickness or the - 1/20th of the depth of the crater and - very small - [in] comparison with the total diameter. I'd say maybe 1 percent thickness layer as compared to the diameter.

149:58:04 Brand: Okay.

[Farouk El-Baz, from the 1971 Visual Observation Debrief - "You talked about the layering in Picard."]

[Worden, from the 1971 Visual Observation Debrief - "Yes, Picard is layered all the way to the bottom, and it was like bathtub rings - successive bathtub rings - because there would be a layer of dark, a layer of light, a layer of dark, and a layer of light. They looked like they were very uniform down into the bottom of Picard - all the way down. I think I tried to count the number of rings one time."]

[Farouk El-Baz, from the 1971 Visual Observation Debrief - "We asked you about the thickness; you said 1/20th of..."]

[Worden, from the 1971 Visual Observation Debrief - "Yes, and that's about as I recall. I think I counted 13 layers at one time. That's just a rough number. But they are very distinctive in Picard. As a matter of fact, the same thing was true of Iris [?]. Those are the only two that really stick out in my mind now, except that almost every crater we saw that was sitting in a mare surface like that, had layering of one form or another in it -like Dawes, for instance."]

[Farouk El-Baz, from the 1971 Visual Observation Debrief - "Dawes had that one very distinct group of layers, and then the talus"]

[Worden, from the 1971 Visual Observation Debrief - "That's right, and the talus down below that. But what you can see of the fresh wall, without talus over it, has layering. The only places you don't see layering in craters is in craters not in highland material or craters on the back side. I never did see any layering or anything on the back side. The back side is a very, very fluffy kind of thing, and it looks very old, very worn, and very worked over. You see big craters, but they're all very shallow and do not have particularly prominent rims; everything is just chopped, and there are multicraters everywhere."]

[Dawes lies on the border between Mare Serenitatis and Mare Tranquillitatis. This 18-km crater gets its name from William Dawes, 1799-1868, an English astronomer. It lies south of Endeavour's original ground track, though the rotation of the Moon is bringing it into better view. It was caught on the Panoramic Camera in image AS15-9562P.]

149:58:04 Brand: Okay, going to V-5. This is Littrow. Al, you mentioned the cinder cones, and there's just some curiosity on the relative size of these cinder cones. And - [to help you] in judging the size, it's 12 kilometers between each line on your V-5 photo. And while we're at it, are the cinder cones fairly evenly distributed or are they concentrated in the spots on this darkest unit?

149:58:59 Worden: They're concentrated in spots on the darkest unit, and they seem to be concentrated in localized areas also within the darker units. There'd be a relatively high density of these small cones, and then a few scattered ones in the - you know, in the outlying areas. But I would say they were concentrated within the darker areas, more on the lowland side, you know, in the valleys and in what looks like the lower areas. And within - within concentrations of cinder cones there seems to be one locus of major activity, one locus of greatest number of cones, and then they thin out beyond that.

149:59:45 Brand: Okay. Maybe you can mark that on your map where you see these concentrations.

149:59:56 Worden: Yes, I can do that, but I think the pictures will be better, Vance, because the cinder cones are much smaller than the definition in the picture.

[CSM Flight Plan page 3-221.]
150:00:03 Brand: Okay. And I'll give you one more, V-8, and that's the landing site. Just like to make sure you try to get an opinion of questions 1 and 2 and the age relationship also on that question we asked earlier about Aristillus and Autolycus and that's all I'll give you right now.
[Al had been assigned visual observation tasks which were defined by various questions for which he was to look for possible answers. Question 1 for the landing site observations asked Al to try and determine which crater was the "parent" of the craters in the South Cluster.]

[Many of the small craters on the Moon are not of direct cosmic origin (i.e. caused by the impact of a meteorite) but, rather, are caused by slower velocity impacts of ejecta from the formation of larger craters. It is believed that either Aristillus or Autolycus is the source of the material that formed the South Cluster.]

[Al's second question relating to the landing site asks him to look out for a colour boundary which may correspond to a lava flow that ran east of the landing site. Al deals with this straight away.]

150:00:30 Worden: Yes. Okay, Vance. I'm over the landing site now and that unit up along the western edge of the Front there to the northeast of the landing site very definitely looks like a flow unit that's - that's flowed along or parallel to the base of the Front.

150:00:52 Brand: Okay. Copy that. I guess you got some other stuff coming up.

150:00:55 Worden: You can make - you can make out some...

150:01:08 Brand: Go. [Long pause.]

150:01:34 Brand: Okay, that's about it, Al. I'll turn you back to Bob and - just some things to mull over.

150:01:42 Worden: Okay, Vance. Thank you much.

150:01:44 Brand: Righto.

150:01:xx Parker: Okay, Al. And we'd like the High Gain Antenna to Auto and when you've got a moment, we'll pass you up a TEI-45 PAD, but I guess there's no big rush on that.

[At all times on the way to the Moon, and while in lunar orbit, the crew has a PAD available to them that gives them the information needed to make the burn to get out of lunar orbit and get back to Earth, without the aid of Mission Control. Before a previous PAD becomes obsolete, Mission Control read up another with a later ignition time. The TEI-45 PAD provides details of an emergency Trans-Earth Injection burn which would occur during the 45th revolution, if required.]
150:02:01 Worden: Okay. And, incidentally, on this Mapping Camera pass, you started that block at "Laser Altimeter, On". Do you want that to start at - at the covers opening or do you want me to go ahead and extend the camera now?
[When Parker read up the Mapping Camera updates at 149:39:12, some of the associated tasks were put back one hour along with a delay in starting the Mapping Camera. Al is wondering why the camera should be uncovered and extended now, when it will not be operational for another hour.]
150:02:21 Parker: We had a PAD that started at "Mapping Camera Covers, Open", and they explicitly took that one away and gave me one that started "Laser Altimeter, On". So I presume they want the first two lines done.

150:02:36 Worden: Okay. Well, I'm going to go ahead and open the covers and extend the camera then.

150:03:01 Worden: Okay, camera's extending.

150:03:04 Parker: Copy.

[Very long comm break.]

[The delay in Mapping Camera operations has opened up a hole in Al's schedule. His next tasks are to receive some updates from Mission Control, and, at 150:30, begin a 30 minute exercise period.]

150:17:06 Parker: And Endeavour, Houston. Over.

150:17:16 Worden: Houston, Endeavour. Go ahead.

150:17:18 Parker: Roger. At your convenience, we'll take P00 and Accept and send you up a state vector, and - we need Accept, and we'll send you a state vector and clock update. And, I've got a TEI-45 PAD, at your convenience.

[Al is to call up program zero, or P00, which places it in a standby state. Then, by pressing Accept, he gives Mission Control access to its memory so they can upload a new, more accurate state vector. This is the six numerical values which define the spacecraft's position and velocity in three axes at a certain time.]

[Mission Control are also going to update the computer's internal clock.]

[Concurrently, Parker will read up the details of the TEI-45 PAD.]

150:17:37 Worden: Okay, Bob. Ready for both.

150:17:42 Parker: Okay, we're talking to you and I've got the TEI-45; [it] says SPS/G&N: 37264; plus 0.60, plus 1.00; 166:38:58.32; plus 2832.6, plus 0290.1, minus 0078.2; 180, 129, 009. Rest of the PAD is NA. Notes: 1. Longitude at Tig plus 163.63. 2. Assumes no plane change. And ullage is 17 seconds...

150:18:57 Worden: Roger. Understand.

150:19:12 Parker: Okay, Al. And ullage is 17 seconds, two quads, Bravo and Delta. Over.

[An interpretation of the PAD follows:

Purpose: This contingency burn is for a TEI burn towards the end of the 45th orbit.

System: The burn uses the SPS engine under control of the Guidance and Navigation system.

CSM weight (Noun 47): 37,264 pounds (16,903 kg).

Pitch and yaw trim (Noun 48): +0.60° and +1.00°. This are to align the SPS thrust vector with the CSM's centre of gravity.

Time of ignition, Tig (Noun 33): 166 hours, 38 minutes, 58.32 seconds.

Change in velocity (Noun 81), fps (m/s): x, +2,832.6 (+863.4); y, +290.1 (+88.4); z, -78.2 (-23.8). These velocity components are expressed with respect to the local vertical/local horizontal frame of reference.

Spacecraft attitude: Roll, 180°; Pitch, 129°; Yaw, 9°. These are expressed with respect to the Landing site REFSMMAT.

At the time of ignition, the spacecraft should be over a lunar longitude of +163.3°.

The PAD details are correct if Al has not carried out the Plane Change burn. This TEI burn also presumes that the Lunar Orbit Plane Change (LOPC) will not be performed, due at 165:12:50 GET. Changing the orbital plane of the CSM is necessary for long stays at the Moon, as the slow rotation of the Moon gradually moves the path of the CSM further away from the landing site. The plane change maneuver would adjust the orbital path of the CSM to coincide with that of the ascending LM, which greatly simplifies rendezvous procedures and makes the most of the LM's limited capabilities.

SPS propellants would be settled in their tanks by firing the plus-X thrusters on the B and D quad clusters on the Service Module for 17 seconds.]

150:19:28 Worden: Okay, Houston. Understand. TEI-45, SPS G&N; 37264; plus 0.60, plus 1.01; 166:38:58.32; plus 2832.6, plus 0290.1, minus 0078.2; 180, 129, 009. That's two jets for 17 seconds, and you want quads B and D used. And this assumes no plane change, and longitude at Tig is 163.63.
[Al's readback contains one small error in the Yaw trim value for the SPS engine.]
150:20:02 Parker: Roger. And, the Noun 48 values are plus 060 and plus 100. Is that right?

150:20:17 Worden: Roger. Plus 100 - plus 060 and plus 100.

150:20:21 Parker: Okay. Readback good.

[Comm break.]

[This is one of the few examples which shows the importance of the readback in checking the accuracy of information which has been read up to a crew.]

150:21:25 Parker: And Endeavour, computer is yours again.

150:21:35 Worden: Roger, Houston.

[Long comm break.]

[The updates to the computer are finished and Al can take control of it once more.]

150:29:26 Parker: And Endeavour, Houston. We'd like to terminate Battery A charge at this time.
[Battery A began charging just over 8 hours ago.]
150:29:36 Worden: Roger, Houston. Terminating A.

150:35:57 Parker: And Endeavour, as you go around the hill, you're looking good. We'll look for you on the other side.

150:36:06 Worden: Okay, Houston. See you on the other side.

[Very long comm break.]

[CSM Flight Plan page 3-223.]

[The lunar day is moving on and, from Earth, what was a first quarter Moon when Apollo 15 arrived, has now waxed to a distinctly gibbous disk. As the Moon approaches full, more and more of the far side will be in darkness. Therefore, Endeavour's far-side passes are also increasingly in the dark as well as out of touch with Houston. Revolution 38 begins at about 150:59 and the spacecraft leaves the Moon's shadow at about 151:03. Al will be spending this time exercising. When he comes over the terminator at about 151:09, just after he has retracted the Gamma-ray boom, he will begin a Mapping Camera operation which will last for one hour while the spacecraft is above a daylit lunar surface. At 151:13:13, the Panoramic Camera will begin 24 minutes of operation, being switched off roughly when it reaches the sub-solar point. The majority of tasks for the upcoming, relatively quiet, near-side pass are concerned with camera operation.]

151:26:11 Parker: And, Endeavour, Houston. How do you read?

151:26:17 Worden: Houston - Houston, Endeavour. Loud and clear.

151:26:19 Parker: Okay. Ready for - the usual updates? [Long pause.]

151:26:29 Worden: Okay. Go ahead.

151:26:30 Parker: Okay. Pan camera photo PAD for your 151:50 in the Flight Plan.

151:26:42 Worden: Go ahead.

151:26:43 Parker: Okay. It's 15:57:14 for T-start. T-stop is 151:58:27. Over.

151:27:02 Worden: Understand. T-start, 151:57:14. T-stop, 151:58:27.

151:27:09 Parker: Roger, Al. And we got a couple of VHF's - we got a single VHF window for you if you want to try and get hold of the crew down below. AOS is 151:51:25 and 152:04:15 for LOS. Over.

151:27:14 Worden: Okay, I understand. AOS with LM is 151:51 and LOS is about 152:04.

[Communication between the CSM and the LM use the VHF/AM radio system. Two independent systems are available, operating at 296.8 MHz and 259.7 MHz. The second system also performed ranging functions, which served as a backup to the LM's rendezvous radar system.]

[The time of Acquisition Of Signal with the LM is a bit optimistic, and is calculated based on a simple line-of-sight model of a smooth Moon. In actuality, the mountains that surround Hadley base will block the reception of Endeavour's transmissions until 151:55.]

151:27:52 Parker: Roger. And if you'll give us cue just a little bit ahead, we'll get them to go to Voice so they can pick you up.

151:28:01 Worden: Okay, will do.

151:28:02 Parker: Okay. And second item, Al, is we're not going to put the Mass Spec. boom out tonight because of the problems we've been having with deployment. And so, we want to delete the following operations of the Flight Plan. Starting on 152:10 - 152:10. We'll delete the boom deployment at 152:10. We will delete the Experiment and Ion Source, On, and Standby, at 152:13. And we will delete the Multiplier, Discriminator, and Ion Source functions at 152:45. Over.

151:28:56 Worden: Okay, Bob. Understand 152:11, delete Mass Spec deployment, that whole line, and then delete the line that turns the experiment on at 152:13, and then at 152:45, delete the multiplier [and] discriminator steps.

151:29:16 Parker: Roger. And, going over to the next page at 153:36, we will delete "Gamma-ray: Gain Step, Shield Off".

151:29:33 Worden: Understand. Delete "Shield, Off" at 153:36.

151:29:37 Parker: Roger. And then going down to 153:46, we'll delete "Shield, On".

151:29:50 Worden: Understand. Delete "Shield, On" at 153:46.

151:29:54 Parker: Roger. And a - a general question here, Al. We've been talking on the ground and we'd appreciate any comments on the general photo results you been having, any difficulties or problems you've been experiencing in the general photographic work, both gegenschein and zodiacal-light type, and surface type. So far, we've generally assumed that negative reporting was - meant that everything was going well. Is that right?

151:30:28 Worden: Hello, Houston, Endeavour.

151:30:30 Parker: Yes, I read you loud and clear, Al.

151:30:35 Worden: Okay. You went away on me there. [garble] question about.

151:30:44 Parker: Stand by, Al. [Long pause.]

151:31:05 Parker: Al, how do you read Houston?

151:31:10 Worden: Okay. I read you loud and clear.

151:31:12 Parker: Okay. Did you copy my question there on comments concerning your procedures on the photo, general - generally both gegenschein, zodiacal light, and surface?

151:31:31 Worden: You say - The question is: do I have any questions on it?

151:31:35 Parker: Roger. My question was: did you copy my question?

151:31:45 Worden: Why don't we start from scratch again, Bob. You were cut there quite a bit when you first started talking and it sounds like I'm reading you okay now. So why we just start all over again.

151:31:54 Parker: Yes, I think we have a little comm problem with the LM, which affected us. Okay. People on the ground have generally been assuming that negative reporting on any difficulties with the command module photo procedures meant that everything was going along swingingly. Is that a correct assumption?

151:32:13 Worden: That is a correct assumption, right.

151:32:16 Parker: Okay. We'll continue to make that assumption. Thank you.

151:32:23 Worden: Yes, so far everything - particularly the zodiacal light and the gegenschein calibration and that sort of thing has been going just as per Flight Plan.

151:32:34 Parker: Beautiful.

[Very long comm break.]

[Much of Endeavour's science data gathering equipment is operating at the moment, except the Mass Spectrometer. The Panoramic Camera stops at 151:37:01. Al is going to try and raise the surface crew of Dave Scott and Jim Irwin on VHF. Dave and Jim are finishing off their day's activities and are about to spend their final night aboard Falcon at Hadley Base. Portions of the following exchange are taken from the Apollo Lunar Surface Journal, edited by Eric M. Jones.]

151:52:05 Worden: Houston, Endeavour.

151:52:08 Parker: Go ahead, Endeavour.

151:52:12 Worden: Okay, Bob. I'm going to try to give a call now, down at Falcon.

151:52:16 Parker: Okay. Stan[d by.] - Go ahead and I'll - You won't get them right off, but I'll tell them to go to Voice.

151:52:24 Worden: Okay. And I'm going to call them on Simplex A.

151:52:28 Parker: Understand. Simplex Alpha.

[Simplex A (Alpha) was the VHF system operating at 296.8 MHz. The simplex mode allowed only one person to transmit at one time.]
151:52:34 Worden: Affirmative.

151:52:37 Parker: Falcon, Houston. Over.

151:52:43 Scott: Go ahead.

151:52:45 Parker: Roger; Al's going to give you a call on simplex Alpha about now.

151:52:52 Scott: Okay, thank you. [Long pause.]

151:53:13 Worden: Hello - Hello, Falcon. This is Endeavour. [Long pause.]

151:53:53 Worden: Hello, Falcon. This is Endeavour.

151:54:08 Worden: Hello, Falcon. Endeavour. [Long pause.]

151:54:27 Parker: Falcon, this is Houston. Al's been calling you.

151:54:36 Scott: Haven't read him yet.

151:54:39 Worden: Hello there, Falcon. This is Endeavour.

151:54:44 Scott: Okay. Endeavour, Falcon. You must be on the other side of the mountains and we'll just stand by until you get over it, because you are always broken over there on the other side. [Long pause.]

151:55:06 Worden: Hello, Falcon. Endeavour.

151:55:12 Scott: Hi, Endeavour; the Falcon. How are you?

151:55:16 Worden: I'm doing fine. How are you doing?

151:55:39 Worden: How do you read me now, Falcon?

151:56:24 Worden: Hello, Falcon. This is Endeavour.

151:56:30 Scott: Endeavour, Falcon. You're broken. How's us?

151:56:32 Worden: You're a little broken too, Dave. How's it going?

151:56:37 Scott: Okay, we'll wait until you get closer overhead, so you get past the mountains.

151:56:40 Worden: Okay, I'm just about overhead now.

151:56:46 Parker: Endeavour, you're about 30 seconds from your Pan Camera [T-start time].

151:56:49 Scott: How are things going up there? Getting lots of good data?

151:56:53 Worden: [answering Parker] Roger.

151:56:59 Worden: Oh, getting lots and lots of good data. How about you?

151:57:03 Scott: Yeah, we are too. Got a little over 100 pounds [of rocks] today.

151:57:09 Worden: Very good.

151:57:11 Scott: Got up the side of the mountain. Got a good look around. Things are going real well.

[The Pan Camera has started and will take 18 frames before Al stops it.]
151:57:17 Worden: Pretty spectacular up beside that mountain, I bet.

151:57:19 Scott: Oh, man, it was super, just super. We got some great pictures for you.

151:57:24 Worden: Good. I hope I got some good ones for you, too.

151:57:27 Scott: Yeah, I tell you, I hope you can see these Rover tracks, because outside the LM here, it looks like a freeway.

151:57:33 Worden: Yeah, I'll bet it does. Well, you can collect you another bunch of rocks tomorrow and bring them home.

151:57:43 Scott: Okay, make a nice little place for them.

151:57:45 Worden: Well, we'll make a place for whatever you bring home.

151:57:47 Scott: Okay, very good.

151:57:50 Irwin: Hey, Al, throw my soap down, will you? And my spoon.

151:57:55 Worden: You forget something, Jim?

151:58:00 Irwin: I really need my soap.

151:58:02 Worden: Don't mind if I use it, do you?

151:58:05 Irwin: Save me a little bit.

151:58:10 Worden: Well, I haven't had a chance to use it yet, but I might tonight.

151:58:16 Scott: I suggest you wait until tomorrow night, Al [too faint].

151:58:21 Worden: Yeah, that's true. I guess it'll pay for us all to do that tomorrow night.

151:58:28 Irwin: Yeah, I tell you, our suits were pretty [too faint] yesterday, but [too faint].

151:58:35 Worden: How are they holding up?

151:58:36 Scott: Very well. Holding up real good.

151:58:39 Worden: Understand the Rover's doing fine.

151:58:42 Scott: Well, the Rover is doing absolutely super. We were going up the side of that mountain like [too faint].

151:58:50 Worden: Sounds great!

151:58:54 Scott: Yes, it's really a super little machine.

151:58:59 Parker: Okay, Al. Pan Camera, Off, please.

151:59:04 Worden: Okay. [Long pause.]

151:59:49 Worden: Falcon, you still there? [No answer.]

[CSM Flight Plan page 3-225.]
152:00:08 Worden: Falcon, can you read Endeavour now? [No answer.]

152:00:16 Parker: And Endeavour, Houston. We still don't have the Pan Camera, Off, as far as we can see.

152:00:32 Worden: Roger. Power coming off now, Bob.

152:00:36 Parker: Okay.

152:00:37 Worden: Sorry about that. I didn't get it turned off quite as quick as I wanted.

152:00:39 Parker: I guess that's what Spence was trying to tell me.

[Spencer Gardner is closely involved with coordinating the photographic elements of the mission.]

[We can present a selection from the 18 images taken on this Panoramic Camera session though readers should be aware that these are relatively large files. Frame AS15-9798P runs just east of the landing site with the hummocky landscape between Conon and Galen at the bottom and crater Santos-Dumont at the top. The landing site is about a third way down. Frame 9800P has been presented here at a higher resolution and the landing site is visible as a light smudge within the centre of the circle. The lightness is due to the disturbance of the soil by the LM's descent engine. The Fresnel Rilles are at the top of the image and crater Conon is half obscured at the bottom left.]

[The Pan Camera is being operated in its stereo mode where it takes images looking forward and then aft so that overlapping imagery from different viewpoints can be made. This is the reason these images will be out of sequence though they are geographically in order. Frame 9802P has an excellent shot of Conon at the bottom of frame. The arcuate depression, Bela is at the centre of frame with crater Hadley C seen impinging of Hadley Rille. The Fresnel Rilles are at the top of the image. Frame 9799P takes our viewpoint out over Palus Putredinus with one of the peaks of the Apennine Front to the south. In 9801P we see Rima Bradley, a graben-type rille, near the centre of the frame.]

152:00:45 Worden: Roger. I went to Standby on your call before?

152:00:49 Parker: Okay. Thank you. Hey, and Al, we'd like to get High Gain Antenna, Auto, from you. And sometime, at your convenience, you might send us down a film usage PAD.

152:01:04 Worden: Okay. I'll set - I'll compile that on the way around the next time.

152:01:11 Parker: Roger. Thank you.

[Comm break.]

[Robert Parker, currently the Command Module CapCom, is filling in as the Lunar Module CapCom as well, during the last few exchanges before Dave and Jim settle down for the night.]

152:03:43 Parker: And Endeavour, Houston. Over.

152:03:49 Worden: Houston, Endeavour. Go ahead.

152:03:50 Parker: Roger. We'd also like, when you turn off the Mapping Camera in the next few minutes, we'd like you to delay turning off the Laser Altimeter and closing the covers until we give you a call from the ground. We'd like to look at the Laser Altimeter on with the Mapping Camera off for a few minutes.

152:04:09 Worden: Okay. Will do.

152:04:11 Parker: Thank you.

[Long comm break.]
152:12:56 Parker: Al, Houston. Over.

152:13:02 Worden: Houston, Endeavour. Go ahead.

152:13:04 Parker: Al, would you turn the Laser off and we'll call you shortly and have you turn it back on.

152:13:16 Worden: Okay, Vance, [means Bob Parker] going off now.

152:13:18 Parker: Roger. Okay. We're ready for it back on. Thank you.

152:13:31 Worden: Back on.

[Long comm break.]
152:18:11 Parker: Endeavour, Houston.

152:18:17 Worden: Houston, Endeavour. Go ahead.

152:18:18 Parker: Roger. We'd like to see the Laser Altimeter, Off at this time, and you can follow up on the rest of those things per the Flight Plan; closing - retracting the Mapping Camera, et cetera, and closing the cover.

[The previous exchange about the Laser Altimeter was part of an attempt to diagnose a problem between it and the Mapping Camera.]
152:18:39 Worden: Okay, Houston. That's in work.

152:18:42 Parker: Okay, and we'd also like you to verify if the Gamma-ray boom is out at the present time.

152:18:58 Worden: That's negative. It's going out now.

152:19:02 Parker: Copy. Thank you.

[Long comm break.]

[With all the changes in the Mapping Camera shutdown operations, Al had missed the deployment of the Gamma-ray boom at 152:10.]

[For the last few hours, Endeavour has been flying sharp-end-forward with the SIM bay facing the ground. Now, in preparation for the night's data collection, Al is to use P20 to make the spacecraft fly blunt-end-forward, i.e. SPS engine facing the direction of travel. Each time this attitude reversal takes place, Al has to first manually roll the CSM clockwise by 40°, thereby avoiding a gimbal lock situation when the maneuver takes place. Ironically, this engine-first attitude is primarily intended to point the Mass Spectrometer's inlet into the direction of travel and Mission Control deleted the upcoming use of this instrument fifty minutes ago at 151:28:02.]

152:25:43 Worden: Houston, Endeavour. [Long pause.]

152:26:09 Worden: Hello, Houston, Endeavour.

[Comm break.]
152:28:26 Parker: Endeavour, you called Houston?

152:28:34 Worden: Houston, Endeavour. Yes. I sure did, Bob.

152:28:37 Parker: Roger. I was talking to Jim and Dave. Go ahead.

152:28:43 Worden: Okay. You still logging Delta-Ts on extend and retracts.

152:28:49 Parker: Yes.

152:28:56 Worden: Well, I guess that means yes. Delta-T in the Gamma-ray extend was 2 plus 37, and on the Mapping Camera, retract was 3 plus 32.

152:29:07 Parker: Roger. Copy, Al.

152:29:12 Worden: Okay.

[Long comm break.]
152:33:10 Parker: And, Endeavour; Houston. We see you going around the corner. You're looking good to us; we'll see you on the other end.

152:33:19 Worden: Okay, Houston. See you on the other side.

152:33:22 Parker: Bye, bye.

[Very long comm break.]

[With the operation of the Mass Spectrometer on this far-side pass now deleted, Al is left with two items in the Flight Plan between LOS and AOS. The first task is to realign the guidance platform, which hasn't been done for a while because of the good alignment at the last opportunity. The second is to eat his evening meal. To recap, realignment of the guidance platform is achieved in association with program 52 in the computer. Al sights on 2 stars, in this case number 41, Dabih (Beta Capricornus), and number 43, Deneb (Alpha Cygnus). Their absolute positions in the celestial sphere are already known by the computer, as is the angle between them. From these sightings, the computer tells Al how far his measured angle between then differs from the computer's knowledge, in this case one hundredth of a degree, and by how much the three gimbals supporting the platform need to be turned, or torqued, to restore ideal alignment. Al will read these angles to Mission Control after AOS.]

[This far-side pass sees Endeavour commencing its 39th orbit of the Moon.]

[CSM Flight Plan page 3-227.]

153:23:11 Parker: Endeavour, Houston. Over.

153:23:19 Worden: Hello, Houston. Endeavour.

153:23:22 Parker: Okay, Endeavour. We've got a couple of long-sort-of dissertations to read to you. One, is a dissertation and two, a question. So if you've got a minute, let me know, and I'll talk to you between bites of your supper.

153:23:43 Worden: Okay. Go ahead.

153:23:44 Parker: Okay. It says here. We've observed the use of P30 for long periods of time and this appears to be degrading the P20 attitude calculations during narrow deadband camera activity. And this is causing a slight increase in RCS usage. If you want to use P30, they're recommending you follow the following procedures. And you won't be doing any of it tonight, obviously, and I think we'll come up and let you copy them down tomorrow. This is just, I guess, to acquaint you with the problem and let you think about it tonight while you're sleeping. The procedures we're recommending, when you use P30, as are follows: One, reselect P20; that is, release P30 once every 30 minutes, and allow the computer to integrate its state vector forward. This is about a 30 second delay. And then, number 2, do not input a Tig time of more than 30 minutes into the future while you're in narrow deadband. Does that make sense to you?

153:24:45 Worden: Yes. Keep talking.

[An earlier electrical short in the Mission Event Timer, at 033:47, popped a circuit breaker and affected the lighting of displays in the Command Module. Al has needed the timer to sequence photography of low-light-level subjects, like the solar corona, zodiacal light, so to get around this problem, he has been using program P30 as a makeshift timer, which counts down to a preset ignition time (Tig).]

[Unfortunately, Al's approach, while ingenious, is placing large demands on the computer when it is also making calculations to fire thrusters and keep the attitude of the spacecraft stable. As a result, the program responsible for maintaining the proper attitude for the cameras (P20; Universal Tracking) is placed at a lower priority and is not getting serviced as frequently. The consequence of this is that the tracking program is getting behind and making errors in estimating its position, causing larger than desired RCS activity. The solution provided by the ground is to restart the tracking program, and then use P30 for less than 30 minute intervals.]

[It is interesting to note that this type of problem is analogous to the problem experienced during Apollo 11's landing. Computational demands on the computer caused it to delay or throw out low priority work. Here, the computer did not restart, as it did in the LM Eagle, but the effects of the excessive work are being noticed.]

[Worden, from the 1971 Technical Debrief - "Solar corona photos ... were done as per Flight Plan. There were no problems with any of the solar coronal passes. Everything worked very well, except that - I should make a comment at this point that the solar corona photography was done using a countdown clock on the DSKY, which I called up by using P30 and loading the T-start time into the computer, in P30, and then letting the computer keep track of the time for me. At this time, there was no lighting in the LEB for the Mission Event Timer, and solar corona photography required that the lights in the spacecraft be turned low. Because of the light problem in the LEB, the rheostats that adjust the integral and numeric slidings were taped in the position that they were in when we had the problem with the AC. This meant that the DSKY in the LEB was at a higher intensity than I would have liked for the solar corona photography. There was considerable light inside the spacecraft as a result of the lighting in the DSKY and the LEB. I turned all of the other lights out and monitored the DSKY in the LEB to do the solar corona photography and all of the other low-light-level photography."]

[Worden, from the 1971 Technical Debrief - "Another comment on the use of P30 for the timing of some of these things in flight, and that is that, after I had used P30 for a while to time the events, I was called by the ground and told not to use P30 so extensively, because I interrupted the integration of the state vector in P20, which meant that the orbital-rate attitude was varying and was actually drifting outside the limits that we required for flight."]

[Worden, from the 1971 Technical Debrief - "My recommendation is that we somehow devise a way of monitoring time on the DSKY, since it's a very convenient way of doing that particular thing. The Digital Event Timer on the main panel is too far away, and it's unusable for that type of activity. It means that the DSKY is really the simple solution, if we can somehow load the computer to count down to a time and then to count minus time to zero and then count, plus time, so that these activities can be monitored."]

153:24:47 Parker: Okay. As I say, we'll come back up and let you copy down some of those specific words again tomorrow, before you get involved. The second long one concerns clarification of Mass Spec. behavior, when it fouled up about 12 hours ago. And they're asking us, to ask you the following questions, to try and clarify what - what was going on. First of all, was the talkback ever one-half barber pole during the extend, while attempting to recycle for retraction? Over.

153:25:22 Worden: The answer to that one is no.

153:25:24 Parker: Okay. Two, was the barber pole indication a half or between a half and three quarters of full during retract?

153:25:44 Worden: Don't know how to answer that one, Bob, because the barber pole itself - if you get a full barber pole, you only get about two thirds.

153:25:54 Parker: Okay. Understand. Did the talkback change state after approximately...

153:25:59 Worden: And I was getting about half of that.

153:26:03 Parker: Okay. You're getting about half of the normal 2/3.

153:26:12 Worden: That's correct.

153:26:13 Parker: Okay. Third question. Did the talkback change state after approximately 3 minutes, or was it a half barber pole all the time during the retraction?

153:26:31 Worden: Well I can't answer that one specifically, since I didn't sit there and watch the barber pole all the time.

153:26:39 Parker: Okay.

153:26:40 Worden: However, I did - When I went back to the Mass Spec., to cycle the thing to Deploy and Retract to see if there was any possibility of the cabling out there getting kinked, that was when I noticed that it went to half barber pole on the retract side.

153:26:56 Parker: Okay. Copy that. And did you - talk the back - did you ever tap the barber pole [means talkback] when it was half barber pole?

153:27:13 Worden: I'm sorry. Say again.

153:27:14 Parker: Did you ever tap the talkbacks to see if you could make it flip over?

153:27:27 Worden: I noticed a couple of times, when I went to Retract, the barber pole [means talkback] would go - it would go full barber pole and then very slowly slip down to about half barber pole and stay there.

153:27:39 Parker: Okay. But did you tap the talkback at any time? Tap?

153:27:45 Worden: Oh, did I tap it? Negative. Negative.

[The Principal Investigators for the Mass Spectrometer experiment are trying to determine the reason for the lengthening times of the boom retraction. Suspecting that there is something hanging up during the retract cycle, they want to see what indication is in the talkback indicator. A gray flag in the window indicates fully extended, and a barber pole is displayed during retraction or extension. The half gray, half barber pole indication occurs when the deploy/retract motor stalls. This half barber pole indication is what the conversation between Al and Houston is focused on. Post mission analysis demonstrated that the motor was indeed stalling, due to the cable connecting the instrument to the SIM bay becoming jammed in the last few inches of retraction when it was excessively cold. Several modifications to the retraction mechanism were incorporated for use in Apollo 16 and 17.]
153:27:48 Parker: Okay. And, during the recycling of the switch, can you estimate the maximum time you were in the Extend position?

153:28:12 Worden: I'm not sure I understand your question. You mean the maximum time I was in the Extend position during the retract cycle?

153:28:26 Parker: Stand by.

[Comm break.]
153:30:16 Parker: Al, what's wanted is the total accumulative time that you went back to the Extend position, and back and forth, while you were trying to recycle it in order to free it. In other words, if you went back to 30 seconds and then to Retract, and then back to Extend for 40 seconds et cetera. What was the total accumulated time, or an estimate thereof, that you were in the Extend position?

153:30:46 Worden: Okay, Bob. I would estimate that I was in the Extend position a total of about 15 seconds.

153:30:56 Parker: Okay. And what was the longest single time?

153:31:02 Worden: Oh, probably 4 seconds.

153:31:05 Parker: Okay. A couple of other small ones, Al. Reminding you that we - we're deleting the cabin pump up from the presleep checklist. And a reminder when we get to the presleep checklist and the crew status, would you please remember to give us the PRDs. We just didn't get that from the crew on the ground and the Surgeons were very anxious to get yours, at least. And we also, I guess, are due some P52 torquing angles.

153:31:39 Worden: Okay. He wants my PRD, even though it's the one that's not working, huh?

153:31:46 Parker: Well - they - Anything is better than nothing.

153:31:55 Worden: I guess you're right. Here's some torquing angles for you, Bob. [I] used stars 41 and 43. Noun 05 was plus 4 balls one. Noun 93 was plus 00028, minus 00031, plus all zeros. And it was torqued out at 152:46:00.

153:32:25 Parker: Roger. Copy. 01, 28, 31, all balls, 152:46:00.

[The results of the P52 platform realignment was that there was a 0.01° error when comparing Al's measured angle between stars Dabih and Deneb and the angle that the computer knows is between them. The X- and Y-axes of the IMU were rotated by 0.028° and 0.031° respectively to realign the platform. The Z-axis had no error and therefore did not require to be torqued.]
153:32:40 Worden: And I've got a film update for you, there, Bob, to give to Spencer.

153:32:44 Parker: Go ahead.

153:32:49 Worden: Okay. The magazines used today, and the exposures. These are a total - a total frame readings, too. Magazine Q is reading 31, magazine F is reading 111, Magazine T is 37 and that one's been changed out for Uniform, for U, Uniform. And Uniform is now reading 31.

153:33:21 Parker: Roger. Copy, Al.

[Very long comm break.]

[By the Flight Plan, at 153:45, Al's meal time is scheduled to end. He is given 5 minutes to go through the presleep checklist though he does not need to bring the cabin pressure up to the required 39.3 kPa (5.7 psia). With only one person in the Command Module, there is not so much breathing down of the air within. At 153:50, he is scheduled to begin a 8¼ hour rest period.]

153:52:40 Worden: Houston, Endeavour.

153:52:43 Parker: Go ahead, Endeavour. [Long pause.]

153:53:04 Parker: Endeavour, Houston. Go ahead.

153:53:09 Worden: Okay, Houston. I got your status reports for you, if you're ready to copy.

153:53:13 Parker: All righty.

153:53:17 Worden: Okay. Crew status, no medication. Everything seems to be fine. PRD is 23163.

153:53:31 Parker: Go.

153:53:32 Worden: And the onboard read-outs: battery C, 37; Pyro BAT A, 37; Pyro BAT B, 37; RCS A, 70; B, 68; C, 69; and D, 70.

153:53:53 Parker: Roger. Copy all that stuff, Al. And, Al, we'd like one final confirmation and that is that you've got Narrow, Reacquire [on the High Gain Antenna] and Pitch is plus 25, Yaw 185. Over.

153:54:13 Worden: That's - that's verified.

153:54:15 Parker: Okay. [Long pause.]

153:54:28 Parker: Okay, Al. That's all we've got. You can turn the light out and go to sleep.

153:54:35 Worden: Okay, I'll do just that.

153:54:38 Parker: Roger. Roger.

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