Apollo Flight Journal logo
Previous Index
Science and a Press Conference Journal Home Page

Apollo 15

Splashdown Day

Corrected Transcript and Commentary Copyright © 2000 - 2009 by Frank O'Brien and W. David Woods. All rights reserved.
Last updated 2009-01-05
[This section covers the thirteenth and final day of the Apollo 15 mission, 7 August 1971.]
Public Affairs Officer - "This is Apollo Control at 281 hours, 27 minutes. The crew of Apollo 15 asleep at this time. Five hours and two minutes remaining until they will be wakened for preparations for entry and Earth-landing later this afternoon. Splashdown clock showing 13 hours, 43 minutes until splash. The spacecraft, at this time, is 74,650 nautical miles [138,252 kilometres] out in space approaching Earth. Velocity continuing to increase; now showing 6,435 feet per second [1,961 metres per second]. Current vector on the spacecraft still showing entry angle and entry interface at minus 6.5 degrees. The vacuum perigee, 21.1 nautical miles [39.1 km]. Maroon team of flight controllers here in the control center settled in for the graveyard shift watching the replay of yesterday's in-flight press conference. At 281 hours, 29 minutes, this is Apollo Control."

[Although moving at only 1,950 meters per second, Apollo 15's velocity has been increasing slowly since it crossed the invisible boundary where the Earth's gravitational pull began to dominate over the Moon's. Slowly at first, Endeavour's velocity will increase rapidly as it is drawn closer to the Earth. Since the spacecraft reached that point 43¼ hours ago, it has gained only 1,100 metres per second in velocity. In the next 8½ hours, its velocity will increase fivefold, to nearly 11,000 metres per second (36,000 feet per second).]

[Flight Plan pages 3-394, 3-395, 3-396, 3-397 and the current page, 3-398.]

286:30:15 [Music: Hawaiian War Chant by Al Kealoha Perry.]

286:32:26 Allen: Su Sois, good Endeavour crew. Su Sois. Rise and shine. It's splashdown day.

[According to journal reader Ken Glover, "Su Sois" seems to mean "To be in front of everyone". We would interpret that as "Let all of us here know that you are up and about."]
286:32:35 Scott: Oh, my, yes!

286:32:43 Allen: Good morning, Dave.

286:32:46 Scott: Good morning, Joe. That got everybody up.

286:32:55 Worden: Morning, J.P.

["J.P." is the nickname of the CapCom, Joe P. Allen.]

286:32:57 Allen: Morning, Alfredo.

286:33:03 Irwin: Joe, sounds like you're really in harmony this morning.

286:33:08 Allen: That's one.

[Long comm break.]
Public Affairs Officer - "This is Apollo Control. Apparently the crew of Apollo 15 is very definitely awake after having the Hawaiian War chant come up the air waves. The heart rates on the cardioscope here jumped somewhat on the Flight Surgeon's console as the music began. That particular version of Hawaiian War Chant done by Al Kealoha Perry. Apollo 15 now 53,782 feet - as you were - miles - nautical miles [99,604 km] from Earth, approaching at a velocity of 7,940 feet per second [2,420 m/s]. 8 hours, 35 minutes till splashdown."

286:39:03 Scott: Okay, Houston; Endeavour. We got a postsleep checklist for you.

286:39:13 Allen: Okay, Dave. Go ahead.

[Immediately after waking, the crew reports their status regarding how they slept and, usually, whether any medication has been taken. They then receive an update from Mission Control of the spacecraft's systems, which includes recording the onboard readings of the oxygen and hydrogen tanks, and the propellant quantity for each of the four Service Module RCS (Reaction Control System) thruster quads.]

286:39:17 Scott: Okay. Okay. About 8 hours apiece on the sleep, and ready for your consumables.

286:39:26 Allen: Roger. At 286 plus 30; RCS total, 36 percent; quad A, 41; [B], 36; [C], 30; [D] 37. H2 tank, 27, 24 and 29 [hydrogen tanks 1, 2 and 3, respectively]; O2 tank, 43, 44 and 37 [again, tanks 1, 2 and 3]. I've got the world's smallest list of updates for your Flight Plan, and I've got the news summary when you're ready.

286:40:07 Scott: Okay. Give us a couple of minutes on those. Thank you.

[Very long comm break.]

286:51:46 Scott: Houston, Endeavour.

286:51:52 Allen: Go ahead.

286:51:57 Scott: Well, we just got our first view of the Earth this morning, and, can you believe it's getting larger and it's getting smaller? We see just a very, very thin sliver of a very large round ball.

286:52:20 Allen: Roger, Dave. I believe that.

[Joe Allen isn't simply being kind and responding in agreement to Dave's comment about the crescent Earth. The Flight Plan includes a diagram of the expected view of both the Earth and the Moon at this time.

Diagram of the Earth from spacecraft.Diagram of the Moon from spacecraft.

The Earth takes up about 10° of the astronauts' field of view, about 20 times that of the full Moon as seen from the Earth. During yesterday's lunar eclipse, the spacecraft was well to one side (and south of) Earth's shadow. Now, in the final hours of the flight home, it is passing beneath the shadow, moving towards the Pacific on the eastern side of Earth's disc. By the time they land, that area will have moved around into daylight. Because Endeavour's flight path has carried it over the night-time side of the Earth, only the slightest glimpse of the daylight side can be seen. Most of the "view" is that of the Southern Pacific hemisphere, where it is midnight in Australia and the mid-winter darkness persists over the south pole. The Moon, meanwhile, is nearly full.]

286:52:31 Scott: And, go ahead with the updates, Joe.

286:52:44 Allen: Roger, Dave. These are the Flight Plan updates for today. And - would you believe - I don't have any DAP load changes to give you, which is fortunate. The first addition is at 288 plus 18. And it reads "X-ray to Off, Alpha Particle to Off."

[The Digital AutoPilot (DAP) is currently configured for Passive Thermal Control (PTC). Verb 48 is (11111) (x1111). Translated: CSM only, Plus-X translations using all four jets, 5 degree deadband, maneuvers at 0.2°/second, either Quads A and C, or B and D used for roll, and all four sets of RCS quads are to be used.]
286:53:24 Scott: Okay, 288:18, X-ray, Off and Alpha, Off. Go.

286:53:29 Allen: Roger. And all the rest are just reminders, really. The first one at - on - at 290, on the UV photo's page, you've already changed the two frames line to read one frame at 20 seconds and the second frame at 2 seconds. A reminder to use mag Papa instead of mag Metro. And, finally, we'd like to remind you to enable all jets before beginning the maneuvers today. And we're - we're thinking now we'll likely do a midcourse 7 correction of about - probably around 5 feet per second [1.5 m/s]. Over.

[As Joe Allen notes at 286:58:39, the upcoming midcourse correction became necessary after the previous day's uncoupled thrusting in support of the science experiments. The crew had used single jets to hold their attitude as this gave finer control over what is now a very light spacecraft. To prevent any further degradation of their trajectory, all maneuvers will use all four RCS jets, working in pairs, to reduce the undesired velocity changes that occur with uncoupled maneuvers.]
286:54:24 Scott: Okay. I got the UV on the change, and the mag Papa on; and enable all jets prior to maneuvers; and you're looking at midcourse 7 at 5 [feet per second, about 1.5 m/s]. That's very interesting.
[Midcourse 7 is formally known as the Corridor Control Burn and is used to fine tune their approach into the narrow corridor of the atmosphere. While Endeavour is still well within the limits for a successful entry, tweaking the trajectory now will ensure that the Command Module will not have to perform extra maneuvers as the computer works to balance the optimal entry profile and targeting to the recovery force. The burn will be performed at 291:58:48.]

286:54:36 Allen: It's also not certain, but we'll keep you posted on that. And that's all the official updates I have for you. I have a news summary, if you'd like to listen.

286:54:46 Scott: Okay. Everybody's [has their headsets plugged] in...; go ahead.

286:54:51 Allen: Roger. And this will be a short one. The rest of it, you can read for yourselves today in the papers. Congress has started a month-long summer recess, setting the pattern for a government-wide exodus likely to make Washington a virtual ghost town for the rest of August. The Senate finally quit at 7:30 Friday night, more than six hours after the House had adjourned at about one in the afternoon. And after passing an 18 billion dollar higher education bill and three key appropriations measures. Besides the Labor-HEW appropriations, the Senate approved, Friday, a $1 billion measure to provide public service jobs mainly for Vietnam veterans and a continuing resolution to fund agencies still without regular appropriations until the 15th of October. In Chile, four [sic] government ministers presented their resignations to president Salvador Allende on Friday, causing the first cabinet crisis since the President took office last November. I have a long list of baseball scores which I think I'll skip over here. In exhibition football, the Buffalo Bills downed the New Orleans Saints, 14 to 10, and the Cowboys won over the L.A. Rams, 45 to 21. In the American Golf Classic at the Firestone Country Club in Akron, Ohio, Jerry Heard is still leading with 7 under par, 133, at the halfway mark. And Bob Lunn is next with a 4 under par, 136. The United States basketball team was eliminated yesterday in the Pan-American games in Columbia, and the U.S. baseball team was upset by the Dominican Republic, 5 to 4. In tennis, Stan Smith is the last seeded player still in competition at the Western Championship in Cincinnati. And today in Chestnut Hill, Massachusetts, Marty Riessen meets Australian Ken Rosewall, and South African Cliff Drysdale meets John Newcombe in the semi-finals of the U.S. professional tennis tournament. And that's all I have from here. Over.

286:58:20 Scott: Okay. Thank you, Joe. That's interesting.

286:58:24 Scott: Hey, Houston, 15. By the way, where did the 5 feet per second come from? Should we get our trusty navigator up there to navigate some more for you?

286:58:39 Allen: Dave, it probably came for - from the uncoupled - thrusting we were doing yesterday. Other than that, I'm not really sure. It's - it's by no means certain. Anyway we're just, I guess - we'll be watching it today and get back with you, with the final bit of information on it.

286:59:01 Scott: Okay. Very good. Just thought maybe we'd get our navigator to navigate again, and it would probably go away, as most of them have done so far.

[Since firing their SPS (Service Propulsion System) engine to get them out of lunar orbit, Endeavour's course has been true. Both the opportunities to refine their trajectory have not been needed. Indeed, midcourse 7 was predicted yesterday to be so small that it might not be worth burning. However, as noted by Allen, the error in their trajectory has built up. Al Worden has been making parallel determinations of their trajectory by making angular measurements between the stars and Earth. He has been so good at it, he jokingly suggested to the flight controllers that if they practice, their answers might eventually converge with his. Normally, the ground's determination of the spacecraft's trajectory is thought to be the more accurate.]
287:00:13 Allen: Endeavour, the Saturday morning weather report of the landing area reads, "High scattered, 2,000 scattered, 15-knot winds out of the east-northeast, 10 miles vis[ibility], and waves going to 4 feet." It should be well above your personal minimum.
[The forecast of the recovery area is excellent: two layers of scattered clouds - an upper layer of cirrus clouds (usually at about 30,000 feet, 10,000 meters) and a few fair weather clouds with bases at 2,000 feet (700 meters). Note that in the world of flying and aircraft, height above the ground is still (as of the year 2000) stated in feet rather than metres.]

[The reference to "personal minimums" refer to a pilots' self-imposed limits for flying, and are often more conservative than the officially published "minimums". For example, a pilot who has just earned his instrument rating in the United States is legally qualified and permitted to land in 200 foot (60 meter) ceilings (the base of the cloud cover) and one-half mile (800 meter) visibility. Landings in these conditions are sufficiently difficult (try it sometime!) that most new instrument pilots will avoid those conditions, opting instead for an airport which might have 500 foot ceilings and one mile visibility.]

287:00:35 Scott: Looks very good. We appreciate that.

287:00:46 Scott: Sounds like the recovery troops have things in hand as usual.

287:00:51 Allen: Yes, indeed.

[All the while the crew has been checking their systems, recording updates, and listening to the news, breakfast is being served.]

[Very long comm break.]

287:32:05 Allen: Endeavour, this is Houston. Requesting Gamma-ray, Gain Step, switch to center, please.

287:32:13 Scott: Roger. Gamma-ray, Gain Step to center.

287:33:19 Allen: And, Endeavour, this is Houston. SIC over and out.

287:33:29 Scott: Hey, Mr. SIC! Congratulations on a super job all the way. Sure appreciate it.

[SIC: Scientific Instrumentation Controller. Allen was the primary CapCom during Dave and Jim's very intense exploration of the lunar surface. Having trained with them for the event, he had proved to be a very capable and integral part of the team. Dave's praise is deeply felt. In the Apollo 15 Lunar Surface Journal, Dave had much to say about Joe's role in the success of the mission. He and Eric Jones talked about the choice of Joe Allen as the Apollo 15 EVA CapCom.]

[Scott - "We knew he was good."]

[Jones - "And you specifically picked Joe Allen for the job?"]

[Scott - "Absolutely. Without question. Joe Allen was selected to be the lunar surface CapCom because of his capabilities."]

[Jones - "By Dave Scott and Jim Irwin."]

[Scott - "I don't recall how that came about, but when we got around to segmenting out the portions of the mission for the support crew, we made a very clear, definite decision that Allen would be the guy. Not that [Bob] Parker [their pre- and post-EVA CapCom] wasn't good. Parker was excellent. But Joe just had this sort of flair for it, as you can see. I mean he was able to fit in, he picked up the geology very quick, he was a master at diplomacy - on both sides. So it was a very easy decision of the guys we had. Karl Henize was very good. Parker was very good. But, for what we wanted to do with this exercise, Allen was the guy."]

287:33:40 Allen: Roger, Dave. Likewise in every way. See you at Ellington [Air Force Base in Houston].

287:33:45 Scott: Okay, very good.

[At about 287:40, the crew is scheduled to exit the PTC barbecue mode when the roll angle equals 71°. Because the time that this roll angle is achieved is so dependent on the time the PTC is started and the actual roll rate, it is impossible to predict ahead of time when the spacecraft will reach the 71 degree mark. In fact, the PTC will not be terminated until 288:27.]

287:55:26 Irwin: Houston, this is 15. [No answer.]

287:55:54 Irwin: Houston, this is 15 with the PRDs - readings.

287:55:59 Parker: Roger, 15. Go ahead.

287:56:03 Irwin: Good morning, Bob. Okay, for Al, it's 25034 and mine is 08041.

287:56:12 Parker: Roger. You got one for Dave?

287:56:16 Irwin: Okay. His is not working any longer.

287:56:19 Parker: Okay.

[Very long comm break.]

[Flight Plan page 3-399.]

Public Affairs Officer - "This is Apollo Control at 288 hours, 5 minutes. Apollo 15 is 46,778 nautical miles [86,633 km] from Earth. Velocity: 8,622 feet per second [2,628 m/s]. We're 7 hours, 5 minutes from landing. Apollo 15 will perform the midcourse correction number 7. Looking right now at time very close to the Flight Plan. Midcourse [7 will occur] somewhere around 291 hours, 56 minutes. And it will be on the order of 5 feet per second [1.5 m/s]. We will use the Reaction Control System attitude thrusters on the Service Module for this midcourse. We will get some more tracking before we firm up the burn and the time. Tracking during the sleep period last night, while the spacecraft was in a stable trajectory, shows that the trajectory was perturbed somewhat during the maneuvering yesterday while the crew was performing some of the experiments and photography work. So a midcourse will be required. At 288 hours, 7 minutes, this is Mission Control, Houston."
[The instruments in the SIM bay have now completed their mission and will be shut down for good. Researchers in the back rooms are ecstatic over the quantity and quality of the data, which will keep them occupied for years.]
Public Affairs Officer - "This is Apollo Control at 288 hours, 22 minutes. The SIM bay experiments have been completed for this Mission. Flight Director Gene Kranz logged the time at 288 hours 17 minutes when the SIM bay was secured for the final time."
[Shutting down the SIM bay is more involved than simply hitting the "off" button. Each experiment is individually powered down and safed. Next, the Gamma-ray boom is partially retracted, and both the Mass Spectrometer and Gamma-ray booms are jettisoned. Although there is no operational requirement to get rid of the booms, this may be a test of their jettison systems. Apollo 15 is essentially an engineering test flight for the SIM bay and every opportunity to test its systems is taken.]
Public Affairs Officer - "This is Apollo Control at 288 hours, 27 minutes. Apollo 15 has ended Passive Thermal Control rotation now. The crew will shortly be realigning the inertial platform and then will go through a series of cislunar navigation star sightings. "

[As is the usual procedure after waking, Al Worden performs an alignment of the IMU (Inertial Measurement Unit) to correct for the drifting which the platform has experienced since the last alignment about 17 hours ago. An Option 3 alignment is performed, which will use the star sightings to establish the spacecraft's attitude accurately in space. Once the attitude is known, the gyros in the platform are "torqued", or rotated, to the reference attitude used for Passive Thermal Control (the PTC REFSMMAT).]

["PTC" orientation is somewhat of a misnomer here, as Endeavour will no longer perform the maneuver for the rest of the mission. To be sure, there are many possible platform orientations that are usable, but as the PTC orientation is satisfactory, there is little need to change it. It is as well suited for the cislunar sightings that follow as any other and has been used for both the inbound and outbound legs of the mission.]

[Obtaining an accurate platform alignment is especially important here. Navigation in cislunar space demands precise measurements of the angles between the Earth (or Moon) and various stars. By starting with a known attitude that has been established accurately, the crew can make highly precise fixes on their position.]

288:33:08 Parker: Apollo 15, Houston.

288:33:12 Irwin: Go ahead, Bob.

288:33:13 Parker: Roger. Correction of the Flight Plan. We'd like to have all crewmembers on the biomed harness for entry. I suspect that means Dave won't be doffing his about now.

288:33:34 Irwin: Okay, I guess we could give you two. The - our trusty CMP has his off and stowed for entry.

288:33:44 Parker: Roger. Copy. [Long pause.]

288:34:12 Parker: Okay, 15. Looks like the surgeons can live with that without too much trouble.

288:34:18 Irwin: Roger.

[As originally scheduled, Dave Scott would be removing his biomedical harness at the same time Jim Irwin would be putting his on, and the monitoring of only Jim would have continued through to entry. The episodes of premature ventricular contractions that both Jim and Dave experienced is certainly the motivation for this request.]

[At this time, a fresh Lithium Hydroxide canister is brought out from storage location A, and the used cartridge is stored in location A5. This will be the final LiOH change of the mission.]
[Long comm break.]
288:37:49 Parker: Apollo 15, Houston. Over.

288:37:54 Irwin: Go ahead, Houston.

288:37:56 Parker: Okay. If you guys have a moment or two, we have some Flight Plan updates concerning entry - entry cue cards and Entry Checklist. Over.

288:38:08 Irwin: Stand by.

[Long comm break.]
288:41:19 Irwin: Well, Bob, it'll be about a half an hour before we're ready to talk about those changes.

288:41:24 Parker: Okay, Jim. Give me a call when you're ready.

288:41:29 Irwin: Okay.

[Everyone on board the spacecraft is currently busy with several tasks. Al Worden is performing the IMU realignment and the subsequent cislunar navigation sightings, Dave Scott and Jim Irwin are changing the Lithium Hydroxide canisters and getting reading on the command module RCS thruster temperatures. While some of these tasks are not necessarily time critical, it is far better to get them completed before moving on to discussing a new set of updates.]

[In preparation for the platform alignment, the Digital Autopilot is changed from the PTC configuration ([11111] [X1111] translated: CSM only, plus-X translations using all four jets, 5 degree deadband, maneuvers at 0.2 degrees/second, either Quads A and C, or B and D used for roll, and all four sets of RCS quads are to be used) to the configuration used for platform alignments ([11102][01111] translated: CSM only, plus-X translations using all four jets, 0.5 degree deadband, maneuvers at 0.5 degrees/second, Quads B and D used for roll, and all four sets of RCS quads are to be used) ]

[Long comm break.]
288:46:34 Worden: Houston, 15, I have some valve temps for you.

288:46:38 Parker: Roger, 15. We're ready to copy.

288:46:42 Worden: Okay. 5-C is 4.5; 5-D is 4.4; 6-A, 4.4; 4.4; 4.6; and 4.5.

288:46:57 Parker: Roger; copy.

[The system test meter displays parameters such as temperatures and pressures of many spacecraft systems.

Panel 101 - the system test meter.

Located in the CM's lower equipment bay, it consists of two rotary switches labeled A through D, and 1 through 6, plus a setting for the transponder. A voltmeter with a scale of 0 to 5 volts provides the output display. By selecting a combination of the two switches, a wide variety of readings can be obtained. When a specific reading is desired, such as the pressure in the oxygen manifold for fuel cell 3, the crewmember selects 2-B on the selection switches. The pressure is then displayed on the meter as volts, which will be converted to PSI by technicians on the ground.]

[The use of a voltmeter is perhaps unfortunate, as it doesn't allow a simple interpretation of the values presented. Documents on board the Command Module do provide suitable conversions for the crew. The awkwardness of obtaining this information is lessened though, as these parameters are not those which require constant monitoring. Using the system test meter also frees up valuable real estate on an already overcrowded Main Display Console.]

[The various setting for the system test meter are:

The six valves read by Al Worden are for the valve temperatures of the Command Module RCS jets; five sets of two thrusters are arranged around the base of the CM, and another set of two thrusters at the apex above the main hatch. In order, the thrusters reported are negative pitch, positive yaw, counterclockwise roll, positive pitch, negative yaw, and clockwise roll.]

[Comm break.]

288:48:21 Parker: Apollo 15, Houston, Be advised, we are looking, at the present time, at a midcourse 7 burn of 5.6 feet per second [1.7 m/s] retrograde. Over.

288:48:34 Irwin: Okay. We copy.

[The retrograde nature of this burn implies that the spacecraft is coming in slightly too fast and requires a burn against their direction of travel. If left unchecked, their re-entry would be slightly shallower than nominal, still within an acceptable range but requiring more correction during the passage through the atmosphere. As highlighted by the PAO announcer, there is also the interplay between the time of the CM's arrival and the rotation of the Earth. Their current error will have a profound effect on where they land. They want to get as close to the recovery forces as possible and at this stage, it is easy to get it right - and so they will.]

[Long comm break.]

Public Affairs Officer - "This is Apollo Control at 288 hours, 55 minutes. Apollo 15 now 42,587 nautical miles [78,871 km] from Earth. Velocity: 9,094 feet per second [2,772 m/s]. The Retrofire Officer expects to have the final midcourse numbers ready about 289 hours, 30 minutes. We'll pass them up to the crew shortly after that. We expect the midcourse [7 burn] at about 291 hours, 56 minutes. Presently, it looks like a 5.6-feet-per-second [1.7-m/s] burn. It will be with the Reaction Control System. Burn time will be on the order of 13 seconds. We're still in the entry corridor on the - on the present trajectory without a midcourse. However, the midcourse would put us in the center of the corridor and that's where we want to be. If we entered on the present trajectory without a midcourse, we would probably land about 60 [nautical] miles [110 km] short of the landing point."

288:58:05 Parker: 15, Houston. We have your torquing angles.

288:58:10 Scott: Roger; thank you.

[It is normally standard procedure for the crew to radio the ground the results of the platform alignment, which includes the amount of drift that has been detected and corrected in the platform, and a measure of the accuracy of the star sightings themselves. At the end of the P52 IMU alignment program, the amount of drift in all three axis that the platform has experienced (and is corrected for by the realignment process) is displayed on the DSKY (Display and Keyboard).]

[When the High Gain Antenna is being used (as is now), a higher telemetry data rate can be supported, which allows for more parameters to be relayed to the ground. Among the items that are included in the additional data are the DSKY displays. Rather than having Al go through the process of formally reading the DSKY, the Guidance Officer has informed Bob Parker that they can see the DSKY, and Al does not need to read the display to the ground. Two displays are of particular interest to the guidance team: Noun 96, which indicates the amount the gimbals have drifted, and hence, the amount they need to be torqued to return to proper alignment, and Noun 05, a quantity which indicates the overall accuracy of the star sightings.]

[Al's latest set of marks were dead on - a measured error of 000.00 degrees as reported by Noun 05 on the DSKY. Usually called out as "five balls", it is the best possible accuracy that the sextant is capable of resolving.]

[Long comm break.]

[Flight Plan page 3-400.]

Public Affairs Officer - "This is Apollo Control at 289 hours. Apollo 15 is maneuvering now to the proper attitude for the cislunar navigation star sightings."

289:01:31 Parker: Apollo 15. Request Omni Charlie, please.

289:01:37 Worden: Roger. Omni Charlie.

[Very long comm break.]

[Now that the guidance platform is accurately aligned to a known orientation, the business of determining the spacecraft's position and velocity can begin.]

[Al will carry out two navigational exercises today using P23 in the computer, both of which will use the Moon as the local reference for measuring their current position. Yesterday, all four of Al's P23s were done with reference to the Earth but now they are approaching the home planet so fast, it does not give a consistent reference as Al tries to take multiple marks. In this exercise, he first calibrates the spacecraft's optical system by taking 5 marks on Alpheratz (Alpha Andromedae). Normally, he takes just a couple but yesterday, Mission Control specifically requested he take 5 marks. He then maneuvers to the correct attitude for the navigational sightings. The exercise consists of Al measuring the angles between selected stars and the Moon. Specifically, Al uses the limb of the Moon either nearest the star or opposite the star, depending on where the terminator is with respect to the star.]

[The measurements are between Altair (Alpha Aquilae) and the Moon's far horizon, Delta Capricorni and the Moon's far horizon, Beta Pegasi and the Moon's near horizon, Markab (Alpha Pegasi) and the Moon's near horizon, and finally Gamma Pegasi and the Moon's near horizon. The results are used by the computer to check that the state vector (the spacecraft's velocity and position at a specified time) would lead to the measured angles and, if not, what change needs to be made to the vector's position (Delta-R) and velocity (Delta-V). These values can be accessed by Al on the DSKY (Display and Keyboard).]

Public Affairs Officer - "This is Apollo Control at 289 hours, 22 minutes. Apollo 15 is 5 hours, 36 minutes from entering the Earth's atmosphere. Endeavour now 40,241 nautical miles [74,526 km] from Earth. Velocity: 9,386 feet per second [2,861 m/s]. And it's 2 hours, 33 minutes to the midcourse burn."

289:32:04 Scott: Houston, Apollo 15. We're ready for your entry updates now if you like.

289:32:11 Parker: Roger, 15. Understand you're ready for the update. Tell Al that was another super set of marks, certainly.

289:32:17 Scott: Yes, that one came out pretty fair, didn't it?

289:32:24 Parker: Okay, 15. The first change is in the Entry Checklist, second page; and, on page 1-2, we wish to delete step 21, which is the "DSKY Condition Light Test."

289:32:46 Scott: Okay. Step 21 deleted.

289:32:48 Parker: You may remember that one from the sim[mulator]; that's the one with the - gives us the P35 and turns the PIPAs off momentarily.

289:32:55 Scott: Yeah, I guess we don't want to do that today. [Garble]...

[The details of this reference are, as they say, "lost to history", but it appears that the DSKY light test has a bug in it that might put the computer into Program 35 (a rendezvous program) and shut off the IMU's accelerometers. Needless to say, this is not a good thing.]

[It is often said that the computers and other spacecraft components perform "flawlessly". While this is usually true, there are often many problems that the ground and crew are aware of that might limit a system's full range of capabilities. If a problem is discovered, and a workaround is found, an "operational limitation" is noted. So long as the system is not operated outside this limitation range, there should be no problems. Such limitations are not exclusive to spacecraft. In an aircraft owned by one of the Journal's editors (O'Brien), a problem was found in the engines' rocker arms that was known by to the engine manufacturer. The manufacturer specified that the ignition timing be changed, which reduced the power output of the engine somewhat. With this limitation in place, no other restrictions as to engine operation were required.]

[Operational limitations often inspire the retelling of the old joke:

Patient: Doctor, whenever I do this (gesturing), it really hurts!

Doctor: Well, don't do that, then!]

289:32:57 Parker: That's - that's a Rog. Okay, the next one, Dave, is on page 6, when we're checking the circuit breaker configuration on panel 8; and we're going to add "SPS Pilot Valve A, Main A and B, Main B, Open. Verify." Over.

289:33:29 Scott: Okay. SPS Pilot Valves Main A and B, both Open, and - Configuration of the circuit breakers on panel 8. Go ahead.

289:33:36 Parker: Okay. Then if we go down to the entry cue card, down to the P67 section.

289:33:44 Scott: Okay. Go.

289:33:45 Parker: Okay. Down there near the middle where it says "Steering commands downrange error minus 6 to 0," that should be changed to "Downrange error minus 24 to 0." Over.

289:34:01 Scott: Rog. Just like it is in the checklist. Right? And I think we noticed that last night looking it over.

289:34:06 Parker: Okay. And next, on the second line under the Noun 68, there's a comment that says "negative [if plus: EMS]." And there's a certain amount of happiness with that statement down here. They say that you can have a positive H dot in P67 nominally and, therefore, the statement on the cue card that this is a fail indication is not a good idea. I understand [Apollo 15 backup CMP] Vance [Brand] discuss[ed] this with Al beforehand.

289:34:39 Scott: Okay. We'll scratch that. I don't think we'll get to a P66 - 67 turnover anyway, but we'll scratch that one out. Thank you, Bob.

[The "P66 to P67 turnover" refers to the two computer programs that might be executed at a point in the middle of in the entry phase. Program 66 is selected when the drag on the CM falls to a predetermined low level, effectively the point where it has left the sensible atmosphere, and is used to maintain attitude and provide targeting. P67 is then called when the CM slams back into the atmosphere again.]

[Normally P66 would not be executed, for it is used only when the CM has "skipped" out of the Earth's atmosphere, perhaps due to an entry angle that was too shallow, or if too much upwards lift is applied during the early part of the entry phase. One scenario is that this would be a planned maneuver, for example, to "stretch" the entry to avoid poor weather. On the other hand, if the entry angle were too shallow, the CM would swing around the Earth to a several thousand mile apogee and re-enter the atmosphere after a full earth orbit. Under worse case conditions, the spacecraft's power and oxygen supplies would likely expire long before the entry occurs.]

[Noun 68 (used in conjunction with Verb 16) is used during entry, and displays the bank angle (roll) of the Command Module, its velocity, and altitude rate. The procedure that Bob Parker refers to describes the kind of entry where the spacecraft is gaining altitude relative to the Earth's surface, such as the case where it has skipped off the top of the atmosphere.]

289:34:48 Parker: Roger. We hope not. And we have a question here, Dave, that we need an answer for, apparently concerning stowage. People are concerned about the hooks on the back of the R-12, the Flight Data File container, which is now stowed in one of the PGA bags. And they are concerned that those hooks be placed in such a way that they will not be in any danger of piercing the aft bulkhead - the pressure bulkhead. So I guess you can tell how they're placed or what's underneath them to prevent such occurrences.

289:35:22 Scott: Okay. We'll make sure of that. And I guess the problem with R-12 was that, once we got all the LM data onboard, we didn't have any place to put it, or else we didn't have any place to put the LM data. And if you have any better suggestions on where to put them, we'll be glad to do it.

289:35:39 Parker: I don't think we have any, right now, Dave. I guess the quickest thing would have been to just put it in the PGA bag with the hooks pointing up.

289:35:48 Scott: Okay. We'll do that.

[The "LM data", or more formally, the LM Flight Data File, is a set of systems and operations manuals and checklists for the LM. Rather than leaving documents that have no further relevance to the mission in the LM when it was jettisoned, Dave and Jim have brought them back to the CSM with them. They carry written information that the crew collected while operating the equipment and flying the spacecraft which may be useful when debriefing the mission. Most certainly, they have also been saved as a memento of the voyage.]

[The concern here is that this large and heavy stack of manuals (easily a foot thick and weighing 10 - 15 kilograms) might be resting on hooks used to secure the space suits. This weight will increase severalfold - to as much as 100 kilos - during a nominal 6-G entry. Parker is expressing worries that the flight data file might be resting on the hooks, which might punch through the aft bulkhead due to the weight of the documents. Such a puncture is serious, as it would result in the depressurizing of the Command Module. The easiest solution appears to be rearranging the material so that the hooks are not pressing against the bulkhead.]

[Scott, from the 1971 Technical Debrief - "We had all the entry stowage done, almost all of it done, the day before entry. On entry day, we found ourselves with an awful lot of time on our hands, which I think was a good idea. Everything was cinched down tightly, and I thought the ground pretty much agreed with where we put everything. I thought they had a fairly good handle on our stowage locations, and we stowed just exactly like we had it on the stowage map. Our comment going into the entry was, 'Gee, we've never had this much time in a simulation before.' We sat there and coasted along."]

289:35:50 Parker: And one reminder, Dave. You guys undoubtedly know it. Just a reminder that you will not have any back lighting for the scroll and no lighting on the roll bug today.

289:36:03 Scott: Okay. No back lighting for the scroll and no lighting on the roll bug. Thank you. [Long pause.]

[Two sets of lights within the EMS (Entry Monitor System) not operating due to the short that tripped a circuit breaker earlier in the mission, at 033:48:00. As there was no clear explanation for the circuit breaker tripping, the ground has advised the crew to leave the circuit open for the duration of the mission. Only a few items are affected, including the EMS's scroll backlighting and the roll indicator. This should not present a serious problem for the crew, as the lighting is only to enhance the display's visibility.]
289:36:28 Scott: Have anything else, Bob?

289:36:30 Parker: No, Dave. That's all I have for the moment.

289:36:33 Scott: Okay. That's pretty easy.

[Comm break.]
289:38:18 Irwin: Houston, we're standing by for a VHF comm check.

289:38:23 Parker: Stand by, Jim. We'll see if they're ready. [Long pause.]

289:38:46 Parker: 15, Houston. We'll have to stand by for another few hours to get you close enough to do that VHF comm check.

289:38:54 Irwin: All right. Roger. We understand. [Long pause.]

[The VHF communications system is intended only for short range communications and is limited to only a few thousand kilometres. Right now, Endeavour is nearly 75,000 kilometres from Earth - too far for reception. The VHF comm check will be performed about 6 hours from now at 294:25:05. At that point the spacecraft will be only 10,000 kilometres from the Earth.]

[The crew have begun using the Entry Checklist and are midway down page 1-1.]

289:39:53 Parker: Apollo 15, Houston.

289:39:57 Irwin: Houston, 15. Go.

289:39:59 Parker: Roger. Could we have a reading of the - an onboard reading of the potable tank quantity, please?

289:40:09 Irwin: 82 percent.

289:40:11 Parker: Copy; 82 percent.

[Comm break.]
289:42:07 Parker: Apollo 15, Houston. Over.

289:42:11 Scott: Houston, 15. Go.

289:42:13 Parker: Roger. Could you guys check the Potable Tank Inlet valve again for us, and find out whether it is in the closed or open position? Once again, what we're seeing is the waste tank increase and the potable tank has been staying constant all morning.

289:42:30 Scott: Okay; last night when you called, I even went down and recycled that valve and made sure it was in the detent in the Open position, which it was.

289:42:38 Parker: Okay. In that case, could you go down and cycle it from closed to open again for us, please?

289:42:45 Scott: Roger. We're doing that right now. [Long pause.]

289:43:08 Scott: Okay, it was still open, and Al cycled it from open to closed and back to open.

289:43:15 Parker: Okay. Thank you. It's no big deal, Dave, nothing to worry about.

289:43:20 Scott: Might as well get everything all trimmed up.

289:43:22 Parker: That's what we're trying to do.

[Water is created as a byproduct of the reaction used to create electricity in the fuel cells. Some of the water is piped to the Command Module, where it is stored in the Potable Water Tank and used for drinking, food preparation and washing. However, far more water is created by the fuel cells than could ever be consumed by the crew. Some is stored in the Service Module, where it is used to cool equipment, and the remainder is shunted to the waste water tank, which is regularly dumped overboard.]

[The problem at hand is that the waste water tank is filling up, which would be the case where the potable water tank is full or the inlet valve to the tank is closed. Since the crew has verified that the inlet valve to the potable water tank indicates it is open, and the tank itself is not quite full, engineers on the ground will have to come up with other solutions as to why the waste tank is filling. If the waste tank were to fill, and overboard dump will be required. Dumping waste water is not a difficult procedure, but it will perturb the trajectory slightly, and the water vapor cloud that results will disrupt the tracking of the spacecraft somewhat. As the spacecraft is so close to the Earth, and the parameters for the next midcourse correction have already been calculated, any alteration of the trajectory is best avoided.]

[From the 1971 Post-flight Mission Report - "The potable water tank quantity began to decrease during meal preparation at approximately 277 hours and failed to refill for the remainder of the flight. The waste water tank continued to fill normally and, apparently, accepted fuel cell water for this period. A similar occurrence had been noted earlier, at 13½ hours, when the potable tank quantity decreased as the crew used the water, and remained constant until a waste water dump was performed at 28½ hours. This decrease had been attributed to a closed potable tank inlet valve until the crew verified in their debriefing that the valve had been open during this time. The amount of water drained from the tank verified that the tank instrumentation was reading correctly.]

["During a postflight fill operation, with the waste tank inlet valve closed, and water introduced at the hydrogen separator, both the potable and waste water tanks filled.]

["The check valve between the fuel cell and waste tank dump leg was tested and found to leak excessively. A tear-down analysis of the check valve was performed and a piece of 300-series stainless steel wire (approximately 0.0085 by 0.14 inch [0.2 by 3.5 mm]) was found between the umbrella and the seating surface. This contaminant could cause the umbrella to leak and yet move around sufficiently to allow adequate seating at other times. The wire most probably came from a welder's cleaning brush and was introduced into the system during buildup. Safety wires and tag wires are of a larger diameter than the one found. The check valve at the potable water tank inlet is of a different configuration and is spring loaded closed. The 1-psi pressure required to open this valve is a large pressure drop compared to the other components at the low flow of 1-1/2 lb/hour, and would, therefore, cause the water to flow to the waste tank.]

["The potable water tank inlet check valve was found to be contaminated with aluminum hydroxide, a corrosion product, of aluminum and the buffer. The potable water tank inlet nozzle was clean and free of corrosion. The check valve corrosion is not believed to have caused the problem, but could have contributed by increasing the crack pressure of the valve."]

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control at 289 hours, 49 minutes. Apollo 15 is 37,858 nautical miles [70,113 km] from Earth. Velocity: 9,709 feet per second [2,959 m/s]. The crew will be taking some ultraviolet photography of the Earth in a short time. This will complete their science tasks for the mission. We'll then do the midcourse burn. [We're] 2 hours, 6½ minutes away from that burn. They will perform some more star sightings after the burn and then the rest of the time will be devoted to their pre-entry checklist. Recovery Carrier Okinawa is reported on the station. Weather in the recovery area is good. Visibility, 12 miles; waves about 3 feet."

290:00:24 Parker: Apollo 15, Houston. Requesting Omni Delta.

290:00:28 Worden: Omni Delta.

[Flight Plan page 3-403. UV photography procedures are on page 3-402 of the Flight Plan.]

[Omni-directional antenna D, one of four low-power S-band antennae around the periphery of the Command Module, is used for communications with Earth while Endeavour is oriented correctly for UV photography. This session follows the pattern of previous periods of UV photography where a Hasselblad body is mated to a specialised UV-transmitting lens and mounted in window 5, itself fabricated from quartz to pass UV. The spacecraft's motion rates are stabilised before photography begins.]

[Eight frames are taken, AS15-99-13491 to 13498, two each through four filters, though only seven appear in the Index of 70-mm Photography. Samples of the sequence include AS15-99-13491 taken through filter 1. When compared to earlier photographs, for example 13487 taken yesterday, the increasing angular size of the Earth is readily apparent. However, the characteristics of the filter contribute a lot of background flare to the image. Frame 13495 is a much clearer shot by being taken through filter 3, while the flare becomes apparent again by 13498 through filter 4. The large, circular artifact is probably a reflection of the camera lens in the window.]

[Once the UV photography of the Earth is complete, a colour image is taken on colour film through the same combination. This is frame AS15-96-13136.]

[Long comm break.]

290:08:21 Parker: Apollo 15. Requesting Omni Charlie.

290:08:24 Worden: Omni Charlie.

[Long comm break.]
Public Affairs Officer - "This is Apollo Control at 290 hours, 8 minutes. Apollo 15 has completed the ultraviolet photography of the Earth and is new maneuvering to an attitude to take some Moon photographs."

[Their maneuvering is taking antenna D away from Earth so C is to be selected to continue clear communications.]

[The final task in their program of UV photography is to take images of the Moon using the same methodology as for the Earth which will help calibrate the results of the experiment. These eight images are AS15-99-13499 to 13506. Those taken through filter 2 are not available and this may be due to them being essentially black. Examples from the others are displayed in this compilation of 13499, 13503 and 13505.]

290:15:10 Parker: 15, Houston. If you'll give us [the] High Gain [Antenna] and Pitch of plus 7, Yaw of 250, then we'll be able to keep High Gain for the next 2 or 3 hours, and I won't have to keep calling you for Omnis. Over.
[This is mistaken. Endeavour is at the correct attitude for the lunar UV photography. Soon, it will be maneuvered to another attitude for realigning the platform and afterwards, to yet another attitude for carrying out the midcourse 7 burn.]
290:15:23 Irwin: Okay; understand, plus 7 and 250 on the High Gain.

290:15:27 Parker: Roger.

[Very long comm break.]
290:25:30 Parker: 15, Houston, We're noticing some drift in roll. If you're not through with the UV photos, we'd like you to retrim back to attitude, please.

290:25:39 Worden: Okay, and we are finished with the UV photos.

290:25:42 Parker: Okay; that takes care of that one.

[Comm break.]
290:27:37 Parker: Apollo 15, Houston. Over.

290:27:41 Scott: Go ahead, Bob.

290:27:42 Parker: Okay; if you guys got a minute, we can do a few things here. Number 1, if you give us Accept, we'll send you some state vector and target loads; and, number 2, we have a couple comments to read to you.

290:27:58 Scott: Okay; you have Accept, and stand by.

290:28:01 Parker: Roger; you're getting the uplink, and we're standing by.

[Long comm break.]
290:31:54 Parker: 15, the computer's yours. You have state [vector], target and REFSMMAT.

[The latest state vector, midcourse correction targeting information, and the updated PTC REFSMMAT have been sent to the onboard computer. These will be used for midcourse correction 7, scheduled for about two hours from now. ]

290:32:01 Scott: Roger. Thank you.

290:32:13 Scott: And, Houston, we're all on. You can go with your comments.

290:32:17 Parker: Okay; first one, news concerning the water business. We've been having you check that valve. It looks to us now as though there's a blockage into the potable tank. You got obviously - a - far more water than you need to survive the rest of the mission, but it does mean that the waste tank will be filling up, and there is a possibility that it will start to vent about an hour or two before EI [Entry Interface]. It's been discussed down here and decided that the best way to do this is - far as not perturbing the vector too much - is to let it relieve overboard and not to do a dump ahead of time or turn the water boiler on ahead of time. In line with this, we might just verify that the Pressure Relief valves down on panel 352 - the water control panel, is in the Relief position. It certainly should be there; it's just a - a little verification to make sure we're - we're not going wrong there. Second, I...

290:33:11 Scott: Okay, that's verified.

290:33:12 Parker: Okay; thank you. Second item is, we suggest that it might be reasonable to put some tape over the SPS light on the EMS to keep you from confusing with the .05g light, in case you have a problem there, Al. That's your option, obviously. It just a suggestion.

290:33:32 Scott: Oh, I don't think he'll have any confusion with that.

290:33:35 Parker: Okay.

290:33:36 Scott: We'll make sure we watch it.

[The SPS light, located on the Entry Monitor System panel, is illuminated any time there is power applied to the Service Propulsion System engine. Adjacent to this light is the 0.05G light on the EMS panel, which comes on when the spacecraft first hits the outer fringes of the Earth's atmosphere. Entry into the atmosphere is defined as when the drag on the spacecraft increases to a point where the deceleration reaches 0.49 meters/second.]

[The suggestion being passed up is for Al to cover the SPS light with some tape so as not to confuse it with the 0.05G light. Certainly an overly cautious, and well-intentioned request from the "back room"; Bob Parker is probably obligated to pass it along to the crew. Far from interpreting the request as patronizing (given the importance of the light and the many of hours training with the EMS), Dave Scott simply laughs it off.]

290:33:38 Parker: And the third question is, from your comments when we were talking about R-12, some people believe you may be asking us a question that you have a problem with stowage of some of the extra LM data file, or have you found a place for that already?

290:33:53 Scott: Oh, no; that's all tucked away in R-3 very - very neatly. We have no - no problem at all in the stowage. We just wanted to locate R-12 in a nice soft spot and secure it down, which it is.

290:34:04 Parker: Okay. We - we were - [ready to] crank up building 45 to find you a location if you needed it. [Pause.]

[Building 45 houses the Command Module and Lunar Module simulators. Bob Parker's somewhat tongue-in-cheek reference was that the a team was ready to start a full simulation run just to find a location for the extra LM Data Files.]

290:34:20 Parker: And, 15; Houston. We've got an entry PAD and a midcourse 7 PAD if you're ready to copy.

290:34:28 Scott: Stand by one, Bob. Let our pad leader get out his pencil. [Long pause.]

[The joke is that there is a person at the launch pad called the Pad Leader, namely Guenter Wendt - a celebrated character - who coordinated a team of technicians during the final moments before the crew were left to themselves atop the launch vehicle. Dave is playing with the title as one of Jim Irwin's roles is to copy down information read up from Earth, namely the Pre-Advisory Data or PADs.]
290:35:00 Irwin: Okay, Bob. I'm ready for midcourse 7.

290:35:02 Parker: Okay. Purpose, midcourse 7. RCS/G&N; 26363; Noun 48's are NA and NA; 291:56:47.90; minus 0005.6; minus all balls, plus 0000.2; roll, 180, 311, 000; HA, NA; HP, plus 0022.3; 0005.6, 0:24, 0005.6; 31, 347.9, 35.3. The rest of the PAD is NA. GDC align stars are Vega and Deneb; roll, pitch, and yaw for the alignment are 100, 137, 316. Burn recommendation is 2 jets, plus-X, quads Bravo and Delta. And the HP in the PAD on Noun 44 there is based on a MSFN trajectory after midcourse 7. Over.

[All these details are copied onto a standard form with the format predefined so as to reduce errors. The numbers will be fed into Program 30 in the computer as part of the pre-thrusting procedures for the burn.]

[Interpretation of the Midcourse correction #7 PAD, also known as the Corridor Control burn PAD follows:

Purpose: The burn is a small one to fine tune the spacecraft's trajectory and ensure it re-enters in the centre of the permitted corridor.

System: The Guidance and Navigation system will control the burn which will be performed using the RCS jets, not the SPS engine.

CSM weight (Noun 47): 26,363 pounds (11,958 kilograms).

Pitch and yaw trim (Noun 48): Since the RCS thrusters are being used for the burn, the gimbals for the SPS engine are not needed. Therefore there is a "NA" (Not applicable) entry in Noun 48.

Time of ignition, Tig (Noun 33): 291 hours, 56 minutes, 47.90 seconds.

Change in velocity (Noun 81), fps (m/s): x, -5.6 (-1.7); y, 0.0 (0.0); z, +0.2 (+0.06).

Spacecraft attitude: Roll, 180°; Pitch, 311°; Yaw, 000°.

HA, expected apogee of resulting orbit: Since the spacecraft is moving faster than the escape velocity of the Earth and is not in a sensible orbit, it makes no sense to define what the apogee resulting from the burn would be. Hence, this entry is NA.

HP, expected perigee of resulting orbit: If the Earth lacked an atmosphere, the midcourse correction would bring the spacecraft to within 22.3 nautical miles (about 41.3 km) of the surface (Of course, the atmosphere does get in the way!).

Delta-Vt (Total velocity change): 5.6 feet/second (1.7 meters/second).

Burn duration or burn time: 24 seconds.

Sextant star: The star used for sextant sighting is number 31 (Arcturus or Alpha Boötis) which will be visible through the sextant when its shaft angle is 347.9° and its trunnion angle is 35.5°.

GDC align stars: Star number 36 (Vega, in the constellation of Lyra) and 43 (Deneb, in Cygnus) to be used for GDC align if the IMU cannot be used. The align angles are 100° in roll, 137° in pitch and 316° in Yaw.

It is recommended that the burn be made using the rearward facing thrusters (Plus-X) on two RCS quads, B and D (Bravo and Delta).]

290:37:17 Irwin: Okay. The readback for the midcourse. It's RCS/G&N; 26363; NA, NA; 291:56:47.90; minus 0005.6, minus all zeros, plus 0000.2; 180, 311, 000; NA, plus 0022.3; 0005.6, 0:24, 0005.6; 31, 347.9, 35.3; Vega and Deneb; 100, 137, 316. Recommendation for the burn configuration, two jet, plus-X, quads Baker and Dog; and the HP of the PAD is based on MSFN trajectory after midcourse 7.

[The "phonetic alphabet", where words are substituted for letters to enhance understanding during radio communications, was updated during the middle of the 1960's. Previously, the sequence began Able, Baker, Charlie, Dog, Easy and so on. Many letters were changed, and the alphabet began Alpha, Bravo, Charlie, Delta, Echo... Despite the "official retirement" of many of the words, old habits die hard, and a mix of the two systems was frequently heard.]
290:38:12 Parker: Roger. Good readback, Jim; and I'll give you entry when you're ready.

290:38:18 Irwin: Okay. Stand by. [Long pause.]

290:38:34 Irwin: Okay. I'm ready for entry, Bob.

290:38:36 Parker: Okay. Entry, area, mid-Pac; 000, 153, 000; 294:41:55, 267; plus 26.13, minus 158.13; 06.1; 36096, 6.49; 1082.4, 36178; 294:58:55; 00:28; Noun 69s are NA; 4.00, 02:13; 00:18, 03:37, 07:42; 04, 140.3, 37.5; 213, down 09.5, right 4.7; lift vector, up. Comments: 1, use non-exit EMS pattern; 2, RET for 90K, 6 plus 04; 3, RET for mains, 8 plus 30; 4, RET for landing, 13 plus 27; 5, constant g, roll right; 6, moonset, 294:56:37. Over.

[This is the preliminary entry PAD, based on the best estimate of tracking at the time. Its provision hedges against the remote possibility of a communication problem later. It will be revised slightly after the midcourse correction burn #7 is evaluated. While the PAD, as read to the crew, is essentially a string of numbers, as with the previous PAD, there is a very strict format associated with it. Both astronauts on the ground and in the spacecraft are using a form that contains all the necessary details for interpreting the numbers.]

[Before interpreting the PAD, it may be useful to explain some of the terminology used. The first important concept is that of Entry Interface, a completely arbitrary event which is defined as the time when the spacecraft (then consisting of only the Command Module) reaches an altitude of 400,000 feet (65.83 nautical miles, 121.92 km). It is chosen as it is easily calculated from the spacecraft's current state vector and does not depend on the vagaries of the atmosphere.]

[A second concept is the 0.05g event. This is the point at which the increasing drag of the atmosphere's outer fringes cause a deceleration measuring a twentieth of a g. For calculation sake, prior to entry actually occurring, it is taken to occur at an altitude of 297,432 feet (48.95 nautical miles, 90.66 km) but it will occur when the spacecraft's guidance system detects a change in velocity of 0.49 m/s2 (0.05g). It triggers a change in the entry program run by the computer and also begins the monitoring of the trajectory by the EMS (Entry Monitoring System).]

[Note that some events in the PAD are tied to the Entry Interface event, others to the 0.05g event.]

[The data passed up for the entry PAD is interpreted as follows:

Purpose: Entry.

Landing target: The landing target is in the Mid-Pacific.

IMU gimbal angles required for trim at 0.05g: Roll, 000°; pitch, 153°; yaw, 000°.

Time of the horizon check: 294 hours, 41 minutes, 55 seconds GET.

Spacecraft pitch at horizon check: 267°. This is 17 minutes before time of entry.

Splashdown point: 26.13° north latitude, 158.13° west longitude.

Maximum number of g's during entry: 6.1.

Velocity at Entry Interface (400,000 feet altitude): 36,096 feet/second (11,002 meters/second).

Entry flight path angle at Entry Interface: 6.49°.

Range to go to splashdown point from 0.05g event: 1,082.4 nautical miles (2,004.6 km).

Predicted inertial velocity at 0.05g event: 36,178 feet/second (11,027 meters/second).

Time of Entry Interface: 294 hours, 58 minutes, 55 seconds GET.

Time from Entry Interface to 0.05g event: 0:28 (seconds).

Planned drag level (deceleration) during the constant g phase: 4.00g.

Time from Entry Interface until their velocity slows sufficiently to allow a circular orbit around the Earth: 2:13.

The practical implication of this is that this is the "capture point" where the CM will no longer be able to skip off the atmosphere. Since the spacecraft will already be within the Earth's sensible atmosphere at this point, drag will continue to slow the spacecraft and the return to Earth is assured.

Time from Entry Interface that the communications blackout begins: 0:18.

Time from Entry Interface that the communications blackout ends: 3:37.

Time from Entry Interface that the drogue parachutes will deploy: 7:42.

Sextant star: 04 (Achernar, Alpha Eridani.)

Sextant shaft angle at Entry Interface minus 2 minutes: 140.3°.

Sextant trunnion angle at Entry Interface minus 2 minutes: 37.5°.

The next three items refer to an attitude check made using the COAS sighted on a star two minutes before Entry Interface.

Boresight star: 213. Since this is not a recognised star number from the Apollo list, we have yet to learn what it refers to.

Boresight Star pitch angle on COAS: Down 9.5°.

Boresight Star X position on COAS: Right 4.7°.

Lift vector at Entry Interface: Up.

Comments in addition to the PAD:

The non-exit EMS pattern is to be used, that is, the entry is not expected to skip off the atmosphere and re-enter.

90,000 feet (27.4 km) will be reached at 6:04 after Entry Interface.

Time of main parachute deployment: 8:30 after Entry Interface.

Time of landing: 13:27 after Entry Interface.

When maneuvering to ensure a constant g force (done after the max-g portion of the entry to assure a constant deceleration), the crew is to roll right.

Moonset (used to provide one more check of the entry progress): 294:56:37.]

290:39:15 Irwin: Okay, Bob. Readback for the entry PAD. It's mid-Pac, 000, 153, 000; 294:41:55, 267; plus 26.13, minus 158.13; 06.1; 36096, 6.49; 1082.4, 36178; 294:58:55; 00:28; Noun 69 is NA; 4.00, 02:13; 00:18, 03:37, 07:42; 04, 140.3, 37.5; 213, down 09.5, right 4.7; up. Comments: Use non-exit EMS pattern; RET for 90K, 6 plus 04; for mains, 8 plus 30; landing, 13 plus 27; constant g, roll right; moonset, 294 plus 56 plus 37. Over.

290:42:37 Parker: Roger. Good readback, Jim. [Long pause.]

290:43:12 Parker: And, 15, we'd like Accept again. It looks like we found some errors in the load that we sent up.

290:43:20 Irwin: Okay; stand by. [Pause.]

290:43:25 Irwin: Okay; you have Accept.

290:43:27 Parker: Thank you.

290:43:44 Irwin: Houston, 15. Picked off the Verb keys zero - on top of you. Sorry about that. It's all yours.

290:43:50 Parker: Okay. [Long pause.]

290:44:11 Parker: 15, we'll clear it. Don't worry.

290:44:16 Irwin: Okay.

[Long comm break.]
290:48:50 Parker: 15, Houston. The computer's yours again.

290:48:57 Irwin: Roger, Bob. [Long pause.]

290:49:49 Parker: Apollo 15, Houston. We would like the VHF turned on even though it's too early to do the comm check. [We would] like it turned on in Simplex Alpha to warm it up, and so we can watch it.

290:50:12 Irwin: Okay, we're turning on Simplex Alpha.

290:50:39 Parker: Thank you, 15.

[Throughout the entire flight, Apollo 15 has communicated with the Earth through the S-band communications system, through a combination of the single high gain and the four omni-directional antennae. S-bands' high frequency (in the gigahertz range) is excellent for long-range communications, but its high power requirements and the highly directional nature of its signal make it impractical for use during entry. The VHF system, previously used for communication between the CSM and the LM, will handle the communication tasks between the spacecraft and the recovery force.]

[Unlike today's radios, which use frequency synthesis through a digital circuit, the 1960's vintage Apollo radios were purely analog devices, and required a period of warm-up to stabilize the circuitry.]

[Also in preparation for re-entry, the crew are donning Mae Wests in case they have to leave the spacecraft in a hurry after landing.]

[A P52 option 3 is being performed, using the PTC orientation. This realignment of the inertial platform is in preparation for the final time that its orientation is changed. Throughout the flight, the platform has been kept in one of a number of defined orientations, eight in all. Most platform realignments are simply to compensate for the drift that occurs in the platform's orientation over a period of time. Every so often, however, when he needs to swing the platform from one orientation to another, Al carries out a double P52. The first of these is simply to determine the platform's drift since the last P52, an important part of understanding the mechanical characteristics of the IMU in case this has a bearing on subsequent flights.]

[The second P52 is intended to swing the platform around to a new orientation. In this case, option 1 is being used which means that rather than being aligned to a REFSMMAT, it is aligned to an orientation which has been calculated to be relevant to an upcoming maneuver - in this case, re-entry. The practical upshot of this is that their FDAI (Flight Director Attitude Indicator, or "8-ball") will display angles which relate simply to their entry trajectory.]

[For both of these P52s, Al uses star 01 (Alpheratz or Alpha Andromedae) and star 10 (Mirfak or Alpha Pegasi) and achieves zero measuring errors each time. Soon, when he completes the first P52, he will bring up the torquing angles on the DSKY from where Mission Control can see them.]

[Long comm break.]

Public Affairs Officer - "This is Apollo Control at 290 hours, 54 minutes. Apollo 15 now 31,707 nautical miles [58,721 km] from Earth. Velocity: 10,674 feet per second [3,253 m/s]. We're an hour and 2 minutes away from the midcourse burn that will be performed at 291 hours, 56 minutes, 47 seconds; Delta-V of 5.6 feet per second [1.7 m/s]. We'll use 2 jets and the duration of the burn will be 24 seconds. Based on a successful midcourse 7, the elapsed time for Entry Interface with the atmosphere at 400,000 feet - will be 294 hours, 58 minutes, 55 seconds. Spacecraft velocity at that time, 36,096 feet per second [11,002 m/s]. And the 'range to go' to the landing point, 1,082.4 nautical miles [2,004.6 km]. The elapsed times of entry events from the entry interface time - we'll begin blackout 18 seconds after Entry Interface. Blackout will end 3 minutes, 37 seconds; drogue chutes, 7 minutes, 42 seconds; main chutes, 8 minutes, 30 seconds; and landing, 13 minutes, 27 seconds. The coordinates of the aim point for landing: 158 degrees, 8 minutes west; 26 degrees, 8 minutes north."
[Flight Plan page 3-405.]
291:00:33 Parker: And, 15, we have your torquing angles.

291:00:39 Scott: Roger.

[Long comm break.]

[Al is now carrying out the second P52 to realign the platform to the entry orientation, known as the Entry REFSMMAT.]

Diagram showing the orientation of the Entry REFSMMAT

[For this orientation, the IMU's X-axis is aligned along the direction of flight but parallel to the local horizontal as exists at Entry Interface. Its Z-axis is parallel to, but in the opposite direction of the vector that comes from the Earth's centre to the point of Entry Interface. The upshot of this arrangement is that if, at Entry Interface, the spacecraft were to have its heatshield pointing forward, its X-axis parallel to the local horizontal, its "wings" level and with the crew "heads down" the FDAI would display roll 0°, pitch 180° and yaw 0°.]

291:03:47 Scott: Houston, 12. [Do] you have the torquing angles?

291:03:53 Parker: Roger, 12. We have the torquing angles.

291:03:56 Scott: Okay. That's through.

[The technical transcript does have "12" being spoken here rather than "15." A check of this section with the tapes is still required.]

[Again, ground controllers in Houston are able to monitor the DSKY inputs and displays. Of particular interest is the Verb 16, Noun 93 display ("Delta Gyro Angles"), which shows the amount the gyros have drifted since the last alignment.]

[Very long comm break.]

Public Affairs Officer - "This is Apollo Control at 291 hours and 11 minutes. Apollo 15 is maneuvering now to the midcourse burn attitude. That burn is scheduled in 45 minutes."

Public Affairs Officer - "This Apollo Control at 291 hours, 29 minutes. We're 27 minutes away from the midcourse burn. And Apollo 15 is 28,159 nautical miles [52,150 km] from Earth. Velocity: 11,347 feet per second [3,459 m/s]. In the next 3 and a half hours, at which time Apollo 15 will enter the atmosphere, that velocity will build to 36,000 feet per second [11,000 m/s]."

291:40:02 Parker: Apollo 15, request Omni Alpha, please.

[The crew are at the top of page 1-2 of the Entry Checklist.]

[Very long comm break.]

Public Affairs Officer - "This is Apollo Control at 291 hours, 46 minutes. We're 10 minutes away from the midcourse burn now. Distance: 26,285 nautical miles [48,152 km] from Earth. Velocity: 11,743 feet per second [3,579 m/s]."

291:51:50 Parker: 15, at 5 minutes to go, you're looking good.

291:51:55 Scott: Roger. Thank you. We're all set.

[Comm break.]
291:54:46 Parker: 15, Houston. Requesting Key Release and Enter to complete the integration and get us down for the burn.

291:55:04 Scott: Houston, the integration should all be done.

291:55:08 Parker: Rog. Somebody on the ground here hasn't seen it, apparently,

291:55:12 Scott: Okay, we've been sitting here for about 5, 6 minutes.

291:55:17 Parker: Rog. We couldn't tell. Sorry about that, Dave.

[Two programs are used for the midcourse correction burn. First, the prethrusting program, Program 30 (P30 - External Delta-V) is started to enter the basic parameters such as the time of ignition and change in velocity. This information was provided to the crew in the midcourse PAD at 290:34:20. It is interesting to note that the burn duration is not entered. Determining the cutoff time will be done in "real time", with the Inertial Measurement Unit sensing the change in velocity during the burn. The burn time calculated by the back room is a very good estimate, but factors such as an incorrect assumption of the spacecraft weight, or substandard thruster performance can alter the exact time of the thruster firing.]

[Next, Program 41 (P41 - RCS Thrusting) is selected. P41 uses the data computed by P30 to calculate the steering commands, maneuver the spacecraft to the burn attitude and control the burn. P41 requires a bit of time to perform a numerical integration of the targeting and steering equations. As such, P41 must be started some time prior to the planned ignition to allow sufficient time for the integration to complete. In the exchange above, it appears that the ground has not seen that the integration has completed, and is worried that the burn might be need to postponed because the necessary calculations have not completed. In fact, the integration had completed, and it isn't quite clear why the ground isn't aware of this.]

[The omnidirectional antennae are only able to handle low bit-rate telemetry, and is limited to critical engineering data. This does not allow ground controllers luxury of the of viewing data that is displayed on the DSKY.]

[Comm break.]

[Flight Plan page 3-406.]

Public Affairs Officer - "1 minute."

291:56:22 Scott (onboard): ...Normal.

291:56:23 Irwin (onboard): Tape Recorder's on High Bit Rate. Record the start.

291:56:29 Scott (onboard): Okay. It worked.

291:56:32 Worden (onboard): Yes.

291:57:04 Worden (onboard): 10, 9, 8, 7, 6, 5, 4, 3, 2, 1...

291:57:14 Worden (onboard): Zero.

291:57:15 Irwin (onboard): ... open.

Public Affairs Officer - "Apollo 15 is thrusting. GNC says it looks like a good burn."

291:58:00 Scott: Okay, Houston; 15 with the burn status report.

291:58:02 Parker: Roger that.

291:58:04 Scott: Okay, Tig was on time. Burn time was 21 and came right out on the money, and it clicked up a couple of seconds after the shutdown to minus .1, 0 and minus .1. Delta-Vc was plus .8.

291:58:21 Parker: Roger. Copy that, Dave. It looked good to us.

291:58:29 Scott: Good.

[Comm break.]

[With the last propulsive burn of the flight, tracking radars on Earth begin the task of providing the range and velocity data that will be used to generate a new state vector. This will be uplinked to the spacecraft in the next few minutes. Soon, Al will be matching this effort by making his own parallel determination of the state vector using sightings of three stars in conjunction with the Moon.]

292:00:07 Parker: 15, Omni Bravo, please.

292:00:12 Scott: Roger. Omni Bravo.

[Comm break.]
Public Affairs Officer - "This is Apollo Control at 292 hours, 1 minute. Telemetry shows Apollo 15 maneuvering to the optics calibration attitude as the crew gets ready to perform some additional cislunar navigation star sightings."

292:02:31 Parker: Apollo 15, Houston. If you'll give us Accept after you get maneuvered to attitude before you go into P23 to start the optics cal, we'll uplink you your new state vector, and then you can press on with the P23s as soon as that's up.

292:02:47 Scott: Roger. [Long pause.]

292:03:01 Scott: You've got it.

292:03:03 Parker: Roger.

[The spacecraft has reached the attitude for calibrating the optics. The computer can be placed in Accept and the new state vector received.]

[Comm break.]

292:04:17 Parker: 15, Houston. The computer's yours.

292:04:23 Scott: Roger.

[Long comm break.]

[Now Al maneuvers to the sighting attitude. Once there, he uses the optics to measure three angles between the Moon and three stars. These are between Gamma Pegasi and the Moon's horizon nearest the star, Alpha Gruis and the Moon's horizon furthest from the star, and finally, Altair (Alpha Aquilae) and the Moon's horizon furthest from the star.]

292:08:27 Parker: And, 15, requesting Omni Charlie.

292:08:31 Scott: Roger. Omni Charlie.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control, at 292 hours, 11 minutes. Apollo 15 is 2 hours, 47 minutes away from the Earth's atmosphere, 3 hours away from landing in the Pacific Ocean, about 285 nautical miles [528 km] north of Oahu, Hawaii. Endeavour's distance from Earth now is 23,494 nautical miles [43,511 km]. Velocity has built to 12,410 feet per second [3,783 m/s]."

Public Affairs Officer - "This is Apollo Control. The Command Module/Service Module separation time listed in the Flight Plan is valid. 294 hours, 43 minutes."

Public Affairs Officer - "This is Apollo Control at 292 hours, 21 minutes. The Apollo 15 backup crew has joined CapCom Bob Parker at his console. Dick Gordon, Vance Brand and Jack Schmitt."

Public Affairs Officer - "This is Apollo Control. Flight Director Gene Kranz has now been joined by the other flight directors for this mission; Gerry Griffin, Glynn Lunney and Milton Windler. And the management officials are beginning to assemble. At the Department of Defense console is Maj. Gen. David M. Jones, the DoD manager for manned spacecraft support. Mission Director Capt. Chester Lee is here. Dr. Rocco Petrone, the Apollo Program Director, and Col. James McDivitt, the Apollo Spacecraft Program Manager."

Public Affairs Officer - "This is Apollo Control at 292 hours, 35 minutes. Flight Dynamics reports that the tracking data accumulated so far since the midcourse burn shows that that burn did what it was designed to do. That is put Apollo 15 in the center of the re-entry corridor. They'll continue to collect data and verify that."

Public Affairs Officer - "This is Apollo Control at 292 hours, 42 minutes, Apollo 15 now 19,927 nautical miles [36,905 km] from Earth. Velocity: 13,434 feet per second [4,095 m/s]. We're 2 hours, 16 minutes away from Entry Interface and about 2½ hours away from landing."

292:56:48 Scott: Houston, 15.

292:56:51 Parker: 15, go ahead.

292:56:53 Scott: Roger. We're ready for logic sequence check.

292:57:00 Parker: And, 15, we're ready for a logic sequence check also.

[The crew are working through the lower half of page 1-2 of the Entry Checklist.]

[In less than two hours, the Command Module will separate from the Service Module. Then, after re-entry, when the CM reaches the denser region of the atmosphere, the various subsystems of the ELS (Earth Landing System) will operate. These complex events, which include the detonation of explosives, are controlled by the SECS (Sequential Events Control System) which orchestrate the Service Module Jettison Controllers and the ELS Sequence Controllers. A check is made of the system prior to operation. Circuit breakers feeding power to the logic, arming, separation and circuitry, are closed; their status checked by ground controllers and a Go given to arm the pyrotechnic devices that will be fired.]

292:57:03 Scott: Okay. Sequential Logic coming on now - number 1, number 2.

292:57:19 Parker: And, 15, you're Go for Pyro Arm.

292:57:23 Scott: 15; Roger.

[Long comm break.]

[Flight Plan page 3-407.]

Public Affairs Officer - "This is Apollo Control at 293 hours. Apollo 15 now 17,680 nautical miles [32,743 km] from Earth. Velocity: 14,190 feet per second [4,325 m/s]. Apollo 15 is 1 hour, 58 minutes away from Entry Interface. 2 hours, 11½ minutes away from landing. During entry, the prime recovery ship, the helicopter carrier USS Okinawa will be about 5 nautical miles [9 km] north of the aimed point. In the vicinity of the carrier, 2 helicopters will be airborne. Call signs, Photo and Relay. Photo helicopter will have the photographers aboard. Relay will carry backup swimmers and act as a radio relay between the carrier, and the spacecraft, and the other helicopters in the area. Swim 2 helicopter will be the prime helicopter to deploy swimmers with the floatation collar. Swim 2 will be 5 nautical miles [9 km] south of the aimed point at entry. Swim 1 will be the backup for Swim 2 and the Swim 1 swimmers will be deployed to recover the parachutes. Swim 1's location during entry, 10 nautical miles [19 km] west and 15 nautical miles [28 km] north of the aim point. The recovery helicopter, the helicopter which will recover the crew will be 10 nautical miles [19 km] east and 15 nautical miles [28 km] north of the aimed point at entry."

Public Affairs Officer - "The recovery helicopter will be piloted by Commander Stephen A. Coakley of Chula Vista, California. His co-pilot, Lieutenant Junior-Grade John M. Murphy, Jr., of La Jolla, California. Crewmen are Aviation Machinist Mate, First Class, Ernest L. Skeen of Oklahoma City, and Aviation Electronic Technician, Second Class, Thomas R. Hardenbergh of East Lansing, Michigan. A Manned Spacecraft Center Flight Surgeon, Dr. Clarence A. Jernigan of Dickinson, Texas will also be aboard Recovery helicopter. Swim 2, the prime flotation collar helicopter, is piloted by Lieutenant Commander, David D. Cameron, Jr., of Palo Alto, California; co-pilot, Lieutenant Junior Grade Stephen M. Lind of Olympia, Washington, crewman Aviation Machinist Mate, Second Class, John H. Driscoll of Whitehouse Station, New Jersey, and Aviation Electronics Technician, Third Class, Bryce E. Devenport, of Glenns Ferry, Idaho. The swim team leader on that helo is Lieutenant Junior Grade, Fred W. Schmidt of Northbrook, Illinois. Swimmer Number 2, Quartermaster, First Class, William C. "Jake" Jakubowski of Lachawanna, New York. Swimmer Number 3, Yeoman, Third Class, Rudy R. Davis of Ashland, Kentucky. Swim 1 is piloted by Lieutenant Donald M. Larsen of Wellman, Iowa; co-pilot. Lieutenant Junior Grade Eric J. Challain of Olympia, Washington. Crewmen are Aviation Machinist Mate, Second Class, Larry G. Parker of Ringold, Georgia and Aviation Anti-submarine Warfare Technician Airman Thomas F. Sharafik of Hayward, Wisconsin. The swim team leader on Swim 1 is Warrant Officer Jerry L. Todd, Sturgis, Michigan, swimmer number 2 is Ship Fitter, Third Class, Frank S. Schroeder, Malvern, Pennsylvania and swimmer number 3, Radioman Seaman Roy Alan Buehler, Carrollton, Missouri."

293:07:10 Parker: Apollo 15, Houston. Over.

293:07:14 Scott: Houston, 15. Go.

293:07:16 Parker: Roger. I thought we'd let you know, from our preliminary tracking, you're sitting right in the center of the [entry] corridor now.

293:07:23 Scott: Great. That's a nice place to be.

293:07:25 Parker: The best.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control at 293 hours, 19 minutes. Apollo 15 now 15,225 nautical miles [28,197 km] from Earth. Velocity: 15,173 feet per second [4,625 m/s]."

Public Affairs Officer - "This is Apollo Control. The flight crew aboard the helicopter which will provide photo coverage for recovery operations; the pilot is Lieutenant Commander John M. Quarterman of Brunswick, Georgia; the co-pilot Lieutenant Junior Grade Ronald D. Martin, Roanoke, Virginia. Crewmen are Aviation Structural Mechanic, Second Class, Douglas P. Walker of Selma, Alabama; and Aviation Machinist's Mate Airman Gregory G. Wahl of Santa Monica, California. The crew aboard the relay helicopter; pilot is Lieutenant Michael T. Boyce, Bainbridge Island, Washington; co-pilot..."

[With the corridor control burn completed, Al Worden heads to the lower equipment bay to make the 45th and final P52 IMU realignment of the mission. This corrects the tiny amount of drift that has occurred since he first aligned it to the entry orientation two hours ago. He sights on star 40 (Altair or Alpha Aquilae) and star 45 (Formalhaut or Alpha Piscis Austrini) and makes an error of only one hundredth of a degree in determining their position. The torquing angles are brought up on the DSKY where Mission Control can see them.]
293:20:50 Parker: And, 15, we copy your torquing angles.

293:20:53 Scott: Roger. Thank you.

[Very long comm break.]

[The crew are well into their checks for entry and landing. As a backup attitude reference for their FDAI displays, they align the GDC (Gyro Display Coupler) to match the IMU's reference, per the top of page 1-3 of the Entry Checklist. Should the IMU fail to give them good attitude information, they can switch to the GDC and have that drive the FDAI. The GDC receives information about the spacecraft's attitude from one of two BMAGs (Body Mounted Attitude Gyros). These are the attitude reference gyros normally used by the SCS (Spacecraft Control System) for overall attitude control but which can be used in case the G&C (Guidance and Control) has problems.]

[Seventeen minutes before they reach Entry Interface, a simple check will be made of the G&N system, whereby Al looks out of the centre window to see whether the Earth's horizon is aligned with a mark inscribed on the pane. In preparation for that, he now maneuvers the spacecraft to a defined attitude which will be held until after the Service Module is jettisoned and which should make that mark align with Earth's horizon. If it doesn't, the G&N system is not working properly and he will control the entry with the SCS instead.]

[The final check of the spacecraft's ability to align itself is carried out. Starcodes were included in the preliminary Entry PAD, along with appropriate angles, with which the COAS and the sextant could be checked while in the current attitude. With that, the spacecraft's optics have performed their last task - they are swung to a 90° shaft angle and powered down.]

Public Affairs Officer - "Relay's co-pilot is Lieutenant Junior Grade Timothy D. Kelly, Long Island, New York; Crewman ADR, First Class, Raymond D. Brooks of Nampa, Idaho; and Aviation Anti-Submarine Warfare Technician Airman Ronald C. Weaver, Madcroft, Wisconsin. The backup swimmers aboard Relay: the swim leader is Lieutenant Junior Grade Jonathan Smart of Belmont, Massachusetts; swimmer number 2 is Ship Serviceman, Second Class, William Ramos-Flores of Bayamon, Puerto Rico, and swimmer number 3 is Boilerman, Third Class, Roderick T. Yonkers, Brookfield, Connecticut."

Public Affairs Officer - "This is Apollo Control with a correction on the home state of Ronald C. Weaver, one of the crewmen on the Relay Helicopter. He is from Madcroft, Wyoming."

[On the EMS (Entry Monitor System), there is a long Mylar tape, 8.75 cm (3.5 inch) wide that displays a intricate pattern of lines which define the relation between velocity and deceleration G-forces during re-entry.

An intricate pattern of lines from the EMS display which define the relation between velocity and deceleration forces.

Two different patterns are printed on the tape; one for a nominal entry, and one for an entry that will skip off the atmosphere and re-enter later. Additionally, there are several test patterns, which are used to verify the EMS's circuits.

Several test patterns which are used to verify the EMS's circuits.

Final preparations for re-entry are beginning now, as Al Worden runs the EMS through a series of self-checks as detailed at the bottom of page 1-3 of the Entry Checklist. Most of the tests are of the EMS's internal circuitry, but it is vitally necessary to test the scroll which displays the acceleration vs. velocity trace. Several sets of patterns on the tape are set aside just for this self-test. As the tape can be moved forward only, it is not possible to back up the tape and "reuse" a test pattern. During the test, the scroll makes a pre-defined series of motions. Once Al is satisfied with its operation, he will scroll the tape past the remaining self-test patterns, and set it to the actual entry monitor pattern.]

293:34:42 Worden: Houston, 15.

293:34:46 Parker: Roger, 15. Go ahead.

293:34:48 Worden: Okay. EMS check worked fine.

293:34:51 Parker: That sounds good.

[During these preparations, virtually all of the Command Module systems are powered up. The heat generated by these systems is readily handled by the thermal control systems (part of the Environmental Control System) within the Service Module. Under moderate power loads, the heat from the Command and Service module systems is absorbed by a water-glycol solution (not unlike that found in the radiator of an automobile) and is rejected to space through two large radiators located around the lower region of the Service Module. A water evaporator system, similar in principle to that of the PLSS sublimators (the Portable Life Support System, worn by the crews on the lunar surface), is also available to remove larger amounts of heat.]

[Unfortunately, once the Command and Service Modules separate prior to entry, the elaborate heat dissipation systems used by the Command Module float away with the rest of Service Module. A special provision must be made, therefore, to manage the heat generated within the Command Module during the 30 minutes between separation and splashdown.]

[Although the active components of the heat rejection system are no longer available after separation, the water-glycol loop still is functional within the Command Module. Shortly before separation, a "chill-down" process is begun, where both the radiators, and the primary and secondary water evaporators are turned on, which cools the water-glycol to the 5°C (low 40°F) range. This doesn't cool the cabin (which remains at about 24°C) but exploits the cooling solution's ability to hold large amounts of heat with little change in temperature (a property known as specific heat capacity - water has, by far, the highest heat capacity of the common liquids). The total amount of heat that can be absorbed by the coolant is still quite limited, but is sufficient to last through entry and to splashdown.]

[The water-glycol solution is used only to cool the electronics within the spacecraft and the cabin. No attempt is made to try to actively cool the spacecraft exterior during its fiery plunge through the atmosphere. The heatshield of the Command Module is more than adequate (and in some cases, excessively adequate) to protect the structure.]

[Very long comm break.]

Public Affairs Officer - "This is Apollo Control at 293 hours, 37 minutes. Mr and Mrs James Irwin, the parents of Apollo 15's Lunar Module Pilot, have arrived in the viewing room here at the Control Center. Also, in the viewing room at this time, Dr. George M. Low, the Deputy Administrator of NASA, and Dale Myers, the Associate Administrator for Manned Space Flight. The MSC Deputy Director Christopher C. Kraft and the Director of Flight Operations Sigurd Sjoberg are in the Control Room proper at this time."

Public Affairs Officer - "This is Apollo Control. Donald K. Slayton, the Director of Flight Crew Operations has joined CapCom Bob Parker and the Apollo 15 Backup Crew at the CapCom Console."

Public Affairs Officer - "This is Apollo Control. Congressman William Archer and his mother, are now in the viewing room. And at 293 hours, 45 minutes; Apollo 15 is 11,611 nautical miles [21,504 km] from Earth. Velocity: 17,024 feet per second [5,189 m/s]."

[To record the view out of the window during re-entry, the movie camera is mounted in a bracket in the right-hand rendezvous (forward-looking) window. A mirror in front of the camera alters the view.]

[Earlier in the day, at 288:46:42, Al read out the temperatures of the injector valves in some of the Command Module's RCS thrusters. These readings were all found to be within an acceptable range, so the crew can skip the step at the bottom of page 1-4 in the Entry Checklist that requires them to preheat these thrusters if needed.]

293:47:42 Parker: Apollo 15, Houston. If you'll give us Accept, we'll send you up a final state vector.

293:47:49 Scott: Roger, Houston. You've got it.

293:47:54 Parker: And, Roger; you're getting it.

[Comm break.]
293:49:49 Parker: And, 15, it's your computer again.

293:49:53 Scott: Roger.

[Long comm break.]
293:55:09 Parker: Apollo 15, Houston. We have another entry PAD for you if you're ready to copy.

293:55:16 Irwin: Okay. Go ahead, Bob.

293:55:20 Parker: Roger, Jim. It's still mid-Pacific; 000, 153, 000; 294:41:54; 267; plus 26.13, minus 158.13; 06.2; 36096, 6.51; 1084.9, 36178; 294:58:54; 00:29; Noun 59s are NA; 4.00, 02:12; 00:18, 03:37, 07:44. Boresight and sextant stars are NA, since you've done them; lift vector is up. Comments, 1, use non-exit EMS pattern; 2, RET of 90K, 6 plus 06; mains, 8 plus 32; landing, 13 plus 29; constant g is roll right; moonset, 294:56:37. Over.

[Now that the corridor correction burn has been successfully performed, tracking stations have generated more accurate times and detail for the upcoming entry. The updated PAD is little different from the one at 290:35:02, but is more authoritative.

The data passed up for the Entry PAD is interpreted as follows:

Purpose: Entry.

Landing target: The landing target is in the Mid-Pacific.

IMU gimbal angles required for trim at 0.05g: Roll, 000°; pitch, 153°; yaw, 000°.

Time of the horizon check: 294 hours, 41 minutes, 54 seconds.

Spacecraft pitch at horizon check: 267°. This is 17 minutes before time of Entry Interface.

Splashdown point: 26.13° north latitude, 158.13° west longitude.

Maximum number of g's during entry: 6.2.

Velocity at Entry Interface (400,000 feet altitude): 36,096 feet/second (11,002 meters/second).

Entry flight path angle at Entry Interface: 6.51°.

Range to go to splashdown point from 0.05g event: 1084.9 nautical miles (2,009.2 km).

Predicted inertial velocity at 0.05g event: 36,178 feet/second (11,027 meters/second).

Time of Entry Interface: 294 hours, 58 minutes, 54 seconds GET.

Time from Entry Interface to the 0.05g event: 0:29 (seconds)

Planned drag level (deceleration or g-force) during the constant g phase: 4.00g.

Time from Entry Interface that velocity will slow sufficiently to allow a circular orbit around the Earth: 2:12.

Time from Entry Interface that the communications blackout begins: 0:18.

Time from Entry Interface that the communications blackout ends: 3:37.

Time from Entry Interface that the drogue parachutes will deploy: 7:44.

Lift vector at Entry Interface: Up.

Comments in addition to the PAD:

The non-exit EMS pattern is to be used, that is, the entry is not expected to skip off the atmosphere and re-enter.

90,000 feet (27.4 km) will be reached at 6:06 after Entry Interface.

Time of main parachute deployment: 8:32 after Entry Interface.

Time of landing: 13:29 after Entry Interface.

When maneuvering to ensure a constant g force (done after the max-g portion of the entry to assure a constant deceleration), the crew is to roll right.

Moonset (used to provide one more check of the entry progress): 294:56:37.]

293:57:29 Irwin: Okay. The readback on the entry PAD, Bob, it's mid-Pac; 000, 153, 000; 294:41:54; 267; plus 26.13, minus 158.13; 06.2; 36096, 6.51; 1084.9, 36178; 294:58:54; 00:29; 4.00, 02:12; 00:18, 03:37, 07:44; lift vector, up; use non-exit EMS pattern; RET for 90, 6 plus 06; mains at 8 plus 32; landing, 13 plus 29; constant g will be roll right; moonset, 294 plus 56 plus 37.

293:58:28 Parker: Roger, Jim. Good readback. And I have some information on landing area and weather and recovery forces, if you're ready to copy that.

293:58:40 Irwin: Roger. Go ahead.

293:58:41 Parker: Roger. Conditions in the recovery area continue to be good. Two thousand scattered, high scattered, visibility 10 miles. Winds are 10 knots, out of the east, and wave heights have come down to 3 feet. Altimeter at 3006. The recovery forces: the aircraft carrier is Okinawa. We have 3 helos: Swim 2, Swim 1, and Recovery. And Swim 2 is estimating to be on station, after splashdown, within 5 minutes. The two '130s in the area will be Hawaii Rescue 1 and Hawaii Rescue 2. Over.

[Bob Parker is reading a standard aviation weather forecast to the crew, and the conditions have changed little over the last four hours. By all standards, the weather is ideal; the winds have reduced to 10 knots from 15 and have changed direction only slightly (to east from east-northeast), and the waves have lowered by a foot. The altimeter setting he refers to is the barometric pressure at the surface, in this case 30.06 inches of mercury (1018 millibars in modern aircraft parlance, 101.8 kPa). Aircraft altimeters are wonderfully simple devices in principle, which operate by comparing the difference between the outside air pressure against that of a sealed, expanding bellows. Altitude is determined by the amount the sealed bellows expands as it reacts to outside air pressure changes, and is displayed on a clock-like instrument.

The "'130s" refer to Lockheed C-130 transports. As of this writing (2000), the C-130 is arguably one of the most enduring aircraft of all time. In the 40 years since it entered service, it has served in many of the world's air forces, and several civilian versions are in production.]

293:59:32 Irwin: Okay. Understand the weather is generally good. It's 2,000 scattered; 10; 10 knots from the east; 3 foot waves; altimeter, 3006. The Okinawa's there. The helos are Swim 2, 1 and Recovery; C-130's are Hawaii Rescue 1 and 2.

293:59:49 Parker: Roger, Jim. That's right. And noting on the altimeter, that means your Delta-H is minus 128.

293:59:57 Irwin: Roger.

[Long comm break.]

[Flight Plan page 3-408.]

Public Affairs Officer - "This is Apollo Control at 294 hours, 3 minutes. We've sent up the final entry PAD now. Those numbers did not change very much from the preliminary PAD. Entry Interface at 294 hours, 58 minutes, 54 seconds. The aim point - or the landing point remains the same: 26 degrees, 8 minutes north; 158 degrees, 8 minutes west. Maximum G load, 6.2. Velocity at entry on the atmosphere, 36,096 feet per second. Range to go at [entry] time 1,084.9 nautical miles. And the elapsed time for events from Entry Interface; begin blackout, 18 seconds; in blackout, 3 minutes, 37 seconds; drogue chutes at 7 minutes, 44 seconds; main chutes, 8 minutes, 32 seconds; and landing, 13 minutes, 29 seconds."
[The crew are at the top of page 1-5 of the Entry Checklist, dealing with the final stowage of items in the cabin. One of the interesting lines in this list is for the crew to check for water in the tunnel area. This is one part of the CM's external skin which is not covered by the heatshield - the forward hatch being the only barrier between the cabin and space - the actual tunnel having been jettisoned with the Lunar Module in lunar orbit. This area may be cold from exposure to deep space (the Sun being off to the side during the PTC barbecue roll).]

[After a check of the batteries that will power the detonation of the various pyrotechnic devices, the crew are ready to power up and arm the SECS, then pressurise the Command Module's RCS system.]

294:06:27 Worden: Houston, 15.

294:06:30 Parker: Roger, 15. Go.

294:06:32 Worden: Rog. We're getting ready to activate Command Module RCS and turning Logic and Arms on.

294:06:41 Parker: And, 15, we're ready to watch that.

294:06:44 Worden: Okay. Logic 1 coming on now. Logic 2 on - now.

294:06:55 Parker: Roger. Your Go for Pyro Arm.

294:06:58 Worden: Roger. Go for Pyro Arm. Okay.

[Comm break.]
294:08:03 Parker: 15 your CM RCS press[ure] looks good to us.

294:08:08 Scott: Roger, Houston.

[The Command Module RCS system has been completely inert during the mission, and now must be pressurized to become operational. Pyrotechnic squibs fire, opening up valves from helium tanks to the CM fuel and oxidizer tanks. Two independent sets of thrusters, fuel, oxidizer and helium tanks comprise the RCS system. After the valves on the helium tanks are opened, regulators maintain a pressure between 1,000 and 1,400 kPa (150 and 205 psi) on the fuel and oxidizer tanks.]

[Like the RCS systems on the Service Module and Lunar Module, the tanks are not pressurized by simply pumping high pressure gas into the tank. This might work on Earth, with the gas filling the upper half of the tank, while the liquid is expelled through a drain tube at the bottom. However, in a weightless environment, blobs of liquid simply float in the tank, often uncovering the outlet to the feed lines. Obviously, there is the need to assure that the fuel and oxidizer is expelled from the tank in a predictable manner.]

[By isolating the pressurizing helium outside a Teflon bladder within the tank, and containing the propellant within the bladder, there are no floating blobs of propellant and gas. The bladder exerts pressure on the tanks contents, which is then forced through the feed lines to the individual thrusters.]

[Comm break.]

Public Affairs Officer - "This is Apollo Control at 294 hours, 8 minutes. Apollo 15 is 8,018 nautical miles [14,849 km] from Earth and velocity; 19,685 feet per second [6,000 m/s]. Endeavour is 50 minutes away from the Earth's atmosphere, 1 hour, 3½ minutes away from landing. Command Module/Service Module separation is still scheduled at 294 hours, 43 minutes."
[The crew moves on to page 2-1 of the Entry Checklist with the setting of the Digital Event Timer to count down to the time of Entry Interface (294:58:54 GET). The EMS is set up making it ready to be initialised by P61 and start operating once 0.05g is sensed by P63. At the bottom-left corner of the EMS panel is the RSI (Roll Stability Indicator), an uncalibrated dial which serves to graphically show the direction of the lift vector generated by the flying characteristics of the CM's shape. By rolling the spacecraft during entry, the direction of lift can be altered, giving a degree of steering to the control systems. The RSI is aligned at this stage. Note that at top and bottom of this dial are two lights which help Al verify that he is in the correct corridor. The upper or lower lights tell him whether there is a need for the lift vector to be up or down to regain the correct entry corridor.]

[The final items on page 2-1 in the checklist are to test the CM RCS thrusters.]

294:10:58 Worden: Houston, 15. Testing Command Module thrusters.

294:11:03 Parker: Roger. We're watching. [Long pause.]

294:11:46 Worden: Okay, Houston; 15. Ring 1, test now.

294:11:50 Parker: Roger. Ring 2 looks good. [Long pause.]

294:12:37 Parker: And, 15, ring 1 looks good to us also.

294:12:41 Scott: Roger, Houston.

294:12:45 Worden: Houston, 15.

294:12:46 Parker: Go.

294:12:47 Worden: Can you see the solenoids operating down there? We can't hear them up here.

294:12:57 Parker: Roger, 15. That's what we're watching. And we verified them all.

294:13:01 Scott: Okay; thank you, sir.

294:13:03 Parker: You're welcome.

[Journal reader, Brett Buck explains why they may not be able to hear the thrusters firing.]

[Journal reader Brett Buck - "I am almost certain that this phenomena is the result of the "priming" effect. The system had been evacuated to some degree before propellant loading, the propellant induced, and then the system had remained unpressurized and unfired until shortly before the test described above. The result is that there is residual trapped gas (very small amount) in the lines, and then no propellant between the two thruster valves in each side (fuel and oxidizer). A few minimum-impulse-bit firings are required to fill up the free space with propellant before the thrusters actually fire.]

["Typically, on the first few pulses sent to these thrusters, nothing happens in the way of thrust, and no reaction is seen in the gyros. After some amount of on-time (in the hundred milliseconds range), the valves and lines are "primed" and the thrusters begin providing thrust and associated rate change and vibration. I can confirm that the actuation of the valves without firing on the Apollo thrusters makes a bit of a sound all by itself (sounds like BBs being dropped into an empty coffee can, sort of a sharp metallic "tink" sound), but it's not really very loud, compared to the actual firing (which you can hear even in a vacuum chamber from vibration transmitted through the test stand)."] [Scott, from the 1971 Technical Debrief - "We went through the CM RCS check, and when Al did the minimum impulse on the hand controller, none of us heard anything. We heard the propellant run through the lines as expected. As I had remembered on Apollo 9, we could hear very positive minimum impulses in the CM RCS. I was very surprised when Al ran around the [attitude control] stick, we didn't hear anything. We quizzed the ground, and they confirmed they could see the solenoids. Then I realized that they had second thoughts about it, and decided that they couldn't really verify that we had RCS. We were thinking along the same lines, too. 'We ought to do something else here before we go 'Separate' to confirm we've got CM RCS.' So, we had transferred SM, transferred back to CM RCS, and the ground suggested that we try 'Acceleration Command' - we were about to reach the same conclusion - to get some good rates. [To Worden] You put in an 'Accel Command' and checked both rings and got some good solid rates. We could see the flashes then. Then after that, particularly after we separated, we could hear the minimum impulse, and there was no question. We had good solid bursts on minimum impulse."]

[Worden, from the 1971 Technical Debrief - "That's right. I think we were all surprised at the noise level when we first checked those. It was quite different from what we heard in the simulator."]

[Scott, from the 1971 Technical Debrief - "Yes. The simulator is much too loud. Except after we got separated and you were pulsing around the entry attitude, then you could hear them."]

[Worden, from the 1971 Technical Debrief - "That's right."]

[Scott, from the 1971 Technical Debrief - "They were very positive and very sharp."]

[Long comm break.]

Public Affairs Officer - "This is Apollo Control. Congressman Bob Casey is in the viewing room now. His district includes the Manned Spacecraft Center."

294:18:01 Parker: Apollo 15, Houston. Over.

294:18:05 Worden: Houston, 15. Go ahead.

294:18:07 Parker: Roger. We were unable to monitor rates down here because we weren't set up for it. And we'd like to suggest that you might go back and repeat that check again. We suggest Accel[eration] Command in SCS; and you might try to monitor rates on board, and we'll try to monitor them down here. What we're looking at is only the solenoids down here and I guess, if you really push, that isn't a verification.

294:18:33 Worden: Okay. We'll do that. [Long pause.]

294:19:07 Worden: Okay, Houston; 15. We're ready to test them now.

294:19:13 Parker: All right. We're ready to watch. [Pause.]

294:19:26 Worden: Okay. They're loud and clear up here.

294:19:28 Parker: 15, we're monitoring good rates. [Long pause.]

294:19:54 Parker: 15, Houston. You copy? We monitor good rates down here also.

294:19:58 Worden: Okay, Houston. We copied, and we're testing ring 1 thrusters now.

294:20:46 Parker: And, 15, ring 1 looks okay to us again.

294:20:50 Scott: Okay, Houston. Thank you.

[Long comm break.]

[Journal reader Brett Buck - "I believe the 'priming' explanation is perfectly consistent with the observations. They fired a few min bits, heard prop run through the lines, but no apparent firing. After a few tries, the thruster started firing audibly and visually."]

Public Affairs Officer - "Distance: 5,933 nautical miles [10,988 km]. Velocity: 21,865 feet per second [6,664 m/s]."
[The crew is beginning to work through the checklist at the top of page 2-2 for the separation of the SM and CM. Next, they go to P61 on the computer to prepare the spacecraft's instrumentation for entry. Data from the entry PAD is entered in: the latitude and longitude of the landing and whether they fly heads up or down; their expected velocity, entry angle at EI and predicted maximum g force; and finally, their velocity and range to go at 0.05g, as well as the time between EI and 0.05g.]

[Once P61 has accepted the last of these, it moves the computer on to P62, which looks after the separation of the CM and SM as well as the maneuvering of the CM prior to re-entry.]

[Mission Control take the opportunity to have the crew check that their VHF communications are working.]

294:25:05 Parker: Apollo 15, Houston. We can try a VHF check now, if you will. [No answer.]

294:26:06 Parker: Apollo 15, Houston. Over. [No answer.]

294:26:44 Parker: Apollo 15, Houston. Over.

294:26:47 Scott: Go ahead, Houston.

294:26:49 Parker: Roger. We're ready to try a VHF check if you will. We'd like you to go to VHF Antenna, Left, and all of you turn off your S-bands and turn on your VHF T/Rs [Transmit/Receivers].

294:27:03 Irwin: Okay.

294:27:05 Parker: 15...

294:27:06 Irwin: Did that once... [Pause.]

294:27:18 Irwin: Did that once, Bob. And I read you loud and clear, but apparently you were not reading us.

294:27:23 Parker: That's apparently the case. And, Jim, I guess all we need is one of you to go to VHF T/R and S-band T/R, Off.

294:27:32 Irwin: Okay, I'll do that. [Pause.]

294:27:42 Irwin: Houston, this is Apollo 15 on Simplex A.

294:27:45 Parker: Roger. 15 on Simplex A; read you 5 by.

294:27:49 Irwin: Roger. I read you the same.

294:27:51 Parker: Okay. And I guess that finishes it.

[Very long comm break.]

[At 294:41:54, seventeen minutes prior to EI, Al is due to carry out the horizon check, a quick and simple test of the Guidance and Navigation System. If this system is doing its job right, then from his couch position on the left, Al should see the Earth's horizon through the windows aligned to an inscribed mark at 31.7°, ±5°.

CM window markings.

Dave Scott's debriefing later indicates that this check occurred after CM/SM Sep.]

[Now, as part of the CM/SM Sep. checklist at the bottom of page 2-3 of the Entry Checklist, the spacecraft is yawed 45° to the left (to 315°) so it is not perpendicular with the entry flight path. This orientation assures that, after separation, the two modules will not collide during entry. As the Command Module is equipped with only rotational thrusters (there is no need for translational maneuvers during entry) the task of ensuring a sufficient separation distance is left to the SM. After the maneuver, the CM will be yawed back in line with their trajectory (to 0°).]

[Jettisoning the Service Module is an intricate task, intended to safely sever the CM-SM interface and also to ensure the Service Module is moved away from the Command Module. As the Service Module is primary source of power, oxygen and cooling, inadvertently separating the two modules would have disastrous consequences for the crew (to say the least!). As with most other events that occur once and demand the highest reliability, a carefully timed series of pyrotechnic are used. Orchestrated by the SECS (Sequential Event Control System), umbilical deadfacing, CM-SM separation, and SM evasive maneuvering is performed in just a few seconds.]

[Beginning the process, the CM pilot Al Worden earlier applied power to the logic circuits of the SECS and also armed the pyrotechnic system which connects the pyrotechnic batteries to their control circuits. After the arming sequence is completed, the actual separation is started by simply flipping the CM-SM SEP switch - it goes without saying that this switch is protected by a metal cover to ensure it doesn't get moved accidentally! The SECS takes over at this point, immediately starting the process of deadfacing the electrical, gaseous and fluid connections between the Command and Service Modules.]

[The first step is to send the command to the Service Module Jettison Controller located in the service module. Once the command is received, the controller starts a timer that will trigger the RCS jets on the SM to move the now derelict hardware away from the CM. Many of the systems onboard the SM are left active to perform the separation. The fuel cells in particular are left operating, for if there is a problem or delay in the separation, the crew would not become dependent on the limited capacity of the re-entry batteries. Electrical power is also needed onboard the Service Module after separation to power the jettison controller and the RCS solenoids (for moving the SM away), and to fire the pyros needed to sever the tie-down connections holding the CM and SM together.]

[Now, simply cutting the electrical connections at this point is ill advised, as the cables are still carrying power and signals between the two modules. Severing these connections with the pyro-powered guillotine surely will result in the shorting and arcing, and would damage the CM systems. To eliminate this possibility, all electrical connections from the SM terminate deep inside the CM as familiar cannon-style plug and socket connectors. As the separation sequence begins, a small pyrotechnic charge fires, moving a series of cams and levers to, quite literally, "unplug" the SM electrical connections from the CM. Reflecting the "one-shot" nature of this permanent disconnection, the plugs and sockets are then locked in place to prevent any possibility of recontacting each other.]

[Once the electrical connections are deadfaced within the CM, the hinged cover protecting the cabling between the CM and SM pivots away so as not to interfere with the CM as it separates. Pyrotechnic charges fire again, propelling guillotine blades through the cable bundles and plumbing that run between the two modules. Now isolated from the Command Module, the Service Module event controller fires three sets of two pyros, each set which is attached to one of the three tension ties which hold the Command Module securely to the Service Module. The Command Module rests on six support pads, which distribute the weight of the CM across the heat shield. Three of these supports contain the tension ties which pass through the base of the heat shield and connect to the CM internal structure. Once the tension ties are severed, springs underneath each of the support pads push the two modules apart.]

[The final event occurs moments after the separation sequence is initiated. Simultaneously, the minus-X thrusters fire, moving the Command and Service Modules apart, and the SM roll thrusters fire for 7.5 seconds to stabilize the SM as it moves away. The minus-X thrusters will continue firing until either the fuel depletes or the fuel cells give up.]

[Early Apollo missions (Apollo 7 through 12) revealed an unexpected problem with this technique. At first glance, firing the translational thrusters to back the SM away, and using the roll thrusters to stabilize it would seen to be a perfectly adequate solution for this maneuver. Imagine the surprise then, when the crews of the earlier missions looked out the window and saw that the SM had somehow "boomeranged" around and was tumbling alongside the Command Module! After extensive analysis engineers discovered that the residual fuel and oxidizer in the Service Module sump tanks acted as a sort of "spring", taking the energy imparted onto them from the RCS jets, and releasing it against the tank walls as it sloshed about.]

[In a paper (Prediction of Apollo Service Module Motion after Jettison [J. Spacecraft and Rocket, June 1971]), a chart implies that any minus-X burn longer than about 200 seconds will result in the SM changing direction. Now, the direction reversal is not due simply to propellant sloshing. Because the SM's mass is not symmetrical over it's axis, any translational/rotational firing will start it tumbling. Since it is still tumbling while the minus-X thrusters are firing, eventually it orients itself to where the minus-X thrusters now have a posigrade (towards the CM) component. This, combined with the propellant slosh, was sufficient to cause the SM to reverse direction and head in the direction of the CM.]

[Remember that the propellants are just floating "loose" in the tank, which of course, is the reason for ullage before most burns. Let's try a simple scenario, where the minus-X thrusters fire for a short time, say 1 second. When the minus-X thrusters fire, the fuel essentially "stands still", and the SM accelerates around it. Now, you have inside the tank, a mass with some velocity. Eventually, the fuel smacks into a tank upper dome, and imparts its kinetic energy to the SM structure.]

[Now, remember these are the RCS jets, not the SPS, and they are not capable of any serious acceleration. Longer minus-X burns will eventually force the propellants down to the top of the tank, but not as much as you might think. Ullage before burns was enough to settle some of the fuel, but not enough to "pin" it down at the bottom of the tank with any certainty. There is lots of propellant still in the lines to the engine, enough to get a good engine start, which in turn, would provide enough acceleration to ensure that the propellants were always at the bottom end of the tank.]

[The problem with the SM jettison was twofold - First, the RCS jets created insufficient acceleration to eliminate the bouncing back and forth of the propellants. Second, The offset CG of the SM, along with the roll burn, caused tumbling which worked against any effort to settle the propellants at the "bottom" of the tank.]

Public Affairs Officer - "Distance, 4,727 nautical miles [8,754 km]. Velocity; 23,437 feet per second [7,144 m/s]. Flight Dynamics reports the latest update on tracking shows the Apollo 15 right in the middle of the corridor. Distance, now 3,211 nautical miles [5,947 km]. Velocity; 26,047 feet per second [7,939 m/s]. This is Apollo Control. We are about 2½ minutes away from Command Module/Service Module separation. Apollo 15 yawing now for that maneuver. Endeavour's in separation attitude now. We show separation. Recovery reports all forces on station ready to support."

294:44:55 Parker: Apollo 15, Houston. Comm check. Over.

294:45:00 Worden: Houston, 15. Loud and clear.

294:45:02 Parker: Roger; same with you.

294:45:06 Worden: And, Houston; 15. We got a good sep[aration].

294:45:09 Parker: Roger. Looks good down here. Thank you.

[Scott, from the 1971 Technical Debrief - "We got the separation and that went very cleanly, another big bang. All the transfers were automatic. You maneuvered around to the entry attitude. We just waited for the time of the entry interface, followed procedures per the checklist, and everything ran very smoothly. The timing worked out. The earliest check I could get on the G&N was about 11 minutes prior to EI, and it was tracking the 29 seconds we had on the pad for the RRT [the time between EI and the 0.05g indication]. So, all the times agreed, and all the guidance systems looked like they were in good shape."]

[Comm break.]

Public Affairs Officer - "Velocity now 30,280 feet per second [9,229 m/s]."

294:47:05 Scott: Okay, Houston. The horizon check was good, and the CMC guidance needles look good.

294:47:14 Parker: 15, Houston. Say again.

294:47:17 Scott: Roger. The horizon check was good and the CMC guidance needles look good.

294:47:22 Parker: Roger; copy. Very good.

[Worden, from the 1971 Technical Debrief - "We had a dark horizon. One of the things that I was curious about, one of the things I checked very carefully, was to see if there was a horizon out there; and there was, in fact, a horizon. It was very clear. We turned the lights in the spacecraft down a little bit to help. The horizon was very clear. When I first saw it, it was about 7 or 8 minutes out from entry interface. It was about 5° above the 31.5° line in the window. As we got closer to Entry Interface, it was obvious that it was progressing right down to the proper point at entry interface. It was very easy to track, and it was a good indication of attitude."]

[Long comm break.]

294:50:17 Irwin (onboard): Okay, Tape Recorder's on High Bit Rate, Record, and Forward.

294:50:25 Scott (onboard): Here, my friend, is a lunar rock.

294:50:28 Worden (onboard): Yes. Floating around in the space of our spacecraft.

294:50:33 Scott (onboard): Yes. Wonder (laughter) - The sequence of panels we go through is somewhat inane.

294:50:41 Worden (onboard): Oh, it really is, isn't it? God!

294:51:13 Worden (onboard): About 8 minutes.

294:51:17 Scott (onboard): This is the most leisurely entry we've ever done.

294:51:19 Irwin (onboard): Yes, I don't understand how - why we have so much time.

294:51:21 Worden (onboard): Stand by. ... fast.

294:51:23 Scott (onboard): It'll go fast.

294:51:25 Worden (onboard): That's because we started 4 hours earlier...

294:51:27 SC (onboard): (Laughter)

294:51:28 Worden (onboard): ...than we normally do.

294:51:29 Scott (onboard): (Laughter) That's true. This is our normal reset burn, right here.

Public Affairs Officer - "10 minutes from entry."

294:51:40 Parker: Apollo 15, Houston. You're looking good, about a minute and a half till handover to ARIA.

294:51:46 Scott: Roger.

[As Apollo nears the Earth's surface, it will go out of range of MSFN (Manned Space Flight Network, whose modern form is the Deep Space Network or DSN). Therefore, flying in the vicinity of the recovery area is a KC-135 (Boeing 707 derivative) aircraft which is fitted out with equipment to provide the necessary link for continued communications with Houston.]

[Comm break.]

Public Affairs Officer - "And ARIA is an Apollo Range Instrument Aircraft. We'll be handling communications through these aircraft."

294:54:28 Parker: Apollo 15, Houston through ARIA 2. How do you read? [No answer.]

[Comm break.]
294:52:00 Scott (onboard): Separation really unloosened a bunch of stuff.

294:52:04 Worden (onboard): Yes.

294:52:05 Irwin (onboard): See my nut come flying by yet?

294:52:07 Scott (onboard): No (laughter). Nor your screw (laughter).

294:52:11 Irwin (onboard): Listen, man, I've got my screw right here.

294:52:59 Scott (onboard): Got your camera all ready, Jim?

294:53:01 Irwin (onboard): Ready.

294:53:02 Worden (onboard): Don't forget it.

294:53:03 Irwin (onboard): I think I'll turn it on at - probably - Oh, look out the window, and you see iona - ionization.

294:53:09 Scott (onboard): Yes.

294:53:15 Irwin (onboard): Probably be just before blackout, I guess. Blackout at PT. Yes. Before zero phase.

294:53:55 Worden (onboard): Looks like 5 minutes.

294:53:56 Scott (onboard): Right on. Time is right on.

294:53:58 Worden (onboard): Great.

294:54:00 Scott (onboard): Can't argue with that.

294:54:04 Worden (onboard): My dynamics - or trajectory's changing somewhere, because that light's coming from a different place now.

Public Affairs Officer - "We're at 3½ minutes away from Entry Interface. Communications through the ARIA will be noisy. We do not have a display up at the moment showing velocity or distance."

294:54:52 SC (onboard): (Sneeze)

294:55:15 Worden (onboard): Oh, that's the Earth down there, baby.

294:55:18 Irwin (onboard): Can you see it?

294:55:19 Scott (onboard): Sure as hell can. Yes, siree, I hope to tell you.

294:55:23 Irwin (onboard): Are we going backwards?

294:55:25 Scott (onboard): It's big and real.

294:55:26 Irwin (onboard): Yes. I can see it. Just barely see it out of my window.

294:55:29 Worden (onboard): Yes, we're going backwards.

294:55:30 Scott (onboard): Encouraging.

294:55:35 Worden (onboard): Just check the needle on the peg here; 51 and a couple of minutes until we're down.

294:55:40 Irwin (onboard): Is that pausing from minimum impulse?

294:55:45 Scott (onboard): It sure is. Man, that's Just bang, bang. That's really neat.

294:55:51 Worden (onboard): I keep thinking that, if I hit the stick quick, that minimum impulse will be less (laughter). Did you ever get that feeling?

294:55:56 Scott (onboard): Yes.

294:55:57 Worden (onboard): There's just a little bit you want to go...

294:55:58 Scott (onboard): It's right then.

294:55:59 Worden (onboard): ...and you try to get it and you can't quite get there. Yes.

294:56:09 Worden (onboard): Oh, yes. Hey - Oh, man, are we moving, too! Son of a gun! Sheeoo!

294:56:21 Scott (onboard): Yes, indeedy. You ought to be able to see it out the - out the hatch window.

294:56:25 Worden (onboard): Oh my, I sure can. Sure a lot of mountains down there. How about that!

294:56:36 Irwin (onboard): Shit, I think that's Alaska out there. That would be right, wouldn't it?

294:56:47 Worden (onboard): Yes. Keep an eye out for the Moon.

294:56:49 Scott (onboard): Yes, keep an eye out for the Moon.

294:56:50 Worden (onboard): We've done it. Oh, we've missed it.

294:56:53 Scott (onboard): 56:37. Oh, Al...

294:56:54 Worden (onboard): We were too busy watching the Earth.

294:56:55 Scott (onboard): ...why don't you pay attention to what you're doing there.

294:56:57 Worden (onboard): Too busy watching the Earth.

294:57:05 Scott (onboard): I'm not sure there's much you could do about it any - any - to correct it anyway.

294:57:09 Worden (onboard): Not at this point. Here comes the needle off the peg. There it goes. Now let me get to 5. Yes, 55.

294:57:17 Scott (onboard): Okay.

294:57:33 Scott (onboard): Neat.

294:57:34 Worden (onboard): Yes.

294:57:35 Irwin (onboard): We just passed south of Alaska.

294:57:37 Scott (onboard): Did we?

294:57:38 Irwin (onboard): Yes.

294:57:41 Scott (onboard): Little earlier than usual.

Public Affairs Officer - "Velocity, 35,710 feet per second [10,884 m/s]; range to splash, 1,725 nautical miles [3,195 km]."

294:57:41 Parker: Apollo 15, Houston, thru ARIA 2. You're - We're getting good data. You look Go.

[Long comm break.]
294:57:48 Worden (onboard): Houston, 15; go ahead.

294:58:05 Scott (onboard): Okay, the needle's off the peg.

294:58:12 Worden (onboard): About right.

294:58:28 Irwin (onboard): What a view! Whew!

294:58:37 Worden (onboard): Okay, we've got about l0 - 20 seconds to entry interface.

294:58:41 Irwin (onboard): More than that. Oh, EI, yes. ... I don't think I'm going to like it.

294:58:55 Irwin (onboard): There's RRT.

294:58:57 Scott (onboard): Okay.

Public Affairs Officer - "Velocity, 35,910 feet per second [10,945 m/s]; range to go, 1,507 nautical miles [2,791 km]. 35 seconds to entry. 36,053 feet per second [10,989 m/s]; range, 1,307 nautical miles [2,421 km]. Should be at Entry Interface."

[In the spacecraft, they mark the time of Entry Interface within a second at 294:58:55.]
Public Affairs Officer - "We're in blackout now and no data."

294:59:06 Irwin (onboard): Getting the ionization?

294:59:08 Scott (onboard): Yes, man.

294:59:09 Worden (onboard): Put your...

294:59:10 Scott (onboard): Yes, look at it. Good.

294:59:11 Worden (onboard): Yes.

294:59:13 Scott (onboard): Ionization?

294:59:14 Irwin (onboard): Everything looks good.

294:59:15 Scott (onboard): Boy, I guess.

294:59:16 Worden (onboard): .01, .02, 4...

294:59:25 Worden (onboard): .05G light.

[On the EMS display, the 0.05g light comes on at 294:59:25 - within a second or two of when Mission Control predicted.]

[During entry, the crew's attention is focused primarily on three displays: The FDAI (Flight Director Attitude Indicator, or more commonly known as the "8-ball"), the DSKY, where entry data such as range-to-go, deceleration and velocity are displayed, and the Entry Monitor System (EMS).

Diagram of the Entry Monitor System (EMS) panel.

The EMS is not a single display, rather, it is a specialized guidance and display system to present critical entry parameters to the crew. Surprisingly, the EMS does not generate guidance or trajectory information for the spacecraft computer, nor can it actively control the spacecraft during entry. Its function is only to display the most relevant data to the crew as they plunge through the atmosphere. Three displays on the EMS provide the situational data necessary to evaluate the progress of the entry: A scrolling display showing velocity vs. deceleration, the RSI (Roll Stability Indicator), and a digital velocity indicator.]

[Most attention is focused on the velocity vs. deceleration display, a 9-cm window behind which is a scrolling Mylar tape marked with the acceptable velocity and G-force boundaries. The tape moves from right to left, and an illuminated index, or "bug", traces the current velocity-acceleration profile onto it. Of course, keeping the Command Module within the narrow entry corridor requires maneuverability within the atmosphere. A modest amount of lift is generated by the Command Module which can be vectored in any direction by rolling the spacecraft. The RSI shows the desired lift vector (up or down) by two lights, and a pointer that displays the current lift vector, which is used to confirm it is within the entry corridor. Finally, a digital velocity meter provides an additional source of velocity data to the crew.]

[Prior to entry, the CM is in a heads-down/lift vector up attitude with the heat shield forward. Program 63 (Entry Initialization) begins executing on the computer. P63 determines and displays entry parameters such as range-to-splashdown, maximum expected G-force, and bank angle. It holds the CM in the correct attitude and senses the point that a deceleration of 0.05g has been reached. Once the program is running, there is little to do but wait for the 0.05g light on the EMS to illuminate, indicating that the first tenuous layers of the atmosphere are exerting their decelerating force on the spacecraft. At this point, P63 automatically runs Program 64 (Post 0.05g) This is an important milestone, reached about 29 seconds after the Command Module passes the Entry Interface, and marks where The EMS scroll begins to run. There is no fixed altitude at which this occurs as it depends completely on spacecraft shape, velocity, and the local atmospheric conditions. Once this boundary is reached, the hard work of entry begins.]

[Program 63, which had been monitoring the entry up to this point, terminates and Program 64 (Entry - Post 0.05G) is started. The DSKY displays the bank (roll) angle commanded by the guidance computer, velocity and acceleration. It is no coincidence that these values are duplicated on the EMS; both systems operate independently, and if one fails, the other can be used to complete the return to Earth. The scroll on the EMS window begins to move to the left in proportion to velocity, registering velocity on a scale at the bottom of the mylar tape. The scroll "bug" moves downward as g forces build up on the spacecraft, and leaves a tracing on an emulsion on the back of the tape, giving essential information on the progress of the entry. The boundary lines pre-printed on the scroll tape describe the limits of velocity and G-load (deceleration) that ensure the CM is within the entry corridor. If the spacecraft is descending too steeply with respect to the corridor, its progress will become apparent on the scroll. At the same time, the roll stability indicator will flash a light (the corridor control light) indicating that upwards lift is necessary to shallow out the entry trajectory.]

[In the movie Apollo 13, the character that portrays Jack Swigert (played by Kevin Bacon) is shown in the simulator performing an entry exercise. The simulator supervisor introduces an anomaly, a "corridor light", which he misinterprets and flunks the simulation. Diagram describing the limits of velocity and G-load.

The error the character made was not to cross-check the "malfunctioning" Roll Stability Indicator against the DSKY display and the entry scroll display. Of course, in reality Jack Swigert handled the procedure expertly.]

294:59:26 Scott (onboard): Okay, Go. EMS scroll...

294:59:28 Irwin (onboard): .05G switch...

294:59:29 Scott (onboard): EMS good.

294:59:32 Irwin (onboard): .05G switch, on; EMS Roll, on.

294:59:34 Scott (onboard): They're both on.

294:59:35 Irwin (onboard): Okay.

294:59:36 Scott (onboard): Okay. Okay, .39.

294:59:42 Worden (onboard): Okay.

294:59:43 Scott (onboard): .5, .1.

294:59:44 Irwin (onboard): .6.

294:59:46 Scott (onboard): .8, 1, 1.3, 2g's, 2g's...

294:59:53 Worden (onboard): Accelerometer and the DSKY.

294:59:56 Scott (onboard): Okay.

294:59:57 Worden (onboard): Scroll look good?

294:59:58 Scott/Worden (onboard): 3g's.

[In the CM, the crew reach 3g at 294:59:58, which rises to 6g within 10 seconds.]

[Slowing the spacecraft to the point where it can no longer escape the Earth's gravity, about 8,200 m/s (27,000 fps), is the primary domain of Program 64. After an initial 6-g deceleration, P64 concentrates on slowing the spacecraft to below escape velocity by maintaining a constant 4-g's. Once the CM has slowed to below orbital velocity, the computer switches to Program 67 (Entry Final Phase) to manage steering and targeting for the final part of the entry. Now, instead of maintaining a constant g level, the deceleration rate will be changed to correct for any undershoot or overshoot to the target. If the entry needs to be "stretched", the computer will calculate a lower rate of deceleration. At a lower rate of deceleration, the Command Module will travel further downrange.]

295:00:01 Scott (onboard): Three and a half.

295:00:03 Worden (onboard): 4.

295:00:04 Scott (onboard): There's 4.

295:00:05 Worden (onboard): 5.

295:00:07 Scott (onboard): There's 5, 6...

295:00:13 Worden (onboard): Scroll looks good.

295:00:14 Scott (onboard): There's 6, 6, 6 there, 6.2. Don't see anything on master alarm.

295:00:22 Worden (onboard): Want the master alarm?

295:00:24 Scott (onboard): Nothing.

295:00:25 Worden (onboard): Huh?

295:00:26 Scott (onboard): Nothing.

295:00:27 Worden (onboard): Okay.

295:00:28 Scott (onboard): 5.6. We roll 180. 5, 4.7...

295:00:37 Worden (onboard): Looking good.

295:00:38 Scott (onboard): 180 roll, 4, 4.4, 4.2, 4.1. Rolling to 150, 117, 092...

295:00:52 Worden (onboard): Okay, looking good.

295:00:54 Scott (onboard): Plus 69, plus 51.

295:00:57 Worden (onboard): Looking good.

295:00:58 Scott (onboard): Plus 49.

295:00:59 Worden (onboard): Okay.

295:01:00 Scott (onboard): 4g's, you're right on.

295:01:02 Worden (onboard): 4g's.

295:01:03 Scott (onboard): Eighty-five, plus 101. Holding 4g's. Lift vector, up.

295:01:10 Worden (onboard): Going up.

295:01:ll Scott (onboard): We're in P67.

295:01:12 Worden (onboard): Good.

[Program 67 remains in control of targeting until the CM reaches about 300 m/s (1,000 fps), which occurs nominally at about 20,000 metres (65,000 feet) altitude.]

[Scott, from the 1971 Technical Debrief - "The re-entry went as planned. The g levels agreed all the way into 6 g's and back out. The G&N was given control after we had a good g time. I compared the G&N and the EMS range to go and they looked close all the way, within about 20 miles. [To Worden.] You were watching the scribe and it looked very smooth and nominal all the way in."]

[Worden, from the 1971 Technical Debrief - "Because of the AC problem we had in the circuit breaker, we didn't have any backlighting in the EMS. There was some concern that we might not be able to see the scribe; but, it was very clear the whole time through entry. One other comment about the EMS was that you called 0.05g and just as you called it, the .05g light came on the EMS. It was very clear. There was no problem seeing it as soon as it came on."]

[Scott, from the 1971 Technical Debrief - "All automatic."]

295:01:18 Scott (onboard): Okay. Minus 51.

295:01:21 Worden (onboard): Okay.

295:01:23 Scott (onboard): And at 4g's. Minus 110.

295:01:31 Worden (onboard): Okay, we're going in.

295:01:34 Scott (onboard): Minus 116.

295:01:35 Worden (onboard): Okay, 450 miles and that's...

295:01:36 Scott (onboard): Okay.

295:01:37 Worden (onboard): ...right where we are on the scroll.

295:01:49 Scott (onboard): Okay, at 399, we're...

295:01:51 Worden (onboard): Okay, we're off the ...

295:01:52 Scott (onboard): ...almost 3g's. Boy, EMS has missed here within about 5 miles.

295:01:55 Worden (onboard): Yes, we're looking good.

295:01:58 Scott (onboard): Seventy-one, minus 70.

295:02:02 Comm tech: 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2.

295:02:00 Worden (onboard): EMS is...

295:02:04 Scott (onboard): Minus 70.

295:02:19 Worden (onboard): Pretty good.

295:02:20 Scott (onboard): Yes.

295:02:23 Worden (onboard): Minus 70...

295:02:24 Scott (onboard): 0kay, there's 3g's.

295:02:26 Worden (onboard): And the scroll shows us right on the range to go.

295:02:30 Scott (onboard): Okay.

295:02:34 Worden (onboard): Couldn't be better.

Public Affairs Officer - "Should be coming out of blackout now."

295:02:38 Comm tech: 1, 2, 1, 2, 1, 2, 1, 2.

295:02:43 Parker: Apollo 15, Houston. How do you read? [Garbled.]

295:02:45 Scott (onboard): Houston, Apollo 15. We're in P67. The EMS and the G&N agree within 15 miles, and everybody's in good shape.

295:02:51 Scott (onboard): Okay, plus 52.

295:02:52 Worden (onboard): Roger. That's where we are. Still pulling 3g's.

295:03:01 Scott (onboard): Okay, stand by.

295:03:04 Worden (onboard): And we're coming right straight down that scroll. Beautiful.

295:03:11 Parker: [Has not heard Scott's transmission clearly.] Apollo 15, Houston. How do you read?

295:03:13 Scott (onboard): Good. Houston, 15. EMS and G&N agree within about 10 miles, and everybody's in fine shape.

295:03:22 Parker: Very good, Dave. Good to hear you again.

[Comm break.]
295:03:28 Worden (onboard): There they are.

295:03:30 Scott (onboard): Okay, 32 degrees ...

295:03:40 Worden (onboard): Okay, 98, Noun 18; boy, that's slick.

295:03:43 Scott (onboard): 10,000 feet per second.

295:03:50 Worden (onboard): My eyes were cocked; 100 miles to go. I'm about 4 miles off; so - Looks like even the scroll's working great.

295:03:59 Scott (onboard): Yes. Great. Hey, now I know why you got to check the tunnel for water.

295:04:07 Irwin (onboard): Yes, boy, I guess. Did you get wet?

295:04:09 Scott (onboard): Yes, man ....

295:04:13 Irwin (onboard): Yes, it really comes barreling out of there, doesn't it? (Laughter)

295:04:19 Scott (onboard): Okay. ...

295:04:20 Worden (onboard): Sixty miles to go. Okay, up.

295:04:24 Scott (onboard): ...? 33 and 46. Boy, they really agree. 6,000 .....

295:04:37 Worden (onboard): Getting our cross range right now.

Public Affairs Officer - "Recovery ship has radar contact showing range about 100 miles."

295:04:44 Scott: Houston, 15; in the blind [i.e. he is getting no response]. EMS and G&N agree within about 10 miles.

295:04:53 Parker: Roger, 15; this is Houston. Read you loud and clear, and copy. [Long pause.]

295:04:52 Worden (onboard): Gee, what makes you feel - sound so hollow?

295:04:55 Irwin (onboard): Sounds like ... is about to make a low pass on us.

295:04:58 Worden (onboard): Yes.

295:04:59 Scott (onboard): We're coming up to 38. Watch your steam pressure, Jim.

295:05:01 Irwin (onboard): Standing by.

295:05:17 Worden (onboard): It's 3,000.

295:05:18 Scott (onboard): No steam pressure yet?

295:05:19 Irwin (onboard): It's going up now.

295:05:20 Scott (onboard): Okay.

295:05:21 Irwin (onboard): Okay, steam pressure's pegged.

295:05:24 Worden (onboard): Okay, we should get - 50K in about another 600 feet. Got 9 miles to go on EMS.

295:05:34 Scott (onboard): Okay. Should be getting a Noun 67 here directly.

295:05:47 Scott (onboard): Okay, Houston; 15 in the blind. Latitude, plus 26.12; longitude, minus 158.17.

295:05:54 Worden (onboard): Okay, we're off the peg.

295:05:55 Scott: And about a 2.2 off the peg.

295:05:56 Irwin (onboard): Okay, Cabin Pressure to Boost/Entry.

295:05:59 Parker: Roger, Dave; we copy. Very good. [Long pause.]

295:06:00 Worden (onboard): Boost/Entry.

[The Cabin Pressure Relief valve is set to its Boost/Entry position so that when the outside pressure rises above the cabin pressure, outside air will be admitted.]
295:06:01 Irwin (onboard): Sequence Pyro, two, to Arm.

295:06:04 Worden (onboard): Pyro to Arm.

[The final pyrotechnic charges, for deploying the apex cover and the chutes, are armed.]
295:06:07 Irwin (onboard): Standing by for 30.

295:06:09 Scott/Worden (onboard): Okay.

295:06:11 Worden (onboard): We're out of 40.

295:06:17 Scott (onboard): Okay, Houston; 15. Out of 40K [40,000 feet, 12,200 metres] and we're showing about a .7, .2, this business now. Everybody's in good shape. [Long pause.]

295:06:27 Irwin (onboard): How's the altitude, Al?

295:06:29 Worden (onboard): Coming up on 30.

295:06:30 Scott (onboard): Okay...

295:06:31 Worden (onboard): Okay, 30K.

[The time is coming up for the ELS (Earth Landing System) to come into play. The SECS (Sequential Events Control System) orchestrates all the events using timers and barometric switches. The system is highly redundant because, like so many systems aboard a spacecraft, the crew's lives depend on it.]
295:06:32 Irwin (onboard): Okay, ELS Logic, on.

295:06:33 Worden (onboard): ELS Logic, on.

295:06:35 Irwin (onboard): ELS, Auto.

295:06:36 Worden (onboard): Auto, on.

295:06:38 Scott (onboard): Okay. Stand by for...

[At 7,300 metres (24,000 feet) the RCS is disabled and the forward heatshield jettisoned.

Diagram of the forward heatshield.

Also known as the apex cover, this part of the heatshield wraps around the CM forward compartment where the parachutes and their mortars are mounted. Once jettisoned, a small parachute attached to it slows it down to take it away from the descending Command Module. 1.5 seconds later, two drogue parachutes are deployed to stabilise the CM's attitude and slow it from 500 km/h to 280 km/h.]

[Scott, from the 1971 Technical debrief - "I gave a call right after blackout. We ended blackout at 3:37 [minutes after Entry Interface] and I called about 3:45 or so [calling out] with our delta [difference] between the EMS and G&N and everything was in good shape. I got no response. I probably made four calls on the way down. I gave the Noun 67 values [which give the range to the splashdown target, the latitude and longitude] when they first came up, and then later on I called them. We heard the Recovery forces radio, but I don't think we ever had two-way radio contact with anybody until we got in the water. I think they heard us in MCC, but we couldn't hear them. We could hear the Recovery forces and apparently they couldn't hear us."]

[Worden, from the 1971 Technical debrief - "That was my impression too. I don't recall any conversation with anyone. There was a terrific amount of radio chatter going on. I don't recall having two-way radio communications with anyone."]

295:06:39 Irwin (onboard): Standing by for drogues at 24. There go the - there goes the apex. There are the drogues.

295:06:50 Worden (onboard): Good drogue.

Public Affairs Officer - "Should be on the drogue chute now."

[The spacecraft is entering the region of the atmosphere where the outside air pressure rises above that of the cabin, so the cabin pressure is being allowed to rise also, via the Cabin Pressure Relief valve.]
295:06:52 Irwin (onboard): Okay, cabin pressure's increasing.

295:06:55 Worden (onboard): All right.

295:06:58 Irwin (onboard): Standing by for mains - at 10.

295:07:01 Recovery (probably the Photo helicopter): This is [garble, probably Photo]. [I] have visual contact. Bearing 120 from the ship, sir.

295:07:02 Worden (onboard): Okay, we're out of 18.

295:07:11 Okinawa: Contact. [Long pause.]

295:07:15 Scott (onboard): Give us a call when you get to 10.

295:07:17 Worden (onboard): Well, coming out of 14, 13, out of 12, 11,000.

295:07:29 Photo: Photo, I lost contact. [Long pause.]

295:07:34 Irwin (onboard): Okay.

295:07:37 SC (onboard): (Sigh)

[At 295:07:35, pilot chutes are deployed which in turn pull the three large main parachutes out. These slow the CM to its final velocity and suspend the Command Module at an angle of 27.5° to the horizontal. This will cause the hull to hit the water "toe first", entering in such a way as to spread the final deceleration over the longest possible time.]
295:07:38 Irwin (onboard): Okay, the mains are up there.

295:07:40 Worden (onboard): And the mains are out, three.

295:07:42 Scott (onboard): Okay...

295:07:43 Worden (onboard): Okay.

295:07:44 Scott (onboard): ...Apollo 15 has good mains.

295:07:45 Worden (onboard): The mains are opening.

Public Affairs Officer - "And he should be on the mains now."

295:07:46 Irwin (onboard): Surge Tank O2, off, Al.

295:07:48 Worden (onboard): Surge Tank O2 coming off.

295:07:51 Irwin (onboard): Repress Package, Off.

295:07:53 Scott (onboard): Let's go, Al.

295:07:54 Worden (onboard): Repress, Off.

295:07:54 Photo: This is Photo, I have visual contact again. I have 140 from the ship, one half mile. Bearing is 130 to - Three main chutes. I have visual contact [on] three main chutes.

295:07:57 Irwin (onboard): Direct O2, Open.

295:07:58 Worden (onboard): Direct O2, Open.

295:08:08 Worden (onboard): ...8,000.

295:08:10 Okinawa: Okinawa, Roger.

295:08:10 Irwin (onboard): ...Pressure Relief, two, Closed.

295:08:11 Worden (onboard): Closed.

295:08:13 Irwin (onboard): CM RCS Logic, on, up.

295:08:14 Scott: [garble], Apollo 15. We're showing about a minus .6...

295:08:16 Worden (onboard): RCS Logic, on.

295:08:17 Scott:...on the miss distance, and...

295:08:18 Irwin (onboard): CM Propellant to Dump.

295:08:19 Scott: ...everybody's in good shape.

[The propellant tanks for the RCS thrusters still contain a fair quantity of the highly noxious fuel and oxidiser, hydrazine and nitrogen tetroxide. Indeed, one complete set of thrusters - the backup RCS ring - has full tanks. This is very hazardous material to have on board after splashdown so the excess propellant is dumped by firing all the thrusters to depletion as the CM sails down on its three main parachutes.]

[Events about to occur will bring a lot of scrutiny to the propellant dump as all is not well with one of Endeavour's parachutes.]

295:08:22 Parker: Roger, 15. We got a visual on you on the screen in here.

295:08:29 Okinawa: Okinawa, Recovery has a recovery beacon contact. Bearing 175 magnetic. [We are] on station.

295:08:35 Okinawa: Okinawa here.

295:08:38 Swim 2: Okinawa, this is Swim 2. I have a visual contact. The bearing is 010, at approximately one mile. My position, 134; Okinawa 8.5 miles. Altitude is about 6,000 feet [1,830 metres] for the Command Module.

295:08:53 Okinawa: Okinawa, Roger. Out. [Pause.]

295:08:59 Swim 1: Okinawa, this is Swim 1. I have recovery beacon, 115 degrees magnetic, at 270, 12 miles, at time 47. Over.

295:09:12 Okinawa: Okinawa, Roger. Out. [Pause.]

295:09:16 Worden (onboard): Pick out the place.

295:09:19 Scott (onboard): Okay?

295:09:20 Worden (onboard): Okay...

295:09:22 Photo: This is Photo. I have - some - something's falling besides the Command Module, I could not tell - tell what it was, though.

[This is probably the forward heatshield.]
295:09:31 Irwin (onboard): Strut locks, four, unlocked.

295:09:34 Recovery: Apollo 15, Apollo 15, this is Recovery. Over.

295:09:39 Scott: Recovery, Apollo 15. Everybody's in good shape, and we're looking at about 3,500 feet.

295:09:44 Recovery: This is Recovery, I have a visual of 165 from me, about 8 miles.

295:09:47 Irwin (onboard): Ten seconds to release.

[With the RCS propellant gone, the RCS plumbing is purged with helium to clear the final traces from the spacecraft.]
295:09:51 Scott (onboard): Go ahead, Jim.

295:09:52 Irwin (onboard): Stand by for purge dump.

295:09:54 Photo: This is Photo. It appears that one of your main chutes is streaming. I can only see two main chutes, and one appears to be streaming.

295:10:02 Okinawa: Yes. - two chutes concurred.

295:10:05 Photo: They have one streaming chute.

295:10:06 Irwin (onboard): Do we have three, Al?

295:10:07 Worden (onboard): We got two.

295:10:08 Scott (onboard): No, we're at 3000...

295:10:09 Irwin (onboard): Stand by for ...

[The Command Module passes 1,000 metres (3,000 feet).]
295:10:12 Photo 1: Okinawa this Photo 1. The extra fuel has been jettisoned and burned off.

295:10:13 Worden (onboard): Okay.

295:10:17 Scott (onboard): Cinch up, gang.

295:10:18 Worden (onboard): Cinch up, gang.

295:10:20 Recovery: Apollo 15, Apollo 15, this is Recovery. Over. [Long pause.]

[Worden, from the 1971 Technical Debrief - "The main chutes came out at 10,000 [feet, about 3,050 meters]; the drogue chutes released just a few seconds before that. The main chutes came out at 10,000 and at about 8,000 [feet, about 2,500 meters] we got the cabin configured and started the fuel dump."]

[Scott, from the 1971 Technical Debrief - [To Worden.] "When you say the mains come out, you saw three chutes. Is that right?"]

[Worden, from the 1971 Technical Debrief - "That's right. I saw the three chutes, come out, reef, then disreefed, and I had three full chutes in view. When we started the fuel dump, my view of the main chutes was obscured by a cloud of fuel that was going by the window."]

[Scott, from the 1971 Technical Debrief - "A big red cloud."]

[Worden, from the 1971 Technical Debrief - "A big red cloud going by the window. When we finished the fuel dump and the view cleared, I could see that one of the chutes as not fully inflated anymore."]

[Scott, from the 1971 Technical Debrief - "I think that was about the time we got the call from Recovery that we had a streamer."]

[Worden, from the 1971 Technical Debrief - "That was just about the same time."]

[The Cabin Pressure Relief valve is set to Dump, allowing full equalisation between the outside and inside air pressures. They pass 600 metres (2,000 feet) at 295:10:43.]

295:10:23 Scott (onboard): Got your VHF beacon on?

295:10:24 Worden (onboard): 3,000...

295:10:25 Irwin (onboard): Yes, it's...

295:10:26 Worden (onboard): ...Jim.

295:10:27 Scott (onboard): 3,000, Jim.

295:10:28 Irwin (onboard): Okay, CM RCS Propellant, two, OFF.

295:10:29 Worden (onboard): Off.

295:10:30 Scott (onboard): Okay.

295:10:31 Worden (onboard): Two, off.

295:10:32 Irwin (onboard): Cabin Pressure Relief Valve to Dump.

295:10:34 Worden (onboard): All right, coming to Dump.

295:10:36 Irwin (onboard): Floods to Postlanding.

295:10:43 Worden (onboard): Coming up on 2,000.

295:10:45 Scott (onboard): How many chutes we got, Al?

295:10:46 Worden (onboard): We got two.

295:10:47 Irwin (onboard): Two.

295:10:48 Worden (onboard): We got a streamer on one.

295:10:49 Irwin (onboard): Floods to Postlanding.

295:10:51 Worden (onboard): Floods to Postlanding.

295:10:52 Irwin (onboard): Stand by for 800.

295:10:55 Photo: This is Photo. Lost contact due to cloud cover.

295:10:58 Recovery: Apollo 15, Apollo 15, this is Recovery. Over.

295:11:03 Scott: Rog, Recovery; 15. You're five square. Everybody's in good shape.

295:11:04 Worden (onboard): Okay, we're out at 1,500, Jim.

295:11:05 Irwin (onboard): Okay.

295:11:06 Recovery: Roger, Apollo 15. If you hear, all units have you in sight, and we are inbound now.

295:11:12 Scott: Roger. [Pause.]

295:11:11 Scott (onboard): Roger.

295:11:13 Worden (onboard): 1,000 feet, Jim.

295:11:14 Irwin (onboard): Okay...

295:11:15 Scott (onboard): ... dump.

295:11:16 Irwin (onboard): Cabin Pressure Relief to Close.

[As Endeavour passes 300 metres (1,000 feet), the Cabin Pressure Relief valve is closed to prevent the ingress of water after landing. When the spacecraft hits the water, it is temporarily submerged and, if they are unlucky, is likely to be pointing apex down for a time.]
295:11:18 Worden (onboard): Closed.

295:11:18 Okinawa: Apollo 15, this is Okinawa. Request your splashdown read-out. Over.

295:11:21 Irwin (onboard): Okay, you ready for Main Bus ties to come Off.

295:11:24 Worden: Main Bus ties coming off.

295:11:25 Scott: Roger. Plus 26.13 minus 158.12.

295:11:26 Worden (onboard): Ready for Bus Ties.

295:11:30 Worden (onboard): Okay.

295:11:28 Recovery: This is Recovery. I have a visual [garble] dead ahead.

295:11:36 Okinawa: Apollo 15, this is Okinawa. You have a streamed chute. Stand by for a hard impact. Okinawa, over.

[The state of the three chutes is well shown in S71-41999, an excellent photograph of the returning spacecraft.]

[From the Apollo 15 Postflight Mission Report - "One of the three main parachutes was deflated to approximately one fifth of its full diameter at about 6,000 feet [about 1,800 meters] altitude. The Command Module descended in this configuration to landing. All three parachutes were disconnected and one good main parachute was recovered. Photographs of the descending spacecraft indicate that two or three of the six riser legs on the failed parachute were missing.

Three areas that were considered as possible causes are:

a. The forward heat shield, which was in close proximity to the spacecraft flight path.

b. A broken riser/suspension line connector link which was found on the recovered parachute.

c. The Command Module Reaction Control System propellant firing and fuel dump.

Onboard and photographic data indicate that the forward heat shield - was about 720 feet (220 metres) below the spacecraft at the time of the failure. The failed link on the recovered parachute implies the possibility of a similar occurrence on the failed parachute. Based on parachute tow tests, however, more than one link would have had to fail to duplicate the flight problem. The two possible causes have been identified as hydrogen embrittlement or stress corrosion."]

["The Command Module Reaction Control System depletion firing was considered as a possible candidate because of the known susceptibility of the parachute material (nylon) to damage from the oxidizer. Also because the oxidizer depletion occurred about 3 seconds prior to the anomaly, and fuel was being expelled at the time the anomaly occurred. Further, the orientation of the main parachutes over the command module placed the failed parachute in close proximity to the Reaction Control System roll engines. Testing of a Command Module Reaction Control System engine simulating the fuel (monomethyl hydrazine) dump mode through a hot engine resulted in the fuel burning profusely; therefore, the fuel dump is considered to be the most likely cause of the anomaly."]

["In order to eliminate critical processing operations from manufacture of the connector links, the material was changed from 4130 to Inconel 718."]

["Based on the low probability of contact and the minimum damage anticipated should contact occur, no corrective action will be implemented for the forward heat shield. Corrective actions for the Reaction Control System include landing with the propellants onboard for a normal landing, and biasing the propellant load to provide a slight excess of oxidizer. Thus, for low altitude abort land landing case, burning the propellants while on the parachutes will subject the parachutes to some acceptable oxidizer damage but, will eliminate the dangerous fuel burning condition. In addition, the time delay which inhibits the rapid propellant dump may be changed from 42 to 61 seconds. This could provide more assurance that the propellant will not have to be burned through the Reaction Control System engines in the event of a land landing."] [A later report, now contained within Apollo Experience Report: Earth Landing System, studied three possible causes for the parachute failure. These were; (1) the burning of the RCS propellant, (2) the failure of riser links, perhaps through hydrogen embrittlement, and (3) possible damage through the contacy of the forward heatshield with the parachute risers. The report's conclusion was that RCS burning was the most likely cause of the failure.]

295:11:43 Scott: Roger. [Pause.]

295:11:53 Scott: Splashdown. Mark splashdown.

[The moment of impact with the water is captured in S71-43543.]

[To help them withstand the rigours of impact with the water, the crew are well strapped in using the restraint system that goes with the couches. However, these restraints have not been without their problems on the flight.]

[Irwin, from the 1971 Technical Debrief - "The screws on the restraint system came loose."]

[Worden, from the 1971 Technical Debrief - "Yes. That was during the lunar orbit, but that's a good thing to mention so that we don't forget it."]

[Irwin, from the 1971 Technical Debrief - "It's surprising in that it came out of the center seat and the right seat, both on the right side."]

[Worden, from the 1971 Technical Debrief - "On the right side, yes. The lower lap belt restraint attach point on the center seat and on the right seat came loose. The small bolts that hold them to the attach point and the nuts all came loose and just floated around. The lap belts came loose. I thought it was kind of funny in lunar orbit. When I took the center couch out, I noticed the attach point on the center couch was gone. And that strap was floating free. I looked around for the little bolt that goes in there, the little screw and the nut that goes in there, and I couldn't find it. I thought to myself at the time, well, I'll just sit and wait and sooner or later it will float by. Sure enough, all four pieces to that thing floated by: Two washers, a bolt and a nut. I just grabbed them as they went by and stuck them on a piece of tape. I kept the tape in one place and then put it all back together again. But I was really surprised that those little things came loose."]

[Scott, from the 1971 Technical Debrief - "I think it's a good idea to have restraint straps, especially if you're going to make a two-chute landing."]

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

[Irwin, from the 1971 Technical Debrief - "We were able to repair the one in the center couch because we got all the parts. On my couch, we never did find the nut for it."]

[Worden, from the 1971 Technical Debrief - "That's right."]

[Irwin, from the 1971 Technical Debrief - "So we ended up just taping this good one up. And it withstood that two-chute impact"]

[Worden, from the 1971 Technical Debrief - "That little piece of grey tape."]

[Scott, from the 1971 Technical Debrief - "Yes. Take lots of grey tape."]

[Worden, from the 1971 Technical Debrief - "Best invention yet."]

[MPEG video file (11.8MB)]

[This MPEG video file has excellent coverage from the point the spacecraft comes through the clouds to splashdown, the latter being a very close-up look at the CM entering the water. Note the plumes of smoke or vapour that seem to emanate from the area of the windows or the pitch jets. The cause of these is unknown at the time of writing.]

[Real Video file (532KB)]

[This Real Video file, taken from NASA's documentary about Apollo 15 includes the splashdown and footage taken from a post-mission press conference.]

[Subsequent communication in this journal is taken from the PAO transcript. This document is reputed to be replete with transcription errors.]

Public Affairs Officer - "Landing velocity on 2 chutes is 28 feet per second, or 32 feet per second, versus 28 feet on 3 chutes."
[Woods - "Could you see water coming up over the windows?"]

[Scott - "Yeah, I think we did. Yeah."]

Recovery: [Garble.] It is in stable 1 position. 3 main chutes are in the water, all visible around the spacecraft. One main chute appears to be still attached to the Command Module. Over.

Okinawa: Hello, this is Okinawa. Mark on top. Over.

Recovery: This is [garble] roger [garble]

Recovery: Apollo 15, this is Recovery. Over.

Scott: Recovery, Apollo 15, everybody's in good shape.

[Scott, from the 1971 Technical Debrief - "We came down expecting to have a rather solid impact, which we had. I had the feeling we hit pretty flat. There was no apparent roll to the spacecraft at all. I could see water up over the windows after we hit. You all got the main [parachute] release and the circuit breakers, and we ended up in a very stable 1 [upright] condition with no rocking or anything."]

[Worden, from the 1971 Technical Debrief - "That was surprising that we went straight down and straight back up, and there wasn't any motion at all, hardly, except for the sea swell."]

Photo: This is Photo, mark 130, 7 miles.

Okinawa: Okinawa read that.

Swim 2: Okinawa, this is Swim 2 on station. Be advised I dropped a smoke on the apex cover bearing approximately 010 to the Command Module at 150.

Scott: Okinawa, [garble] requests permission to drop our main chutes.

Okinawa: This is Okinawa, permission granted.

[Release of the parachutes is the first item in the post-landing section of the checklist, at the bottom of page 3-2. Then, with the craft in the upright, stable I position, the post-landing ventilation system is brought into play.]

[Scott, from the 1971 Technical Debrief - "Went through the postlanding checklist, and stood by for the collar and the swimmers. I thought the cabin atmosphere was just fine. Nobody had a tendency, I think, to get seasick."]

[Worden, from the 1971 Technical Debrief - "One thing we commented on is that, when I first turned the postlanding vent on, Dave got a face full of water."]

[Scott, from the 1971 Technical Debrief - "Yes, but it didn't get me any wetter than I already was because when we started into reentry, all the water in the tunnel came down on me. So I got bathed from top to bottom."]

[Worden, from the 1971 Technical Debrief - "When I turned the postlanding vent on, you got a face full."]

[Scott, from the 1971 Technical Debrief - "That's something you might think about in the future, making sure you mop the tunnel up. There's an item on the checklist that says 'check the tunnel for water,' but it doesn't say what to do about it. We had a little moisture up in the tunnel, but I was very surprised that so much water came up in that tunnel on the way in. Just like a bucketfull. Wasn't any problem."]

Recovery: [garble] we're standing clear.

Recovery: Apollo 15, this is Recovery. Roger your [garble] on 243.0.

Scott: Recovery, 15. We're in good shape.

Recovery: [garble] we in contact. ARIA 1 copying you loud and clear, go ahead.

[During our 2004 review of the mission with Dave, we let him watch the re-entry and recovery footage available on DVD from Spacecraftfilms.com..

[Woods - "How long ago since you last saw that footage or have you ever had a chance to watch the footage of re-entry?"]

[Scott - "First time I've seen it. We may have seen part of it after the flight. I don't recall. But again, when it's over, it's over. Shoo. Away you go."]

[At this point in the film, we see the first of the divers jumping into the water.]

[Scott - "There goes Fred Schmidt. His hobby was shark hunting. Lovely guy. There you go. Yeah, those guys were really good."]

[Woods - "What's going on inside the CM at this point?"]

[Scott - "We're just cleaning up the switches and powering down. In the checklist, you know, shut everything off, keep the radio on, get out the life preservers."]

[Woods - "Was there much chat among yourselves, congratulations and all that sort of stuff?"]

[Scott - "Not much. Pretty much getting ready to get picked up. I mean, it's not over till it's over, you know?"]

[Woods - "Because there would be a popular thought derived from the Apollo 13 film where they show the end of the mission as being where Tom Hanks shakes hands with the rest of his crew and that's now the image that will go forward in history. But actually, you guys are busy."]

[Scott - "Probably did something like that, you know."]

Recovery: [garble]

Recovery: We're in contact. We're in contact.

Recovery: [garble] copying you loud and clear, [garble]. Okay, ARIA 1.

Photo: The Command Module is still riding very well. The one main chute is still attached [garble] Command Module. The heat shield appears to have burned very evenly around the base of the Command Module. There is no real evidence of it streaming up the sides. [garble] is approaching the spacecraft. The swimmer appears to be taking a good look at the Command Module before he goes in. Swim 2 may be preparing to grapple for one of the main chutes.

Recovery: [garble] Recover chutes if at all possible. Over.

ARIA: ARIA [garble].

Public Affairs Officer - "Recovery reports the swimmers will be going in shortly. One parachute still attached to Command Module. We would like to recover those parachutes."

Recovery: [garble]. The Command Module, swimmers leaving the helicopter, 2 swimmers in the water.

ARIA: [garble]

Recovery: Two swimmers in the water are swimming towards the Command Module.

Recovery: Okay, two swimmers are cautiously approaching the Command Module. One swimmer is swimming around the Command Module at this time. The swimmers have their [garble] Command Module [garble] the Command Module now.

Recovery: The swimmers now are connecting the sea anchor. Swimmers deployed the sea anchor.

Public Affairs Officer - "Swimmers deploying the sea anchor now."

Recovery: [garble] the sea anchors [garble].

Recovery: It's a beautiful day out here, the sea state is almost a zero sea state, it's very calm, almost like a lake. The cloud cover is scattered cumulus. Got about [garble].

Recovery: The swimmers cut all the drag lines attached to the Command Module.

Recovery: The other swimmer there is attaching another raft to the main parachute, and the lead swimmer is now deploying the sea anchor. Command Module at the present time is oriented down wind.

Public Affairs Officer - "Splash time 295 hours, 11 minutes, 58 seconds."

Recovery: Swimmers now moving in the flotation collar [garble] swimmer [garble] recovery thumbs up from the swimmer. He is okay and the collar is now at the Command Module.

Spacecraft: [Garble.]

Public Affairs Officer - "Swimmers attaching the flotation collar now."

Recovery: [garble] the Command Module is pointing directly at the Photo Helicopter now.

Spacecraft: [Garble.]

Public Affairs Officer - "A preliminary look at the splash point shows it to be 158 degrees, 4 and one half minutes west, 26 degrees, 4 minutes north. Based on these preliminary numbers, that would be a miss distance of 5 and one half miles."

Recovery: [Garble.]

Spacecraft: [Garble.]

Recovery: [Garble.] Over.

Recovery: All right. [garble]

Recovery: [garble] Swimmers are now pulling the floatation collar around the Command Module. Both the VHF antennas appear to be resting on the Command Module. The flashing light is erected but it is not working, has not been turned on.

Recovery: This is recovery [garble].

Public Affairs Officer - "Recovery reports the Okinawa now 3½ miles from the Command Module."

Spacecraft: MARK [garble] Houston.

Recovery: The swimmers have the flotation collar almost completely around the Command Module.

Recovery: [garble] Now the swimmers now have the [garble]

Public Affairs Officer - "The ship now reports correction on that 6 1/2 miles from the Command Module."

Recovery: The swimmers now have the flotation collar around the Command Module and it is afloat. The flotation collar is completely inflated.

Public Affairs Officer - "Recovery reports flotation collar completely inflated."

Recovery: The swimmer [garble] flotation collar and request [garble] flotation collar to the [garble]. One swimmer is proceeding around to the window of the spacecraft and he's looking in at the astronauts. We have a contact with the swimmer he has visual communications with the Astronauts in the Command Module. The swimmers now crawling into [garble] to deliver the recovery raft. The swimmer is taking his [garble] recovery raft around in the doorway. The swimmer is approaching the Command Module.

Public Affairs Officer - "Helicopter moving in to drop another raft now."

Recovery: The recovery raft is being inflated. Recovery raft is inflated. It is being positioned along side of the Command Module next to the flotation collar.

Recovery: The swimmers are taking the recovery raft to the flotation collar. One swimmer managed to inflate the recovery platform. I can see Swim 1 in the distance. He is putting the swimmer in the water to attach the raft to the apex cover. The swimmers now have the recovery raft attached. One swimmer is getting into the recovery raft as he tried to remove the [garble] where they can move more freely.

Recovery: [garble] to recovery 001 to [garble] bring the astronaut's flotation equipment out.

Recovery: Recovery is approaching the Command Module. They have [garble] approaching the water. The [garble] is approaching the water, and is touching the water with [garble]. The Command Module is moving around on the surface of the water is usually [garble] 001. The swimmer now has the recovery net on the raft platform and he is removing the equipment back up to the recovery helicopter. Recovery is now moving away.

Public Affairs Officer - "The ship reports that the helicopter has now delivered some life vests to the swimmer, and he will pass those into the crew and they will don them before being hoisted into the helicopter. We have heard from the crew since the landing they report their in good shape."

Recovery: [garble] we see the waves from the helicopter, And cannot tell exactly what the swimmer is doing. It appears he is climbing up on the Command Module and securing the raft to the hatch side.

Recovery: The hatch to the Command Module is now open.

Public Affairs Officer - "Hatch is open now."

[Scott, from the 1971 Technical Debrief - "We gave the swimmer thumbs up, which he relayed. I guess by then they had heard us and that everybody was in good shape. We cleaned up the cabin as per checklist. We powered down, egressed, got picked up, and I thought that all went very smoothly. Just exactly as we had trained in the Gulf. The same Scuba team leader was there, and he did the same thing. The only anomaly there was that the swimmer couldn't get the hatch closed all the way. That left me with a rather uneasy feeling leaving the spacecraft - even though the seas were calm - with an open hatch. That just didn't make me too warm. I don't know why he couldn't get it closed. It looked like the dogs [the lugs around the periphery of the door that hold it closed] were all the way backed off, and I saw him vent the counterbalance. It was open about 3 inches."]

[Worden, from the 1971 Technical Debrief - "It was open more than that. It was open a good 6 inches at the open end."]

[Scott, from the 1971 Technical Debrief - "I don't know why it didn't get closed. That's something that we ought to make sure that the swimmers are maybe briefed on - malfunction procedures with that hatch. It would be a shame to have it sink."]

Recovery: [garble] the Astronauts are passing their flotation equipment in to them.

Public Affairs Officer - "Handing in the life vests."

[Scott, during 2004 review - "See the guy on the right in the water? He got a great picture. He took a picture of Fred Schmidt reaching in and shaking my hand."]

[The nearest image we have to the one Dave talks about is AP15-71-H-1242, seen here from the Apollo Archive Image Gallery.]

Recovery: The swimmers talking to the Astronauts. We are now trying to close the hatch again. Seems to be having some minor difficulty in regards to the cords. As we told you [garbled]. We're waiting now for the astronauts to start their equipment, equipment prior to egressing the Command Module. [Garble] my captain here says at the moment the swimmers are preparing to [garble] the hatch and get ready for the astronauts to affirm that they are ready to leave the Command Module. The swimmers are [garble] to clear it up [garble].

Public Affairs Officer - "The ship reports it's about a half mile away from the Command Module now."

Recovery: [Garbled] the swimmers now opening the hatch again.

Public Affairs Officer - "The swimmer is reopening the hatch now."

Recovery: [Garbled] The first astronaut is climbing out of the Command Module. He is the second astronaut in the doorway of the spacecraft. He is on the recovery raft. The first astronaut is in the recovery raft. He is climbing out of the Command Module. [Garbled] The second astronaut is now in the recovery raft. The third astronaut is now out of the Command Module and all three are in the recovery raft. The swimmer is taking [garble] preparations for closing the Command Module hatch. The swimmers' closing the hatch.

Speaker: Roger. The swimmers again are closing the hatch.

Public Affairs Officer - "Recovery swimmers are moving around [garble] the hatch helicopter moving in now."

Speaker: And Recovery [garble]. The Command Module.

Public Affairs Officer - "The ship reports that the wind is very light in the recovery area, makes it more difficult for the helicopters to hover. They prefer to have just a little bit more wind."

[If a helicopter tries to hover close to the surface in still air, its own downwash begins to return to the rotors, creating a great torus of unstable recycling air around the aircraft. The pilot has to use more power to maintain lift within the down-draft. A little wind blows the downwash away, keeping this torus from forming.]

[The crew are winched aboard the helicopter using a little basket sent down by the winchman.]

[O'Brien - "That doesn't look like the most glorious way to get on."]

[Scott - "No. That's not bad It's quick and it's safe and they know what they're doing. That's a Billy Pugh net.."]

[Woods - "The reason for the name, 'Billy Pugh net'. Do you know where it comes from?"]

[Scott - "Yeah, it's the guy who invented it. His name was Billy Pugh. I think it came out of someplace in Texas, in the Gulf of Mexico, some guy came up with the idea long before we showed up. But I don't remember exactly. It's a nice name."]

Speaker: The C [garble]

Spacecraft: [garble]

Speaker: The first astronaut is in the helicopter.

Speaker: [garble] the Command Module. The swimmer has the recovery [garble].

Public Affairs Officer - "The Okinawa reports, the first crewman into the helicopter is the commander, Dave Scott."

Speaker: [garble]

Speaker: [garble] The astronaut is approaching the helicopter.

Speaker: [garble] The second astronaut is in the helicopter.

Public Affairs Officer - "The second astronaut in the helicopter was Jim Irwin."

Speaker: The Recovery is headed [garble].

Recovery: The Recovery net is now in the [garble] platform. The third astronaut is getting into the net. They are now set for hoisting. He has cleared the Command Module in the water. The third astronaut is on his way up to the recovery helicopter.

Public Affairs Officer - "Al Worden now on his way up to the helicopter."

Recovery: [garble] the third astronaut is in the helicopter. [garble]

Recovery: Astronaut Alfred Worden is in the aircraft [garble].

Recovery: Okinawa this is Recovery [garble].

Okinawa: Okinawa, Rober. [?]

Recovery: Okinawa, Swim 2 is on [garble].

Recovery: Okinawa [garble].

Recovery: Okinawa tower [garble].

Photo: Photo to Okinawa tower [garble].

Okinawa: Roger this is Okinawa Tower.

Photo: Photo, roger.

Public Affairs Officer - "Cigars now being passed out in the control center."

Okinawa: [garble] Roger, Photo.

Okinawa: Roger, Photo. Your winds are calm [garble].

Photo: Photo, Roger.

Okinawa: [garble]

Public Affairs Officer - "The cigars are poised but not yet lit. They won't be lit until the crew is safely on deck. And the American flags are being broken out in the Control Center now. Each of the controllers with a small American flag."

Recovery: Okinawa, this is [garble]

Recovery: Okinawa [garble].

Okinawa: Recovery [garble] about 8 knots.

Okinawa: Recovery, this is...

Public Affairs Officer - "And the flight controllers are readying a plaque of the Apollo 15 crew patch which will be hung on the wall of the Control Center right after the crew touches down on the carrier, to join the crew patches of all the other Gemini and Apollo missions."

(Air Force hymn)

Captain Huff: Colonel Scott, Colonel Irwin, Major Worden. It is indeed a pleasure to welcome you back from your historic mission. We were here to see you depart with your TLI burn, and it's even a greater pleasure to be here today. Chaplain Peters would you ask an invocation please.

Chaplain: May we pray. Our Father we are grateful for the success of this mission, for the work accomplished by Astronaut Scott, Irwin and Worden. As we learn of your Universe, may we also learn of your purpose for mankind to live in peace. Amen.

Hayward: Well gentlemen, what can we say on the recovery force, but how great it is to have these three magnificent astronauts back here on the primary recovery ship. We had an exciting moment there, and it turned out just great. To these three astronauts, I say, as the commander of the recovery forces, that it's a great privilege for me to represent all of them in saying to them, how proud we are, and how great an accomplishment we think they have pulled off here, and how professionally they have executed this lunar mission from Canaveral to the Moon and back here in the Pacific, back to USS Okinawa. Fellows, there's no group any place that has more pride in what you've done than this recovery force, and I say that not just as recovery force people, but as Americans we are mighty proud of you. We have here today, to represent the US Air Force, and I must say, to all of us, who are pretty well aware that this Apollo 15 crew is an all Air Force contingent, and we're honored to have with us, 2 of the Air Force's finest General officers, Brigadier General, Pete Everest, who commands the aerospace rescue and recovery forces, and also General Clay, who has just taken over as Commander in Chief of [garble] the United States Air Force, Pacific, and I know General Clay has some welcoming remarks he'd like to make. General.

Clay: Colonel Scott, Major Worden, and Colonel Irwin, certainly, I'd want to offer my congratulations and welcome you home. I think particularly also, you well realize the tremendous pride our nation takes in your accomplishment. And I would be somewhat less than truthful if I didn't state also, there's a peculiar glow that the Air Force feels as a result of your mission. More importantly, however, it seems to me that this mission represents - the successful mission, Apollo 15 represents a culmination of a superb team effort on part of so many elements of our national life, the executive department, the congress, scientists, and engineers, and I'm sure they all share with you the pride in the accomplishment. It's a pleasure for me to say it's a tremendous thrill for me to be here to extend my congratulations. It's certainly been a wonderful and historic mission, and I can't help but also complement you on your superb selection of music. Thank you, Colonel Scott.

Scott: Thank you General Clay, and thank you, crew of the Okinawa. The crew of the Endeavour is glad to be aboard. We appreciate the fine pick up, and it's been my experience, the Navy always makes a fine pick up, whether we land 6 miles from the carrier, or 6,000, They're always there right on the spot, and we certainly appreciate it. It's great to be back. We had a great time on the trip. I think we accomplished a lot. We had a lot of support from a lot of people, and I'd just like to say that we appreciate every bit of it, and we could not have done the mission, we couldn't have gone one step without the support of the many, many thousands of people involved. Thank you very much.

Worden: Not that I'm shaky, it's just that I don't have my sea legs yet, you lucky stiff, you've been out here for a while. We just finished, probably the most fantastic 12 days I've ever had in my life, and I guess only one thing surpasses the excitement, and the intense feeling I had on the flight, and that was sort of the feeling I had when I saw you all today. It sure is nice to be back, and it sure is good to see you all. Thanks a bunch for the pick up.

Irwin: This is a very proud moment for me. It's proud to be part of this great team that could send us to the Moon and bring us back. The recovery was just, just excellent. Of course, I feel very happy to be aboard a more sea worthy craft than we just got off of. Also, I'd like to say, that I hope all of you, all around the world enjoyed our voyage to the Moon as much as we did, on the flight. Thank you all.

Music: [Anchors Aweigh]

Public Affairs Officer - "This is Apollo Control. ... We are securing this line now."

This concludes the Apollo 15 Flight Journal.

Previous Index
Science and a Press Conference Journal Home Page