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Lunar Orbit

Apollo 15

Day 4: Lunar Encounter

Corrected Transcript and Commentary Copyright © 1998 by W. David Woods and Frank O'Brien. All rights reserved.
Last updated 2016-06-21

[It is July 29, 1971, and Apollo 15 is approaching the Moon on the fourth day of the mission.]
Public Affairs Officer - "This is Apollo Control at 65 hours. The crew [are] now about 2½ hours into their rest period. About 5 hours remaining before they're scheduled to awaken. We have an update on the S-IVB impact. The Saturn third stage is scheduled to hit the Moon now at 79 hours, 24 minutes, 42 seconds Ground Elapsed Time. The coordinates have changed slightly. We're now showing the impact point at .997 degrees south, that would be 0.997 degrees south, and 11.872 degrees west. Apollo 15 at this time is 31,470 nautical miles [58,282 km] from the Moon and traveling at a speed, with respect to the Moon, at 3,653 feet per second [1,113 m/s]."

Public Affairs Officer - "This is Apollo Control at 66 hours, 1 minute. Apollo 15, at present time, continuing at its Passive Thermal Control mode and the crew [are] about 4 hours away from the scheduled time of awakening. In the Passive Thermal Control mode, the spacecraft is rotating about its longitudinal axis at the rate of about 3 revolutions per hour to maintain uniform exposure to the Sun and the proper thermal control of the spacecraft. This slow roll is set up by the crew prior to beginning their sleep period and on this mission we've had very good luck with the - that attitude holding and very small deviations. On occasion - [On] previous missions we have noted that occasional[ly], when the Passive Thermal Control mode is set up, that it will begin to diverge after several hours if it's not put into a very stable position and it has, on occasion, been necessary to awaken the crew and get them to reestablish the Passive Thermal Control. However, as I mentioned, we're holding very stable and would see no reason for having to reestablish the Passive Thermal Control mode. Apollo 15, at the present time, is 29,258 nautical miles [54,186 km] from the Moon and the spacecraft velocity is 3,669 feet per second [1,118 m/s]. The cabin temperature has been holding steady at around 65 to 70 degrees [Fahrenheit, 18 to 21° Celsius] and pressure; about 5.2 pounds per square inch [35.9 kPa]. And all spacecraft systems appear to be functioning about as expected at the present time. In Mission Control, we've been using this quiet period to do such things as recalibrate recorders and review activities that will be coming up tomorrow. Also, Flight Director Glynn Lunney has been going over, with some of the flight controllers, the techniques that will used for the landing on the Moon, which this shift will handle [tomorrow]. And we now show 3 hours, 56 minutes until scheduled crew awakening time. This is Apollo Control; standing by at 66 hours, 3 minutes."

Public Affairs Officer - "This is Apollo Control. We've been monitoring all systems on the spacecraft since putting the crew to bed. And everything continues to be normal. Flight Director Glynn Lunney, at the moment, is going around the room double-checking the status with each of his flight controllers. And there appears to be no change in status. Apollo 15, at the moment, is 27,152 nautical miles [50,285 km] from the Moon, and the spacecraft's velocity is 3,686 feet per second [1,123 m/s]. At 67 hours; this is Apollo Control."

Public Affairs Officer - "This is Apollo Control at 68 hours. We're continuing to get a good solid tracking data from the Manned Space Flight Network stations at Honeysuckle Creek and [at] Parkes[, both] of Australia and all systems functioning normally on the spacecraft. We have about 2 hours remaining in the crew's rest period. And on awakening, activities will begin to pick up for the crew as we near Lunar Orbit Insertion [LOI]. During the day's activities, they'll have a midcourse correction. That will be a small burn of about 73 hundredths of a second with the Service Propulsion System engine, which will occur at about 73 hours, 30 minutes, 59 seconds, and Lunar Orbit Insertion is scheduled for 78 hours, 31 minutes, 34 seconds. The Saturn third stage, the S-IVB, is scheduled to impact the Moon at 79 hours, 24 minutes, 42 seconds. And also, prior to Lunar Orbit Insertion, the crew will be jettisoning the door on the Scientific Instrument Module [SIM] of the Service Module, exposing the cameras and other sensors to the lunar environment. At the present time, we show Apollo 15 [to be] 24,930 nautical miles [46,170 km] from the Moon and the spacecraft velocity [is] up now to 3,707 feet per second [1,130 m/s]."

[Flight Plan pages 3-067, 3-068, 3-069 and the current page 3-070.]
Public Affairs Officer - "This is Apollo Control at 69 hours. We're just about 1 hour now from awakening the crew. On getting up this morning, the crew's first activity, following breakfast, will be to prepare cameras for photographing the jettisoning of the Scientific Instrument Module door. About three and a half hours after awakening, they are scheduled to perform the final mid-course correction en route to the Moon. That maneuver [is] scheduled to occur at 73 hours, 30 minutes, 59 seconds. ... Apollo 15 is now 22,758 nautical miles [42,148 km] from the Moon. The spacecraft velocity is 3,733 feet per second [1,138 m/s]."

Public Affairs Officer - "This is Apollo Control at 70 hours. We're standing by to put in a call to the crew if we don't see some signs of activity in the spacecraft first, indicating that they are up and about. The 8 hour rest period is scheduled to be over at this time and the crew does have a rather busy day of activities ahead of them, so we do plan to get them going pretty much on schedule. Apollo 15, at the present time, is 20,582 nautical miles [38,118 km] from the Moon and travelling at a speed of 3,764 feet per second [1,147 m/s]. Here, in Mission Control, we'll be handing over the shift shortly. Flight Director Gerry Griffin will be coming on to replace Flight Director Glynn Lunney. And - We've just had a call to the crew. We'll stand by, and pick up the response here."

070:00:31 Parker: Apollo 15, Houston. Over. [Long pause.]

070:00:59 Scott: Hello, Houston; Apollo 15.

070:01:01 Parker: Roger. Good morning, Dave. It's time to rise and shine.

070:01:06 Scott: Okay, Bob. Good morning.

070:01:10 Parker: And we've got the usual quota of checklist changes, Flight Plan updates, et cetera. When you guys are ready, give me a call. Looks like you guys had a good night's sleep last night, for you anyway, Dave.

[Dave was the only crewmember wearing his biomedical harness overnight, allowing the Flight Surgeon to monitor his heartrate and respiration.]
070:01:27 Scott: Okay. Felt pretty good. We'll get organized and give you a call here in a few minutes.

070:01:31 Parker: Roger.

[Very long comm break.]

[As well as having breakfast, tasks for the first hour of the day are to complete the four items in the postsleep checklist and, as mentioned by CapCom Bob Parker, copy down the changes to the Flight Plan which will shortly be read up to them. The postsleep checklist begins with a status report from the crew, an update on the use consumables so far and a stirring of the contents in the cryogenic storage tanks for O2 and H2.]

Public Affairs Officer - "Our spacecraft communicator at the moment is astronaut Bob Parker and he'll be replaced shortly by the oncoming CapCom, astronaut Joe Allen. ..."
[Actually, Joe Allen will not take over the CapCom seat for over an hour.]
070:26:05 Scott: Houston, Apollo 15.

070:26:12 Parker: Roger. Good morning.

070:26:17 Scott: Good morning. I have a consumables report for you, and sleep report.

070:26:22 Parker: Okay. We're ready to copy.

070:26:29 Scott: Okay. On the Commander: PRD - 7½ hours sleep; CMP: 25012, same sleep; LMP: 08013, same amount of sleep. On the consumables: [At] 70:15 [GET]: RCS; [quad A to D] 90 [percent remaining], 87, 84, 88. On the H2 [tanks 1 to 3]; 90 [percent remaining], 89, 60. O2 [tanks 1 to 3]; 88 [percent remaining], 89, and 65. Over.

[These values are based on reading from gauges on the Main Display Console. Note the reading for O2 tank 3, which one of the flight controllers is about to query.]
070:27:24 Parker: Roger. And, before I read that back, we did not catch the Commander's PRD reading.

070:27:37 Scott: That was 23046.

070:27:42 Parker: Roger. Copy. Understand we have Commander's PRD 23046, 7½ hours sleep for all three crewmen; 25012 for the CMP; and 08013 for the LMP. And we have consumables update, based on our figures from the ground. For 70:00, we have [RCS] 84 percent total, and we have [quad A to D] 85, 84, 84 and 85. And for H2 [tank 1 to 3] we have 91, 90 and 60. For O2 [tank 1 to 3] we have 89, 90 and 73. Over.

070:28:39 Scott: Roger. I - I'm ready for any update of Flight Plan update you might have.

070:28:44 Parker: Okay. First we have Flight Plan update for the day. We'll start out at - Stand by.

[Comm break.]

[Rotation of the spacecraft in its PTC (Passive Thermal Control) mode regularly takes the currently selected omni-directional antenna away from the Earthward side of the spacecraft. The ground or a crewmember must switch to another to reestablish the radio link to Earth.]

070:31:21 Parker: 15, Houston. You back with us again?

070:31:31 Irwin: Roger. We've been here all along, Bob.

[Jim is adopting his usual role as the copy secretary for Flight Plan updates.]
070:31:33 Parker: Roger. We had the usual signal break when we went around in PTC there. Let me ask you one question. The EECOMs are interested in getting a verification on the O2 tank 3 read-out, since there's a difference of 8 percent there. And, then after we get that, we'll proceed with this update. It's a very long one, so I guess you might as well...

070:31:53 Irwin: Okay. Stand by.

070:31:54 Parker: ...drag out your Flight Plan.

070:32:10 Irwin: Okay. We're reading - 74 onboard.

070:32:15 Parker: Roger. Understand 74. Okay, Jim. And we'll start this Flight Plan update at 71 hours, so you can tell me when you get there.

070:32:29 Irwin: Okay. I'm there.

070:32:30 Parker: All right. At 71 hours, you want to add the following information. "High Gain Antenna [HGA] on MSFN cue," and note that we won't stop PTC. We'll have to give you the numbers [for the HGA angles], depending on where you are - in PTC, as we come around at this point. Second line is "S-band Aux TV, to Science, Pan Camera Mode, to Standby." That's a "Verify." "Pan Camera, Power, On. Pan Camera Self Test, to Heaters. Mapping Camera, On, to Standby. Then after five minutes, Pan Camera Power, Off, and S-band Aux, TV, Off." Copy?

070:34:05 Irwin: Okay. Here's the readback, Bob. At 71 hours, "High Gain Antenna on MSFN cue, S-band Aux TV, to Science, Pan Camera Mode, to Standby." That's a "Verify." "Pan Camera Power, On; Pan Camera Self Test, to Heaters; Mapping Camera, On, to Standby; after five minutes, Pan Camera, Off, and S-band Aux, TV, Off."

070:34:31 Parker: Roger. That's good. Okay. Next item at 71:15. This will be a line added in after the "CM/LM Pressure Equalization Decal." And the line says, "Press Equal valve, close." Over.

070:35:02 Irwin: Roger. At 71:15, "Pressure Equalization valve, close."

070:35:06 Parker: Roger. And next one is on 73 hours and 15 minutes.

070:35:20 Irwin: Okay. Go.

070:35:21 Parker: Okay. And at 73:15, we will delete the line referring to waste water dump. "Waste Water Dump" will be deleted.

070:35:34 Irwin: Okay. I copy. Delete the "Waste Water Dump."

070:35:37 Parker: Okay. Next one will be at 81:42. 8 1 4 2. [Long pause.]

070:36:04 Irwin: Go.

070:36:06 Parker: Okay. And, in the configuration for the camera there, we're changing that from "CM4" to "CM3" on the second line.

070:36:21 Irwin: Okay. "CM3" is [garble] to "CM4."

[This defines the window through which photographs of the terminator are to be taken. Window 3, the central window of the five, installed in the spacecraft's main hatch, is to be used instead of window 4, the right-hand, forward looking, rendezvous window.]
070:36:24 Parker: Roger. Next one's on 84:24, 84:24. [Long pause.]

070:36:41 Irwin: Okay; go.

070:36:42 Parker: Roger. [This] also [concerns the] configuration of the camera, and we'll change that one also to "CM3" instead of "CM4."

070:36:55 Irwin: I copy.

070:36:56 Parker: Roger. And then over on the other side of the page at 84:40, again terminator photos. The first one, the first line there 84:40 will now read "EL, On" and the time will be "T start minus 1:40," one, four, zero.

["EL" refers to the electric (motor driven) Hasselblad kept in the Command Module. The change affects the time, relative to when the Mapping Camera is started, that window photography will commence as the spacecraft flies over the Moon's terminator. "T start" is the time the mapping photography begins and the Hasselblad photography is to begin 1 minute, 40 seconds before then.]
070:37:22 Irwin: Okay. I copy.

070:37:25 Parker: And then at 84:42, "EL, Off" will now be at "EL, Off, parenthesis, T-start."

070:37:41 Irwin: I copy.

070:37:42 Parker: Okay. And we have two general notes. One refers to SIM [bay] door Jett[ison], and it's a reminder that we verify that the Lexan shield is mounted in - window 5, with the cardboard shade off, for a photograph of SIM door Jett. At - this is about 74 hours.

[As part of the procedure to jettison the door over the SIM bay, shown of page 3-76 of the Flight Plan, the crew are requested to observe and photograph the event through window 5. As this window is transparent to ultraviolet light, a shield made from Lexan, which is opaque to UV, should be put over to window to minimise the crew's exposure. Since UV will reflect off the cabin surfaces, this safeguard is desirable even with indirect sunlight.]
070:38:10 Irwin: Okay. I understand.

070:38:11 Parker: Okay, and second one is with respect to the Optics Cal[ibration]s. And I guess that we should explain here that - people who are wringing their hands down here about the fact the we looked at a little bit of a bias drift when you guys zeroed the optics the first day, and we sent up some procedures yesterday saying to be careful when you are doing it for P23. And then everybody else got - decided that we ought to be careful when we did it for other things besides P23. And so, we have the following procedures, which are, basically, to avoid trunnion rates for all optics zeroing, so that we don't get any - possible shift on the mirror calibration. And the procedures are twofold. First - I guess you might write them down some place - if the Optics power is off, place Zero switch, off, before turning the Optics power on. And then, after the power is on, drive the Optics manually to a Trunnion of less than 10 degrees before placing the Zero switch, on. Over.

070:39:28 Irwin: Okay, Bob. If Optics power off, then Optics Zero switch, Zero?

070:39:39 Parker: Roger. It really is, "if Optics power off, place the Zero switch to off before turning the Optics power on."

[Comm break.]
070:42:16 Parker: 15, Houston again. [No answer.]

070:42:41 Parker: 15, Houston. [Pause.]

070:42:49 Irwin: Bob, would you read that procedure again? I want to make sure I have it correct. I have Optics power, off, then Optics Zero switch, Zero.

070:43:04 Parker: Okay, Jim. The thing is, if your Optics power is off, we - as it will be like this morning, is off, and the Zero switch is already on, as it probably is this morning, we want you to place the Zero switch to off before you turn the Optics power on, because, otherwise, it will then automatically zero without you having control over it. Do you understand?

070:43:28 Irwin: Okay. We understand.

070:43:30 Parker: Okay. And - the corollary...

070:43:33 Irwin: Read the - read the rest of it after the Op...

070:43:37 Parker: Okay. And then after, - Okay; I'll - I'll read it through from the beginning again. "If Optics power off, place Zero switch, off, before turning Optics power on. Then, drive Optics manually to Trunnion less than 10 degrees before placing Zero switch, on." Over.

070:44:14 Irwin: Okay. That was after the Optics power on. Drive optics until Trunnion is less than 10 degrees before Zero switch, on.

070:44:24 Parker: Roger. And the corollary to that is if the Optics power is already on, then we drive the Optics power manually to a Trunnion of less than 10 degrees before placing the Zero switch, on. That's the second part.

070:44:42 Irwin: Okay. We copy.

070:44:44 Parker: Okay. And then I have an update to your Contingency Checklist, page 4-3 which pertains to LOI burn rules if you can get that out.

070:44:58 Irwin: Stand by.

070:44:59 Parker: Roger.

[Comm break.]

[The Contingency Checklist carries a wide range of procedures which the crew can fall back on in an emergency situation. Some of these seem to be based on experience gained during Apollo 13 when the LM had to be powered up in a hurry and used as a lifeboat. A few examples of procedures covered are; a 30-minute activation of the LM, use of the AGS (Abort Guidance System) to set up a PTC, powering the CSM from the LM.]

070:46:59 Irwin: Okay, Bob. I have the Contingency Checklist.

070:47:01 Parker: Okay, I got 4 - page 4-3.

070:47:09 Irwin: Stand by. [Pause.]

070:47:20 Irwin: Okay; I have 4-3.

070:47:22 Parker: Okay. And these changes are basically in the table there. - We'll start out under the heading of "Burn time." And that first one will be change from "00 to 1:36," now, instead of "1:35." So, it'll be 1:36 in the first burn time. The second line will be "1:36 to 1:57." And the third line will be "1:57 to 2:13." And the fourth line will be "2:13 to 3:11." Over.

070:48:15 Irwin: Copy.

070:48:17 Parker: Okay, the next one in the second column, "Delta-VM," the lines will be 0 to, or "0-640, 640-784, 784-900, 900-1313." Over.

070:48:55 Irwin: I copy.

070:48:57 Parker: Okay, and, in the second block, the lower block, under the updates for the times and angles, we have the following readings under the "Update" column. The GET [Ground Elapsed Time] of LOI ignition is "78:31:34.2," the second time is "79:01:34.2," and the angles are "144, 358, and 68." Over.

070:49:49 Irwin: Okay, copied on the update time, "78:31:34.2, 79:01:34.2; 144, 358, and 68."

070:50:03 Parker: Roger. And, be advised, this also changes your little graph over on the side there. Primarily what it does, is to enlarge the mode 130 region by about 10 feet per second on either side and it changes the "LOI plus 30 abort Delta-V" line by essentially extending it and raising the left-hand corner just a wee bit. We could read up the lines to it if you want, but I'm not sure you really need those. Over.

070:50:38 Irwin: Okay; understand.

[It is interesting to note that while it is a simple matter to read up lists of text and numbers, there is no facility to transmit images; illustrations, graphs and diagrams; from Mission Control to the spacecraft, except through verbal description. The contemporary facsimile machine is big and bulky and cannot even be considered for inclusion in the spacecraft. The next generation of spacecraft, the Space Shuttle and the Mir space station, will benefit from increasingly sophisticated communications, including means of receiving imagery. This extends to TV uplinks so that the ground can demonstrate procedures to the crew.]
070:50:43 Parker: We're coming up on another Omni switch, and we'll be back with you in a minute, Jim.

070:50:52 Irwin: Roger.

[Comm break.]
Public Affairs Officer - "And this is Apollo Control; as we come up through a rotation of Passive Thermal Control and lose lock with one of the Omni[-directional] antennas. ... The distance from the Moon now 18,674 feet per sec [correcting himself] - nautical miles [34,584 km]; approaching the Moon at 3,797 feet per second [1,157 m/s]. ... At 70 hours, 52 minutes Ground Elapsed Time; this is Apollo Control."

Public Affairs Officer - "Every 2 hours the spacecraft analysis - This is Apollo Control again. Hopefully the line is up properly. Every 2 hours the spacecraft analysis room [SPAN room] in the back of the Mission Control Center here prepares a report on the status of the spacecraft systems. The report issued at 70 hours Ground Elapsed Time, a little over an hour ago, is very short; about 3 quarters of a page; the entries under thermal, displays and controls, instrumentation, power distribution and sequencing, communication, crew systems, guidance and control, propulsion and power; all have entries such as: 'No change in status,' 'Our systems performance has been normal.' Under fuel cells and cryogenics, the statement reads: 'The fuel cells are normal, delivering approximately 75 amperes to the spacecraft systems. The cryogenic system is normal with approximately 817 pounds [371 kg] of oxygen remaining and approximately 67.8 pounds [30.8 kg] of hydrogen remaining. The Command Module batteries; battery A has 39 amp-hours remaining; battery B, 39; battery C, 37.8. No change in the LM batteries.' And that is the extent of the report from the spacecraft analysis room issued at 70 hours Ground Elapsed Time."

070:53:17 Parker: Okay, 15; we're back with you.

070:53:33 Parker: 15, Houston; we're back up.

070:53:40 Irwin: Okay. We read you.

070:53:41 Parker: Okay. Understand you really - didn't feel you needed the complete update to that graph, Jim. [Long pause.]

070:54:56 Parker: Jim, this is Houston. Is that a verify on the fact that you don't want the update on the graph? Over.

070:55:06 Irwin: I think we can do it ourselves, Bob.

070:55:08 Parker: Oh, Roger. Okay, and that's all the update we have for you at the moment. You might be interested in knowing that that water dump you guys scheduled last night before you went to bed, was at a very opportune time. Your PTC shifted plus or minus 2½ degrees all night.

[Although PTC is started with much care, that is, as nearly perfectly along the X- (longitudinal) axis as possible, it is almost impossible to maintain indefinitely. The spacecraft's centre of gravity alters as fuel and other consumables slosh in their tanks or the crew moves around. Small accelerations are imparted by these influences and by water dumps. As PTC degrades, the CSM/LM stack begins to diverge off of its original spin axis, exactly like a child's spinning top that is slowing down. Of course, the stack is not losing overall momentum but rather, new rates are added along the Y-axis and Z-axis at the expense of X-axis rotation.]
070:55:26 Scott: Well, very good.

070:55:32 Parker: We'll be up with the news in a while.

070:55:39 Scott: Okay.

[Long comm break.]

[Flight Plan page 3-071.]

[With breakfast over, the crew gets down to the business of the day. After reading up appropriate angles for pointing the HGA, Mission Control will monitor the Panoramic and Mapping Cameras in the SIM bay via telemetry. Al will check the EMS (Entry Monitor System) for its ability to accurately display changes in velocity. The cabin pressures in the two spacecraft will be equalised and, at about 72:20, the crew are due to put their suits on, except for their helmets and gloves, in preparation for the jettison of the SIM bay door.]

[Scott, from 1998 correspondence - "Suits on or off was a function of the risk of depressurization which in turn depended on the situation at the time, the configuration and status of the ECS [Environmental Control System], and experience on previous flights - in terms of systems performance, primarily ECS. Helmet and gloves off was intermediate - close to full suits in terms of protection - but close to no suits in terms of operations. That is, the time required to don helmet and gloves was quite short relative to donning the complete suit - but operating the spacecraft in suits but without helmet and gloves was relatively easy compared to operating in a fully pressurized suit. Operating with helmet and gloves on, but not pressurized was also not difficult, much closer to no suits than to pressurized suits. This subject is not simple and required considerable planning and preparation as well as safety and the tradeoff between operational flexibility and comfort versus the security provided by full suits.]

["During the SIM bay [door] jett, we probably went to suits because the SIM bay had never before been jettisoned (the experience factor) and thus presented a certain amount of uncertainty relative to its effect on the CSM and the ECS. However, the first SIM bay [door] jettison was not so uncertain that helmet and gloves on were required.]

["All of these suit/no-suit situations were discussed and debated in great detail among many elements of the total organizational system before each flight - and then various anomalies were simulated and rehearsed as well as discussed and analyzed to prepare the flight procedures, Flight Plan, and Mission Rules.]

["Many anecdotes on this subject! In the early days, it was thought that the crew could don suits, helmets, and gloves within 5 minutes - which was the requirement for the design specification leak rate in the CSM caused by a puncture. Quite an amusing scenario to witness such a fire drill! That requirement did not last long! Apollo 7 is another story. And the loss of the Salyut 1/Soyuz 11 crew less than a month before the A-15 launch caused some of the higher level folks in Washington to attempt to require us to wear suits during re-entry - which of course was eventually not required by the overall 'system.'"]

[During our review in 2004, Dave discussed such a fire drill he had with his crewmates who would eventually fly with him on Apollo 9.]

[Scott - "You know, its sort of funny, because I remember on Apollo 1 before the fire, we had a fire drill, if you will. Jim [McDivitt], Rusty and I had our little blue suits and we were in the spacecraft. They said, 'OK. You've got a puncture. Got to get your suits on, in whatever it was, five minutes, because you're leaking.' [Laughs.] It was funny. We couldn't do it. On the lunar surface when Jim [Irwin] and I started suiting, we said, 'OK, we're gonna suit up now,' until we got finished with all our suit integrity checks before we went out the hatch. Took two hours."]

[O'Brien - "Where's the time spent? Just trying to wiggle things on?"]

[Scott - "Time was spent putting stuff on, checking it out, making sure it was all connected. Suit integrity checks, comm checks. And you had to follow the procedures, obviously. Hardest work you did on the whole mission. Hardest training too, because it was so boring, you know, putting all that stuff on. But you had to be very careful. And it just takes a long time for two guys to put all that stuff on in a confined environment. Backpack, OPS, comm, helmets, bio sensors, huh, food stick, water bag; all that stuff just takes a long time."]

[Woods - "So when you‘re coming up to the jettison of the SIM bay door and you have to get your suits on and there‘s three of you, that, presumably, is an even more complex, cumbersome task?"]

[Scott - "Not really, because we didn‘t have a backpack. We didn‘t have the EVA stuff. You know, the PLSS and the OPS and the thermal gloves and the LEVA and all that stuff. Much easier inside the Command Module."]

[O'Brien - "And you weren‘t wearing the LCG?"]

[Scott - "We didn‘t use the LCG."]

[The three-man crew of Soyuz 11 had died in their re-entry spacecraft after leaving the Salyut 1 space station less than a month before Apollo 15's launch. A small pressure equalisation valve had opened prematurely from the shock of undocking. The crew were asphyxiated though their automatic systems brought them to a pinpoint landing on Earth. They had not been wearing suits so as to make room in the tiny spacecraft for the third man.]

071:01:30 Parker: 15, Houston. We have a Pitch of minus 30 and a Yaw of 85 for the High Gain Antenna, and we'll give you a mark when to go.

071:01:41 Parker: Uh, go now.

[The spacecraft is rotating about once every 20 minutes in its PTC mode. The pointing angles Mission Control have just read up will therefore only be valid for a short period of time. Once the HGA has acquired the signal from Earth, it will automatically track the Earth, even as the spacecraft rotates, until it reaches the limits of travel of its articulation. At most, it will track the Earth for about 10 minutes at a time.]
071:01:46 Irwin: Okay; minus 30 and 85.
[Comm break.]

[With the data link to Earth established, the Panoramic Camera is powered up and its heaters switched on, while the Mapping Camera is placed in Standby mode. For about 5 minutes Mission Control will receive telemetry from them. This procedure is part of the updates read up to the crew at 070:32:30.]

071:03:28 Parker: And, 15, we're getting you on High Gain and receiving...

071:03:39 Irwin: Okay; we understand you're getting the data.

071:03:42 Parker: That's affirmed.

[Long comm break.]
071:11:33 Irwin: Houston, this is 15.

071:11:36 Parker: Roger; go.

071:11:40 Irwin: Roger. We just want to confirm the position of the switches on the Mapping Camera and Pan Camera. We have the "Mapping Camera On" is Standby, and the "Pan Camera, Power," off. Is that correct?

071:11:54 Parker: Roger. If you finished [the procedure], that's the correct position.

071:12:02 Irwin: Okay.

[By now, the gathering of engineering data on the SIM bay cameras should be complete. The HGA will have lost its link with Earth and communication is continuing using the omni-directional antennas on the CM.]
071:13:45 CapCom: 15. We'll take Omni Delta at this time please.

071:13:52 Irwin: Roger; Omni Delta.

[Long comm break.]
071:19:51 CapCom: And, 15, we'd like Wide and Manual on High Gain [Antenna], please.

071:19:58 Scott: Roger.

[Long comm break.]
071:24:00 CapCom: Apollo 15, this is Houston. Select Omni Bravo, please.

071:24:08 Irwin: Omni Bravo.

[Although there are four omni-directional antennas around the periphery of the CM, communications can be maintained by switching between two antenna on opposite sides of the spacecraft, usually B and D.]
071:34:25 Allen: Apollo 15, Houston,

071:34:31 Irwin: Go ahead, Joe. [No answer.]

071:34:39 Irwin: Go ahead, Joe.

071:34:40 Allen: Stand by, Jim. I'll wait until the comm's a little better.

[Long comm break.]
071:39:01 Allen: Hello, 15; this is Houston.

071:39:08 Irwin: Go ahead, Joe.

071:39:10 Allen: Good morning, Jim. This is your friendly News Reporter on duty now. And I wondered if you'd be interested in something from the local newspapers?

071:39:21 Irwin: Oh, yes. We certainly would.

071:39:26 Allen: Roger. This is from the MOCR Gold Bugle and Taglich Zeitung News. The Administration effort to rescue Lockheed Aircraft cleared a major hurdle in the Senate yesterday when an amendment to deny favored status was rejected 60 to 35. Houston unemployment rose to 4.1 percent in June, an increase of a full percentage point from May, which is the highest in 6 years. And this morning's Post reports that the checkout of Falcon went on with a few words from Worden and virtually nothing from the other astronauts. However, I think that's incorrect and I enjoyed talking to you very much yesterday. In sporting news, Houston dumped Philadelphia, 6 to 3, and is now in fourth place, 10 games behind the Giants. And an interesting note from the North. Bart Starr underwent surgery yesterday for a bicep tendon transplant and will be out of action for at least 12 weeks. And that's all from the Daily Zeitung this morning.

071:40:54 Scott: Thank you, Joe. Enjoyed it.

[Scott, from the Apollo 15 Lunar Surface Journal - "Do you know the reason we did the German thing?"]

[Eric Jones, from the Apollo 15 Lunar Surface Journal - "Because it was von Braun's program."]

[Scott, from the Apollo 15 Lunar Surface Journal - "Sure. A lot of people involved, especially in Huntsville, with the Rover and all that stuff, were Germans. So, maybe one of the reasons Joe and I batted it back and forth was 'cause it was his program."]

071:40:58 Allen: Roger, Dave. Good morning.

071:41:05 Scott: Morning. [Long pause.]

071:41:29 Allen: Al, this is Houston. And we're standing by for your null bias EMS check if you've gotten to that yet.

071:41:43 Worden: Roger. The Delta-V test was good, and the null bias was 1.0.

071:41:52 Allen: Roger. Copy.

[Long comm break.]

[The Delta-V test of the EMS is performed daily as its accuracy is crucial to achieving a safe re-entry at the end of the mission, as well as monitoring the progress of burns.]

071:49:16 Allen: 15, this is Houston.

071:49:22 Irwin: Do ahead, Joe.

071:49:25 Allen: Roger, Jim. Just wanted to tell you to expect all your updates on time except the PAD; and we're going to delay the PAD to 72 [hours] plus 50 [minutes] because of very good tracking data we'll be getting in those last few extra minutes there.

[The left-hand column of the Flight Plan displays details of tasks Mission Control must carry out with the spacecraft. These are usually reminders of required updates. At 72:20, there is a note for Mission Control to update two PADs (Pre-Advisory Data). The first is for the upcoming midcourse correction 4, and the second is required for an abort situation. The quality of the data read up to the crew for MCC4 will be improved by gathering more trajectory data from the radio dishes currently pointed at the spacecraft. Therefore it will be delayed by 30 minutes.]
071:49:52 Irwin: Okay; understand. Expect the PAD about 72:50.

071:49:52 Allen: Roger.

[Very long comm break.]

[Flight Plan page 3-072.]

[The next item in the Flight Plan is to prepare the 16-mm DAC (Data Acquisition Camera) to film, at 12 frames per second, the jettison of the SIM bay door in two hours time. The camera will be looking out of window 5, the quartz paned, UV transmitting window, with the Lexan shield in place to protect the crew from UV exposure. The Flight Plan calls the jettison to be filmed using magazine E with its 16-mm stock.]

072:04:21 Worden: Hello, Houston; 15. [No answer.]

072:04:45 Worden: Hello, Houston; 15.

072:04:48 Allen: Go ahead, 15. This is Houston. We hear you now.

072:04:54 Worden: Morning, José. Say, listen; on this - on the door jettison photography, we've got about 50 percent left on mag[azine] A, and we thought we would go ahead and use that.

072:05:13 Allen: Good morning, Alfredo. We copied you, but I'm not sure that I understand your question.

072:05:23 Worden: Okay, Joe. It's not a question. Just wanted to let you know, on the 16 millimeter photography for the SIM door jett, the Flight Plan called out mag - stand by one. Yes; it called out mag Echo, and we're going to use mag Alpha instead. We['ve] got about 50 percent left on it. Just letting you know.

072:05:48 Allen: Okay, Al. Thank you. And, by the way, is that the maneuver where the SIM bay door jettisons the spacecraft?

[It really depends how you look at it. One is jettisoning the other. This is engineers' humour.]
072:06:00 Worden: It has been variously known as that kind of a maneuver, yes.

072:06:04 Allen: Roger. I'm looking forward to that.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control. Everything this morning [is] going along on schedule. [The] Next major event in the mission will be the midcourse correction number 4 maneuver, at the nominal Flight Plan time of 73 hours, 31 minutes, 14 seconds. Looking at a desired velocity change of 5.3 feet per second [1.6 m/s]. The burn will be with the Service Propulsion System on bank B only. All other major burns of the SPS and, in and out of lunar orbit will be made with both banks. Bank A having to be switched on manually. Following the midcourse correction, the SIM door jettison; that is the Scientific Instrument Module door covering the scientific gear for orbital science task back in the Service Module. This takes place at 74 hours and 1 minute. The door is 5 feet wide and 9, 9½ feet long [1.5 by 2.9 metres] and weighs about 170 pounds [77 kg]. An explosive cord going all the way around the interior of the door will be detonated to actually shear the metal. It's been pregrooved where it can shear along that line, also some booster explosives at each corner of the door will push it out away from the spacecraft at approximately 7 feet per second [2.1 m/s]. The crew at this time will have on their pressure suits in a soft condition, unpressurised, but with helmets and gloves on for the SIM door jettison. This is the first time that the SIM door - the SIM Bay has been flown on any Apollo mission. It will be on all the remaining Apollo missions, a so called J-Mission series. Apollo 15 is now 15,505 nautical miles [28,715 km] from the Moon, approaching at 3,870 feet per second [1,180 m/s]. Rejoining live air/ground. At 72 hours, 16 minutes, Ground Elapsed Time; this is Apollo Control."

072:22:13 Allen: Apollo 15, Houston.

072:22:18 Worden: Houston, 15. Go ahead.

072:22:21 Allen: Roger, 15. I have a maneuver PAD, PC plus 2, when you're ready to copy.

072:22:31 Worden: Okay, Joe; stand by.

072:22:34 Allen: Roger. [Long pause.]

Public Affairs Officer - "This is Apollo Control. The PC plus 2, the PAD referred to by spacecraft communicator, Joe Allen, is the Pericynthion plus 2 hours Abort PAD, which would be a maneuver..."

072:23:21 Worden: Okay, Joe. I'm ready; go ahead.

072:23:24 Allen: Roger. PC plus 2, SPS/G&N. 66313; plus 1.23, minus 0.12; 080:29:13.47; plus 3189.4, minus 2437.0, minus 1356.5; 175, 079, 332; all other is NA; ullage, none; other, burn equals SPS docked. Over.

072:24:42 Worden: Roger, Joe; copy. Plane change plus 2, SPS/G&N; 66313, plus 1.23, minus 0.12; 080:29:13.47; plus 3189.4, minus 2437.0, minus 1356.5; 175, 079, 332; no ullage; and that burn equals SPS docked.

[PC actually stands for "pericynthion" and it is unclear why Al Worden has used the term "plane change" in its place. He may be simply playing with the terminology, using alternative phonetic names for 'PC' rather than 'Papa Charlie'. This practice is common among the Apollo crews. There is a plane change maneuver in lunar orbit but that will not happen until 165 hours GET. The notation "PER+2" is also used in the Flight Plan to refer to the PC+2 maneuver.]

[All the Apollo missions, from Apollo 12 onwards, flew to the Moon on a hybrid free return trajectory. The free return trajectory, used by Apollo 8, 10 and 11, would have the spacecraft coast around the Moon and continue on the way home to Earth, if no action was taken by the crew except for course corrections. This was inherently safe though it severely constrained the areas of the Moon accessible to the spacecraft. To access areas away from the equator, the hybrid version was developed. While this also loops the spacecraft around the Moon, it doesn't send it directly towards Earth. If an abort situation develops before LOI (Lunar Orbit Insertion), as happened on Apollo 13, or the LOI burn cannot be made, an additional burn is required to reestablish the Earthbound trajectory, a so-called "flyby" maneuver. Then, to bring the crew home faster, a longer burn is made. This is the PC (Pericynthion) plus 2 burn, though in Apollo 15's case, the two functions would be combined in a single burn, small enough to be carried out by the LM descent engine if needs be.]

[Readers should note that there are a wide variety of terms used to describe the high and low points in a lunar orbit. For example "aposelene" and "periselene" respectively are commonly seen. Strictly speaking, there are four terms used by the people of Apollo. If a spacecraft has been launched from Earth then the terms "apocynthion" and "pericynthion" should be used. "Apolune" and "perilune" are intended for describing the orbits of spacecraft that have been launched from the Moon.]

[In the event of an abort, the PC+2 burn is timed to occur two hours after the spacecraft's closest approach to the Moon and although the closest approach is during the swing around the far-side, PC+2 would happen in view of Earth.]

[An interpretation of the PAD follows:

Purpose: The purpose of the PAD is the PC plus 2 hours burn to re-establish the free-return trajectory in the event of an abort and bring the spacecraft to a well-defined ocean landing site.

System: The burn would be made using the Guidance and Navigation System controlling the Service Propulsion System engine.

CSM Weight (Noun 47): 66,313 pounds (30,079 kg).

Pitch and yaw trim (Noun 48): +1.23° and -0.12°.

Time of ignition, Tig (Noun 33): 80 hours, 29 minutes, 13.47 seconds.

Change in velocity (Noun 81), fps (m/s): x, +3,189.4 (+972.1); y, -2,437.0 (-742.8); z, -1,356.5 (-413.5). These velocity components are expressed with respect to the local vertical/local horizontal (LVLH). In other words, with respect to the piece of real estate directly below them. Since they would be in the lunar sphere of influence if this burn were to be made, then it would be lunar real estate.

Spacecraft attitude: Roll, 175°; Pitch, 79°; Yaw, 332°. These attitude angles are given with respect to the orientation of the guidance platform at that time.

As the SPS propellant tanks are nearly full, no ullage burn is required to settle the propellant. The burn would be made with the LM still docked.]

072:25:14 Allen: Readback's correct, Al. Thank you.

072:25:19 Worden: Roger.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control. To recapitulate, the Pericynthion plus 2-hour Abort PAD, read up to the crew; ignition time for such an abort, should it become necessary, would be at 80 hours, 29 minutes, 13.47 seconds Ground Elapsed Time, [it] would be a docked burn with the Lunar Module still attached, using the Service Propulsion System, total velocity change posigrade 3,189.4 feet per second. Should be getting the maneuver PAD up to the crew before too long for midcourse number 4 at 73 hours, 31 minutes ignition time. Standing by live on air/ground; this is Apollo Control at 72:27."
[Other tasks around this time: the line which carries H2 to the fuel cells to purge them can be heated electrically. This is powered up around this time in preparation for an upcoming purge. The H2 is very cold and could freeze the water by-product if care is not taken. Normally, the heat of the power generating reaction is enough to keeps the cells from freezing.]
072:38:44 Allen: Apollo 15, this is Houston. We need P00 and Accept to give you a state vector and a target load, and we'll uplink when we get the next Omni.
[As a result of their tracking, Mission Control have a set of values for the state vector which they believe are more accurate than the one currently in the CM computer. The computer is placed in an idle state by program 00 and switched to a mode whereby it can accept data uplinked from Earth. The state vector is seven numbers which describe the spacecraft's position and velocity in three axes at a defined time. Additionally, the Delta-V they are to achieve with their next burn is also sent up. This is the "target load".]
072:39:02 Worden: Okay, Joe. You have it.

072:39:05 Allen: Roger; thank you.

[Long comm break.]

[One of the crewmembers, usually Al as CMP, is due to realign the gyroscopically stabilised platform in the CM's IMU (Inertial Measuring Unit). The procedure uses P52 in the computer.]

072:42:38 Allen: Apollo 15. This is Houston with the maneuver PAD [for] midcourse 4, when you're ready.

072:42:49 Worden: Okay. Stand by one, Joe.

072:42:53 Allen: Roger; standing by.

072:43:45 Irwin: Okay, Joe. I'm ready to copy the midcourse 4 PAD.

072:43:50 Allen: Roger, Jim. Midcourse 4, SPS/G&N; 66531, plus 1.23, minus 0.12; 073:31:14.02; plus 0001.9, minus 0003.6, plus 0003.5; 038, 240, 331 - [Apollo] 15, hold off the P52; we're commanding, and go to P00 and Accept, please.

072:44:53 Scott: Yes. Roger, Joe.

[It would seem that whoever was going to realign the platform had not realised that Mission Control still had control of the computer. They had taken it to program 52 instead of P00 (program 00).]
072:45:01 Irwin: Okay. We - we're back in P00 and Accept. I forgot, there's no uplink activity light in the LEB.
[All the indicator lights in the DSKY (Display and Keyboard) are not operating since the circuit breaker supplying them popped at 33:48. Training has probably conditioned Al to glance the uplink activity light and if it is off, to believe the computer is free.]
072:45:11 Allen: Roger, 15. I'll continue with the PAD. HA is NA, NA; 0005.4, 0:01, 0003.2; 23, 106.1, 17.6. The rest is NA. GDC align, Vega, Deneb; roll align, 209, 009, 349; ullage, none. Other: LM weight, 36256; SIM door jett attitude is nominal. Single bank Bravo burn. High Gain: Pitch, 21 [degrees]; Yaw, 243. Over.

072:46:36 Irwin: Okay, Joe. Readback for midcourse 4, SPS/G&N; 66531; plus 1.23, minus 0.12; 073:31:14.02; plus 0001.9, minus 0003.6, plus 0003.5; 038, 240, 331; 0005.4, 0:01, 0003.2; 23, 106.1, 17.6. Vega and Deneb; 209; 009; 349. No ullage. LM weight, 36256; SIM door Jett, attitude nominal. Single bank burn on Bravo. High Gain: Pitch, 21; Yaw, 243.

[An interpretation of the PAD follows:

Purpose: Such was the accuracy of the TLI (Translunar Injection) boost by the third stage of the Saturn V launch vehicle, that the crew have only had to use two of the four occasions which were planned for midcourse corrections. This PAD is for the second of these two, MCC-4. System: The burn will be made using the SPS engine, controlled by the Guidance and Navigation System.

CSM weight (Noun 47): 66,531 pounds (30,178 kg).

Pitch and yaw trim (Noun 48): +1.23° and -0.12°. These are the angles away from the longitudinal axis the SPS engine bell will be set to for the burn.

Time of ignition, Tig (Noun 33): 73 hours, 31 minutes, 14.02 seconds.

Change in velocity (Noun 81), fps (m/s): x, +1.9 (+0.58); y, -3.6 (-1.1); z, +3.5 (+1.07). These velocity components are expressed with respect to the LVLH frame of reference (that is, with respect to the horizontal plane of the Moon directly beneath them and their orbital path).

Spacecraft attitude: Roll, 38°; Pitch, 240°; Yaw, 331°. The attitude figure is with respect to the IMU orientation at the time of the burn.

Delta-Vt: 5.4 fps (1.65 m/s). This is essentially a vector sum of the above velocities and as such represents the total velocity change.

Burn duration or burn time: 1 second.

Delta-Vc: 3.2 fps. (0.98 m/s). This is the fps value that will be entered into the EMS to give it backup control of the burn. The value is smaller than Delta-Vt because the EMS cannot compensate for the tail-off impulse generated by the engine after the cut-off command. By entering a lower number, (and should the G&N system fail to shut the engine down) the burn would be stopped early enough by the EMS, that the extra thrust from the tail-off would bring the final Delta-V to the required value.

Sextant star: Star 23 (Denebola, in Scorpio) should be visible in the sextant when shaft and trunnion angles are 106.1° and 17.6° respectively. This is one of the attitude checks the crew will make prior to the burn.

GDC align stars: Stars Vega (number 36) and Deneb (number 43) to be used for backup GDC align.

As well as the IMU, two gyro assemblies, associated with the GDC (Gyro Display Coupler) are available for attitude determination. These are normally aligned to match the IMU but in case this cannot be achieved, the crew have a backup method of aligning them. They would aim the scanning telescope at two stars, adjusting the attitude of the entire spacecraft until the stars are aligned with the telescope's reticule in a certain way. The by dialling in the angles: x, 209°; y, 9°; z, 349°; they would be able to align the GDCs appropriately to achieve the engine burn.

The extra notes associated with the burn are as follows: No ullage burn is required. The burn is to be made using only the B bank, the SPS control system which is known to be working perfectly. The burn is too short to make it worthwhile bringing bank A in manually. Mission Control want to observe telemetry from the spacecraft during the burn so they are giving a pair of angles to point the HGA at Earth. Note that the only the CSM weight was given in the PAD. The LM weighs in at 16,445 kg (36,256 pounds).]

072:47:34 Allen: Roger, Jim. Sounds good, and it's your computer.

072:47:41 Irwin: Roger.

[Long comm break.]

[P52 platform realignments are carried out regularly, and always before a maneuver so that everyone can have maximum trust that the spacecraft is indeed pointing in the direction they want before they light the engine. As they have throughout the translunar coast, the platform is realigned to the PTC REFSMMAT. An explanation of this attitude reference can be found in the Journal at 011:14:12.]

Public Affairs Officer - "This is Apollo Control. To recap the numbers just read up to the crew of Apollo 15 by their spacecraft communicator, there is a so-called maneuver PAD for the midcourse correction burn number 4 for the time of ignition of 73 hours, 31 minutes, 14 seconds. Total velocity change of 5.4 feet per second [1.65 m/s]. Burn time: 1 second and it'll be with the Service Propulsion System on Bank B. Rejoining so much scratchy air/ground as we drift through from one Omni antenna to the other. This is Apollo Control."

072:52:55 Scott: Okay, Houston. Gimbal angles are up [on the DSKY display]. We'll torque them on the minute.

072:53:00 Allen: Roger, 15.

[Comm break.]
072:54:13 Scott: Houston, 15. Did you get the gyro torquing angles?

072:54:17 Allen: Roger, Dave. We got them. Thank you.

072:54:22 Scott: Okay.

[Very long comm break.]

[The results from the platform realignment were that the three gimbals, x, y, and z, had to be moved (or torqued) by +0.012°, -0.051° and -0.015° respectively. The two stars used were number 10, Mirfak, in Perseus, and number 20, Dnoces.]

[Dnoces is not a generally recognised star name. Try spelling it backwards. The Apollo stars had to be distributed across the full sky and as some areas of sky have no particularly bright stars, three relatively dim stars were included. Along with two other stars in the Apollo list (3 Navi and 17 Regor) Dnoces had no common name. The Apollo 1 crew, in early training at the time, found this cumbersome and decided to give them names: Ivan (Navi) is Gus Grissom's middle name, Roger (Regor) is for Roger Chaffee and Second (Dnoces) is from Edward H. White II. Though these names were entirely unofficial, they have crept into some more orthodox astronomical sources over time. (With thanks to Henry Spencer.)]

[The PTC (Passive Thermal Control) roll is stopped and the spacecraft maneuvered to the correct attitude for the midcourse correction burn.]

[Flight Plan page 3-075.]

073:12:29 Allen: Apollo 15, Houston. Requesting the High Gain [Antenna], when convenient.

073:12:38 Scott: Roger, Joe.

[Long comm break.]

[Midcourse correction burn 4 is coming up and the crew are preparing for it. Joe Allen is reminding them that Mission Control want to monitor the burn by telemetry via the HGA. The details of the burn are entered into the computer using program 30. The actual control of the SPS engine will be carried out using P40.]

[A purge of the fuel cells should also be taking place about now. The heaters in the H2 purge line are then switched off.]

073:16:27 Allen: Apollo 15, Houston. Just a reminder to load the DAP and then go on back.

073:16:39 Scott: Roger, Joe.

[Very long comm break.]

[The DAP (Digital AutoPilot) is "loaded" simply by a string of digits entered in the DSKY, which specify the current vehicle configuration, which thruster quads to use, and what deadband to maintain. It is likely that the crew has forgotten to reconfigure the DAP for the burn.]

[Final preparations are made for the midcourse correction burn. This occurs at 073:31:14.81 GET. A small table of rules that apply to the burn are given on page 3-074 of the Flight Plan. These define the limits of attitude deviation and burn time that should cause the crew to terminate the burn. They also define how the residual velocities should be trimmed.]

Public Affairs Officer - "10 seconds to burn."

073:32:26 Scott: Okay, Houston. [Apollo] 15 with the burn status report.

073:32:30 Allen: Go ahead, Dave. This is Houston.

073:32:35 Scott: Okay. I guess you could see it was a nice smooth burn. On time. Burn time was a second. Delta-VGX at the end of the burn was .2 [feet per second]; there was no trim; residuals were plus .2, minus .1, plus .1; Delta-VC was a minus 2.3.

[The actual burn time is given in the Mission Report as 0.91 seconds. Delta-VGX is the amount of velocity still to be gained along the spacecraft's X-axis when the engine stopped. The residual figures are the differences between desired and gained velocity, as resolved into x, y and z components.]
073:32:56 Allen: Roger, Dave. We copy. And we think you're bragging, but you have a reason to. Beautiful burn.

073:33:06 Scott: It's all this nice machinery up here, Joe.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control. Midcourse maneuver number 4 was on time; burn time of 91 hundredths of 1 second. The crew reported no residuals or no trim: that is no tweaking maneuvers to take out any errors or dispersions in the burn. Apollo 15 is now 12,421 nautical miles [23,004 km] out from the Moon, approaching at a velocity of 3,974 feet per second [1,211 m/s]. [The] crew [is] coming up on a suit circuit integrity check in preparation for jettisoning the SIM bay door, that is the panel covering the Scientific Instrument Module in the - back in the Service Module. The comment from the Guidance Officer was that the burn could not have been more nominal. At 73 hours, 37 minutes Ground Elapsed Time, live on Apollo 15 air/ground, this is Apollo Control."
[Once they have the burn out of the way, their next task is for the already suited crew to don their helmets and gloves and carry out a check to ensure that the suits, and their associated plumbing, do not leak. As a safeguard, the crew will wear their suits while they jettison the SIM bay door. Also for the door jett, they must maneuver the spacecraft to a predetermined attitude.]

[The cylindrical surface of the Service Module is fabricated from 25-mm (1 inch) thick aluminium honeycomb sandwiched between two aluminium sheets. These are formed as bolt-on doors so access can be gained to equipment inside for installation and checkout. In place, the doors provide structural support for the CM and Launch Escape System, and must do so, even under multiple-g loading during boost.]

[The doors cover six sectors within the SM body, as defined by the radial structural beams which emanate from a central tunnel at the module's core. Previously, sector 1 was vacant, sometimes carrying ballast to keep the SM's centre of gravity within limits. Later, third H2 and O2 tanks were added in the wake of Apollo 13 and for the extended operations of the J-class missions (Apollos 15 - 17). Apollo 15 is the first mission to have the SIM (Scientific Instrument Module) included in this sector, a package of cameras and instruments which will photograph and measure the Moon surface and environment in unprecedented detail. Its door has a length of explosive cord around its periphery, set within a groove. To expose the SIM bay to space, this cord will be detonated and the door pushed away by further charges. The door jettison is scheduled for 74 hours.]

073:52:37 Scott: Okay; Houston, 15.

073:52:41 Allen: Roger. Go ahead.

073:52:46 Scott: Okay. Suit pressure integrity check is okay. The flow was about .3 or .4 [pounds per minute]. And we're proceeding into the setup for the SIM bay door jettison, and we'll give you a call when we get everything ready before we blow it.

073:53:03 Allen: Roger, Dave. Sounds good.

[Comm break.]

[Page 3-76 of the Flight Plan carries the procedure for the SIM bay door jettison. The first few item are verifications of some switch positions. Next, on a cue from Mission Control, power is applied to the Panoramic Camera.]

073:54:45 Irwin: Houston, this is 15. We're ready to turn Pan Camera Power, On, if you are.

073:54:54 Allen: Roger, Jim. Go ahead.

073:54:58 Irwin: Okay. It's coming on now.

[Comm break.]
073:57:14 Allen: 15, Houston.

073:57:21 Irwin: Go ahead, Houston.

073:57:23 Allen: Jim, we're not sure that the cameras are running properly. We want you to check the two SEB circuit breakers on panel 5, in, and confirm for us that you got the right talkback when you turned them On.

[Although the Panoramic Camera's power switch has been placed in the on position, Mission Control are not receiving the telemetry they expect. The first item they check are the circuit breaker for the SEB (Scientific Equipment Bay).]
073:57:39 Irwin: The two circuit breakers on panel 5 are in. Stand by. [Long pause.]

073:58:00 Irwin: Joe, there's no talkback called out here on the [line in the checklist which says] "Pan Camera Power, On."

073:58:20 Allen: Roger. We copy. And, Jim, apparently, when you turn the power on, you should get about 2 seconds of barber pole, and then back to gray. It may very well have happened and you just didn't notice it.

[These procedures are being carried out for the first time as Apollo 15 is the first mission to have the SIM bay implemented. The checklist does not mention that they are to look out for the 2 second indication on the talkback when they switch the Pan Camera on.]
073:58:44 Irwin: Okay. Stand by. [Long pause.]

073:59:19 Irwin: Houston, this is 15. Do you want us to turn the Pan Camera Power on again and check that talkback a little more carefully?

073:59:41 Allen: Jim, that sounds like a good...

073:59:43 Irwin: Houston, 15.

073:59:44 Allen: ...idea to us. Would you turn the Pan Camera Power off, wait 30 seconds, and then go back on, watching the barber - the - the barber pole indication, please.

073:59:56 Irwin: Okay, that's in work.

[Comm break.]

[Often a good idea in troubleshooting; turn it off and back on again. The crew now realises that they have not got power to the Panoramic Camera because the one of the last items in the P40 checklist was to switch the AC power in the Service Module off. This was the checklist they used for the midcourse correction.]

[Flight Plan page 3-077.]

074:01:12 Irwin: Houston, this is 15.

074:01:15 Allen: Roger. Go ahead.

074:01:19 Irwin: Roger. We have the SM/AC Power, Off, down on 180 [sic], per the P40 checklist. Should we put that power on?

074:01:28 Allen: Jim, that's affirmative. That power should be on, and that's probably our problem. Thank you.

074:01:35 Irwin: Okay. [Long pause.]

Public Affairs Officer - "This is Apollo Control. The SIM [bay] door jettison has been delayed momentarily, until the switches are in the proper position; getting power to the SIM cameras down in the SIM Bay. It's not a time critical event."

074:02:03 Scott: Okay, Houston. The SM/AC Power is on, and the Pan Cameras are [means singular] coming back to power at this time.

074:02:12 Allen: Roger.

074:02:16 Scott: And we got a barber pole for 2 seconds.

074:02:24 Allen: Roger. As advertised. Thank You, Dave.

[The camera must be powered up for two minutes before being switched to Boost.]
074:02:30 Scott: Okay. I guess that's a spot in the clean-up of the P40 that didn't get carried over in the Flight Plan.

074:02:37 Allen: We concur. [Long pause.]

074:03:08 Allen: 15, verify Map Camera, Standby, please.

074:03:17 Scott: Stand by. Okay; Mapping Camera going Standby.

074:03:23 Allen: Roger.

074:03:29 Scott: The - the Mapping Camera is in Standby now, but it required a - a change.

074:04:00 Scott: Okay; Houston, 15. I - do you want the Mapping Camera in Standby for the door jett.

[The procedure in the Flight Plan has the Mapping Camera going to Standby after the door is jettisoned. Dave seems to want to have it switched on during the event.]
074:04:06 Allen: That's affirmative, 15. Map Camera, Standby.

074:04:13 Scott: Okay. [Long pause.]

074:04:41 Irwin: Houston, would you like the SM sector AC Power, Off, for the SIM door jettison?

074:04:48 Allen: That's right, Jim. Per the checklist, the first one in step four.

074:04:56 Irwin: Okay. We just wanted to confirm it.

074:04:59 Allen: Roger. Sounds like a good idea. I think we have a bug or two in this procedure. [Long pause.]

[While life-critical procedures were simulated endlessly before the flight, less threatening details, like the interaction of the MCC-4 and the SIM bay door jettison procedures, were less well rehearsed, resulting in the problem of something being turned off when something else assumed it would be turned on.]
074:05:23 Allen: Apollo 15, Houston.

074:05:31 Scott: Go ahead, Houston,

074:05:34 Allen: Roger, Dave. We're ready for Pan Camera Power to Boost. On your step 2 there, you are Go for SIM door jettison. And we want you to watch the Fuel Cell Reactant valves after the jettison, per the checklist - just a reminder of that. Over.

[As this is a new procedure, there is a worry that the shock of the explosive cord being detonated and the SIM bay door being pushed clear will cause the valves supplying H2 and O2 reactants to the fuel cells to shut. This would disable the fuel cells if not dealt with immediately.]
074:05:58 Scott: Okay; understand. And we are in boost, and we'll give you a mark when we blow the door.

074:06:07 Allen: Roger. And we will be standing by for a description.

074:06:12 Scott: Roger. [Long pause.]

074:06:43 Irwin: Okay, Houston; 15. SIM [bay] door jett. - 3, 2, 1...

074:06:47 Irwin: Mark.

074:06:52 Scott: [I] felt a little shudder, but not too much.

[Comm break.]

[Scott, from the 1971 Technical Debrief - "In general, that was a very slight bump. You could hardly feel it. I think there's no need to suit up in the future. However, I think the suiting operation was a good exercise, because it gave us a chance to run through the descent time line. What we had planned to do was to wake up and suit up in the order in which we do it during the descent day to make sure we didn't have any problems and to see what the time line looked like. And I think we learned a few things in doing that suit up in zero-g, which Jim and I had never done in the 7LB [their model of suit]. We learned a few things and I think it helped us on descent day to get a little ahead of the time line. But as far as a requirement, would you both agree that I don't think there's any requirement to be suited to blow the SIM door? It's just not that big a shock. It was the lightest pyro charge by far of anything we had. Jim took photos of it."]

Public Affairs Officer - "This is Apollo Control. We mark the time of actual SIM [bay] door jettison at 74 hours, 6 minutes, 47 seconds. ..."
[As part of the SIM door jettison procedure, the Alpha Particle Spectrometer was switched on and, even though the instrument is not pointing at the Moon's surface, data should begin arriving at Mission Control. Except for short periods, it will stay on for virtually the rest of the mission.]

[Lunar rock samples from earlier missions were found to contain traces of uranium and thorium, two elements which through their radioactivity, decay to form radon-222 and radon-220 among other elements. As these isotopes are gaseous, they ought to be detectable from lunar orbit by their emission of alpha-particle radiation as they further decay. The Alpha Particle Spectrometer can recognise the distinctive energies of these alpha particle emissions so the data can be correlated with the spacecraft's groundtrack to identify possible areas of volcanism or other features which might cause the concentration of uranium and thorium to vary. This effect is well known on Earth where, in some areas, the cellars of houses have to be vented to prevent the build-up of radon gas, a carcinogen, within the confines of the house. Emissions from the Moon of gases like CO2 and water vapour should also be detectable as they would be expected to include a small amount of decaying radon gas.]

[Built into the same casing as the X-ray Spectrometer, the Alpha Particle Spectrometer has ten detectors and onboard calibration sources. The outputs from the detectors are added together, digitised and sent to the spacecraft's telemetry system. The depleted silicon surface-barrier detectors are optimised for particles with an energy range of 4.7 to 9.1 MeV. Collimators in front of each detector restrict the field of view to approximately 45°.]

074:08:17 Scott: Okay, Houston. We have negative visual on the SIM door as of yet. And the fuel cells looked okay. The RCS Bravo primary talkback went to barber pole and is reset, and otherwise no reaction in here.
[During the first hours of the flight, when there were regular shocks from explosive detonations, the crew had to regularly reopen valves supplying propellant to the Service Module's RCS system. Though the Fuel Cell Reactant valves have held, one of the RCS valves has closed from the shock and has had to be reset.]
074:08:34 Allen: Roger, Dave. We copy. And we assume you didn't notice any debris of any kind either.

074:08:47 Scott: Nothing in particular, Joe, and Jim's got a visual now.

074:09:18 Scott: Okay, Houston. Jim's got it out of his window, and he's taking pictures, and he says it's slowly tumbling.

074:09:26 Allen: Roger. [Long pause.]

[Jim is filming the door with the 16-mm Data Acquisition Camera. He is using magazine A and a frame rate of 12 frames per second.]
074:09:51 Allen: And, 15, just out of interest, we saw a good healthy jolt in our Doppler data down here during jett time.

074:10:02 Scott: Gee, that's very interesting because I would say that the jolt in here was very minor. [Long pause.]

[The radio signal from the spacecraft, as well as providing a communications link with Mission Control, has its frequency constantly monitored on Earth. Changes in the frequency of the received signal reflect very accurately changes in velocity along the line of sight of the ground based antenna. This is the Doppler effect, widely used in science to remotely measure motion, from speeding cars to distant stars. The spacecraft itself could not supply a frequency stable enough for this process. Instead, it synthesises its carrier from the radio signal received from Earth. This has the advantage of doubling the frequency shift caused by velocity changes and thus increasing the sensitivity of the Doppler system. Mike Dinn was among the team at the Honeysuckle Creek Tracking Station in Australia.]

[Mike Dinn, from 2001 correspondence - "The ground station generates an S-band carrier (2106.40625 MHz) which is coherently related to a very accurate and stable frequency standard. (The tracking stations had/have the best frequency standards in the world). This signal is received and locked onto and tracked by the spacecraft. The receive frequency value is then coherently multiplied by 240 over 221 and transmitted back to Earth at 2287.5 MHz (So the receive/transmit hardware combination is known as a transponder. The 240/221 ratio was/is used in aircraft IFF transponders before its space use). The received signal is locked onto and tracked at the ground station, and the difference between the transmitted and received frequencies is extracted. When the 240/221 is taken into account, the frequency difference is the two-way Doppler shift. This value was then sent from the station to network headquarters, usually at teletype speeds and usually every ten seconds.]

["The station doing the above was referred to as doing two-way tracking. Other stations in view but not transmitting also supplied useful Doppler data by locking to the receive frequency and determining its value with respect to their frequency standard. This was referred to as three-way data. At lunar distance, Honeysuckle would be typically two-way, with three-way S Band data from Goldstone, Hawaii, Guam and Carnarvon.]

["Now all the above is to do with Doppler. In addition, the S-band carrier was modulated with a digital code called a PRN type (pseudo random noise). This code was received and retransmitted from the spacecraft, and received back on Earth. There, the receive code was extracted and 'slid' past the transmit code until the two were in coincidence. The amount of slide was a measure of time and hence distance. The code was sufficently long to have no ambiguities at lunar distance, and had enough bits to give a high resolution. Also the code had the same number of ones as zeroes so there was no overall DC bias. Hence the title 'pseudo random noise'. Also modulated onto the S Band carrier were the up voice at 1.25 MHz (I think) and on the downlink were subcarriers for telemetry (1.024 Mhz) and voice/biomed (1.25 MHz). All this modulation was PHASE modulation hence the reference to PM.]

["The CSM and LM were basically the same systems but operated at different frequencies. The S-IVB was on the same frequency as the LM but of course they were never switched on at the same time. The S-IVB was tracked on some missions so that its impact point on the Moon was known and used when the lunar packages (ALSEP) detected the Moon quakes. Of course Murphy was alive and well in Apollo 13 which was the first mission where the S-IVB had the batteries to last the distance to the moon. So when the LM had to be fired up we had a lot of difficulty in coping with the two sources in the beamwidth on the same frequency. There's a whole story there that has not really been told. Hamish's book [Tracking Apollo to the Moon by Hamish Lindsay, published by Springer] is the first one to describe it.]

["In addition to the coherent PM communications both spacecraft had FM transmitters, on different frequencies but still in S-band. The CSM was used only for TV I think, but the LM one was used for TV and could also be used for telemetry and voice I think, but I'm not sure now. In later missions the lunar rover also had its own S-band communication system, but I don't think it had a transponder - just discrete up and down frequencies. The astronaut backpacks and EVA voice were relayed via the LM."]

074:10:29 Scott: Houston, 15. I guess the consensus would say that the - the shock was about one-tenth of the other pyros we've seen up to this point.
[Other pyrotechnic events to which Dave would be comparing this, are separation of the CSM from the launch vehicle and extraction of the CSM and LM from the S-IVB.]
074:10:42 Allen: Roger, Dave. We copy. Can you still see the world's largest lens cap [the SIM bay door] out the window?

074:10:56 Scott: We'll check.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control. Some distance and velocity figures. Altitude now 10,915 nautical miles [20,215 km] out from the Moon. Approaching at a velocity of 4,042 feet per second [1,232 m/s]. Successful jettison of the SIM bay door at 074:06:47; a few moments late because of getting into the right power set-up for the equipment in the SIM Bay, primarily the Mapping and Panoramic Cameras. [We] rejoin the air/ground as it proceeds toward Lunar Orbit Insertion later today. At 74 hours, 16 minutes Ground Elapsed Time; this is Apollo Control."

074:34:47 Allen: 15, this is Houston.

074:34:53 Worden: Houston, 15. Go ahead.

074:34:57 Allen: Roger. We've looked ahead in - several hours in our Flight Plan, and we have - see no further inconsistencies between the checklist and the Flight Plan like the small problem we just had with the power. So, [I] just wanted to advise you of - of this, and just follow the Flight Plan as usual. Over.

074:35:22 Worden: Okay, Joe; we'll follow the cookbook. Thank you.

074:35:25 Allen: Roger, Al.

[Very long comm break.]
Public Affairs Officer - "This is Apollo Control. Apollo 15 just crossed the 10 thousand [nautical] mile mark in its approach to the Moon. Distance now 9,975 nautical miles [18,474 km] out. Velocity; 4,092 feet per second [1,247 m/s]."
[The crew can take off their suits, also known by the designation PGA (Pressure Garment Assembly).]
074:49:47 Allen: Apollo 15, this is Houston.

074:49:52 Worden: Houston, 15. Go.

074:49:55 Allen: Roger. I've got a preliminary maneuver PAD for LOI [Lunar Orbit Insertion] when you're ready.

074:50:02 Scott: Okay; stand by one. [Pause.]

074:50:14 Irwin: Okay; stand by one.

[Comm break.]
074:51:26 Allen: And, Apollo 15, if you will give us P00 and Accept, please, we'll give you a preliminary state vector, target load, and a REFSMMAT.

074:51:37 Irwin: Okay; you've got P00 and Accept.

074:51:39 Allen: Roger.

[Once they have control of the computer, Mission Control will send up three items for the spacecraft's memory. The state vector update is based on tracking since the SIM bay door was jettisoned, giving the spacecraft a slight push. Flight controllers are working towards the crucial LOI burn and in preparation for this, they are sending up a value for the Delta-V the engine will have to achieve to enter the desired orbit around the Moon. Additionally, they have calculated the orientation the spacecraft will be in for the burn and are sending up a new REFSMMAT that matches this orientation so that the spacecraft's attitude displays will all read zero during the burn.]
074:51:40 Irwin: And I'm ready to copy the preliminary PAD, Joe.

074:51:44 Allen: Roger, Jim. Just out of curiosity, has the SIM bay door long since disappeared from view?

074:51:52 Irwin: Yes, I looked for it a few minutes ago and couldn't see it any longer.

074:51:56 Allen: Okay, thank you. And I'll go ahead with the maneuver PAD. LOI, SPS/G&N; 66244; plus 1.21, minus 0.12; 078:31:34.48; minus 2894.5, minus 0766.4, minus 0112.3; Roll, pitch and yaw, all zips. 0169.5, plus 0058.3; 2996.4, 6:40, 2990.2; 25, 267.1, 228. The rest is NA. GDC align, Vega - Deneb on zero degrees mark. Roll align, 264; 090; 349. No ullage. LM weight, 36258. Over.

074:54:06 Irwin: Roger, Joe. Readback for LOI: SPS/G&N; 66244; plus 1.21; minus 0.12; 078:31:34.48; minus 2894.5, minus 0766.4, minus 0112.3. All zips for roll, pitch and yaw. 0169.5, plus 0058.3; 2996.4, 6:40, 2990.2; 25, 267.1, 228. Vega and Deneb on the zero mark. 264; 090; 349. No ullage. LM weight, 36258.

074:55:08 Allen: That sounds good, Jim. Thank you.

[Comm break.]
Public Affairs Officer - "This is Apollo Control. To translate what that stream of numbers means, it's a preliminary maneuver PAD for the Lunar Orbit Insertion maneuver later on today. With a time of ignition as it stands now of 78 hours, 31 minutes, 34 seconds. Velocity change [retrograde that is]; of 2,996 feet per second [913 m/s]. Burn time; 6 minutes, 40 seconds, which would produce a lunar orbit for the pericynthion of 58.3 nautical miles [108 km], apocynthion of 169.5 nautical miles [313.9 km]. Apollo 15; 9,269 nautical miles [17,166 km] out from Earth [means Moon]. Velocity; 4,137 feet per second [1,261 m/s]."
[A fuller interpretation of the PAD follows:

Purpose: The maneuver is a preliminary LOI PAD which can be used to get the spacecraft into lunar orbit.

System: The burn will use the SPS engine, controlled by the spacecraft's Guidance and Navigation system.

CSM weight (Noun 47): 66,244 pounds (30,048 kg).

Pitch and yaw trim (Noun 48): +1.21° and -0.12°.

Time of ignition, Tig (Noun 33): 78 hours, 31 minutes, 34.48 seconds.

Change in velocity (Noun 81), fps (m/s): x, -2,894.5 (-882.2); y, -766.4 (-233.6); z, -112.3 (-34.2). These velocity components are all given with respect to the LVLH (Local vertical/local horizontal) frame of reference.

LVLH is a frame of reference that is relative to a line drawn from the spacecraft to the centre of the body it is orbiting, or whose sphere of influence it is in.

Diagram to explain the Local Vertical/Local Horizontal frame of reference

Imagine the point where this line intersects the planet's surface. We can further imagine a flat plane at this point parallel to the horizontal. Obviously, as the spacecraft moves across the planet, the absolute orientation of this plane keeps changing but it provides a useful reference for orbital velocity computation. In this arrangement, the plus-Z axis is along the vertical line towards the planetary centre, the plus-X axis is in the direction of orbital motion parallel to the local horizontal and the plus-Y axis is perpendicular to the orbital plane.

With this, we can make more sense of the velocity components given in the PAD. The large figure for x shows that the burn is largely retrograde, against the spacecraft's motion. The figure for y shows a degree of velocity is being added out of the spacecraft's arrival orbital plane. This will be part of ensuring it ends up in the correct plane for the landing site. The figure for z is small in comparison and is away from the Moon's centre.

Spacecraft attitude at Tig: All three values are zero for this (or "zip" in the crew's parlance). The IMU platform is to be aligned to an orientation that matches the spacecraft's attitude at LOI. This arrangement means that the FDAI (Flight Director Attitude Indicator) on the Main Display Console will read zero in all axes, providing an easy reference for pointing the spacecraft in case the crew have to take manual control. When making major engine burns near planets (especially ones without atmospheres) it is wise to make critical attitudes easy to maintain for fear of impacting the surface if a mistake is made.

HA, expected apocynthion of resulting orbit: 169.5 nautical miles (313.9 km).

HP, expected pericynthion of resulting orbit: 58.3 nautical miles (108 km).

Delta-Vt (Total velocity change): 2,996.4 fps (913.3 m/s).

Burn duration or burn time: 6 minutes, 40 seconds.

Delta-Vc: 2,990.2 fps. (911.4 m/s). This figure is entered into the EMS so that it can shut down the SPS engine in case the G&N system fails. The figure is made slightly lower than Delta-Vt so that if it is called upon to perform the cut-off, it does so early enough to take the tail-off impulse from the engine into account. A small compensation is made for the fact that the SPS engines thrust vector is slightly different to the spacecraft's X-axis as measured by the EMS accelerometer.

Sextant star: Star 25 (Acrux, in Crux, the Southern Cross) visible in sextant when shaft and trunnion angles are 267.1° and 228° respectively. This is a check that the spacecraft is in the proper attitude.

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 264°, 90°, 349°.

Since the tanks in the Service Module are full, there is no need to perform a ullage burn to settle their contents.]

074:56:51 Allen: Apollo 15, your computer.

074:56:56 Scott: Roger. Thank you.

[Very long comm break.]

[Flight Plan page 3-078.]

[Throughout the translunar coast, the IMU platform has been aligned with the PTC orientation, one which is parallel with the plane of the ecliptic (see 011:44:58 for a fuller description). Soon, they will alter that alignment to the orientation required for the LOI burn, but first, it will be realigned to PTC orientation. This will yield a measurement of the platform's drift and the state of health of its mechanisms. Immediately after, it will be aligned to the LOI orientation.]

[For the realignment, the spacecraft is maneuvered to a specific attitude so that the sextant can be pointed at the required stars. The Flight Plan also includes angles for pointing the HGA, as this is going to be a busy period and Mission Control want to acquire extra telemetry about the health of the spacecraft. Using the High Gain Antenna, a higher data rate can be achieved, which gives controllers on the ground a better look at the spacecraft.]

[The Gamma-ray Spectrometer is switched on at around 75:05. Two experiments are now sending their data to Earth, even though both are measuring only the deep space environment.]

075:15:19 Scott: Houston, 15. The first P52 is complete, and I trust you got the torquing angles.

075:15:31 Allen: Roger. Dave - We copy.

075:15:37 Scott: Okay, and processing the second one [the second P52 realignment].

075:15:41 Allen: Dave, did you copy? We got the torquing angles. Thank you.

075:15:48 Scott: Okay, and the second P52 is in work.

075:15:53 Allen: Roger.

[Long comm break.]

[The second P52 realigns the platform to the correct attitude for the LOI burn.]

075:19:15 Scott: Okay, Houston; 15. The second P52 torqued out at 75:19 [GET].
[The reference to "torqued out" generally refers to the final action of the IMU alignment, that is, repositioning the platform to its new, more accurate orientation. Simplified, the gimbals are rotated, ("torqued") to the new orientation. During the occasions where the IMU orientation is simply being updated to compensate for the inevitable mechanical drift of the platform, this "torquing" is on the order of only a fraction of a degree. However, when the platform is torqued to a new reference frame, which is the case in changing from a PTC REFSMMAT to the LOI REFSMMAT, the angular rotations can be significant.]
075:19:24 Allen: Roger.
[Very long comm break.]

[Flight Plan page 3-079.]

[At about 76:00, the crew change a lithium hydroxide canister in the B receptacle. Number 8 goes in to replace 6, which is stowed in compartment B6.]

Public Affairs Officer - "This is Apollo Control at 76 hours, 08 minutes Ground Elapsed Time. [The] Apollo 15 crew [are] rather quiet during the past hour or more as they coast in toward the Moon. They're now 6,331 nautical miles [11,725 km] out from the Moon. Velocity continuing to build up; now showing 4,401 feet per second [1,341 m/s]. Here's a call now from the crew."

076:08:41 Worden: Houston, 15

076:08:59 Allen: Go ahead 15.

076:09:04 Worden: Roger, Joe. Delta-V test, Null Bias Check. The null bias is 1 foot per second per 100 seconds.

[Al is on page G2-5 in the CSM G&C Checklist. The Delta-V Test, Null Bias Check is a test of the capability of the EMS (Entry Monitor System) to accurately meter changes in velocity.]
076:09:16 Allen: Okay, Al. We copy. Thank you.

076:09:22 Worden: Roger.

076:09:24 Allen: And, Al, you'll be interested to know that the SIM bay data we're getting so far looks very good.

076:09:33 Worden: Okay, Joe. And you'll be interested to know that there's a very thin, crescent Moon in front of us.

076:09:42 Allen: Roger. We've been suspecting that all along.

076:09:53 Worden: And it may be thin, but it's big.

[Very long comm break.]

[As seen from Earth by an observer in the northern hemisphere, the Moon is a crescent nearing first quarter. (For those not familiar with astronomical conventions, first quarter looks like a half disc.)

Diagram of Moon's phase as seen from Earth

The Sun is illuminating the right-hand, or eastern limb. But from the crew's perspective, far to the western limb, the Moon is visible only as a thin sliver and not only is it appearing larger, they are also sensing the roundness of the Moon as a great sphere with three dimensions. The amount of sunlit lunar surface visible to the crew is decreasing. In about an hour, at about 77:28, the spacecraft will enter the Moon's shadow. Then, if the they have an opportunity to look out, they would see the Moon's surface only dimly lit by reflected light from the Earth. If they were to look homeward, the crew would see the "half-Earth", centred approximately on the southern Atlantic Ocean. Later, as they pass behind the Moon out of sight of both the Earth and the Sun, they will only be sure of the Moon's presence by the lack of stars across an area of view.]

Public Affairs Officer - "This is Apollo Control at 76 hours, 11 minutes. We're in the process of a shift change in the Control Center now. Flight Director Milt Windler and his team relieving Gerry Griffin and his team of flight controllers. ... This is Apollo Control at 76 hours, 24 minutes. ..."
[Karl Henize is relieving Joe Allen at the CapCom console. The crew have half an hour exercise period. After that, Al goes to page S1-15 of the CSM Systems checklist and performs a check of the secondary glycol cooling loop before the spacecraft enters lunar orbit.]
Public Affairs Officer - "This is Apollo Control at 76 hours, 39 minutes. Apollo 15 is 5,003 nautical miles [9,266 km] from the Moon, velocity; 4,595 feet per second [1,401 m/s]. ... We'll continue to monitor live."

076:40:50 Worden: Houston, this is 15. The Pre-LOI Secondary Glycol loop check looked good.

076:40:54 Irwin: [Unintended comm] Did you turn it?

076:41:00 Henize: 15, we concur.

076:41:15 Henize: And, 15, I have a TEI-4 PAD for you any time that you have time to copy it.

[Apollo 15 is about to be committed to lunar orbit. Once in orbit, it requires firing the SPS to take the spacecraft out of lunar orbit and onto a return trajectory for Earth and the burn must be accurate to achieve this. If an emergency situation arises which entails an abort, the crew must have the PAD for such a burn so they can execute the abort successfully. However, if the abort situation includes a loss of communication with Earth, the crew need to already have a suitable PAD to hand so they can go ahead and get out of lunar orbit themselves, without help from Mission Control. Therefore, at no time in lunar orbit is there a moment when such an abort PAD will not have been read up to the spacecraft. Even before lunar orbit is achieved, Mission Control have calculated such an abort PAD in the RTCC [Real Time Computer Complex]. They have based it on an ignition after 4 orbits of the Moon and as it is for a Trans-Earth Injection, it is called a TEI-4 PAD. While the data in this PAD is still current, another will be read up to ensure that the crew always have at least one valid PAD for a return home, even if they have to do it all themselves.]
076:41:24 Worden: Okay; stand by one.

076:42:46 Worden: Okay, Karl. I'm ready to copy the TEI-4 PAD.

076:42:48 Henize: Roger. TEI-4, SPS/G&N, 40015; plus 0.59, plus 1.21; 087:12:40.06; plus 3121.1, minus 2074.0, minus 0643.0; 182, 057, 329; the rest is NA. Ullage, 4 jets, 12 seconds, and this assumes burn undocked; and no DOI; and the roll, pitch, and yaw angles assume landing site REFSMMAT. And that's all.

[An interpretation of the PAD follows:

Purpose: The burn is intended for a TEI abort on the 4th revolution about the Moon. System: It uses the SPS engine under the control of the Guidance and Navigation system.

CSM weight (Noun 47): 40,015 pounds (18,150 kg). Notice that this value is substantially less than has been seen in previous abort PADs. This is because the burn would be used only after entry into lunar orbit when roughly half of the SM propellants would have been used up on the LOI burn.

Pitch and yaw trim (Noun 48): 0.59° and 1.21°.

Time of ignition, Tig (Noun 33): 87 hours, 12 minutes, 40.06 seconds.

Change in velocity (Noun 81), fps (m/s): x, +3,121.1 (+951.3); y, -2,074.0 (-632.2); z, -643.0 (-196.0). These velocities are expressed with respect to the local vertical/local horizontal. We can see that the burn would be mostly prograde, in the same direction as the orbital motion. The large y component shows that a large impulse goes towards taking the spacecraft out of its orbital plane. There is a small z component away from the Moon's centre.

Spacecraft attitude at Tig: Roll, 182°; Pitch, 057°; Yaw, 329°. This attitude would be with respect to the landing site REFSMMAT. The IMU platform will have been aligned to that attitude after LOI.

This is an abbreviated P30 PAD so other details will be taken from a previous P30.

SPS propellants are settled in their tanks by firing the plus-X thrusters on all four quads around the Service Module for 12 seconds. The details of the burn assumes that the CSM is without the LM and that the spacecraft has not been placed in the descent orbit, one in which the low point is only 17 kilometres. See commentary at 082:26:36 for more about the descent orbit.]

076:44:39 Irwin: ...6; plus 3121.1, minus 2074.0, minus 0643.0; 182, 057, 329; 4 jets, 12 seconds, assumes burn undocked; and no DOI; landing site REFSMMAT.

076:45:01 Henize: Roger, Jim. The part [of the readback] I got was correct, but we had a loss of comm for the first part. Would you read the - about the first 10 [items] back to me again.

076:45:15 Irwin: Roger. TEI-4, SPS/G&N; 40015...

076:45:49 Irwin: Houston, this is 15. Did you get all the readback?

076:45:52 Henize: 15, this is Houston. We're having a comm problem down here on the ground and I need to check still your Noun 48 and your Noun 33.

076:46:04 Irwin: Okay. Noun 48, plus 0.59, [Noun 33] plus 1.21; 087:12:40.06.

076:46:14 Henize: That's all correct, Jim.

[Long comm break.]
076:52:16 Scott: Houston, 15.

076:52:18 Henize: 15, go ahead.

076:52:23 Scott: Roger. The LM/CM Delta-P is .5.

076:52:27 Henize: We copy.

[Long comm break.]

[This pressure difference reading is requested at the bottom of page 3-79 of the Flight Plan.]

[Flight Plan page 3-080.]

077:02:18 Scott: Houston, Apollo 15.

077:02:21 Henize: 15, go ahead.

077:02:26 Scott: Roger, Karl. All the systems checks are complete and everything looks good.

077:02:32 Henize: Very good.

[The crew have made a wide ranging systems check covering the Caution & Warning, SPS, RCS and the ECS before committing their craft to lunar orbit. They have completed this ahead of schedule.]
Public Affairs Officer - "This is Apollo Control at 77 hours, 08 minutes. Apollo 15 [is] now 3,728 nautical miles [6,904 km] from the Moon. Velocity; 4,875 feet per second [1,486 m/s]. The Flight Dynamics Officer [FIDO] just provided the Flight Director with some times. We expect Loss Of Signal [LOS] as Apollo 15 goes behind the Moon at 78 hours, 23 minutes, 31 seconds. If the Lunar Orbit Insertion burn is not performed, we should acquire the spacecraft signal at 78 hours, 46 minutes, 43 seconds; if we have a nominal LOI burn, we should acquire at 78 hours, 55 minutes, 09 seconds. The FIDO has also taken the final vectors on the S-IVB and here is the final update on the impact time and co-ordinates for the third stage of the Saturn V. Impact time: 79 hours, 24 minutes, 41 seconds; co-ordinates; .9970 south latitude, 11.8719 west longitude. And at 77 hours, 10 minutes; this is Mission Control, Houston."

Public Affairs Officer - "This is Apollo Control at 77 hours, 23 minutes. We're 1 hour away from LOS now. And Apollo 15 is 3,044 [nautical] miles [5,637 km] from the Moon. Velocity; 5,083 feet per second [1,549 m/s]. We're 1 hour, 7 minutes, 42 seconds away from the Lunar Orbit Insertion burn which will be performed behind the Moon."

077:24:31 Scott: Houston, Apollo 15.

077:24:37 Henize: 15, go ahead.

077:24:56 Henize: 15, this is Houston. Go ahead.

077:24:57 Scott: Houston, Apollo 15.

077:25:05 Henize: 15, this is Houston. Go ahead.

077:25:11 Scott: Okay. We've just made a little mission-rules review up here, and I have one question for you - relative to the circuit breaker on bank A procedure at 6 minutes. Our interpretation of the mission rules said that, if we have a bank B ball valve close prematurely, then we would leave that circuit breaker closed until shutdown, and close - or - until 10 seconds prior to shutdown, using that as our good bank rather than closing it in 6 minutes. And this is in reference to the cue card - at the bottom where it discusses one ball valve closing prematurely.

077:26:06 Henize: Stand by.

077:26:11 Scott: Okay.

077:26:46 Scott: Houston 15. I'll just repeat it once here, maybe in simpler terms. If bank B closes prematurely, then we'll leave the Pilot Valve [circuit breaker] on A closed until 10 seconds prior to cut-off, instead of at 6 minutes.

[To recap, there is an electrical short in the A control bank for the SPS, which will come on simply by arming it. For an accurately timed LOI burn, they will use the B bank to ignite the engine under computer control. Five seconds into the 6:40 duration burn, they will manually bring the A bank into use, taking it out at 6 minutes and allowing the B bank to finish the burn under computer control. Dave is concerned about the forty seconds after the A bank finishes, when the B bank alone is feeding propellant to the engine. In the unlikely, but possible, scenario of the B bank cutting out, he is suggesting allowing the A bank to operate up to 6:30 into the burn.]
077:27:05 Henize: Roger, we copy.

077:27:28 Henize: 15, Houston. We copy your question and we concur.

077:27:35 Scott: Okay, thank you. Everything else, I think, we have squared away.

077:27:41 Henize: Roger. Milt [Windler, Flight Director] says we owed you a review before every burn. Are you interested in a quick run through of what happens at LOI?

077:27:53 Scott: Sure, why not. Let's do it.

077:27:56 Henize: Okay. As I have it here, starting at T minus 2 - T minus 2 minutes, we close the Main B Pilot Valve circuit breaker. At T minus 5 seconds, we Pro[ceed, i.e. press the Proceed button on the DSKY]. Then the Delta-V Thrust A & B switches both go to normal. At T plus 5 seconds, we close the Main A Pilot Valve circuit breaker; and, at T plus 6 minutes, assuming nominal burns, we open the Main A Pilot Valve circuit breaker; and, after that we avoid PUGS manipulation. And a reminder here is - don't forget to turn on the DSE because we're vitally interested in that single-engine [means single-bank] burn performance.

[After the A bank is switched off, near the end of the burn, Mission Control do not want to the crew to make any adjustments of the mixture ratio to the engine. The control for this is labelled PUGS (Propellant Utilization Gauging System) and is on the LMP's side of the Main Display Console.]
077:28:53 Scott: Okay, Houston; we're right with you. We've just gone through that and - we understand it. Thank you.

077:28:58 Henize: Very good.

[Comm break.]
077:30:37 Henize: 15, this is Houston. If you'll give us Accept, we'll send up a new state vector.

077:30:46 Scott: Roger; you got it. P00 and Accept.

[Mission Control are uplinking a freshly computed state vector to the guidance system and are about to read up the details of the Lunar Orbit Insertion (LOI) burn.]

[Apollo 15 has entered the Moon's shadow and will re-emerge into sunlight about seven minutes before losing communications with Earth. The instruments in the SIM bay which had been working have now been switched off in preparation for LOI.]

077:30:54 Henize: Okay; and I have an LOI PAD for you whenever you're ready to copy.

077:31:01 Irwin: Okay Karl, I'm ready to copy.

077:31:04 Henize: Okay. LOI, SPS/G&N; 66244; plus 1.21, minus 0.12; 078:31:45.91; minus 2897.5, minus 0776.4, minus 0044.1; all zips for roll, all zips for pitch, all zips for yaw; 0169.6, plus 0058.4, 3000.1, 6:41, 2993.9; 25, 267.1, 22.8; the rest is NA. Set stars are Vega and Deneb; 264, 090, 349. No ullage; LM weight 36258. Single-bank burn time is 6 plus 52; and just a reminder that, if bank B doesn't burn, we are expecting you to go into lunar orbit on bank A.

[A preliminary PAD for Lunar Orbit Insertion was read up about 2½ hours ago. This is the final version and is based on more recent tracking data. The preliminary PAD would be perfectly adequate to perform the LOI task but to a lesser accuracy. There is a form on page 3-081 of the Flight Plan to write these details down prior to the data being entered under Program 30. An interpretation of the PAD follows:

Purpose: The purpose of the burn is to place Apollo 15 in an initial lunar orbit.

System: The propulsion system used for the burn is the SPS engine, under the control of the Guidance and Navigation System (with a little bit of manual help for Bank A).

CSM Weight (Noun 47): 66,244 pounds (30,048 kg).

Pitch and yaw trim (Noun 48): +1.21° and -0.12°.

Time of ignition, Tig (Noun 33): 78 hours, 31 minutes, 45.91 seconds.

Change in velocity (Noun 81), fps (m/s): x, -2,897.5 (883.2); y, -776.4 (236.6); z, -44.1 (13.4). These velocities are expressed with respect to the local vertical/local horizontal. The large negative x component shows the retrograde nature of the burn and there is a sizeable out-of-plane or y component.

Spacecraft attitude at Tig: The most recent P52 platform realignment placed the platform in the correct alignment for the LOI burn. The spacecraft will be aligned to match so the angles for the spacecraft's attitude are zero in roll, pitch and yaw.

HA, expected apocynthion of resulting orbit: 169.6 nautical miles (314.1 km).

HP, expected pericynthion of resulting orbit: 58.4 nautical miles (108.2 km).

Delta-Vt (Noun 81): 3,000.1 fps (914.4 m/s). This is the total velocity change after vector summation of the three velocities.

Burn duration or burn time: 6 minutes, 41 seconds.

Delta-Vc: 2,993.9 fps (912.5 m/s). This figure is entered into the EMS to allow backup control of the SPS engine.

Sextant star: Star 25 (Acrux, in Crux) visible in sextant when shaft and trunnion angles are 267.1° and 22.8° respectively.

GDC align stars: Stars Vega (number 36) and Deneb (number 43) to be used for GDC align if they cannot be aligned to the IMU. The angles to be used in this case are 264°, 90°, 349°.

SPS propellants do not require settling in their tanks as they are full.

The weight of the LM is 36,258 pounds (16,446 kg).

The thrust of the SPS engine is slightly reduced when propellants are fed through only one control bank so Mission Control include a burn time of 6 minutes and 52 seconds in case one bank does not work.

Mission Control finish the PAD with a reminder that if the good control bank, bank B, does not work, the crew will have to manually control bank A to achieve the burn as, unlike most other maneuvers, there will be no second chance to get this burn right. The spacecraft is in the correct position for LOI just once and the burn must happen then or not at all.]

077:33:10 Irwin: Okay, Karl. LOI PAD readback: SPS/G&N; 66244; plus 1.21, minus 0.12, 078:31:45.91; minus 2897.5, minus 0776.4, minus 0044.1; all zeros for roll, pitch, and yaw; 0169.6, plus 0058.4, 3000,1. 6:41, 2993.9; 25, 267.1, 22.8. Vega, Deneb; 264, 090, 349. No ullage. LM weight, 36258. Single-bank time, 6 plus 52.

077:34:09 Henize: That's all correct. And it's your computer now, 15.

077:34:23 Irwin: Roger. And we also understood that, if bank A doesn't light, we'll take it on in with Bank - I mean, if Bank B doesn't light, we'll take it on in with bank A, We don't need to discuss that.

077:34:31 Henize: Roger.

[Long comm break.]
Public Affairs Officer - "This is Apollo Control at 77 hours, 36 minutes. We've just passed up the final LOI burn PAD to the crew. Ignition time: 78 hours, 31 minutes, 45.91 seconds. Delta-V, or change in velocity of 3,000.1 feet per second [914.4 m/s]; burn time of 6 minutes, 41 seconds; the expected resulting orbital parameters: 169.6 by 58.4 nautical miles [314.1 by 108.2 km]. And the Flight Director has updated by a few seconds the acquisition times after LOI. The loss of signal time remains the same: 78 hours, 23 minutes, 31 seconds. The 'no burn' acquisition time is 78 hours, 46 minutes, 44 seconds. And the nominal burn acquisition time is 78 hours, 55 minutes, 03 seconds. Apollo 15 now 2,368 nautical miles [4,386 km] from the Moon. Velocity; 5,368 feet per second [1,636 m/s]. At 77 hours, 38 minutes; this is Mission Control, Houston."

077:40:41 Henize: 15, this is Houston. I have a map update, when you have time to copy.

077:40:52 Irwin: Okay. Stand by one, please.

[Long comm break.]

[By using Verb 49, Apollo 15 is being maneuvered to the correct attitude for the LOI burn. This attitude matches the platform orientation because the last P52 realignment set it to the correct attitude for LOI.]

077:49:14 Irwin: Houston, 15. I'm ready to copy the map update.

077:49:19 Henize: Roger, 15. I have four times for you, beginning with LOS. 78:23:31; 78:33:27; 78:55:03; 78:46:44. That's all.

077:49:49 Irwin: Copied. 78:23:31, 78:33:27, 78:55:03, 78:46:44.

077:50:00 Henize: That's correct.

[Very long comm break.]

[There is a box in the corner of page 3-80 of the Flight Plan for Jim to enter these times. They tell the crew when to expect certain events during their first pass behind the Moon.

Note that the burn is due to begin 1¾ minutes before the spacecraft passes the 180° line of longitude.]
Public Affairs Officer - "This is Apollo Control at 77 hours, 57 minutes. Telemetry shows that Apollo 15 has maneuvered to the maneuver attitude - [correcting himself] the burn attitude. Spacecraft is now 1,431 nautical miles [2,650 km] from the Moon and velocity has increased to 5,966 feet per second [1,818 m/s]."

Public Affairs Officer - "This is Apollo Control at 77 hours, 59 minutes. The Guidance Navigation and Control Officer [GNC] reports now that Apollo 15 has completed the sextant star check."

[Flight Plan page 3-083.]
078:03:47 Henize: 15, this is Houston. Everything is looking in good shape down here, and you have a Go for LOI.

078:03:59 Scott: Roger. Houston, 15. Understand. Go for LOI.

078:04:03 Henize: And a note here from EECOM that, due to destratification in your oxygen tanks, you may get a cryo pressure light; don't worry about it. That's during the burn.

078:04:17 Scott: Okay. Roger. Understand the cryo pressure.

[Very long comm break.]

[A characteristic of the cryogenic fluids in the Service Module is that they become stratified in zero gravity. This causes a problem in reliably monitoring the pressure of the tanks. Mixing the tank contents eliminates this problems, but is done only at specified intervals. A side effect of the LOI burn is that the acceleration induced will cause some mixing, and may confuse the quantity and pressure sensors within the tank. Houston is informing the crew that an alarm may result from this, and to disregard it.]

[The crew have been performing the P40 SPS Thrusting item in their checklist which readies the SPS engine, its control systems and other important items for the upcoming burn to place them in lunar orbit.]

Public Affairs Officer - "This is Apollo Control at 78 hours, 07 minutes. Apollo 15, now, is less than 1,000 nautical miles from the Moon; distance 985 nautical miles [1,824 km]. Velocity; 6,428 feet per second [1,959 m/s]. We're 15 minutes, 45 seconds away from Loss Of Signal as Apollo 15 will go behind the Moon. We're 23 minutes, 50 seconds away from ignition of the Lunar Orbit Insertion burn. At 78 hours, 08 minutes; this is Mission Control, Houston."

Public Affairs Officer - "This is Apollo Control at 78 hours, 10 minutes. The viewing room behind the Mission Operations Control Room is beginning to fill up now, as we near the Loss Of Signal. All of the Flight Directors are beginning to assemble in the Control Room proper."

Public Affairs Officer - "This is Apollo Control. We're 5 minutes away from Loss Of Signal now and Apollo 15 is 490 - 484 nautical miles [896 km] from the Moon. Velocity; 7,185 feet per second [2,190 m/s]."

078:20:35 Henize: 15, this is Houston.

078:20:35 Scott: Houston, 15. Go.

078:20:44 Henize: Gentlemen, everything looks perfect down here, and - all we can say is, "Have a good burn."

078:20:53 Scott: Okay, thank you. We'll see you on the other side.

078:20:56 Henize: Roger.

[Very long comm break.]

[Prior to this first Loss Of Signal (LOS), a check is made to ensure the tape in the Data Storage Equipment (DSE) is actually moving. Later, once Mission Control have reacquired a signal from the re-emerging spacecraft, the tape will be commanded by Mission Control to rewind and playback the telemetry collected from the spacecraft during the burn to allow engineers to monitor its performance.]

Public Affairs Officer - "One minute to LOS."

Public Affairs Officer - "And we've had Loss Of Signal. And at that time we showed Apollo 15 [at] 293 nautical miles [543 km] from the Moon. Velocity; 7,624 feet per second [2,324 m/s]. We'll take this line down now and come back up just prior to the no-burn acquisition time. That's 78 hours, 46 minutes, 44 seconds. We'll come up just prior to that time and stand by. At 78 hours, 24 minutes; this is Mission Control, Houston."

[Apollo 15's trajectory, established three days earlier by the S-IVB stage, has taken the spacecraft behind the Moon and out of radio communication with Earth. It will make its closest approach to the Moon's surface about midway around the far-side, where, at 078:31:46, the SPS engine will fire for 6 minutes 38 seconds in a maneuver called LOI (Lunar Orbit Insertion). This slows the spacecraft enough that it no longer has the velocity to swing back out in the general direction of Earth. Instead, it stays in the Moon's vicinity, set to orbit it until, six days later, it regains enough velocity from another SPS burn to leave. Once the LOI burn is completed, Verb 66 is executed which sets the CM state vector into the LM state vector and the spacecraft is maneuvered to an attitude which permits the S-Band High Gain Antenna to point towards Earth, which it can only do within limits set by its gimbal mounting mechanism and by the fact that the spacecraft itself must not be in the way.]

[For a fuller discussion of the factors which must be considered when calculating the LOI burn, see our separate essay on Lunar Orbit Insertion.]

078:30:22 Irwin (onboard): ...with a ... Minus 35.

078:30:25 Scott (onboard): Roger.

078:30:27 Irwin (onboard): You guys got all your oxygen?

078:30:30 Scott (onboard): Yes.

078:30:31 Irwin (onboard): Okay.

078:30:33 Worden (onboard): Minus 5 and a Pro, and a Delta-V thrust of plus 5 ... Okay. Pilot Valve, open. Everything else looks good.

078:30:47 Worden/Scott (onboard): One minute.

078:30:59 Worden (onboard): Okay. We've got ... here.

078:31:13 Worden (onboard): Average g is on.

078:31:19 Irwin (onboard): EMS Mode, Normal.

078:31:20 Scott (onboard): EMS Mode's on.

078:31:27 Worden (onboard): And we settle down for the Delta-V thrust.

078:31:29 Scott (onboard): Yes.

078:31:33 Worden (onboard): Sit back and...

078:31:34 Scott (onboard): Looks good.

078:31:38 Worden (onboard): Clear to Pro.

078:31:39 Scott (onboard): Okay. 99 Pro. Ought to be okay.

078:31:44 Worden (onboard): And the Delta-V Thrust is on.

078:31:46 Scott (onboard): Okay.

078:31:47 Worden (onboard): B valves.

078:31:48 Scott (onboard): Ignition. 1...

078:31:49 Worden (onboard): Ignition.

078:31:50 Scott (onboard): ...2, 3, 4, 5...

078:31:53 Worden (onboard): A's coming on. Okay...

078:31:54 Scott (onboard): ...there.

078:31:55 Worden (onboard): ...A valves. PC is reading about 90.

078:31:59 Scott (onboard): Okay.

078:32:01 Worden (onboard): Looks like it's running smooth.

078:32:02 Scott (onboard): ... Okay. The EMS and the Delta-V and the DSKY look good. And we have tight limits. Very smooth.

078:32:35 Scott (onboard): Okay, the DSKY and EMS look good. Still in the tight limits.

078:32:51 Scott (onboard): A minute, and you're tracking Pitch 41.

078:32:56 Worden (onboard): Hmm! Right on, huh? Okay, the pressure's running 95; holding steady.

078:33:05 Scott (onboard): Okay. Keep going on tight limits.

078:33:17 Scott (onboard): The DSKY and the EMS agree. ... watch for the loose limits?

078:33:24 Worden (onboard): Yes. I should be able to ... loose limits.

078:33:27 Scott (onboard): Okay.

078:33:30 Irwin (onboard): Five degrees, Dave. And the balance - unbalance is holding very well. About minus 180.

078:33:35 Worden (onboard): Right on the center of the roll dead band.

078:33:37 Scott (onboard): Dead on it - right on the side of the roll.

078:33:39 Worden (onboard): ... on the roll.

078:33:40 Scott (onboard): Not even on the side. It's only at 4 degrees.

078:33:51 Worden (onboard): We have a Pitch 34. It'll probably stretch out after we go to the single bank insertion.

078:33:57 Scott (onboard): Yes.

078:33:59 Worden (onboard): Any ... loose limits?

078:34:03 Scott (onboard): DSKY and EMS agree pretty well.

078:34:15 Worden (onboard): The DSKY and the EMS are about 12 feet per second difference - is all. That's pretty good.

078:34:21 Scott (onboard): Mm-hmm.

078:34:23 Worden (onboard): ... still no loose limits?

078:34:30 Scott (onboard): That view meter's not even registering.

078:34:50 Worden (onboard): Did you get your watch started on time, Jimmer?

078:34:52 Irwin (onboard): We'll find out.

078:34:54 Worden (onboard): No, I mean, did you?

078:34:55 Irwin (onboard): Yes.

078:34:57 Worden (onboard): Okay, because we need you to tell us at 6 minutes.

078:34:59 Irwin (onboard): Yes, I will.

078:35:03 Scott (onboard): How are the pressures looking over there, Jim?

078:35:04 Irwin (onboard): Beautiful. About 170 on both.

078:35:08 Scott (onboard): Okay.

078:35:09 Worden (onboard): ... about 18?

078:35:10 Scott (onboard): No, we're about 12...

078:35:11 Irwin (onboard): PC is reading 95 and holding steady.

078:35:13 Worden (onboard): Are we 12 feet per second - difference between the EMS and Delta-V?

078:35:18 Scott (onboard): Somebody would chew his ass if it didn't.

078:35:22 Irwin (onboard): PC is creeping up just a little bit.

078:35:25 Worden (onboard): Okay, we're tracking Pitch 33.

078:35:34 Scott (onboard): Okay. Should be approaching the tight limits, Jim.

078:35:48 Irwin (onboard): Okay, you're in tight limits now. About 2½ minutes to go.

078:35:51 Scott (onboard): Okay. We're looking good here.

078:35:55 Irwin (onboard): Okay.

078:35:56 Worden (onboard): PC's about to cross over.

078:35:57 Irwin (onboard): Pc's holding about 90 - 96.

078:36:00 Worden (onboard): Okay, we've had cross over.

078:36:02 Scott (onboard): Okay.

078:36:03 Worden (onboard): It crossed a little, but mot much.

078:36:05 Irwin (onboard): Hey, listen. Your PC went up about 2 - about - 2 percent, and it's up to about 98 now.

078:36:13 Scott (onboard): Okay, the EMS and the DSKY are about l0 feet per second difference. We're at tight limits. About 2 minutes to go. G&N's tracking 638.

078:36:29 Worden (onboard): Okay.

078:36:48 Irwin (onboard): Five minutes.

078:36:50 Scott (onboard): Okay. EMS and the DSKY are within about 10 feet per second. Track at 638. Tight limits.

078:37:03 Worden (onboard): Okay. Give me a countdown at 6 minutes.

078:37:06 Irwin (onboard): Okay.

078:37:09 Scott (onboard): You want Jim to count down at 6 minutes?

078:37:10 Worden (onboard): Yes.

078:37:11 Irwin (onboard): You want me to give you a 10-second count?

078:37:13 Worden (onboard): Yes.

078:37:14 Irwin (onboard): Okay.

078:37:24 Worden (onboard): A little dead band in there in the roll?

078:37:26 Scott (onboard): Mmhmm.

078:37:28 Worden (onboard): Okay, about 10 feet per second difference between the EMS and the DSKY, and we're looking good.

078:37:33 Scott (onboard): Pc's varying between about 96 and 98. Looking good thoughl

078:37:37 Irwin (onboard): Countdown. 10, 9, 8, 7, 6, 5, 4, 3, 2, 1...

078:37:47 Irwin (onboard): 6 minutes.

078:37:48 Scott (onboard): Okay.

078:37:49 Worden (onboard): Can you reach it?

078:37:51 Scott (onboard): Pilot Valve A is out. PC is down to 94.

078:37:54 Worden (onboard): Okay, we'll need another countdown to the...

078:37:56 Scott (onboard): Yes.

078:37:57 Worden (onboard): ...shutdown then.

078:37:58 Scott (onboard): Yes.

078:38:00 Worden (onboard): Okay. Can you reach them there, Dave?

078:38:01 Scott (onboard): Yes. About 20 seconds to go.

078:38:06 Worden (onboard): You've got 10 seconds overburn, don't forget.

078:38:08 Scott (onboard): Yes.

078:38:15 Irwin (onboard): Start the countdown?

078:38:17 Scott (onboard): Yes, looks good.

078:38:19 Irwin (onboard): 10, 9, 8, 7, 6, 5, 4, 3, 2, ...

078:38:27 Scott (onboard): Shutdown.

078:38:28 Worden (onboard): Okay.

078:38:29 Scott (onboard): Automatic. Okay, Jim.

078:38:32 Irwin (onboard): Okay...

078:38:33 Worden (onboard): Oh, we log zero!

078:38:34 Scott (onboard): Look at that.

078:38:35 Worden (onboard): We'll burn them.

078:38:36 Scott (onboard): ... Look at that, pal!

078:38:37 Irwin (onboard): Did you...

078:38:38 Worden (onboard): Oh, I didn't...

078:38:39 Scott (onboard): (Laughter)

078:38:40 Irwin (onboard): Ohh!

078:38:41 Worden (onboard): ...dream any...

078:38:42 Scott (onboard): Look at that!

078:38:43 Worden (onboard): Jim, Jim. Let's clean it up, Jim.

078:38:44 Irwin (onboard): Okay...

078:38:45 Scott (onboard): But whoo.

078:38:46 Irwin (onboard): Stand by for gimbal motors, Al.

078:38:47 Scott (onboard): Fantastic!

078:38:51 Irwin (onboard): Stand by for gimbal motors.

078:38:52 Worden (onboard): I thought I just gave you one.

078:38:53 Irwin (onboard): I don't see it.

078:38:54 Worden (onboard): I'll try it again. All right, number one coming off.

078:38:59 Irwin (onboard): One, two...

078:39:02 Worden (onboard): Two's...

078:39:04 Irwin (onboard): ...three, four. Okay. TVC Servo Power 1 and 2, Off.

078:39:09 Worden (onboard): Off.

078:39:11 Irwin (onboard): Main Bus Tie's coming Off.

078:39:12 Scott (onboard): I believe it!

078:39:16 Irwin (onboard): Yes, sir, that was beautiful.

078:39:17 Scott (onboard): That was fantastic!

078:39:18 Irwin (onboard): That was beautiful.

078:39:20 Scott (onboard): That is the best burn I've ever seen and I've seen 10, I mean 11. that isn't real! I've never seen one come out that good.

078:39:29 Irwin (onboard): Well, that's just superior cunning and skill, men.

078:39:31 Scott (onboard): Yes. It's got to be. Certainly (laughter).

078:39:35 Worden (onboard): Okay, Jim. Clean up the rest.

078:39:37 Irwin (onboard): Okay, you got all the data? Got the EMS data?

078:39:41 Worden (onboard): Yes, got that.

078:39:42 Irwin (onboard): EMS Function's Off.

078:39:43 Worden (onboard): Okay, Off.

078:39:44 Irwin (onboard): EMS Mode to Standby.

078:39:45 Worden (onboard): Standby.

078:39:46 Irwin (onboard): RHC and THC; locked.

078:39:48 Worden (onboard): Locked.

078:39:49 Irwin (onboard): Deadband, Max.

078:39:50 Worden (onboard): Max.

078:39:51 Irwin (onboard): Translation Control Power, Off.

078:39:52 Worden (onboard): Off.

078:39:53 Irwin (onboard): ROT Control Power Direct, two, Off.

078:39:54 Worden (onboard): Direct's Off.

078:39:55 Irwin (onboard): BMAG Mode, three, Rate 2.

078:39:56 Worden (onboard): Rate 2.

078:39:57 Irwin (onboard): CB Direct Ullage, two, open.

078:39:59 Worden (onboard): Direct Ullage, open.

078:40:00 Irwin (onboard): CB SPS Pitch 1 and Yaw 1, open.

078:40:03 Worden (onboard): Pitch 1, Yaw 1, open.

078:40:05 Irwin (onboard): SPS Pilot Valve Main B, open.

078:40:07 Worden (onboard): Main B, open.

078:40:08 Irwin (onboard): PCM Bit Rate going Low.

Public Affairs Officer - "This is Apollo Control at 78 hours, 45 minutes. We're about a minute and a half away from the no-burn Acquisition Of Signal [AOS] time. If we get a signal at that time it will mean that Apollo 15 did not perform the lunar orbit insertion burn. We're 9 minutes and 38 seconds away from acquisition time for a normal burn. Of course if we get a signal anytime between those 2 times, it will mean that Apollo 15 has had a partial lunar orbit insertion burn. We'll stand by live through this period."

Public Affairs Officer - "We're 15 seconds past the no-burn signal time now and still don't have a signal."

Public Affairs Officer - "We're a minute and a half past the no-burn acquisition time now, so it's obvious that Apollo 15 has done a burn. We'll continue to stand by live up through the nominal acquisition time. I believe Goldstone has AOS. No. That signal was from the S-IVB instrument unit, not the spacecraft. We're 3 minutes away from the nominal acquisition time now... 1 minute to go... 10 seconds. AOS on the Command Service Module. We'll allow a little time now for antenna lock up before attempting to talk to the crew but we did get Acquisition Of Signal on time, indicating a good burn."

078:56:19 Henize: 15, this is Houston. How do you read?

078:56:25 Scott: Hello, Houston, the Endeavour's on station with cargo, and what a fantastic sight.

078:56:30 Henize: Beautiful news. Romantic, isn't it?

078:56:19 Scott: Oh, this is really profound; I'll tell you, fantastic!

Public Affairs Officer - "First words from Dave Scott in lunar orbit."

[In the excellent To A Rocky Moon by Don E. Wilhelms, there is an anecdote about Apollo 14 Commander Alan Shepard who, on hearing this exchange while waiting to participate in a TV interview, revealingly grumbled, "To hell with that shit, give us details of the burn." In our review in 2004, we discussed Dave's enthusiasm further.]

[Scott - "We would get the burn data and get all that stuff. We're in good shape. We really were in good shape. If we had come around the horn and they said, 'Hey you guys got a real problem. You got a propellant leak.' Or 'You got a ...' Okay, fine. We get on with the problem. But everything's fine so why not enjoy the view?"]

[Harland - "Those test pilot guys."]

[Scott - "No. You can't pin it on test pilot guys. You have to pin it on individuals. Not because the guys are test pilots, because the guys are individuals."]

[Harland - "It's test pilot guys who weren't interested in the science on the Moon."]

[Scott - "Ah. There were a lot of test pilot guys who were interested in the science. In the beginning, you know, it goes back to the Right Stuff and the pyramid, Chuck Yeager, all these personalities and characteristics that have to do with people. And they're all different but they were classified as different kinds of people because when you started out it was spam-in-the-can and none of the real test pilots went to the Mercury program because there was a better career for them in what they liked - flying airplanes. The second group broke through in a sense in that the McDivitts and Bormans and Armstrongs or whatever said, 'Hey, this might really be good stuff.' So they went to NASA. Then we came along. I looked at it and thought, 'Gee, this is where the McDivitts and the Bormans and the Armstrongs go. Yeah, that's pretty good. Not bad. Give it a shot.' But to try and characterise an individual by group, say test pilots don't enjoy science. I think that's wrong because test pilots have to learn science and be stimulated to become scientists."]

[Harland - "You mean they have the discipline to learn science?"]

[Scott - "Sure. It's sort of like - you know I think Jim Lovell enjoyed the science part - the geology part. And that's because he learned from Lee Silver."]

[Harland - "Have you ever thought it would - because 13's CSM was - Shepard's crew were slated for 13 and got shoved to 14 to give them more time. Have you ever thought it would have been much more fitting if it had been Shepard's crew who were on 13 and had the emergency and fought their way home and Lovell's crew who ultimately went to Fra Mauro and did the exploration because it would be much more in Shepard's image to be the battling home guy."]

[Scott - "Yes, that's true. Sure."]

[Harland - "And Lovell would have been more happy to..."]

[Scott - "...do the geology, and Haise. Yeah. Lovell, Haise. They really [got into] it."]

[Harland - "If they hadn't flipped [with Shepard] at that point then Shepard would have got his triumphant flight without having to go on the Moon and do the geology stuff and Lovell would have been perfectly happy to go to the Moon and get out there."]

[Scott - "That's true. Too bad. But it's a good point. Very good point. So, yeah, people didn't really like hearing all this esoteric stuff. But it's so beautiful, you just can't avoid it. You can't pass it up. You want to tell everybody."]

[We compared Dave's evident wonder at seeing the Moon close-up to the relative disinterest apparent from the comments made by some of the crew of Apollo 8]

[Woods - "Tell me about the beauty of being on orbit looking down upon the Moon and your thought processes. You're seeing it as a visitor who has just arrived. You've got a whole day where, apart from your light flash experiment, you can spend quite a bit of time looking down at the place. You're not seeing a world out there. You're now part of that landscape. You're flying above it. You are into the landscape in a sense."]

[Scott - "Well, I think one of the things that helped us appreciate and enjoy it was having been taught to appreciate and enjoy it by the likes of Farouk El-Baz and Hal Mazursky. Don't forget Hal Mazursky. I mean Lee Silver and all the other guys too but they gave us orbital view too, if you will, Mazursky and El-Baz. And, when we got down and saw it, after having seen a lot of photos and heard a lot of discussion and even the guy who was a volcanologist, who lectured to us on the fact that it was all volcanics and not impact - lovely man, great lecturer. He was very interesting and very - when we had these briefings after dinner in the crew quarters - he was very enjoyable, as was Mazursky and El-Baz or whatever. But when you get that appreciation and understanding of what you're looking for on the surface, then you can really enjoy it. And without that, it's just like Apollo 8 - plaster-of-paris boring. Yeah, they missed the point."]

[Woods - "'Like sand my kids have played in.'"]

[Scott - "They didn't get the chance to really understand it so they said it's really boring. Even post-flight interviews, 'Nah, there's nothing there. It's boring.' That's because they didn't have an opportunity to learn it and understand it, and we did. So we come around the corner and looked down at the Moon and here's all these things we've been told about in reality. And they're much better than the photos. And you say 'Wow, look at that stuff. Wow, look at Aristarchus. Look at Humboldt, Copernicus, all that stuff. Wow!; It's even better than these guys who had lectured to us and got us stimulated. So it's all back to the guys who teach you."]

[Woods - "you are 180 degrees from the Frank Borman scenario"]

[O'Brien - "I mean he was just so damn scared of mission failure at the time. I don't know if that's a fair..."]

[Scott - "No, I don't think that's fair. Frank's not scared of anything."]

[O'Brien - "Maybe not fear of failure but just so focussed on mission success."]

[Scott - "You have to look at the situation and put it in historical perspective. Frank's job was to get there and get back."]

[O'Brien - "In one piece."]

[Scott - "That's the thing he had to do and Frank Borman is totally focussed on things. So the fact that there's some great scenery -and I would do the same thing - doesn't interest me. Get there, go around, make sure you don't screw up and go home. And the rest of it? Find one rock, seen them all, press on. So you gotta put it in context. But at the same time, the Apollo 8 guys really, I don't think, had an opportunity to appreciate - maybe they were so focussed on starting and stopping the engine, which is about what they had to do, that they never had a chance to get into it."]

[Woods - "Jim obviously got into it. I mean, Jim was good at verbalising even [garble] because that's the type of person that he is."]

[Scott - "Yeah. Because I think Jim was the type of person that was relaxed about it."]

[Harland - "He wasn't in command though."]

[Scott - "And that's a big difference too. Jim was there. Frank was responsible for making it work. Jim wasn't. And there's - and we've talked about that a little bit too, because the left-seat/right-seat theory is pretty interesting, which we can talk about later on. But I think Jim had the opportunity to enjoy what he saw. Frank didn't."]

[Harland - "He had the responsibility."]

[Scott - "Yeah. It goes even, without getting too far back, Apollo 7 and all the controversy on Wally. Well, Wally handled things very poorly. On the other hand, his job was to get it right, and when the commander has to get it right, the peripheral stuff has to go away. In Wally's case, a TV show? I'd have done the same thing. I wouldn't have done it the way he did it but a TV show cannot interrupt the success of the mission when you're not sure about the success of the mission. You're not sure this thing's going to work. So Borman on 8? Geeze. Boy, that's sort of an uptight kind of thing in that you want to watch everything on the spacecraft and monitor it and make sure something doesn't slip away because you're not paying attention to the spacecraft. And I would do the same thing and say, 'Man, I'm in lunar orbit now. I'm gonna watch like a hawk. Every gauge, every dial, every switch, so we don't make a mistake.'"]

078:56:49 Scott: And we've got a burn status report for you.

078:56:52 Henize: Okay. We're ready to copy whenever you're ready to give it.

078:56:58 Scott: Okay. I think our trusty pilot has a first for you on this one. Burn time was 6 plus 38, ignition was on time; the residuals were 0, 0, and 0. Delta Vc, minus 4.8; the fuel, 33.25; the oxidizer, 33.3.

078:57:31 Henize: That's a beautiful job up there.

078:57:37 Scott: And it was a very smooth burn all the way, Karl. There was not a ripple. I guess the only little thing we might comment on was that we had a little PUGS operation after 6 minutes.

[The operation of the Propellant Utilization Gauging System after 6 minutes is despite Mission Control's request that they leave it alone. The ground controllers had wanted to gather data on the operation of the engine when it is being fed by only one bank.]

[The SPS (Service Propulsion System) doesn't burn its fuel and oxidizer in perfectly accurate proportions. As a pressure fed engine, it is particularly subject to the vagaries of pressurization fluctuations, leading to uneven consumption of fuel and oxidizer. The end result is that, during a long engine burn, the cumulative effects of either the fuel or oxidizer burning in too large a quantity results in a large unbalance of propellants. Allowed to continue uncorrected, large amounts of fuel or oxidizer would be left in the tanks without the other to burn. The solution in Apollo, is to have the crew manually adjust the engine mixture ratio while the engine is burning to ensure that the propellants are being depleted equally.]

[By having quantity gauges within the tanks, and essentially, totalizers in the propellant lines, the SPS makes it possible to determine the relative quantity of propellants consumed during a particular burn. On the Main Display Console there is a meter that indicates the amount of imbalance, relative to the amount of oxidixer consumed. If the meter went outside of a particular range (too much or too little oxidizer being consumed) a crew member manually adjusts the engine mixture ratio so that propellants are consumed equally. Normally, the SPS engine mixture ratio is 1.6 but small excursions outside of this value do not significantly affect engine performance.]

[Scott, from the 1971 Technical Debrief - "That was a pretty novel burn. It all worked out pretty much as we had seen in the simulator. The only surprising things about the burn were the residuals, all of which were zero. At that point, we were convinced we had a pretty good guidance system. No trim. It was a very smooth burn. Everything worked as advertised. [To Worden] Do you have anything else on that?"]

[Worden, from the 1971 Technical Debrief - "No, I was impressed with the smoothness with which the engine came on and the smoothness with which the guidance worked. There were no abrupt changes; the gimbal motors were very smooth. It did jump around very, very slightly, but there were no big oscillations. We were right on trim when the burn started. The procedures worked fine. At 5 seconds after ignition, I pushed the circuit breaker in, and we got the second bank on. I could see the chamber pressure come up an estimated 3 percent when the second bank came on. It gave us a positive indication of the bank coming on. We pulled the circuit breaker 10 seconds before cutoff, and it shut down right on time. Dave was ready on the switches to shut down at the burn time plus 10 seconds. The burn was terminated automatically and, like Dave says, no residuals."]

[Irwin, from the 1971 Technical Debrief - "I think you got that circuit breaker at 6 minutes."]

[Scott, from the 1971 Technical Debrief - "That was the 6-minute call. That's right."]

[Irwin, from the 1971 Technical Debrief - "As for the PUGS operation, the unbalance was in normal and stayed constant at about minus 200 until crossover. After crossover, it started to increase out of the green band, so I had to give it a decrease and brought it back to normal. It looked like it needed the decrease position and was left in the decrease position for the remainder of the burn."]

[O'Brien - "Did they have to have a PUGS?"]

[Scott - "That started really early on. No, they had to have a PUGS because early on in the mixture of the propellants. If you didn't have the proper ratio, or mixture, you would get anything from a shutdown, to a bubble, to a blow-up or whatever."]

[O'Brien - "It was that sensitive to the mixture?"]

[Scott - "Pre-Block I design kind of stuff nobody ever used. But you've gotta go back and put everything in historical perspective. You say, 'Now, gosh, we can schedule all the propellant flow and balance it and pressurise it.' But the PUGS, when I first got on the program in '66, was a very big deal because they had no experience in such an engine so they didn't really understand how the mixtures would work. And the way you worked the PUGS was really pretty interesting. I don't remember it now. But I remember in the beginning that, boy, you have a single engine and you gotta have a propellant utilization system to make sure that everything is balanced, that fuel and oxidizer are balanced when they go into the chamber. Mixture ratio is very important in a rocket engine."]

[O'Brien - "When you think of it, why would you then not have a PUGS or its equivalent for the LM?"]

[Scott - "Because by the time they got the descent engines and things like that, the engineering and integration was more sophisticated in terms of everything from the valves and the chambers and the flow and the spray inside the chamber and the heating and all that, they knew a lot more about it."]

[Woods - "That was just in the 3 or 4 years between the development of the SPS and the development of the LM engines?"]

[Scott - "Yeah, sure. Just like in the beginning of Apollo, when they designed the ECS, they designed it for in-flight maintenance. And it didn't change. We still had places in the Environmental Control System where you could do an in-flight replacement. They didn't change a lot of it. So you gotta remember, in the beginning of Apollo and all these things, nobody had any experience at all with this stuff and there wasn't even time between Gemini and Apollo to incorporate what we learned in Gemini. There wasn't time. They didn't know that much about it. That's why it was in there. Of course, if you could make it closed loop, they would have but they didn't know that much about it. It's all new stuff and it had to be reliable, especially on things like Apollo 8. Gosh, I wouldn't have flown without a PUGS. Of course you can argue the other side is what if the PUGS doesn't work right? You know, but on the other hand, for the time of the decade, it was pretty clever. It gave you the comfort that somebody could watch the mixture ratio which, if it weren't right, it quits. You know, you talk about labor-intensive. Here's another example. When I flew on Gemini, we didn't have enough memory in the computer to include a re-entry program when we launched. So I had to read in from a tape the re-entry program. You say, 'Why didn't you put it on the computer?' It only had four thousands words or whatever it was. Didn't have the capability. Technology wasn't there. And so you had a lot of things the crew had to do, they don't have to do today."]

[Scott, from the 1971 Technical Debrief - "That [burn] put us in a pretty nice lunar orbit. We enjoyed the scenery and had plenty of time to get ready for DOI [Descent Orbit Insertion], and I think that's a great idea. You do the first rev to take a look at what is there. The time line was very smooth with no problems, and we got ready for the DOI.]

["One of the things I might mention that is different from the simulator is that we always use Pc (combustion chamber pressure) in the simulator for our cue to start. In the real world, a physiological cue is far better. I mean you don't have to look at the PC to know when to start the watch. When it comes on, it is on; and you know darn well the engine is on. When it is off, it is off; and you know it. That is something you cannot possibly simulate, but that is something to be aware of."]

[Irwin, from the 1971 Technical Debrief - "I might make a comment in that connection, Dave. The valve indicator actually opened about one-half second before I got any physical sensation that they were burning. I would see it move, and a fraction of a second later, I could feel the light off."]

078:57:50 Henize: Okay; we copy.

078:58:22 Scott: And Houston. After our first few minutes of looking here, I don't think we'll have any trouble at all finding new things for you for 6 days.

078:58:30 Henize: Good enough.

078:58:40 Henize: 15, Houston. We'd like to know the position of the PU valve and also the Unbalance meter reading.

078:58:57 Irwin: The Flow Valve is in decrease right now. The Unbalance is reading about -25, and I put it in the increase position for about 10 seconds after 6 min - after 6 minutes.

078:59:16 Henize: Okay, Jim. We copy.

[Very long comm break.]

[Here, Jim Irwin is mentioning that he had to decrease the amount of oxidizer going to the SPS engine during the LOI burn. The -25 reading indicates that the engine burned 25 pounds less oxidizer than would be expected if the mixture ratio of 1.6 was maintained exactly. Placing the Flow Valve to the Incr(ease) position allowed more oxidizer to flow to the engine. Other switch positions were Decr(ease) and Norm(al).]

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