This section primarily covers the eleventh day of the mission, 5 August 1971. Apollo 15's CSM (Command Service Module), Endeavour, has left the vicinity of the Moon and has begun to fall to Earth. The last burn performed by the crew, the Trans-Earth Injection burn, placed them on a path that would have had the spacecraft pass over Earth's far side at an altitude of about 35 kilometres, had the planet been devoid of atmosphere. Of course, Earth does have an extensive envelope of gas which the spacecraft will intercept, losing its momentum through the prodigious generation of heat. By that time, Endeavour will be travelling at nearly 11 kilometres per second under the pull of Earth's gravity. But now the Moon's gravity is dominant; the spacecraft is coasting at a little over 1 kilometre per second and is slowing as it continues to rise away from the Moon.
The primary objective of the day is for Al Worden to perform an EVA (Extra-Vehicular Activity) out through the main hatch and along the side of the Service Module to the SIM (Scientific Instrument Module) bay. There he will retrieve film magazines from the Panoramic and Mapping Cameras and take an opportunity to visually inspect the bay. Throughout their time in lunar orbit, the SIM bay has experienced a few problems and since it will be destroyed along with the Service Module when it re-enters the atmosphere, engineers are keen to gather as much information as they can to aid troubleshooting. The eye of a test pilot is a welcome opportunity to see if any mechanical manifestations of the symptoms exist.
This is Apollo Control. The astronauts appear to be sleeping soundly at this time, this based on the biomedical data we have on our Command Module Pilot Al Worden. And we have about 5¼ hours remaining in this sleep period. The spacecraft is in the Passive Thermal Control mode, rotating at the rate of about 3 revolutions per hour to maintain the proper thermal equilibrium, and has, at the present time, two 24 foot [7 metre] booms extended from the Service Module, one boom holding the Mass Spectrometer experiment, the other the Gamma-ray Spectrometer. Just before we said goodnight to the crew at the scheduled time in the Flight Plan of 228 hours, 50 minutes, they reported that the indicator in the spacecraft showed that the Mapping Camera had not retracted on command. After checking this, primarily with the thermal engineers to determine that there would be no problem as far as the film that's held in the camera's magazine, we elected to leave the camera deployed - it's on some rails that extend out from the SIM bay - and work with it tomorrow. It presents no serious problem. The concern initially was that perhaps, without retracting the camera and closing the SIM - the doors over the camera, that the film in the cassette, which is now exposed, would get too warm. However a check with the thermal people in the back rooms indicated that the film should - should experience no thermal problems. The temperature should remain well within acceptable limits, even with the camera and the magazine extended. And the camera was left in the - in the position that it is in, and one of the things that will be attempted tomorrow is to determine if perhaps the doors, which close over the camera once it is retracted, are possibly jammed against it. Also one thought was that perhaps before we began the Passive Thermal Control rotation of the spacecraft, that the area of the SIM bay where the camera was located may have become quite cold, causing the problem to occur, and perhaps causing something to freeze up and stop the camera from retracting. So the present configuration of the spacecraft is with the two booms deployed 24 feet [7.3 metres], the Mapping Camera deployed, and [the spacecraft] rotating about its longitudinal axis at the rate of 3 revolutions per hour. At the present time Apollo 15 is 16,668 nautical miles [30,869 km] from the Moon, and the spacecraft velocity is 3,910 feet per second [1,192 m/s]. At 230 hours, 34 minutes; this is Apollo Control, Houston.
This is Apollo Control at 232 hours, 27 minutes Ground Elapsed Time. 3 hours, 17 minutes remaining until crew awake time. The crew of Apollo 15, asleep at this time. No word for them - from them in a couple of hours or more. Present distance from the Moon; 21,006 miles, nautical miles [38,903 km]; velocity now 3,827 feet per second [1,166 m/s]. Maroon Team of Flight Controllers settled in for the night shift. And at 232 hours, 28 minutes Ground Elapsed Time, this is Apollo Control.
This is Apollo Control; 233 hours, 26 minutes Ground Elapsed Time. Apollo 15 crew still apparently asleep as they coast homeward from the Moon. Now at 23,194 nautical miles [42,955 km] out from the Moon, approaching Earth at a velocity of 3,795 feet per second [1,157 m/s]. Slightly over two hours, 2 hours and 18 minutes remaining in the scheduled sleep period. Flight controllers on the graveyard shift, here in Mission Control, watching a playback of the television from the three EVAs.
This is Apollo Control; 234 hours, 44 minutes Ground Elapsed Time. 1 hour remaining in the Apollo 15 crew rest period. And, here in Mission Control, got a clock counting down to splash; showing now 60 hours, 26 minutes; which is tentatively the time from now until splashdown in the North Pacific just north of Hawaii on the seventh of August. Apollo 15 is now 26,130 nautical miles [48,393 km] out from the Moon, en route to Earth; velocity, 3,761 feet per second [1,146 m/s]. We'll bring that air/ground circuit live, hopefully prior to the first call to the crew in approximately an hour from now. At 234 hours, 46 minutes Ground Elapsed Time, this is Apollo Control.
This is Apollo Control at 235 hours, 45 minutes Ground Elapsed Time. And the clock has run out on the sleep period, rest period, scheduled for the crew. Spacecraft communicator Joe Allen preparing to call the crew for the wake-up call.
235:45:46 Allen: Good morning, Endeavour. This is Apollo Control in Houston, Texas, tuning the band [i.e. about to play some "wake-up music" to the crew]. Over. [Long pause.]
235:46:21 Scott: Good morning, tuning the band. This is Endeavour. Go. [Pause.]
235:46:30 Allen: Roger. Good morning, Endeavour. This is Houston with CSM consumables and a few good words about your Flight Plan, when you're ready. [Pause.]
235:46:46 Scott: Just stand by one.
235:46:48 Allen: Okay, Dave. And you troops sure start the day early up there, I must say. [Pause.]
235:46:59 Scott: Yeah, seems that way, doesn't it?
235:51:01 Scott: Okay, Houston. We've located the Flight Plan. Go ahead with your updates. [Pause.]
235:51:13 Allen: Endeavour, this is Houston. Were you calling? [Pause.]
235:51:21 Scott: Rog, Joe. We've located the Flight Plan. Go ahead with your update.
235:51:27 Allen: Okay, Dave. I guess, let me start with the CSM consumables. At 235 plus 30, RCS total, 41; quad A: 43, 40, 38, 41; H2 tank 1, 41, 40, 36; O2 tank 1, 56, 58, 45. And the only immediate other thing I have for you, Dave, is a comment on the maneuver at 236 hours - about the Gamma-ray boom retract. We'd like for you to confirm - I'll be back when...
Comm break.
235:53:31 Allen: 15, this is Houston. How do you read?
235:53:38 Scott: Last I heard was gamma-ray. Go ahead.
235:53:42 Allen: Okay. The rest of that mysterious transmission is essentially the following, Dave. We've got a funny in that gamma-ray experiment and - so we're going to - to want to modify the use of it a little bit today. It should be no major imposition, but the Flight Plan calls out for the Gamma-ray boom to be retracted at 236 hours. We'd like to modify that by saying, turn the Gain Step, Shield, Off, at that time and we'll want you to retract it about 10 minutes later. We'll give you a cue for that. Over. [Pause.]
235:54:27 Scott: Okay. Gain Step, Shield, Off, at 236 and stand by for your cue for retraction.
235:54:36 Allen: That's correct, Dave. I've got a few other good things here, but there's no hurry on any of them. [I would] be willing to stand by, if you wanted to get squared away and give me a call later, or whatever you'd like to do. It's your preference.
235:54:54 Scott: Well, let's go ahead, Joe. We're getting squared away up here.
Scott, from the 1971 Technical debrief: "It seems like, particularly with the SIM bay, that we really never had enough time to do our housekeeping. We were always busy trying to keep up with things. I'm not sure whether it was because of the amount of equipment on board or because we had to constantly pay attention to our SIM bay operations. But it seems like we were always pressed on the housekeeping. We had to eat fast, had to get ready for the next thing fast, and, in general, we never had a lot of time to sit around and wait to get to the Moon; nor did we have a lot of time to sit around and wait to get home. We always had something to do. And it was mostly because the housekeeping took a fair amount of time.
Scott (continued): "One thing we all commented on was that it would be better if, when you awaken, you ate first and took care of your cleanup activities before you got into the operational part of the day. To try and combine operations with eating sort of compromised both. A guy would be halfway through fixing a meal and he'd have to go turn on some SIM bay thing, which means you didn't do either one very efficiently. After waking up, you should eat, clean up and then go to work. You'd be more efficient.
Scott (continued): "There are a number of things you have to do in the spacecraft which aren't really called out in any time line. We have an eat period and then we have a rest period and vice versa. You can't go from an eat period to a rest period. There are a lot of things that have to be done, most of which are called out in the presleep checklist. You can't just go finish your dinner and in two minutes do the presleep checklist and go to bed. You have to have a transition period during which you chlorinate the water, change a canister, everybody take their last urination for the day, and clean things up in general. You have to have a period of time there to get ready to go to bed."
235:54:58 Allen: Okay. If you have the Flight Plan then, let me add the following. At 236 plus 45, add the step, "X-ray to On". [Pause.] And then turning over several pages...
235:55:25 Scott: Roger. 236:45; X-ray, On.
235:55:27 Allen: Okay. And turning over several pages to 241 plus 25. [Pause.]
235:55:43 Scott: Go.
235:55:44 Allen: Roger. After the step "O2 heaters 1, 2 and 3 to Auto", add "O2 tanks 1 and 2, 50 Watt Heaters, Main B, 2, to Open." And "O2 tank 3, 50 Watt Heater, Main A, 1, to Open." Over. [Long pause.]
235:56:31 Scott: Okay. 241:25; O2 Heater - or O2 Tank 1 and 2, 50 Watt Heaters, Main B to Open, and O2 Tank Heater - They're 50 Watt also? Main A, 1, Open? [Long pause.]
235:56:54 Allen: Stand by, Dave. I'm sorry about this one. Stand by.
235:57:01 Scott: Okay. [Long pause.]
235:57:26 Allen: Okay, Endeavour. Let me try that again. Had a typographical error down here. It should read "O2 Tank 1, 50 Watt Heater, Main B, 1, Open"; and "O2 Tanks 2 and 3, 50 Watt Heaters, Main A, 2, Open". Over. [Pause.]
235:57:53 Scott: Okay. O2 Tank 1, 50 Watt Heater, Main B, 1, Open; and Tanks 2 and 3, 50 Watt Heaters, Main A, 2, Open.
235:58:04 Allen: That's correct, Dave. I apologize for the slow start there. Now I've got some DAP load changes that cover the times from about 247 hours to 252 hours. And - the change is apparently because of a mis - of a mistake in the Flight Plan you have on board that we, in the meantime, have caught down here. And - so there are several deletions and additions during that time. The first one starts at 247 plus 28.
235:58:44 Scott: Go ahead, I've got it.
235:58:48 Allen: Okay. Delete your Verb 48, 11111 and X1111, and add - stand by a second. [Pause.]
235:59:09 Scott: That's twice. [Pause.]
Dave Scott and Joe Allen work well together and it is likely Dave is teasing Allen about the frequency of his pauses during these updates. Joe is reading up a revised DAP load status. These are the numbers that are entered into the computer to make the DAP operate in a desired fashion.
235:59:14 Allen: I'll be very careful from here on. Stand by. [Long pause.]
235:59:59 Allen: Okay, D.R. [i.e. David Randolph Scott] I'm ready to try it again. You've deleted at 247:28 the line with all the funny number ones, and you're supposed to delete, in the DAP load column, also that same entry. It's in the time column, I guess. And then turn the page.
236:00:15 Allen: Okay. Go to 248 hours, on the next page, and in the notes column, change the DAP load status to read 11101. And the rest is the same. And this DAP load status continues through the PTC until 251 hours. [Pause.] And the next change is at 251 hours and 4 minutes. [Long pause.]
236:01:10 Scott: Okay. 251:04, and I got the other three changes. Go ahead.
236:01:17 Allen: Okay. Delete the Verb 48 line and the DAP load over in the time column there. [Pause.]
236:01:37 Scott: Okay.
236:01:38 Allen: And the next change is at 251:47. Delete the Verb 48 line and the DAP load in its corresponding time column. [Pause.]
236:01:58 Scott: Okay. And I guess over in the notes column, we're still carrying 11101. Right?
236:02:06 Allen: That's affirm, Dave. And starting at 252 hours, your DAP load status should read 111 - Stand by. [Long pause.]
236:02:29 Allen: Okay. Let me try again. Starting... [Long pause.]
236:02:57 Allen: Okay, starting at 252 plus 00 hours, in the notes column, the DAP load status should read 11101 times 1111 [means 11101 X1111]. And this should be carried through the rest period until 261 hours. Over.
236:03:31 Scott: Okay, Joe. You were saying something there about 252:30, as we lost comm. I got the entry at 252:00. Was there any change at 252:30?
236:03:43 Allen: Negative, Dave. The change at 252:00 should just be continued through until 261 hours. And that's just the DAP - DAP load status - should be changed correspondingly through until that time. [Pause.]
236:04:05 Scott: Okay. I see. And then we're - we're just 11101 all the way.
236:04:10 Allen: That's correct. [Long pause.]
This long series of changes are really intended to make a simple change to the status of the Digital Auto Pilot, the routine in the computer that maintains the desired spacecraft attitude. The setting of the fourth bit to a zero has the effect of changing the deadband from ±5° to ±0.5°, essentially tightening up the control of the PTC rotation and maintaining it throughout the day and rest period.
236:04:29 Scott: Okay. Go ahead with your next. [Pause.]
236:04:37 Allen: Dave, that's all I've got for the time being. And I think I'd be afraid to go ahead much further, if you're really counting those times. Maybe I should start keeping score on you as well.
236:04:52 Scott: [Laughter.] Okay. [Pause.]
236:05:00 Allen: We're happy for the time being. We're - we're standing by for a crew status report at your convenience. And we'll be watching for the Gain Step Shield to come Off.
236:05:15 Scott: Okay. We'll get right back with you in about 5 or 10.
236:05:18 Allen: Thank you.
Comm break.
The discriminator in the Gamma-ray Spectrometer has been switched off and the crew are waiting for a cue from Mission Control to retract the boom on which it is mounted. Meanwhile, Al Worden stops the PTC rotation and proceeds with a P52 realignment of the spacecraft's gyroscopically stabilised guidance platform. The platform will be realigned to the orientation defined by the PTC REFSMMAT and as a reference, Al will use two stars, Aldebaran and Procyon. The amount by which the three gimbals supporting the platform must be rotated or torqued is to be reported to Earth but Mission Control can see them appear on the CM's DSKY (Display and Keyboard) as it is monitored via telemetry.
236:18:01 Allen: Endeavour, this is Houston. We'd like for you to retract the Gamma-ray boom for us, please, and we'll be watching for your torquing angles. Also, if you'd like some news reporting in the background, I have the morning news here, if you're interested in that at all. Over. [Pause.]
236:18:27 Scott: Rog. Gamma-ray going to Retract now, and stand by on the news. [Pause.]
236:18:39 Allen: Okay. Roger. You can use that for background for the P52, I guess. President Nixon in effect declared US responsibility for offensive ground combat operations in Vietnam at an end. With the draft still in limbo, Selective Service went ahead today with the lottery to determine the order in which next year's nineteen-year-olds will face military service. Secretary of State William P. Rogers plans to go to the United Nat - Nations to push for a more energetic international relief effort for East Pakistan today. The Senate Armed Services Committee completed action on a 21 billion dollar military buying bill that meets most Nixon Administration weapons requests. President Nixon and his family will fly to Manchester, New Hampshire, and then to a private island in Maine this weekend, when visits to New Hampshire also are planned by four Democratic presidential hopefuls and Republican challenger Rep - Paul N. McClosky, Jr. Predicted weather for recovery day is 2,000 feet scattered, 10 miles vis, and waves approaching 6 feet. Wind is north by northeast, 18 knots. I have a long list of baseball scores here, which I'll just glance over. In the American League, New York beat Cleveland 7 to 3. I've had a local request for the Dodgers who lost to the Astros 2 to 0. The American Classic Golf Tournament starts today at the Firestone Country Club in Akron, Ohio. And the winner will get $30,000 dollars. Sounds to me like the pay's pretty good, and I expect the hours are short. The US Pan American Team went on a fantastic Gold Medal spree yesterday, winning 17 - rather 16 of the 17 medals at stake. The only one the Americans escaped getting was the Gold Medal in weight lifting. And the total in the games, which are being held in Colombia, is 78 for the United States, 36 of them gold, and 51 for Cuba, 12 of them are gold. And I'll end with a story, comparable only to that incredible contest between the Apollo 15 All Stars and the North American Rockets. Last night in the Texas League, 21-year-old right-hander Tom Walker, pitching far Dallas-Fort Worth team, pitched a 15-inning, no-run, no-hit game against Albuquerque. He retired the last 21 men in a row. Only four Albuquerque players got on base and all of them were on walks. Walker got the first 18 batters out before he walked the first one. He threw 153 pitches in the game, and the no-hitter is an all-time record in the Texas League and may very well be an all-time record in Major League Baseball. Walker's manager told him that if he did not win the game by the end of the 15th inning, he was going to have to pull him out. Walker said his arm felt a little tired, but he felt okay, understandably. Like doing three EVAs I expect. And that's all the news for - for this morning.
236:22:42 Scott: Boy! It sounds like he's as good as our very own Blinky.
236:22:49 Allen: That may well be, Dave. I - That never occurred to me.
236:22:57 Allen: At least the equal thereof.
236:23:02 Scott: Rog. At least almost.
Comm break.
Once the P52 is out of the way, the Flight Plan calls for a period of cislunar navigation exercises. This requires Al to make a series of sightings of Earth and stars as part of his brief to be able to get Endeavour home should communication with the Manned Space Flight Network be lost. The data from these sightings are processed by program 23 (P23) in the computer. Although a box in the Flight Plan claims that this exercise "will be performed on a non-interference basis with other crew activities", both the crew and flight controllers act as if it is essential. The Flight Plan also has the P23 exercise before breakfast but, as later comm reveals, the crew are getting on with eating to they can get tidied up prior to the EVA.
236:25:17 Allen: Endeavour. We've copied the torquing angles. Thank you. And, Dave, if you can get a volunteer to work on the Mapping Camera for us, we'd like to try to pull that Mapping Camera in and get the covers closed in preparation for the EVA. We're not quite sure the position that the camera's in right now and the procedure I'll - can read up step by step, but it's basically to open the covers, try to extend the camera, we'll confirm the extension, and then we'll have you retract the camera and ultimately retract the covers. And I'll be standing by for your advice on this. Over. [Pause.]
After the final use of the Mapping Camera yesterday evening, the crew found that it would not retract into the SIM bay. After some troubleshooting before the start of the rest period, it was decided that it could be safely left out without danger to the film within its magazine as long as the spacecraft was rotating in PTC and the heat loads spread. However, the PTC has ceased and will not be restarted before Al carries out his EVA. There is some worry that the film may suffer temperature extremes.
236:26:08 Scott: Okay, Joe. We'll see if we have time to work on that. But, it's my understanding we do not have to have it retracted for the EVA. [Long pause.]
236:26:28 Allen: Dave. That's my understanding, too. I think - the main reason - for wanting to do this, if time is available and it's, o - and it's only - would be a nicety - would be it - gives us a warm feeling regarding the film. [Long pause.]
Journal contributor Dave Edwards suggests that the broken nature of Allen's comm may be due to him relaying information to the CM while listening to the back room engineers. He sorts it out in his head and gives it a second try.
236:27:41 Allen: Dave, just to complete that last statement, you're correct. We don't have to have that device retracted for the EVA. But, apparently, it - it gives the film people a nice feeling regarding their film not getting too cold or too hot. That's the reason for that.
236:28:02 Scott: Okay. Well, let us see if we can get to it.
236:28:05 Allen: Rog. Just give a whistle.
236:28:10 Scott: Okay. And we sort of flip-flopped that P23 and eat period so that we can take advantage of our setup for eating and all. And we'll get on with P23 as soon as we finish breakfast.
236:28:23 Allen: Sounds good.
Comm break.
236:29:43 Allen: Apollo 15, this is Houston. All other things being equal, troops, we'd prefer that you do the P23 before you begin the eat period, because it gives us an hour of pointed X-ray data during your eat period. [Pause.]
236:30:06 Scott: Okay, Joe; but I guess the inequality is the stowage situation in here and assuring that we can get properly prepared for the EVA. So - we'll start the P23 in probably about - oh - 5 minutes or so, because we're almost through eating. But we sort of have to take advantage of our configuration in here in order to stay with the time line later on.
236:30:29 Allen: That's fine, Dave. We understand, thank you.
Very long comm break.
As the Commander, Dave uses his situational awareness in the Command Module to ensure they keep ahead of the timeline. His motto, practised while on the Moon, is "Get ahead and stay ahead." He works effectively with the flight controllers to negotiate the best outcome for the mission and its objectives.
Meanwhile, Al begins the procedure for navigating the CSM home without Mission Control's help, using P23 and sightings on stars and Earth.
Prior to taking the sightings, he places Endeavour's attitude control to "Free" and back to "Auto". The DAP status bit that determines the deadband is set to narrow it to ±0.5°, then he manoeuvres the CSM to the optics calibration attitude. A sighting is made on star 20 (Dnoces) to provide a calibration of the spacecraft's optical system. Finally, he manoeuvres the CSM to the sighting attitude. Here he makes three sets of angle measurements from Earth's horizon to one of three stars; Bellatrix, in Orion; Pollux, in Gemini; Capella, in Auriga. These angles allow the computer to determine the spacecraft's position and velocity in space with respect to Earth.
Worden, from the 1971 Technical debrief: "We tried to follow the no-comm schedule on the P23s, and there were some periods where we couldn't follow that because of some other things going on. But, I felt that the on-the-job training on the way out was very valuable, because when we started those P23s on the way home, I had a pretty good feeling for what had to be done and how to handle that whole program. Even after the first set of P23s, we had a pretty good feeling about the computation of the onboard state vector because the ground called up and said that they weren't going to update our state vector because our vector was almost as good as theirs.
Worden (continued): "I think the reason the P23s worked out as well as they did was the fact that I'd done considerable work at MIT on their simulator practising P23s. That made a great deal of difference to me. I had a much better understanding of which horizon to look for and mark on and of how to maneuver the spacecraft with minimum impulse, which can be kind of tricky."
Scott, from the 1971 Technical debrief: "Especially with a light spacecraft."
Worden, from the 1971 Technical debrief: "Especially with light spacecraft. It is really responsive to even minimum impulse. The system of doing the P23s, the maneuvering that we did, and the procedures for going through the P23s worked even smoother in flight than it ever had in the simulator."
Scott, from the 1971 Technical debrief: "The overall concept of how the state vectors were updated and continued on board worked very well. It was obvious that we kept our onboard state vector comparable to the ground state vector all the time. There was no question that we could have completed the navigation on board and made a very acceptable, if not precise, reentry with an onboard vector all the way."
Worden, from the 1971 Technical debrief: "Yes. I definitely had that feeling.
Worden (continued): "One more comment about the P23s before we leave that area. The Earth was a very thin crescent when we did the P23s on the way back home. We had some discussion preflight about taking marks toward the limb of the crescent on the Earth. You don't want to get out too far on the limb. All the stars that were picked were pretty much in the center of the crescent. Never had any problem locating the horizon working on that part of the crescent or taking those marks which kind of surprised me. It's a lot easier than I thought it would be."
236:43:20 Allen: Endeavour this is Houston. [Pause.]
236:43:29 Scott: Go ahead.
236:43:31 Allen: Roger. I've got some information about your midcourse [correction opportunity] 5, which is scheduled to come up here [at 238:46]. We have a firm decision that there will not be a midcourse 5 maneuver required and the numbers behind that are a Gamma of minus 6.69 [degrees, with respect to the local horizon at Entry Interface]; your vacuum perigee is 18.4 [nautical miles, 34.1 km], and the midcourse 5 correction that we're showing now would be 3/10ths of a foot per second. The corresponding midcourse 7 correction runs at about 1.8 feet per second. And, based on that new information, we're wondering if you're still interested in doing the UV photography at its scheduled time, or waiting until after the - the EVA. And we're also wondering what your choice will be on the solar corona photography. Over.
The deletion of midcourse correction 5 frees up an amount of time before the EVA. Yesterday evening, Dave asked to delay a session of ultraviolet photography until after Al gets back inside. Now that more time is available, Mission Control wonder if Dave wishes to reinstate the UV session, forgetting that his original reason for delaying it was that the equipment, (UV-capable lens, film) was stowed beneath other items in preparation for the EVA. Once they begin pulling items out, they begin floating about the cabin and almost take on a life of their own.
Note that the vacuum perigee, the lowest point of their path around Earth had there been no atmosphere in the way, has dropped from last night's value of 40 km. This far out, the slightest change in their current velocity has profound influence on their final trajectory. By the same token, the inevitable error range in their knowledge of their state vector (velocity and position), leads to a substantial range of uncertainty regarding that final trajectory. As they approach Earth, the error range will narrow and the size of further midcourse corrections will become better known.
236:44:39 Scott: Okay. That's pretty fantastic guidance, ain't it? Let us - take another look at the Flight Plan here and come right back at you.
236:44:47 Allen: Okay, Dave; fine. And no hurry on - on the - on that decision. We would like the Gamma-ray [Gain] Step Shield, On, now, please. [Pause.]
236:45:06 Scott: Okay. Gamma-ray Gain Step, On.
236:45:10 Allen: Thank you. [Pause.]
236:45:15 Scott: And, Joe, I guess on the corona photography, mag R has been ex - expended. As far as the UV, is not so much a problem of time. It's a problem of stowage. It's stowed way down deep in one of Endeavour's lockers here and to get at it requires quite a bit of manipulation of bags. And that's the reason we wanted to delay that if it was possible.
236:45:41 Allen: Okay, Dave. We understand that. And that - that sounds like it's a far more reason - reasonable to delay that. The timing's not critical as far as we're concerned. We just wanted to give you a balanced workday.
236:45:58 Scott: Okay; fine. We don't mind loading up a little after the EVA, because it really saves us a lot of work in the long run. And you might wonder why we didn't put - the UV stuff somewhere else, but there's just nowhere else to put it but in it's - in its own proper little spot.
236:46:44 Allen: No, we understand. Thank you.
Very long comm break.
With the P23 exercise completed, Al manoeuvres the spacecraft to an attitude required for the second period of X-ray astronomy, this time aiming the X-ray Spectrometer at a mid-galactic latitude. This area of the celestial sphere will provide control data for subsequent measurements, essentially characterising the background flux of x-rays from space.
236:58:29 Allen: Okay, Dave. Thank you. And we see that we've got the X-ray going. We'd like for you to change the setting on the Gain Step. Give us a one-click increase, which'll move us from - the position 7 back to position 1. Over.
236:58:50 Scott: Okay. You've got a one-click increase.
236:58:56 Allen: Okay. We see it, Dave, and Jim's Bio looks clean to us down here. Thank you.
This is Apollo Control. The crew reported during the last exchange, that the - each of the three crewmen had a good seven hours sleep during the night. And also the ground advised the crew that the magnitude of midcourse number 5 - midcourse correction burn number 5, as shown by present tracking, is so small that it will be deleted. It's now showing around 3/10 of a foot per second. Meanwhile, the space flight meteorology group of the National Weather Service said this morning, that the end-of-mission weather conditions are expected to be satisfactory in the area north of Hawaii where Apollo 15 will splash down Saturday. The forecast is for scattered clouds with good visibility, east-northeast winds 15 to 20 knots, and seas to 6 feet. Temperatures will be in the upper 70's. Splashdown clock still counting, now showing 58 hours, 7 minutes to Apollo 15 splashdown. At 237 hours, 4 minutes Ground Elapsed Time, standing by on air/ground until the crew is put to bed again tonight, this is Apollo Control.
237:36:06 Allen: Rog, Dave. A couple of miscellaneous items I'd like to ask you about. First of all, the trench sends their congratulations to whoever's doing the P23 for us. The errors are less than one sigma - and they're awarding the honorary Vasco da Gama Navigation Award for excellence in this. Secondly, we're puzzling over your remark about magazine Romeo [the high-speed black and white film magazine], which you reported to us was exhausted. And we're wondering if you just read - the frame number from the mag and, if so, what it read. Over. [Long pause.]
237:36:57 Worden: Yeah. Joe, this is Al. The last reading of Romeo, I think, was 110. [Pause.]
237:37:10 Allen: Okay, Al. Thank you. And were you doing the P23 for us?
237:37:17 Worden: Si. [Pause.]
237:37:23 Allen: Okay. I'll tell you a little something about Vasco da Gama later on. Another easy item here; you're going to come up on a bat[tery] charge - I guess Bat B charge - starting at 239 hours, and we'd like to delay that to 244 hours, please.
237:37:46 Scott: Okay. Delay the Bat B charge to 244. And be advised - you've got to know that we've got best navigator in trans-Earth lunar space up here.
237:38:00 Allen: At least one of them, I'm sure.
237:38:01 Scott: In fact, the only one.
237:38:03 Allen: Rog. We copy. And, finally, I'd like to get a volunteer to take a whack at this - configuring the Map Camera properly. And it's going to be a few short steps, and if it works, great; we'll have a lot of good engineering data regarding the thermal properties of that beauty. And if it doesn't work, we're just going to turn it off and leave it. And - when somebody's ready to do that, I'll go through the steps. There are not too many.
237:38:36 Scott: Okay, Joe. Somebody'll be ready in just a few minutes.
237:46:42 Scott: Okay, Houston; Endeavour. If you want to try your camera techniques again, let's give it a whirl.
237:46:49 Allen: Okay, Endeavour. I've got five steps here, and I think it's easiest for me just to read them to you and have you carry them out rather than copying them down. And the first one - first two steps...
237:47:01 Scott: Rog.
237:47:02 Allen: ...on panel 181, verify Logic Power, Main A circuit breaker, Closed. [Pause.]
237:47:16 Scott: Okay, verified.
237:47:17 Allen: And same panel, verify Logic Power switches, two of them, to Deploy/Retract.
237:47:26 Scott: Verified.
237:47:28 Allen: Step 3 on panel 278, the Experiment Covers Deploy circuit breaker, Main A to Closed. [Pause.]
237:47:44 Scott: Verified. Closed.
237:47:47 Allen: Step 4 on panel 230, the Map Camera, verify Standby.
237:47:56 Scott: Verified to Standby.
237:47:59 Allen: Okay, and coming up on step 5 and let me read through this - and - I'll stand by for questions then, if there are some. We want the Map Camera Track to Extend; and, simultaneously, we want the Experiment Cover Map Camera/Laser Altimeter to Open, and we want those two things done simultaneously.
237:48:33 Scott: Okay. Understand. Go to Extend and open the Covers, Map Camera/Laser simultaneously.
237:48:37 Allen: Roger. And a note on that - I guess - on the Map Camera Track to Extend, we'll be watching that for about between 4 and 5 minutes or until you get a gray talkback on there. And - we think this is going to clear up our problem and if it doesn't, we're just going to turn the whole ball of wax off and go ahead and do the EVA as normally planned. Over.
237:49:13 Scott: Okay, Joe. In three seconds, we'll execute.
237:49:32 Scott: Well, I got a gray on the Mapping Camera. How 'bout that.
The talkback indicator for the Mapping Camera's Extend/Retract function is meant to show barber pole (striped) while the camera is on the move. When it reaches the limit of its travel, the talkback changes to gray. Since they tried retracting it last night, it has been barber pole. The gray indication Dave has seen means that the camera is fully out again and the short length of time taken implies that it had hardly moved in on retraction.
237:49:43 Allen: Okay; stand by. [Pause.]
237:49:53 Allen: Dave, do you have a gray on the door as well?
237:49:59 Scott: That's affirm, but I did not get a barber pole on the door. It just stayed gray.
237:50:06 Allen: Okay; that's good. That just means that it was open already.
237:50:13 Scott: Right.
237:50:15 Allen: Okay. Then that - that's worked out fine. Apparently, we were having a temperature problem with that thing before, and we're back in business just like normal. We'd like now the Mapping Camera Track to Retract, and that'll take I guess about 4½ minutes. [Pause.]
237:50:38 Scott: Okay. Map Camera Track going to Retract now.
237:56:59 Allen: Endeavour, this is Houston. Be advised that because we're not going to do a midcourse 5, we'll continue the X-ray pointing to about 238 plus 30, and we'll be coming at you with a list of the steps at 238 hours that you can delete because we're not doing the midcourse.
237:57:23 Scott: Okay. Fine. [Long pause.]
237:57:44 Allen: And, Dave, could - could you have someone check the barber pole on our Map Camera, Track, to see if you have the gray-Retract indication, please.
237:58:01 Scott: Rog, Joe. I been watching it. You got about 7 minutes and 20 - 20 seconds now and it's still barber pole.
The indication means that the Mapping Camera is still stuck, likely near its extended position.
237:58:10 Allen: Okay. That's what we're showing down here. And stand by. [Long pause.]
237:58:28 Allen: Okay, Endeavour. We're satisfied with that Mapping Camera exercise. Two more requests on that. Go to Off with the Extend/Retract switch, and to Off with the Mapping Camera/Laser Altimeter Cover switch, please. And we're finished with that.
237:58:54 Scott: Okay; Extend/Retract to Off; and a Map Camera/Laser Altimeter's going of Off.
237:59:03 Allen: That's right, Dave. And a note for Al. We think that the magazine Romeo, based on the frame count you gave us, still has enough frames left to take the solar corona pictures. And we'll have some special words for Al on how he's to take those pictures. I guess, we'll delete a few of the solar corona requirements. Also, word about the PRD configuration for the EVA. Apparently, we'll want the CMP to have the PRD whose number reads 25028. And, I guess, that's the one you've been carrying, Dave. And, Jim, will - will use the one that reads 08031, but we would like to have him reconfirm this number before he starts the EVA. Over.
238:00:13 Scott: Okay. Let me get that checklist here Joe; standby. The CMP is 250 - say again.
238:00:22 Allen: Roger. We want Al to wear the PRD that's now reading 25028. That will distinguish it from the other two with no ambiguity. And Jim to take the one that begins 080, and we want him to give us the full reading off of that before he starts the EVA, though.
238:00:46 Scott: Well, we'll have to give it to you now, because it will be in the suit and we won't be able to get to it.
238:00:50 Allen: That's fine. Any time. Any time. [Long pause.]
238:01:28 Scott: Okay. The one Jim will wear will be 08037.
238:01:37 Allen: Okay, Dave. Thank you. And if you'll give us P00 and Accept, we'll let you have a new state vector.
238:01:49 Worden: Rog. You've got it.
Comm break.
Program zero-zero is the computer's 'do-nothing' state which is appropriate for those times when Mission Control were updating areas of its memory by radio link. Apollo crews usually referred to this program as P00, pronounced "Pooh" as in the classic children's character invented by A. A. Milne.
238:06:03 Scott: And, Houston; Endeavour. [Do] you want to go through the change in the Flight Plan at 238 hours, if you have it?
238:06:13 Allen: Standby. [Long pause.]
These are deletions intimated by Allen ten minutes ago.
238:06:34 Allen: Okay, Dave. This involves delaying the SIM bay turnoff until 238 hours and 30 minutes. And in detail, at 238 plus 05, delete the P30 external Delta-V, and the Verb 49 maneuver. Lines: at 238 plus 20, delete sextant star check; at 238 plus 28, delete all the steps from there starting with circuit breaker SCS, et cetera, up to 238 plus 55, ending with RHC Power Direct, two, Off, et cetera. Over.
238:07:41 Scott: All right. I got all that. Thank you.
Long comm break.
From this point, the crew can begin their preparation for the EVA. The only other item prior to that are the taking of a few images to calibrate the solar corona pictures taken earlier in the mission.
This is Apollo Control. Coming up in a few seconds, on Apollo 15's exit of the Lunar Sphere of Influence.
238:14:37 Allen: Hello, Endeavour, this is Houston.
238:14:43 Scott: Houston, Endeavour. Go.
238:14:45 Allen: Be advised at my mark, you are leaving the sphere of lunar influence; and it's downhill from here on in.
238:14:54 Allen: Mark.
238:14:59 Scott: Rog. Thank you, Joe. That's nice to know.
238:15:07 Allen: Did you notice anything there, Dave? Discontinuity in velocity or anything like that?
238:15:17 Scott: Well, Joe. That's one of the mysteries that we'll probably have keep to ourselves.
238:15:22 Allen: I was afraid of that.
Long comm break.
After 7¼ days having the Moon as its chief gravitational influence, Endeavour now "feels" the gravity of Earth as the stronger force and its velocity begins to increase. Trajectory computations are changed over to be Earth-centric and the Moon's velocity in its orbit is taken out of the reckoning.
The conversation between Joe Allen and Dave pokes gentle fun at the news media's inability to fully grasp the concepts behind this imaginary boundary. Many continued to believe that there was a physical jump felt by the crew, a belief perhaps fed by the jump in the velocity numbers due to the change in reference frame.
Woods, from 2000 correspondence: "Was this the inspiration behind this exchange?"
Scott, from 2000 correspondence: "Well, that's one of those little mysteries that we'll have to leave for future researchers....!!!! It all goes along with the culture of lunar exploration!"
238:21:56 Allen: Endeavour, this is Houston. [Pause.]
238:22:02 Scott: Go ahead.
238:22:03 Allen: Rog, Dave. We're looking down the line here towards the EVA. And the Surgeon's getting good biomed data on Al now, except one of the three EKG sensors is apparently marginal, and there's some noise creeping in. We're just wondering what your standard procedure is regarding sensoring before the EVA exercise. If he's going to resensor, it's probably no problem; if he's not planning to, maybe we ought to talk it over a little. Over.
238:22:37 Scott: Okay. We're all three all sensored, ready to go. If they have a problem, let's get it squared away right now.
238:22:45 Allen: Okay. Do you have, - Maybe Al could try pressing down on the three EKG leads, one at a time, for us; that may help us out.
238:23:01 Scott: Okay. Here we go. The upper right. [Long pause.]
238:23:17 Allen: Okay.
238:23:22 Scott: Okay. The upper center is being pressed. [Long pause.]
238:23:36 Allen: Okay.
238:23:41 Scott: Okay, the lower left. [Long pause.]
238:23:57 Allen: Okay. Stand by.
238:24:02 Scott: Okay. [Long pause.]
238:24:56 Allen: Dave, it looks to us like it's one of the two top sensors, and we're wondering how difficult it would be to reseat both of them now. [Pause.]
238:25:11 Scott: Okay. I'll tell you what we'll do. A little further down the line here, we'll take care of both of those. We'll resync them and reseat them and everything.
238:25:24 Allen: Okay, fine. Thank you.
238:25:29 Scott: And thank you for thinking ahead on that one.
This is Apollo Control. With the exiting by [the] Apollo 15 spacecraft [out] of the arbitrary and imaginary lunar sphere of influence, the displays in Mission Control, having to do with velocity and distance, switched over at that time from lunar reference to Earth reference. The crossing occurred at 238 hours, 14 minutes, 51 seconds. At this moment, Apollo 15 is 177,225 nautical miles [328,220 km] out from Earth, approaching at a velocity of 2,855 feet per second [870 m/s]. Landing clock showing 56 hours, 40 minutes until splashdown. Midcourse [Correction] 5 burn, because of its small magnitude, about three-tenths of a [foot per] second would be needed, will not be done, which allows the crew more time to take care of other items with the SIM bay equipment, do a little troubleshooting, and a little more pad time for preparing for today's EVA by Al Worden in which he will go hand over hand back to the Service Module to retrieve film cassettes from the Mapping and Panorama Cameras. At 238 hours, 31 minutes Ground Elapsed Time, this is Apollo Control.
Preparation for the EVA will begin with powering down the instruments in the SIM bay, retracting the booms and closing covers.
238:46:24 Scott: Houston, Endeavour. Can't seem to get the Mass Spec. boom all the way in and I guess Al's had a little trouble with it now and again with the barber pole being half - the talkback being half barber pole. And seems to flutter there, close to the gray position, and doesn't really come all the way in. [Pause.]
Deployment of the Mass Spectrometer's boom has been an increasing problem throughout its use. The problem is correctly suspected to be caused by the mechanism being affected by cold. The spacecraft is being held in a constant attitude and if heat from the Sun cannot get in to warm the boom's systems, they quickly radiate their heat into space.
238:46:47 Allen: Okay, Dave. We copy. Let us think about that.
238:46:53 Scott: Okay. And we're going ahead with the dumps, if that's okay? [Pause.]
238:47:05 Allen: Okay. [Long pause.]
238:47:17 Scott: And if you'd like a visual check of just exactly where that's hanging up, why we can give it to you in a couple of hours. We'll have Al go out and take a look.
238:47:26 Allen: That's not a bad idea. Does he know about this plan yet?
238:47:32 Scott: Well, I don't know. We'll check with him. Yeah, he nods his head like he'd probably be obliged to do that.
238:47:40 Allen: Okay. Break it to him gently, though.
238:47:44 Scott: Okay.
238:47:46 Allen: And, Dave. While I got you here, I do want to comment that the first change in the Flight Plan is to delete the step at 238 plus 23 that says "enable all jets." We think that there is a - a certain chance that that Map Camera may be stuck out, and we particularly don't want RCS jets A4, A2, B1 and B4 to be enabled, because they may give us trouble with that camera. [Pause.]
238:48:30 Scott: Okay. Understand, Joe. We'll scratch that step and make sure A4, A2, B1 and B4 stay off.
The four RCS thrusters mentioned are those whose exhaust would, if used, most likely impinge upon the Mapping Camera. A photograph taken of Endeavour during the rendezvous shows the relationship of this camera to these jets.
238:48:38 Allen: Okay. And I'll - Standing by to read you some more photo PADs, just at your convenience.
238:48:48 Scott: Go ahead. I've got the Flight Plan out. [Pause.]
238:48:55 Allen: Okay. If you'll turn to page 3-352, which is the Corona Window Calibration and UV photos procedures page.
238:49:11 Scott: I've got it.
238:49:15 Allen: Okay. The attitude involved in the corona photographs should read 057, 005, 025. And the time on that, 239 plus 08. And the High Gain [Antenna] numbers, pitch, minus 48; yaw, 238. [Pause.]
238:50:03 Scott: Okay. 057, 005, 025 at 239:08. Minus 48 and 238 for the High Gain.
238:50:13 Allen: That's correct, and moving down a couple of lines, the shutter speed should be changed from 1/500th to 1/125th. And change the inhibit jets line to read "damp rates for 5 minutes." CMC Mode to Free. [Long pause.]
238:50:58 Scott: Okay. Understand. Scratch inhibit jets, and substitute damp rates for 5 minutes, and then CMC, Free, and the 1/125th replaces the 1/500th on the camera.
238:51:11 Allen: That's correct, Dave. And moving down a little further, delete the line, "cycle 1 frame, change shutter" and delete the line "cycle 1 frame." And finally, change the last line, enable all jets to read, "CMC Mode, Auto." [Pause.]
238:52:44 Scott: Okay, delete line, "cycle 1 frame" and "cycle 1 frame"; and CMC Auto, replaces "Enable all jets."
238:52:52 Allen: That's correct and assuming you're going to take the UV photographs after the EVA, I have a photo PAD for that, if that assumption is correct.
238:53:06 Scott: Looks like that assumption is probably correct, Joe, and we'll take the photo PAD later on. Let us get on with corona [photography], or we won't make it.
238:57:25 Allen: Apollo 15, Houston. [Long pause.]
238:57:34 Scott: Houston, 15. Go.
238:57:36 Allen: Rog, Jim. We understand you're going to delete [means postpone] the UV photographs, but after you complete the corona window calibration, you will have to do the first step in the UV photos trans-Earth coast procedures, there. And that first step is Verb 49 maneuver to Earth UV photo attitude, and it lists the attitude there. We need this for thermal reasons.
238:58:08 Scott: Rog. We'll do that.
Long comm break.
Since the Passive Thermal Control was stopped three hours ago, the spacecraft has adopted various stable attitudes which have tended to heat one side of the spacecraft and chill the other. During the planning for the morning's activities, thought has been given to the temperature extremes sustained by Endeavour's systems, carefully balancing operational requirements with thermal ones. Mission Control want to ensure that after an extended period of pointing the X-ray Spectrometer to deep space, the heat load will be shared around the spacecraft's body. Therefore, the crew will manoeuvre to the UV photo attitude as planned even though they are not carrying out the photography. Once the SIM bay film magazines are retrieved, the thermal constraints will lessen.
239:05:50 Worden: Hey, Joe. Just a point of clarification on the backing to be used for the corona. I don't know whether you're aware or not, but the backing that fits into window 4, which is the right-hand rendezvous window, has two different mounting pads for the camera, one is 250 and the other is 80. And the 80 is pointing 12 degrees below the X-axis, and I just wanted to check and see if you wanted us - if that's the proper pad or if you wanted us to use the 80 or the 250 pad.
239:06:23 Allen: Al, use the 80. The one pointing 12 degrees above the X-axis.
239:06:30 Worden: Okay, Joe. Thank you.
Very long comm break.
The flight controllers in Mission Control are about to change shift as the Gold Team under Flight Director Gerry Griffin takes over from Milt Windler's Maroon Team. The crew will don their suits in preparation for depressurising the spacecraft and opening the hatch. Al will then go outside to retrieve film canisters from the SIM bay.
