At 86 hours into the mission, the crew of Apollo 15 have just commenced their first rest period in lunar orbit. The spacecraft is in the descent orbit; one which has a low point, or pericynthion, just to the east of the Hadley landing site, ready to deliver the Lunar Module, Falcon, to the correct position above the Moon from where it can begin its descent in 22½ hours time, on July 30, 1971, the fifth day of the Apollo 15 mission.
All the science instruments in the spacecraft's SIM (Scientific Instrument Module) bay are operating and sending data to Earth; by direct radio link when crossing the Moon's near-side, via a tape recorder called the DSE (Data Storage Equipment), when over the far-side and out of communication with Earth.
During this rest period, the Mass Spectrometer, on the end of its boom, is gathering its prime body of data as the CSM (Command/Service Module)'s attitude has been specifically set to face the instrument's inlet towards the direction of travel. This enables it to sample the lunar atmosphere with the minimum of contamination from the gases that are routinely emitted by the spacecraft. Program 20 is slowly rotating the spacecraft to keep the side that carries the SIM bay facing the Moon with the engine bell facing the direction of travel.
Only the data from the Gamma-ray Spectrometer is degraded because radiation from the plutonium-filled fuel cask (RTG or Radioisotope Thermoelectric Generator) on the still-attached LM is being registered by the instrument's detector.
This is Apollo Control; 88 hours, 19 minutes Ground Elapsed Time. Apollo 15 just went out of sight behind the Moon again. Nearing the end of the fifth lunar revolution. During the front side crossing, there were no communications from the crew of Apollo 15; apparently they're settling in for the scheduled rest period. Telemetry showed the cabin pressure holding at 5.5 pounds per square inch [37.9 kPa]. The Lunar Module Pilot was hooked up to the biomedical telemetry. His heart rate was showing around 56 beats per minute. Apollo 15 is in a 9- by 58-nautical mile [16.7- by 107.4-km] elliptical lunar orbit. Thirty five minutes until the spacecraft comes around the front side again. Flight Director Gene Kranz and the White Team is getting his 10-hour shift organized for the morning hours. Quite a few cups of coffee around the room. At 88 - 88 hours, 21 minutes Ground Elapsed Time, this is Apollo Control.
This is Apollo Control. 90 hours, 48 minutes into the mission of Apollo 15. Now nearing midpoint of the seventh lunar orbit. Some 22 seconds until Acquisition Of Signal in this front side pass on revolution number 7. During the sixth revolution there were no communications with the crew of Apollo 15. All systems look good on the ground on telemetry. A Flight Surgeon commented that the Lunar Module Pilot [Jim Irwin] - We have just had AOS or Acquisition Of Signal according to Network [one of the flight controllers positions] - At any rate, the Flight Surgeon commented that the Lunar Module Pilot, the only one of the three instrumented with the biomedical telemetry sensors, appeared to be soundly asleep. Apollo 15 is now in an 8- by 57-nautical mile [14.8 by 105.6-km] lunar orbit. Velocity; 5,454 feet per second [1,662 m/s]. Present altitude; 27.3 nautical miles [50.6 km]. It's unlikely there will be any communications with the spacecraft. And at 90 hours, 50 minutes Ground Elapsed Time; this is Apollo Control.
This is Apollo Control at 93 hours, 30 minutes Ground Elapsed Time. Apollo 15 now crossing the front side of the Moon on the eighth revolution. Some 18 minutes left during this front side pass. Spacecraft communicator Robert Parker will be calling the crew in the next minute or so, wake them up to begin the day's business, primarily, landing on the Moon. Flight Director Gene Kranz is gathering the other - from the flight controllers, the various items that he wants brought up, passed to the crew for them to think about during the far-side pass. He's now telling CapCom to give the crew a call. We'll come up live with air/ground and join this first call.
While the crew have been asleep, Mission Control have been keeping watch over the spacecraft's systems. To accomplish this during Loss of Signal (LOS) on far-side passes, the DSE records the telemetry channel as well as the SIM bay data. Mission Control remotely operates the DSE while the crew are asleep; putting it in the record mode just before LOS, then rewinding it and replaying the tape after AOS. Astronaut Bob Parker has been the overnight CapCom.
093:31:32 Parker: Apollo 15, Houston. [Long pause.]
093:32:06 Irwin: Houston, 15.
093:32:07 Parker: Good morning, Jim. We're waking up you [sic] a little early to tell you a few things before you go around the corner because you only have four minutes in the old Flight Plan. So, if you guys are awake and ready to listen, I'll give you a few words. [Pause.]
The Flight Plan indicates a wake-up time of 93:45 and LOS at about 93:49, seventeen minutes from now. Mission Control considers they need more time to talk to the crew before LOS and are rousing them 13 minutes early.
093:32:23 Irwin: Okay, Bob. Go ahead.
093:32:25 Parker: Okay. At the moment - Okay, one short one. We'd like you to go High Gain Antenna to Auto so we don't lose you just before you go around the corner there.
093:32:46 Parker: Okay...
093:32:47 Irwin: We're in Auto.
093:32:48 Parker: ...And at the moment, [Apollo] 15, you're sitting in a 58.8- by 7.6-[nautical mile, 108.8- by 14.1-km] orbit; and, at PDI [Powered Descent Initiation], we're extrapolating you to approximately 33,000 feet [10,000 metres]. This is with a plus or minus 9,000 feet [2,750 metres] on top of it, due primarily to the uncertainty of the RLS [Radius of the Landing Site from the centre of the Moon]. Because of this, we're pretty well decided we're going to do a DOI [Descent Orbit Insertion] trim, but we're holding a decision on that until after we get the [tracking] data for this pass, which we'll process, of course, while you're behind the Moon. We're talking about something like a 6-foot-per-second [1.8-m/s] burn and probably targeting for 50,000 feet [15,000 metres] at PDI. As far as the rest of the spacecraft [is concerned], all your systems look good. No problems at all during the night. We do have a Pan Camera problem, which may or may not be serious. We're going to look at it later on today after [the] Circ[ularisation burn], and we'll be coming up with a procedure for Al [Worden] for that later on in the day. A short item. We'd like a - during your eat periods if you have the time, also would like you to give us a Gain Step - on the Gamma-ray [experiment in the SIM bay] - up of 1. And we'd like to get a medication report, too, this morning. We apparently missed that last night. Over. [Pause.]
Bob Parker has packed a lot of information into this report. Most important is the intention to carry out a burn to trim their descent orbit, an orbit so named because it is from this that the LM, Falcon, will initiate its descent to the lunar surface. Soon after the DOI burn at 082:39:48, tracking data showed that the spacecraft was in a 108.9- by 17.6-km (58.8- by 9.5-nautical mile) orbit, which was expected to change to 108.5 x 16.1 km (58.6 by 8.7 nautical miles) after several revolutions of the Moon.
Across a one year period between 1966 and 67, five Lunar Orbiter spacecraft were sent to carry out photo-reconnaissance of the Moon, mostly in support of the Apollo program. Tracking data revealed that the orbits of these spacecraft were being perturbed by regions of higher density in the Moon's crust that were particularly associated with the circular maria. Subsequent analysis suggests that the majority of these mass concentrations or "mascons" are due to denser mantle material having been brought nearer the surface by the impact that formed the basins, and also by the layers of dense basalt which fill these basins to form the maria. Mascons have a profound effect on lunar orbits and complicate the mission planning process for Apollo because, over a remarkably short time, the orbit's shape becomes increasingly elliptical, and would eventually intersect the surface if unchecked.
As later high-precision gravity maps of the Moon would reveal, Apollo 15 happens to be orbiting over two of the most intense mascons, those associated with Mare Serenitatis and Mare Imbrium. Overnight, the orbit's pericynthion has dropped further than expected, to 14.1 km (7.6 nautical miles). At this altitude the landscape is whizzing beneath them at nearly 7° per second.
Compounding their dropping pericynthion is the problem of knowing where the landing site actually is! The latitude and longitude of Hadley is known quite well, though not as well as for previous landing sites as only medium resolution imagery from Lunar Orbiter probes is available. However, the distance of the landing site from the Moon's centre (Radius of Landing Site or RLS) is known to only plus or minus 2,750 metres (9,000 feet). If the controllers were to leave the orbit alone, they estimate an altitude of about 10,000 metres (33,000 feet) at the time Falcon begins its powered descent to the Moon.
David Woods, from 1999 correspondence with Scott: "Why did [the pericynthion of the descent orbit] have to be restored to 50,000 feet? I imagine this was done to allow the descent to occur as planned so that the computer would be dealing with well known situations and expected numbers from the landing radar and because it was what you had trained for. However, I wonder if another reason might have been to allow greater clearance over the mountains during the approach."
Scott, from 1999 correspondence: "50,000 feet was the point at which the overall descent trajectory, maneuver plan, sequence of descent guidance algorithms, and other procedures, including landing radar, were initiated. The mountain clearance occurred later, and was not a factor in the 50,000 feet initiation point."
Scott, from the 1971 Technical debrief: "We expected a long time ago, I think during the data priority meetings, [that we would] see some orbital perturbations out of plane due to the mascons. We had them [Mission Planning] put in the Flight Plan an extra period of time to do a DOI trim burn, if it was required. Prior to descent day, after the DOI, just before going to bed, in order to plan the next morning, we asked what was the probability of doing the DOI trim burn, and they said very remote. The next morning, they called up and said we were going to have to do a DOI trim burn. Fortunately, we had the time allocated in the Flight Plan to do it."
Irwin, from the 1971 Technical debrief: "It seems to me that the perilune had degraded quite a bit during the night."
Scott, from the 1971 Technical debrief: "When we got up the next morning, they told us that PDI was going to be 33,000 plus or minus 9,000 feet, which meant that we could be down to 24,000 feet at PDI. ... Well, that was a cue to me that we were definitely going to do a DOI trim burn, and I expected a 6-foot-per-second burn, which we prepared to do. That threw a little glitch into our thinking that morning, because we planned that morning to try and get everything done early. Because we had run through the suited exercise good once before, we got ahead of the game there, and we were able to get that burn done. I think it should be included in the Flight Plan if there's any question at all about it. If there's a 10 percent probability that you're going to have to do it, you should probably stick it in there. You really need the time to get in the LM and get it cranked up."
Another item Bob Parker has mentioned to them is a problem with the Panoramic Camera. Houston has determined that there is a problem in the camera's velocity/height sensor, known as the "V over H" sensor. During an exposure of the film, any motion of the spacecraft over the Moon's surface would smear the image if no compensation were made by moving the film to match. The degree of compensation required depends on the altitude of the spacecraft. A low orbit makes the landscape pass by faster due to its greater proximity. The "V over H" sensor measures the rate at which image detail passes across a detector and its output provides the degree of compensation required. Mission Control will discuss it in more detail after the "Circ maneuver," a maneuver by the CSM to circularise its orbit at about 110 km (60 nautical miles) once the LM has departed.
According to the Apollo 15 Mission Report, the "V over H" sensor problem is due to poor contrast making it difficult for the sensor to detect the movement of the surface below. Several changes will be made before Apollo 16, including increasing the lens aperture, removing an infrared filter, repositioning the sensor and the addition of a larger lens hood.
093:34:28 Irwin: Okay. Copied all that. And no medication.
093:34:35 Parker: Copy. And we have a [CSM] consumable update for you as of 93:30. RCS [Reaction Control System] total was 75 [per cent remaining], quad Alpha, 76; Bravo, 75; Charlie, 74; Delta, 77; hydrogen 2, tank 1, 84 [per cent]; [tank] 2, 81; and [tank] 3, 54; oxygen 2, tank 1, 82; tank 2, 86; tank 3, 68. Over. [Pause.]
093:35:32 Irwin: Okay. Got the consumables update.
093:44:41 Parker: And, Apollo 15, Houston. You're looking good going around the horn. Systems all look good. At your convenience, while you're down the SIM bay area there, we'd like also the Mass Spec[trometer] Discriminator to High. Over.
093:44:58 Scott: Okay; understand. Mass Spec. Discriminator to High.
093:45:01 Parker: Roger.
Very long comm break.
Switching the Mass Spectrometer's Discriminator between Low and High adjusts the sensitivity of its detector.
This is Apollo Control. Just had Loss Of Signal with Apollo 15 as it passed behind the Moon near the end of the eighth revolution. During the wake-up call after the crew responded, spacecraft communicator passed up 2 or 3 items that the crew should be thinking about, such as doing the so-called DOI trim maneuver, which is an optional item shown in the Flight Plan, at 96 hours, 17 minutes. It's rather like a midcourse correction maneuver in trans-Earth or translunar coast. If required, it would be done. And apparently the pericynthion has drifted somewhat lower during the night than was anticipated. That coupled with the uncertainty in the radius of the landing site, that is the height of the landing site from the center of the Moon, there's much thought being given to doing the DOI trim maneuver to raise the pericynthion - or start of - the point at which the Power Descent Initiate or landing phase would begin - raising that point from what would be estimated to be at 33,000 [5.4 nautical miles, 10.1 km] back up to about 50,000 feet [8.2 nautical miles, 15.2 km]. [Apollo 15's] present orbit measures 7.6 nautical miles [46,000 feet, 14.1 km] pericynthion by 59 nautical miles [109.3 km] apocynthion. The magnitude in the maneuver being considered is somewhere in the ball park of 6 feet per second [1.8 m/s], being done on the far-side of the Moon to raise pericynthion. More discussion will follow during the next front side pass on the ninth revolution, which begins with AOS in 45 minutes. At 93 hours, 51 minutes Ground Elapsed Time; this is Apollo Control.
Apollo 15 has commenced its 9th orbit of the Moon and the crew is having their breakfast. Shortly after AOS, the spacecraft will be maneuvered to an attitude that permits TV pictures of the surface to be beamed to Earth.
094:05:20 Irwin (onboard): Your candy, Dave, is in that bag over there. Your breakfast is right here.
094:05:25 Scott (onboard): Thank you. You're a good guy.
094:05:27 Irwin (onboard): Well, looks - looks like it's about the best way to do it here.
094:05:57 Scott (onboard): No, 33.
094:05:59 Irwin (onboard): Is it actually a what, plus or minus...
094:06:00 Scott (onboard): What?
094:06:01 Irwin (onboard): ...9?
094:06:02 Scott (onboard): Yes.
094:06:05 Irwin (onboard): Yes; 33's not so bad, except a...
094:06:08 Scott (onboard): Plus or minus 9; that's a 24.
094:06:12 Irwin (onboard): [Garble].
094:06:19 Scott (onboard): I don't know whether we can or not. Let me ...
094:06:29 Irwin (onboard): Put a - put a 50-degree mark on the window.
094:07:58 Scott (onboard): Yes. I know it, I want to get ahead. We got - got time to do it now. I just like to get everything done we can, and I'd like to be sitting and waiting.
094:09:47 Worden (onboard): We should have turned that cabin fan off last night. It wouldn't have been so cool - been less noisy.
094:09:58 Scott (onboard): Well, I tell you, I woke up at one time - and I listened to the noise, and I thought the thing was off. I thought to myself, 'Great, somebody got up and turned the cabin fan off.'
094:10:11 Irwin (onboard): I was burning up down there. I just about got up and got the hoses ... them down there.
094:10:16 Scott (onboard): Boy, you should have done that before you went to bed. Get yourself some air.
094:10:19 Irwin (onboard): Yes.
094:10:26 Scott (onboard): Did you get any sleep, Jim?
094:10:28 Irwin (onboard): Yes, about like the first night.
094:10:31 Scott (onboard): Well, you should have got up and got the hoses then. You need your sleep, babe.
094:10:39 Irwin (onboard): Yes.
094:10:58 Scott (onboard): Huh! We're moving it. I can't believe it!
Rev 9 begins at about 094:11.
094:11:11 Scott (onboard): The [garble]! That biomed is working.
094:11:15 Irwin (onboard): Al has them.
094:11:16 Scott (onboard): Oh, thanks. Son of a gun.
094:14:07 Scott (onboard): Well, I reckon what we ought to do is the burn, and then get suited. Burn and then get suited, you know - finish up the burn. You can put on your suit; get it out of the way. Go clear out the tunnel.
094:15:58 Scott (onboard): Yes. It really is.
094:16:07 Irwin (onboard): I couldn't tell whether the spacecraft was moving or whether Dave was shifting in his couch.
094:16:24 Scott (onboard): Yes, we must have used a fair amount.
094:16:27 Irwin (onboard): Need some more? I can get it for you.
094:16:31 Scott (onboard): [Garble] any more [garble].
094:16:38 Irwin (onboard): You ready?
094:16:40 Scott (onboard): Yes. Don't push. Just let it go, Jim. Pull it out and let it - and release it. Pull the handle out.
094:16:48 Irwin (onboard): Again?
094:16:49 Worden (onboard): Just pull out - now let go. That a boy. You don't - you don't push it in. Have you been pushing it in?
094:16:55 Irwin (onboard): Sometimes it sticks.
094:16:56 Worden (onboard): No, it never - no, it - it - you - it counts up and - it has a little accumulator in there.
094:17:06 Irwin (onboard): Here.
094:17:09 Scott (onboard): Now, just pull it out and - and let it - and leave it go.
094:17:12 Irwin (onboard): Okay.
094:17:13 Scott (onboard): The accumulator builds up, and then it'll shoot you. That's where you get your measurement.
094:17:29 Scott (onboard): Take a shot of cold right here.
094:17:31 Irwin (onboard): All right.
094:17:32 Scott (onboard): [Garble] than caught short.
094:17:37 Irwin (onboard): Ready?
094:17:38 Scott (onboard): Yes.
094:17:39 Irwin (onboard): [Garble].
094:20:20 Worden (onboard): [Garble].
094:21:23 Scott (onboard): [Garble] hot chocolate I just grabbed?
094:21:25 Worden (onboard): Yes, sure.
094:21:26 Irwin (onboard): [Garble].
094:21:35 Scott (onboard): [Garble] this good stuff is for the kid's stamina.
094:22:00 Scott (onboard): That all right?
094:22:06 Irwin (onboard): The opposite end.
094:22:10 Scott (onboard): There. Eat it.
094:24:34 Irwin (onboard): Al, I'll leave some bacon squares for you.
094:24:49 Scott (onboard): [Garble] remembered.
094:24:54 Worden (onboard): [Garble].
094:24:55 Scott (onboard): 100 hours and 13 minutes, I think we ...
094:24:58 Worden (onboard): Hmm.
094:25:31 Scott (onboard): You like bacon squares? I'll leave you some, too.
094:25:35 Worden (onboard): Too much salt. Too dry and salty for a whole meal. I don't [garble].
094:27:11 Worden (onboard): Ten minutes until AOS. Huh!
094:27:15 Irwin (onboard): You going to get this PAD on the next rev?
094:27:17 Worden (onboard): Mm-hmm.
094:27:18 Scott (onboard): Al, why don't you end I switch off here when ...
094:27:24 Irwin (onboard): I'd like to take a crap if I can work it in, Dave.
094:27:28 Scott (onboard): Okay.
094:27:29 Irwin (onboard): Tell me when.
In the following announcement, the PAO announcer seems to be a minute behind as he actually speaks at 94:35 and AOS is two minutes away, not one.
This is Apollo Control; 94 hours, 34 minutes Ground Elapsed Time. Slightly over a minute before predicted acquisition of Apollo 15 as it makes the ninth lunar revolution front side pass. During this pass, we'll have Command Module television camera view of the landing site as the spacecraft swoops down to something like 7 [nautical] miles above the surface. We're awaiting word from the Network controller that we've had Acquisition Of Signal. The crew should be finishing up their breakfast meal period.
We've had Acquisition Of Signal. Let's join the air/ground for the initial communications on this ninth revolution.
094:37:28 Parker: Apollo 15, Houston. [No answer.]
094:38:01 Parker: Apollo 15, Houston. Over. [No answer.]
094:38:19 Parker: Apollo 15, Houston. Over. [Long pause.]
094:38:48 Scott: Houston, Apollo 15. You're 5 by [5, meaning loud and clear].
094:38:50 Parker: Roger. You're 5 by also. And we got three more Flight Plan updates due you, if you're ready. [Pause.]
094:39:04 Scott: Okay. Go ahead.
094:39:05 Parker: Okay. First one I'd like to mention's at 95:02 - 95:02. And it reads, in addition to those two lines on the O2 Heaters at the top of the page, we want to add a third line that says "cb O2 Tank 100 Watt Heaters, 3, Main B, Open. Panel 226." Over. [Pause.]
094:39:48 Scott: Okay; understand. "cb O2 Tank 100 Watt Heaters, 3, Main B, Open."
The oxygen tanks in the Service Module hold large quantities of O2 gas but they can only do so at extreme low temperatures and, even then, the pressures within the tank are high. The feed system that supplies O2 to the spacecraft systems is designed to operate with this high source pressure, regulating it where required. As the gas is consumed, the temperature and therefore the pressure within the tank fall. Normal operating pressure is then restored by powering a number of electric heaters inside the tanks. Manual and automatic controls are available for this.
094:39:53 Parker: Roger. And after you guys give us the PDR [means PRD or Passive Radiation Dosimeters] read-outs, we'd like to exchange the CMP and CDR PDRs because, Dave, yours appears to be malfunctioning, and they'd like to have two working ones on the surface. Do you copy?
094:40:16 Scott: Okay; understand. Exchange CMP and CDR PRDs.
094:40:21 Parker: Okay. And the next updates for the LM Activation Checklist. And while you're going - getting that, I'll give you a little update on our expectations for the DOI burn.
094:41:28 Parker: Okay. We'll delete the third line of step 2. And we'll add a step 5, which reads: 1, "LMP's Suit Isol valve to Suit Flow; Commander's Suit Isol valve to Suit Flow, for 15 seconds." And then "Suit Disconnect, for both." And then 2, is "Suit Gas Diverter, Push/Cabin." What we're doing here, Dave, is basically making sure that we're blowing any glass particles that might have settled in through the little holes into the inlet hoses. Going to blow those out. Over. [Long pause.]
The glass particles that Mission Control are worried might be in the suit hoses come from the broken pane in front of the tapemeter in the Lunar Module. Dave and Jim discovered the damage when they first entered the LM during the translunar coast at 034:33:07.
094:42:26 Scott: Okay; understand. Step 2, scratch the third line. Step 5, "LMP and CDR Suit Isolation to Suit Flow for 15 seconds," and then "Suit Disconnect, for both." And then "Suit Gas Diverter, Push/Cabin." And that sounds like a pretty good idea.
094:42:41 Parker: Okay. And, I'll give you a few clues as to what's liable to be coming up for the DOI trim burn. Currently, we're showing a 5.87 [nautical mile, 10.9 km,] perilune on rev 14, which is 35,000 feet plus or minus 9,000 [10,600 metres ±2,700 metres] with that RLS uncertainty. And what's being proposed now is not an SPS burn, because it'll be very short, but an RCS burn of 20 seconds which is 3.2 foot per second [1 m/s], which would raise us to 50,000 feet [15,240 metres]. [It] will cost us about 27 pounds of gas [12.2 kg], and we're looking at a TIG time [of ignition] of 95:56 [GET], which, you will note, is 20 minutes early - earlier than in the Flight Plan, which means we're going to have to compress some of that stuff together [meaning the checklist items prior to 95:56]. Over.
094:43:35 Scott: Okay. Understand 95:56. And looking over the Flight Plan, it looks like, had we gone on the original DOI trim, we had about 40 minutes of SIM [bay instrument] data there. Maybe we can just scratch that. [Long pause.]
094:44:06 Parker: Roger, Dave. We're just going to have to trim that SIM stuff off a little bit early, because we don't have the time right here.
094:44:15 Scott: Okay. I guess what I'm thinking is, it takes us a lot of time to go through that. Turn it on and turn it off. And, of course, we could always use time, but we'll get it. [Long pause.]
094:45:24 Parker: Dave, we don't show you turned anything on this morning; it's just a long protracted business of turning it off. And I guess, that was - used to be starting after the TV pass. And I guess that - what we're saying right now is it looks like we're going to start turning that off during or before the TV pass.
094:45:44 Scott: Okay. You're right, Bob. We'll do that; that looks good.
This last exchange may reflect the fact that it is early in the morning for the crew. Perhaps they just misread the Flight Plan. Dave may have thought there were experiments to activate before the DOI trim burn, whereas they are simply to power down most of the instruments.
094:45:47 Parker: Okay, and we'll be getting you a real [DOI trim] PAD coming up some time soon.
094:45:55 Scott: Okay; we'll be standing by. [Long pause.]
094:46:28 Parker: And, Dave, if practicable, we'd prefer to have it turned off before or after the TV, because then we can watch it being turned off; otherwise we can't see it during the TV. But you can certainly turn part of it off before and part after. [Pause.]
094:46:48 Scott: Okay; understand. We - we'll do it sometime other than the during the TV.
094:46:54 Parker: Correct.
Comm break.
The Auxiliary channel of the S-band radio system can be manually switched to carry either TV or, if in the Science position, data and telemetry from the SIM bay. Therefore, during the TV transmission, the ground cannot see how the equipment responds to being powered down.
094:48:08 Parker: Okay, Dave. And we got a few updates here for the time after the TV pass, if you're ready to copy. Some other stuff that we are moving up because of this. [Pause.]
To accommodate the earlier DOI trim maneuver, other events, which Robert Parker refers to as 'stuff,' particularly the platform realignment [P52], are being rescheduled to occur earlier than planned.
094:48:27 Scott: Okay; ready to copy. Go ahead.
094:48:30 Parker: Okay. At 95:28, we will schedule a "P52, option 3." [Pause.]
094:48:47 Scott: Okay. "P52, option 3."
094:48:49 Parker: Okay. At 9...
094:48:50 Scott: At 95:28.
094:48:51 Parker: Roger. At 95:33, we'll delete the "P00 at pitch, 033." [Pause.]
094:49:05 Scott: Okay; delete "P00 at pitch, 033" at 95:33.
094:49:09 Parker: Roger. At 95:35, we will delete "P52 option 3," and that's the one we've moved up by 7 minutes [to prepare for the early burn].
094:49:20 Scott: Roger. Go ahead.
094:49:21 Parker: Roger. And at 95:43, we will delete the "P52 option 1," because we will be staying on [the] landing site REFSMMAT.
094:49:33 Scott: Okay; very good. Go ahead.
As part of the preparation for the DOI trim, Al was originally to alter the orientation of the gyro stabilised platform at the heart of the IMU (Inertial Measurement Unit) to match the desired spacecraft attitude during the burn. This is normal for major burns as it makes it easier to monitor the spacecraft's attitude during the burn by having the FDAI (Flight Director Attitude Indicator) or "8-ball" read zero in all three axes.
The normal procedure for this is to realign the platform to the existing orientation, in this case the landing site REFSMMAT, so that a measurement of the platform's drift can be made. Then the platform is swung around to the new orientation. The P52 realignment procedure has to be carried out twice for this.
Having decided to carry out the DOI trim burn earlier, Mission Control are looking for ways to reduce the workload for the crew leading up to the burn. Since the burn is a small one and will be carried out using the RCS system, a trade-off can be made between the small magnitude of the burn, the need to aim it accurately and the time left for the crew to prepare. Therefore, they have elected to leave the IMU orientation as it is and aim the spacecraft and its thrusters by maneuvering to the appropriate roll, pitch and yaw angles as displayed on the FDAI prior to firing the thrusters.
094:49:35 Parker: And at 95:30, we're going to start - we're going to move the activities that start around 95:47 to 95:55. Those will be moved up to 95:30. [Pause.]
These items are concerned with preparations for the DOI trim burn. (GDC (Gyro Display Coupler) alignment, DSE configuration, maneuvering to the correct attitude for the burn, configuring the SIM bay experiments.)
094:49:55 Scott: Okay. Do you want - Okay, I got it. Fine.
094:49:59 Parker: That's that little block there. And the time to show on the Flight Plan anyway is 95:56 for the DOI trim. [Pause.]
094:50:12 Scott: Rog; 95:56. [Long pause.]
The crew is currently preparing for a TV transmission scheduled to last 10 minutes.
094:51:06 Scott: Houston, 15. Is that all you have?
094:51:08 Parker: Roger. Sorry Dave. That's the end - for now.
094:51:15 Scott: Okay. [Pause.]
094:51:25 Worden: Houston, 15.
094:51:27 Parker: Go.
094:51:31 Worden: Okay, Bob. We've got the TV turned on if you want to catch it down there.
094:51:36 Parker: Rog. We'll do our best.
Comm break.
094:52:50 Scott: Okay; Houston, 15. We're coming up on the edge of [Mare] Crisium, and we've got a good picture up here.
094:52:55 Parker: Rog. Don't see anything down here yet, but we're anticipating. [Long pause.]
094:53:52 Parker: 15, can we verify that you're in Transmit on the TV switch, please?
The picture from the TV camera can be viewed on its associated monitor while switched to Standby to allow a crewmember to adjust the focus, zoom and aperture before going 'live' to Mission Control. In this mode, the video signal that the camera is sending out to the spacecraft's S-band system has a full set of synchronising pulses but no picture; essentially black. Mission Control only get a picture when the camera is switched to Transmit. As the crew are getting a good picture on the TV monitor, it is easy to miss the Standby/Transmit switch and think that the image is reaching Earth.
094:54:07 Scott: Okay; that was the problem. We've got it.
Television picture from the spacecraft now coming in on the large Eiderphor projector at the front of the Control Room. Meanwhile, in the viewing room, among the people watching the television pass this morning are Mrs. Jim Irwin, Mrs. Dave Scott, Mrs. Scott's mother Mrs. Isaac Ott, Apollo 11 Commander Neil Armstrong and Doctor Wernher von Braun.
On 16th March, 1966, Dave Scott had been the pilot aboard Gemini VIII, commanded by Neil Armstrong. This flight was notable in that Neil and Dave carried out the first successful docking in space. However, the flight was aborted early when a thruster became stuck in the On position, causing the spacecraft to gyrate. Armstrong had to use his reentry control thrusters to regain attitude control and, as a result, they had to return to Earth immediately. Armstrong is evidently following Dave's exploits closely.
The TV coverage begins somewhere over the highlands just west of Mare Crisium. The Sun is quite high giving few shadows and features are difficult to distinguish. The first recognisable landmarks are two prominent bowl-shaped craters with raised rims.
094:55:34 Parker: Okay, 15. We got it now. Couple of big holes in the ground out there.
094:55:42 Scott: Rog.
094:55:46 Worden: That's right, Bob. [Long pause.]
Apollo 15 is travelling in its usual east to west path, slowly going north as the inclination of the orbit takes it towards the landing site at 26°N. Al has the TV camera at window 1, looking south of the spacecraft's ground track as they fly over the highlands between Mare Crisium and Mare Serenitatis. The nearer and most northerly of the two "big holes" visible in the TV picture is Hill, formerly Macrobius B, but more recently named after George W. Hill, 1838-1914, an American astronomer. It is 16 km in diameter. Behind it and further south is 20-km Carmichael, previously known as Macrobius A but now named after an American psychologist, Leonard Carmichael, 1898-1973.
Many of the smaller craters on the Moon, particularly those near the limits of telescopic visibility from Earth, were labelled after a larger craters nearby, with a suffix added from A to Z. Since the Apollo program, some of these names have been changed by the International Astronomical Union according to the convention of naming lunar features after deceased scientists.
094:56:31 Worden: Okay; Houston, 15. If you want to orient yourself on a TV there, Bob, we just came over Macrobius A, and the small crater that you just saw - we just went by, is Römer J. We're coming up on - on Römer K here in a moment, which means that very shortly, we'll be coming up over the Littrow Rille - Rimae Littrow.
Al probably means they just came over Hill (Macrobius B) the nearest of the two big craters they have just passed. Römer J is visible for just an instant at the bottom of the image. The majority of the view is over Sinus Amoris (Bay of Love).
It seems likely that the camera's 6:1 zoom lens is set near its longest focal length and Al is having some difficulty keeping the picture steady.
Scott, from 1999 correspondence: "It is somewhat more difficult to point things in 0G without some form of support."
The 12-km crater, Römer K is now called Franck after James Franck, 1882-1964, a German physicist.
094:56:57 Parker: Roger. We've got our little charts out here.
094:57:04 Worden: Okay. [Long pause.]
094:57:21 Worden: Okay, that looked like Römer J we're just coming up on now. In fact, we'll pan down into it.
Judging by the surrounding terrain, the crater Al is calling Römer J may actually be Brewster (formerly Römer L) which was named after a Scots optician, David Brewster, 1781-1868. It now shows up very clearly on the TV as a bowl-shaped crater, 11 km in diameter. Easily visible is the slumping of material down the crater walls to cover a relatively flat floor.
094:57:31 Parker: Beautiful shot.
Comm break.
094:58:55 Worden: Okay, Bob. You can see we're up over one of the Littrow Rilles now. You can see the rille cutting diagonally there from about - 6 o'clock to 2 o'clock across the picture, and you can see some of the wrinkle ridges. In fact, there's a beautiful wrinkle ridge right below us right now.
Rimae Littrow itself is outside Mare Serenitatis but there are other, related rilles just within the mare. The TV picture shows some small craters with a minor rille running between them. When Al points the camera down, he gives us a fine view of part of Dorsa Aldrovandi.
094:59:12 Parker: Roger. I believe you. I see it.
094:59:14 Worden: I'll pan up along the wrinkle ridge so you can see. And they're a very, very distinctive thing, now we're out over Mare Serenitatis. You can see some of the Littrow rilles in the background there, some of the graben-type rilles, and some of the wrinkle ridges down on the - on the far - or on the - on the close corner here. [Long pause.]
The Moon exhibits two major types of rille: sinuous rilles and grabens. Hadley Rille is a fine example of a sinuous rille, believed to have been carved by large volumes of flowing, low viscosity lava, though at the time of Apollo 15, there is still some debate in the lunar geology community as to its origin. Grabens are the result of stresses in the early Moon related to the formation of the basins and the mare within them. Two long, roughly parallel faults allow the terrain between to drop as either side moves apart. Grabens can be seen stretching across the lunar landscape through mare and highland alike and they are often grouped into systems of concentric rilles at the margins of the maria.
As the spacecraft coasts between Dorsa Aldrovandi and Dorsa Smirnov, Al aims the TV camera south towards Borel (formerly le Monnier C), a 5-km crater named after Felix Borel, 1871-1956, a French mathematician.
094:59:50 Worden: Yeah, we should be coming up on the inner ridge system here in a moment, and we - we'll try and pan down along the - the inner ridge. [Long pause.]
095:00:12 Worden: Yeah. That looks like the inner ridge system there, and if your picture's like mine, you should be picking it up pretty well. [Long pause.]
This is Dorsa Smirnov, the largest of the wrinkle ridges in Mare Serenitatis. This picture is not as clear as the earlier view of Dorsa Aldrovandi.
095:00:35 Worden: Those ridges in places look like they could be nothing more than a - than a - than a flow that stopped there - flow front. In other places, they look like the - like a - like it's buckled material underneath, folded to - to give it some elevation.
This is the favoured theory to account for the wrinkle ridges. The mare consist of layer upon layer of basalt, up to many kilometres in depth, which fill the huge impact basins. The basalt is solidified from countless lava flows which welled up to cover the shattered landscape. It is denser than the surrounding crustal material, so over the aeons it has tended to sink, especially in the center where the mare is thickest. The unequal sinking causes peripheral compression forces which push the rock upwards along lines of weakness, often forming concentric rings within a circular mare.
For a while, the TV is looking at Deseilligny, a 6.6-km crater about 120 km south of the spacecraft and named after Jules Deseilligny, 1868-1918, a French selenographer (one who studies the Moon as a geographer studies Earth). Al then tilts the camera down to see the 7.6-km crater Sarabhai which is almost below the spacecraft. The image gives a good, close-up view of this "simple" crater with its symmetrical bowl shape and sharp, raised rim. The crater is named after Vikram Ambalal Sarabhai, 1919-1971, an Indian astrophysicist.
095:01:23 Parker: And that was a good one, Al [meaning the view of Sarabhai]. And if someone, who's not just looking out the window, will give us P00 and Accept, we'll send you up a - not P00, just Accept. Pardon me. We'll give you state vectors and targets...
095:01:37 Worden: Okay.
095:01:38 Parker: ...while we're taking a view.
095:01:43 Worden: You got it. [Long pause.]
Al returns the camera to the southern horizon of Mare Serenitatis. About 120 km south is the distinct raised rim of Bessel, which at 16 km, is the largest crater on this mare. It is named after the German astronomer, Friedrich Wilhelm Bessel, 1784-1846, who pioneered the measurement of stellar distances by the use of parallax.
Apollo 15's present altitude now 7½ nautical miles [13.9 km, 45,600 feet] above the lunar surface.
095:02:08 Worden: Bob, I'm going to pan forward a little bit, and you can see the beginnings of the Apennine Front showing up on the far side of Serenitatis.
095:02:15 Parker: Roger. We see that. [Pause.]
095:02:24 Worden: And off on the left there, that's the Haemus Mountains around south of the Apennines. [Long pause.]
Al is still looking too far south to see the Apennine range of mountains. All the distant peaks in the TV coverage are the Montes Haemus range which form the southwestern rim of the Serenitatis basin. The Haemus range actually forms an inverted 'V' shape with the Montes Apenninus, as the latter range form the southeastern rim of the Imbrium basin, meeting where the two great maria touch. The Apennine Front is the really the steep side of the Apennine range which faces into Imbrium and which is still in shadow.
095:02:41 Worden: See how - when you're coming up at low altitude on these mountains, how - how striking they are in the distance? It's really hard to miss them, you can see them a long ways away.
095:02:52 Parker: I hope you can miss them. [Pause.]
095:03:02 Worden: Guess that's up to you guys.
It is by the accuracy of work done by the Flight Dynamics people in Houston, and the quality of the tracking data supplied to them by MSFN (Manned Space Flight Network) that Apollo 15 can orbit so close to the Moon, especially given the inaccuracy of the landing site's known elevation. Al notes that Mission Control are as responsible for the spacecraft missing the mountains as the crew is.
095:03:04 Parker: Rog. Speaking of that, the burn attitude's going to be 104 degrees [in pitch], so you might keep that in mind when you get done here. You're getting kind of close to it now, or - beginning to get close to it.
Bob Parker is reminding the crew that they are still slowly rotating the spacecraft in the orb-rate maneuver, keeping one side of the spacecraft facing the Moon, and they are slowly approaching an attitude which is very near that required for the DOI trim burn. If they prevent the spacecraft from going too far past their intended burn attitude, they will save RCS fuel.
The TV image shows that the spacecraft is approaching the western edge of Mare Serenitatis. The shadows are lengthening and the topography of the landscape is becoming more distinct. Crater Hornsby comes into view, and soon after we see the unusual formation, Krishna. This feature had been photographed the previous day and is image AS15-91-12400. A wrinkle ridge appears to run from it northwards toward the camera.
095:03:51 Worden: There's a very interesting little fissure just below us here, Bob. It looks like there might be a little flow coming out of it, but it's - it's almost an arrowhead-shaped affair. And, it certainly doesn't have any features like any - any impact. It's very sharp and distinct and makes a very distinct arrowhead. Here we come up on the ridges on the west side of Serenitatis, just at the foothills of the Hadley Apennines.
These are Rimae Sulpicius Gallus which lead to a distinct crater further to the south, Sulpicius Gallus. The term "Hadley Apennines" is an informal name for the general mountainous area around the landing site, derived from the large mountain, Mount Hadley.
095:04:18 Worden: And you can see, there is - there is some relief as we look back to the south there, there is some very distinct relief in - in - in the shore of Serenitatis, with some wrinkle ridges that follow the contour.
Al is pointing the TV at Dorsum Buckland, a wrinkle ridge which runs parallel to Montes Haemus but 50 km into Mare Serenitatis. This is part of the concentric system of ridges defining the extent of the mascon in the centre of the mare. William Buckland, 1784-1856, was a British naturalist. In the foreground of the TV picture are two small, simple craters, Aratus C and D. Aratus was a Greek poet, 315-245 B.C.E., who is noted for writing the oldest known description of the 48 ancient constellations.
095:04:34 Worden: And some - what look like fairly distinct arcuate rilles that also follow the contour. I think that when we get up very close here, you can see...
The spacecraft is just crossing the foothills near Promontorium Fresnel, the cape between the two great maria where the Haemus and Apennine ranges meet. Looking back towards Mare Serenitatis, we can see discontinuous linear features which appear like a partially formed sinuous rille.
095:04:44 Worden: ...In - in the field of view there right now is a lineament that looks like it might be some sort of a collapsed lava tube, and you can also see down in here the - the mare material looks like it's pooling in the - in the foothills of the mountains; and in some places, you can even see what appears to be a frozen shoreline, so to speak.
Where the basalts of the maria meet the mountains of the basins containing them, it is sometimes possible to discern a slight inflection at the bottom of the slopes just above the current shoreline. It is believed that when the lavas which formed the maria were hot and molten, they reached further up the slopes. As they cooled, the maria contracted and receded slightly - isostatic settling - leaving a frozen shoreline behind.
As the spacecraft nears the Hadley landing site, the craters Aratus and Aratus B are visible.
095:05:24 Parker: Rog. We can take black now, too.
095:05:27 Worden: Okay. [Pause.] Okay, Bob. I'm going to take the TV out of this window and get it located in window 3, so we can all have a good look at the landing site.
Al pulls the camera away from the window 1 and positions it in the central, hatch window, number 3. He is barely in time to catch a few seconds of Hadley Rille as he tries to steady the camera on a landscape that is slipping by very quickly.
The first view we get of the rille is as we glimpse it snaking past the base of the 3.5-km high Hadley Delta. St. George crater on its northern flank is still in shadow. When the camera does settle, we are looking at the rille further upstream, southwest of the landing site, where it turns to run east-west towards St. George. As Al tries to track it, the thrusters of the LM come into view.
095:06:01 Worden: Sorry about that; we're just a little bit late, but you can see the edge of the rille [Hadley Rille] there as we go beyond it. And you can see the blocky features inside the rille. And now we're out across the plain on the other [western] side. That was very fast.
095:06:16 Parker: That was a quickie. [Long pause.]
The spacecraft is near its pericynthion and its extreme low altitude of 13.9 km (7.5 nautical miles) has caused the landing site to speed beneath the spacecraft and through the camera's field of view at nearly 7° per second, much quicker than the 0.1° per second at their normal 110 km (60 nautical miles) height. Al can only keep a feature in the frame for a few seconds at most, and eventually he allows the field of view to track across the crater fields of Palus Putredinus before returning to look southwards through window 1.
095:06:44 Worden: Okay. In the field of view right now, Bob, is the beginnings of Bradley Rille, and you can see it cutting back off to the southwest there.
095:06:53 Parker: Roger. Looks kind of like our rille.
095:06:58 Worden: Yeah. It does, doesn't it?
Comm break.
Rima Bradley is sited about 100 km WSW of the landing site and runs within the Imbrium Basin, crossing the contact between Palus Putredinus and the lighter-toned Apennine Bench Formation to the south. It is roughly parallel to the rim of the basin and is named after the English astronomer, James Bradley, 1692-1762. It is a graben-type rille and does not really look like Hadley Rille. As they coast towards Montes Archimedes, a range of hills south of the large, flooded crater of the same name, the light is becoming very oblique and only the peaks are lit.
095:09:22 Worden: Okay, Bob. I guess that about does it. We're at the terminator, and we'll pick up the attitude [for the trim burn] now.
This is Apollo Control. At the conclusion of the television pass, the crew held up a sheet of paper on which appeared to be written the word 'finis' [meaning end].
095:12:51 Parker: And, Apollo 15, Houston. We've got a DOI trim PAD for Jim when he's ready to copy. [Long pause.]
095:13:26 Irwin: Morning, Bob. I'm ready to copy.
095:13:29 Parker: Roger, Jim. The P30 PAD. Purpose, DOI trim, RCS/G&N; 38264; Noun 48 is NA; 095:56:42.50; plus 0003.1, the last two Noun 88s [means Noun 81s] are 0; 180, 104, 359; Noun 44 is 0059.4, plus 0009.6; 0003.1, 0:20, 0003.1; 30, 192.8, 11.1 the rest of the PAD is NA. GDC Align stars are Vega and Deneb, roll, pitch and yaw are 288, 340, 346. It's a 4-jet RCS burn and we do not want to trim any retrograde residual, so any extra burn you get in that direction, we will not trim. Over. [Pause.]
Explanation of the PAD is as follows.
Purpose: The purpose of this PAD is to trim the shape of the descent orbit.
System: The burn will be made using the RCS engines under the control of the G&N system.
CSM Weight (Noun 47): 38,264 pounds (17,356 kg).
Pitch and yaw trim (Noun 48): These values are not applicable to this manoeuvre because the RCS is being used.
Time of ignition, TIG (Noun 33): 95 hours, 56 minutes, 42.5 seconds GET.
Change in velocity (Noun 81), fps (m/s): X, +3.1 fps (+0.94 m/s); Y, 0; Z, 0. These velocities are made with respect to the local vertical frame of reference. The burn is entirely prograde so has the effect of raising their pericynthion by nearly three kilometres.
Spacecraft attitude: Roll, 180°, Pitch, 104°; Yaw, 359°. These attitude angles are with respect to the IMU platform as aligned to the Landing site REFSMMAT.
HA, expected apocynthion of resulting orbit (Noun 44): 59.4 nautical miles (110.0 km).
HP, expected pericynthion of resulting orbit (Noun 44): 9.6 nautical miles (17.8 km).
Delta-VT: 3.1 fps (0.94 m/s). This is the total velocity change experienced by the spacecraft.
Burn duration or burn time: 20 seconds.
Delta-VC: 3.1 fps. The EMS will be used for backup monitoring of the burn with this figure being entered into its Delta-V display.
Sextant star: Star 30 (Menkent, in Centaurus) visible in sextant when its shaft and trunnion angles are 192.8° and 11.1° respectively.
GDC Align stars: Stars 36 (Vega in Lyra) and 43 (Deneb in Cygnus) to be used for GDC (Gyro Display Coupler) Align in case the IMU is not available for this task.
GDC Align angles: 288°, 340°, 346°.
The letters 'NA' mentioned in the PAD mean 'not applicable'. The PAD is written onto a standard layout and in this case, not all the boxes are to be filled. Additional notes are that they will use all four RCS quads, and as the burn is of a small magnitude, the crew is not to make any further burns of the RCS to try to correct any apparent error in the final velocity. (The difference between the desired velocity and that actually obtained is known as the residual velocity.)
095:15:21 Irwin: Okay, Bob. DOI trim PAD readback. RCS/G&N; 38264; 095:56:42.50; plus 0003.1, 0 and 0 for Y and Z; 180, 104, 359; 0059.4, plus 0009.6; 0003.1, 0:20, 0003.1; 30, 192.8, 11.1. Vega and Deneb; 288, 340, 346; 4-jet RCS, no trim of any retrograde residual.
095:16:10 Parker: Roger. Copy. Correct, and one last comment: We will not be passing you up a TEI-9 - TEI-19 PAD at this time.
The PAD will be read up by Ed Mitchell at 097:10:34, after he has taken over as CapCom for the preparation and execution of the landing. Mitchell was the Lunar Module Pilot on the Apollo 14 mission.
095:16:23 Irwin: Understand.
095:16:26 Parker: And that should take care of all little squares in that MSFN update box at 28 - at 95:25. [Pause.]
095:16:41 Irwin: Repeat the last one, Bob.
095:16:44 Parker: Roger. I was just telling you that fills - that takes care of all squares there at the MSFN update at 95:25. We've taken care of all those in one way or another this morning.
This is Apollo Control. At 8 o'clock Houston time, astronaut Harrison 'Jack' Schmitt will make a briefing in the Houston News Center on the Apollo 15 EVA periods, they three EVA periods. Still up live here on the ninth frontside revolution of the Moon by Apollo 15. Another 21 minutes until Loss Of Signal. The crew presently is maneuvering to the burn attitude for the DOI trim maneuver, which will be an RCS burn. The burn time of 20 seconds. Looking for 3.1 feet per second [0.95 m/s] change in velocity to raise the pericynthion. Ignition time is 95 hours, 56 minutes, 42 seconds Ground Elapsed Time. Up and 'live'; this is Apollo Control.
095:24:45 Parker: And, 15, people down here are recommending that you terminate your roll at this attitude to help your P52 before you press on to the burn attitude.
095:24:58 Worden: Hey, very good, Bob. Thank you. We will.
Comm break.
The spacecraft's optics look through apertures in the CM hull on the opposite side from the main hatch. Therefore, to view the required stars for the P52 platform realignment the spacecraft must be facing the correct way. Mission Control believe that stopping the spacecraft's roll at the present angle will help achieve the correct alignment.
095:26:21 Irwin: Houston, this is 15 with some retraction times for you.
Throughout the operation of the SIM bay, Al Worden monitors the time taken for the various deployment mechanisms to operate.
095:26:24 Parker: Okay, go ahead.
095:26:28 Irwin: On the Mass Spec., it was - on the Mass Spec., it was 02:33. On Gamma-ray, 03:09.
095:26:37 Parker: Copy, thank you.
095:26:47 Irwin: It was 2 minutes and 33 seconds, 3 minutes and 9 seconds.
095:26:58 Parker: Say again, 15. Was that 233 seconds, and 3 minutes and 9 seconds?
095:27:08 Irwin: No; 2 minutes and 33 seconds, 3 minutes and 9 seconds.
095:27:12 Parker: Roger. We had that; thank you. [Long pause.]
These timings for the booms to retract are very near the expected times given in the Flight Plan and this will reassure Mission Control that there is currently no problem with the deployment mechanism.
095:28:17 Worden: Houston, 15.
095:28:19 Parker: Go ahead.
095:28:24 Worden: Okay, Bob. I'm sitting looking right at the surface with the optics in this attitude. Give me a good roll angle to go to.
095:28:30 Parker: Okay; stand by. [Long pause.]
The call from Parker at 095:24:45 GET to stop the spacecraft's roll was erroneous as the optics aren't even pointing at the sky, never mind near the stars they intend to use for the P52.
095:29:19 Parker: Stand by. We're talking about it guys.
095:30:13 Parker: Roger, 15. Now that we told you to stop [the roll], why don't you press on to the burn roll on 180 [degrees].
095:30:24 Scott: Okay; thanks a lot.
095:30:27 Parker: [Laughter.] For what? And now, if you lose High Gain [Antenna] by going to the burn attitude before you go around the corner, it will be Omni Delta in the burn attitude.
095:30:40 Scott: Roger. Omni Delta.
Long comm break.
Bob Parker's 'For what?' seems to be an admission that Mission Control slipped up when calling for the roll to be stopped. Fuel will have been wasted stopping the roll and then starting it again to get to the correct roll angle.
The HGA (High Gain Antenna) is an articulated array of four parabolic dishes and a feedhorn which can track Earth as the spacecraft alters attitude. If, while they maneuver to the attitude for the burn, the HGA is taken beyond the limits of its movement, the crew can used omni-directional antenna D, mounted on the periphery of the CM.
095:34:17 Parker: And, Apollo 15, we'd like Track Auto [on the HGA] as you go around the corner here. It'll help us keep you on data for a couple of minutes there at the end. And we've got a couple of stars for you, if you want to take any more advice. And that's a 25 and 26.
095:34:39 Scott: Okay; 25 and 26. And you've got Auto.
095:34:43 Parker: Thank you.
Mission Control may be trying to make up for its error. Since the maneuver was stopped, it doesn't make any sense to go to one roll angle for the P52, and then to the burn angle. The new stars can be used for the P52 at the burn roll attitude. Star 25 is Acrux, in the Southern Hemisphere constellation of Crux, and Star 26 is Spica, in the constellation Virgo.
