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Apollo 15

Day 5, part 3: Activating the Lunar Module

Corrected Transcript and Commentary Copyright © 1998-2023 by W. David Woods and Frank O'Brien. All rights reserved.
Last updated 2023-10-27
Index to events
TEI-19 contingency manoeuvre PAD 097:13:54 GET
LM DAP [Digital Auto Pilot] data 098:36:09 GET
SEP[aration] time read up 098:41:59 GET
P24 Rate aided optics tracking PAD 098:43:57 GET
Flight Plan page 3-105.
Apollo 15 is about to make a tracking pass over the landing site so that Dave can get a close look at the landing site. They are still on Flight Plan page 105.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
096:56:16 Mitchell: 15, Houston. 1 minute to T-horizon.
096:56:22 Worden: Rog, Ed.
Long comm break.
The landmark will be on their horizon in one minute. Strictly speaking, it will not be visible until after that because it is hidden from view by the elevated land to its east, the Swann Range.
Like other landmarks in the Hadley area, these explorers chose to name this range of hills after one of the geologists, Gordon Swann, who had trained them for the scientific content of their mission. Another example is a prominent outcrop visible from the LM after they landed called Silver Spur.
AS15-84-11250 - Silver Spur, named after Lee Silver, a Caltech geologist who trained the astronauts - Image by NASA/Johnson Space Center.
The HBO miniseries for television, 'From the Earth to the Moon', gives an account of how Lee Silver was brought from Caltech to train the crews as geologists on top of their skills as pilots. His inspiration was rewarded with this extraordinary, layered feature bearing his name.
While the crew slept, the Sun rose over the Hadley Plain. Now Dave is going to use this pass across the landing site to get his first direct look at conditions on the surface with the aid of the sextant. In particular, he is looking to see whether there are any features which could prove to be a hazard for a Lunar Module coming in to land. This observation is particularly important in light of the poorer imagery available to the planning teams before the flight. The robotic Lunar Orbiter spacecraft had concentrated on acquiring high resolution imagery of the equatorial sites that the first landing missions were limited to reaching. Only medium resolution imagery of Hadley was available so this sighting is valuable in double checking that there are no obstacles like large single boulders or great boulder fields awaiting them.
At this point in the mission, the Flight Plan splits, with separate pages for the LM and the CSM. Indeed, the two LM crewmembers have individual time lines within their Flight Plan.
LM Flight Plan page 3-106.
CSM Flight Plan page 3-107.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
097:01:43 Scott: Houston, Apollo 15.
097:01:48 Mitchell: Go ahead, 15.
097:01:53 Scott: Okay; looks like FAO [Flight Activities Officer] owes us one. I had no trouble picking up Index Crater at all. The surface looks generally smooth. I saw no big boulders. I saw more craters than we're normally used to seeing [in the simulator], but I think that's because of the [low] resolution of the [Lunar Orbiter] photography. I can see a - a fair amount of boulders in the bottom of the rille. Most of the surface seems to be pretty subdued and rounded. I did see some debris around some of the fresher craters. And, of course, I don't know exactly what size, but if we're looking at 3-feet resolution on this, I'd - I'd say I didn't see anything larger than - I guess, at the most, maybe 15 feet or so, but that's - that was a unique rock. The - the area, in general, looks pretty good. I don't think we'll have any problem picking it up, and I don't think Al will have any problem at all identifying Index Crater.
AS15-87-11718b - A labelled version of 11718 to show the primary features of the site - Image by NASA/Johnson Space Center.
Index is a reasonably distinctive crater, by virtue of having a lobe on its north rim. It lies adjacent to the landing site and will be used both for taking sightings from orbit, a procedure Al will be carrying out over the next few revolutions, and to act as a guide for Dave as he approaches the landing site later today. It is the last of four craters of similar size which form a line leading up to the point of touchdown. The others were named Matthew, Mark and Luke in the order leading towards Index.
By the time of the landing, the rising Sun will render many of the craters Dave is familiar with almost invisible. Dave talks about this further in the Apollo Lunar Surface Journal by Eric Jones before and after 104:39:32. Eric believes Dave's reference to 15 foot boulders must be to those lying within Hadley Rille as there is nothing like that up on the mare surface. Dave pointed out to me that the North Complex, a cluster of low hills and craters north of the landing site, did harbour this size of boulder.
Scott, from the 1971 Technical debrief: "One of the questions on the landing site was general terrain relative to boulders, debris, and craters. A couple of months before the flight, we had worked out a plan whereby we do the low altitude landmark tracking technique without the spacecraft rate drive in order to take a look at the landmark through the sextant. There had been some question as to whether or not we could see anything. I took a look on Rev 10, and it was as we had expected based on previous flights and fidelity of the optics. I could see the landing site very well. I could see Index Crater and the rille very well. I determined that there was no problem relative to boulders and debris, and it looked pretty smooth and flat. It was a comforting feeling to know that we wouldn't have a rockpile to land in. If the advertised resolution of 3 feet was correct, we had no problem with boulders on the order of 3 feet and above. This was subsequently verified when we got there. It was a nice thing to have behind us in the way of validating the surface at the landing site because of the poor resolution of photography we had from Orbiter. The technique worked very well. It was easy to track in Inertial Attitude. I think you found that during your J-1 track, also, didn't you Al? I think you could have done your landmark tracking without a spacecraft rate drive."
Worden, from the 1971 Technical debrief: "I almost feel that way, yes. The J-1 tracking was really easy. With a high rate in the optics, it was fairly easy to track if it was off track. You have some roll in there, so that you're not coming through zero on the track."
Scott, from the 1971 Technical debrief: "But the optics are very easy to control, have a very positive response, and once you lock on the target, you can stay right on it."
Worden, from the 1971 Technical debrief: "That's right."
Scott, from the 1971 Technical debrief: "That gets us down to lunar landmark recognition. Of course, the landing site at Hadley was particularly unique, when relative to landmarks. When I looked at it through the optics, I could recognise the craters that lead into Index and Index crater quite well, even though there didn't seem to be as many shadows, crater shadow, as I had expected."
097:03:03 Mitchell: Okay, Dave. We copy. Thanks a lot.
097:03:09 Scott: Rog.
Long comm break.
Dave ought to be donning his biomedical harness and his suit, without helmet and gloves, about now.
Scott, from the 1971 Technical debrief: "We set up a plan on the LOI day to try out our sequence of suiting for PDI day. As a result, we changed our minds on PDI day to make it a little bit more efficient."
Worden, from the 1971 Technical debrief: "You two put your suits on and then went into the LM to zip them up."
Scott, from the 1971 Technical debrief: "Because it's a lot easier zipping up the 7L-B suits in the LM and it gave us a chance to do the tunnel work shirtsleeve. We helped you [Al] get your suit on. It is worth while to run through suit donning because the first day we did it we had you put your suit on. Then we put our suits on in the Command Module. That was a sort of chore. Jim suggested we suit up and go to the LM before zipping them up. That made it a lot easier. We recommend cleaning the tunnel out or putting the suits on unzipped, cleaning the tunnel out, and then the CDR and LMP transferring to the LM to do their suit zip. It would be a good idea to have a little trial run one of the days on the way out."
Worden, from the 1971 Technical debrief: "As to the time line, that works out much better, too, because while you were over there putting suits on and zipping them up, that gave me a chance to put my suit on which is done in parallel rather than sequentially."
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
097:10:34 Mitchell: Apollo 15, Houston. If there's someone available to copy a TEI-19 PAD, I'll give it to you.
097:10:43 Worden: Okay; hold for about 5 [minutes], will you please, Ed?
097:10:47 Mitchell: Will do.
Comm break.
This is Apollo Control. That completes our playback of the accumulated tape. We'll continue to stand by live now. Dave Scott, in that playback, reported the surface of the landing site appeared to be subdued and rounded. He said nothing larger than about 15 feet [4.5 metres] or so. And also added that it should be no problem for Al Worden to track on the - on the site from the Command Module.
097:13:48 Scott: Okay, Houston; go - go ahead with the TEI PAD.
097:13:54 Mitchell: Roger, 15. TEI-19: SPS/G&N 38009; plus 0.61, plus 1.05; 115:27:55.59; plus 2845.1, minus 0831.7, minus 0219.7; 180, 102, 346. The rest, NA. Ullage, 4 jet, 12 seconds; and some notes. One is, burn is undocked; two, assume Circ.; three, longitude at TIG is 166.0 [degrees] west; and the fourth note is, the attitude's based on landing-site REFSMMAT. [Long pause.]
Interpretation of the PAD follows: The final notes state that subsequent items are not applicable to this PAD, that SPS propellants would be settled in their tanks by firing the plus-X thrusters on all four quads around the Service Module for 12 seconds, and that the burn would be made without the weight of the LM. The PAD assumes that Al has completed the orbit circularisation burn. The spacecraft would be over the lunar longitude of 166° west on the lunar surface at ignition, and the spacecraft's attitude for the PAD assumes that they are using the landing site orientation for their attitude reference.
Although this abort is without the LM, it does not necessarily mean that Al would be returning alone. If the LM crew need to return soon after landing, they could reach orbit, dock, transfer to the CSM and jettison the LM in plenty of time for this TEI-19 abort.
David Woods, from 1999 correspondence with Scott: "Some of the abort PADs read up during lunar orbit have TIGs which are during the crew's scheduled sleep periods. It may seem somewhat odd that an option to return home would be scheduled just when a tired crew are switching off for the day and perhaps one would expect that a time would be chosen when the crew are likely to be alert for what would be a very critical burn, should it be used. Do you have any comment on the timing of Abort PAD TIGs?"
Scott, from 1999 correspondence: "Problems are not selective in time - therefore, it does not matter what the crew might be doing when the problem occurs, and an abort will be needed."
097:15:24 Scott: Okay, readback. TEI-19: SPS/G&N; 38009; plus 0.61, plus 1.05; 115:27:55.59; plus 2845.1, minus 0831.7, minus 0219.7; 180, 102, 346; 4 jet, 12 seconds; burn undocked; assume Circ.; longitude 166.0 west at TIG, and landing site REFSMMAT.
097:16:00 Mitchell: That's affirm; and we have a few centiseconds update for your CMC clock, whenever you're ready.
The basic unit of time in the computer is the centisecond (1/100 of a second). Mission Control can remotely update the computer's knowledge of time, once a crewmember has given them access to it.
097:16:11 Scott: Okay, you want P00 and Accept?
097:16:13 Mitchell: That's affirm.
097:16:16 Scott: You got it.
Comm break.
097:17:51 Mitchell: [The] computer's yours, 15.
Long comm break.
Mission Control has corrected the CSM computer's clock.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
097:23:23 Mitchell: Falcon - rather, Apollo 15, Houston. Omni Charlie, please. [Pause.]
097:23:35 Worden: Houston, 15. Go ahead.
097:23:38 Mitchell: Omni Charlie, please, Al.
097:23:43 Worden: Okay, Omni Charlie. [Pause.]
097:23:51 Mitchell: Haven't had a chance to say good morning, Al, so good morning.
097:23:58 Worden: Good morning, Edgar.
Long comm break.
Finally, Ed Mitchell drops his businesslike stance and gets around to exchanging greetings with the crew.
In situations where the HGA (High Gain Antenna) is not being used, the crew can select one of four omni-directional antennas on the CM's skin to communicate with Earth.
Al is working on another platform realignment.
That was the Command Module Pilot Al Worden exchanging good morning greetings with spacecraft communicator Edgar Mitchell.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
097:29:23 Mitchell: Apollo 15, Houston.
097:29:28 Worden: Houston, 15. Go ahead.
097:29:30 Mitchell: Rog. We need to redo the REFSMMAT update that we gave you a little while ago. Could we have P00 and Accept please? [Pause.]
097:29:41 Worden: Okay, Ed. You caught me just in time, doing a P52.
There are two P52 realignments in the Flight Plan about this time. The first, at 97:19, would have been carried out had there been no DOI trim burn and would be a conventional Option 3 P52 using the landing site REFSMMAT. The second is for cases where a DOI trim burn has occurred and it is therefore the one Al is to complete.
As well as raising the pericynthion of their orbit, the DOI trim burn has also changed the time of the landing slightly as the overall orbit is slightly higher than before and therefore of a slightly longer period.
The uplink of the updated REFSMMAT was quite timely, as Al was in the process of performing a platform realignment, and will be able to use the new values immediately. Had the updated REFSMMAT come later, it would not be used until the next scheduled alignment.
097:29:43 Mitchell: Rog...
097:29:44 Worden: I'll go back to P00.
097:29:45 Mitchell: ...what - what we were hoping to do.
097:29:50 Worden: Okay; you got it now.
097:29:51 Mitchell: Roger. Here it comes. [Long pause.]
097:30:05 Mitchell: The story here, Al, is that, apparently, the block update changed some registers in the REFS - REFSMMAT and screwed it up a bit.
097:30:16 Worden: Rog.
Comm break.
Houston has sent up several computer updates on this near-side pass, and one of these has accidentally written over storage used for the platforms orientation, the REFSMMAT. A note on the computer term, "registers" used by Ed Mitchell at 097:30:05: The contemporary definition of register is a computer component that is able to perform arithmetic and logical operations on data. The Apollo Guidance Computer had only one accumulator, a term which today is often used interchangeably with the word "register". In the software design of the computer, memory locations were reserved for well defined values, such as mathematical constants or frequently used variables (such as a REFSMMAT). This use of the term probably dates back to earlier computers, such as the Univac series, where registers and other hardware functions were referenced by a memory address.
097:31:46 Mitchell: 15, Houston. The computer's yours. And, Al, before you do [P]50 [correcting himself] [P]52, be advised you can use the Systems Test Meter on the backside for any of the normal LM checkout functions; on the front-side, we'll watch it for you. And go ahead and leave the test meter in whatever position you're - you're testing with. You understand?
097:32:12 Worden: Rog, Ed. Understand.
097:32:13 Mitchell: Okay; proceed with your P52.
097:32:18 Worden: Okay; thank you.
Long comm break.
As Al proceeds with the P52 realignment, he inadvertently uses Option 3 instead of 1. However, the spacecraft is about to disappear around the far side and Mission Control will not have a chance to pick this up until AOS.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
097:35:32 Mitchell: Apollo 15, Houston. Thirty seconds to LOS.
097:35:38 Worden: Rog, Ed.
Very long comm break.
The details of this fifteenth P52 platform realignment are that Al used stars 41 (Dabih, Beta Capricorni) and 42 (Peacock, Alpha Pavonis). It has only been a couple of hours since the last P52 so the resulting angles through which the platform had to be torqued are: X, +0.01°; Y, -0.009°; Z, -0.029°. He achieved 'four balls 1' the the star angle difference which is a check of his accuracy and which is a good result. Al will report this data to Mission Control at 098:54:18.
On this far-side pass, Dave and Jim begin their transfer to the Lunar Module as Apollo 15 begins its eleventh orbit.
During this period behind the Moon, Al will don his biomedical harness and suit without the helmet and gloves. He was scheduled to do this five minutes before LOS. However, it is unlikely he would have done so having had to execute a P52 alignment twice due to the error in the initial REFSMMAT. Other tasks for Al include purging the fuel cells, a waste dump and manoeuvring to the undocking attitude. Meanwhile, Dave and Jim clear the tunnel of the probe and drogue to allow passage to the LM. Jim enters first and begins activating the lander's O2 and water supplies, the electrical, communications and cooling systems and checking out the caution and warning system. At Jim's request, Al will switch off the power being fed to the LM through the tunnel umbilical cable. Dave enters with their helmets and gloves and joins in with the activation of the LM.
In the CM, Al prepares two cameras, the Hasselblad and the CM's DAC (Data Acquisition Camera, a 16-mm movie camera) in the left, forward-looking rendezvous window to photograph the undocking and separation of the two spacecraft. He replaces one of the CM's lithium hydroxide canisters putting number 10 into port B, stowing the exhausted number 8 in compartment B6. He then begins to aid the activation of the LM by supplying necessary information from the CSM's systems. These will include the current Ground Elapsed Time and a read-out of the spacecraft attitude with respect to the IMU to allow a coarse alignment of the LM's guidance system.
After AOS, radio traffic will be three way and the use of the individual spacecraft's call signs will resume. Al's CSM is Endeavour while Dave and Jim will be using Falcon for the LM.
And we've had Loss Of Signal now. While on the backside of the Moon, on this tenth revolution, and going into the eleventh revolution, Scott and Irwin will be getting suited up. By the time we reacquire on the frontside of the Moon. They should be in the Lunar Module and beginning to power up and check out the LM prior to undocking and separation at 100 hours, 14 minutes. As the spacecraft went around the corner, Al Worden was in the process of doing a program 52, which is a platform alignment. This is normally performed prior to and following maneuvers with the spacecraft, aligning the stable platform used as an attitude reference by the guidance system. We'll be reacquiring the spacecraft in approximately 40, 45 minutes. During this period, while we're out of contact, we plan to replay the videotape of this morning's television transmission from Apollo 15. That tape is about 15 minutes in duration. At 97 hours, 37 minutes, this is Apollo Control.
097:54:08 Worden (onboard): [Yelling] In case you guys are wondering, I'm dumping.
Rev 11 begins at about 097:58.
LM Flight Plan page 3-108.
CSM Flight Plan page 3-109.
098:03:00 Worden (onboard): Fuel cell purge, huh? Okay, fuel cell purge. Two for 2 hours. Two of them on.
098:03:59 Worden (onboard): [Yelling] Hey, we're going to maneuver.
098:05:09 Worden (onboard): Yes, must be [garble] low.
There is nearly a 12-minute break in the onboard recording at this point.
098:16:50 Scott (onboard): [Garble]?
098:16:52 Worden (onboard): Well, we're getting there. Slowly.
098:16:58 Scott (onboard): What?
098:16:59 Worden (onboard): We're getting there slowly.
098:17:01 Scott (onboard): [Garble].
098:17:04 Worden (onboard): Yes. I think so.
098:17:12 Scott (onboard): When you almost get there, how about [garble]?
098:17:19 Worden (onboard): Okay.
098:17:21 Scott (onboard): [Garble].
098:17:22 Worden (onboard): All right.
098:17:23 Scott (onboard): [Garble] coming up [garble] to AOS [garble] up to - be ready for AOS.
098:17:31 Worden (onboard): I think I'm just about ready.
098:17:36 Scott (onboard): [Garble].
098:17:39 Worden (onboard): Yes. Where is the tape? Anybody know?
098:17:44 Scott (onboard): It's over - [garble].
098:17:48 Worden (onboard): Okay.
098:17:50 Scott (onboard): [Garble].
098:20:13 Worden (onboard): [Garble].
098:20:33 Worden (onboard): Oh, what the hell.
098:21:40 Scott (onboard): Hey, Al.
098:21:41 Worden (onboard): [Yelling] Yes.
098:21:46 Scott (onboard): [Garble].
098:21:47 Worden (onboard): [Yelling] What?
098:21:55 Scott (onboard): [Garble].
098:21:57 Worden (onboard): [Yelling] What?
098:21:58 Scott (onboard): Did you [garble]?
098:22:00 Worden (onboard): [Yelling] No. You guys are too far ahead.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
This is Apollo Control at 98 hours, 22 minutes and we're now about 2 minutes from reacquiring Apollo 15 on its eleventh revolution of the Moon. Flight Director Glynn Lunney just asked all of his flight controllers to be on their toes for this revolution. The frontside pass, he said, would be a very - a very busy one. The crew will be primarily involved with the activation checklist on board the Lunar Module - Scott and Irwin. Coming up on the succeeding two revolutions, 12 and 13, we'll have some important landmark trackings being performed by Al Worden in the Command Module updating the knowledge of the landing site and of the spacecraft state vector - or orbital parameters. And we're now about 1 minute from reacquiring Apollo 15.
098:22:58 Worden (onboard): Okay. Let's see.
098:23:02 Scott (onboard): Ready?
098:23:03 Worden (onboard): You want P - Okay.
098:23:04 Scott (onboard): [Garble].
098:23:06 Worden (onboard): Okay.
098:23:21 Scott (onboard): Okay there, Endeavour. How do you read the Falcon on...
098:23:23 Worden (onboard): Hey, loud and clear.
098:23:24 Scott (onboard): Say again?
098:23:25 Worden (onboard): Beautiful!
098:23:26 Scott (onboard): Good.
098:23:27 Irwin (onboard): And, Al, how do you read me?
098:23:28 Worden (onboard): Read you loud and clear, Jim.
098:23:30 Irwin (onboard): Ah, you're beautiful.
098:23:31 Worden (onboard): Hey, did you say something about TEPHEM? Did you want a TEPHEM, Dave?.
098:23:38 Scott (onboard): stand by.
098:23:39 Worden (onboard): Okay. I'll give it to you if you want.
098:23:43 Scott (onboard): Stand by. Configure for Simplex A.
098:23:45 Worden (onboard): Okay.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
And we've had Acquisition Of Signal.
The signal from the spacecraft is very noisy for the first 1.5 minutes, though extremely faint voices can be heard. The noise then drops a little and the onboard conversation in the LM can be picked out.
098:23:57 Scott (onboard): Okay, Al. How do you read on A?
098:23:59 Worden (onboard): Loud and clear, Dave.
098:24:00 Scott (onboard): That's nice.
098:24:01 Irwin (onboard): And, Al, how do you read me?
098:24:02 Worden (onboard): Loud and clear, Jim.
098:24:03 Irwin (onboard): Very good.
098:24:05 Scott (onboard): Okay. Now you can give me your TEPHEM.
098:24:07 Worden (onboard): Okay.
098:24:18 Worden (onboard): Ready to copy?
098:24:19 Scott (onboard): Go.
098:24:20 Worden (onboard): Just like SIM. All balls in the R1. R2 is 32251. R3 is 26157.
098:24:31 Scott (onboard): Okay. All balls, 32251, 26157.
098:24:34 Worden (onboard): Great.
098:24:44 Worden (onboard): Want a clock sync?
098:24:46 Scott (onboard): Stand by 1.
098:25:35 Scott [in Falcon, talking to Worden in Endeavour]: Okay, Al. Verb 06 - 6 - Verb 06 Noun 65; I'll give you a mark.
098:25:37 Worden (onboard): Give me a mark. I'm waiting.
098:25:46 Scott: 3, 2, 1, Mark.
098:25:46 Worden (onboard): Okay. 98:25:45.60.
098:25:53 Scott (onboard): Okay. 25:45.60.
098:25:56 Worden (onboard): Roger.
As Apollo 15 emerges around the Moon's limb, Dave and Al are updating the clock in the LGC (Lunar Module Guidance Computer) with a time mark from the CMC (Command Module Computer). Noun 65 will present the CMC's time and Dave can compare it with the clock in the LM.
098:26:01 Mitchell: Apollo 15, Houston; standing by.
098:26:06 Worden (onboard): And I'm coming up to get the umbilical now.
098:26:08 Scott (onboard): Read you loud and clear.
098:26:10 Scott: Roger, Houston. This is Falcon. Read you loud and clear.
098:26:13 Mitchell: Okay, Falcon; reading you. We have a lot of noise on the loop - maybe it'll go away in a moment.
098:26:22 Irwin: Okay. Let's hope so. [Long pause.]
098:26:51 Scott: Okay, Endeavour, Another Noun 65 if you're ready.
Communication with Earth, using the omni-directional antennas on the LM and CSM, are poor. The radio link using the HGA will be reestablished soon, improving the comm with Al but the LM comm will still be poor.
098:26:59 Worden: On your mark.
098:27:00 Scott: 3, 2, 1...
098:27:02 Scott: ...Mark.
098:27:03 Worden: Okay. 98:26:59.60.
098:27:09 Scott: Okay. We're within three hundredths.
098:27:12 Worden: Okay.
098:27:41 Mitchell: Endeavour, Houston. Do you read?
098:27:46 Worden: Hello, Endeavour, Houston, this is Endeavour. Loud and clear.
098:27:50 Mitchell: Okay, Al. We read you through the static. Let us have Narrow on the High Gain [Antenna], please.
CapCom Ed Mitchell is asking for the HGA to be switched to a narrow beam setting. This concentrates the antenna's radio energy across a narrower angle, making it stronger for a receiving antenna sited within the centre of the beam, but also requiring a greater pointing accuracy.
098:28:01 Worden: Okay, you've got it. Narrow and Reacq.
In the Reacq(uire) mode, the HGA will continue to point at Earth as long as it stays within its limits of travel. If it loses lock, it will orient itself to a pair of angles dialled into two rotary knobs on the bottom right of panel 2.
098:28:09 Irwin: And, Houston, this is Falcon. We're going to configure for secondary S-band transmitter and receiver.
098:28:21 Mitchell: Okay, Falcon. Press on with secondary S-band. [Long pause.]
098:28:28 Irwin: Roger.
Like most systems on both spacecraft, there are two sets of S-band communications antennae on the LM. These are independent of the VHF system, which is used only for communications between the LM and CSM, for communication with the surface crew when they are near the LM, and for ranging by the CSM. The LM's S-band system is used for communications between the LM crew and Earth. The most promenent S-band antenna is a steerable, high gain antenna mounted on the upper, starboard side of the ascent stage. This system is supplemented by two omnidirectional antennae, mounted on the forward and aft faces of the ascent stage. The omni antenna are used if, for any reason, the steerable antenna cannot be used. This is usually when the LM's attitude does not allow the steerable to be pointed towards Earth, or if it has difficulties acquiring Earth.
098:29:06 Irwin: Houston, this is Falcon. How do you read?
098:29:15 Mitchell: Endeavour, Houston. Verify [that] on your last P52, you used option 1.
098:29:25 Worden: Houston, Endeavour. Go ahead.
098:29:28 Mitchell: Roger, Al. Verify that on your last P52, you used option 1.
098:29:39 Worden: I think that's a negative, Ed. I used option 3. Stand by one and I'll check.
098:29:45 Mitchell: Roger. We're standing by.
098:29:46 Irwin: Houston, how do you read Falcon?
098:29:49 Mitchell: Falcon, Houston. You're coming through; we have a lot of static on the line and they're trying to clear it up now. You're way down in the mud.
The expression "way down in the mud" means it is difficult for Mitchell to separate the crews voices from the noise. The signal to noise ratio is very poor.
098:30:06 Irwin: Okay. I can give you my time with that - [garble] time - 97:54:55.
098:30:19 Worden: Houston, Endeavour.
098:30:22 Mitchell: Go ahead, Endeavour.
098:30:26 Worden: Okay, Ed. I did do that on an option 3.
098:30:30 Mitchell: Okay. We'll have some words for you, and we're ready to uplink to you, Endeavour, if you'll give us - P00 and Accept.
Within what is a very busy timeline, Mission Control have to decide whether to accept the current alignment of the platform or to have Al repeat the P52 procedure.
098:30:39 Worden: Okay, you got P00 and Accept.
098:30:41 Mitchell: Falcon, Houston. Your S-band check is okay. You can press on, and I'll have your updates for you in a little while.
098:30:51 Irwin: Roger. [Long pause.]
098:31:04 Mitchell: And, Apollo 15; Houston. I'm going to hold off reading you any PADs at the moment until we can clear up our comm on the ground.
Mitchell refers to "Apollo 15" because he is referring to both spacecraft. He has PADs for both.
098:31:15 Irwin: Roger.
098:31:28 Mitchell: Falcon, Houston. Bring up your steerable [antenna], please. See if that helps our comm.
098:31:35 Irwin: In work.
Comm break.
We think the noise coming on the communication circuits at the present time is due primarily to the fact that the Lunar Module is still using the omni[-directional] antennas for communication. We've asked Scott and Irwin to bring up the LM steerable antenna and once they get that in operation we expect that the noise on the circuit will drop off significantly.
098:33:10 Irwin: Houston, this is Falcon. We're locked up on the - the High Gain. How do you read?
098:33:14 Mitchell: Okay, Jim. Reading you loud and clear now; that has seemed to improved our comm. And I'm - I'm ready to start with the PADs. I'll start with the CSM first, Al - whenever you're ready.
098:33:30 Irwin: Okay; he's working right now. Are you ready for an E-memory dump on the Falcon?
098:33:35 Mitchell: Stand by. [Long pause.]
098:34:06 Mitchell: Falcon, Houston. We're ready for the E-Mod [Erasable Memory Module] dump.
098:34:13 Irwin: Okay; Stand by. [Pause.]
098:34:22 Mitchell: En - Endeavour, Houston. The computer's yours.
098:34:29 Worden: Rog, Houston. [Long pause.]
The Erasable Memory Dump, which is in process at the moment, allows the Flight Controllers here in Mission Control, to look at the Erasable Memory Module in the Lunar Module Guidance Computer and see that everything is in order.
098:34:55 Mitchell: And, Endeavour; Houston. We will stay with the REFSMMAT you have.
In view of Al using the incorrect option for his last P52, Mission Control have elected to stay with the alignment they have. The small error should be taken out when the LM crew align their platform and when Al next realigns the CSM platform.
098:35:03 Worden: Okay, Ed. Thank you. [Long pause.]
098:35:59 Mitchell: Falcon, Houston. Give us P00 and Data. I have an uplink for you.
098:36:06 Scott: Roger, P00 and Data.
098:36:09 Mitchell: And I'm ready to give PADs, Falcon, whenever you want them.
098:36:17 Scott: [To Worden] Okay, Al; I'm checking it.
Jim's conversation with Al in the CSM has inadvertently been switched to the main comm circuit.
098:36:18 Scott: Go ahead, Ed.
098:36:21 Mitchell: All right, your LM DAP [Digital Auto Pilot] data first. CSM weight, 37679; LM weight, 36630. Your GDA [Gimbal Drive Actuator] drive angles onboard are good. [Pause.]
Spacecraft weight, or more accurately, its mass is very critical in calculating what is known as the "Moment of Inertia". This changes significantly as a function of mass and is used to calculate the firing times of the thrusters needed to establish known rates of rotation. Of course, all of these functions are under the control of the DAP (Digital AutoPilot), a set of algorithms in the CMC which are calibrated to accept values for vehicle mass in pounds. In metric units, the values loaded in the DAP are 17,091 kg for the CSM and 16,615 kg for the LM.
098:36:46 Scott: Okay; copy. CSM weight is 37679; LM weight, 36630.
Readers ought to be aware of NASA's common, though incorrect use of the term "weight" when they are really referring to "mass".
098:36:54 Mitchell: That's affirm. AGS abort constants. 224...
098:37:02 Scott: Go ahead.
098:37:03 Mitchell: ...plus 60442; 225, plus 29365; 226, plus 60449; 305, minus 01659; 662, minus 55021; 673, minus 32306.
The numbers read up to Falcon are intended for the AGS. The three digits are a memory location in the AGS computer, and the five digits represent data to be loaded there.
098:37:41 Scott: Okay; readback on the AGS abort constants. 60442, 29365, 60449, 01659, 55021 and 32306.
098:37:59 Mitchell: Affirm. The first 3 are plus, the last three are negative.
098:38:05 Scott: That's affirm. Houston, Falcon.
098:38:11 Mitchell: Go ahead, Falcon.
098:38:15 Scott: Okay. Everything is in order up to this point as far as the checkout goes, with the exception of the - LGC [LM Guidance Computer]. When we pushed in the LGC circuit breaker, we got a program light - with a 400 and R1. A Verb 5 Noun 9 gave us an 1105, which seems to be of little consequence; just thought you might like to know.
098:38:41 Mitchell: We copy, Dave.
Comm break.
Error code 1105 means the computer thinks that a downlink is happening too fast. However, as this occurred on powering the LGC, Dave correctly assumes it is just the result of a messy start-up of what is a very complex, logical device, and that it is nothing to worry about.
098:39:56 Mitchell: Falcon, Houston. The computer's yours.
098:40:01 Scott: Roger.
Comm break.
The four landing gear at the corners of the Lunar Module's descent stage are due to be deployed at about this time. The gear were designed to be folded in towards the descent stage to allow the LM to fit into the SLA (Spacecraft/Launch vehicle Adaptor), the conical fairing atop the Saturn V's S-IVB stage.
098:41:04 Mitchell: And, Endeavour; Houston. Are you about ready for your PADs?
098:41:14 Worden: Rog, Ed. Stand by one. [Long pause.]
098:41:43 Worden: Okay, Houston. Endeavour's ready to copy.
098:41:45 Mitchell: Okay. Falcon, the first one's a SEP[aration] time, if you would like that one, too. [Pause.]
098:41:56 Scott: Houston, Falcon. Go ahead; we'll stand by.
098:41:59 Mitchell: Okay. SEP: GET 100:13:56.00 - the pitch angle of 108 [degrees] [Pause.].
This is the time that the two spacecraft are due to undock and separate. There is a box in the Flight Plan to accept this data at 100:13. In the event, a poor connection of an umbilical to the probe mechanism will cause the undocking to delayed by a few minutes.
098:42:18 Worden: Understand, Ed. That's GET of 100:13:56.00. And that's a pitch angle of 108.
098:42:29 Mitchell: That's affirm, Al. Okay, the next one is CSM DAP data. [Pause.]
098:42:42 Worden: Okay; go.
098:42:43 Mitchell: Roger. CSM weight, 37679 [pounds, 17,091 kg]; pitch [trim], 0.49; yaw [trim], 1.04.
098:43:02 Worden: Understand. The DAP data is weight, 37679; pitch trim is 0.49; and yaw trim is 1.04. And do you have some signs on those?
098:43:14 Mitchell: It's a good readback, and say again your last?
098:43:21 Worden: Roger, Ed. I need a sign on the pitch and yaw trims.
098:43:24 Mitchell: All right - Let me check that.
098:43:29 Worden: Okay. [Pause.]
Mitchell checks with the controller sitting at the GNC console. For Apollo 15, the GNC controllers are Gary Coen, R. Watson, J. Kamman, L. Canin, J. DeAtkine.
098:43:39 Mitchell: It's affirm, Al, they're both positive. [Pause.]
098:43:47 Worden: Understand; they're both plus.
098:43:49 Mitchell: Okay; your P24 is next.
P24 is the program for "Rate aided optics tracking." Al will use it to rotate the spacecraft at an appropriate rate to roughly point the optics located on the back of the CM towards the landing site while he views it through the sextant. In particular, Al is to sight the appropriately named "Index" crater, which is right beside Falcon's intended target. Sighting and marking its position will help Mission Control refine the position of the landing site.
098:43:55 Worden: Okay; go ahead.
098:43:57 Mitchell: T-1, 100:46:29; T-2, 47:07; TCA, 47:37; T-3, 47:59; roll, pitch, and yaw are 008, 296, 000; north, 3 nautical miles. Noun 89, longitude-over-2, plus 2.149. Latitude and altitude are nominal. [Long pause.]
Explanation of P24 PAD follows: Additional notes state that at TCA, the spacecraft will be 3 nautical miles (5.6 km) north of the landmark. Noun 89, the final item, includes a value for the spacecraft's longitude when divided by two. This division by two is to give greater accuracy within the constraints of its limited range of permitted values. Therefore the true value for the longitude is (2.149 times 2) +4.298°.
098:44:58 Worden: Roger, Ed - Ed - Understand. P24 landmark tracking PAD: T-1 at 100:46:29; T-2, 47:07; TCA, 47:37; T-3, 47:59. It's a roll of 008; pitch, 296; yaw, 000. Expected north at 3 nautical miles. And understand the longitude-over-2 is plus 02.149, and latitude and altitude are as in the Flight Plan.
098:45:32 Mitchell: Good readback, Al. [Pause.]
098:45:39 Irwin: And, Houston, this is Falcon. ED [Explosive Devices] batteries both reading 37 volts.
The ED batteries are also known as the pyro(technic) batteries.
098:45:46 Mitchell: We copy that, Falcon; thank you. [Pause.]
098:45:52 Scott: Okay, Endeavour; Falcon. We're ready for a Docked IMU Coarse Align, if you are.
098:45:59 Worden: Okay, Falcon. Stand by one.
098:46:01 Scott: Okay; give us a call when you are in Min[imum] Deadband, Attitude hold.
098:46:05 Worden: Rog. [Long pause.]
The IMU in the LM is about to be aligned by reading the angles already in the CSM's IMU and transferring them across to the LM with appropriate translation between the two spacecrafts' coordinate systems.
As with the P52 realignments that Al makes in the CSM, the LM must be held steady while sightings are taken on the stars. The LM's RCS is not ready to be used for this so the CSM's RCS will be used instead.
The "deadband" is the range of attitudes on either side of the ideal that the vehicle is allowed to drift to before active measures are taken by the spacecraft's control system to correct it. While the spacecraft's attitude is within the deadband, there is no thruster activity. When it drifts to the limits of the deadband, the DAP works out which thrusters to fire to restore the correct attitude.
The deadband is usually set to narrow (±0.5°) or wide (±5.0°). The narrow setting is more costly in RCS propellant and is only used when high pointing accuracy is required.
098:46:21 Worden: Okay, Dave; we're there.
098:46:23 Scott: Okay; if you [could] read us your gimbal angles, please. [Pause.]
098:46:33 Worden: Okay; R1 is plus 001.24, R2 is plus 101.66, R3 is plus 005.37.
Al uses Verb 6 (display decimal values) to call up the three values residing in Noun 20 (current gimbal angles). These angle readings are in hundredths of a degree.
098:46:47 Scott: Plus 001.24, 101.66, 005.37.
098:46:54 Worden: Rog.
Long comm break.
Al holds the docked spacecraft in a steady attitude while Dave begins the alignment of the LM's guidance platform.
Performing this initial alignment of the IMU is done in two steps. First, a coarse alignment of the LM's IMU is performed while the spacecraft are docked, using the known orientation of the CSM's IMU as a reference. Since there is no computer-to-computer connection between the CSM and LM, gimbal angles of the CSM's IMU are recorded manually from the DSKY. To make these values usable for the LM's IMU, simple calculations are made with the recorded gimbal angles to account for the different orientations of the coordinate systems of the two spacecraft. Additionally, the difference in roll orientation between the two spacecraft that existed during docking is obtained from scribed marks in the docking tunnel (this value is generally quite small, in this case a nearly perfect -0.1° as reported by the crew at 034:44:38).
This part of the procedure was rather melodramatically portrayed in the movie "Apollo 13", during the emergency LM activation immediately after the explosion. It should be noted that this process uses only simple addition and subtraction, and doesn't require a slide rule!
Calculations completed, the crew then instructs the computer to drive the gimbals of the LM's IMU to this orientation. While not sufficiently accurate for precise maneuvering, the platform now has a reasonably good idea of "which way is up."
The second step in preparing the IMU for use is the fine alignment. Using the Alignment Optical Telescope (AOT) located between the two crewmembers, star sightings are taken which are used to determine the orientation of the spacecraft, and subsequently, the intended orientation of the platform.
The AOT itself is a remarkably ingenious device, whose elegance is in the simplicity of its design. Unlike the CSM's sophisticated sextant and telescope systems, the AOT is a simple, unity power telescope with a 60 degree field of view that is manually rotated between six fixed positions: Forward, forward right, aft right, aft, aft left, and forward left. It incorporates two methods of using the stars to determine the orientation of the platform. One is for in-flight use, the other for when the LM is on the surface.
Sighting the stars is done against an illuminated reticle on which is inscribed a pair of cross-hairs, for use when the LM is flying; and a pair of radial lines and spirals which come into play for surface realignments.
Layout of AOT reticle.
In both cases, the computer is told which of the six detents the AOT is currently in and which star is to be marked.
In-flight method of use of AOT reticle.
To mark on a star during flight, the LM is maneuvered to make the star move across the X and Y cross-hairs, with marks being taken when it is coincident with each axis. The computer can define two intersecting planes from these, whose vertex points to the star. A similar pair of marks on another star gives the two vectors the computer requires to calculate the IMU's orientation. Program 52 in the LM's computer is used for this procedure.
This first method is not used for the initial IMU alignment as the LM is still attached to the CSM, whose mass makes it undesirable to try maneuvering the entire stack from the light end. Instead they use the second method which uses P57 in the LM computer. This is normally used on the lunar surface. It is also a simple two step process once the computer knows which star is being viewed at which detent. First, the reticle is rotated until it is between the two radial lines (the "cursor") and the "Mark X" switch is pressed, yielding the "shaft angle".
Measurement of shaft angle using AOT reticle.
The reticle is rotated again until the star is between the two "spirals" and the "Mark Y" switch is depressed, giving the "reticle angle".
Measurement of reticle angle using AOT reticle.
Calculations performed by the computer convert this information into a vector to the star. This process is repeated with a second star, and when completed, the computer is able to determine the IMU's orientation which can now be accurately aligned.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
098:50:45 Mitchell: Falcon...
098:50:46 Scott: Houston, Falcon. We got about 9 minutes 'til sunset here.
098:50:51 Mitchell: Okay, Dave. And we have a clock update for you of about 66 centiseconds if you'll give us P00 and Data, please.
098:51:01 Scott: Okay; P00 and Data. You got it. [Pause.]
098:51:09 Scott: And, Houston; Falcon. We'd like to do the RCS pressurization now since we're a tad ahead, if - you're ready to take that?
098:51:18 Mitchell: Okay; we're ready, Falcon; go ahead.
Pressurisation of the LM's RCS is not due until about 99:10.
098:51:23 Scott: Okay. [Long pause.]
098:51:48 Mitchell: And, Endeavour, Houston. When you get a moment, we'll take your read-outs from the last P52.
098:51:58 Worden: Okay, Ed. [Pause.]
It will be a couple of minutes before Al recalls the required values from the computer and has them ready for Mission Control.
098:52:03 Mitchell: Falcon, the computer's yours.
098:52:08 Scott: Roger.
Comm break.
098:53:09 Scott: Houston, Falcon. A slight pause here while we look at the landing site; we're going right over it.
The next time they pass over Hadley, in about 2 hours time, Al will be taking marks on Index crater using the sextant while the spacecraft is rotated to keep the optics pointed roughly at the landing site.
098:53:16 Mitchell: Ah. Roger. [Long pause.]
098:53:31 Scott: Okay; a few interesting differences there. Index is much more subtle than we've seen on the simulator. And Earthlight is much sharper with a much deeper shadow.
098:53:43 Mitchell: Copy, Dave. [Long pause.]
Earthlight Crater sits just north west of the South Cluster on the plain at Hadley. Its name commemorates a science fiction novel by Arthur C. Clarke of the same name. In the opening chapter, Clarke described a monorail ride across the Apennines near Hadley and then onward for about 900 kilometers to an astronomical observatory in the crater Plato on the northern edge of the Imbrium Basin.
Dave's comment about the subtlety of Index presages the difficulties he and Jim Irwin will later experience when they try to locate themselves on the surface.
098:54:03 Worden: Houston, Endeavour. Here are the P52 numbers.
098:54:07 Mitchell: Say again, Endeavour.
098:54:11 Worden: Roger; I got the P52 numbers for you.
098:54:13 Mitchell: Ready to copy, Al.
098:54:18 Worden: Okay, Ed. Stars 41 and 42; Noun 05 was plus four balls 1. Gyro torquing angles were minus 00.010, minus 00.009, minus 00.025. And they were torqued out at 97:39 even.
098:54:47 Mitchell: Copied that, Al. And could you give us your LM power switchover time, please? [Pause.]
098:54:58 Worden: Roger. That was at 97:35.
This is the time Al stopped the electricity supply from Endeavour to Falcon. From now on, the LM will depend on its batteries as its only electrical supply.
098:55:03 Mitchell: We copy that. And what was the result of the VHF check; does it work okay?
098:55:11 Worden: That was satisfactory both ways - far as I know.
098:55:14 Mitchell: Thank you.
098:55:18 Scott: Rog, Houston. It was good both ways. [Pause.]
098:55:28 Scott: Hey, Endeavour; Falcon. Did you copy that on the difference between Earthlight [Crater] and Index [Crater].
098:55:33 Worden: Rog.
098:55:34 Scott: Okay. [Pause.]
098:55:41 Scott: And, Houston. The RCS looks good up here on the Falcon.
Dave is noting that the RCS pressurisation is complete and successful.
098:55:45 Mitchell: And it looks good down here, Dave.
098:55:50 Scott: Okay. We'll pick up the alignment now and get back to you later on with the RCS checkout.
098:55:55 Mitchell: Okay.
Very long comm break.
LM Flight Plan page 3-110.
CSM Flight Plan page 3-111.
Dave is carrying out a P57 realignment of the Lunar Module's IMU. This is the Spiral/Cursor technique which is normally reserved for alignments on the lunar surface.
Irwin, from the 1971 Technical debrief: "[To Scott] Your alignment went real well. You didn't have any trouble seeing the stars."
Scott, from the 1971 Technical debrief: "Yes, I did too. I had a tough time seeing Dabih. Dabih was a good star as far as position goes, but it was a very difficult star to see as far as alignment goes. If you can pick out bright stars, it'll sure help you. I guess the message there is, even if you don't have a NAV[igation] star, I think I'd ensure I had a good bright star for those alignments through the AOT. But the alignment went very well. The P57 docked is a very practical technique. You get a good alignment out of it, and subsequent drift checks showed that we had a good platform."
Al has put his helmet and gloves on and is checking the integrity of the suit. He will remove them shortly after LOS in about half an hour having made a check of the integrity of the CM forward hatch.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
At the present time Scott and Irwin are aligning the stable platform used as an attitude reference by the Lunar Module guidance system. We presently show the docked spacecraft in an orbit 62 by 9.4 nautical miles [114.8 by 17.4 km] and presently at an altitude of about 10.6 nautical miles [19.6 km].
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
099:10:39 Scott: Houston, Falcon. That P57 up here, docked, works pretty well. [Long pause.]
099:11:22 Scott: Houston, Falcon, do you have the torquing angles?
099:11:24 Mitchell: That's affirmative.
Rather than reading them out, Dave has brought the gimbal torquing angles up on the LM's DSKY from where Mission Control are able to read them by telemetry. According to a table on page 7-6 of the Apollo 15 post-flight Mission Report, Dave used stars 42 (Peacock, Alpha Pavonis) and 37 (Nunki, Sigma Sagittarii). The table says he used the P52 method which is not the case as P57 was used. The torqueing angles are relatively large: X, +0.171°; Y, -0.236°; Z, -0.663°. This is to be expected as the prior alignment was based on angles brought across from the CSM and is considered a coarse alignment.
099:11:29 Scott: Okay; we'll torque them at 11:30.
099:11:34 Mitchell: Roger. [Pause.] Observe the five balls there.
Dave's sighting of the two stars chosen for the P52 alignment, and his measurement of the angle between them, was as accurate as the system is capable of; five balls means 000.00°. Crews like to have this number as low as possible and Mitchell is complimenting Dave on the accuracy of his work. The number represents a comparison of two angles; the known angle between the two stars, the measured angle between them. All zeroes means that to one hundredth of a degree, the two angles are identical.
099:11:47 Scott: Yeah; a couple of interesting things, we have [a] reflection off the Command Module apparently from Earthlight. And it's sort of tough to track the star with the Command Module deadbanding, but seems like if you get the star in the crosshairs, why, the optics take care of it for you.
099:12:03 Mitchell: Copy. [Long pause.]
"Deadbanding" is the CM's motion back and forth within the preset deadband range.
Dave is commenting that during his IMU alignment, the combined CM/LM was not completely steady, but was moving around slightly. At Dave's request at 098:46:01, Al set it to its minimum setting, ±0.5°. Although this amount sounds insignificant, it can complicate the alignment of the platform when crews are sighting on stars. He is also pointing out that stray reflections of light from Earth are coming off the Command Module and interfering with the sighting process.
099:12:23 Mitchell: And, Falcon; Houston. Will you - you verify the roll CAL for us, please? [Pause.]
The Flight Plan asks the crew to take a note of the angle between the two spacecraft at 97:49. They had already done this during their first entry into the LM on the second day of the mission.
099:12:34 Irwin: Roger. Minus .1.
099:12:37 Mitchell: Copy, Dave. [Long pause.]
099:13:11 Scott: Okay, Endeavour; Falcon. Mid [correcting himself] - min[imum] deadband no longer required.
099:13:15 Worden: Okay. [Pause.]
099:13:22 Scott: Okay, Houston; Falcon. We're ready for the RCS checkout, if you are.
099:13:28 Mitchell: We're ready to go, Falcon.
099:13:32 Scott: Roger. [Long pause.]
099:14:25 Scott: Okay, Houston; Falcon. Do you have your High Bit Rate?
099:14:32 Mitchell: That's affirm, Dave.
099:14:37 Scott: Okay. And, Endeavour. We need you in a wide deadband Attitude Hold.
099:14:44 Worden: Okay; wide deadband Attitude Hold.
099:14:47 Scott: Roger.
Dave is ensuring everyone is ready for the series of checks he is about to make to the RCS on the LM's ascent stage as he will be firing the thrusters.
Al must have the CSM's DAP set to use a wide deadband. During these RCS hot fire checks, Falcon will be moving the combined CSM/LM stack around by several degrees, and they do not want the CSM's RCS compensating for this by trying to tightly hold attitude and wasting its fuel.
Additionally, Dave is making sure that Mission Control are receiving telemetry from the LM at the high bit rate as they will wish to observe the many parameters in the RCS.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
099:17:30 Scott: Endeavour, Falcon. Do you have any jet fires going on over there?
099:17:38 Worden: I haven't detected any, Dave.
099:17:41 Scott: Okay.
099:17:45 Worden: You want me to go Free now?
099:17:47 Scott: Rog. Go Free, please. [Long pause.]
By switching the CMC to its 'Free' mode, the CSM control attitude control system stops trying to bring the spacecraft into the deadband. Dave seems to have noticed some attempt by the CSM to oppose his firings of Falcon's thrusters and wants the CSM RCS disabled in the meantime.
099:18:10 Scott: Okay, Endeavour. We'll be firing the direct coils.
099:18:16 Worden: Okay.
Comm break.
Scott and Irwin are now preparing to fire each of their attitude control thrusters in the Reaction Control System in a check out here.
[Download MP3 audio file. Clip courtesy John Stoll, ACR Senior Technician at NASA Johnson.]
099:20:47 Scott: Okay, Endeavour. Hot fire check is complete. Everything looks good. You can go back to wide deadband Attitude Hold.
099:20:52 Worden: Okay. And I'm going to turn the roll jets off and put the hatch in, if you don't mind.
099:20:57 Scott: Oh, good. [Pause.]
099:21:07 Mitchell: And, Falcon; Houston.
099:21:08 Scott: And, Houston, Falcon. How did it look down there?
099:21:10 Mitchell: I was just going to tell you, Dave, hot fire check looked good here.
099:21:16 Scott: Okay. They're nice and positive, aren't they?
099:21:20 Mitchell: That's affirm. [Long pause.]
Although Dave has spent many hours in the LM simulators, this is the first time he has had a chance to try the real thing and he seems to approve of the responsiveness of the RCS controls. Note that with Ed Mitchell, who flew on Apollo 14, he is talking to someone who has already been there.
The docking probe and drogue have been reinstalled. Al is closing the CM forward hatch while Jim closes the LM overhead hatch.
099:21:47 Scott: Endeavour, Falcon. Could you verify RCS thruster, B-3, Off, and the Transponder, Off, please?
Thruster B-3 aims up towards the LM. The reason for it being disabled may be to avoid impingement on part of the LM.
099:21:54 Worden: I'll verify both those.
099:21:56 Scott: Thank you. [Long pause.]
099:22:38 Worden: And, Falcon; Endeavour. I'm cocking the latches now.
099:22:41 Scott: Okay.
Long comm break.
Al has extended the probe to engage the three capture latches on the its tip with the LM's drogue. He then retracts the probe slightly so that it firmly grips the drogue. He then cocks the twelve docking latches around the rim of the tunnel ready for release. These have been holding the CSM and LM together since the early hours of the mission. Now only the capture latches are holding the two spacecraft together against the pressure of the cabin. Al then reinstalls the forward hatch.
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