We have about 2 minutes now before Apollo 15 goes behind the Moon on the 11th revolution. Both spacecraft, Endeavour and Falcon, appear to be in very good shape at the moment, and we'll be giving the crew a Go for undocking and separation, which will occur at about 100 hours, 13 minutes, 56 seconds; right on the scheduled Flight Plan time.
099:29:18 Mitchell: Okay, Apollo 15; Houston. You're Go for undocking. You're 45 seconds from LOS, and we observed your Rendezvous Radar test. Falcon, also, we have not seen you reset the DAP [Digital Auto Pilot].
099:29:35 Scott: Okay, understand. I'll get the DAP reset, and the tapemeter looks like it works fine.
099:29:40 Mitchell: Very good, Dave. Glad to hear it.
The tapemeter displays the distance and distance rate in two modes. During the descent it will be the altitude and altitude rate meter relative to the lunar surface using data from the Landing Radar. During ascent and rendezvous, it will display the range and range rate between the Command Module and the Lunar Module derived from Rendezvous Radar data. Proper operation of the tapemeter was a concern since the initial inspection of the LM at 34:30 when the crew found the outer glass pane of the instrument had broken.
And we've had Loss Of Signal. That last report from Dave Scott that the tapemeter appears to be working well. That's the - one of the onboard indicators used to read out the Rendezvous Radar and also the Landing Radar altitude and altitude rate information, and is one of several means available to the crew and to the guidance system for getting that needed information. As Apollo 15 went around the corner, the spacecraft was in an orbit of 61.9 nautical miles [114.6 km] at its high point and 9.4 nautical miles [17.4 km] at its low point passing over the landing site. Apollo 15, Endeavour and Falcon, will be undocking, as we said, at 100 hours, 13 minutes, 56 seconds; which will be shortly before we reacquire the spacecraft on the 12th revolution. During the 12th and 13th revolutions, Al Worden will be tracking a crater near the landing site, Index Crater. This information will be used to update the knowledge of where the landing site is precisely and also where the spacecraft orbit is with respect to the landing site. Now this information will be fed into the Falcon computer just prior to powered descent. Shortly we're going to replay the videotape of this morning's television transmission from the spacecraft in lunar orbit and we'll be reacquiring in about 45 minutes. This is Apollo Control at 99 hours, 32 minutes.
As Al removes his helmet and gloves, Dave and Jim are putting theirs on in preparation for the landing. Aboard both spacecraft, this far-side pass is mostly spent preparing for undocking and separation. Al sets up a Hasselblad and a DAC (Data Acquisition Camera, the small, variable frame-rate Maurer movie camera) for photography of the departing Lunar Module out of window 2 of the Command Module. He carries out a maneuver to trim the attitude of the combined stack with the CSM towards the Moon and the LM away from it. Note that this is only a trim to a maneuver carried out over two hours ago.
Dave and Jim do a suit pressure integrity check, but find it does not hold pressure well enough at the first try.
Irwin, from the 1971 Technical debrief: "Probably our biggest surprise of the activation, was the pressure integrity check. When we obviously did not have integrity, we tried going to the secondary canister and still didn't have any integrity. We decided to press on through it and do the rate check, which we did. Then, later on, I guess it was about 10 minutes before undocking, we came back and redid the pressure integrity check. Of course, we cycled through it right from the start; and this time, it worked out great. I think we had a 1/10th drop in 1 minute."
Scott, from the 1971 Technical debrief: "I guess on the first one, we had something like 1 psi drop in 1 minute, didn't we?"
Irwin, from the 1971 Technical debrief: "Yes. It was obviously something open, and I don't know whether the valve was just not seating properly or just what it was."
Scott, from the 1971 Technical debrief: "Okay, you cycled the valve back there several times. We both fiddled with the detent and had a good detent in it, but couldn't come up with an answer."
Irwin, from the 1971 Technical debrief: "Well, I guess the ground never came back to us with anymore words on it either."
Scott, from the 1971 Technical debrief: "There was a question in my mind as to what the mission rule was at that time. I guess the mission rule was to undock and press on, which we were going to do had we not gotten a good check. But it was a good thing we started that check a little early. It gave us a chance to come around and do it again. The message is to get ahead and stay ahead; that's why we stayed 10 to 15 minutes ahead. Every time we got to a point in the time line where we could do something, we went ahead and did it, even though it was a little early."
They are to undock by Al extending the probe, then, once motions of the two craft relative to each other have settled, the three capture latches are released.
Immediately after undocking, he is to move the CSM away, or translate in a minus-X direction, at 0.3 metres per second (one foot per second) to separate the two spacecraft and avoid a collision. In the LM, Jim is also to film the undocking and separation while Dave pitches the LM up 90° and left 60° to allow Al to visually inspect the landing gear.
099:31:28 Worden (onboard): Okay, Falcon; Endeavour. I got the hatch in and you want to verify your hatch closed?
099:31:35 Scott (onboard): Okay, that's verified. Closed and locked.
099:31:37 Worden (onboard): Okay, I'll do a hatch integrity check then.
099:31:40 Scott (onboard): Okay.
099:32:43 Scott (onboard): Okay, Endeavour; Falcon. Our radar checks out okay, and your B-B, Off, and transponder, off, are no longer required.
099:32:49 Worden (onboard): Okay. Thank you.
099:32:53 Irwin (onboard): And, Al, we're going B data.
099:33:00 Worden (onboard): Okay.
099:38:34 Worden (onboard): Falcon, Endeavour. Your transponder checked out okay.
099:38:37 Scott (onboard): Oh, very good. Thank you.
099:47:15 Worden (onboard): Okay, Falcon; Endeavour. We're maneuvering to Sep attitude.
099:47:19 Scott (onboard): Okay.
099:47:30 Scott (onboard): Okay, Endeavour; Falcon. Have you vented the tunnel?
099:47:33 Worden (onboard): Roger.
099:47:34 Scott (onboard): Okay; thank you.
099:47:53 Scott (onboard): Hear that noise with us, Al?
099:47:58 Worden (onboard): Okay.
Rev 12 begins at about 099:51.
099:57:59 Scott (onboard): Okay, Al, are you about in attitude now?
099:58:03 Worden (onboard): Right, Dave. About 5 degrees to go.
099:58:05 Scott (onboard): Okay. We're down to...
099:58:09 Irwin (onboard): Oh, yes. We should...
099:58:10 Scott (onboard): ...just about everything and it's all shipshape.
099:58:13 Worden (onboard): Good.
099:58:21 Scott (onboard): Even the old broken tape meter seems to work.
099:58:27 Irwin (onboard): That figures.
099:58:58 Worden (onboard): Okay, we're at attitude now.
099:59:01 Scott (onboard): Okay; thank you.
100:03:15 Worden (onboard): Okay, Falcon; Endeavour. Doing the trim maneuver.
100:03:18 Scott (onboard): Okay.
100:03:53 Worden (onboard): Okay. We're setting at attitude and I've got 10 minutes -
100:03:56 Worden (onboard): Mark - to go.
100:03:57 Irwin (onboard): Okay, we're right with you.
100:04:09 Scott (onboard): And we're right on the attitude.
100:04:11 Worden (onboard): Okay, good.
100:04:49 Scott (onboard): Okay, Al, at 5 minutes to go, we need a - 06 20. Okay?
100:04:56 Worden (onboard): Okay, you want it now?
100:04:59 Scott (onboard): No, let's wait down until 5 minutes. Okay?
100:05:02 Worden (onboard): Okay.
100:05:03 Scott (onboard): I'd like to give them as much time on the platform as we call.
100:08:44 Worden (onboard): Coming up on 5 minutes in 10 seconds.
100:08:46 Scott (onboard): Okay, I'll give you a mark.
100:08:53 Scott (onboard): 3, 2, 1...
100:08:55 Scott (onboard): Mark.
100:08:57 Worden (onboard): Okay. 35975, 10818, 35995.
100:09:10 Scott (onboard): Give me that last one again.
100:09:11 Worden (onboard): Okay. 35995.
100:09:17 Scott (onboard): Okay. 35915, 10818, 35995.
100:09:24 Worden (onboard): The last two were okay. The first one was 35975.
100:09:29 Scott (onboard): Okay; 75. I don't write too good with gloves on.
This is Apollo Control. We're now about 2 minutes from re-establishing radio contact with Endeavour and Falcon. And when next we hear from the 2 vehicles, they should be separated and moving apart at the rate of about 1 foot per second [0.3 m/s]. About a second after separation, Al Worden was to fire the thrusters on the Command Module for about 3 seconds to give them that 1 foot per second separation velocity. The Flight Dynamics Officer [FIDO] reported that we're seeing a consistent downtrack error of about 15,000 feet [about 4,600 metres] per revolution. This is not unduly large, and is the sort of error that will be taken out by targeting the powered descent at the time of ignition and also by updating the state vector or the LM guidance systems knowledge of the orbit that it is in. This sort of an error can comfortably be removed prior to the beginning of the powered descent.
And we're coming up now on 30 seconds until reacquisition. The first order of business will be to confirm the undocking and separation.
And the guidance officer has just reported that a review of the Erasable Memory on the Lunar Module shows that the LM guidance system Erasable Memory is in very good condition. And we've just had Acquisition Of Signal.
On coming around the Moon's eastern limb, Dave reports to Mission Control that things have not gone according to plan.
100:18:13 Mitchell: Endeavour, Houston. Standing by for a Sep report.
100:18:21 Scott: Okay, Houston; this is the Falcon. We didn't get a Sep, and Al's been checking the umbilicals down on the probe [garble].
100:18:33 Mitchell: Okay. We didn't read that, except no Sep. [Long pause.]
Dave Scott reporting we have not gotten separation. They said they were going to be checking the probe umbilicals. We'll stand by for further reports.
The two spacecraft have not separated because they have not undocked. Specifically, the term "Separation" refers to the maneuvers which puts distance between them after they have disengaged the capture latches and undocked.
100:18:54 Scott: Okay, Houston; Falcon. We got no Sep, and Al's going back into the tunnel to check the umbilicals now. And I guess we'll stand by for your recommendation.
100:19:07 Mitchell: Okay, Falcon. We copy. And we'll have some words in a minute.
100:19:13 Scott: Okay. [Pause.] There was not even any motion on the probe.
100:19:23 Mitchell: Roger. We copy. [Long pause.]
100:19:48 Mitchell: Falcon, Houston. We have no probe temp[erature data], which indicates the umbilical is probably not well connected.
100:19:58 Scott: Okay. Well, that's just what he's checking. Thank you. [Long pause.]
100:20:47 Mitchell: And, 15; Houston. Be advised that we have plenty of time here on the Sep, up to 40 minutes or so. Procedures will be to get vertical or get - now get vertical on the orb rate ball and standard Sep procedures.
100:21:06 Scott: Okay, fine. We can handle that. [Pause.]
The removable probe assembly is connected to the rest of the spacecraft via two umbilicals which supply power for the extension and latch release mechanisms, and which carry the signals from various sensors which indicate the health and state of the assembly. Since telemetry about the temperature of the probe is not reaching Mission Control, they are surmising that an umbilical is not connected properly and that the command to disengage the capture latches may not have got through.
Note that although the two spacecraft are being held together by the three capture latches, these are more than adequate to hold the seal between the CSM and LM once a hard dock and the docking latches had compressed the interface.
To recap the situation here, you heard Dave Scott report that we did not get a separation. The preliminary indication is that we may have an umbilical that is not properly connected in which case power would not flow to the probe and this appears to be the most likely cause at the moment. The Flight Dynamics Officer has reported that we can go up to about 40 minutes without separating before we run into problems in an on-time powered descent.
100:21:41 Scott: Hey, Al, I hope you made sure the Extend/Release switch was Off when you went in there.
Dave's worry is that if the switch to extend the probe is in the On position, and Al reconnects the umbilical, the probe would immediately extend. With the docking latches unset, the two craft would separate but with the CM forward hatch removed, the CM cabin would immediately evacuate.
100:21:50 Worden: Rog.
100:21:51 Scott: Okay.
Comm break.
100:22:59 Mitchell: Apollo 15, Houston. We're seeing the telemetry on the probe now. I presume that [loose umbilical plug] may have been our problem.
100:23:09 Scott: Okay, very good. [Pause.]
100:23:18 Worden: Okay, David. I'm venting you down now.
Al has replaced the forward hatch in the Command Module and is venting the trapped air out of the tunnel.
100:23:21 Scott: Okay; good show. [Pause.]
100:23:27 Worden: And that probe was loose in the - the umbilical was loose in Victor [its socket].
100:23:31 Scott: Okay, I'm glad you found something. [Pause.]
The indication here on the ground that we had...
100:23:41 Falcon: Go ahead and take your time. And when you get all squared away, give us about 5 minutes or so, and we'll be all set.
100:23:45 Worden: Okay.
100:23:49 Mitchell: And there's plenty of time to get a good hatch integrity check, 15, and do the procedure leisurely.
100:23:59 Worden: Okay, Ed. That's in work now.
Comm break.
The - the indication here on the ground that we had a loose umbilical to the probe was a - an off-scale high temperature reading on the probe which indicated that that umbilical was not connected. Al Worden, on inspection, confirmed that indeed, the umbilical was loose. We presume at this point that we'll be able to go ahead with a normal undocking.
100:25:10 Irwin: Houston, Falcon. In the meantime, can I give you the gimbal angles under Verb 06 Noun 20. [Pause.]
Verb 06 Noun 20 means display (in decimal) the current gimbal angles from the IMU.
100:25:24 Mitchell: This is Houston; go ahead.
100:25:30 Scott: Okay. The GET was 100:08:56; and the CSM, 35975, 10818, 35995. The LM, 30009, 28836, zip, zip, zip, zip four [00004].
100:26:01 Mitchell: We copy.
Comm break.
Now that the problem with the probe's umbilical is fixed, the crew can work to regain the time line. While Al is rechecking the integrity of his hatch's seal, Jim is reading up the IMU angles for both the CSM and the LM. The Flight Plan requires that these are noted prior to undocking so Mission Control can verify their attitude. Al would have read the CSM angles across to the LM at their request. With the undocking still to occur, Jim's read-out is redundant.
100:27:04 Mitchell: And, Endeavour; Houston. Reminder: We want the Sep in a local vertical attitude.
100:27:04 Worden: Rog; understand. Local vertical. [Long pause.]
100:27:28 Scott: Houston, Falcon. You know, we've - You might run out of an attitude and a time, and it might save a little gas. [Long pause.]
The attitude of the stack would have aligned with the local vertical; CSM toward the Moon, LM away from it, at the planned time of undocking. As they have come further around in their orbit, the Moon's curve has altered the local vertical and they must remaneuver to match it in time for the undocking. The time for undocking is now uncertain and Dave is asking Mission Control to define undocking times and the appropriate angles for those times to which they should maneuver. This should prevent them trying to chase the Moon's curve.
100:27:53 Mitchell: Okay. In 2 minutes, we have an angle of 55.7 [degrees]. We're working on one for 5 minutes later.
100:27:59 Unidentified voice: Go ahead.
100:28:03 Scott: Well, it's going to take fairly sizeable maneuver, and it takes a little while to maneuver [at] two-tenths of degree per second.
100:28:08 Mitchell: Rog; understand. We're getting another for you for 5 minutes from now. [Long pause.]
100:28:23 Scott: Better make it 10.
100:28:27 Mitchell: Yeah; we'll have one for every 5 minutes, Dave.
100:28:33 Scott: Okay. [Long pause.]
100:28:51 Mitchell: And 15; Houston. We're not going to be able to make the P24 this pass, we don't believe. So don't worry about it. [Long pause.]
100:29:08 Worden: Rog. [Long pause.]
P24 is the landmark tracking of the landmark near the landing site which Al Worden was scheduled to perform from the Command Module. We'll be doing that again on the next revolution. And at the moment we're standing by for another attempt at undocking and separation.
100:30:04 Mitchell: Endeavour, Houston. Let's head for a - an inertial pitch gimbal angle at the 30 degrees. And we may have to touch that up, but that's approximate. [Long pause.]
100:30:24 Worden: Okay, Houston; Endeavour. Going towards 30 degrees pitch.
100:30:51 Mitchell: And, Endeavour; Houston. That angle is good for 100 hours and 38 minutes [GET], and it's not very critical. We'll use it anytime around there. [Pause.]
100:31:08 Worden: Yeah. Roger, Houston.
Long comm break.
Our Guidance and Control Officer estimates that it will be about 6 minutes before the spacecraft are in the proper attitude for separation.
This is Apollo Control. At the moment we're awaiting the spacecraft to maneuver into the proper attitude for separation. Again to recap, a separation was to have occurred about 4 minutes prior to reacquiring spacecraft on the 12th revolution. Dave Scott, once reacquired, reported that separation had not occurred. On the ground we noticed at that time an indication of a high temperature - off scale high on the probe assembly which indicated that we possibly did not have electrical power to the probe, which in turn, is an indication that the umbilical is either not connected or not firm in its seating. On removing the hatch and inspecting the tunnel, Al Worden reported that this was, in fact, the case and he tightened up the umbilical. The hatch has now been secured and we would expect to have a normal separation. The principal effect of the late separation will be to remove the possibility of doing the landmark tracking which Al Worden was scheduled to do on this revolution.
Note that off-scale-high does not mean that the probe was extremely hot. Depending on the sensor and the support electronics, a broken connection might be read as a value far above or below its expected range.
Worden, from the 1971 Technical debrief: "I guess there was an anomaly that happened during maneuvering to an undocking attitude. I checked things off on the Flight Plan as we went. We went right down the line on the Flight Plan and the checklist. We released the docking latch, put the suit on, and did a suit circuit integrity check. We installed the hatch, got a LM/CM Delta-P, and went right on down the time line. We did a Verb 49 maneuver to the undocking attitude and the Sep attitude, went into P41 SCS [using the RCS to move away from the LM] and the whole thing. We went through the undocking, checklist and got the probe circuit breakers in. I guess the major thing is that everything was nominal, except when I went to Release on the probe Extend/Release switch; nothing happened. Nothing.
Worden (continued): "I rechecked the circuit breakers and hit the Extend switch again, but nothing happened. At that point, there wasn't anything I could check inside. The only two things that you've got are the circuit breakers and the switch. So, I figured that there had to be something back in the tunnel. I went back and pressurized the tunnel. I looked in the tunnel and there was nothing there that was out of order. So I thought I'd go ahead and check those connectors again. I pulled the connectors off and put them back on. I figured that if that wasn't it then we had a serious problem. I put the hatch back in, depressurized the tunnel, and went through the checklist again, depressurizing the tunnel. We got a new attitude from the ground, which was the local vertical attitude. That time it worked fine. That's really a mystery to me."
Scott, from the 1971 Technical debrief: "We got a couple of good calls from the ground on that; one when we came around the corner. I called and told them we had not had a Sep and that you were in the tunnel checking the umbilicals. Right away they came back and said they had no TM [telemetry] on the probe, which gave them the indication that there was something loose on the umbilicals, and that was, of course, the last thing to check. Soon after you checked everything they reported getting their TM, so that was a pretty good confirmation that that was the problem. Then, I thought another good call was immediately or very soon after. They came up and said no problem on the time, that we had 40 minutes to get the Sep done and just go to the local vertical attitude, somewhere around there, which was a big help to us. Jim and I were trying to plan ahead to make sure we didn't get too far behind the time line and get hooked into having to delay PDI rev. We were trying to plan our next series of events for a late separation. It was nice to have that call, to know that we had 40 minutes to get things squared away and move on."
Worden, from the 1971 Technical debrief: "The MCC-H came up with an attitude after you'd requested that they give us the time and an attitude. We went to that attitude and we were there 4 or 5 minutes before the time. It worked out fine."
Scott, from the 1971 Technical debrief: "I thought that was a very good recovery for an off-nominal situation."
Slayton, from the 1971 Technical debrief: "It sounds like you guys were ahead of it, though, by the time you came around the corner."
Worden, from the 1971 Technical debrief: "Yes, that's right. There was only one way to go."
Scott, from the 1971 Technical debrief: "You check the switches and the circuit breakers, and the next thing you have to do is go into the tunnel."
Worden, from the 1971 Technical debrief: "Anyway, we got undocked and from there on it went pretty well, except that the undocking was too late to do that low altitude P24. So we skipped that."
100:36:11 Worden: Okay, Falcon; this is Endeavour. And I'm all set up again. The tunnel's sealed in and the pressure's good.
100:36:17 Scott: Okay, very good. Give me a minute.
100:36:19 Worden: Okay. And I'll stop the maneuver at local vertical.
100:36:26 Scott: Okay. Have you - Are you in Attitude Hold now?
100:36:29 Worden: Negative. Will be in just about another 10 degrees.
100:36:35 Scott: Okay.
That's Al Worden and Dave Scott talking back and forth between Endeavour and Falcon.
100:36:44 Worden: Okay. As you get all set, I need about one minute to get P47 up.
100:36:47 Scott: Okay. [Long pause.]
100:37:23 Worden: Okay, Dave. About a minute and a half.
100:37:28 Scott: Okay; a minute and a half 'til you get to your attitude?
100:37:31 Worden: 'Til we're ready to Sep.
100:37:32 Scott: Okay; good. [Long pause.]
100:38:13 Worden: Okay; let's go on one minute.
100:38:16 Scott: Okay; you got P47 running. You can Go anytime you want to.
Program 47 is the Thrusting Monitor Program, which is used to display the results of all thrusting procedures that are not explicitly controlled by the spacecraft computer. Al is using it to monitor changes in the spacecraft's velocity imparted by the undocking procedure and by the subsequent separation maneuver. The display resulting from Verb 06, Noun 83 will show the accumulated velocity changes along each of the three axes.
100:39:02 Worden: 10 seconds.
Al set the event timer to count up to the moment of separation. The process is controlled by a switch on the upper-right of panel 2 on the Main Display Console. The centre position of this switch is Off. In the 'down' position, it retracts the probe. The 'up' position is momentary (i.e. it does not stay in that position when let go) and commands the probe to extend and the capture latches to disengage.
There are two procedures for undocking the LM when it is manned, one of which is called a "soft undock". The other simply has the probe being extended and the LM pushed away by the force of that extension. Since the Extend command also pulls in the capture latches, the LM continues to move away once the probe has reached the end of its 25-cm stroke.
The "soft undock" minimises unintended LM velocity with respect to the CSM. The Probe Extend switch is only momentarily held in Extend. While this extends the probe, it allows the three capture latches to reset so that at full extension the LM is not set adrift, but rather remains attached by the latches re-engaging in the drogue. Once the motions between the two vehicles have stabilised, the latches are released by another operation of the Probe Extend switch. The separation can then be completed by controlled firings of the RCS thrusters. This seems to be the method used by the Apollo 15 crew.
If the switch command to release the capture latches were to fail, the probe includes arrangements to allow a suited crewmember to manually release them from either side of the tunnel. The CMP can pull a handle from the CM side while a button in the centre of the probe tip can be accessed through the drogue by a LM crewmember. In either case, the cabin must be depressurised and the corresponding hatch must be removed to allow access.
It is thought that the reason for using the soft undock procedure stems from the suggestion that Apollo 11's navigation errors were compounded by the effect of remaining air pressure in the tunnel between LM and CSM adding unintended velocity to the LM.
100:39:03 Scott: Roger. [Long pause.]
100:39:20 Scott: Okay; we're on the capture latches. Good.
100:39:22 Worden: Rog. [Long pause.]
The probe has been extended and the LM drogue has re-engaged on the probe's docking latches. Having waited for the relative motions between the two spacecraft to settle, the capture latches are disengaged and the CSM is translated in a minus-X direction by firing all four RCS thrusters for one second.
100:39:37 Worden: And you're on your own.
100:39:43 Scott: Okay; good clean Sep. [Long pause.]
You heard Al Worden and Dave Scott report separation and we confirm that on the ground, a good clean separation at 100 hours, 39 minutes, 39 seconds.
As the two spacecraft slowly separate, both movie and still cameras are covering the event. Al has a 16 mm DAC running in the CM using magazine B.
Initially Al starts the film for the unsuccessgul pass at 00:23. Then at 00:51, the shot changes. It is the same view of docking target but at the second attempt. The moment of undocking by the technique of probe extension occurs at 01:08 and LM is released from the capture latches at 01:14.
Although the Flight Plan calls for DAC movie photography from the LM, this does not exist in the Apollo 15 16-mm collection
100:40:22 Mitchell: Endeavour, Houston. Be advised your current attitude is a good one for your P52, if you'd like to hold it.
100:40:31 Worden: Okay, Ed; if you think we can't get there for the P24s.
100:40:37 Mitchell: Negative. You've only got 6 minutes. They say "No way."
Landmark tracking by the Command Module of the landing site is an essential part of obtaining accurate guidance information needed by the Lunar Module. The delay in the undocking and separation maneuver has made tracking of the landing site impossible on this pass. Other tasks, such as the critical LM inspection and a platform alignment are more pressing. The tracking procedure will be performed on the next orbit.
The LM crew, meanwhile can proceed with their preparations for the descent and landing. They will defer the check of the DPS (Descent Propulsion System, pronounced 'dips') until after they have observed the landing site.
100:40:43 Worden: Okay. We'll hold this.
100:40:47 Irwin: Okay. Falcon's going to yaw left. [Long pause.]
Comm break.
Dave is performing the pitch and yaw maneuver which will bring the four landing gear into Al's view and allow him to visually check that they have all extended properly.
Woods, from 1999 correspondence with Scott: "What would have happened if one or more of the gear hadn't deployed? Were there contingencies to try and deploy them by troubleshooting - probably - or by some external intervention - unlikely, I would have thought? Would it have been a case of do as much data gathering in lunar orbit as possible?"
Scott, from 1999 correspondence: "Yes, I am sure there were mission rules and procedures for a gear problem. At a minimum, one would probably attempt to release the gear with a CSM nudge; or if all else failed, land with the gear as is and hope that it locked down, being ready to abort if not."
100:41:32 Scott (onboard): Okay. Falcon's going to pitch up 90.
100:41:34 Worden (onboard): Roger.
100:42:00 Worden: And you got four good-looking gear. [Long pause.]
100:42:30 Worden: And, Falcon, Endeavour. Looks like you got one radar there that's - rotating away from me [DSE has 'rotating quite freely'].
Comm break.
The LM has two radar units. Al is most likely talking about the Rendezvous Radar, the dish for which dominates the 'forehead' of the ascent stage. It's function is to seek out the CSM's transponder and thereby provide the computer with the necessary information to effect a successful rendezvous. Its dish antenna can rotate as it searches for and locks onto the CSM. The Landing Radar is mounted under the LM and it feeds information to the computer on their altitude and velocity over the ground, It is operated in two positions depending on where the LM is in its approach. The early part of the descent is carried out with the crew facing up. At about 3,000 metres, the LM pitches over for the final descent with the crew facing forward. The landing radar must be able to rotate to accommodate the changing attitude.
100:42:39 Scott (onboard): Okay. We've got you in sight; we're looking straight at you. It's really pretty.
100:42:43 Worden (onboard): Roger?
Five photographs are taken from the LM showing Endeavour set against the Moon below. The first two are taken as they pass the eastern shore of Mare Serenitatis.
It is possible to work out the distance to the CSM from these photos. We know the lens focal length (60 mm), we have crosses from the Reseau plate which are marked at precisely 10-mm intervals, allowing us to accurately measure the size of the whole Hasselblad frame (52.58 mm). Using photo software we can measure the number of pixels for these and for the image of the CSM itself. We also know the diameter of the CSM (154 inches or 391 cm).
AS15-87-11695 - CSM over the eastern shore of Mare Serenitatis at 24.1°N, 29.8°E. CSM is at about 22 metres range - Image by NASA/Johnson Space Center.
AS15-87-11696 - CSM over the eastern shore of Mare Serenitatis at 24.2°N, 29.5°E. CSM is at about 24 metres range - Image by NASA/Johnson Space Center.
The next three photos are taken as they pass over the centre of Mare Serenitatis. Of the three, the middle image, 11698, is the sharpest as the other two are slightly blurred by camera shake.
AS15-87-11697 - CSM over central Mare Serenitatis north of the crater Bessel. CSM is located over 25.3°N, 20.0°E, and is at about 89 metres range - Image by NASA/Johnson Space Center.
AS15-87-11698 - CSM over central Mare Serenitatis north of the crater Bessel. CSM is located over 25.4°N, 19.8°E, and is at about 91 metres range - Image by NASA/Johnson Space Center.
AS15-87-11699 - CSM over central Mare Serenitatis north of the crater Bessel. CSM is located over 25.5°N, 18.7°E, and is at about 98 metres range - Image by NASA/Johnson Space Center.
That was Al Worden confirming to Dave Scott and Jim Irwin aboard Falcon that they have 4 good looking landing gears. The principal effect of the late undocking is, as I mentioned, going to be to delete the possibility of doing the program 24 landmark tracking on this revolution. We do have another opportunity on the next revolution to do that landmark tracking, although, we would prefer to have two revolutions of the tracking prior to the powered descent, we can get by with a single revolution of the landmark tracking.
We've had a drop out in communications while the spacecraft is maneuvering to a new attitude and we'll be reacquiring on the High Gain Antenna shortly and that should clear up the communications. Again to repeat the situation. On reacquiring the spacecraft at the beginning of the 12th revolution, Dave Scott reported that we had not gotten separation at the scheduled time. On the ground we had an indication through a high temperature indication telemetered back from the spacecraft that perhaps the umbilical to the probe assembly was not firmly connected. On inspecting the assembly, Al Worden found that this was in fact the case. He reseated it in it's receptacle, closed out the hatch area, and at 100 hours, 39 minutes, 39 seconds we again attempted successfully this time the undocking and separation. With no electrical power to the probe assembly, the undocking could not occur. The probe is electrically actuated and when it receives the proper electrical signal it extends and gives you the separation. At that point the Command Module piloted by Al Worden, fires thrusters to increase the separation rate at about 1 foot per second [0.3 m/s], and this was successfully done on the second try. Again the principal effect of this late separation makes it impossible to do the landmark tracking on this revolution. We will do it on the succeeding revolution and this should be adequate for the powered descent. We would expect at this point, that the landing will occur at the normal time.
100:43:58 Mitchell: Endeavour...
100:43:39 Scott: Roger. We're Low Bit Rate and Aft Omni.
100:47:38 Mitchell: Okay, Falcon. We're reading you well now. Give us High Bit Rate, please. [Pause.]
100:47:48 Irwin: Roger. High Bit Rate.
100:47:53 Scott: And, Houston, we're ready to go with the DPS throttle check, whenever you are.
100:47:56 Mitchell: Okay; we're ready. Let's go.
100:48:01 Scott: Okay. [Pause.]
100:48:07 Mitchell: And, Endeavour, Houston. Give us P00 and Accept; we have an uplink for you.
This is an uplink of the ground's latest calculation of Endeavour's state vector. They also send up a target load for the upcoming Circ maneuver.
100:48:14 Worden: Okay. P00 and Accept.
100:48:18 Worden: Got it?
100:48:21 Mitchell: Roger, Al. [Long pause.]
100:48:40 Scott: Minimum is 11, soft stop, 52; max, 100.
They are testing the Thrust/Translational Hand Controllers (TTHC) in the LM. Minimum thrust is registered as 11 per cent, the "soft stop" is at the bottom end of what is called the "Critical Zone" for the engine. The DPS is not permitted to be operated between 65 per cent and 92.5 per cent thrust because of excessive erosion on the nozzle throat. They are reading the values off of one of the analogue gauges on the Commander's panel.
100:48:52 Mitchell: Copy. [Long pause.]
100:49:11 Scott: LMP is 11; soft stop, 51; max, 100.
100:52:41 Mitchell: We copy. And it looks good this time.
100:52:49 Scott: Okay. And the circuit breaker is still in.
100:52:52 Mitchell: Roger, Roger. And we're ready to give you an uplink, if you'll give us P00 and Data, please.
100:52:58 Scott: Stand by. Let's run the LMP check here. [Pause.]
100:53:14 Mitchell: And it looked good here, Falcon.
100:53:19 Scott: Okay. Thank you. [Long pause.]
Al ought to be carrying out a P52 platform alignment just now but the delayed undocking has upset his time line. Soon Mission Control will tell him to skip it as they are happy with the current alignment anyway.
100:53:31 Mitchell: And, Falcon; Houston. Do you know if the circuit breaker was out, or did it pop? Can you verify what - either?
100:53:41 Scott: No, I can't verify either. We checked them over before undocking and - I can't tell you whether it popped or was open.
100:53:49 Mitchell: Okay; we understand. Thank you.
100:53:53 Scott: Rog. [Long pause.]
100:54:08 Scott: Okay, Houston. We'll take the uplink anytime you want to give it to us.
The nearest LM uplink shown on the Flight Plan is one to send up gyroscope compensation numbers for the LM computer if they are required.
100:54:12 Mitchell: Okay. Here she comes.
Comm break.
100:55:26 Scott: Okay; Endeavour, Falcon. We're going to run the [rendezvous] radar checkout now. [Pause.]
100:55:36 Mitchell: And, Falcon, the computer's yours.
100:55:50 Scott: Rog. [Pause.]
100:55:56 Scott: Falcon, Endeavour. [Pause.] I mean Endeavour, Falcon. [Long pause.]
100:56:11 Scott: Okay; Houston, Falcon here. Would you give the Endeavour a call. Tell them we're going to run the radar checkout now, please. We seem to have lost contact.
100:56:18 Mitchell: Roger. Endeavour, Houston. Falcon is calling, and he's ready for the rendezvous radar check. [No answer.]
100:56:41 Mitchell: Endeavour, Houston. Do you copy? [No answer.]
100:58:29 Scott: Endeavour, Falcon. Simplex A and B. How do you read?
100:58:35 Worden: I read 5 square, Falcon.
100:58:37 Scott: Okay. Well, we lost you there somewhere along the way. We need to check out the radar and Houston seems to not be able to get a hold of you either.
100:58:44 Worden: Okay. I'm in.
100:58:46 Mitchell: We're reading you now, Al.
100:58:48 Worden: Okay, Ed...
100:58:49 Scott: I was...
100:58:50 Worden: Okay, Ed; I was off for a couple of minutes reconfiguring inside here.
100:58:55 Mitchell: Roger.
100:58:56 Mitchell: Okay, Al. If you'll go back to Simplex A, then we'll give you the voice ranging, and we'll check out the radar.
100:59:06 Worden: Okay. I'm Simplex A.
100:59:10 Scott: Okay. Voice ranging coming up. We're going to check the radar.
Comm break.
This is a check of the Rendezvous Radar which works with a transponder in the CSM.
101:03:06 Scott: Okay. Maybe we're just in too close. We're looking at .79 mile. We'll press on.
101:03:11 Worden: Roger. [Long pause.]
Worden, from the 1971 Technical debrief: "We did check out the VHF against the rendezvous radar. I think I reset the VHF three times, and it came up each time with half the value that the rendezvous radar had in it. This made me wonder at the time how good the VHF was operating, and it subsequently turned out that it was operating just fine. I don't know what caused the difference in the range between the rendezvous radar and the VHF at that close range, because it was 0.79 mile, or something less than a mile, I think."
Scott, from the 1971 Technical debrief: "Yes, we had on the Noun 78. In the LGC, we had 0.78; you had 0.4; and the tape meter had 0.78. Of course, the Noun 78 is just a tape meter read-out, but you did have, for some strange reason, just half value."
Worden, from the 1971 Technical debrief: "I reset that thing three times, and I think it came up with the same value each time."
Scott, from the 1971 Technical debrief: "I might add, in the LM, we could tell when you were resetting. It was audible, so we tried to observe a no-comm silence period while you were getting your reset. There's no question there that you reset."
