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Apollo 15

Day 8, part 2: Rendezvous and Docking

Corrected Transcript and Commentary Copyright © 1998-2020 by W. David Woods and Frank O'Brien. All rights reserved.
Last updated 2020-07-26
During Apollo's early years, much bureaucratic energy within NASA was spent trying to settle on the method to be used to get to the Moon. Three schemes were laid out, two of which had widespread support throughout the organisation, the other struggled to be heard and was often ridiculed.
Direct ascent, using either an extraordinarily large booster called "Nova" or a Saturn V and a cut-down Apollo spacecraft, would hurl a lander from the Earth to land on the Moon. This lander would be large enough to make another direct ascent from the lunar surface back to Earth. Many felt this would represent the simplest and easiest way to achieve Kennedy's goal and, for a while, the cause was championed by Robert Gilruth, the leader of the Space Task Group, an organisation that was the precursor to the Manned Spacecraft Center, now the Johnson Space Center in Houston.
Although a few people at the Marshall Space Flight Center (MSFC), who designed and built rockets under Wernher von Braun, were also keen on the idea of a Nova-class super-booster, von Braun's centre preferred EOR (Earth Orbit Rendezvous). This would use smaller launch vehicles of the Saturn V class by having double launches from Cape Canaveral and assembling or fuelling the Moon-bound vehicle in Earth orbit. Though many saw it as MSFC's excuse to build more vehicles and increase their importance within NASA, others realised that building the Saturn V was far more achievable than the Nova. However, both direct ascent and EOR assumed a single large vehicle would go to the Moon and return intact.
A team at Vought Astronautics near Dallas, under the leadership of Thomas Dolan, had previously studied a daring but highly efficient means of achieving the goal. When applied to the Apollo program, this technique would allow the mission to be realised with only one Saturn V. By limiting the mass that has to be taken to the lunar surface and subsequently lifted off again, and therefore keeping a mother ship in lunar orbit, huge savings could be made in the mass of the original launch vehicle. However, the scheme, known as LOR or Lunar Orbit Rendezvous, relied on being able to achieve a rendezvous and docking around the Moon; this at a time when the process hadn't even been demonstrated near the safety of Earth. Nevertheless, convinced of the benefits of LOR, and with an almost religious zeal, John Houbolt of Langley, Virginia, took the idea and pushed it hard through levels of bureaucracy and entrenched positions in NASA to eventually win over the whole organisation to the idea.
Only when NASA had decided how to get to the Moon could it start thinking about the strange contraption that is now about to lift-off and fly towards Al Worden's Endeavour and about how, exactly, two craft flying at incredible speeds around a planet or moon could arrange to meet up and, oh so gently, come together.
Thus the task that the crew of Apollo 15 are about to perform is central to the way Apollo was conceived. The commander of this mission, Dave Scott, along with Neil Armstrong, participated in the first successful demonstration of docking after a rendezvouas on Gemini VIII. He was the Command Module Pilot during Apollo 9, when these skills were applied to the all-up test of the entire Apollo system in Earth orbit. Now on this, his third space flight, he will put the techniques he helped to refine into good use by getting himself and Jim Irwin off the Moon and on board a ship that can take them home to Earth.
For a fuller discussion of the mechanics and concepts involved, readers should go to Frank O'Brien's article on Lunar Orbit Rendezvous.
Endeavour has just disappeared around the Moon's far side after an extended period when the Command Module Pilot Al Worden failed to communicate with Mission Control. Some of the information about the upcoming lift-off of Falcon's ascent stage was hurriedly read up when communication was reestablished just before LOS (Loss Of Signal).
CSM Flight Plan page 3-267.
Rev 48 begins at about 170:40.
Now he is alone for the last time and he has a few housekeeping duties to perform in preparation for the arrival of 77.3 kilograms of rock samples. For the first time in three days he puts on his suit, without helmet and gloves. He unstows a jettison bag from compartment R13 and places four exhausted lithium hydroxide canisters from compartment A9 in it. These will be jettisoned later in the mission when Al leaves the spacecraft to retrieve the film magazines from the SIM bay. He installs a filter in the cabin fans to catch dust carried over from the LM, and installs springs and clips on various compartments and panels. Temporary stowage bags are placed on either side of the Lower Equipment Bay (LEB) and coveralls are made ready for Dave and Jim. The vacuum cleaner is also unstowed though it is probably already assembled, having been required after the discovery, on the second day of the mission, of a broken tape meter face, when it was used to catch glass particles floating around the LM cockpit. With these tasks out of the way, Al can commence a short meal break, scheduled to last only 20 minutes.
CSM Flight Plan page 3-269.
Falcon's lift-off is due in about 35 minutes time and we join the mission with CapCom Ed Mitchell coordinating communications with two spacecraft.
171:03:57 Mitchell: Endeavour, Houston. Standing by.
171:04:03 Worden: Hello, Houston; Endeavour.
171:04:05 Mitchell: Okay, Al. Loud and clear.
171:04:11 Worden: Okay, Ed. I'm in Reacq, Narrow now.
Al may be wanting to reassure Mission Control that he is on top of the spacecraft's communications in light of the quiet spell just before Loss Of Signal. With the spacecraft still in the same attitude it was in at the last realignment of the guidance platform, Al can have the High Gain Antenna (HGA) ready in the proper position to communicate with Earth as soon as the home planet comes into view. Angles are given in the Flight Plan to achieve this.
171:04:15 Mitchell: Roger. And, Falcon, your [AGS values for addresses] 047 [and] 053 are okay. Al, did you get the TPI and lift-off time for the direct ascent before LOS? Over.
171:04:30 Worden: Affirmative.
The numbers 047 and 053 are AGS (Abort Guidance System) computer addresses whose contents indicate the location of the LM on the surface. While the crew is on the surface, ground engineers are constantly refining the location of the LM landing point, and ask the crew to update the computer with this information.
TPI is Terminal Phase Initiation, a firing of the LM ascent stage's engine to begin the final approach to Endeavour. That time, and the one for the direct ascent lift-off, were part of the data hurriedly read up to Al before the last LOS. Mitchell still has to finish giving Al the entire PAD, which he is just about to do.
171:04:31 Mitchell: Okay. Let us have P00 and Accept, and we'll give you an uplink.
171:04:39 Worden: You have it.
This uplink was also to have occurred at the last near-side pass. It puts a freshly calculated state vector in Endeavour's computer which defines the spacecraft's position and motion at the time of LM lift-off.
171:04:40 Mitchell: Okay. Let me give you the coelliptic PAD, Al.
171:04:47 Worden: Go ahead.
171:04:48 Mitchell: Okay. At - lift-off is 171:40:13.41. And GET is CSI, 172:35:08.00, and Noun 37, your TIG TPI is 174:27, all zeros. Readback.
There were two rendezvous strategies used on Apollo. The first two landing missions, 11 and 12, used a two orbit, four-hour method known as a coelliptic rendezvous. This took a step-by-step approach that was more forgiving of error. To help squeeze in a longer surface EVA on the final day, the remaining Apollo missions used a shorter method known as direct ascent. This built on earlier experience to combine multiple orbital corrections into one burn that would take an ascent stage from an initial orbit straight onto an intercept path to the CSM. This halves the time and therefore can be completed within a single lunar orbit. If Mission Control or the crew aren't happy with the direct ascent approach, they can fall back onto the coelliptic method and pay the time penalty.
Houston is providing burn times for both rendezvous schemes. Updates for both direct ascent and the coelliptic method, were sent up to the LM at 170:40:39 and Al got the update for direct ascent just before he went behind the Moon. This update is for the coelliptic rendezvous. The three burn times are for the lift-off of the LM from the surface, the time of the Coelliptic Sequence Initiation (CSI), which circularizes the LM orbit after ascent to 83 km (the LM initially is in an elliptical, or egg-shaped 83- by 17-km [45- by 9-nautical mile] orbit after ascent) and the Terminal Phase Initiation, which is a burn that places the LM in an intersecting orbit with the Command Module. A direct ascent rendezvous bypasses the CSI burn, instead performing the TPI burn soon after lift-off.
Frank O'Brien, from 2004 mission review: "Now the type of rendezvous you are doing is a direct rendezvous. Gemini 8 was 2 or 3 orbits if I'm not mistaken."
Scott, from 2004 mission review: "Four."
O'Brien, from 2004 mission review: "OK. But the geometry and the basic mission parameters were basically the same. I understand Gemini did a lot of very odd rendezvous, at least in the early development. But what you did on [Gemini] 8 pretty much paralleled what you did coming back on 15."
Scott, from 2004 mission review: "No. On 8, we did phasing maneuvers and everything else. It was M=4. And this on 15 was the first direct rendezvous. And one of the reasons we had a little extra propellant was we used that [direct ascent] and didn't do LM phasing and went straight on in, which was the original intent of the rendezvous way back when, and they didn't get the confidence factor up until we got to 15 when we did the direct ascent rendezvous, which was, in the early days, the ultimate objective. But because of dispersions and uncertainties and lack of knowing about this rendezvous thing. You know, you go away back, it was a big mystery doing a rendezvous. Whoa, boy, woo, man, magic mysterious stuff! Now it's just - but, you know, much more - this [15] was straight off - choof, bang."
It is worth noting here that Apollo 14 carried out the first direct ascent rendezvous from the lunar surface although Dave and Jim were heavily involved in the development of the technique during the hiatus after Apollo 13.
O'Brien, from 2004 mission review: "If I'm not mistaken, for a direct rendezvous, even the slightest dispersions can really screw you up."
Scott, from 2004 mission review: "No, not really, because you've got built in corrections with the midcourse and all that sort of stuff. I think it was pretty tolerant. And, of course, if you did have a big glitch like shutting down a minute early or something like that, you could go into a phasing on 15. You needed to get the LM in orbit. Once you got it in orbit, you could start fooling around with corrections if you had to. CSI, CDH, see on Gemini, coelliptic sequence initiation was the first, then we did constant delta-H on the next. I think we did first a phasing maneuver, then CSI, then CDH, then went on in, and by the time we got to Apollo 15 with the launch trajectory - insertion trajectory set all that up."
O'Brien, from 2004 mission review: "So you are going straight from insertions to TPI?"
Scott, from 2004 mission review: "Yeah. You went into orbit then to TPI because that's the critical burn. You gotta calculate that one carefully. That's where you get all the solutions and that's where you decide which solution you want, which is not trivial because you have the PGNS, the AGS, the onboard charts in the LM, you have G&C on the Command Module."
David Woods, from 2004 mission review: "And the ground?"
O'Brien, from 2004 mission review: "So that's five sources?"
171:05:30 Worden: Okay. I understand on a direct ascent, it's lift-off, 171:37:22.36; TPI, 172:29:39.00; CSM weight, 35995; coelliptic lift-off, 171:40:13.41; CSI, 172:35:08.00; TPI, 174:27:00.00.
171:05:59 Mitchell: Okay, Al. That's a good readback. And, Al, let me advise you that be - because of your orbit, the TPI is going to be non-nominal in angle, about the - about the same Delta-V; however, a different angle. We'll have more words after insertion.
171:06:20 Worden: Okay. Do you want the gyro torquing angles on that last P52?
171:06:24 Mitchell: That's affirmative. I'm ready to copy.
171:06:29 Worden: Okay. Minus 4 balls 6, minus 00017, and minus 00017, and they were torqued out at 170:06.
The last realignment of Endeavour's guidance platform, which is done in conjunction with program 52 in the computer, was carried out during Al's extended communication break. The three sets of figures, the first of which is 00006, are accessed by calling up Noun 93 on the DSKY (Display and Keyboard) and they mean that the three gimbals within the IMU (Inertial Measurement Unit) needed to be rotated by -0.006°, -0.017° and -0.017° to restore the correct orientation. Al used stars 01 (Alpheratz, Alpha Andromedae) and 44 (Enif, Epsilon Pegasi) for the alignment. In the test of his sighting accuracy, he scored a perfect 'all balls', there being no difference between his measured angle between these stars, and the known angle between them.
171:06:43 Mitchell: Copy minus 4 balls 6, minus 3 balls 17, minus 3 balls 17, torqued at 170:06.
171:06:57 Worden: Roger.
171:06:58 Mitchell: And give us Auto on the High Gain [Antenna]. And, Al, we're not going to bother with your - P27 PAD readup, unless you're especially wanting it.
171:07:13 Worden: Negative, Ed. [Long pause.]
P27 is a program which allows the computer to be updated manually, in this case by Al. Before LOS, Mission Control were to read up the appropriate data for the state vector but with time running rather short, they have decided to bypass this step.
171:07:57 Scott: And, Endeavour; Falcon. You're five square to us on the relay. How do we sound?
171:08:04 Worden: Hello, Falcon; Endeavour. You're loud and clear.
171:08:10 Scott: Okay. We're all set. Ready to - get us some warm chow?
171:08:16 Worden: Yes, sir. [Pause.]
171:08:23 Scott: Great. I'll tell you, cold tomato soup isn't too good. [Long pause.]
In the long and difficult struggle to reduce weight and power consumption in the LM, simple amenities like hot water for food preparation were eliminated.
171:08:59 Mitchell: Endeavour, the computer is yours.
171:09:04 Worden: Roger, Houston. [Long pause.]
171:09:23 Mitchell: Endeavour, Houston.
171:09:28 Worden: Go ahead, Houston.
171:09:29 Mitchell: Al, were you having any comm difficulties before LOS on the - our last pass. We lost you for about 20 to 25 minutes.
171:09:39 Worden: Sure didn't notice any, Ed. I was busy down in the LEB, but I didn't get any - any signal in the head-set indicating that we'd lost S-band lock, and I had the Squelch Off.
171:09:50 Mitchell: Okeydoke.
Long comm break.
171:14:29 Mitchell: Endeavour, Houston. Omni Delta.
171:14:36 Worden: Omni Delta.
171:14:37 Mitchell: And, Falcon; Houston. I have some PIPA biases, when you'd like them.
171:14:49 Scott: Stand by, Ed.
Comm break.
The PIPAs (Pulsed Integrating Pendulous Accelerometers) are one of the two sensing types of components in the IMU. Three of these devices measure acceleration forces on the spacecraft in three axes, and by integrating these accelerations over time, allow the calculation of the resultant velocity changes. Like the gimbal assembly, PIPA's have a tendency to drift from absolute accuracy. This drift is rather well understood and much can be determined in pre-flight qualification testing. Therefore the computer is instructed to make allowances for this drift by applying a small bias against the information provided by the PIPAs. As on all flights, engineers on the ground are continually evaluating the performance of the PIPAs against previous history, and if there is a discrepancy, recommend changes in the bias values used by the computer.
171:16:06 Mitchell: Falcon, Houston. Verify Slew. We're about to hand over.
171:16:15 Irwin: Okay, we're going Slew.
Comm break.
171:17:26 Mitchell: Falcon, Houston. Handover complete. Verify Auto, please.
171:17:37 Irwin: Roger. Going back to Auto.
Comm break.
During the period that ground tracking stations "handover", that is, switch from one station to the other, the signal is interrupted for a few moments while one station ends its transmission, and the next one reacquires the spacecraft. In such an interruption, the electronics which control the spacecraft's antenna will automatically begin moving it to search the sky for a signal. Switching the antenna control to Manual (Slew) from Auto will ensure that the antenna will continue to point at the Earth. Once the handover is complete, and a good signal is again received by the LM, the antenna mode will then be switched back to Auto.
Meanwhile, Al is configuring various cameras so he can broadcast and record the final stages of the rendezvous and the docking. The TV camera is mounted in the right-hand rendezvous window and the DAC (Data Acquisition Camera, a 16-mm movie camera) looks out of the left-hand rendezvous window. It is loaded with a colour film magazine, mag C, and will operate at 6 frames per second.
Motion film is normally shot and displayed at 24 frames per second (25 on European TV systems). However, much of the film in the Command Module's Maurer DAC was shot at frame rates far lower than this in order to reduce usage and save film. Subsequently, when TV and film producers include this footage, they almost invariably run it at the standard speed and, in the case of the docking film, will show the docking occurring at four times actual speed. Many space purists are scornful of this unintended tampering with historical truth but the speed-up does have the advantage of displaying the grace of the operation within the layman's attention span. Readers should be aware that, strictly speaking, much of the Apollo orbital footage in the public domain is shown at the wrong speed.
171:21:29 Mitchell: And, Falcon; Houston. I still have some PIPA biases I need to give you.
Long comm break.
171:26:06 Mitchell: Okay. Falcon, Houston. Observe you're into Verb 83 at lift-off minus 12. We're right on schedule. I have a couple of updates for you, please. [No answer.]
Verb 83 displays rendezvous parameters.
171:26:34 Mitchell: Falcon, Houston. Do you read? [No answer.]
171:26:55 Mitchell: Falcon, Houston. In the blind while we're looking at our comm problem. Your PIPA bias: Verb 21, Noun 01, Enter. Enter it - put that in if you hear me.
The performance of the PIPAs are still within acceptable values, and this update only constitutes "fine tuning" of the guidance platform. This was a small shift in the bias, only 0.39 and 0.46 cm/sec2 respectively in the X and Y axis. This shift had resulted from removing and reapplying power to the inertial measurement unit while the LM was on the surface, and is considered to be not unusual.
From the Apollo 15 Mission Report, "For the first time, accelerometer biases were updated while on the lunar surface to correct for the small expected shifts experienced when the system was powered down. Since the lunar surface bias determination technique had not been totally proven, only half of the measured shift in the X accelerometer bias was corrected. As a result, some bias error existed during ascent and contributed about 2 ft/sec to the radial velocity error."
171:27:40 Scott: Houston, Falcon.
171:27:42 Mitchell: Okay, Falcon. There we have you. We had a little net problem. I have a PIPA bias update for you.
171:27:51 Scott: Well, stand by. You ready to watch the APS pressurize?
The tanks for the APS (Ascent Propulsion System) remain unpressurised until just before first firing of the engine. Then, explosively actuated valves from two helium tanks are operated to bring the tanks up to a working pressure of 1,270 kPa (184 psi). Mission Control will monitor the pressurisation of each tank so that a leak is caught early. If a tank had been found to be leaking, lift-off would have been carried out as soon as possible to minimise propellant loss. In such an off-nominal scenario, Al would have made the maneuvers to rendezvous to the LM in its unplanned orbit.
171:27:57 Mitchell: Okay, let's let her go.
171:28:00 Scott: Okay, here comes tank 1. And we'll stand by for your call for tank 2.
171:28:13 Mitchell: Roger. [Pause.]
171:28:22 Mitchell: Okay. Go with tank 2, looks good.
171:28:27 Scott: Okay. Tank 2 coming now. [Pause.]
171:28:34 Mitchell: Looks good down here.
171:28:39 Scott: Okay, thank you. Looks good up here.
171:28:41 Mitchell: And, Dave, you're Go for the direct rendezvous. Both guidance systems look good; PGNS is your recommendation.
171:28:49 Scott: Roger. Go for direct on the PGNS. [Long pause.]
In the style of American space personnel down the ages, the rather awkward abbreviation PGNS, meaning the Primary Guidance and Navigation System, was reduced to the simple spoken term "pings" for verbal brevity.
171:29:19 Mitchell: Falcon, are you still with us?
171:29:24 Scott: Roger.
171:29:25 Mitchell: Okay. Have a couple of numbers I need to read for you, Dave, when you're ready.
171:29:35 Scott: Okay. Pencil's out. Go ahead.
171:29:38 Mitchell: Okay. PIPA bias is Y PIPA: Verb 21, Noun 01, 1454 Enter; and the data is 04366 Enter. X PIPA: Verb 21, Noun 01; address, 1452 Enter; data 04672, Enter.
LM Flight Plan page 3-270.
CSM Flight Plan page 3-271.
171:30:08 Scott: Okay. Here's the readback on that Ed. Verb 21, Noun 01, 1454 Enter; 04366. And, then Verb 21, Noun 01; 1452 Enter; 04672.
These updates to the drift coefficients of the PIPAs need to be entered into the computer. The Verb 21, Noun 01 sequence allows the crew to update the computers memory directly. Memory locations 1452, 1454 and 1456 correspond to the drift coefficients for the three PIPA's for the X, Y and Z axis, respectively. While directly manipulating a running computer's memory seems rather unorthodox, it is not an unheard-of practice at the time of Apollo. In these days, before even time-shared systems, halting the computer, entering data through a switch register or setting sense switches was the closest thing to an "interactive" system.
This author (O'Brien) has fond memories performing such tasks, spending many long nights in college programming room-sized computers, stopping them to check a result, changing a memory location, and resuming the programming.
171:30:23 Mitchell: That's a good readback. And when you have your Timeline Book out, I'd like to change some range and range-rate numbers because of this ellipticity of the Command Module orbit.
171:30:37 Scott: Okay, Ed. Do you want those PIPA biases loaded now?
171:30:41 Mitchell: That's affirm.
171:30:44 Scott: All right. [Long pause.]
171:31:28 Scott: Okay, Ed. What are the changes in the Timeline Book?
171:31:31 Mitchell: Okay. The range and range-rate at insertion: range-rate is 137; range, minus - sorry, the range is 137; range-rate, minus 431; at plus 5 minutes, range 117; range-rate, minus 398; and at 10 minutes, range is 98, range-rate, minus 355.
171:32:10 Scott: Okay, I copied that data.
171:32:14 Mitchell: Good enough. [Long pause.]
171:32:30 Worden: Falcon, Endeavour, on VHF. How do you read? [Long pause.]
171:32:47 Scott: Okay, Falcon; Endeavour. How do you read us now? [We read you] 5 by?
171:32:52 Mitchell: Loud and clear. [Long pause.]
171:33:05 Mitchell: And, Falcon; Houston. We'd like you to change your 053 number to plus 01722.
171:33:20 Irwin: Copy. The 053 to plus 01722.
171:33:25 Mitchell: That's affirm. [Long pause.]
171:34:00 Mitchell: Falcon, Houston. Can you make your VHF check, so we can hand over the network, please?
171:34:07 Scott: Roger. We tried [at 171:32:47] and I got no response, and I'll stand by. We should be hot miked to the Endeavour. [Pause.]
171:34:28 Scott: Okay, Houston. We've had trouble on the VHF check - as he approaches the mountains back there - we usually don't get him until he's almost overhead, because of the interference.
171:34:37 Worden: Okay, Falcon, there you are. I've got you now.
171:34:38 Scott: Oh, okay.
171:34:40 Mitchell: Understand VHF check is good now...
171:34:41 Worden: Reading you 5 square on VHF there, Dave.
171:34:47 Scott: Rog. VHF check is Go, Ed. Falcon here.
Communications between the spacecraft and Earth are through the S-band antennas, but a VHF radio is used for transmissions between the CSM and LM. Lower powered and non-directional, it is ideal for the relatively short distances between the two spacecraft, typically never more than a few hundred miles and in line of sight. The CSM also uses the VHF transmissions for ranging information between itself and the LM, necessary for rendezvous calculations.
171:34:53 Mitchell: Endeavour, Houston. We're going to hand you over now.
171:34:59 Worden: Endeavour, Roger. [Residual static ends; long pause.]
171:35:28 Scott: Vox - Hey, Houston, Falcon. How do you read on Vox?
171:35:31 Mitchell: Okay, loud and clear, Dave, and you're Go for lift-off. And I assume you've taken your explorer hats off, and put on your pilot hats.
171:35:42 Scott: Yes sir, we sure have. We're ready to do some flying.
171:35:49 Irwin: Standing by for one minute.
171:35:50 Scott: Okay.
171:35:51 Irwin: Guidance steering is in.
Guidance steering is a command entered by Jim Irwin into the AGS, indicating that it should take its guidance information and generate steering commands to the RCS. These commands are actually blocked, in essence, by the guidance mode control switch, which when in the PGNS setting, will allow steering commands only from that system. If the need to use the AGS arose, the guidance mode control switch would be changed to the AGS setting, blocking the PGNS, and the steering commands generated by the AGS would be used.
171:35:52 Scott: Okay. [Long pause.]
171:36:22 Mitchell: Mark. One minute.
171:36:25 Scott: Okay, Ma - Master Arm is On; I have 2 lights. [Long pause.]
171:36:56 Irwin: Average G is on. [Pause.]
The DSKY is counting down the seconds before ignition, and between T-0:35 and T-0:30, its display blanks to indicate it is now calculating the "average G", that is, the average acceleration the LM is experiencing, and applying it to the LM's state vector. Of course, the LM is still on the surface, but the averaging must begin before the ascent engine ignites.
171:36:59 Mitchell: [Garble.] [Long pause.]
171:37:16 Scott: Abort Stage; Engine Arm to Ascent. 99 Pro[ceed]. [Pause.]
The final moments before ascent are filled with last minute manual tasks. First, pressing the Abort Stage button causes the ascent and descent stages to separate, using explosive bolts to sever the four attachment points holding the stages together. At the same time, explosive charges drive guillotine blades through the bundles of wiring and plumbing to sever those connections.
Next, the ascent engine is armed, which allows the engine controller to open the valves on the engine. At T-five seconds, the DSKY displays Verb 99, which asks the crew if it can proceed with engine ignition. By entering "Pro"(ceed), the crew is allowing the computer to continue with the countdown and ignite the engine.
171:37:25 Scott: Good lift-off.
18 seconds before lift-off, Jim started the 16 mm DAC camera running at 6 frames per second on Mag BB. The resulting film covers the whole of the ascent and will continue to record for an additional 25 seconds after the engine is shut down. In the following video clip, the speed of the film's replay has been adjusted to match real time and married with the air-ground audio.
H.264 MP4 video file.
171:37:26 Scott: Automatic. Yaw left. Pitch over. [Long pause.]
(Music - "Air Force Song")
As soon as Dave says "Automatic", the air-ground recording is filled with music.
Woods, from 1999 correspondence: "Soon after Falcon lifted off the lunar surface, the 'Air Force Song' was heard on the air/ground. I have conflicting reports of the source of this. Was it yourself in Endeavour? I don't think the LM would have carried a tape player. It seems to express a certain confidence in the system to be playing music at this time. Was it a prearranged idea or something thought up ad hoc."
Worden, from 1999 correspondence: "I must confess that I played the song during the lunar lift-off. I thought I was playing it only for Houston. But then I found out that someone had turned on the switch that relayed my voice to the Lunar Module. So, Dave and Jim had to perform the pre-launch checklist with the song playing in their ears. Dave was not too happy about that, but I didn't know at the time that Houston had turned the radio loop around on me. I actually had this in the back of my mind during the flight, and just went ahead and played it during the lunar ascent."
Journal contributor and music aficionado Kevin White has analysed this version of the music and was able to identify the specific recording used by Al. He supplies the following information about it. "'The U.S. Air Force'(Song), also commonly referred to as 'Off We Go', written by 'The Flying Baritone' Robert MacArthur Crawford in 1938. Performed by Concert Arts Symphonic Band Conducted By Felix Slatkin - The Military Band. Recorded 1958 in Hollywood, California, Capitol Records - W1056. Originally titled 'Army Air Corps', it was written for the U.S. Army Air Corp and later re-titled with the establishment of the U.S. Air Force in 1947."
171:37:43 Scott: Stable about 306.
After the LM has ascended only about 15 metres, the pitchover maneuver is performed. At this point, the pitch attitude of the LM is holding at 306 degrees, which is read off of the FDAI or "8-ball". If the LM were on a level surface, the pitch angle would be 0 degrees. At a pitch angle of 306, the spacecraft has rotated 54 degrees "nose down".
This ascent profile is quite different from launches seen on Earth. Launch profiles from the Earth are essentially vertical during the first few minutes of the boost to escape the bulk of the atmosphere, which is a significant source of drag on the vehicle. The horizontal component that is necessary for orbital flight, is held back to allow the atmosphere to become thinner. The lack of an atmosphere on the Moon allows the LM to increase its horizontal velocity almost immediately without the drag penalties.
Note that this is the first time that Mission Control, and the TV networks, have been able to watch and record the moment of lift-off from the Moon by virtue of the independent TV and communications system built into the Lunar Rover, now parked 100 metres east of the blasted descent stage. With the Rover's camera under the control of Ed Fendell, Mission Control in Houston had hoped to be able to follow the rising ascent stage by tilting up as it left the Moon. Unfortunately, the tilt mechanism of the camera's support had become loose during Falcon's stay. Were the camera to be tilted up or down much beyond the horizontal, it would flop to its maximum angle, unable to return without Dave or Jim's helping hand. Now that no human hand would go near the camera for the foreseeable future, Fendell dare not use the tilt control at all for fear of never regaining the horizon. Therefore, viewers get to watch Falcon's ascent stage smartly depart the frame. Over the next days, weeks, maybe months, Mission Control hope to view the landing site under changing lighting as the Sun crosses the lunar sky and sets in the west.
171:37:53 Scott: Hey, good smooth ride, Ed.
Scott, from 1971 Technical debrief: "The pitchover of the LM was very smooth. The spacecraft seemed to be more stable than we'd seen in the simulator. The oscillations due to the PGNS fuel saving program were somewhat less than I expected. Everything went very smoothly and very slow. We had a great view of the rille as we went across."
171:37:56 Mitchell: Roger. Copy now.
Looking good. Altitude, 2,400 feet [730 metres].
171:38:05 Scott: All looks good at 30 [seconds]. [Long pause.]
171:38:24 Mitchell: Falcon, you're Go at...
171:38:25 Scott: [Garble.]
171:38:26 Mitchell: ...1 minute. Auto start; normal shutdown.
171:38:31 Scott: Roger. Auto start and normal shutdown.
171:38:33 Mitchell: Both guidance systems are good, Dave.
171:38:38 Scott: Okay, looks good up here. [Pause.] It almost sounds like the wind whistling, doesn't it?
Woods, from 1999 correspondence: "I take it you were referring to the sound of the ascent engine. Do you think that would be due to the propellant in the pipework of the engine, or to the exhaust gases impinging on the engine bell?"
Scott, from 1999 correspondence: ";I would guess that it was the propellant going though the plumbing. But remember, we were right on top of the engine combustion chamber - somebody during E2M [From the Earth to the Moon, the TV series made by Tom Hanks on the Apollo program] pointed out that LM pilots flew closer to the rocket engine than anybody ever (I wonder?)."
In the Apollo 15 Lunar Surface Journal, Eric Jones also discussed the ascent engine's noise with Dave.
Jones, from the Apollo 15 Lunar Surface Journal: "Was it noisy in there when it was firing?"
Scott, from the Apollo 15 Lunar Surface Journal: "Nope. Hardly heard a thing. And you'll hear a comment when we get to that point; but one of the things I recall is that it sounded like the wind was blowing through a window. And we made a comment about that. I don't know what we expected, but nobody ever had mentioned that to us."
Jones, from the Apollo 15 Lunar Surface Journal: "It never occurred to me to ask anybody what the noise level was. Now, people were in helmets, admittedly, and suited."
Scott, from the Apollo 15 Lunar Surface Journal: "But, compared to [Earth] launch...Launch was noisy. This was very quiet. Very quiet. You heard a swishing sound. Shhhhhhhhh."
Jones, from the Apollo 15 Lunar Surface Journal: "Were you wearing helmets at Saturn V launch?"
Scott, from the Apollo 15 Lunar Surface Journal: "Oh yeah; you bet. Fully suited. We wore the suits on launch, but not on re-entry.
"Our [lunar] ascent was right up the Rille. Nobody planned it that way, but it could not have been a better trajectory, because we went right up the rille. We turned the corner and flew up the rille. 'Where would you like to go when you're taking off from the Moon?' 'I'd like to fly up the rille!' Thank you very much, Floyd Bennett or whoever planned the trajectory. And you see that on the film. It's in the Apollo 15 movie. That's the only reason I've ever seen it."
After transcribing this, Eric looked at the sequence in the Apollo 15 movie and, indeed, it looks as though, when they got to the rille, they turned to the right and flew up the rille.
Scott, from the Apollo 15 Lunar Surface Journal: "It was also very low g. The pictures show the thing popping off the ground. Pop? I think we went from 1/6th g to maybe a half or whatever. You weren't being pushed hard. We were standing up and you would think, boy, all those g's standing up. Not really. You could hardly tell."
During our correspondence, Dave had more to add about the experience of ascent from the Moon.
Scott, from 1999 correspondence: "Truly amazing - the LM launch and ascent were so quiet, especially when compared to Titans and Saturns! And after the music and exchange with Houston, it was almost peaceful - some vehicle oscillation (periodic at a couple degrees) and the periodic sound of a slight wind, pulsing at about 2-3 seconds in frequency. And, of course, the view of the Rille as we flew right along the course, face down - just spectacular - could not have been a better farewell - most pleasant and certainly indelible."
During our review in 2004, Dave watched the complete 16-mm film of the ascent from Spacecraftfilms.com's Apollo 15 DVD set. Dave told us he had never watched this footage before in its entirety. One of the characteristics of its imagery is the way the field of view gently cycles around.
Woods, from 2004 mission review: "The gentle wobble or nodding thing, that's just the RCS cycling through its deadband?"
Scott, from 2004 mission review: "Yes. Because the [ascent] engine's fixed. Great geology, isn't it? Well the camera ran finally! Yeah. Fantastic. Look at all that stuff. They never really looked at that one. There's an awful lot of geology in there. Awful lot of variable things - wrinkle ridges, depressions, chains."
O'Brien, from 2004 mission review: "You're also seeing it at an altitude a heck of a lot lower than the Mapping Camera is, I'm sure."
Scott, from 2004 mission review: "Yeah, because you're close."
171:38:55 Irwin: Boy, what a view of the rille, huh? Boulder tracks slip down into it.
(Music - "Air Force Song")
That music is from the CSM downlink.
171:39:25 Scott: [Garble] on the [garble]. [Long pause.]
Network corrects that to say it's from the LM downlink.
The PAO announcer was correct in the first instance.
171:39:53 Irwin: [Garble]. Right on profile. [Long pause.]
Jim is referring to charts which show the expected relationship between altitude and velocity. He is comparing these profiles to the read-outs from the computer.
171:40:19 Mitchell: Falcon, Houston. You're looking good at 3 minutes.
171:40:25 Scott: Okay. [Garble].
171:40:30 Scott: Roger. The only thing unusual I noticed is the RCS Oxidizer manifold pressure oscillates every time the jets fire. That's backing up to the [garble].
171:40:44 Mitchell: Copy. [Pause.]
171:40:48 Scott: [Garble] thirty. [Long pause.]
Altitude, 30,000 feet [9,150 metres]. Velocity, 2,129 feet per second [649 m/s].
171:41:26 Mitchell: Falcon, Houston. You're Go at 4. [Long pause.]
42,000 feet [12,800 metres] now.
171:42:25 Scott: [Garble, probably "Rendezvous"] radar lockup.
171:42:26 Irwin: 5 minutes. Both [PGNS and AGS are] good. [Long pause.]
171:42:53 Mitchell: Falcon, Houston. You're still looking good. Your PGNS is showing a slight radial error, but it's a little bit lower than nominal. But everything's Go.
171:43:05 Scott: Rog. Understand. [Long pause.]
171:43:35 Irwin: [Garble] rendezvous radar lock on, huh?.
171:43:37 Scott: Yup.
Scott, from 1971 Technical debrief: "When we attempted to get a lock-on with the radar - we had previously been given the numbers for setting the antenna - I pushed the circuit breaker in [at] about 4½ minutes and didn't get a lock. I waited until about 5½ minutes and still had no indications of signal strength on the AGC [The Apollo Guidance Computer]. I slewed it up, down, left, and right in high [rate] for about 5 seconds in each direction. I received no response on the AGC [Automatic Gain Control meter, essentially a signal strength indicator]. I don't have an explanation for that."
171:43:38 Irwin: A thousand [feet per second] to go. [Garble] 500.
171:43:41 Scott: Okay. [Long pause.]
171:44:06 Mitchell: Falcon, Houston. Trim AGS.
171:44:11 Scott: Roger. Understand. Trim the AGS. [Garble] connection?
At this point, Dave is asking that the crossfeeds (also known as the APS-RCS interconnect) between the ascent propellant system, and the RCS propellant system be opened. Fuel and oxidizer from the ascent engine system is transferred (the fuel and oxidizer are identical in the two systems) to partially "recharge" the RCS tanks. This has several advantages. Most importantly, at this late stage of the ascent, a stable orbit is assured, even if the RCS had to be used in the event of an ascent engine failure. Later maneuvers place more reliance on the RCS than the APS, and a large RCS fuel margin is welcome, as it increases the available options if problems develop.
171:44:19 Mitchell: Falcon, Houston. Trim in-plane only.
171:44:24 Scott: Roger, in-plane only on the AGS. [Garble].
171:44:28 Irwin: [Garble] go.
171:44:29 Scott: Engine Arm is Off. Okay. We'll shut down on the PGNS. Okay, Auto shut down. [Garble] the AGS [address] 500.
171:44:51 Scott: [AGS address] 502. [Garble.]
The AGS address 500 and 502 are the velocity-to-go vectors in the X and Z axes, the two axes which define the orbital plane. Uncertainties in the shutdown dynamics of the ascent engine, like all the large engines on spacecraft, mean that even if the engine shuts down precisely when commanded, there will still be errors in the final velocity. By referring to the velocity-to-go display on the DSKY or AGS, the crew can trim these errors down to a small value (usually 0.1 or 0.2 feet per second) by using the RCS.
Dave is calling for the X and Z velocity-to-go values from the AGS as he trims the LM's velocity.
Scott, from 1971 Technical debrief: "After automatic shutdown, we attempted to trim the AGS. I couldn't get the X-axis less than 2 ft/sec, because it kept building. That was not unlike what we'd seen in the simulator on previous rendezvous. ... It seem[ed] like the AGS continued to build like it was still calculating and still projecting the orbit to the insertion parameter."
171:45:01 Irwin: AGS Master Alarm.
171:45:06 Mitchell: Copy.
171:45:09 Irwin: Hey, we got a Master Alarm on the AGS, but we trimmed the AGS.
From the Apollo 15 Mission Report: "Abort guidance system warnings and master alarms occurred right after insertion into lunar orbit and at acquisition of signal prior to Lunar Module deorbit. The first one was reset by the crew; the second persisted until lunar impact. Performance of the abort guidance system appeared normal before, during, and after the time of the alarms."
"After the warning at insertion, the crew read out the contents of the computer self-test address 412, but there was no indication of a test-mode fail. The crew did not, however, reload all zeros into address 412 as is required to reset the flip-flop which controls the test-mode fail output in the computer. Consequently, a second test-mode fail would not have caused an Abort Guidance System warning. The fact that a second warning did occur restricts the location of the failure to the output circuit of the computer, the Signal Conditioner Electronics assembly, or the Caution and Warning System."
The mission report concludes that there was a fault in the self-test circuitry, and that additional grounding was necessary.
171:45:17 Mitchell: Okay, is your...
171:45:18 Scott: Stand by for a tweak or a trim.
171:45:21 Mitchell: Okay...
171:45:23 Irwin: That's the self test. Okay.
171:45:29 Scott: PGNS says it's in a 40.6 by 8.9. [nautical mile orbit, 75.2 by 16.5 km
171:45:40 Mitchell: Roger, we copy. Guidance still looks good to us.
171:45:46 Scott: Okay. [Pause.]
171:45:57 Mitchell: Falcon, your AGS still looks good.
171:46:02 Irwin: Okay, we copy.
171:46:03 Scott: Okay. Understand. AGS still looks good. [Long pause.]
171:46:16 Mitchell: Falcon, Houston. No tweak [burn].
171:46:22 Scott: Roger, no tweak. Thank you. [Pause.]
171:46:29 Worden: Okay, Falcon; Endeavour. I got you locked up on the VHF at 127 [nautical miles separation, 235 km].
Worden, from 1971 Technical debrief: "I waited until I got a state vector from the ground, and the first thing I tried to do was get the VHF locked up, but it wouldn't lock up. I guess I reset the VHF range four times before it finally locked up. The first good solid range I received was at 136 [nautical] miles [252 km]. That was a closer range than what we normally saw in the simulators. I guess it was because of the orbit that I was in at the time."
171:46:36 Scott: Okay, I understand. 127, Al. [Pause] You reading?
171:46:44 Worden: Roger, go ahead.
171:46:46 Scott: Okay, we're pitching up [to] the radar track attitude. We didn't get a lock on it on the way up. We'll give you a call as soon as we get locked up.
171:46:52 Worden: Okay. I was watching for that, and I'll let you know.
171:47:18 Scott: And, Houston, we're watching the roll angle.
171:47:24 Mitchell: Falcon, Houston. We have you at a 42 by 9 [nautical mile orbit, 77.8 by 16.7 km]. You're looking good.
171:47:31 Scott: Okay. 42 by 9.
171:47:47 Scott: [Garble], Jim? [Pause.]
171:48:14 Irwin: [Garble] [Long pause.]
171:48:34 Worden: There, you're locked on now.
171:48:38 Scott: Roger. We're locking up now.
171:48:39 Worden: Roger. [I've] got good signal strength on you.
171:48:45 Scott: Roger. [Pause.]
From the Apollo 15 Mission Report: "Acquisition with the rendezvous radar during ascent was unsuccessful. The radar antenna was pre-positioned prior to lunar lift-off to an approximate Lunar Module guidance-computer designated position for acquisition following insertion. In this position, acquisition would have been accomplished when the Command Module came into the rendezvous radar antenna field of view. A review of lift-off television data revealed rendezvous radar antenna movement during the first 2 seconds of flight. Analysis has also shown that expansion of the ascent engine plume, after being deflected from the descent stage structure, exerts sufficient pressure on the antenna to overcome gimbal friction and move the antenna. Radar acquisition apparently was not accomplished because the radar antenna moved. Rendezvous radar tracking during ascent is not required."
The Lunar Module's Rendezvous Radar works with a transponder on the CSM to present the LM crew with range, range-rate and direction to the CSM. The range and range-rate are derived conventionally through analysis of the timings of the carrier signal received from the transponder. The antenna dish, mounted above the LM porch and movable side-to-side and up-down (the shaft and trunnion axes) has a four-lobed feedhorn arrangement at its focus. If the dish is pointing directly at the CSM, the signal level from each feedhorn will be equal. Misalignment gives differences in the output from each feedhorn which is processed into vector information and which can, under automatic control, be used to drive the antenna to point at the CSM. However, the antenna must be near enough to the correct angle to have some CSM signal reach at least one feedhorn.
171:48:55 Worden: VHF range has us at 117 [nautical miles, 217 km] now. 117.
171:49:00 Mitchell: Endeavour, Houston. We're ready to uplink you.
171:49:05 Worden: Go ahead. You've got P00 and Accept. [Pause.]
171:49:19 Worden: What kind of range is radar giving you, Dave?
171:49:43 Mitchell: And, Falcon; Houston. We will not uplink a state vector to you, your PGNS and AGS are both good. And we will keep them independent.
171:49:56 Scott: Falcon, Roger.
Comm break.
171:51:53 Mitchell: Endeavour, Houston; the computer's yours.
171:51:59 Worden: Roger.
171:52:06 Mitchell: Okay, Falcon; Houston. I have a MSFN TPI for you and some words.
171:52:16 Irwin: Go ahead. I'm ready to copy the TPI, Ed.
171:52:19 Mitchell: Okay, it's an off-nominal TPI angle. Delta-VX, 66.3; Delta-VY, plus 7.8; Delta-VZ, minus 31.2; total 73.7. TPF Delta-V will be 26.0. You're going to be pointed almost along the line of sight for TPI. You can omit the roll maneuver for TPI, your choice. And you will undoubtedly break lock.
TPF is the Terminal Phase Final.
In a perfect rendezvous maneuver, both the CSM and LM would be in the same orbital plane, with the CSM in a perfectly circular orbit. Neither is the case here. The spacecraft are in somewhat different orbital planes, and the CSM's orbit is somewhat elliptical. To compensate for the out-of-plane error, the TPI will introduce a change in velocity of 7.8 feet per second in the Y-axis, which will place the LM is an orbital plane nearly matching that of the CSM's.
Scott, from 1971 Technical debrief: "The ground had told us that out TPI would be somewhat different from the nominal, even to the extent that we would not have to do the Yaw-Roll maneuver but we would break radar lock. I think their first cut on the solution was a little off, because their subsequent TPI [solution] and ours led us into an almost nominal TPI. We could see this trend coming, as we were doing everything nominal, just as planned."
To apply metric units to the velocity numbers from Mitchell:
Delta-VX, fps (m/s): +66.3 (+20.2)
Delta-VY, fps (m/s): +7.8 (+2.4)
Delta-VZ, fps (m/s): -31.2 (-9.5)
Total, fps (m/s): 73.7 (22.5)
TPF Delta-V, fps (m/s): 26.0 (7.9)
O'Brien, from 2004 mission review: "You have about a zillion different computers and things to come up with your rendezvous solutions. Everything from the PGNS, the AGS, you had the onboard charts, the ground is taking care of everything. How did the charts work?"
Scott, from 2004 mission review: "In simple terms you needed range, range-rate and angle, and time. And the Clohessy-Wilshire equations allowed you to draw a curve on a chart which was a nominal curve. And at certain points, you would have a known range, range-rate and angle to the target, all body-centered coordinates. What you did on the charts was to, at the time, specify, look at the range, range-rate and angle to the target and match that with the nominal. And if it didn't match, you would change the range, range-rate or angle by cranking in a correction off another chart. You can lose communications with the ground. You can lose the PGNS and the AGS and still do the rendezvous because all you need is a watch and the COAS and the radar."
O'Brien, from 2004 mission review: "You were able to take marks with the AOT, I imagine."
Scott, from 2004 mission review: "No, not the AOT."
O'Brien, from 2004 mission review: "Really? Because, especially when you are talking large distances, the COAS isn't going to give you a very accurate angle measurement?"
Scott, from 2004 mission review: "Oh yeah. Sure. COAS is fine. A grease pencil on the window's fine too. I just put a little grease pencil... the COAS goes out, you mark the window with a grease pencil. Works! That's the beauty of the Clohessy-Wilshire equations. They were elegant and just beautiful because you could rendezvous with just nothing but you had to practice a lot and you had to get the feel of it 'cos you knew just about where you were and it would compute TPI and you do TPI and you are on your way and unless you purposely screwed it up, you'd get there. I mean you had to make an effort to screw it up. It's beautiful. That's why we have all the confidence in this stuff. The confidence is based on the fact that it was set up right by these guys that wrote these very elegant equations that went into the computer - computers are very sophisticated, obviously - but they gave you a manual backup that you could do on a piece of paper. After you used it a while, you could almost draw the curve on a piece of paper."
Woods, from 2004 mission review: "And Al was taking marks on you as well. He was generating a solution in parallel to yours."
Scott, from 2004 mission review: "Al did the whole rendezvous, mirror image, with everything he had onboard too. And the rule was, if we didn't make a major burn within one minute, he burned and took over."
171:53:03 Irwin: Okay, on the PAD I have plus 66.3, plus 7.8, minus 31.2; and total for 73.7, and 26.0 for TPF.
171:53:16 Mitchell: That's affirm. And the approach at TPF is going to be right along the local horizontal.
171:53:25 Scott: Okay, thanks for the information, Houston. I think if radar's working good and we get a good solution, we will probably stay heads up and go ahead and accept the breaklock.
171:53:35 Mitchell: Roger. Roger. And, Endeavour; Houston. The same goes for you. Your attitude, if you were to have to make the burn, would be along the line of sight as well.
171:53:51 Worden: Endeavour, Roger.
171:53:55 Scott: And, Houston; Falcon. I have a visual on the Endeavour now. And the COAS is exactly boresighted; the radar needles are boresighted, and the PGNS needles are boresighted, and the AGS needles are boresighted, so we're looking pretty good.
The COAS (Crew Optical Alignment Sight) provides Dave with an aligned reticle through which he can look to ensure that the LM is aligned with the CSM during the rendezvous. Additionally he can display relative alignment in velocity terms using the radar, PGNS or AGS to drive a pair of needles, the crosspointers.
171:54:10 Mitchell: Very good, Dave.
171:54:23 Mitchell: And, Falcon; Houston. As far as we can tell, your AGS is completely Go. We see no reason for the master alarm yet.
171:54:33 Scott: Understand. [Long pause.]
171:55:07 Scott: Okay, Endeavour; Falcon. I'm looking at about 94 [nautical] miles [range, 174 km], 355 feet per second [closure rate, 108 m/s].
171:55:14 Worden: Oh, Roger. I'm looking at 94 [nautical] miles also.
171:55:14 Scott: Okay, good show. And the PGNS state vector agrees with that. [Pause.]
171:55:40 Mitchell: And, Falcon; Houston. You're go for an APS TPI. You have 180 feet [per second] available [on the APS].
At this time, the amount of fuel remaining in the APS is quite low, and to speak of percentages is almost meaningless. Since the quantity that is used often during the rendezvous is the Delta-V for the upcoming maneuvers, it is more useful to speak of the remaining APS capacity in feet per second. Here, the need to reduce the LM's weight is more apparent than ever, as the amount of fuel available is almost perfectly matched to the mission requirements, with little, if any, margin for error. The 180 feet per second value of remaining APS capability translates to only 5 seconds of burn time. Still, the TPI is a sufficiently large maneuver that the APS is the preferred engine to use, saving wear and tear on the RCS jets in case of an off-nominal rendezvous and docking.
171:55:48 Scott: Oh, Roger. Understand. Go for the APS TPI, thank you. [Long pause.]
TPI will be performed behind the Moon. LOS on the LM in 19 minutes, 12 seconds; on the Command Module, 20 minutes, 01 second.
171:56:38 Worden: Falcon, Endeavour. You got your lights on, Jim?
171:56:44 Worden: Okay. [Long pause.]
171:56:59 Mitchell: Falcon, Houston.
171:57:04 Scott: Houston, Falcon. Go.
171:57:05 Mitchell: Be advised your direct rendezvous TPI charts are No Go because of this elliptical rendezvous. Your midcourse charts are good.
171:57:19 Scott: Okay. Understand. The TPI charts are No Go, and the midcourse charts are good.
Using a "defense in depth" philosophy, there are several techniques that are available to the crews in both the CSM and LM for rendezvous. In addition to the PGNS and AGS on the LM, and the CSM with it's own rendezvous capability, and Houston all calculating their own solutions, there are charts onboard the LM that will allow the crew to calculate their position, rate and necessary burn times. Prepared in advance of the mission, they presume many basic assumptions; that the CSM is in a near-circular orbit, and all the maneuvers will be in the same orbital plane. These assumptions are not relevant in this case, and as a result, the crew has been told not to use them. To generate a set of charts that would apply for all reasonable cases would be a tremendous job, and would end up producing a huge document that would be difficult to use and interpret.
Long comm break.
LM Flight Plan page 3-272.
CSM Flight Plan page 3-273.
172:01:08 Scott: Roger. Tracking light's on. [Pause.]
172:01:20 Scott: I don't see your tracking lights. [Long pause.]
Range about 70 [nautical] miles [130 km] now."
172:02:13 Worden: Falcon, Endeavour. I don't have your lights.
172:02:28 Scott: Okay. [Long pause.]
172:03:08 Scott: Houston, Falcon. What's your LOS time?
172:03:24 Mitchell: Falcon, Houston. LOS in 12 minutes.
172:03:31 Scott: Roger; 12 minutes. Okay.
172:03:37 Worden: Yes. I got your lights now, Dave.
172:03:39 Scott: Okay. Very good. [Long pause.]
Worden, from 1971 Technical debrief: "...I looked in the sextant and didn't see anything. I looked in the telescope and didn't see anything, but there was still some sunlight shafting into the telescope. It was still pretty bright out there, so I couldn't see anything. When we finally got into darkness, I'd estimate 12 to 15 degrees from the center of the telescope, I picked up a flash out of the corner of my eye. I manually drove the telescope over to that point and picked you up in the sextant. You came in loud and clear in the sextant. The light was really bright. I asked you about your tracking light about that time and you said you had it turned on and you could see it flashing."
Falcon is in a lower, and therefore faster orbit and is catching up on Endeavour, which is ahead in the chase. As they approach LOS around the western limb, and before they pass the terminator the Sun is behind Falcon as seen by Al and is causing flare in the optical systems.
Falcon is still on the primary guidance system. The crew trimmed the numbers in the secondary system at insertion.
172:04:30 Worden: Okay, Falcon; Endeavour. I'm getting some large updates on you there, Dave, on the first mark.
172:04:38 Scott: Okay. [Pause.]
But both guidance systems are good. And they're operating on PGNS."
172:04:49 Worden: That's right. Yes, that's right. VHF's going okay. First optics is - is off. I bypassed to them. I'll take the third.
172:05:09 Mitchell: Falcon, Houston.
172:05:14 Scott: Houston, Falcon. Go.
172:05:16 Mitchell: Roger, we need to tweak up your PIPAs a little bit more, Dave, before TPI.
172:05:24 Scott: Okay, fine. Pencil's out; go ahead.
172:05:27 Mitchell: Address 1452, 05210; address 1456, 03170. And those are both Verb 21, Noun 01.
172:05:50 Scott: Okay, we copy. A Verb 21, Noun 01; 1452 should be 05210, and 1456 should be 03170.
172:06:02 Mitchell: Good readback.
Another update to the drift coefficients of the PIPA needs to be entered into the computer.
Comm break.
This is Apollo Control. Biomedical monitoring was on Dave Scott during lift-off. His heart rate at lift-off was 74."
172:07:34 Worden: Okay, Dave. The first update was the only large one. The rest of them are all falling in.
172:07:38 Scott: Okay, very good.
Comm break.
172:09:09 Scott: Okay, Houston; Falcon. We're seeing a fairly large difference in Z between the onboard solutions and the ground solutions. But, I guess that can be expected at the recycle.
172:09:18 Mitchell: I'm checking it for you now, Dave. Your PGNS and AGS seem to agree pretty well.
172:09:26 Scott: Roger. And I think we can expect a fairly large Z at the recycle.
172:09:28 Mitchell: I'll give back some words on the MSFN TPI in a minute.
172:09:35 Scott: Roger. [Long pause.]
172:10:08 Mitchell: Falcon, Houston. We're going to watch it for a few more minutes and see how they converge the other solution.
172:10:16 Scott: Roger. [Long pause.]
172:10:57 Worden: Okay, Dave. I've got a recycle solution for you. Roger. Minus 69.4, minus 6.2, plus 12.0.
Ground tracking stations are monitoring the progress of the CSM and LM.
172:11:14 Mitchell: Endeavour, Houston. I need Omni Alpha.
172:11:22 Worden: Omni Alpha. [Long pause.]
172:12:15 Mitchell: And, Falcon; Houston.
172:12:21 Scott: Houston, Falcon. Go.
172:12:22 Mitchell: Roger, FIDO thinks you had a good solution, but not a great solution before. He's now saying the Z component will be - should converge to about a minus 19. And if it does, your approach angle with be more nominal - rather than along the horizontal.
172:12:42 Scott: Okay, that sounds like we're all converging to the same spot. Thank you.
172:12:46 Mitchell: We agree, Dave.
Comm break.
172:14:14 Irwin: Okay, Houston; Falcon. Our polar plot is showing us pretty nominal. I guess we'll probably stay with the nominal procedures on the TPI.
The rendezvous maneuvers have little margin for error, where only a few feet per second miscalculation in one maneuver can result in large corrective maneuvers later, a good reason for preserving the life of the RCS thrusters. Given the subtle differences in all the sources working together on the task (the two computers and guidance systems on the LM, the CSM's computer and VHF ranging, ground controllers using radar and telemetry data from the spacecraft, and backup manual charts on all three locations), each will come up with a slightly different solution. As a result, the calculations are repeated several times, and results compared. Ideally, all solutions will converge to the same result as the rendezvous progresses. In reality, a slightly misaligned platform or a component that is performing imperfectly (but still within acceptable margins) will create a complex set of solutions that might never agree. In cases like this the ground controllers, who have a wealth of computing power and performance history on the components, will make a recommendation as to which solution is preferred.
172:14:23 Mitchell: Roger, Falcon. We have you a minute to LOS. Your solutions look good in both computers. We'll see you on the other side. And be advised, we did monitor your lift-off, and we can confirm you lifted off.
172:14:40 Scott: Well, very good. That's nice to know, thank you much. Save the tapes for us, will you.
172:14:51 Mitchell: Say again, please.
172:14:55 Scott: Save the TV tapes for us, will you please.
172:14:58 Mitchell: Will do, and you're 30 seconds from LOS, Falcon.
172:15:04 Scott: Roger. See you around the corner.
172:15:06 Mitchell: Roger, Roger, Dave. [Long pause.]
172:15:20 Irwin (onboard): Okay. That's LOS.
172:15:22 Scott (onboard): Okay.
We have had Loss Of Signal from the Lunar Module. [We are] about 40 seconds away from LOS on the Command Module.
172:15:47 Mitchell: And, Endeavour; Houston. I have you 30 seconds from LOS.
172:15:49 Irwin (onboard): Why don't we have our helmet and gloves on? When we going to dock?
172:15:51 Worden (onboard): Jim, never mind; never mind.
172:15:55 Worden: Endeavour, Roger. See you on the other side.
172:15:57 Mitchell: Okeydoke, Al.
Very long comm break.
This is Apollo Control. We've had Loss Of Signal on Endeavour now. Terminal Phase Initiation [TPI] for their rendezvous will be performed behind the Moon at 172 hours, 29 minutes, 39 seconds. We will reacquire both spacecraft just a few minutes before the TPF [Terminal Phase Final], the terminal phase braking as they're rendezvousing. Had 2 'firsts' on this lift-off. First time we've seen it on television, also the first melodious lift off. The Air Force song coming from the Lunar Module and its Air Force crew, they perhaps would have to alter the lyrics a little to "Off we go into the wild black yonder from the lunar surface." We'll reacquire the Command Module at 173 hours, 1 minute, 40 seconds. The Lunar Module at 173 hours, 3 minutes, 29 seconds. At 172 hours, 17 minutes; this is Mission Control, Houston.
Of course, the PAO Announcer does not realise that the music came from Al Worden in the Command Module.
From the Apollo 15 Mission Report: "After insertion, a Lunar Module state vector was uplinked from the ground and an automatic maneuver was made to the rendezvous tracking attitude. The rendezvous was completed using a minimum-key-stroke [automatic sequencing] computer program. This program was new for this flight, and was designed to relieve the Command Module Pilot's workload. The computer automatically sequenced through the rendezvous maneuvers and tracking periods. It was initiated at the pre-terminal phase initiation program and was terminated with the final rendezvous computer program, which maneuvered the Command and Service Module to the desired tracking attitude just prior to docking. The program functioned as anticipated and allowed the Command Module Pilot much greater time for optical tracking and systems monitoring.
"There was some difficulty at first in actually seeing the Lunar Module tracking light because the Lunar Module was not centered in the scanning telescope. After going into darkness, the light was observed at about 15 degrees from the center of the telescope. After two marks were taken, the optics tracked the Lunar Module in the center of the sextant. A total of 18 optical and 19 VHF marks were taken before the final solution was initiated. The maneuver to the Terminal Phase Initiate attitude was a small maneuver of approximately 20 to 30 degrees in pitch."
Scott, from 1971 Technical debrief: "We made a 3-second automatic [TPI] burn using the APS. We had the prescribed 10-second ullage, and everything went nominally. ... [To Worden] Did you have any trouble picking us up after the burn after you had loaded your P76?"
Worden, from 1971 Technical debrief: "No, I did not have any trouble picking you up. We were close enough then so that there was no problem seeing the light in the telescope. You were out of the sextant field of view [28 times magnification] on the first marks I took, and so I had to go to the telescope [unity magnification]. There was no problem at that point. The range was close enough so that I could see the light without any problem."
From the Apollo 15 Mission Report: "After the Lunar Module performed the Terminal Phase Initiation maneuver, the actual velocity changes were inserted into the computer. The Command and Service Module then was maneuvered automatically to the tracking attitude. Ten optics and nine VHF marks were taken prior to the first midcourse correction and 18 optics and 11 VHF marks were taken prior to the second midcourse correction. All solutions were compared with the Lunar Module solutions and were within the prescribed limits. The Lunar Module subsequently accomplished the maneuvers based on its own solutions."
LM Flight Plan page 3-274.
CSM Flight Plan page 3-275.
The two midcourse corrections are computed from the optical and radar fixes that both spacecraft are taking. Al's computer in the CSM and the two computers in the LM, the PGNS and the AGS, arrive at separate conclusions for these burns based on their own systems for measuring attitude and acceleration and the sightings taken of the other craft, giving a three-way check that no single system is making wayward calculations. Thus the midcourse correction burns keep any small errors in the TPI burn from building up into large errors.
Scott, from 1971 Technical debrief: "...It looked like the CSM [computer] and the AGS were both trending towards a higher midcourse than the PGNS; but since we were on the PGNS and it was apparently running all right, we accepted the PGNS solution and burned it."
Though all three computers are coming up with acceptable solutions, they all have errors. With more sightings, another computation is made for the second midcourse correction burn. This will correct for the errors left over from the first burn.
Scott, from 1971 Technical debrief: "...We all proceeded for final comp[utation] at the same time for midcourse 2. [The numbers] were a little bit larger, indicating that we might have had a better solution had we burned the CSM or AGS [solution] at midcourse 1. This sort of indicates the PGNS was a little behind on the solution."
LM Flight Plan page 3-276.
CSM Flight Plan page 3-277.
172:16:06 Scott (onboard): Why do we have to have it this way?
172:16:09 Irwin (onboard): It'd help to have your glove on - and your helmet on just to keep the Sun out of your eyes, you know.
172:16:13 Scott (onboard): Yes, but we don't have anything in the procedures, do we ?
172:16:18 Irwin (onboard): Well, I think there's something about doing it optional.
172:16:21 Scott (onboard): Huh! Yes, I think that's [garble].
172:16:42 Irwin (onboard): That sure was a sporty lift-off.
172:16:44 Scott (onboard): I thought it was sort of springy. It looked - it's the soup.
172:17:39 Irwin (onboard): And it's tracking good.
172:17:42 Scott (onboard): Our - Okay, turning elliptical.
172:17:45 Irwin (onboard): It's coming to 8.
172:17:47 Scott (onboard): State vector's...
172:18:16 Scott (onboard): Okay.
172:18:17 Irwin (onboard): Now you select [garble].
172:18:19 Scott (onboard): Okay.
172:18:21 Irwin (onboard): Careful.
172:19:01 Scott (onboard): Now we're to [garble].
172:19:05 Irwin (onboard): [Garble] total.
172:19:09 Scott (onboard): [Garble].
172:19:17 Irwin (onboard): Okay, AGS - C component is exactly what the ground computed it: 19.1. They came up with - 19.
172:19:24 Scott (onboard): Huh. Well - got a [garble] computer there.
172:19:36 Worden (onboard): Okay. Four seconds to final comp.
172:19:39 Scott (onboard): Okay, fine.
172:19:41 Worden (onboard): Final comp.
172:19:44 Scott (onboard): Did you get a bunch of good marks?
172:19:47 Worden (onboard): Yes, sir. 19 and 18.
172:19:49 Scott (onboard): Beautiful.
172:20:37 Scott (onboard): Okay, take the end of your first mark and total the answer in minutes. Let me turn that down. Twenty-six minutes.
172:20:56 Worden (onboard): Okay. I've got the answer now.
172:20:58 Irwin (onboard): Go ahead, Al.
172:20:59 Worden (onboard): Okay, minus 69.1, minus 6.1, plus 16.1.
172:21:07 Irwin (onboard): Copy, minus 69.1, minus 6.1, and plus 16.1.
172:21:11 Scott (onboard): Okay, want to get these numbers, Jim? I mean, tell me the elevation and so on.
172:21:25 Scott (onboard): Okay, here's a Noun 50 in.
172:21:27 Irwin (onboard): [Garble] okay. [Garble].
172:21:34 Scott (onboard): Right. There's a [garble] you better jump. No, no, that's not Noun 81.
172:21:38 Irwin (onboard): [Garble].
172:21:39 Scott (onboard): Here's Noun 81.
172:21:40 Worden (onboard): Okay, Dave, I'm maneuvering.
172:21:41 Scott (onboard): Okay. Let us give you the numbers first, Al. Okay...
172:21:44 Worden (onboard): Go ahead.
172:21:45 Scott (onboard): Okay; 70.3; plus 5.9; and minus 17.7.
172:21:55 Worden (onboard): Okay, that's official burn attitude.
172:21:57 Scott (onboard): That's correct.
172:22:02 Worden (onboard): Okay, [garble] I'm in attitude and only [garble].
172:22:06 Scott (onboard): Beautiful.
172:22:14 Worden (onboard): [Garble].
172:22:15 Scott (onboard): Good.
172:22:18 Irwin (onboard): Well, I came up with exactly the same numbers as the PGNS, and X and Y, there's a difference of 2 and 3.
172:22:27 Scott (onboard): Okay.
172:22:30 Irwin (onboard): I think we'll move. You got the burn attitude?
172:22:36 Scott (onboard): I maneuver now?
172:23:11 Scott (onboard): Okay, Endeavour, did you get our numbers for the burn?
172:23:58 Scott (onboard): Maneuver.
172:24:41 Irwin (onboard): Roger. Copy. Okay. It's picking up [garble] for AGS.
172:26:09 Scott (onboard): We have 3 and a half minutes to go, Al.
172:26:11 Worden (onboard): Roger. Understand. [Garble].
172:26:16 Scott (onboard): Excuse me.
172:26:17 Irwin (onboard): Yes, Dave. Get your engine.
172:26:21 Scott (onboard): Yes. [Garble].
172:26:57 Irwin (onboard): Should be a 3-second burn.
172:26:58 Scott (onboard): Okay, 3-second burn. Don't start until I tell you.
172:27:04 Irwin (onboard): Go AGS to maximum to normal. Okay, at 30 seconds, it's Engine Arm to Ascent, manual ullage, and Pro. And AGS to Auto.
172:27:15 Scott (onboard): I should [garble]. Nothing in it.
172:27:38 Irwin (onboard): Mark; 2 minutes.
172:27:40 Worden (onboard): [Garble].
172:27:43 Irwin (onboard): And everything looks good.
172:28:35 Irwin (onboard): Mark at 1 minute, Dave.
172:28:36 Scott (onboard): Okay...
172:28:38 Scott (onboard): Mark; 1 minute.
172:28:40 Irwin (onboard): Okay. AGS going to Auto now.
172:28:43 Scott (onboard): Okay, AGS to Auto.
172:28:52 Scott (onboard): Okay. You give me the time. I'll get the ullage.
172:28:55 Irwin (onboard): Okay.
172:29:06 Irwin (onboard): Okay.
172:29:07 Scott (onboard): Average g low. Abort Stage, push. Engine Arm to Ascent. Standing by for 10 seconds.
172:29:28 Scott (onboard): Ullage. Trouble.
172:29:39 Irwin (onboard): Three.
172:29:42 Scott (onboard): Okay. Auto Shutdown and Auto Ignition. We're trimming.
172:29:48 Worden (onboard): Dave? Did you remember the up-link?
172:29:51 Scott (onboard): Okay. In fact, I think it is.
172:29:54 Irwin (onboard): Didn't like it worth a damn. Okay, Dave. We'll be done in a minute with this.
172:30:06 Scott (onboard): Okay, there you go; .2, .2, and .4.
172:30:18 Irwin (onboard): I don't like tragedy.
172:31:48 Scott (onboard): Okay, Al. We're starting them over.
172:32:29 Irwin (onboard): [Garble].
172:33:16 Scott (onboard): We freaked up at 23: 38 - about 100.
172:33:20 Irwin (onboard): I think we're ...
172:33:34 Scott (onboard): We have one mark. Now doing 40.
172:33:43 Irwin (onboard): Make that zero burn at this close mode.
172:33:45 Scott (onboard): Never touch it. Really?
172:33:46 Irwin (onboard): Yes.
172:35:10 Irwin (onboard): Right on the nominal line, Dave.
172:35:12 Scott (onboard): Really?
172:35:13 Irwin (onboard): Yes.
172:35:24 Scott (onboard): Hey!
172:37:17 Irwin (onboard): Watch it. Tail's going to bump it.
172:37:20 Scott (onboard): Okay.
172:37:23 Irwin (onboard): Next thing's - no - no [garble].
172:37:31 Scott (onboard): Okay. [Garble].
172:37:36 Irwin (onboard): You want to grab this?
172:37:37 Scott (onboard): We already picked the [garble]?
172:37:39 Irwin (onboard): If he could talk, you could get him.
172:37:42 Scott (onboard): State vector agrees with [garble]. I don't know. I think - Let's see what - We might borrow anything off our equipment.
172:37:50 Irwin (onboard): Let's see.
172:37:51 Scott (onboard): Here's your [garble] pocket.
172:37:58 Irwin (onboard): Let's see, what - [garble] I remember, we've got a [garble] to do.
172:38:21 Irwin (onboard): How you doing over there, Albert?
172:38:25 Worden (onboard): Doing just fine, but it's back to end-to-end, and I've got much in motion.
172:38:30 Irwin (onboard): Very good. And reading the procedures and checking...
172:38:32 Scott (onboard): Oh, yes! Bad update! What do you know. I've been looking for it and I finally saw it, but it's not very funny.
172:38:41 Irwin (onboard): Want to check on it?
172:38:42 Worden (onboard): What'd you see?
172:38:43 Scott (onboard): That's your tracking light. You're...
172:38:45 Worden (onboard): Oh, good.
172:38:46 Scott (onboard): Yes, you're right down the path.
172:38:48 Worden (onboard): Yes, so are you. Your light is right through the money.
172:38:51 Scott (onboard): Is it really? Yours - yours is really dim. About like a - maybe a fourth magnitude star? Okay, let's really hit them.
172:39:28 Irwin (onboard): Brighten it up to three.
172:39:51 Scott (onboard): Okay, there she is. Oop!
Rev 49 begins at about 172:39.
172:40:03 Irwin (onboard): Especially about this problem. Make it stick.
172:41:11 Scott (onboard): Okay. Know what you got to do, Jim?
172:41:14 Irwin (onboard): Yes. I'll take it. I think that's going out there.
172:41:19 Irwin (onboard): [Garble] burning.
172:41:21 Worden (onboard): You guys coming up on final comp.
172:41:23 Scott (onboard): Okay. We got 20 seconds or so.
172:41:25 Worden (onboard): Why don't you mark final comp. Get you back with us.
172:41:29 Scott (onboard): All right, I sure will. 10 seconds. 3, 2, 1...
172:41:41 Scott (onboard): Mark.
172:41:44 Worden (onboard): Gotcha.
172:41:45 Scott (onboard): Okay.
172:41:46 Worden (onboard): Only 3 seconds difference between us.
172:41:47 Scott (onboard): Well, it's a 3-second burn, so that makes sense.
172:41:55 Irwin (onboard): No, I don't need it. We have to go to coffee in a minute.
172:41;59 Scott (onboard): Yes.
172:42:01 Irwin (onboard): Okay, Al. We've got a minus 1.1, 0, and a minus 1.1.
172:42:07 Worden (onboard): Okay, and I got a plus 1.5, and a minus .2, and plus 1.9.
172:42:12 Scott (onboard): How about that! That's very nice. Think we'll burn our solution on time. That's - it sort of took an [garble].
172:42:20 Worden (onboard): Okay, go ahead and burn your solution.
172:42:22 Scott (onboard): All right. We'll burn our solution.
172:42:27 Worden (onboard): I'll buy that.
172:42:35 Irwin (onboard): Got the AGS and redo solution.
172:42:37 Scott (onboard): All righty. It's reading straight, now.
172:43:42 Irwin (onboard): Mark; 1 minute to the midcourse.
172:43:46 Worden (onboard): Roger.
172:44:08 Irwin (onboard): Houston's money?
172:44:12 Scott (onboard): Yes, I guess they're using it.'
172:44:15 Irwin (onboard): Looking forward.
172:44:16 Scott (onboard): Here, you'll like this.
172:44:19 Irwin (onboard): [Garble] I want to plop.
172:44:47 Scott (onboard): There you go.
172:44:48 Irwin (onboard): [garble] and the pink [garble].
172:44:51 Worden (onboard): Can't you get it all?
172:44:54 Scott (onboard): One more cycle now. Okay, we got it all in.
172:44:58 Worden (onboard): Okay.
172:44:59 Scott (onboard): Consider it down there, Jim. It's really 2222s.
172:45:18 Worden (onboard): Oh, you're shining in the sunlight now! Boy, is that pretty!
172:45:27 Scott (onboard): Who's shining in the sunlight?
172:45:31 Irwin (onboard): Us, I think.
172:46:15 Worden (onboard): Yes, I can see in the sunlight now, too.
172:46:18 Irwin (onboard): Okay. We've got our first mark. We should be up with you.
172:46:22 Worden (onboard): I believe I can even make out the shape.
172:46:25 Irwin (onboard): Hey, that's it!
172:46:27 Scott (onboard): No, sure can't.
172:46:30 Irwin (onboard): Hey.
172:46:34 Scott (onboard): It's unreal.
172:46:45 Irwin (onboard): Think you can call another one up?
172:46:48 Scott (onboard): Hmm! You sure if you got the right thing?
172:46:52 Irwin (onboard): Seems to be [garble].
172:46:57 Scott (onboard): Okay. Can't put too much [garble]. Seems to be squared away though, now.
This is Apollo Control at 173 hours. We're just under a minute away from Acquisition Of Signal with both the Command Module and the Lunar Module. We'll be getting a TPI burn report from Falcon soon after acquisition. And Falcon will be starting the rendezvous braking maneuver a few minutes after acquisition. We expect television to begin at about 173 hours, 10 minutes, as scheduled in the Flight Plan and see this rendezvous. We'll stand by live now for the first conservation."
We have acquired both vehicles now, we'll stand by."
173:02:27 Mitchell: Falcon, Houston. Standing by.
173:02:33 Scott: Roger, Houston. Falcon had a good TPI. It burned a small midcourse 1, and a small midcourse 2. Presently, we have a visual on the Command Module and all the solutions have been agreeing very well.
173:02:45 Mitchell: Okay. Did you write down your solutions, Dave?
173:02:51 Scott: Yes, we got them all in.
173:02:53 Mitchell: Okay. We'll ask you for them later.
173:02:57 Scott: Okay.
Comm break.
Range is about 2½ [nautical] miles now [4.6 km]. Range-rate, 29 feet per second [8.8 m/s]."
173:03:58 Worden: Houston, Endeavour.
173:04:00 Mitchell: Hello, Endeavour. Standing by.
173:04:05 Worden: Okay, TV's up to [garble].
173:04:07 Mitchell: Say again. [Pause.]
173:04:13 Mitchell: Roger, copy. TV's on. [Long pause.]
173:04:31 Mitchell: Endeavour, Houston. We're not tracking your High Gain [Antenna], yet.
173:04:38 Worden: Okay. [Long pause.]
173:05:23 Mitchell: We have your picture, Endeavour.
173:05:33 Worden: Roger. [Pause.]
173:05:44 Worden: Okay, I've got you visually there, Falcon. [Long pause.]
173:06:46 Worden: Yes, you're looking good.
Comm break.
173:07:50 Worden: You're very garbled, Dave. Say again.
Scott, from 1971 Technical debrief: [To Worden] "We saw you in the daylight all the way in. The ground told us that we would approach somewhat off nominal and that we would be almost horizontal during TPF [the final braking maneuver], which we were. As we approached the braking, we came through the first [braking] gate at about 25 feet/second [7.6 m/s], and our final solution the PGNS had given us a TPF of 25 feet/second; so that ought to match pretty well. There was no braking at the 6,000-foot [1,800-metre] mark. At the 3,000-foot [900-metre] mark, I braked down to 20 feet/second [6 m/s]. At 1,500 feet [450 metres], as I was coming back to 10 feet/second [3 m/s], I noticed I had a visual line of sight rate [of] up and left. The radar needles [on the cross-pointer display] were not giving me any indication; so I checked to see that we were on low mode on the [cross-pointer] needles, and we were. If anything, the vertical needle was displaced just a little bit to the right.
"I could see by our attitude in the ball that we were coming in out of phase. We had some out-of-plane correction at the beginning of TPI. What was surprising was that I had to start making corrections up and left in a tight deadband [0.5° per second] attitude hold to keep the COAS on the Command Module. The radar needles were not giving me any indication of out-of-plane rates - line-of-sight rates."
Cross-pointer displays are installed on both the Commander's and Lunar Module Pilot's Main Display Console. Similar in operation to the glideslope and localizer needles on an aircraft's Instrument Landing System display, they provide velocity rate information during landing and rendezvous. The apparent failure of the Commander's cross-pointer display, which provides information on the horizontal and vertical rates between the CSM and the LM, could have been from several causes, from an incorrect switch setting to a broken wire. The Apollo 15 Mission Report concluded, "The most probable failure is an open in the signal return line (from the display). Rate information could still be deduced from the (rendezvous radar) antenna position data which is displayed on the flight director attitude indicators. Ground tests and checkout might not show this kind of failure."
173:08:04 Scott: Okay, I got you at 1.28 [nautical] mile [2.37 km].
173:08:08 Worden: Okay, we're right with you. [Long pause.]
173:08:32 Mitchell: Endeavour, Houston. Give us Auto on the High Gain [Antenna], please.
173:08:40 Worden: On Auto. [Long pause.]
173:09:13 Scott: Okay, one [nautical] mile and 27 feet per second on the radar.
Range: 1.85 km. Range-rate: 8.2 m/s.
173:09:17 Worden: Roger.
Comm break.
173:10:31 Mitchell: Endeavour, Houston. Do you have the Falcon on your monitor?
173:10:45 Worden: No, I wasn't watching it, Ed. Stand by one.
173:11:05 Irwin: Okay, 3,000 feet, braking down to 20 [fps]. [Long pause.]
Range: 900 metres. Range-rate: 6.1 m/s.
173:11:51 Mitchell: Don't waste any time on it, Al. [Long pause.]
173:12:18 Irwin: Okay, 1,500 feet, braking down to 10.
Range: 450 metres. Range-rate: 3 m/s.
Comm break.
173:14:11 Irwin: Okay, 500, braking to 5.
Range: 150 metres. Range-rate: 1.5 m/s.
Comm break.
The final stages of rendezvous and docking on all Apollo lunar flights have been the subject of intensive documentation and Apollo 15 is no exception. Both spacecraft are photographing the arrival of the other on still and movie film, and the approaching Falcon is being televised by Al to Mission Control and the world.
This is 16 mm coverage of Falcon's arrival at Endeavour.
H.264 MP4 video file.
Jim is using magazine TT to photograph Endeavour as they approach. His sequence starts with AS15-88-11955, where the CSM is little more than a dot against space. It continues to 11975 where the CSM is positioned for docking. The sequence will include shots taken to record the state of the SIM bay and particularly the V over H sensor.
AS15-88-11955 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
AS15-88-11956 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
AS15-88-11957 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
AS15-88-11958 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
AS15-88-11959 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
AS15-88-11960 - CSM Endeavour photographed from the approaching LM - Image by NASA/Johnson Space Center.
173:15:18 Irwin: [Garble].
173:15:29 Worden: [Garble] Falcon [garble]. [Pause.]
173:15:44 Scott: Okay, Houston. We're station-keeping at about 120 feet [37 metres] or so.
Now Mission Control want to use this opportunity to have Dave and Jim inspect the SIM bay.
Scott, from 1971 Technical debrief: "You maneuvered to the SIM bay [observation] attitude, and the ground called us to take a look at the V/H sensor on the Pan Camera and to take some pictures."
173:15:50 Mitchell: Roger. Dave, during the Command Module pitch-around, and we'd like for you to take a look at the V-over-H sensor in the SIM bay, if you can. Do you know how to spot it?
173:15:44 Scott: The which sensor?
173:16:07 Mitchell: V-over-H.
173:16:17 Irwin: Yes, it's - it's on the Pan Camera gadget.
173:16:20 Scott: Okay, I guess we're not - Well, Al's talking to us.
173:16:26 Mitchell: Okay, what we're looking for is to see if anything is in the way of the lens of that sensor. If you're not familiar, I can give you a page number in your LM Data Systems Book. Just take a look at it.
173:16:50 Scott: Okay, stand by one.
173:16:56 Worden: No, it's not - it's not on the lens, Dave. It's right alongside the lens on the body of the camera...
173:17:00 Mitchell: We've got a picture of it, Al.
173:17:01 Worden: ...it tells us what speed to take the picture at.
173:17:05 Scott: Okay, we'll get a picture of it.
173:17:06 Worden: Okay. [Long pause.]
173:17:20 Worden: Okay. I'll go ahead and do your pitcharound. [Long pause.]
173:17:40 Worden: And, Dave, give me - give me a call when you start.
173:17:45 Scott: Okay. [Long pause.]
173:17:59 Scott: Houston, what page is that on in the LM Systems book?
173:18:02 Mitchell: Okay. It's page 43 in the LM's System's Bo - Data Book.
173:18:10 Scott: Okay.
173:18:11 Mitchell: Okay. On the right-hand side, Dave, you see that one little line that says, "Mapping and Pan Cameras N2 [nitrogen] Press[ure] Systems Assembly."
173:18:21 Scott: We haven't got it out yet. Stand by.
173:18:23 Mitchell: Okay. [Long pause.]
173:18:35 Worden: Yes, I'll go the higher rate, Dave. [Long pause.]
173:19:01 Worden: Okay, here we go.
173:19:01 Irwin: Go ahead. [Pause.]
173:19:11 Scott: Hey, it looks good, you're going the right way. [Long pause.]
173:19:37 Mitchell: Dave, while he's pitching, I'll tell you - should be about the middle of the SIM bay by the Mapping Camera. [Long pause.]
173:20:18 Scott: Very nice maneuver, Endeavour. [Long pause.]
AS15-88-11961 begins a sequence of images that show the CSM being rotated by Al to reveal the SIM bay to Jim's camera as Sinus Successus on the northeastern edge of Mare Fecunditatis slips by below.
AS15-88-11961 - CSM Endeavour rotating while being photographed from the LM - Image by NASA/Johnson Space Center.
AS15-88-11962 - CSM Endeavour rotating while being photographed from the LM - Image by NASA/Johnson Space Center.
AS15-88-11963 - CSM Endeavour rotating while being photographed from the LM - Image by NASA/Johnson Space Center.
AS15-88-11964 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
Scott, from 1971 Technical debrief: [To Worden] "I thought your maneuver worked out very well. We put ourselves in a tight deadband attitude hold and just watched you maneuver around and we ended up looking right at the SIM bay. We took a look and I could not see anything wrong with your V/H sensor, although I have to admit that neither Jim nor I knew exactly what to look for. It was there and wasn't obscured."
173:21:05 Scott: Okay, Houston. We don't see it labeled in here. Where - is it labeled on the picture?
173:21:10 Mitchell: Negative. As soon as you have the picture, I'll tell you where to look.
173:21:15 Scott: Okay, we got the picture; tell us where to look.
173:21:17 Mitchell: Okay, way over on the right-hand side, where it says, "Mapping and Pan Cameras N2 Press System Assembly."
173:21:34 Mitchell: It's on the right picture.
173:21:41 Scott: The one with the covers open?
173:21:43 Mitchell: That's affirm. Between the end of that arrow and the lens, about halfway, is a little dot that represents the V-over-H assembly. Now, the camera lens will be covered - rather it will be folded up so you will not be able to see it; however, that is the item you are looking for, represented by the small circle about halfway in between the end of the arrow and the lens of the camera.
173:22:12 Scott: Okay, I see a small circular object there just - just to the right of the handle, and I don't see anything covering it.
173:22:23 Mitchell: Are you talking about the diagram, or in the SIM bay?
173:22:28 Scott: No, in the SIM bay.
173:22:30 Mitchell: Okay. That's what we wanted to know.
173:22:37 Scott: Yes, it's a little round black...
173:22:39 Mitchell: That's it - that's it.
173:22:40 Scott: ...holder type of affair, right?
173:22:44 Mitchell: If you can snap a picture of it, we'd appreciate it.
173:22:54 Scott: Okay, we'll get one, Ed. Stand by. [Long pause.]
Diagram showing location of V/H sensor with respect to Panoramic Camera.
This diagram, from the J-mission Apollo News Reference, shows the Panoramic Camera with the V/H sensor arrowed just to the lower right of the lens. AS15-88-11972 does not show the sensor because of the attitude of the spacecraft.
Jim takes a further 9 photographs of Endeavour as the two spacecraft station-keep above the northeastern shore of Mare Fecunditatis. The early images from this sequence show a pair of craters on the mare known as Taruntius N and Taruntius O. N is now named after James Smithson, 1765-1829, a British chemist.
AS15-88-11965 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11966 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11967 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11968 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11969 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11970 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11971 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11972 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
AS15-88-11972 is an excellent example from the end of this sequence with the instruments of the SIM bay well displayed. To the right of the SM is Asada, formerly Taruntius A, a 12-km crater now named after Goryu Asada, 1734-1799, a Japanese astronomer. Just visible on the left of the frame is the northeastern rim of the dominant crater of this area, Taruntius. This 56-km crater is named after a Roman mathematician, philosopher and astrologer, Lucius Taruntius Firmanus, c. 86 BCE.
AS15-88-11973 - CSM Endeavour photographed from the LM to photo document the SIM Bay - Image by NASA/Johnson Space Center.
In these pictures of the CSM, window 5 of the is pointing more or less towards the LM and the small boom carrying the EVA floodlight can be seen protruding towards its line of sight. Behind that window, Al is busy taking pictures of Falcon.
Al's photographs of Falcon are on magazine Q. AS15-96-13034 and 35 are taken through one of the rendezvous windows while the nose of the CM is facing the LM.
AS15-96-13034 - The ascent stage LM Falcon photographed from the CSM during station keeping - Image by NASA/Johnson Space Center.
AS15-96-13035 - The ascent stage LM Falcon photographed from the CSM during station keeping - Image by NASA/Johnson Space Center.
Six further images, AS15-96-13036 to 13041, are taken through window 5 and show the EVA boom visible in the frame as well as the ascent stage of the LM. These were taken at the same time as Jim was taking the SIM bay shots.
AS15-96-13036 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
AS15-96-13037 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
AS15-96-13038 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
AS15-96-13039 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
AS15-96-13040 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
AS15-96-13041 - The ascent stage LM Falcon photographed from the CSM's window 5 during station keeping. In the foreground is the EVA light - Image by NASA/Johnson Space Center.
It is worth making mention of the excellent efforts of Kipp Teague in helping to make the Hasselblad photography of Apollo available over the years. Kipp diligently acquired, processed and placed many images from the Apollo collection on his Project Apollo Archive. More recently, he placed all the unprocessed high-resolution scans on Flickr. The Apollo Flight Journal is indebted to Kipp for his work.
173:23:31 Scott: Okay, we've got the picture, Houston, and we'll proceed on with the docking.
173:23:34 Mitchell: Thank you, sir. [Pause.]
173:23:39 Worden: Okay, I'll pitch back around now, Davy.
173:23:40 Scott: Okay. [Long pause.]
173:24:01 Mitchell: And, Falcon; Houston. Do you have any comments on the SIM bay, anything look out of the ordinary?
173:24:09 Scott: No, it looks very clean. The doors are all covered, and all the booms are retracted; and it looks neat and tidy.
173:24:16 Mitchell: Thank you.
Comm break.
As Al returns the CSM to the docking attitude, Jim takes two more photographs, AS15-88-11974 and 11975.
AS15-88-11974 - CSM Endeavour photographed from the LM as it rotates to the docking attitude. In the background is Sinus Concordiae, a bay on the eastern side of Mare Tranquillitatis - Image by NASA/Johnson Space Center.
AS15-88-11975 - CSM Endeavour photographed from the LM in its proper attitude for docking - Image by NASA/Johnson Space Center.
173:25:26 Worden: Okay, where'd you go?
173:25:30 Scott: We should be right where we were. Have you completed your maneuver?
173:25:33 Worden: Roger.
173:25:34 Scott: Okay, we're in the same inertial attitude, I'll come back around to you. Just stay there.
Comm break.
Scott, from 1971 Technical debrief: [To Worden] "The next little funny occurred when you maneuvered back to your original attitude, which I assume you did."
Scott, from 1971 Technical debrief: "No, that is where the confusion existed in that attitude. When we were at the first stationkeeping attitude, I did not check that against the Flight Plan to make sure the gimbal angles were all the same. I did the pitch-around maneuver for SIM bay photography per Flight Plan and just put the numbers in from the Flight Plan. Then when I did the maneuver back, I went back into the Flight Plan attitude and that is where the difference in that position was."
Scott, from 1971 Technical debrief: "I could not figure that one out because we ended up pointing at you eyeball to eyeball and did a maneuver over and a maneuver back and we were not pointing at you any more."
Scott, from 1971 Technical debrief: "That is right."
Scott, from 1971 Technical debrief: "That is because you went back to a different attitude. You started from TPF attitude and you went back to the Flight Plan attitude."
Scott, from 1971 Technical debrief: "Right."
173:27:24 Worden: There you are. [Long pause.]
173:28:03 Scott: Okay, Endeavour. Would you handle station-keeping, we're going to pitch and yaw now.
173:28:09 Worden: Okay. [Pause.]
Falcon approached Endeavour with the crew's eyes forward and the forward hatch facing the CSM. Dave needs to pitch over by 90° to have the docking port and the drogue face the CSM. This aligns the X-axes of both spacecraft. He will also have to yaw so that the COAS in his overhead docking window looks directly at a target that Al mounts in window 4, the right-hand rendezvous window.
Diagram of the relative orientation of the LM and CSM during docking.
173:28:20 Scott: Pitching down. [Long pause.]
173:29:09 Scott: Okay. [Long pause.]
LM Flight Plan page 3-279.
CSM Flight Plan page 3-279.
173:30:09 Scott: Okay. Endeavour, it's all yours.
173:30:14 Worden: Okay, Houston. Ready to get [garble, should be "Pyro"] Arm, On.
173:30:21 Mitchell: Stand by.
173:30:26 Worden: Roger. I'll [garble] turn on the [Sequential Events Controller] Logic when you're ready.
173:30:29 Mitchell: Okay, bring it on.
173:30:34 Worden: Logic 1 - Logic 2. [Pause.]
173:30:48 Mitchell: Go for Pyro Arm.
173:30:56 Worden: Roger.
Long comm break.
173:35:52 Worden: I got barberpole.
173:35:54 Scott: [Garble. May be "There, I got you."].
173:35:56 Mitchell: Roger.
173:35:58 Scott: [Garble.] [Pause.]
173:36:11 Worden: Okay. You ready to come in?
173:36:13 Scott: All set. [Pause.]
173:36:28 Scott: Hard dock.
From the Apollo 15 Mission Report - "Beginning at terminal phase finalization, the spacecraft was maneuvered to the Crew Optical Alignment Sight [COAS] tracking attitude to monitor the Lunar Module and to verify line-of-sight rates. The Lunar Module assumed a station keeping position with the Command and Service Module and a maneuver was initiated to allow photographs to be taken of the Scientific Instrument Module bay. After this was accomplished, the spacecraft were maneuvered to the docking attitude. The docking was initiated and completed by the Command and Service Module. Again, the closing rates were approximately 0.1 ft/sec [0.03 m/s], and the docking was completed by thrusting along the longitudinal axis on contact until capture latch engagement was indicated."
Worden, from 1971 Technical debrief: "Docking, except for one thing, I guess, was completely nominal all the way down the line. I went right through the pre-docking checklist, and you got lined up. I got lined up on target and closed on you. I think the closing rate was a little bit low. I think it would have been better if I had had a little faster closing rate. I guess maybe I was about 0.1 feet/second [0.03 m/s] when I came in - maybe even a little less than that. There were no problems with control. I felt it was pretty smooth all the way in; but when we made first contact, the probe did not slide right into the drogue as I had sort of expected it would, so I thrusted a little bit more after contact before we finally got it in all the way."
Woods, from written communication: "Simulating the rendezvous, did they have the simulators such that, not only did you get the dials and displays doing what you wanted, but your visual view of the approaching spacecraft was pretty accurate?"
Scott, from written communication: "By the time we got to Apollo 15 it was very, very good. It really was. The out-of-the-window displays were excellent, because, you know, they had a model with a camera. It wasn't computer generated. The star field was great too. At the end of the day, the simulators were really good, especially for the technology available to have done it."
173:36:30 Mitchell: Roger. Roger. Copy hard dock. And, Falcon, if you'll give us 105 [degrees pitch] and 67 [degrees yaw, on the steerable S-band antenna], we should have your steerable [antenna].
173:36:41 Irwin: Roger. 105 and 67. [Pause.]
173:36:51 Scott: Good show, Endeavour. It's nice to be aboard again.
173:36:53 Worden: Welcome home.
173:36:55 Scott: Thank you. [Pause.]
173:37:06 Mitchell: And Falcon, Houston. Now that we have the steerable [antenna] back, when you get a moment, pull the ECS Auto Transfer, Open, and then the Glycol Pump 1, Open.
173:37:23 Scott: Roger. ECS Auto Transfer is Open - and I'll open the Glycol Pump 1 now.
173:37:29 Mitchell: Roger. We want to get a little data down here.
173:37:36 Scott: Okay, do you want us to select 2, or just let it run?
173:37:38 Mitchell: Negative. Just wait for 30 seconds.
173:37:43 Scott: Okay, we'll stand by for your call.
173:37:45 Mitchell: Thank you.
173:37:49 Irwin: And, Houston; Falcon. Do you have an update for us for the LM weight/CSM weight?
173:37:54 Mitchell: Roger. Stand by. LM weight, 5444 [pounds, 2,469 kg].
173:38:09 Irwin: Roger. LM weight 5444.
173:38:11 Mitchell: And I don't have the CSM weight at the moment. And you can close the Glycol Pump 1 first and then the Auto Transfer.
173:38:21 Scott: Roger. Closing Glycol Pump 1 now - Auto Transfer now.
173:38:28 Mitchell: Roger, and I thank you. [Long pause.]
Docking time was 173 hours, 36 minutes, 27 seconds.
173:39:05 Worden: Go ahead. All right, I got it. [Long pause.]
173:39:36 Mitchell: And, Endeavour; Houston. A couple of changes to the Command Module - LM/Command Module transfer list on stowage items, when you get a break.
173:39:54 Worden: Okay, Houston. Stand by one.
173:40:05 Mitchell: And, Falcon, we'll take Data and uplink you.
173:40:11 Scott: You've got it.
173:40:12 Worden: Okay, Houston; Endeavour. You might as well give me those updates now.
173:40:18 Mitchell: Okeydoke, Endeavour. On page 2 - 283...
173:40:33 Worden: Okay, go.
173:40:35 Mitchell: Okay, Al. About the middle of the LM to Command Module transfer list, the second Decom bag and the fourth Decom bag - scratch.
173:40:50 Worden: Understand. Scratch second and fourth Decom bags.
173:40:53 Mitchell: That's affirm. And the - at the bottom, write "Collection bag, 3, in [compartment] A9."
173:41:19 Worden: Understand. Add "Collection bag, 3, in A9."
173:41:21 Mitchell: Roger. And they're going to give you a - a section of core stem, three sections long, you'll have to put that on the left-hand tray along A1 and A2, and secure it with - with either your LM tiedown rope or your extra webbing in there.
The unexpectedly long core stem is the result of Dave and Jim being unable to break apart two of the five joins in the six-section deep core. A vice was mounted on the Lunar Rover for helping with this task but when Dave went to use it, he found that it had been mounted back to front. Mission Control have had to think of a place in the Command Module to store the 1½-metre rod and have decided on a space along two of the storage cabinets which lie across the base of the cabin, beneath the couches.
173:41:40 Worden: Roger. I understand. The core tubes go along A1, A2, tied down on the tray.
173:41:43 Mitchell: That's affirm. You got it. [Long pause.]
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