Author Topic: Apollo 11 lunar landing audio - Flight and Guidance loops  (Read 8746 times)

Offline joema

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I've edited together excerpts of the Flight and Guidance comm loops for the Apollo 11 landing. This emphasizes the Guidance back room decision process in handling the computer problems. I have excluded several non-essential parts, so this audio .mp3 file is about 4 min 40 sec of the approx 12 min powered descent:

4 megabyte .mp3:

Many of the key decisions were made by computer expert Jack Garman, who was 24 years old. This is him receiving an award from NASA for his work on the Apollo 11 mission:

Background: Only two weeks before the Apollo 11 mission, during a simulation the flight controllers incorrectly called an abort due to a minor LM computer problem. Unlike today, the computer would just spit out a numeric error code, some of them quite obscure. Some were serious and others less so. These errors were called "Program Alarms". Each one would sound a claxon in the LM cockpit, so were quite distracting.

Due to that botched simulation, a meeting was called to discuss how to better handle such situations. Gene Kranz told Jack Garman to look up all the error codes. The hand-written notes he used during the Apollo 11 landing can be seen here:

Explanation of dialog in audio file. Time is offset into audio file, not offset into descent. Where possible I identified the speakers by voice, but some were a guess, so please correct as necessary.

Clarification on callsign AGC: The computer in the CM and LM were essentially identical from a hardware standpoint. By convention the CM computer was called AGC (Apollo Guidance Computer) and the LM computer LGC (Lunar Guidance Computer). However the callsign for the backroom computer team was always AGC, whether dealing with the CM or LM.


00:00: Gene Kranz (Flight Director): Polling flight controllers for continuing PDI (Powered Descent Initiation to lunar surface).

00:17: Neil Armstrong: "Houston are you looking at our delta H". (Is the difference between inertial nav altitude and radar altitude within limits to tell the on-board AGC computer to accept radar data)

00:18: "Program Alarm"

00:20: Charlie Duke (CapCom): "Looking good"

00:22: Neil Armstrong: "It's a 1202" (He sees the error code on the LM display)

00:21: Gene Kranz (Flight Director): "Is he accepting it, Guidance? (Does Guidance Officer Steve Bales see Armstrong hitting the accept button to switch from inertial to radar altimeter?)

00:28: "1202, 1202 alarm, what's that?" (Sound of papers turning)

00:33: Jack Garman (AGC Computer Specialist): "It's executive overflow, if it does not occur again, we're fine....continue"

00:41: Neil Armstrong: "Give us a reading on the 1202" (He wants to know how serious it is)

00:44: Steve Bales (Guidance Officer): "We're....we're go on that, Flight".

00:45: Gene Kranz (Flight Director): "We're go on that alarm?"

00:47 Steve Bales (Guidance Officer): "If it doesn't reoccur, we'll be go".

00:51: Jack Garman: "It's continuous that makes it no-go, if it reoccurs we're fine" (Correcting Guidance Officer's statement)

01:04: "We have another 1202 alarm"

01:10: Jack Garman: "Single alarm, tell them to leave it alone and we'll monitor it, OK?"

01:13: Steve Bales (Guidance Officer): "OK, we'll monitor his delta H, Flight". (Delta H is the difference between radar altitude and inertial altitude. Bales mistakenly thinks Garman wants to monitor this remotely for the astronauts)

01:14: Jack Garman: "We'll monitor his alarm, Steve". (The computer alarm is what they'll monitor, not delta H).

01:28: "Throttle down" (The LM descent engine is variable thrust and must decrease throttle as fuel burns off to maintain proper descent rate).

01:30: Neil Armstrong: "Better than the simulator" (LM throttle behavior is smoother/better than the simulator)

01:31: Jack Garman: "Get those guys out of there!" (By telemetry he sees the astronauts using a computer mode he fears is worsening the problem)

01:36: Charlie Duke (CapCom): "You want them to stay out of 68?" (Noun 68 is a computer mode which allows the astronauts to monitor their delta H, but Garmin fears the additional processing task is causing a CPU overload).

01:41: Jack Garman: "Yeah, AGC, the noun 68 may well be causing the problem" (Each two-digit computer command was called a noun).

01:50: Jack Garman: "Make sure he does *nothing* approaching P64, do you understand?" (Program P63 was run during braking phase, P64 runs during the approach phase. For fear of worsening the problem, Garman doesn't want the astronauts keying in any optional tasks as they near the P63-to-P64 switchover)

01:55: Jack Garman: "Off that DSKY as TGO (Time to Go) comes down" (Garman doesn't want the astronauts touching the DSKY computer keyboard any more for fear of making things worse).

02:03: Gene Kranz (Flight Director): "Everybody hang tight, 7 1/2 minutes" (7 1/2 minutes into powered descent)

02:04: Gene Kranz: "Descent 2, fuel crit" (The LM has two independent fuel monitoring systems, one for each fuel tank. They estimate system 2 is more accurate, so will monitor that).

02:08 Gene Kranz: "Is it converged?" (Has the inertial altitude and radar altitude converged to similar numbers, which indicates confidence)

02:10: Steve Bales (Guidance Officer): Yes.

02:31: Buzz Aldrin: "1201" (Another type of CPU overload, indicating computer is falling behind and must disregard less essential tasks).

02:33: Steve Bales (Guidance Officer): "What alarm, Jack?"

02:34: Jack Garman: "Same type, we're go"

02:39: Gene Kranz: "How's our margin looking, Bob?" (How is the fuel margin? Since the engine is constantly throttling up and down, one engineer was assigned to extrapolate remaining flight time based on current trends)

02:42: "Four and a half, looks good" (Four 1/2 min. flying time remaining)

02:47: Jack Garman: "We have another 1202 alarm"

02:49: "Roger, no sweat"

02:53: Gene Kranz (Flight Director): "How about you TELCOM...Guidance, you happy?" (Because of the computer errors, Kranz is polling the flight directors to ensure vehicle is still controllable and on the right trajectory).

02:59: Jack Garman: "We have another 1202 alarm"

03:02: "You don't have to keep calling it up, we can monitor it"

03:05: Gene Kranz: "OK, the only callouts from now on will be fuel" (They are so short on fuel, no other flight controllers should call out any non-fuel items)

03:10: "60 seconds: (60 seconds flying time remaining until abort)

03:15: Buzz Aldrin: "Light's on" (Low fuel warning light is on)

03:19: "He's done a lot of RCS" (They can tell Armstrong is vigorously maneuvering the LM, expending a lot of Reaction Control System fuel)

03:23: "30 seconds" (30 second flying time remaining until abort)

03:28: Buzz Aldrin: "Contact light" (66 inch-long probes extending beneath LM touch lunar surface, indicating to pilot that touchdown is imminent)

03:33: "Shutdown" (Sound of clapping. Flight controllers via telemetry can tell pilot has shut down engine and is on surface).

03:35: Jack Garman: "How's that for you?"

03:45: "Keep your eye on the computer" (If an immediate lunar liftoff is required the computer will be needed. They are worried the previous problems will interfere should this be needed)

03:53: "Keep your eye on it, don't relax yet" (Despite touchdown, still worried about computer in case an immediate liftoff is needed).

04:01: Gene Kranz: "OK all flight controllers, about 45 seconds to T1 stay/no stay" (Should a cabin pressure leak or other problem require an immediate liftoff, flight controllers will be polled 45 sec after touchdown to assess this)

04:11: "Take note of all your little alarms there" (Joking with Jack Garman about his hand-written notes each computer alarm)

04:35: Steve Bales (Guidance Officer): "Hey, Jack....thank God we had that meeting...good show" (Bales remembers the meeting they had just before launch to discuss this type of computer problem and prepare for it).
« Last Edit: 07/21/2014 05:12 pm by joema »