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  Apollo 10 and the Abort Guidance System

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Author Topic:   Apollo 10 and the Abort Guidance System
Obviousman
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From: NSW, Australia
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posted 05-22-2009 08:29 PM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
In doing my daily summaries, I recounted the infamous Apollo 10 AGS incident. I'm a little confused about it now, though, and hope that someone might help enlighten me.

As I said in the summary, my understanding is that the AGS had two modes: AUTO and ATT(itude) HOLD. In AUTO, the system would start searching for the CSM and try to rendezvous with it, which explained the pitching and gyration of the LM.

The crew - and mission report - seem to say it was a switch problem. Just prior to the incident, Gene switched from AUTO to ATT HOLD. Tom, not realising this had been done, returned the AGS mode switch back to AUTO, thinking he was putting into ATT HOLD.

A collector bought the LM cue cards from Gene, though, and it clearly shows that the mode switch was meant to be in the AUTO position. Was this a checklist error? The mission report didn't mention it.

Can someone help me straighten this out in my head?

Proponent
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posted 05-24-2009 07:09 AM     Click Here to See the Profile for Proponent     Edit/Delete Message   Reply w/Quote
I'd love to hear the answer to that question, and there's another thing that puzzles me. Wouldn't this switch have been a toggle switch, which would have been, say, up for AUTO and down for ATT? Wouldn't Stafford and Cernan likely have been familiar with which mode was selected by which switch position? In that case, had Stafford attempted to set the switch to the correct position after Cernan had already done so, wouldn't he likely have NOT altered its position?

ilbasso
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posted 05-24-2009 05:37 PM     Click Here to See the Profile for ilbasso   Click Here to Email ilbasso     Edit/Delete Message   Reply w/Quote
I believe it's a three-way toggle - AUTO, ATT HOLD, and MANUAL (or perhaps it was OFF).

I also recall having heard at the time that there were two redundant switches for the AGS and that Stafford had set his one way and Cernan the other. That sounds iffy to me now.

Obviousman
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posted 05-25-2009 02:38 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
Tom Stafford discusses it during the flight.

At 148 hrs 28 min 52 sec GET he starts to talk about the switch, and how it can look different when you are in a different position. He said he was floating a little and it looked right, but he found that if you pulled yourself down a little you'd see it wasn't. He relates how a similar situation arises in the CM with another switch.

Obviousman
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posted 05-25-2009 03:02 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
You can see the switch here:

It is a three-position switch with full up as AUTO, centre as ATT HOLD, and fully down as OFF.

Proponent
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posted 05-25-2009 06:25 AM     Click Here to See the Profile for Proponent     Edit/Delete Message   Reply w/Quote
Thanks, everybody--that explains it thoroughly.

I remember reading in a book written circa 1960 about the Atlas ICBM that pairs of two-position toggle switches were used in Atlas launch facilities in place of three-position toggles precisely to eliminate errors like this. I had assumed that would be a general aerospace practice, but I suppose that in a flying vehicle, especially in the LM, weight concerns drive one toward three-position switches.

Obviousman
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posted 05-25-2009 06:58 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
Don't forget that MY question is still open.

Was it a crew error, or was it a checklist error?

ilbasso
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posted 05-25-2009 09:49 AM     Click Here to See the Profile for ilbasso   Click Here to Email ilbasso     Edit/Delete Message   Reply w/Quote
My recollection about the two switches may have been that both the PGNS and AGS switches were set to AUTO and that caused the conflicting commands to the LM computer.

paulfjeld
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From: salem, ma, usa
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posted 05-27-2009 10:04 AM     Click Here to See the Profile for paulfjeld     Edit/Delete Message   Reply w/Quote
That cue card is VERY curious. Based on the Mission Report and the onboard voice, it was clear that the staging was supposed to be done in AGS, ATT HOLD. What is a little bizarre is that the AGS pointing was set (through the DEDA) to Z-axis at the CSM instead of a more useful direction for the upcoming burn.

What makes sense is that Stafford was uncomfortable with the attitude rate indicator, which showed a yaw drift, which turned out to be caused by stiction in that gyro. In the hurly-burly of staging, he decided that AUTO was the easier option - not realizing the mischief that was set up to be unleashed by auto pointing and his decision to select MAX deadband instead of MIN, as per the checklist. In MAX at staging there is NO deadband in AGS, hence the wild swinging back and forth.

What doesn't make sense is that a top test pilot can't figure out the position of a critical switch and just "sets" it in whatever way it can move. If it WAS supposed to be in AUTO and Cernan had already put it there, would Stafford have set it back to ATT HOLD? The switches had little glowing strips on the switch tips and SIDES. It is really hard to be confused about position if you are near the design eye point (ie controlling the LM).

So what is worse? Not following procedures or not knowing how to throw a switch?

As for the cue card, it makes no sense to have up something that is obviously wrong. So I have my doubts that it flew.

SpaceAholic
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From: Sierra Vista, Arizona
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posted 05-27-2009 11:04 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Obviousman:
You can see the switch here:
What LM config does your drawing reflect?

Earlier configs of Panel 3 used a three position rotary knob for this function. As can be seen from an example of Spider's backup panel 3 within my collection, the MODE CONTROL knob was used at least through Apollo 9. By Apollo 11 panel 3 was modified to the toggle. Haven't seen any interior shots of Snoopy's panel 3 to resolve which of the configurations was applicable to Apollo 10.

paulfjeld
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From: salem, ma, usa
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posted 05-27-2009 11:43 AM     Click Here to See the Profile for paulfjeld     Edit/Delete Message   Reply w/Quote
Here is a still from some onboard film of Stafford punching the DSKY. I've indicated the switches.

SpaceAholic
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posted 05-27-2009 12:00 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Awesome Paul... resolves a knowledge shortfall - at least for me. Takk Skal Du Ha! (I note you have a nice Norwegian name).

paulfjeld
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From: salem, ma, usa
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posted 05-27-2009 12:55 PM     Click Here to See the Profile for paulfjeld     Edit/Delete Message   Reply w/Quote
Vær så god! (I was born there.)

Larry McGlynn
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posted 05-27-2009 08:18 PM     Click Here to See the Profile for Larry McGlynn   Click Here to Email Larry McGlynn     Edit/Delete Message   Reply w/Quote
Paul, while I don't have the exact technical information concerning what happened during the Apollo 10 LM gyrations, I can tell you that Gene Cernan used the cue card to describe the incident in detail to me and his assistant, Claire Johnson, in 2006. At the time, Gene commented on how important the cue cards were to him and Tom Stafford during the flight.

Gene also provided a signed certificate of authenticity stating that the artifact flew on the Apollo 10 mission.

The cue card was part of a five piece set of the cue cards flown during the mission as well as the LM timeline flight data file also flown during Apollo X flight.

I have known Gene for a few years now and he has been pretty straight with me about the artifacts in his collection.

I wish I had seen your response last week, I would have asked him about it at the Apollo X reunion.

You are welcome to come down to my home and look at the piece in person. We live within a few miles of each other.

paulfjeld
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From: salem, ma, usa
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posted 05-27-2009 09:49 PM     Click Here to See the Profile for paulfjeld     Edit/Delete Message   Reply w/Quote
Larry, well, if Gene states unequivocally that it was a flown item, I >will not< call him a liar. I met him and got to chat with him off and on in the MOCR during the Apollo Soyuz mission and he was a decent guy then and seems to be a decent guy now.

The really puzzling thing is that it makes no sense, that cue card, in light of the transcripts and the technical reports. You want the vehicle to be in ATT HOLD when you stage in orbit so you keep a stable attitude. AUTO is a guided mode (with steering commands continuously calculated). Maybe it just makes no sense to me in my present understanding of the LM systems, but I really think there is a story here.

In '94 I read the Mission Report for Apollo 10 and saw the graphs and read between the lines where the engineers were basically saying that the crew's explanations didn't hold water and there was nothing to do about it so the "anomaly" was closed. I called Owen Maynard, one of the chief Apollo engineers, about it and he basically agreed with the report but took responsibility for it since the training was really to blame and Joe Loftus reported to him. He then phoned me back to say that I shouldn't make a big deal about it since Stafford was an important player in the space business! (Mind you, I'm sure Stafford is not remotely that small a guy.)

The Grumman guidance and nav engineer I've talked with was livid with the crew after the mission and went to Houston to clear things up but came out believing that the program white-washed the whole thing. There is still a lot of heat there, surprisingly.

At the very least, something doesn't fit and seeing the complete Apollo 10 timeline and checklists would be very useful. For example, if you are going to do an APS burn soon after staging, why would you have Z-axis pointing at the CSM in that DEDA address? Does the checklist show the AGS address sequence in it? We might be able to suss something out that way.

I think I really >do< want to barge into your home and see your collection, but perhaps you'll be at the MIT Apollo anniversary do sometime and we could link up there and talk about it? Thanks regardless!

On edit: replaced excuses with explanations; now that I remember things, there was only one Grumman engineer who was livid about the thing.

Obviousman
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posted 05-28-2009 03:09 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
I believe Larry also owns the LM checklist manuals from Apollo 10, and have asked him to check if that also says the AGS Mode Switch was to be in the AUTO position.

I did a search through the NTRS but can only find procedures for later LMs available online.

To me it is a real disconnect.

Were the cue cards in error, not having caught up with a change to the checklist?

I'm going to start looking through various resources at my disposal to understand the system better, to see if it could have been an error in the checklist.

It seems such a mystery and after 40 years! I can't wait to find out the answer.

Obviousman
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posted 05-28-2009 06:19 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
BTW, does anyone have a URL for the audio of the incident? The Apollo Archive version is "censored", with the expletive removed. Other portions of the same event have been removed.

BTW, looking back over the transcript, at 4 days 6 hours 41 minutes 15 seconds, Gene says ".... X-translation two jets, guidance control AG. And you are in attitude hold deadband MIN, so far staging - actually be better up there if you want. I think that would be better for staging, otherwise you're going to bang those thrusters all over the place...."

spaced out
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posted 05-28-2009 08:45 AM     Click Here to See the Profile for spaced out   Click Here to Email spaced out     Edit/Delete Message   Reply w/Quote
Regarding the cue card, isn't it possible that this particular card was used at a different point in the mission timeline, when the AGS was supposed to be switched to AUTO mode, perhaps during the rendezvous with the CSM?

That would explain why some of the settings are not those you would expect to see at that point in the mission.

Cernan picked up on the reference to the AGS setting when he was looking at the card but obviously after 40 years he's not necessarily going to analyze the steps and remember exactly which mission phase that particular cue card applied to.

Just a suggestion.

paulfjeld
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posted 05-28-2009 10:14 AM     Click Here to See the Profile for paulfjeld     Edit/Delete Message   Reply w/Quote
spaced out, you nailed it!

They are >DPS< and >APS< config cards, for use during a burn and you definitely want the PGNS or AGS running things. I didn't notice the reference to the propulsion systems. I bet the LM timelines have the switch positions for staging...

Obviousman
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posted 06-01-2009 06:49 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
The only way to confirm it is to see what the checklist said for the staging manoeuvre. I believe that is contained in the Apollo Operations Handbook for the LM. It's not available for download via NTRS; does anyone have a copy?

Larry McGlynn
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posted 06-01-2009 10:17 PM     Click Here to See the Profile for Larry McGlynn   Click Here to Email Larry McGlynn     Edit/Delete Message   Reply w/Quote
You might try this link. Look at pages 39, 40 and 41.

It should give you an explanation of the commands and switches.

Obviousman
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posted 06-03-2009 06:04 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
It's an excellent reference, but..

1. It's for LM10 and after. Apollo 10 used LM4.

2. It still doesn't have a checklist.

They must have had a LM checklist, and although I suspect it will show the switch was meant to be in the ATT HOLD position... I'd still like to confirm it!

Obviousman
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posted 05-25-2014 10:11 PM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
Did anyone ever find the checklist for the Apollo 10 LM?

dtemple
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posted 05-28-2014 03:53 PM     Click Here to See the Profile for dtemple   Click Here to Email dtemple     Edit/Delete Message   Reply w/Quote
Would anyone accept pilot error as an explanation for the explanation of the Apollo 10 LM AGS "anomalous event?"

moorouge
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posted 05-29-2014 01:27 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
The Mission Report for Apollo 10 goes through the possible causes in section 15.2.14. It concludes -
It is, therefore, concluded that the anomaly was caused by the inadvertent cycling of the abort guidance mode control switch, followed immediately by an incorrect output of the yaw rate gyro. In diagnosing the yaw rate gyro problem and in reacting to it, the abort guidance mode switch was transferred to the AUTO position, resulting in high vehicle rates during the staging sequence.
Does 'inadvertent' equate with 'pilot error'?

Fra Mauro
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posted 05-29-2014 12:12 PM     Click Here to See the Profile for Fra Mauro   Click Here to Email Fra Mauro     Edit/Delete Message   Reply w/Quote
Sounds like pilot error to me. If it was, it's interesting that either one of these two astronauts flew again, considering the magnitude of the error.

chet
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posted 05-30-2014 05:36 AM     Click Here to See the Profile for chet   Click Here to Email chet     Edit/Delete Message   Reply w/Quote
Perhaps NASA was more impressed by the magnitude of the recovery.

BA002
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posted 06-01-2014 05:38 AM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
Looking at the 16mm movie, there are a few frames in which you can clearly see the ladder sweeping past the window. Given that all this took place during staging, I suppose the most immediate threat would have been colliding into the descent stage?

BA002
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posted 06-01-2014 06:18 AM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
And back to the original question of whether is was checklist error or pilot error: in the Apollo 10 air-to-ground voice transcription at 04 07 10 42, Charlie Duke informs the crew that Houston has noticed that in the checklist at 14 minutes prior to insertion there is no mention of putting the switch into the ATT HOLD position and that that may have been the cause of the mix-up.

On the other hand, the crew seems to have been aware that it should have been in ATT HOLD so I suppose one could argue that this was not a case of either checklist error or pilot error but of both.

garymilgrom
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posted 06-01-2014 06:22 AM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by BA002:
Looking at the 16mm movie...
Where can I find the 16mm movie you refer to? Thanks.

BA002
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posted 06-01-2014 11:42 AM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
In my case, I refer to the Spacecraft Films DVD set for Apollo 10. This particular scene was captured by the DAC on Magazine F.

Not sure if you can find it on YouTube or something similar.

Captain Apollo
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posted 06-01-2014 05:06 PM     Click Here to See the Profile for Captain Apollo   Click Here to Email Captain Apollo     Edit/Delete Message   Reply w/Quote
I guess you all know this - See 1.41.

BA002
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posted 06-02-2014 01:23 PM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
No, I didn't, thanks!

That is the footage I mean but on the DVD there is a different soundtrack. Which is interesting in itself but somehow this is slightly more to the point and riveting!

Captain Apollo
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posted 06-02-2014 02:09 PM     Click Here to See the Profile for Captain Apollo   Click Here to Email Captain Apollo     Edit/Delete Message   Reply w/Quote
This is the revolution before?

All times are CT (US)

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