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Source code for the Apollo 11 Guidance Computer

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Re: Source code for the Apollo 11 Guidance Computer

#51

Post by hcrisp »

Isn't it true that the AGC was initially designed to be the sole navigation computer, but when the implementation did not meet the requirements for accuracy (due to accelerometer and gyroscope drift), they switched to a ground-based radar system? This meant the AGC became the back-up in case the communications system failed. Does anyone know if the AGC was ever used to make a mission-critical decision in the absence of the ground-based radar system?

Edit: I think it was actually the PGNCS that was made back-up [1]. Sorry the comment about Kalman filter had me confused. Apparently PGNCS was still used for maintaining orientation, controlling rockets, and navigation during planned outages.

1: http://en.wikipedia.org/wiki/Apollo_PGNCS

Re: Source code for the Apollo 11 Guidance Computer

#52

Post by hcrisp »

RogerL wrote: post #49
mrweasel wrote: post #20

It's of cause fun to have this code to look at, but is it really useful? I don't mean it in a condescending way, but is this actually someone at, say SpaceX, looks at and goes: "Oh so that's how they did that"?

It's achingly beautiful to the pocket protector set (me!). This source code, for example, contains the very first Kalman filter ever used - Kalman was invited over to Moffett field to give talks about his paper, which led to his theory was used in LM code. But I think everyone is very aware of the state of the art at the time, and things have advanced a lot since then. It is impressive to see them cramming that into…

Wasn't it the PGNCS that had the Kalman filter? See my comment nearby which confused it with AGC.

Re: Source code for the Apollo 11 Guidance Computer

#53

Post by dalke »

NextPerception wrote: post #45
dalke wrote: post #37

Earlier quoted context omitted.

On the other hand, how much of that institutional knowledge is still useful? Certainly some of it is, but I think experience with the F1-B shows that new knowledge, like 3-D printing, means that parts of the old knowledge aren't needed.

I am a mechanical designer by profession and just want to point out that even I who use a 3D printer on a daily basis can't think of any other manufacturing method it has made completely obsolete. It is more like just another tool in my tool belt that adds another way to make something. As with any tool it has it's advantages and it's drawbacks and will only make sense to use it in certain scenarios.

Certainly. That's why I said "parts" and not "all".

What I meant is described in slightly more detail at http://arstechnica.com/science/2013/04/how-nasa-brought-the-... , in the section "3D printing goes to space"

> Using state of the art manufacturing processes where possible actually reduces cost—even if a newer manufacturing method is more expensive, the cost reductions gained from the design simplifications more than tip the scales. In particular, Dynetics and PWR are using techniques like selective laser melting and hot isostatic pressing (HIP) to "grow" entire complex engine parts out of metal powders. The Dynetics team is focusing as much as possible on reducing welds and joins, and therefore reducing assembly and manufacturing.

Re: Source code for the Apollo 11 Guidance Computer

#54

Post by dang »

DanBC wrote: post #7

Not quite sure why this links to the code, and not the top level which has a lot more useful information (such as the simulator needed to run the code). http://www.ibiblio.org/apollo/ There's some more information here: http://googlecode.blogspot.co.uk/2009/07/apollo-11-missions-...

Thanks. We changed to that from http://www.ibiblio.org/apollo/listings/Comanche055/.

Edit: persuaded to change it back. See https://news.ycombinator.com/item?id=8066666.

Re: Source code for the Apollo 11 Guidance Computer

#56

Post by kghose »

If you are into such things, do take a look at the orbiter project (http://orbit.medphys.ucl.ac.uk/) and the NASSP add-on (http://nassp.sourceforge.net/wiki/Main_Page). I spent many an after-school night flying to the moon by punching codes on a keyboard. It was amazing.

edit: Here's a video https://www.youtube.com/watch?v=7VDV6Gdxakc

Re: Source code for the Apollo 11 Guidance Computer

#57

Post by RogerL »

hcrisp wrote: post #52
RogerL wrote: post #49

Earlier quoted context omitted.

It's achingly beautiful to the pocket protector set (me!). This source code, for example, contains the very first Kalman filter ever used - Kalman was invited over to Moffett field to give talks about his paper, which led to his theory was used in LM code. But I think everyone is very aware of the state of the art at the time, and things have advanced a lot since then. It is impressive to see them cramming that into…

Wasn't it the PGNCS that had the Kalman filter? See my comment nearby which confused it with AGC.

It is my understanding that the AGC is the computer within the PGNCS. Terminology varies, as the last link below from NASA notes.

So far as I can tell, the AGC maintained the state vectors for the KF. Ground control would run batch mode least squares solutions, and pass it on to the LM, where the updates to the state vector would be applied by hand. I freely admit to not having worked through the code, but I believe the state vector update computations occur here: http://www.ibiblio.org/apollo/listings/Comanche055/MEASUREME...

sources: http://www.ieeecss.org/CSM/library/2010/june10/11-Historical...

http://en.wikipedia.org/wiki/Apollo_Guidance_Computer

http://en.wikipedia.org/wiki/Apollo_PGNCS http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2009001...

Re: Source code for the Apollo 11 Guidance Computer

#58

Post by b_emery »

nsxwolf wrote: post #34

Do the famous 1201 and 1202 error codes make an appearance here? My assembly skills aren't good enough to find them, I'm afraid.

Hadn't heard about this but found this link. Great story:

http://www.dailykos.com/story/2012/08/25/1124164/-Neil-Armst...

Re: Source code for the Apollo 11 Guidance Computer

#59

Post by davegauer »

For anyone interesting in learning more about this computer system, I highly recommend _Digital Apollo: Human and Machine in Spaceflight_ by David A. Mindell.

The hardware limitations! The incredibly low bug count! The memory hand-woven by ladies in a factory! I was blown away by the capabilities of the Apollo computer systems. The craft could have been practically unmanned.

Even more impressive, the computers could fly the craft while ALSO being interrupted by and adjusting to human intervention at nearly every step of the process. The pilots and the engineers practically battled over who would be in control of the craft. Fascinating stuff!

Re: Source code for the Apollo 11 Guidance Computer

#60

Post by daveslash »

cramerica wrote: post #26

There are some pretty great comments in here: ALARM_AND_ABORT.agc - http://www.ibiblio.org/apollo/listings/Comanche055/ALARM_AND... TC WHIMPER -1 # YES. DON'T DO POODOO. DO BAILOUT. From the Guidance Computer Data Cards - http://www.ibiblio.org/apollo/CMC_data_cards_15_Fabrizio_Ber... "POODOO abort, does software restart (ENEMA) and "GO TO POOH" (flashing Verb 37) unless "AVERAGE G" is running then only software rest…

I like the note at the top of http://www.ibiblio.org/apollo/listings/Luminary099/BURN_BABY...

At the get-together of the AGC developers celebrating the 40th anniversary of the first moonwalk, Don Eyles (one of the authors of this routine along with Peter Adler) has related to us a little interesting history behind the naming of the routine.

It traces back to 1965 and the Los Angeles riots, and was inspired by disc jockey extraordinaire and radio station owner Magnificent Montague. Magnificent Montague used the phrase "Burn, baby! BURN!" when spinning the hottest new records. Magnificent Montague was the charismatic voice of soul music in Chicago, New York, and Los Angeles from the mid-1950s to the mid-1960s.

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