Lunar Module Source Code

wandrson · July 5, 2016, 4:49pm

A view from cutting edge of yesteryear…

wandrson · July 5, 2016, 5:04pm

You will particularly appreciate the part where he talks about problems with the Apollo 14 landing due to the ‘published engine specs’ being wrong… Guess people not following specifications isn’t new!

Raymond · July 5, 2016, 5:35pm

If you want… you can build your own.
http://www.galaxiki.org/web/main/_blog/all/build-your-own-nasa-apollo-landing-computer-no-kidding.shtml

Bill · July 5, 2016, 6:07pm

Some men were in a bar bragging about their job accomplishments. One held up his hand, “I have a Super Bowl ring for each finger.” Another exclaimed, “I run one of the largest companies in the world!”

This went on for quite awhile until they noticed a silver-haired guy sitting quietly, nursing his drink and listening to the banter. They taunted him: “Hey old man, what do you do? You must have something to talk about…”

To which the retired astronaut replied, “I walked on the Moon.”

Bill · July 5, 2016, 6:08pm

I have been wanting to build a working replica of the Apollo Guidance Computer. I am thinking an Arduino may be able to simulate the processor with another one managing the display and keypad.

wandrson · July 5, 2016, 6:08pm

I long for the day when so many humans can say things like that so that no one understands the joke.

DanielHooper · July 5, 2016, 9:03pm

The guy who built that is the perfect amount of crazy.

Related: there’s a whole sub-branch of moon landing denial centered around the difficult to understand pre-modern architecture that this computer used.

zmetzing · July 5, 2016, 9:21pm

Blasphemy! At the very least, put it into an FPGA.

Emulators suck.

wandrson · July 5, 2016, 9:28pm

From a 1971 Rolling Stone interview of the programmer in the post above:

[quote]
But can a scientist work efficiently if he has just stoked up? “Certainly,” says Eyles. “He can smoke all the pot he wants to.” Does it actually help? “Well, I wouldn’t be surprised. I’ve written computer programs while I was stoned which have turned out to be pretty good programs. Not that they were anything that anyone’s life would have depended upon before they had been tested by me and other perfectly straight — at the time at least — people. It’s just a matter of mental relaxation.”

Read more: http://www.rollingstone.com/politics/news/extra-weird-looking-freak-saves-apollo-14-19710318#ixzz4DZWeHj9L
Follow us: @rollingstone on Twitter | RollingStone on Facebook[/quote]

jonathan_brandenburg · July 5, 2016, 10:37pm

It is an interesting phenomenon… Two (or more teams) collaborate for weeks or months and agree on an interface between two systems. Then, the teams go their separate ways to build their part of the system, ignoring the interface specification (often for good reasons) without changing the design document or at least letting the other party know of the changes.

Frustrating!
jb

DanielHooper · July 5, 2016, 11:29pm

It’s possible they had just not characterized it well – especially since they couldn’t just take it into space to test it!

zmetzing · July 6, 2016, 9:39am

Reminds me of a project I’m currently working on… except for the “agree on an interface”.

wandrson · July 6, 2016, 12:44pm

LUMINARY was never completely bug free. Allan told me about a fascinating series of events that could have easily prevented the first moon landing and might have caused disaster. Allan was the principal designer of the LM’s descent guidance program which steered the LM by gimballing and throttling the descent engine. Whenever the computer commanded the engine to increase or decrease thrust, the engine (and LM) reacted after a short time lag. Allan’s descent program needed a routine to accurately estimate the new thrust level, which could be accomplished by reading the “delta-V” (change in velocity) measured by the LM’s accelerometers. He wrote a short routine that took into consideration, i.e., compensated for, the engine’s lag time, which TRW’s “interface control document”, full of useful information for the programmers, said was 0.3 seconds. It took 0.3 seconds for the LM’s descent engine to achieve whatever thrust level the computer might request. The final version of the thrust routine, which was put into the LM, was written by Allan’s friend Don Eyles. Eyles was sufficiently enthusiastic about the programming challenge that he found a way of writing it which required compensating for only 0.2 of the 0.3 seconds. The IBM 360 simulator showed Eyles’ program worked beautifully. His routine was aboard Apollos 11 and 12 which landed successfully. However, telemetry transmitted during the landings later showed something to be very wrong. The engines were surging up and down in thrust level, and were barley stable. A guy at Johnson Space Center called Allan and informed him that the LM’s engine was not a 0.3-second-lag engine afterall. It had been improved some time before Apollo 11’s launch such as to lower the lag time to only 0.075 seconds. Correction of this item in the interface control document had simply been overlooked. Once this discrepency was discovered, the IBM 360 simulator was reprogrammed to properly simulate the actual, faster engine. Running on the simulator, Don Eyle’s thrust program, with the 0.2-second compensation, exhibited the surging that had occured on the real flights. But here’s the most interesting fact: the simulator also showed that had Allan Klumpp chose to “correct” Don Eyles’ program by compensating for the full 0.3 seconds that was printed in the document, the LM would have been unstable and Apollo 11 would never have been able to land. By pure luck, Don Eyles was creative enough to write the thrust routine in a way that kept the LM just inside the stability enveloppe and allowed successful landings!

wandrson · July 6, 2016, 12:46pm

Aparently the code is available for preusal

https://code.google.com/archive/p/virtualagc/downloads