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How They Built the Software of Apollo 11
LinuxScribe tips a piece up at Linux.com with inside details on the design and construction of the Apollo 11 code. There are some analogies to open source development but they are slim. MIT drafted the code — to run on the Apollo Guidance Computer, a device with less grunt than an IBM XT — it had 2K of memory and a 1-MHz clock speed. It was an amazing machine for its time. NASA engineers tested, polished, simulated, and refined the code. "The software was programmed on IBM punch cards. They had 80-columns and were 'assembled' to instruction binary on mainframes... and it took hours. ... During the mission, most of the software code couldn't be changed because it was hard-coded into the hardware, like ROM today... But during pre-launch design simulations, problems that came up in the code could sometimes be finessed by... computer engineers using a small amount of erasable memory that was available for the programs. The software used a low-level assembly language and was controlled using pairs or segments of numbers entered into a square-shaped, numeric-only keyboard called a Display and Keyboard Unit... The two-digit codes stood for 'nouns' or 'verbs,' and were used to enter commands or data, such as spacecraft docking angles or time spans for operations." Reader Smark adds, "The Google Code Blog announced today that the Virtual AGC and AGS project has transcribed the Command Module and Lunar Excursion Module code used during the Apollo 11 moon landing. The code is viewable at the VirtualAGC Google Code Page."
This is an Apollo DSKY BTW. A Classic command would have been
[VERB]66[PRO]
Which loosely translated means give me manual control, I need to land this sucker. If you watch the descent movies you will hear "P66" being called out by the LMP a few minutes before landing. Interesting to note that the 6 is right beside PRO. I wonder if there is a bit of clever UI design in that.
http://michaelsmith.id.au
Shoehorning a piece of software into an "open source" angle really doesn't do any justice to open source or the software you're writing about.
Instead of writing about open source software, write about good software that happens to be open source. If there is really good software where we know something about the code, like this Apollo software, then write about that. Discuss the collaborative development the engineers did, talk about the open source clone over at Google Code, but calling this "like opensource but only for NASA" is a massive distraction.
Journey to the Moon: The History of the Apollo Guidance Computer
by Eldon C. Hall
ISBN: 156347185X
If anyone is ever in the Mountain View area the Computer History Museum has one of them on display.
Richard Feynman's book 'What Do You Care What Other People Think?' also mentions the software development scheme used for space shuttle hardware in the context of the Rogers Commission report on the Challenger accident.
ISBN: 0393320928
1: Download the excellent sim Orbiter:
http://orbit.medphys.ucl.ac.uk/
2: Download the Apollo addon NASSP:
http://nassp.sourceforge.net/wiki/Main_Page
3: Download the virtual AGC/AGC software:
http://www.ibiblio.org/apollo/
4: ?????
(Literally, spend hours trying to figure out how to fly, how to get into orbit, reading the detailed manuals, etc etc etc)
5: Profit!
I don't believe there was a screw up of computer guidance in Apollo 11. Armstrong landed way off-target because there were large boulders in the way that weren't accounted for properly in the survey photos. This is why they used up almost all of their descent fuel.
This Apollo computer has specs almost identical to ancient 1970s home technologies like the Atari VCS/2600 game console (1 megahertz, 2K ROM). Or an Atari 400/Commodore VIC-20 computers (1 megahertz, ~8K RAM). That gives you a rough idea of how "weak" the computer inside Apollo truly was.
"I disapprove of what you say, but I will defend to the death your right to say it." - historian Evelyn Beatrice Hall
Just to be pedantic, it was actually the Commander (Armstrong) who actually flew the LM to the surface, not the misnomered LMP, who mainly monitored things and called out warnings and readings. So if anyone said P66 (which the transcript doesn't indicate literally happened), it was more likely the Commander, who would've entered the program. The transcript has Armstrong saying "I'm going to..." when he goes into P66.
Those who anthropomorphize science and/or nature already believe in an intelligent designer.
They overshot the original intended landing point by about 4 miles because of a timing error--the descent burn started about four seconds late.
The rocks-and-boulders-and-crater thing you're thinking of was a different issue.
The meek may inherit the earth, but the strong shall take the stars.
The typical keyboard has more than most computers in the 60s. The average gamer keyboard boasts more processing and storage power than the average computer of the 70s.
Basically, they flew to the moon on two keyboards and a programmable mouse.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
The LM initially overshot because the crew were distracted by alarms caused by the computer being unable to process all its tasks simultaneously. These alarms, in turn, had been triggered because ground simulations hadn't taken account of hardware powering up in a random order which generated data from two radars instead of one, which overloaded the computer.
Armstrong's boulder avoidance flying was undertaken after the crew realised they'd overshot the target site by 4 seconds.
(Unfortunately I find this subject insanely fascinating)
"That gives you a rough idea of how "weak" the computer inside Apollo truly was."
Or how strong the programmers where.
Most of the code in most programs is for things like UI, security, data validation, help systems and so on.
Very little code is there to do the actual work.
The Apollo system was built to be used by a few highly trained people. It didn't need a help system.
I would rather think of how good the programmers where and frankly the hardware people where than compare it to what we have 40 years latter.
If you want to think about just how far they had come how fast.
This was built only 42 years before men landed on the moon. http://en.wikipedia.org/wiki/Spirit_of_St._Louis
I would say holy freaking jump batman for the moon landing!
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.