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Build Your Own NASA Apollo Landing Computer (no kidding)

January 30, 2008
by joskirps

Apollo 11 computerWould you like to own the computer Neil Armstrong used to land on the moon in 1969?

Well, that's possible now, because a geek named John Pultorak created a working reproduction of the Apollo Guidance Computer (AGC), wrote a complete manual that will allow you to build your own Apollo flight computer clone and released it in the puclic domain. Well, I think that's just incredible!

John Pultorak, who is a 54 year old Lockheed Martin software engineer, built his own Apollo AGC in his basement. He completed it in 2005 - it took him 4 years to build it (working about 10 hours a week on the project) and he spent about $3, 000 for the required hardware. When finished, he created a fantastic 1,000 page documentation which includes detailed descriptions and all schematics of the computer.

Neil Armstrong computerUsing his manuals you are now able to build your own Apollo Guidance Computer, and you'll probably even need less time than John did, as all the research has already been done. Of course the manuals also include the required software code for the Apollo computer.

The Apollo AGC itself is a piece of computing history, it was developed by the MIT Instrumentation Laboratory and it was a quite amazing piece of hardware in the 1960s. It was the first computer to use integrated circuits (ICs), running at 1 Mhz it offered four 16-bit registers, 4K words of RAM and 32K words of ROM. The AGC mutlitasking operating system was called the EXEC, it was capable of executing up to 8 jobs at a time. The user interface unit was called the DSKY (display/keyboard, pronounced "disky"); an array of numerals and a calculator-style keyboard used by the astronauts to communicate with the computer.

Each Apollo mission featured two AGC computers - one in the Apollo Command Module ("CM", that's the spacecraft orbiting the moon) and one in the Apollo Lunar Module ("LM", that's the spacecraft that landed on the moon). The command module (CM) had two DSKYs; one located on the main instrument panel and another located in the equipment bay. The lunar module (LM) had a single DSKY for its AGC.

By the way, when Neil Armstrong and Buzz Aldrin landed on the moon they did have some trouble with the AGC which reported several unusual "program alarms" and guided them towards a large crater with rocks scattered around it. Armstrong took manual control of the lunar module (with Aldrin calling out data from the radar and computer) and guided it to a landing with about 30 seconds of fuel left.

So if you'd like to build your own Apollo computer, here are the manuals:

1. Overview [8. 1 MB]: Introduces the project.
2. CTL Module [9. 9 MB]: Design and construction of the control module.
3. PROC Module [6. 7 MB]: Design and construction of the processing (CPU) module.
4. MEM Module [6. 8 MB]: Design and construction of the memory module.
5. IO Module [7. 0 MB]: Design and construction of the diskplay/keyboard (DSKY) module.
6. Assembler [0. 5 MB]: A cross-assembler for AGC software development.
7. C++ Simulator [5. 2 MB]: A low-level simulator that runs assembled AGC code.
8. Flight Software [2. 8 MB]: My translation of portions of the COLOSSUS 249 flight software.
9. Test & Checkout [0. 9 MB]: A suite of test programs in AGC assembly language.

Apollo 11 Neil Armstrong

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permalink | 1 comments

George Watson said,
on August 7, 2008:

It was recently disclosed by Aldrin why they had a problem with the computer on lunar descent. Buzz left the guidance system on while the descent radar was also on. His reasoning was if the descent had to be aborted he didn't want to have to turn on the guidance while they were doing their abort rocket burn to escape from crashing (pretty smart).The Lunar module engineers didn't design the computer for that much simultaneous input from both systems. They thought only the descent radar would be needed during descent. The computer kept giving the too much data overload alarm.
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