The virtual Apollo Guidance Computer

I remember on the trip home on Apollo 11 it suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.

– Neil Armstrong [1]

On this day 40 years ago, the Apollo 11′s Eagle lunar module landed on the Moon. As Neil Armstrong and Buzz Aldrin became the first humans to walk on the lunar surface, Michael Collins orbited the Moon inside the Columbia command module, experiencing “an aloneness unknown to man before”, as aviator Charles Lindbergh put it [2].

[ photo courtesy of NASA ]

The Apollo program was an enormous technical achievement. I shall forever be amazed at how the engineers who worked on this program managed to accomplish so much with the technology they had available at the time. The rocket engine was a relatively recent technology back then, the transistor had been invented in 1947, the integrated circuit had been invented in 1958, and the microprocessor had not even been invented yet. In particular, the Apollo Guidance Computer (AGC) was a wonderful work of ingenuity: it was the world’s first modern real-time embedded system, and it led to the development of fly-by-wire systems.

To commemorate the 40th anniversary of the Apollo 11 mission, the command module code (Comanche054) and the lunar module code (Luminary099) have been transcribed from scanned images by the Virtual AGC and AGS project! [3] The code can be found here.

For example, take a look at the following modules: ascent guidance, Kalman filter, master ignition routine. Yes, programming the AGC seems to have been a spartan endeavor! ;-) If you happen to dislike vintage assembly programming languages, take a look at the yaAGC code, which is written in C.

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References

[1] The Greening of the Astronauts, Time Magazine, December 11, 1972.

[2] Robin McKie, How Michael Collins became the forgotten astronaut of Apollo 11, The Observer, July 18, 2009.

[3] Nathaniel Manista, Apollo 11 mission’s 40th Anniversary: One large step for open source code…, The official Google Code blog, July 20, 2009.

Curta Calculating Machines

Until fairly recently, I had never heard of Curta calculators. These little mechanical marvels were invented by Curt Herzstark (1902-1988) in the late 1930s, and from the late 1940s until the early 1970s they were popular portable calculators. Eventually, they were replaced by portable electronic calculators.

When 5MB weighed over a ton

Try to guess what this is…

Here’s the answer:

In September 1956 IBM launched the 305 RAMAC, the first computer with a hard disk drive (HDD). The HDD weighed over a ton and stored 5MB of data.

If 5MB of stored data weighted over a ton, then that is over 200 grams per KB! If data storage technology had not developed since 1956, my laptop’s hard disk drive would weigh over 16,000 tons!