Apollo 12 at 35

neutron_p writes "Thirty-five years ago this week, the sedentary, fine-grained powder began to rise, billow and race off toward the horizon. Soon after - at 1:54:35 a.m. EST on Nov. 19, 1969 - the lunar module Intrepid landed, bringing two more humans to the surface of another world. Apollo 12 commander Pete Conrad and lunar module pilot Alan Bean would be on the Moon for more than 31 hours, with crewmate Dick Gordon orbiting above in the command module Yankee Clipper."

Comments

Re:amazing programing in 256k, and no serious bugs

[Steve1952]

256K Hah! The Apollo landing module had 2K of RAM and 36K of ROM. Now that's tight!

Re:amazing programing in 74k, and no serious bugs

[RealProgrammer]

From abc.net.au:

Do this with a computer that has barely 5,000 primitive integrated circuits, weighs 30 kg and costs over $150,000. In order to store your software, the computer doesn't have a disk drive, only 74 kilobytes of memory that has been literally hard-wired, and all of 4 Kb of something that is sort of like RAM.

NASA explains it a little better, noting that the 74KB is actually 37KW, using 16-bit words:

• Hardware

  The guidance computer is a general-purpose digital machine with a basic word length, in parallel operations, of 15 bits with an added bit for parity checks. The instruction code includes subroutines for double and triple operations. Memory cycle time is 11.7 microseconds with a single addition time of 23.4 microseconds. The 'core rope', used for the fixed memory, has a capacity of about 36,864 words with an erasable memory (of ferrite core planes) of 2,048 words. The processor is formed from integrated circuits (ICs). The total computer weight is 29.5 kg. The fixed memory contains programmes, routines, constants, star and landmark co-ordinates and other pertinent data. The erasable memory acts as an intermediate store for results of computations, auxiliary programme information, and variable data supplied by the G&N and other systems of the spacecraft.

read and drool: AGC, DSKY and more

[goon]

for those who where not around here's some links to the AGC, DSKY and more:
*Apollo Guidance Computer (AGC)

*slash article with source code listing

*Simulation of Apollo Guidance Computer

*DSKY

They had bugs...

[Goonie]

The Apollo 11 landing was nearly aborted due to computer problems, according to this account which goes into some detail.

I love the bit where the writer describes the recommendation by the software engineer to ignore the reported errors as "a gutsy call". There's these guys, in a tiny little spacecraft, about to land on the moon, with most of the world watching, and the prestige of the USA and indeed democracy and capitalism at stake. The computer's screaming error messages. If you call for an abort, the moon effort is a flop (at least temporarily). If you call proceed and the thing craters, you're going to be the guy whose screwup killed two American heroes. "Gutsy"...more like balls of titanium!

Re:They had bugs...

[earendil]

The problem that is usually quoted occurred somewhat earlier than that, during the beginning of the descent. Specifically, it was what is known as a "1202 alarm", which was a warning from the real-time part of the computer that it had more tasks to do than it had time for. The reason for this was that the astronauts had forgotten to turn off the rendezvous radar that was going to be used when docking with Columbia, so that the radar interrupts were overloading the task queue. Fortunately, the software was robust enough that the more high-prioritised tasks were still running, so they could land despite this problem.

The landing procedure wasn't quite that critical; sure, the estimate was only 20 seconds of fuel remaining (later revised to 45), but he had after all done 100-odd test landings before. However, he was focused enough on the landing that he didn't turn notice the contact probes touching the ground, and only turned off the landing engine when they were down. The idea was to turn it off as soon as the contact light lit to avoid engine backblast damaging the lander. No harm done though.

The missions were actually of three types. Apollo 11 was a "G" type mission, with a more limited lander, and may be considered the last of the test flights. Apollo 12-14 were "H" missions, which was basically the same as "G", but included the full instrument package which had been removed due to concerns about fuel margines, while 15-17 were "J" type missions which had an improved lander with twice the payload capacity, an LLRV (rover), better moon suits, a bay of science equipment for the command module and so forth.

An intriguing incident with Apollo 12 was that they launched despite fairly threatening clouds in the vicinity, and the rocket was hit twice by lightning during the ascent. Needless to say, this spooked the astronauts a fair bit.

http://www.hq.nasa.gov/alsj/frame.html