Fri
Jul 19 2019
04:31 pm

Margaret Hamilton (seen above with a printout of the Apollo 11 guidance software) was the first programmer hired for the Apollo project at MIT. In 1965, she was put in charge of the MIT Instrumentation Laboratory team who wrote the software for the Apollo Guidance Computer.

The computer was primitive by today's standards. It had the equivalent of 5000 or so transistors, 74KB of OS and navigation programming, 4K of RAM work space, operated at about 2 MHz, and had about 20 operation codes in its instruction set. It weighed in at about 87 pounds with the display/keyboard module. The command module had a similar computer. The only backup was a sextant and a slide rule.

The software was written on paper, transcribed to punched cards, compiled on a computer, and embedded onto magnetic core memory "ropes" by hand.

The AGC worked flawlessly, even when it failed. During the lunar landing, Neil Armstrong reported numerous "1202" errors that almost caused the landing to be aborted. NASA mission control contacted the MIT team who told NASA they could ignore it. It appears the rendezvous radar was in an incorrect setting and it was overloading the computer which was busy with the landing radar. The software was designed to cache the data, reboot itself, and start back up where it left off.

President Obama awarded Hamilton the Medal of Freedom, saying “her example speaks of the American spirit of discovery that exists in every little girl and little boy who know that somehow to look beyond the heavens is to look deep within ourselves." You can read more about her at the above link.

Trivia: The AGC source code was posted on Github by some guy who transcribed it from scanned images of the printouts. Check out some of the issue reports.

bizgrrl's picture

In a remote corner of the


In a remote corner of the Mojave Desert
, Google created a breathtaking portrait of unsung Apollo software pioneer Margaret Hamilton using moonlight reflected on 107,000 solar panel mirrors.

R. Neal's picture

Source code trivia

Some interesting functions include BURN_BABY_BURN, the master ignition routine, the PINBALL_GAME_BUTTONS_AND_LIGHTS routine that controlled the cockpit display and keyboard, names that reflected the culture of the times, and the presumably critical yet obscurely named P37 "return to Earth" routine.

Another of my favorites is the TIME_OF_FREE_FALL routine, which according to its comments can be used for either Earth or Moon coordinates by changing three variables.

Some of the comments are entertaining, too. It seems the programmers didn't completely trust the Astronauts:

P63SPOT3	CA	BIT6		# IS THE LR ANTENNA IN POSITION 1 YET
		EXTEND
		RAND	CHAN33
		EXTEND
		BZF	P63SPOT4	# BRANCH IF ANTENNA ALREADY IN POSITION 1

		CAF	CODE500		# ASTRONAUT:	PLEASE CRANK THE
		TC	BANKCALL	#		SILLY THING AROUND
		CADR	GOPERF1
		TCF	GOTOP00H	# TERMINATE
		TCF	P63SPOT3	# PROCEED	SEE IF HE'S LYING

P63SPOT4	TC	BANKCALL	# ENTER		INITIALIZE LANDING RADAR
		CADR	SETPOS1

		TC	POSTJUMP	# OFF TO SEE THE WIZARD ...
		CADR	BURNBABY
R. Neal's picture

Bonus: AGC simulator

Bonus: AGC simulator

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