The Apollo Guidance Computer

When Apollo 11 left Earth in 1969 the most advanced pieced of technology was the command capsule where the 3 astronauts would ride to the moon. At the heart of this module was the Apollo 11 guidance computer. While it wasn’t the most advanced computer of the day, it was the most advanced and reliable. Known as the Apollo Guidance Computer (AGC).

This rather simplistic machine by today’s standards (the AGC had about 1/6th the computing power of today’s TI-83 handheld graphing calculator) it was nonetheless, a very capable machine. Built by hand and thoroughly tested, the computer had almost no chance of it crashing.

The Display and Keyboard (DSKY) User interface of the AGC

Each Apollo Mission landing on the moon had 2 of these computers: one on the Lunar Module and one in the Command Module.

During Armstrong’s descent to the lunar surface a number of warnings came from the AGC. These 1201 alarms as they were referenced meant the computer was overloaded with no additional space left to make computations. The reason for this alarms was that the rendezvous radar that would be used to reconnect with the orbiting Command Module was intentionally left on during the descent to the surface. The reason for this was in case the Lunar Module ran into problems during the descent and had to abort the landing, it would then need to immediately start making adjustments so they could once again align with the Command Module. Because this piece of equipment was on and sending data to the navigation computer, it caused the AGC to overload.

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