Testing the Apollo Spacecraft
Ken Shirriff (via Alexis Gallagher):
To test all the components of Apollo, NASA created (and patented) a complex system called Digital Test Command System. The testing control room (pictured below) sent digital commands to the spacecraft, to control and monitor all parts of the spacecraft.
At the spacecraft, racks of test equipment decoded the digital commands and operated components. The Apollo Guidance Computer (AGC, below) needed to be operated remotely, which brings us back to the Computer Buffer Unit. It converted test commands into serial data for the AGC.
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Apollo test hardware had corrosion problems in the Florida humidity. To solve this, they zip-tied a desiccant packet inside. If the humidity sensor turned pink, you needed to replace the packet. The box was pressurized with nitrogen through a valve to keep moisture out.
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