The earliest human spaceflights were guided by navigational computers on the ground; there was no onboard computation. But starting with project Gemini, computers have been an essential part of every space mission. When the first piloted Gemini flew in 1965, most computers were the size of a room, and so it was a remarkable technological achievement to shrink a computer down to a size (2 cubic feet) that could fit into the small capsule. Onboard computing power enabled Gemini to carry out tasks such as rendezvous and docking even though the computer was underpowered by today's standards. It contained 4,000 words of memory, about a thousandth the size of a handheld personal digital assistant today. The Apollo computer that controlled the lunar landing had only 32,000 words of memory.

Early Spaceflight Computers

The computers used in spaceflight have always been a mixture of leading and lagging technology. The...