This book documents the development of spacecraft computers from the earliest missile guidance efforts to the current Space Station and satellite onboard systems. This book developed out of a presentation at the Johns Hopkins University’s Applied Physics Laboratory in 2009 for the Workshop on Flight Software.
Computer onboard spacecraft evolved from the computers used to guide missiles. The computers allowed for a degree of autonomy for the spacecraft, allowing operations to continue without direct ground communications.
The early missile guidance computers were located in underground bunkers, and transmitted their steering commands to the missile via a radio link. The missiles of the day had no inertial guidance (and, GPS was years in the future), and went ballistic after the engine burned out, a period of several minutes. After that, the laws of physics took over.
The early manned missions such as Project Mercury, were basically a man in a can atop a ballistic missile, and did not incorporate computing power. The later Gemini and Apollo missions relied more and more on onboard compute power, while driving the state of the art.
The early Earth-orbiting spacecraft again did not make use of computers, but did have the capability of storing commands onboard for execution at a later time. This storage was sometimes on magnetic tape.
One of the first computers onboard a spacecraft was the OBP (On-Board Processor) on the OAO Orbiting (Astronomical Observatory) spacecraft. Later, the Advanced Onboard Processor (AOP) was developed as a follow-on.
The NASA Standard Spacecraft Computer (NSSC-1) was developed at Goddard Space Flight Center as a general unit for a wide variety of spacecraft missions.
The “Care and Feeding” of the onboard computers took on an increasingly important role. Ground support environments, usually hosted on mainframes, developed as the onboard systems became more sophisticated.
Computers for Planetary missions and manned spacecraft developed along similar lines, but with differing requirements. All of these efforts drove the state-of-the-art in microelectronics manufacturing. The effects of radiation on electronics in space dictates the use of specially hardened units.
The onboard computing architecture of the International Space Station and the Constellation Project is discussed.
Two projects are examined: The Spacecraft Supercomputer, and the FlightLinux Project.
A list of references in included.
This book discusses primarily unmanned US spacecraft. Minimal coverage is given to the planetary of manned missions, or foreign efforts.
