Computers in Spaceflight: The NASA Experience /By James E. Tomayko
With the start of NASA (National Aeronautics and Space Administration), the use of computers were extensive. They also flew computers in orbit, to the moon, and to Mars. Initially it was the "UNIVAC", which was a cumbersome mainframe. This has gradually improved to medium-sized computers in spaceflight operations, and the multiple on-board machines. NASA often found itself behind the state of the art in computer solutions due to deliberate over-emphasis of reliability and safety. This is mostly on unmanned spacecrafts because the absence of human pilots. Whilst even the manned space shuttles possesses the same feature, for ground systems fairly leading technology exists. Computers are used for guidance and navigation functions such as rendezvous, re-entry, and mid-course corrections, as well as for system management functions, data formatting, and attitude control. This has helped the current spacecrafts to be more versatile. NASA's impact on computing driven by ground support requirements was largely in the area of operating systems and other software and not as much in hardware, whereas many of the on-board computers had to be custom built.
The former requirements were satisfied with batch processing while the on-board technology requires being real-time. In order to ensure the reliability and not to have a "crash" or an abnormal end, on-board solutions also calls for redundancy at a higher cost and effort. This will have to be balanced with other considerations such as weight, size and power on a spacecraft. Currently NASA’s attention is on developing solutions to support number of missions together, task distribution and economical means of ensuring reliability. These solutions are also expected to underscore the dependence on communications that has characterized NASA's far-flung flight operations since the beginning.