The Space Shuttle flight vehicle is composed of a reusable Orbiter vehicle, an external tank containing ascent propellants used by the Orbiter main engines, and two reusable solid rocket boosters. The Shuttle system is being designed to provide frequent, economical access to space and return for scientific and applications satellites beginning in the early 1980 timeperiod. Payloads up to 65,000 pounds, 15 feet in diameter, and 60 feet in length can be accommodated by the Orbiter. Current technology is being applied to achieve the lowest cost for placing payloads into earth orbit. The Orbiter avionics system is a key element in the development of the Shuttle system.The Orbiter avionics system provides the command, control, and monitoring for the mated Shuttle vehicle. The avionics include functions for guidance and navigation, flight control, communications and tracking, rendezvous, instrumentation, displays and controls, data processing, payload verification, systems management, and electrical power distribution and control.The basic Orbiter avionics system employs five computers in a general-purpose computer complex which interfaces with the various Orbiter subsystems through 24 one-megabit data buses and remote multiplex/demultiplex units located at the subsystems. All primary guidance, navigation and control functions are performed by the computers, with manual override permitted. Special features of the avionics implementation include redundancy management, software partitioning, switch scan, and ground uplink command of Orbiter subsystems via computer update. In addition to each computer main memory size of 65,000, 32-bit words redundant mass memories provide for storage of 8.3-million words of Orbiter and pay-load software which may be updated in orbit from the ground.