The computer system for Spacelab.

The primary task of the Spacelab computer system is the supervision of the basic subsystems by computer control for both normal operation to reduce operator workload and for checkout. The system has five computers, three of which are used for the control, navigation and guidance of the vehicle and two of which are used for system data management. The computer system is centered around two data bus systems, one for subsystems and one for experimenters. Each data bus system is a duplex, self clocking system with a 1 MBPS bit rate which is controlled by its own input/output unit. The computer is a general purpose 64 K, 16 bit computer with a cycle time of 920 ns, packaged in one long ATR with a weight of about 30 kg. The hardware instructions include fixed and floating point operations and addressing capability for bytes, words and double words. Interrupts and DMA are implemented together with a memory expansion up to 128 K words.