ON-BOARD PROCESSING FOR THE NOVA SPACECRAFT

Abstract

A major hardware change to the TRANSIT Navy Navigation Satellite System (NNSS) is underway. A new generation of satellites called NOVA are being built which have onboard a general purpose minicomputer, high precision clock, orbit adjustment system (OATS), and disturbance compensation system (DISCOS). This paper describes the software and processing for the on-board computer. The software is a system of interrupt driven, real-time programs which perform various data management and control functions and allows great flexibility in the operation of the satellite. In addition to loading special programs and data and dumping specified regions of memory, data management includes loading and then retransmitting navigation message data and collection of both telemetry (TM) data and DISCOS thruster firing data. Through its interface with the spacecraft TM and command systems, the on-board computer also serves as a powerful control device, especially in the orbit adjust phase immediately after launch. It has already been demonstrated with a previous version of these satellites that this highly flexible software system can be quickly reconfigured after launch to recover from failures to other satellite hardware systems. Also described in this paper are other satellite subsystems which interact with the flight computer and the system of ground support computers and software.