NEW CONCEPTS AND TRENDS IN SPACECRAFT TELEMETRY, COMMAND AND CONTROL SYSTEMS

Abstract

This paper presents a new family of telemetry and command front-end products, as applied to spacecraft ground segment systems. The general philosophy behind both check-out systems and command and control stations has recently evolved from large host computers to a more distributed architecture, where more processing for either recovering telemetry data or encoding commands is done at the front-end level. The overall reliability and safety of such systems have also called for communications oriented subsystems, complying with international standards (ETHERNET, IEEE 488, CCITT X25...). For the same reasons, satellite manufacturers and operators are now requesting more integrated front-end subsystems, which include in one unit subcarrier modulation (PSK or FSK) and baseband functions (Telemetry synchronisation or command encoding), as well as the corresponding built-in test capabilities. The 3000 series family of products complies with all the criteria enumerated above. Furthermore, it offers a line of matching telemetry and command units, available in both overall check-out (O.C.O.E.) and Telemetry, Tracking and Command (T.T.&C.) versions, thus facilitating the complete integration of a spacecraft system from ground test to in-orbit operation. The choice of industry standards such as the VME bus, the hostbased development of firmware in “C”, also ensure product modularity, allowing easy expansion or adjustments to the specific requirements of particular missions or programs. The 3000 series complies with the European Space Agency (E.S.A.) PSS-45 and PSS-46 standards, which are compatible with NASA/GSFC Aerospace Data Systems Standards and the NASCOM message format. These concepts are illustrated in the application of the 3000 series products in the EUTELSAT II program. Architectures for both the ground check-out systems and the control stations are presented; technical choices for system set-up and control and communications in-between subsystems are discussed. Future trends and new standards in spacecraft telemetry, command and control systems are presented, and particularly the implementation in the 3000 series products of the recommendations from the Consultative Commitee on Space Data Systems (C.C.S.D.S) on “Packet” Telemetry and Telecommand, as well as channel coding (Viterbi and ReedSolomon algo- rythms) using proprietary developments of VLSI circuits.