Macintosh II Based Space Telemetry and Command (MacTAC) System

Abstract

NASA’s reaction to requirements for the Space Station Freedom era’s telemetry data systems has been the continuing effort to combine a modular design approach with stateof-the-art VLSI technology for developing telemetry data processing systems. As part of this effort, NASA’s Data Systems Technology Division, in cooperation with Clemson University, is developing a Macintosh II based Telemetry and Command (MacTAC) system. This system performs telemetry data processing functions including frame synchronization, Reed-Solomon decoding, and packet reassembly at moderate data rates of 5 Mbps (20 Mbps burst). The MacTAC is a low-cost, transportable, easy to use, compact system designed to meet requirements specified by the Consultative Committee for Space Data Systems (CCSDS) while remaining flexible enough to support a wide variety of other user specific telemetry processing requirements (e.g., TDM data). In addition, the MacTAC can accept or generate forward data (such as spacecraft commands), calculate and append a Polynomial Check Code (PCC), and output this data to NASCOM to provide full Telemetry and Command (TAC) capability. Semi-custom VLSI gate arrays perform the return link functions of NASCOM deblocking, correlation, and frame synchronization. Reed-Solomon decoding (for error detection) and packet reassembly are also performed by modern microprocessor and semi-custom VLSI components. The local user interface is a standard Macintosh application with the wellknown look and feel of the Macintosh environment. A remote interface is possible via Ethernet which allows the system to be completely controlled from any location capable of generating the required remote operating commands. Return link data may be viewed in real time on the local or remote user interface screen in a variety of formats along with system status information. In addition, data may also be archived on SCSI disks for later retrieval and analysis as needed. This paper describes the general architecture and functionality of this MacTAC system including the particular custom telemetry cards, the various input/output interfaces, and the icon driven user interface.