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Evolution of a Stand-Alone Telemetry Collection Processor for an Autonomous Command and Data-Handling System, 15-9061

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Principal Investigators
Michael E. Epperly
Martin B. Holder
Paul H. McGaugh
John M. Stone

 Inclusive Dates: 01/01/98 - 07/01/99

Background - SwRI seized an opportunity to advance its capabilities to provide the next generation of space data systems by developing a fully Consultative Committee for Space Data Systems (CCSDS) compliant safe-mode spacecraft computer. A safe-mode computer provides limited communication with the satellite if the main processor fails or is off-line.

Approach - This research project developed a telemetry collection module (TCM) to be used in conjunction with the SwRI command telemetry module (CTM) to implement a CCSDS-compliant, safe-mode system. A custom interface bus, located on a motherboard containing these modules, allows the TCM and CTM to communicate with each other. The CTM collects and parses incoming ground commands, and then passes these commands to the TCM for execution. The TCM collects various telemetry/command data and presents the data to the CTM for formatting and downlinking to the ground station. The TCM is based on SwRI’s extensive virtual machine environment (VME) interface experience. The VME interface provides an open architecture, allowing spacecraft computers to be configured for specific missions with minimum nonrecurring engineering (NRE). The first task for this effort was to select a micro-controller that contained desirable built-in features such as digital input/output (I/O), error detection and correction, pulse width modulation, counter/timers and a watchdog timer. Having these features internal to the microcontroller chip eliminates the additional circuitry, powers consumption of discrete components, and increases overall system reliability. In addition to the internal functions described, the microcontroller must endure the harsh space environment, including a wide temperature range and significant radiation exposure. The UTMC radiation-hardened 80C196 microcontroller was selected for the TCM. The TCM was designed to operate from -30°C to +50°C and withstand a space-radiation environment of 30 kilorads total dose with no latch up. The TCM memory architecture consists of 16 kilobytes of SRAM, 256 kilobytes of EEPROM (16 kilobytes/page), 32 kilobytes of shared SRAM (16 kilobytes/page) and 8 kilobytes of PROM, all on a single 6U format VME board. To complement the memory resources, the I/O located on the TCM includes one redundant 1553 channel, one RS-232 (5V) serial port, 32 digital I/O, 45 analog inputs, 3 analog outputs, and 50 thermistor inputs.

Accomplishments - The designed and fabricated board has completed functional verification and testing. Interface testing with the CTM was emulated using commercial digital I/O cards. The TCM will be delivered to a client for technical evaluation in its command and data-handling test-bed. The TCM internal research effort has also resulted in SwRI’s winning the contract to build the mechanism control electronics chassis for another client, which will use a modification of the TCM that accommodates a master VME interface without the analog circuitry.

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SwRI-developed TCM has completed functional verification and testing.

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