Michael E. Epperly

A reconfigurable, radiation tolerant S-Band radio for space use

Southwest Research Institute (SwRI) is developing a reconfigurable, radiation tolerant, communication system that addresses the needs for low-cost, quick turn spacecraft, as well as the reliability and connectivity required in harsh radiation environments of higher orbit systems. The core of such a Flexible Communication Platform (FCP) centers on a Software Defined Radio (SDR) architecture providing S-Band (2 GHz) communications. The Digital Processing Unit (DPU) fits in a 1U form factor and forms half of a two-slice approach (RF front-end is on a separate slice). The architecture of the DPU is based on the Virtex-4, an SRAM-based FPGA from Xilinx. SRAM-based FPGAs, however, have significant limitations in spacecraft systems due to radiation susceptibility of the FPGA programming cells. SwRI chose to implement a combination of triplicated logic (TMR) and Configuration Memory Scrubbing, specifically in an external RAD-Hard device, to mitigate radiation effects on the system. The flexible design of the DPU allows rapid integration into multiple target mission architectures. When coupled with the RF front-end, the FCP is capable of communicating from LEO and MEO orbits using a variety of wideband signals and protocols.

Very high power planar power distribution for spacecraft bus control

Typical spacecraft power distribution system include some type of spacecraft power bus controller that serves as the summing point for the solar array, the battery, umbilical power and general spacecraft loads. 12A bus controller for a 3.2KW spacecraft routes currents in excess of 135A leading most manufacturers to use manual, expensive, point to point wiring to accomplish this task. By its very nature, such a connector pin and labor intensive operation has questionable reliability issues. A planar solution would be simple and ideal but is actually quite difficult since existing standards for a printed circuit boards current carrying capability stop at 35A. SwRI has invested Internal Research funds to explore the limits of heavy copper PC boards for very high current power distribution.

Spacecraft and instrument Level-0 command and data handling subsystem

A Level-0 processor is a low-level command processor intended to control the spacecraft whenever the main processor is off-line. Such an event can happen during early orbit activities, during load shedding operations or during an anomaly (like the upset of the main processor due to cosmic radiation). During these periods, the safe mode processor collects a subset of normal housekeeping telemetry, formats it, and downlinks it along with the command link control word information required by the CCSDS Telecommand recommendations. This subset of normal telemetry collection includes housekeeping telemetry from critical spacecraft subsystems such as attitude control, power regulation, solar array control, and payload maintenance. To determine the optimal number of interfaces and telemetry points, SwRI polled several spacecraft vendors and used this information to implement Level-0 CCSDS command processing/telemetry collection. This paper presents Southwest Research Institutes continuing development of flexible Level-0 command and telemetry collection hardware.