Software-defined radio technology will benefit missions (1) that are expected to have a long operational life where enhancements and communication with assets not defined at launch are possible, (2) that communicate with different assets during different stages of operation, and (3) that will require enhanced capabilities such as autonomous operation and integrated navigation. The Space Telecommunications Radio System (STRS) project at the NASA Glenn Research Center analyzed the Crew Return Vehicle mission scenario, which exhibits many of these criteria. The Crew Return Vehicle was intended to function as a “lifeboat” for the International Space Station, providing an emergency, highly automated, escape mechanism. The Crew Return Vehicle scenario includes communications with many assets during its mission including the International Space Station, Tracking and Data Relay Satellite (TDRS), the Global Positioning System (GPS), and possibly the space shuttles for space operation and air traffic control for landing. Although the Crew Return Vehicle mission is no longer being considered, its communication architecture is similar to that of the planned Crew Exploration Vehicle mission, and the analysis and conclusions apply to the Crew Exploration Vehicle mission.
Two major tradeoffs were analyzed for this scenario: (1) the impact of allocating the transceiver functions in space-reconfigurable devices and (2) the estimated spacecraft resources needed to implement an open architecture. The potential of software-defined radio to reduce the number of radios and increase capability was also evaluated.
Waveform implementation in processor software is limited by the ability of general-purpose processors and shared-bus architectures to provide significant throughput for high-rate needs. High-speed signal processing can be implemented in field-programmable gate arrays (FPGAs) or in application-specific integrated circuits (ASICs). Reconfigurable FPGAs are extremely flexible but are less power efficient than ASICs or nonreconfigurable FPGAs. The analysis targeted FPGA implementations that would reduce power consumption. An analysis tool developed by the program was used to evaluate the communications requirements by waveform components and mission phase, and a vendor-provided tool was used to estimate power dissipation for the expected clock rates of the design.
The analysis compared the cost of implementing the scenario with three different software radio architectures: the Department of Defense’s Software Communication Architecture (SCA), an optimized version of the SCA, and a proposed STRS architecture. Each was compared with an optimal nonreconfigurable radio solution. The modeling analysis showed that the software-defined radio architectures increased power from 10 to 40 percent and increased mass from approximately 10 to 30 percent, with the STRS architecture having the least impact and full SCA consuming the most resources. Reconfigurable technology allows a number of waveforms to operate at different times over different mission phases using the same hardware (a likely scenario for Crew Exploration Vehicle operation); thus, radio reduction is possible. Reducing the number of radios reduces mass and power resources, helping to offset the increased resources needed to adhere to a common open architecture, such as STRS or SCA. Further work will continue to quantify the benefit of radio reductions, operational improvements, and other considerations of using software radio technology for space exploration.
Reinhart, Richard C.; Kacpura, Thomas J.; and Johnson, Sandra K.: Software-Defined Radio Architecture Framework Developed for Space-Based Radios. Research & Technology 2005, NASA/TM--2006-214016, 2006, p.18. http://www.grc.nasa.gov/WWW/RT/2005/RC/RCD-reinhart1.html
Kacpura, Thomas J.; Reinhart, Richard C.; and Johnson, Sandra K.: Reconfigurable, Software-Defined Waveform Developed on the Basis of the Software Communications Architecture. Research & Technology 2005, NASA/TM--2006-214016, 2006, pp. 20-21. http://www.grc.nasa.gov/WWW/RT/2005/RC/RCD-reinhart3.html
Glenn contacts: Richard C. Reinhart, 216-433-6588, Richard.C.Reinhart@nasa.gov; and Sandra K. Johnson, 216-433-8016, Sandra.K.Johnson@nasa.govLast updated: October 12, 2006
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