4-5. Structural Configuration Options For the Space Station Freedom Solar Dynamic Radiator ADRIAN TYLIM Summary The growth version of the Space Station Freedom electrical power system contains a second phase that adds at least 50 kWe of user electrical power. This is provided by two 25 kWe solar dynamic power modules (SDPMs), one on the port and one on the starboard side. Each SDPM contains a closed Brayton Cycle (CBC) thermodynamic engine that operates between the temperatures of the fluid at the receiver outlet and the compressor inlet. The solar dynamic radiator (SDR) enables the CBC to reject the waste heat to the surrounding space environment. Previous studies in earlier program phases have opted to locate the SDR longitudinally (i.e. perpendicular to the Space Station Freedom transverse boom such that the SDR deploys in front of the SDPM concentrator). The low natural frequency of the baseline SDR for this configuration potentially compromises the ability of the fine pointing and tracking (FP&T) control system to meet a 0.1 degree pointing accuracy requirement. In order to achieve a higher first modal frequency in the design of the SDR, three alternative configurations that meet this requirement have been studied. These options included a modified baseline vertical configuration and two alternative configurations that locate the SDR in the transverse direction (i.e. parallel to the Space Station Freedom transverse boom such that the SDR deploys symmetrically towards port and starboard sides). The merits of these three alternative options based on space shuttle cargo capabilities and location, with respect to the SDPM supporting structure, thermal performance, drag, concentrator shading, mass and other issues of concern, are discussed. Results indicating the advantages and disadvantages of each option are presented. Introduction The Rocketdyne Division of Rockwell International Corporation, under contract to the National Aeronautics and Space Administration Lewis Research Center, is responsible for the electrical power system (EPS) that will supply electricity to the US space station to be in orbit by the mid 1990s. The EPS consists of an initial baseline of photovoltaic (PV) arrays providing 75 kWe of power to the user. In order to meet the growing power demands of the space station, the program includes an option to provide additional power capability in increments of 50 kWe. Each increment consists of a pair of two 25 kWe solar dynamic power modules (SDPMs). Figure 1 depicts a schematic of a SDPM. The SDPM is a complete power system, most components of Adrian Tylim, Rockwell International/Rocketdyne Division, 6633 Canoga Avenue, Canoga Park, CA 91303, USA. Paper number IAF-ICOSP 89-4-5.
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