Abstract
The space shuttle ultra high frequency (UHF) communications system is planned to provide radio frequency (RF) coverage for astronauts working underside of the space shuttle Orbiter (SSO) for thermal tile inspection and repairing. This study is to assess the space shuttle UHF communication performance for astronauts in the shadow region without line-of-sight (LOS) to the space shuttle and space station UHF antennas. To insure the RF coverage performance at anticipated astronaut worksites, the link margin between the UHF antennas and extravehicular activity (EVA) astronauts with significant vehicle structure blockage was analyzed. A series of near-field measurements were performed using the NASA/JSC anechoic chamber antenna test facilities. Computational investigations were also performed using the electromagnetic modeling techniques. The computer simulation tool based on the geometrical theory of diffraction (GTD) was used to compute the signal strengths. The signal strength was obtained by computing the reflected and diffracted fields along the propagation paths between the transmitting and receiving antennas. Based on the results obtained in this study, RF coverage for UHF communication links was determined for the anticipated astronaut worksite in the shadow region underneath the space shuttle.
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