Space Shuttle UHF communications performance evaluation

Abstract

An extension boom is to be installed on the starboard side of the Space Shuttle Orbiter (SSO) payload bay for thermal tile inspection and repairing. As a result, the Space Shuttle payload bay Ultra High Frequency (UHF) antenna will be under the boom. This study is to evaluate the Space Shuttle UHF communication performance for antenna at a suitable new location. To insure the RF coverage performance at proposed new locations, the link margin between the UHF payload bay antenna and Extravehicular Activity (EVA) Astronauts at a range distance of 160 meters from the payload bay antenna was analyzed. The communication performance between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous was also investigated. The multipath effects from payload bay structures surrounding the payload bay antenna were analyzed. The computer simulation tool based on the Geometrical Theory of Diffraction method (GTD) was used to compute the signal strengths. The total field strength was obtained by summing the direct fields from the antennas and the reflected and diffracted fields from the surrounding structures. The computed signal strengths were compared to the signal strength corresponding to the 0 dB link margin. Based on the results obtained in this study, RF coverage for SSO-EVA and SSO-ISS communication links was determined for the proposed payload bay antenna UHF locations. The RF radiation to the Orbiter Docking System (ODS) pyros, the payload bay avionics, and the Shuttle Remote Manipulator System (SRMS) from the new proposed UHF antenna location was also investigated to ensure the EMCEMI compliances.

Lunar Surface Propagation Modeling and Effects on Communications

“…To determine the signal strength and distribution, including the lunar terrain effects, computer simulations were performed using the computational electromagnetic technique -GTD [7]- [12]. The RF coverage may be determined from computed results and receiver thresholds.…”

“…The Geometrical Theory of Diffraction (GTD) [7]- [12] is capable of taking into account the reflections and diffractions off three-dimensional (3-D) lunar terrain. For detail and specific terrains and objects around the antenna, such as astronauts and the lunar vehicle, we propose using GTD to provide more accurate and reliable results.…”