The Space Shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. It is shown that a simplified analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit-energy-to-thermal-noise power spectral density ratio to achieve a 10/sup -5/ coded bit-error probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5-dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes. For the Ku-band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I=21.6 dB.>

This paper is intended to provide a comprehensive description of the Space Shuttle communications and tracking system design, development, and system operations. Areas of special innovative communications techniques implemented by the Space Shuttle such as source encoding, channel encoding, spread spectrum, and digital modulation are emphasized. In addition, the role of the Electronics Systems Test Laboratory in the development of the system is discussed.

This paper describes the current work at NASA/Johnson Space Center in the area of RF coverage analysis and performanceassessment for the Space Shuttle Program communication and tracking radio links. Trajectories, antenna data, ground station and Shuttle hardware performance characteristics and RF link math models were assimilated to generate RF link performance predictions for the three basic mission phases-ascent, on-orbit, and descent. Results identify some earlier deficiencies that required re-configuration of the ground station. Overall performance is currently satisfactory.