The spread spectrum acquisition and tracking performance for the ShuttleS-band andKu-band communication links are analyzed and compared to test results. TheS-band link requirements are more severe than those of theKu-band links, hence, different despreader designs were developed for the two systems. TheS-band despreader acquires pseudonoise code lock by examining all possible code phases in half chip steps while theKu-band despreader acquires pseudonoise code lock by continuously sweeping a tau-jitter loop. Both despreaders employ a tau-jitter loop for code tracking. The code tracking performance is computed for the tau-jitter loop and compared to that of the more complex delay lock loop.

One mission of the Shuttle is to place payloads into Earth orbit or on escape trajectories and to recover payloads from Earth orbit. In order to properly deploy and retrieve such payloads, operational and diagnostic communications must take place between the payloads and the Shuttle. The results of such communications, in the form of tracking, commands, and telemetry, will be interpreted both aboard the Shuttle and on the ground. To accommodate a diverse set of payloads for both NASA and DOD programs, multimode avionic equipment dedicated to payload communications is being installed aboard the Shuttle. This equipment, operating at RF and baseband and providing capability for digital and analog signal forms, will furnish all required capabilities to communicate with both attached and detached payloads.