Space Shuttle radar performance predictions and verification

The Space Shuttle Ku-band integrated radar and communication system is operated in a communications mode for transmissions between astronauts in the orbiting Shuttle and mission controllers at the Lyndon B. Johnson Space Center (JSC). In the radar mode the Ku-band system provides a relative position vector, range rate, and angle rates for flight control purposes during operations with other spacecraft. The measurements are made available for use by the astronauts and by the onboard computers. The quality of the radar measurements impacts Shuttle flight dynamics and fuel consumption. Thorough acceptance testing ensures that functional Ku-band systems are delivered to the National Aeronautics and Space Administration (NASA) for Shuttle installations. A series of helicopter flights and balloon tests at White Sands provided measurement bias and noise estimates. With continuing use of the Ku-band system on Shuttle flights, a procedure is needed for ongoing evaluations of radar performance. This need is addressed by preflight testing and mission data analysis. Testing is carried out at the John F. Kennedy Space Center (KSC) before each flight and after the change of a line replaceable unit (LRU). Functional testing is performed between flights. System sensitivity is verified after an LRU change, along with a functional test of tracking capability. Mission data analysis provides an evaluation of performance quality. Regression procedures are used to estimate noise in range, range rate, and angle measurements. Signal-to-noise ratio estimates are made to relate the observed random error levels to signal quality. Reference to radar cross section (RCS) models verifies an acceptable system sensitivity. The combination of system testing at KSC and data analysis at JSC provides an ongoing evaluation of radar performance and mission readiness