Shuttle radar topography mission: an innovative approach to shuttle orbital control

On February 11, 2000, the space shuttle Endeavour lifted off to tackle an ambitious mission: make the most comprehensive map ever of planet Earth. The successful 11-day Shuttle Radar Topography Mission (SRTM) produced the most complete terrain map of the world. Radar inteferometry was used to derive surface elevation by calculating the differences between measurements taken from slightly different locations. The payload consisted of a main antenna and an electronics package in the shuttle's payload bay with an outboard antenna at the end of a 200-foot mast extended once the shuttle is in orbit. Maintaining the planned orbital profile was crucial to guarantee complete coverage of the entire land coverage with no gaps between radar swaths. Orbital maintenance was accomplished during trim maneuvers executed approximately once per day. Maneuver design was constrained significantly by the presence of the delicate 200-foot mast. During the flight, seven trim burns were performed using a 'fly-cast' maneuver which required a set of precisely timed pulses to minimize loading on the mast. All maneuvers were successful and kept the orbit within required limits. Extensive interaction with the Johnson Space Center Flight Dynamics Office ensured proper design and execution of the orbital control.