System Identification of a Nonlinear Mode for the Shuttle Radar Topography Mission

A study is presented to identify a nonlinear bending mode for a 60-m space structure. This study was done in support of the Shuttle Radar Topography Mission (SRTM) and postflight height reconstruction efforts. For this purpose, one linear model and three nonlinear models of the structural mode were considered and evaluated. The best model was determined based on in-flight data collected during the mission and was implemented as part of the final ground software that was used for reconstructing relative radar antenna motion for the SRTM interferometer payload. High accuracy estimates of the relative states were essential for supporting the motion compensation algorithm used in the radar interferometry processor for calculating the desired topographic maps. The improvement resulting from identifying nonlinear modal behavior contributed to meeting mission performance requirements.