Possible Orbit Scenarios for an InSAR Formation Flying Microsatellite Mission

Multistatic interferometric synthetic aperture radar (InSAR) is a promising future payload for a small satellite constellation, providing a low-cost means of augmenting proven “large” SAR mission technology. The Space Flight Laboratory at the University of Toronto Institute for Aerospace Studies is currently designing CanX-4 and CanX-5, a pair of formation-flying nanosatellites slated for launch in 2009. Once formation flight has been demonstrated, a future multistatic InSAR formation-flying constellation can exploit sub-centimeter inter-satellite baseline knowledge for interferometric measurements, which can be used for a myriad of applications including surface deformation, digital terrain modeling, and moving target detection. This study evaluates two commonly proposed InSAR constellation configurations, namely the Cartwheel and the Cross-Track Pendulum, and considers two ‘large’ (~kilowatt) SAR transmitters (Cand X-band) and one microsatellite transmitter (X-band, 150W). Each case is evaluated and assessed with respect to the available interferometric baselines and ground coverage. The microsatellite X-band transmitter is found to be technically feasible, although the lower available transmitter power limits the operating range. The selected transmit band determines the maximum allowable cross-track baseline between receiver satellites in the constellation. Additionally, the Cartwheel and Cross-Track Pendulum configurations offer different available baselines and ground coverage patterns, namely, the Cartwheel eliminates the near-zero cross-track baseline component that contributes to DEM height errors but adds a coupled along-track baseline, while the Cross-Track Pendulum offers the advantage of independent cross-track and along-track baseline components. Ultimately, the primary application for the InSAR data will dictate the transmit band used, the desired baselines, and the receiver constellation configuration.