Single pass interferometric synthetic aperture radar spacecraft formations for planetary exploration

The dissertation investigates formations of a space based exploration system consisting of an interplanetary capable spacecraft and two smaller deployable spacecraft. Spacecraft formations are optimized for single pass spot-light interferometric synthetic aperture radar (IFSAR) imaging during planetary flybys. Two major system models are developed; (1) relative spacecraft motion, and (2) pixel height measurement variance.; A generalized nonlinear relative motion model is developed. Assumptions of circular orbit and/or equal gravity gradient are applied to the nonlinear model and shown to yield relative motion equations commonly found in the spacecraft formation flying literature. An analysis shows that the generalized trajectory model with an equal gravity gradient assumption provides sufficient accuracy for a single pass IFSAR flyby.; A pixel height variance model is developed to address issues unique to single pass multiple baseline space based systems. A bistatic IFSAR system is assumed with the radar transmitter aboard the leader spacecraft and radar receivers aboard all three spacecraft. Modeled noises include internal sensor noise, spatial decorrelation noise, non-parallel ground track (grid rotation) decorrelation noise, and system parameter uncertainties. With expected observation ranges in excess of 500 kilometers, large baselines are required to maximize IFSAR height sensitivity. An analysis of optimal correlation is presented that extends the work of Rodriguez & Martin (1992) to include model uncertainties. Analysis also considers the ability of post processing algorithms to unwrap the modulo-2π phase difference measurements, an issue of particular concern for large baseline IFSAR systems. This issue is addressed through development of maximum baseline constraints computed from post processing algorithm performance specifications.; Four IFSAR formation scenarios are investigated. Each mimics the planned flyby of the Kilauea volcano by the Air Force TechSat 21 multiple spacecraft demonstration. The scenarios include (1) free-fall cluster formation, (2)  optimal formation throughout observation assuming adequate thrust, (3) free-fall flyby after optimal initial formation, and (4) multiple target regions of interest. All scenarios estimate pixel height error and azimuth resolution. Results demonstrate pixel height errors at the spot-light aim point to range from 1 to 4 meters over the several 1-second subaperture lengths, and 0.2 to 0.5 meters over the 47-second full aperture length.