<h2>AAS 99-124</h2>
<h2>Low Propellant Solutions to Aperture Synthesis Using Distributed Satellite Systems: Applications to TECHSAT21                                    </h2>
<h4>R. Sedwick, E. Kong, D. Miller                                                                                                                                                      </h4>
MIT Space Systems Lab, Cambridge, MA                                                                                                                                      
<h2> Abstract </h2>
Aperture synthesis using distributed satellite systems opens up new possibilities of space-based surveillance of Earth. However, it brings with it new challenges for maintaining the geometry of the array in the presence of gravitational tidal forces and environmental perturbations. Balancing the radar need to position the individual apertures in specific relative orientations, with the desire to minimize the propellant consumed to do so, leads to the need for creative techniques which exploit the natural orbital motion of the satellites to sweep out the image plane. This paper quantifies these environmental perturbative effects, first through dimensional analysis to derive the various scaling laws needed to conduct design trades, and then through a rigorous analysis of a specific formation flying mission: the Air Force space-based radar system (TechSat21). For TechSat21, 0.5 cm/sec/orbit of DV is required to counteract secular terms arising from environmental perturbations, such as J2. Periodic variations in relative motion are about 0.018% of the array's dimension, or 9 cm for a 500 m array, if left unchecked.