Analysis of Thruster Requirements and Capabilities for Local Satellite Clusters

This paper examines the propulsive requirements necessary to maintain the relative positions of satellites orbiting in a local cluster. Formation of these large baseline arrays could allow high resolution imaging of terrestrial or astronomical targets using techniques similar to those used for decades in radio interferometry. A key factor in the image quality is the relative positions of the individual apertures in the sparse array. The relative positions of satellites in a cluster are altered by "tidal" accelerations which are a function of the cluster baseline and orbit altitude. These accelerations must be counteracted by continuous thrusting to maintain the relative positions of the satellites. Analysis of propulsive system requirements, limited by spacecraft power, volume, and mass constraints, indicates that specific impulses and efficiencies typical of ion engines or Hall thrusters (SPT's) are necessary to maintain large cluster baselines. In addition, required thrust to spacecraft mass ratios for reasonable size clusters are approximately 15µN/kg. Finally, the ability of a proposed linear ion microthruster to meet these requirements is examined. A variation of Brophy's method is used to show that primary electron containment lengths on the order of 10 mm are necessary to achieve those thruster characteristics. Preliminary sizing of the linear ion microthruster is given.