Micronewton Thruster Requirements for Earth-Orbiting Imaging Formations

摘要

Previous studies have explored options for separated spacecraft interferometers for planet detection as well as optical imaging of astrophysical objects. As others have noted, one of the benefits of Earth-orbiting formations is the potential to reduce the propellant required to complete image (u-v) plane filling maneuvers by taking advantage of gravity-gradient forces. In this work, the equations of motion for each of the three spacecraft in a linear formation are numerically integrated using an acceleration profile previously proposed by DeCou to produce a gradual filling of the image plane. The analysis also includes the addition of the J_2 perturbing acceleration and provides the detailed spacecraft position, velocity, and thrust histories for a maneuver as well as the maximum baseline rate of change and ΔV. Results suggest that micronewton thrusters under development for other missions requiring precision spacecraft control might be enabling for the Earth-orbiting imaging formation considered here. For one of the reference cases in geostationary orbit with a maximum baseline of 1 km and an allocated maneuver time of five days, the maximum thrust and throttling rate are approximately 87 μN and 0.24 μN/min, respectively, with a maximum baseline rate of change of 2.4 cm/s and ΔV of 6 cm/s for a single maneuver (one observation). The same reference case with thruster cancellation of the J_2 acceleration results in a maximum thrust of 2.1 mN and ΔV of 3.6 m/s. The maximum thrust, baseline rate of change, and ΔV are presented for maneuver times of one to five days, maximum baselines of 250 m and 1 km, and a formation altitude of 35,786 and 20,000 km. Three propulsion technology options- pulsed plasma, field emission electric propulsion, and colloid- are discussed as possible candidates for this role. Two solution strategies are proposed to the problem raised by the J_2 perturbation.