Spacecraft formation flight exploiting potential fields

Abstract

The potential benefits that can be reaped from a distributed satellite system have led to the proposal of several multi-spacecraft missions by both NASA and DoD. One such benefit is the reconfigurability of these multi-spacecraft systems. This ultimately led to additional requirements being levied onto these missions, such as the general astrophysical imaging requirement for the Terrestrial Planet Finder (TPF) mission. Cluster reconfiguration, however, is an effort extensive operation. In this thesis, the operation of multi-spacecraft systems in three different potential fields are exploited such that spacecraft formation can be held with as little effort as possible. The first potential field considered is the Earth's gravitational field. Based upon the sparse aperture radar requirements, the terminal conditions required to keep the Air Force TechSat 21 Earth orbiting clusters in closed formations were derived. Using the Linear Quadratic formulation, the optimal reconfigurations required to initialize and resize the clusters were then determined. Based upon the current system design, the results show that both these maneuvers can be accomplished in as little as half an orbital period with the resizing maneuver costing at least 25% of the budgeted AV.

(cont.) The second potential field considered is the operation of a multi-spacecraft interferometer operating in a gravitational free environment. In this case, the optimal trajectories were determined from a combination of the science requirements, being framed as part of the cost function, and the required electrical energy. Based upon the proposed scientific plan, the interferometer that is primarily designed for planet detection should be able to meet its imaging requirement of 1000 images with only 26% of the allocated resources. The final potential field exploited in this thesis is the operation of the TPF interferometer in a self-induced electromagnetic field. Using only electromagnets to control spacecraft formation, this Electromagnetic Formation Flight (EMFF) concept requires no propellant, thus eliminating all pollution and contamination issues that are associated with it. In terms of mass fractions, power demands and volume requirements, the EMFF design is in fact comparable to the currently designed propulsion-based system. To further demonstrate the viability of the EMFF concept, controllability issues for the systems were also investigated.