Parallel Estimation and Control Architectures for Deep-Space Formation Flying Spacecraft

Abstract

The formation flying of precisely controlled spacecraft in deep space can be used to implement optical instruments capable of imaging planets in other solar systems. The distance of the formation from Earth necessitates a significant level of autonomy and each spacecraft must base its actions on its estimates of the location and velocity of the other spacecraft. Precise coordination and control is the key requirement in such missions and the flow of information between spacecraft must be carefully designed. Doing this in an efficient and optimal manner requires novel techniques for the design of the on-board estimators. The use of standard Kalman filterbased designs can lead to unanticipated dynamics-which we refer to as disagreement dynamics-in the estimators' errors. We show how communication amongst the spacecraft can be designed in order to control all of the dynamics within the formation. We present several results relating the topology of the communication network to the resulting closed-loop control dynamics of the formation. The consequences for the design of the control, communication and coordination are discussed.

Asynchronous Switching Decentralized Controllers for Spacecraft Formations

“…One such example, interferometric imaging systems, is our primary motivating application, although the work described here applies to a wide range for formation control problems. Several interferometric flight projects based on formation flying have been studied including Darwin (Fridlund, 2000), Terrestrial Planet Finder (TPF) (Hadaegh et al, 2000) and Starlight (formerly ST-3) (Gorham et al, 2001).…”

“…Depending on the application this may include movable platforms, optical delay lines, and precision piezoelectric actuators on the individual mirrors. The optical path length requirements translate into spacecraft relative positioning requirements in the micrometer to centimeter range (Fridlund, 2000), (Hadaegh et al, 2000) .…”