Carrier Differential GPS for Real-Time Control of Large Flexible Structures

Abstract

Current laboratory tests demonstrate vibration and orientation control of a highly flexible vehicle using only the GPS carrier to measure motion. A 30 ft long test structure has been constructed that is suspended from above, and moves in a manner analogous to that of a flexible orbiting platform. Experiments show simultaneous rigid-body orientation and elastic vibration control by closing a feedback loop from the GPS differential carrier phase (DCP) measurements to onboard thrusters. Use of the subcentimeter-level differential position information in DCP measurements is challenging because of inherent, and arbitrarily large, measurement biases (cycle ambiguities). This paper presents a new bias ambiguity resolution algorithm that combines measurements taken during motion of the structure with a model of the platform dynamics to initialize the unknown biases. The techniques presented are applicable to systems that exhibit relative motions with frequencies ( 1 cm) that are detectable by current receivers.