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

E. Harrison Teague, Jonathan P. How and Bradford W. Parkinson

Abstract:	Current lab tests demonstrate vibration and orienta- tion control of highly flexible vehicles using only the GPS carrier to measure motion. A 30-foot long test structure has been constructed that is suspended from above, and moves in an analogous way to a flexible orbiting platform. The test structure is outfitted with an array of GPS antennas for motion sensing, and an array of compressed air thrusters for control actuation. The sensor has shown better than 0.5 degree rotational accuracies as measured with respect to on board rate gyroscopes. We have shown simultaneous rigid-body orientation and elastic vibration control by closing a feedback loop from the GPS differential carrier phase (DCP) measurements to the thruster commands. Central to the success of the GPS deformation sens- ing system is the sub-centimeter level differential po- sition information available from GPS carrier track- ing. However, it is challenging to use this accuracy due to inherent, and arbitrarily large, measurement biases. Bias resolution (akin to cycle ambiguity res- olution) has been solved for vehicle navigation and attitude determination problems. We show bias es- timation for an antenna array mounted on a structure whos relative antenna motions due to flexibility are on the same order of magnitude as those due to overall attitude changes. This research is a significant step toward general dis- tributed antenna array GPS carrier based sensing sys- tems. Our techniques are applicable to systems that exhibit relative motions with frequencies (< 10 Hz) and deflections (> 1 cm) that are detectable by cur- rent receivers.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1355 - 1365
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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