A method is presented for fast estimation of the angular rate of a tumbling spacecraft in a low-Earth orbit from sequential readings of Earth's magnetic eld. Useful as a backup algorithm in cases of rate gyro malfunctionsor during the initial acquisitionphase, the estimatorconsists of an extended Kalman lter, based on the assumptionthat the inertial geomagnetic eld vector does not signi cantly change during the short sampling time. As the external disturbance torque is neglected, an analytic solution of Euler's equations can be used in the lter's propagation phase, allowing a signi cant savings of computation time compared to numerical integration of Euler's equations. Contrary to most existing angular rate estimators, the spacecraft's attitude is neither used nor estimated within the proposed algorithm. Moreover, the body-referenced geomagnetic eld observations are not differentiated with respect to time as an external pre ltering procedure but are directly processed by the lter. This processing gives rise to a colored effective measurement noise, which is properly handled via approximate Markov modeling and application of Bryson and Henrikson's reduced-order ltering theory. A simulation study employing a standard tenth-order International Geomagnetic Reference Field model is presented to demonstrate the performance of the algorithm.
The spinning and oscillatory motions of small orbiting satellites can be damped exploiting the magnetic energy dissipation occurring in onboard soft magnetic strips, cyclically excited by the oscillation of the earth field component along their axis. In this paper we investigate the role played by the intrinsic magnetic properties of the material, the aspect ratio of the strips, and their mutual arrangement in achieving maximum energy dissipation under typical spacecraft working conditions. Grain-oriented Fe-Si, mumetal, and Fe-based amorphous alloys, all endowed with near-rectangular hysteresis loops, are considered. Their energy loss behaviour is calculated when, either as single strip samples or arranged into an array of strips, they are subjected to a slowly oscillating magnetic field of defined peak value, emulating the action of the earth magnetic field on the travelling satellite. The strip size and array layout leading to maximum energy loss are predicted. Amorphous alloys, combining high saturation magnetization with flexible hysteresis loop properties, are shown to lead to the best damping behaviour under both oscillating and spinning satellite motions. In the latter case the Fe-Si strips appear to provide comparably high damping effects, while inferior behaviour is always predicted with mumetal samples
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