Three-Dimensional Position Determination Based on Earth's Geomagnetic Field (GSC-13880)

Abstract:
Although GPS provides a free signal for very accurate position finding, space-qualified GPS equipment is expensive. Also, accuracy better than 50 km is not needed for many low Earth orbiting spacecraft, particularly solar and stellar observers. Even spacecraft using GPS could benefit from a real-time coarse position estimate to reduce their time toGSFC's deterministic position-finding technique reduces computation requirements, shortens the time needed for a first fix, and eliminates the need for all a priori position data (except knowing the hemisphere). The algorithm applies a novel correction scheme to an initial position estimate. The initial, very coarse estimate (from 10 km to 1,000 km, depending on magnetic latitude) of the three components of position is obtained by processing sensed magnetic field and attitude values with quadratic equations. The correction scheme uses two iterative methods: Newton-Raphson, a fast but not robust method, and successive substitution, a robust but slow method. The initial estimate is used as a first guess for the Newton corrector. If this fails to converge, the initial estimate is used as a first guess for a limited number of successive substitutions, followed by the Newton corrector.

Type of Offer: Licensing



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