TWOSTEP: A fast robust algorithm for attitude-independent magnetometer-bias determination

A fast robust algorithm is developed for the inflight estimation of magnetometer biases when the attitude is not known. This algorithm combines the convergence in a single step of an heuristic algorithm currently in use with the correct treatment of the statistics of the measurement, and does this without discarding data. The new algorithm works well even when the magnetometer bias is comparable in magnitude to the ambient magnetic field. The algorithm performance is examined using simulated data for both spinning and inertially stabilized spacecraft.