REQUEST: A recursive QUEST algorithm for sequential attitude determination

QUEST is a well-known algorithm for least squares fitting of the attitude quaternion of a spacecraft to vector measurements. QUEST, however, is a single time point (single frame) batch algorithm; thus, measurements that were taken at previous time points are discarded, The algorithm presented provides a recursive routine, which considers all past measurements. The algorithm is based on the fact that the so-called K matrix, one of whose eigenvectors is the sought quaternion, is linearly related to the measured vector pairs and on the ability to propagate K, The extraction of the appropriate eigenvector is done according to the classical QUEST algorithm, This stage, however, can be eliminated, and the computation simplified, if a standard eigenvalue-eigenvector solver algorithm is used.