An improved algorithm to determine the relative attitude during rolling phase of spacecraft rendezvous and docking

Relative attitude is computed with improved TRIAD algorithm when relative position is far and relative attitude is large during rolling phase of spacecraft rendezvous and docking. On the precondition that the distances between identification points on target spacecraft and the centre of camera lens have been worked out with existing algorithms, orthogonal basis is constructed in each vector space. Rotation matrix can be calculated by the transformation of orthogonal basis and relative attitude can be computed further. The orthogonal basis reflects the relative attitudes between two coordinate systems exactly, avoiding the shortage that traditional TRIAD algorithm can not reflect the rotation along body axis and will induce the large computing errors even wrong results. Improved TRIAD can be used to calculate large attitude. Simulations show that the algorithm is more reliable, more accurate and is not confined to the size of attitude. It is superior to traditional TRIAD algorithm remarkably.