Patent ID: 7616326

Claim:
A system to determine displacement of an object moving in a principal direction substantially within a plane, and having lateral and transverse directions orthogonal to the principal direction and each other, the system comprising: a wedge capable of reciprocating along the principal direction between a first and a second position, and comprising first and second surfaces spaced apart to form laterally opposite sides of at least a portion of the wedge, the opposite sides spaced apart a distance varying in a known manner along the principal direction; a mirror fixed to the wedge to move therewith; a mount system supporting and aiming the mirror with respect to a satellite; a first sensor spaced away from the first surface to detect a first distance reflecting a proximity therebetween in the lateral direction; a second sensor spaced away from the second surface to detect a second distance reflecting a proximity therebetween in the lateral direction; and a processing element determining movement of the wedge in the principal direction by adding values, reflecting the first and second distances, thereby cancelling the effect of a mechanical error in the lateral position of the wedge between the first and second sensors.