Motion detector for space surveillance

Claim 1

A motion detector responsive to incident radiation, comprising: an elongate four-sided frustopyramidal box with a first pair of longitudinal walls bisected by a plane of symmetry and a second pair of longitudinal walls converging toward said plane of symmetry from a wider closed end toward a narrower entrance and accessible to incident radiation, at least the walls of said second pair having reflective inner surfaces; a concave radiation reflector at said closed end with a vertex in said plane of symmetry and a focus near said entrance end; and radiation-sensing means in the vicinity of said focus confronting said concave reflector for illumination by incident beams of parallel rays approaching said entrance end at a plurality of predetermined azimuthal angles with reference to said plane of symmetry and reflected at least once in said box by a wall of said second pair, said radiation-sensing means having a receiving area substantially narrower than said entrance end at least in a direction perpendicular to said plane of symmetry, the length of said box being so related to the angle of convergence ∝ included between said second pair of walls and said plane of symmetry that incoming beams traversing said entrance end at azimuthal angles ±(2n+1)·α undergo n reflections at said second pair of walls before reaching said concave reflector, n being an integer ranging from 0 to a maximum of 3, said incoming beams being converted by said concave reflector into converging beams undergoing each a further reflection at said second pair of walls before impinging from different directions onto said radiation-sensing means.