Abstract: A non-contact sensing system for monitoring the position and orientation of a rigid body in space having at least three distinct point light sources mounted on the rigid body. At least two position sensor heads are fixedly mounted within detection range of light from the light sources, each position sensor head having a position sensitive detector. The lights are illuminated one at a time and in sequential arrangement and a processor computes the position in three-dimensional space of an illuminated light source with data provided simultaneously by both position sensitive detectors. The processor means also computes the position of the object in all six degrees of freedom using the three-dimensional positional data of all three light sources.