A corner reflector consists of three mutually perpendicular mirrors that reflect light back in the direction of the source. The many uses of this principle include bicycle reflectors, automobile tail lights, and radar targets or markers on ships, especially on lifeboats. NASA has put corner reflectors on the Moon to measure its orbit. A corner reflector is also known as a cat's eye reflector or a cube reflector.
The product of reflections in two perpendicular mirrors is a half-turn about the intersection line of the mirror planes. Reflecting again in a third mirror perpendicular to both of the others results in a central inversion (reflection in a point). The center of inversion is the common point of intersection of the mirror planes. The image of a vector (in our case, the vector of the light ray) under central reflection is an oppositely directed vector.