In satellite laser ranging (SLR) a global network of observation stations measures the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. This provides instantaneous range measurements of millimeter level precision which can be accumulated to provide accurate measurement of orbits and a host of important scientific data. The laser pulse can also be reflected by the surface of a satellite without a retroreflector, which is used for tracking space debris.
Laser Ranging System of the geodetic observatory Wettzell, Bavaria
Satellite Laser Ranging
A retroreflector is a device or surface that reflects radiation back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, which does this only if the mirror is exactly perpendicular to the wave front, having a zero angle of incidence. Being directed, the retroflector's reflection is brighter than that of a diffuse reflector. Corner reflectors and cat's eye reflectors are the most used kinds.
A gold corner cube retroreflector
Eyeshine from retroreflectors of the transparent sphere type is clearly visible in this cat's eyes.
Bicycle retroreflectors
"Aura" around the shadow of a hot-air balloon, caused by retroreflection from dewdrops