Which technique involves transmitting a signal from a ground station, reflecting off retro-reflectors on satellites, and receiving back at the station?

• A. Satellite laser ranging
• B. Lunar laser ranging
• C. Doppler orbitography
• D. Baseline interferometry

Answer: (A)

Transmitting a signal from a ground station to a satellite, having it reflect off passive retro-reflectors on the satellite, and receiving it back at the ground station is Satellite laser ranging. The retro-reflectors bounce the laser light back toward the source regardless of the angle of incidence, so by timing the round trip very precisely you determine the satellite’s distance and refine its orbit. This contrasts with lunar laser ranging, which uses reflectors on the Moon instead of satellites; Doppler orbitography relies on Doppler shifts of signals to infer motion, not reflected light, and baseline interferometry uses phase differences between signals at multiple antennas to measure angles rather than range via reflection.