Pass (spaceflight)

A pass, in spaceflight and satellite communications, is the period in which a satellite or other spacecraft is visible above the local horizon, and therefore available for radio communication with a particular ground station, satellite receiver, or relay satellite (or, in some cases, for visual observation). The beginning of a pass is termed acquisition of signal; the end of a pass is termed loss of signal. The point at which a spacecraft comes closest to a ground observer is the time of closest approach.