The timing and duration of passes depends on the characteristics of the
orbit a satellite occupies, as well as the ground
topography and any
occulting objects on the ground (such as buildings), or in space (for planetary probes, or for spacecraft using relay satellites). The longest duration ground pass will be experienced by an observer directly on the
ground track of the satellite.
Path loss is greatest toward the start and end of a ground pass, as is
Doppler shifting for Earth-orbiting satellites. Satellites in
geosynchronous orbit may be continuously visible from a single ground station, whereas satellites in
low Earth orbit only offer short-duration ground passes (although longer contacts may be made via relay satellite networks such as
TDRSS).
Satellite constellations, such as those of
satellite navigation systems, may be designed so that a minimum subset of the constellation is always visible from any point on the Earth, thereby providing continuous
coverage. ==Prediction and visibility==