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 or satellite receiver (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.[1] The point at which the spacecraft comes closest to the ground observer is the time of closest approach.[1]
The timing and duration of passes depends on the characteristics of the orbit a satellite occupies, as well as the topography and any occulting objects at the ground location.[2] An observer directly on the ground track of the satellite will experience the greatest pass duration.[3] Path loss[4] and Doppler shifting[5] are greatest toward the start and end of a pass.
Coverage
Satellites in geosynchronous orbit may be continuously visible from a single ground station, whereas satellites in low Earth orbit only offer short-duration passes.[3] Satellite constellations, such as those of satellite navigation systems, may be designed so that a subset of the constellation is always visible from any point on the Earth, providing continuous coverage.[2]
Prediction and visibility
A number of web-based and mobile applications produce predictions of passes for known satellites.[6] In order to be observed with the naked eye, a spacecraft must reflect sunlight towards the observer, in what is called a satellite flare. Thus, naked-eye observations are generally restricted to twilight hours, in which the spacecraft is in sunlight but the observer is not.
See also
- Ground track, the path on the surface of the Earth directly below a satellite
References
- 1 2 "AOS, TCA, and LOS". Northern Lights Software Associates. Retrieved 17 November 2015.
- 1 2 Wood, Lloyd (July 2006). Introduction to satellite constellations: Orbital types, uses and related facts (PDF). ISU Summer Session. Retrieved 17 November 2015.
- 1 2 Del Re, Encrico; Pierucci, Laura (eds.). Satellite Personal Communications for Future-generation Systems. Springer. p. 19. ISBN 1447101316. Retrieved 17 November 2015.
- ↑ Richharia, Madhavendra (2014). Mobile Satellite Communications: Principles and Trends (Second ed.). Wiley. pp. 106–107. ISBN 1118810066. Retrieved 17 November 2015.
- ↑ Montenbruck, Oliver; Eberhard, Gill (2012). Satellite Orbits: Models, Methods, and Applications. Springer. p. 229. ISBN 3642583512. Retrieved 17 November 2015.
- ↑ Dickinson, David (July 11, 2013). "How to Spot and Track Satellites". Universe Today. Retrieved 17 November 2015.
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