Astronomy:Pass (spaceflight): Difference between revisions
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A pass, in spaceflight and satellite communications, is the period in which a satellite or other spacecraft is above the local horizon and available for radio communication with a particular ground station, satellite receiver, or relay satellite (or, in some cases, for visual sighting). The beginning of a pass is termed acquisition of signal (AOS); the end of a pass is termed loss of signal (LOS).[1] The point at which a spacecraft comes closest to a ground observer is the time of closest approach (TCA).[1]
Timing and duration
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).[2] An observer directly on the ground track of the satellite will experience the greatest ground pass duration.[3] Path loss is greatest toward the start and end of a ground pass,[4] as is Doppler shifting for Earth-orbiting satellites.[5]
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[3] (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.[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; thus, naked-eye observations are generally restricted to twilight hours, during which the spacecraft is in sunlight but the observer is not. A satellite flare occurs when sunlight is reflected by flat surfaces on the spacecraft. The International Space Station, the largest artificial satellite of Earth, has a maximum apparent magnitude of –5.9,[7] brighter than the planet Venus.[8]
See also
- Ground track, the path on the surface of the Earth directly below a satellite
- Satellite revisit period, the time elapsed between observations of the same point on Earth by a satellite
- Satellite watching, as a hobby
References
- ↑ 1.0 1.1 "AOS, TCA, and LOS". Northern Lights Software Associates. http://www.nlsa.com/definitions/aos_defined.html.
- ↑ 2.0 2.1 Wood, Lloyd (July 2006). "Introduction to satellite constellations: Orbital types, uses and related facts". ISU Summer Session. http://personal.ee.surrey.ac.uk/Personal/L.Wood/publications/lloyd-wood-isu-summer-06-constellations-talk.pdf. Retrieved 17 November 2015.
- ↑ 3.0 3.1 Del Re, Encrico; Pierucci, Laura, eds (6 December 2012). Satellite Personal Communications for Future-generation Systems. Springer. p. 19. ISBN 978-1447101314. https://books.google.com/books?isbn=1447101316. Retrieved 17 November 2015.
- ↑ Richharia, Madhavendra (2014). Mobile Satellite Communications: Principles and Trends (Second ed.). Wiley. pp. 106–107. ISBN 978-1118810064. https://books.google.com/books?isbn=1118810066. Retrieved 17 November 2015.
- ↑ Montenbruck, Oliver; Eberhard, Gill (2012). Satellite Orbits: Models, Methods, and Applications. Springer. p. 229. ISBN 978-3642583513. https://books.google.com/books?isbn=3642583512. Retrieved 17 November 2015.
- ↑ Dickinson, David (July 11, 2013). "How to Spot and Track Satellites". Universe Today. http://www.universetoday.com/103382/how-to-spot-and-track-satellites/.
- ↑ "ISS Information - Heavens-above.com". Heavens-above. http://www.heavens-above.com/satinfo.aspx?SatID=25544.
- ↑ "HORIZONS Web Interface". Jet Propulsion Laboratory. http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=mb&sstr=299.