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जैसे जैसे पृथ्वी वर्ष के दौरान सूर्य के चारों ओर घूमती जाती है वैसे वैसे सूर्य-समकालिक कक्षा बनाए रखने के लिए, उपग्रह की कक्षा को ठीक उसी समान दर पर अयन करना चाहिए | सीधे ध्रुवों के ऊपर से गुजरने वाले उपग्रहों के लिए, यह नहीं होगा | लेकिन पृथ्वी के भूमध्यरेखीय उभार के कारण, एक मामूली कोण पर झुकी कक्षा बलाघूर्ण के अधीन अयनांश का कारण बनती है, यह पता चला है कि ध्रुव से लगभग ८ डिग्री का एक कोण एक १०० मिनट की कक्षा में वांछित अयनांश निर्मित करता है |<ref name="phy6" />
[[ar:مدار قطبي]]
[[bg:Полярна орбита]]
[[ca:Òrbita polar]]
[[cs:Polární dráha]]
[[es:Órbita polar]]
[[fr:Orbite polaire]]
[[it:Orbita polare]]
[[he:מסלול קוטבי]]
[[lt:Poliarinė orbita]]
[[hu:Poláris pálya]]
[[nl:Polaire satellietbaan]]
[[ja:極軌道]]
[[no:Polarbane]]
[[nn:Polarbane]]
[[pl:Orbita okołobiegunowa]]
[[pt:Órbita polar]]
[[ru:Полярная орбита]]
[[sk:Polárna dráha]]
[[tr:Kutupsal yörünge]]
[[zh:极轨道]]
]]
A '''polar orbit''' is an [[orbit]] in which a [[satellite]] passes above or nearly above both [[Geographical pole|pole]]s of the body being orbited (usually a planet such as the [[Earth]], but possibly another body such as the [[Sun]]) on each revolution. It therefore has an [[inclination]] of (or very close to) 90 [[Degree (angle)|degree]]s to the [[equator]]. Except in the special case of a polar [[geosynchronous orbit]], a satellite in a polar orbit will pass over the equator at a different [[longitude]] on each of its orbits.
Polar orbits are often used for earth-mapping, [[earth observation satellite|earth observation]], and [[reconnaissance satellite|reconnaissance]] satellites, as well as for some [[weather satellite]]s. The [[Iridium satellite constellation]] also uses a polar orbit to provide telecommunications services. The disadvantage to this orbit is that no one spot on the Earth's surface can be sensed continuously from a satellite in a polar orbit.
It is common for near-polar orbiting satellites to choose a [[sun-synchronous orbit]]: meaning that each successive orbital pass occurs at the same local time of day. This can be particularly important for applications such as remote sensing of the atmospheric temperature, where the most important thing to see may well be ''changes'' over time, which you do not want to see aliased onto changes in local time. To keep the same local time on a given pass, it is desirable for the orbit to be as short as possible, which is to say as low as possible. However, very low orbits of a few hundred kilometers would rapidly decay due to drag from the atmosphere. A commonly used altitude is approximately 1000 km; this produces an orbital period of about 100 minutes.<ref name="phy6">{{cite web | url = http://www.phy6.org/Education/wlopolar.html | title = Polar Orbiting Satellites | publisher = Dr. David P. Stern | date = 2001-11-25 | accessdate = 2009-01-21 }}</ref> The half-orbit on the sun side then takes only 50 minutes, during which local time of day does not greatly vary.
To retain the sun-synchronous orbit as the Earth revolves around the sun during the year, the orbit of the satellite must [[precess]] at the same rate. Were the satellite to pass directly over the pole, this would not happen. But because of the Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque which causes precession; it turns out that an angle of about 8 degrees from the pole produces the desired precession in a 100 minute orbit.<ref name="phy6" />
A satellite can hover over one polar area a large part of the time, albeit at a large distance, using a polar [[highly elliptical orbit]] with its [[apogee]] above that area. This is the principle behind a [[Molniya orbit]].
==See also==
*[[List of orbits]]
*[[Vandenberg AFB]], a major United States launch location for polar orbits.
*[[Orbit|Orbits]]
==References==
{{reflist}}
==External links==
* [http://www.braeunig.us/space/orbmech.htm Orbital Mechanics] (Rocket and Space Technology)
{{orbits}}
{{DEFAULTSORT:Polar Orbit}}
[[Category:Astrodynamics]]
[[Category:Earth orbits]]
[[ar:مدار قطبي]]
[[ca:Òrbita polar]]
[[cs:Polární dráha]]
[[es:Órbita polar]]
[[fr:Orbite polaire]]
[[zh:极轨道]]
]]
A '''polar orbit''' is an [[orbit]] in which a [[satellite]] passes above or nearly above both [[Geographical pole|pole]]s of the body being orbited (usually a planet such as the [[Earth]], but possibly another body such as the [[Sun]]) on each revolution. It therefore has an [[inclination]] of (or very close to) 90 [[Degree (angle)|degree]]s to the [[equator]]. Except in the special case of a polar [[geosynchronous orbit]], a satellite in a polar orbit will pass over the equator at a different [[longitude]] on each of its orbits.
Polar orbits are often used for earth-mapping, [[earth observation satellite|earth observation]], and [[reconnaissance satellite|reconnaissance]] satellites, as well as for some [[weather satellite]]s. The [[Iridium satellite constellation]] also uses a polar orbit to provide telecommunications services. The disadvantage to this orbit is that no one spot on the Earth's surface can be sensed continuously from a satellite in a polar orbit.
It is common for near-polar orbiting satellites to choose a [[sun-synchronous orbit]]: meaning that each successive orbital pass occurs at the same local time of day. This can be particularly important for applications such as remote sensing of the atmospheric temperature, where the most important thing to see may well be ''changes'' over time, which you do not want to see aliased onto changes in local time. To keep the same local time on a given pass, it is desirable for the orbit to be as short as possible, which is to say as low as possible. However, very low orbits of a few hundred kilometers would rapidly decay due to drag from the atmosphere. A commonly used altitude is approximately 1000 km; this produces an orbital period of about 100 minutes.<ref name="phy6">{{cite web | url = http://www.phy6.org/Education/wlopolar.html | title = Polar Orbiting Satellites | publisher = Dr. David P. Stern | date = 2001-11-25 | accessdate = 2009-01-21 }}</ref> The half-orbit on the sun side then takes only 50 minutes, during which local time of day does not greatly vary.
To retain the sun-synchronous orbit as the Earth revolves around the sun during the year, the orbit of the satellite must [[precess]] at the same rate. Were the satellite to pass directly over the pole, this would not happen. But because of the Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque which causes precession; it turns out that an angle of about 8 degrees from the pole produces the desired precession in a 100 minute orbit.<ref name="phy6" />
A satellite can hover over one polar area a large part of the time, albeit at a large distance, using a polar [[highly elliptical orbit]] with its [[apogee]] above that area. This is the principle behind a [[Molniya orbit]].
==See also==
*[[List of orbits]]
*[[Vandenberg AFB]], a major United States launch location for polar orbits.
*[[Orbit|Orbits]]
==References==
{{reflist}}
==External links==
* [http://www.braeunig.us/space/orbmech.htm Orbital Mechanics] (Rocket and Space Technology)
{{orbits}}
{{DEFAULTSORT:Polar Orbit}}
[[Category:Astrodynamics]]
[[Category:Earth orbits]]
[[ar:مدار قطبي]]
[[bg:Полярна орбита]]
[[ca:Òrbita polar]]
[[cs:Polární dráha]]
[[es:Órbita polar]]
[[fr:Orbite polaire]]
[[it:Orbita polare]]
[[he:מסלול קוטבי]]
[[lt:Poliarinė orbita]]
[[hu:Poláris pálya]]
[[nl:Polaire satellietbaan]]
[[ja:極軌道]]
[[no:Polarbane]]
[[nn:Polarbane]]
[[pl:Orbita okołobiegunowa]]
[[pt:Órbita polar]]
[[ru:Полярная орбита]]
[[sk:Polárna dráha]]
[[tr:Kutupsal yörünge]]
[[zh:极轨道]]
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