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Polar orbit

A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of about 60–90 degrees to the body's equator.^[1]

Launching satellites into polar orbit requires a larger launch vehicle to launch a given payload to a given altitude than for a near-equatorial orbit at the same altitude, because it cannot take advantage of the Earth's rotational velocity. Depending on the location of the launch site and the inclination of the polar orbit, the launch vehicle may lose up to 460 m/s of Delta-v, approximately 5% of the Delta-v required to attain Low Earth orbit.

Usage

Polar orbits are used for Earth-mapping, reconnaissance satellites, as well as for some weather satellites.^[2] The Iridium satellite constellation uses a polar orbit to provide telecommunications services.

Near-polar orbiting satellites commonly choose a Sun-synchronous orbit, where each successive orbital pass occurs at the same local time of day. For some applications, such as remote sensing, it is important that changes over time are not aliased by changes in local time. Keeping the same local time on a given pass requires that the time period of the orbit be kept as short, which requires a low orbit. However, very low orbits rapidly decay due to drag from the atmosphere. Commonly used altitudes are between 700 and 800 km, producing an orbital period of about 100 minutes.^[3] The half-orbit on the Sun side then takes only 50 minutes, during which local time of day does not vary greatly.

To retain a Sun-synchronous orbit as the Earth revolves around the Sun during the year, the orbit must precess about the Earth at the same rate (which is not possible if the satellite passes directly over the pole). Because of Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque, which causes precession. An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.^[3]

References

^ "ESA - Types of Orbits". 2020-03-30. Retrieved 2021-01-10.
^ Science Focus 2nd Edition 2, pg. 297
^ ^a ^b Stern, David P. (2001-11-25). "Polar Orbiting Satellites". Retrieved 2009-01-21.

External links

Orbital Mechanics (Rocket and Space Technology)

[esa-1] "ESA - Types of Orbits". 2020-03-30. Retrieved 2021-01-10.

[2] Science Focus 2nd Edition 2, pg. 297

[phy6-3] Stern, David P. (2001-11-25). "Polar Orbiting Satellites". Retrieved 2009-01-21.

[1]

[2]

[3]

@@ Line 1: / Line 1: @@
+{{short description|Satellite orbit with high inclination}}
 [[File:Polar orbit.ogv|thumb|200px|Polar orbit]]
-A '''polar orbit''' is one in which a [[satellite]] [[pass (spaceflight)|pass]]es above or nearly above both poles of the body being [[orbit]]ed (usually a planet such as the [[Earth]], but possibly another body such as the [[Moon]] or [[Sun]]) on each revolution. It therefore has an [[inclination]] of (or very close to) 90 [[Degree (angle)|degree]]s to the [[equator]]. A satellite in a polar orbit will pass over the equator at a different [[longitude]] on each of its orbits.
+A '''polar orbit''' is one in which a [[satellite]] [[pass (spaceflight)|pass]]es above or nearly above both [[Poles of astronomical bodies|poles]] of the body being [[orbit]]ed (usually a planet such as the [[Earth]], but possibly another body such as the [[Moon]] or [[Sun]]) on each revolution. It has an [[inclination]] of about 60–90 [[Degree (angle)|degree]]s to the body's [[equator]].<ref name="esa">{{cite web |url = http://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits |title=ESA - Types of Orbits |date=2020-03-30 |access-date=2021-01-10}}</ref>
+Launching [[satellite]]s into polar orbit requires a larger [[launch vehicle]] to launch a given payload to a given altitude than for a [[near-equatorial orbit]] at the same altitude, because it cannot take advantage of the [[Earth's rotation]]al [[velocity]]. Depending on the location of the [[Spaceport|launch site]] and the [[Orbital_inclination|inclination]] of the polar orbit, the launch vehicle may lose up to 460 m/s of [[Delta-v]], approximately 5% of the Delta-v required to attain [[Low Earth orbit]].
-==Earth orbits==
+==Usage==
-Polar orbits are often used for earth-mapping, [[earth observation satellite|earth observation]], capturing the earth as time passes from one point, [[reconnaissance satellite]]s, as well as for some [[weather satellite]]s.<ref>Science Focus 2nd Edition 2, pg. 297</ref> 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.
+Polar orbits are used for [[Earth observation satellite|Earth-mapping]], [[reconnaissance satellite]]s, as well as for some [[weather satellite]]s.<ref>Science Focus 2nd Edition 2, pg. 297</ref>
+The [[Iridium satellite constellation]] uses a polar orbit to provide telecommunications services.
+{{anchor|nearPolarOrbit}}Near-polar orbiting satellites commonly choose a [[Sun-synchronous orbit]], where each successive orbital [[pass (spaceflight)|pass]] occurs at the same local time of day. For some applications, such as [[remote sensing]],  it is important that ''changes'' over time are not aliased by changes in local time. Keeping the same local time on a given pass requires that the [[frequency|time period]] of the orbit be kept as short, which requires a low orbit. However, very low orbits rapidly [[orbital decay|decay]] due to [[drag (physics)|drag]] from the atmosphere. Commonly used [[altitude]]s are between 700 and 800&nbsp;km, producing an [[orbital period]] of about 100 minutes.<ref name="phy6">{{cite web |url=http://www.phy6.org/Education/wlopolar.html |title=Polar Orbiting Satellites |first=David P. |last=Stern |date=2001-11-25 |access-date=2009-01-21}}</ref> The half-orbit on the Sun side then takes only 50 minutes, during which local time of day does not vary greatly.
-==Sun orbits==
-Near-polar orbiting satellites commonly 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 atmospheric temperature, where the most important thing to see may well be ''changes'' over time which are not aliased onto changes in local time. To keep the same local time on a given pass, the [[Frequency|time period]] of the orbit must be kept as short as possible, this is achieved by keeping the orbit lower to the Earth. However, very low orbits of a few hundred kilometers rapidly decay due to drag from the atmosphere. Commonly used altitudes are between 700&nbsp;km and 800&nbsp;km, producing 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 vary greatly.
-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, which is not possible if the satellite were to pass directly over the pole. Because of the Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque which causes precession; an angle of about 8 degrees from the pole produces the desired precession in a 100-minute orbit.<ref name="phy6" />
+{{anchor|precessingSV}}To retain a Sun-synchronous orbit as the [[Earth's orbit|Earth revolves]] around the Sun during the year, the orbit must [[Nodal precession|precess]] about the Earth at the same rate (which is not possible if the satellite passes directly over the pole).
+Because of Earth's [[equatorial bulge]], an orbit [[orbital inclination|inclined]] at a slight angle is subject to a [[torque]], which causes [[precession]]. An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.<ref name="phy6" />
 ==See also==
 *[[List of orbits]]
 *[[Molniya orbit]]
+*[[Tundra orbit]]
 *[[Vandenberg Air Force Base]], a major United States launch location for polar orbits
@@ Line 20: / Line 24: @@
 ==External links==
-* [http://www.braeunig.us/space/orbmech.htm Orbital Mechanics] (Rocket and Space Technology)
+* [https://web.archive.org/web/20120204054322/http://www.braeunig.us/space/orbmech.htm Orbital Mechanics] (Rocket and Space Technology)
 {{orbits}}