Areostationary orbit

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A simulation of a 4-satellite constellation in areostationary orbit

An areostationary orbit, areosynchronous equatorial orbit (AEO), or Mars geostationary orbit is a circular areo­synchronous orbit (ASO) approximately 17,032 km (10,583 mi) in altitude above the Mars equator and following the direction of Mars's rotation.

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An object in such an orbit has an orbital period equal to Mars's rotational period, and so to ground observers it appears motionless in a fixed position in the sky. It is the Martian analog of a Geostationary orbit (GEO). The prefix areo- derives from Ares, the ancient Greek god of war and counterpart to the Roman god Mars, with whom the planet was identified.

Although it would allow for uninterrupted communication and observation of the Martian surface, no artificial satellites have been placed in this orbit due to the technical complexity of achieving and maintaining one. [1] [2]

Characteristics

The radius of an areostationary orbit can be calculated using Kepler's Third Law.

[3]

Where:

VariableDefinitionValue
TRotational Period88,642 seconds
G Gravitational constant 6.674×10−11 N⋅m2/kg2
MMass of central object6.4171×1023 kg
a Semimajor axis 20,428 km

Substituting the mass of Mars for M and the Martian sidereal day for T and solving for the semimajor axis yields a synchronous orbit radius of 20,428 km (12,693 mi) above the surface of the Mars equator. [4] [5] [6] Subtracting Mars's radius gives an orbital altitude of 17,032 km (10,583 mi).

Two stable longitudes exist - 17.92°W and 167.83°E. Satellites placed at any other longitude will tend to drift to these stable longitudes over time. [6] [7]

Feasibility

Several factors make placing a spacecraft into an areostationary orbit more difficult than a geostationary orbit. Since the areostationary orbit lies between Mars's two natural satellites, Phobos (semi-major axis: 9,376 km) and Deimos (semi-major axis: 23,463 km), any satellites in the orbit will suffer increased orbital station keeping costs due to unwanted orbital resonance effects. Mars's gravity is also much less spherical than earth due to uneven volcanism (i.e. Olympus Mons). This creates additional gravitational disturbances not present on earth, further destabilizing the orbit. Solar radiation pressure and sun-based perturbations are also present, as with an earth-based geostationary orbit. Actually placing a satellite into such an orbit is further complicated by the distance from earth and related challenges shared by any attempted Mars mission. [2] [7] [8]

Uses

Satellites in an areostationary orbit would allow for greater amounts of data to be relayed back from the Martian surface easier than by using current methods. Satellites in the orbit would also be ideal advantageous for monitoring Martian weather and mapping of the Martian surface. [9]

In the early 2000s NASA explored the feasibility of placing communications satellites in an areocentric orbit as a part of the Mars Communication Network. In the concept, an areostationary relay satellite would transmit data from a network of landers and smaller satellites in lower Martian orbits back to earth. [10] [11]

See also

Related Research Articles

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A geosynchronous orbit is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds. The synchronization of rotation and orbital period means that, for an observer on Earth's surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day. Over the course of a day, the object's position in the sky may remain still or trace out a path, typically in a figure-8 form, whose precise characteristics depend on the orbit's inclination and eccentricity. A circular geosynchronous orbit has a constant altitude of 35,786 km (22,236 mi).

<span class="mw-page-title-main">Geostationary orbit</span> Circular orbit above Earths Equator and following the direction of Earths rotation

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<span class="mw-page-title-main">Phobos (moon)</span> Largest and innermost moon of Mars

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A geosynchronous satellite is a satellite in geosynchronous orbit, with an orbital period the same as the Earth's rotation period. Such a satellite returns to the same position in the sky after each sidereal day, and over the course of a day traces out a path in the sky that is typically some form of analemma. A special case of geosynchronous satellite is the geostationary satellite, which has a geostationary orbit – a circular geosynchronous orbit directly above the Earth's equator. Another type of geosynchronous orbit used by satellites is the Tundra elliptical orbit.

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References

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