Anareostationary orbit,areosynchronous equatorial orbit (AEO), orMars geostationary orbit is acircularareosynchronous orbit (ASO) approximately 17,032 km (10,583 mi) in altitude above theMarsequator and following the direction of Mars's rotation.
An object in such an orbit has anorbital 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 aGeostationary orbit (GEO). The prefixareo- derives fromAres, the ancientGreek god of war and counterpart to theRoman godMars, with whom the planet was identified.
Although it would allow for uninterruptedcommunication andobservation of the Martian surface, noartificial satellites have been placed in this orbit due to the technical complexity of achieving and maintaining one.[1][2]
The radius of an areostationary orbit can be calculated usingKepler's Third Law.
Where:
| Variable | Definition | Value |
|---|---|---|
| T | Rotational Period | 88,642 seconds |
| G | Gravitational constant | 6.674×10−11 N⋅m2/kg2 |
| M | Mass of central object | 6.4171×1023 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 of20,428 km (12,693 mi) above the surface of the Mars equator.[3][4][5] 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.[5][6]
Several factors make placing a spacecraft into an areostationary orbit more difficult than a geostationary orbit. Since the areostationary orbit lies between Mars's twonatural satellites,Phobos (semi-major axis: 9,376 km) andDeimos (semi-major axis: 23,463 km), any satellites in the orbit will suffer increasedorbital station keeping costs due to unwantedorbital 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 andrelated challenges shared by any attempted Mars mission.[2][6][7]
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 advantageous for monitoring Martian weather and mapping of the Martian surface.[8]
In the early 2000sNASA 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.[9][10]
