An areostationary orbit (abbreviated ASO) is a circular areosynchronous orbit in the Martian equatorial plane about 17,000 km (11,000 mi) above the surface, any point on which revolves about Mars in the same direction and with the same period as the Martian surface. Areostationary orbit is a concept similar to Earth's geostationary orbit. 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. The modern Greek word for Mars is Άρης (Áris).
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To date, no artificial satellites have been placed in this orbit, but it is of interest to some scientists foreseeing a future telecommunications network for the exploration of Mars. The proposed Mars One mission includes a communications system featuring amongst others things an areostationary satellite. An asteroid or station placed in areostationary orbit could also be used to construct a Martian space elevator for use in transfers between the surface of Mars and orbit.
Formula
Orbital speed (how fast a satellite is moving through space) is calculated by multiplying the angular speed of the satellite by the orbital radius:
By this formula we can find the geostationary-type orbit of an object in relation to Mars (this type of orbit above is referred to as an areostationary orbit if it is above Mars). The areogeocentric gravitational constant GM (which is μ) for Mars has the value of 42,828 km3 s−2, and the known rotational period (T) of Mars is 88 642.66 s. Since ω = 2π/T, using the formula above, the value of ω is found to be approximately 7.088218×10−5 s−1. Thus, r3 = 8.5243×1012 km3, the cube root of which is 20,427 km; subtracting the equatorial radius of Mars (3396.2 km) gives 17,031 km.
Stationkeeping
Any satellites in areostationary orbit will likely suffer from increased orbital station keeping costs, because the Clarke belt of Mars lies between the orbits of the planet's two natural satellites. Phobos has a semi-major axis of 9,376 km, and Deimos has a semi-major axis of 23,463 km. The close proximity to Phobos in particular (the larger of the two moons) will cause unwanted orbital resonance effects that will gradually shift the orbit of areostationary satellites.