Gravity-gradient stabilization

Gravity-gradient stabilization (a.k.a. "tidal stabilisation") is a method of stabilizing artificial satellites or space tethers in a fixed orientation using only the orbited body's mass distribution and the Earth's gravitational field. The main advantage over using active stabilization with propellants, gyroscopes or reaction wheels is the low use of power and resources. It was first used for low Earth orbit and tested unsuccessfully for geosynchronous orbit in the Applications Technology Satellites ATS-2, ATS-4 and ATS-5 from 1966 until 1969.

The principle is to use the Earth's gravitational field and tidal forces to keep the spacecraft aligned in the desired orientation. The gravity of the Earth decreases according the inverse-square law, and by extending the long axis perpendicular to the orbit, the "lower" part of the orbiting structure will be more attracted to the Earth. The effect is that the satellite will tend to align its axis of minimum moment of inertia vertically.

An example of gravity-gradient stabilization was demonstrated during NASA's TSS-1R mission. Just prior to tether separation, the tension on the tether was about 65 N (14.6 lbs).

See also

• Gravity gradiometry
• Space tether
• Tidal locking

External links

• NASA on ATS-2
• Gunter's Space Page on ATS 2, 4 and 5
• A new kind of Earth Sensor using a proof mass on a MEMS created by EPFL students