Aerodynamic and gravity gradient stabilization for microsatellites

Abstract

When the orbital altitude of a satellite is relatively low, for example, less than 500 km, the method of aerodynamic stabilization can be considered. In particular, this method is very effective when the satellite is small. The aerodynamic restoring torque can be provided by a very light tail stabilizer which is several meters downstream from the main body of the small satellite. An aerodynamic stabilization system has been installed in the Cosmos-149 and another one in the Cosmos-320. One of the disadvantages in using the aerodynamic stabilization is that no rolling stabilization can be achieved. The gravity gradient stabilization method has been used in many satellites. One of the examples is the Eole satellite. In the recent years, many small satellites have adopted this method owing to its long life and continuous Earth pointing characteristics. The main disadvantage is the poor pointing accuracy with respect to the orbiting reference coordinates. This disadvantage can be overcome with the aid of a small reaction wheel. Both pitch and roll orientations can be stabilized. However, no yawing motion stabilization can be achieved by using the pure passive gravity gradient method. The purpose of this paper is to combine the aerodynamic and gravity gradient stabilization methods together so that all the three axes stabilizations can be obtained. We shall consider the attitude motion of a microsatellite under the action of both gravity gradient torque and aerodynamic torque. The set of nonlinear equations of motion will be solved numerically with specified initial condition. The satellite operates in a circular orbit with 500 km altitude. The history of the attitude stabilization will be investigated and discussed in detail.