Orientation and Stabilization of Dual Spin Satellites using Aerodynamic Torque

Nadir pointing satellites can experience large atmospheric torques during low perigee parking orbits. Countering these torques can quickly saturate the momentum wheels or consume unacceptable amounts of reaction gas, making earth pointing near perigee impossible or impractical. This paper describes a technique which allows dual momentum wheel spacecraft to exploit this aerodynamic torque to achieve a stable, aerodynamically neutral orientation. In addition, this torque, coupled with the spacecraft gyro-dynamics and orbit rate, results in a natural alignment of the momentum wheel bias vector with the orbit plane normal. From this known orientation, returning to nadir pointing is simple, requiring only a 90° rotation around the pitch axis. Nutation damping and longitudinal stability are achieved by torquing the momentum wheels using a simple control law.