Spacecraft propulsion using angular momentum transfer based on gravity gradient effects

Typical spacecraft propulsion systems depend upon the transfer of linear momentum through the expulsion of propellant using rocket motors or ion thrusters. This paper presents a method of spacecraft propulsion in which rotational angular momentum is transferred to orbital angular momentum due to the influence of gravity gradient effects. By applying torque to maintain a specific orientation with respect to the gravity gradient, the spacecraft orbital angular momentum is increased or decreased. If momentum wheels or control moment gyroscopes are used, no propellant is required and orbital maneuvers may be performed using solely electrical power. The equations of motion are presented along with analysis of the resulting change in orbital elements, demonstrating the relationship between spacecraft orientation and effective propulsive thrust. Simulation of the equations of motion is used to demonstrate the performance of the proposed technique and is verified by comparing results using both Lagrange dynamics and Newton-Euler dynamics. Although the resulting effects of this approach are small in comparison with conventional propulsion methods, it may be useful in applications such as exploration of asteroids and small moons, deorbiting of decommissioned satellites, or simply to reduce the requirements of a primary propulsion system