There is an interaction between gravitational tidal forces and the instantaneous moment of inertia of any massive extended body. A mechanism that changes the altitude of a spacecraft orbiting a central mass by periodically changing its instantaneous moment of inertia tensor is discussed. This can be achieved most simply by connecting two bodies with a tether of adjustable length and does not rely on any chemical propellant. By using a series of reasonable approximations, a formula for the rate of change of height is given in terms of accessible data. This formula predicts that by suitably varying the length of a 50 km connecting tether a connected system can rise at about 300 m an hour in low earth orbit. © 2002 Elsevier Science Ltd. All rights reserved.
Gratus, J., & Tucker, R. (2003). An improved method of gravicraft propulsion. Acta Astronautica, 53(3), 161–172. https://doi.org/10.1016/S0094-5765(02)00202-3