component of F perpendicular to r is included.) For situations where propellant consumption may be a problem (such as long-duration satellites or space stations), alternative means may be used to provide the control torque, such as reaction wheels or control moment gyroscopes. Notes References Sidi, M.J. "Spacecraft Dynamics & Control. Cambridge, 1997. Thomson, W.T. "Introduction to Space Dynamics." Dover, 1961. Wertz, J.R. "Spacecraft Attitude Determination and Control." Kluwer, 1978. Wiesel, W.E. "Spaceflight Dynamics." McGraw-Hill, 1997. Astrodynamics Spaceflight concepts