An "Invariant" Property of Satellite Motion in a Dissipative Medium

A simple expression is derived for near-circular orbits which relates die difference in instantaneous angular momentum of a satellite as observed at two different times from the same station to the dissipative perturbing forces which acted on the satellite during that time interval. This expression is valid for an arbitrarily asymmetric gravity field. Possible applications to the measurement of very short-term atmospheric density variations and to the improvement of knowledge about the earth's shape and gravity field are described.