An efficient short-arc orbit computation.

Short-arc orbits can be evaluated by means of least squares polynomial approximations. Such orbit computations do not significantly increase the computation time when compared to widely used semi-short-arc techniques which utilize externally generated orbits. The sufficiently high-degree polynomial approximation of the second time derivatives x", ÿ and z" evaluated from a gravitational potential model at regular (two-minute) intervals and averaged initial conditions (position and velocity vectors at the beginning, the middle and the end of a pass) reproduces the U.S. Defense Mapping Agency precise ephemeris of the Navy Navigation Satellites to about 5 cm RMS in each coordinate.