Satellite orbit error due to geopotential model error using perturbation theory: Applications to ROCSAT-2 and COSMIC missions

A program in FORTRAN 77 is designed to compute satellite orbit error due to geopotential model error. The program is self-contained and is based on an approximate analytical orbital theory that describes the radial, along-track and cross-track positional perturbations of a satellite in a near-circular orbit. Use of the approximate formula reduced programming effort in computing eccentricity functions and the transformation coefficients from Keplerian perturbations to radial, along-track and cross-track perturbations. With this program, the RMS orbit errors due to the EGM96 model error are estimated to be 0.56 m for ROCSAT-2, 64.09 m for COSMIC at a 400-km altitude, and 1.69 m for COSMIC at a 800-km altitude, respectively. The EGM96 model will yield an orbital accuracy consistent with the ground resolution of ROCSAT-2's optical camera, but will not yield the required sub-meter level orbital accuracy for COSMIC in the operational phase, which is for retrieving meteorological data.