Orbit analysis and maneuver design for the Geoscience Laser Altimeter System

The Geoscience Laser Altimeter System (GLAS) of the Earth Observing System (EOS) is planned to make ice sheet elevation measurements over Antarctica and Greenland. Measurements of ice sheet elevation distribution will be used to determine the polar ice sheet volume changes and their contributions to global sea level as well as the contribution to Earth's global climate change. Since the laser altimetry of the ice sheet requires highly accurate knowledge of the satellite and since GLAS requires a near circular low altitude orbit, the use of a frozen orbit is suggested to restrict the variations of orbital elements and altitude. The frozen orbit was studied earlier by G. E. Cook and many authors extended his work thereafter. This research includes a new representation with higher even and odd degree zonal harmonics in the frozen orbit analysis to get a complete form of solutions as well as linear, quadratic and cubic polynomial approximations. These analytic solutions are sufficiently accurate to meet the orbit planning requirements for the GLAS mission.; Ice science requires a near-polar orbit for adequate coverage of the ice sheet and a long repeat ground track cycle. Thus the maneuver design for the GLAS orbit needs accurate ground track prediction and propagation including the effects of geopotential, luni-solar, atmospheric drag perturbations and others. One purpose of this research is to obtain analytic ground track prediction and propagation error models that satisfy GLAS mission requirements and orbit control requirements. Based on the atmospheric science and the orbit maneuver analysis, the 11 day repeat orbit is optimal for the calibration and verification phase. Polar science analysis suggests that the 183 day repeat orbit with the 11 day subcycle meets the spatial and temporal sampling requirements during the polar mapping phase. The University of Texas Orbit Processor (UTOPIA) software is used to achieve estimation of new initial conditions for more complete force model for both 11 day and 183 day repeat orbits.