Improving the orbits of GPS block IIA satellites during eclipse seasons Original Research Article

During Sun-Earth eclipse seasons, GPS-IIA satellites perform noon, shadow and post-shadow yaw maneuvers. If the yaw maneuvers are not properly taken into account in the orbit determination process, two problems appear: (1) the observations residuals increase since the modeled position of the satellite’s navigation antenna differs from the true position, and (2) the non-conservative forces like solar radiation pressure or Earth radiation pressure are mismodeled due to the wrong orientation of the satellite’s surfaces in space. In this study we consider the yaw maneuvers for the computation of solar radiation pressure and Earth radiation pressure acting on a box-wing like satellite. Also the computation of the satellite’s navigation antenna position takes into account the yaw maneuvers. Two models are tested for the yaw maneuvers of GPS-IIA satellites, the existing attitude model with nominal yaw rates and an upgraded version based on the real yaw attitude estimated from PPP (Precise Point Positioning) phase residuals. Additionally, for GPS-IIR and GLONASS-M the existing yaw attitude models with nominal yaw rates are tested. Moreover, two models are tested for the orientation of the solar panels of GPS-IIA satellites during yaw maneuvers, one assuming that the panels point as perpendicular as possible to the Sun and the other assuming a specific pitch attitude during the shadow and post-shadow turns. The attitude models of increasing complexity are introduced into the computation of daily orbits based on real GPS+GLONASS tracking data for the years 2007 and 2008. From the solutions including the box-wing model with nominal attitude to the one with the most refined attitude models, the average improvements in the orbits of GPS-IIA satellites during eclipse seasons are quantified as follows: orbit overlap errors decrease from 0.075 to 0.063 m, orbit prediction errors after the first 3–9 h decrease from 0.155 to 0.095 m, and after four days decrease from 6.77 to 3.28 m.