Combined radiation pressure and thermal modelling of complex satellites: Algorithms and on-orbit tests

In an era of high resolution gravity field modelling the dominant error sources in spacecraft orbit determination are non-conservative spacecraft surface forces. These forces can be difficult to characterise a priori because they require detailed modelling of: spacecraft geometry and surface properties; attitude behaviour; the spatial and temporal variations of the incident radiation and particle fluxes and the interaction of these fluxes with the surfaces. The conventional approach to these problems is to build simplified box-and-wing models of the satellites and to estimate empirically factors that account for the inevitable mis-modelling. Over the last few years the authors have developed a suite of software utilities that model analytically three of the main effects: solar radiation pressure, thermal forces and the albedo/earthshine effects. The techniques are designed specifically to deal with complex spacecraft structures, no structural simplifications are made and the method can be applied to any spacecraft. Substantial quality control measures are used during computation to both avoid and trap errors. The paper presents the broad basis of the modelling techniques for each of the effects, and gives the results of recent tests applied to GPS Block IIR satellites and the low Earth orbit satellite altimeter JASON-1.