Generation of an Optimum Target Trajectory for the TerraSAR-X Repeat Observation Satellite

Abstract

TerraSAR-X (TS-X) is a new generation, high resolution synthetic aperture radar (SAR) satellite for scientific and commercial applications. The launch of the satellite into a sun-synchronous dusk-dawn orbit with an 11-day repeat period is planned on top of a Russian DNEPR-1 rocket for 2006. The requirement for the TSX orbit is that the spacecraft shall fly over the same regions following identical flight paths relative to ground. The most important orbit control requirement is to maintain the satellite osculating orbit within a maximum absolute distance of 250 m from a target orbit. For dedicated operations this prescribed maximum distance is lowered to 10 m. This paper addresses the design and computation of the target path, the so-called reference orbit. The high accuracy orbit control requirements pose tight constraints on the generation of the target trajectory. Due to the high non-linearity of the problem, former strategies based solely on analytical calculus are not accurate enough. Instead the combination of numerical perturbation analysis and sequential optimization is shown to be more effective. It enables automation of the analysis and can be easily applied to all Earth remote sensing satellites.