Comparison of ENVISAT's attitude simulation and real optical and SLR observations in order to refine the satellite attitude model

摘要

The Astronomic Institute of the University of Bern (AIUB) in cooperation with other three partners is involved in an ESA study dedicated to the attitude determination of large spacecraft and upper stages. Two major goals are defined. First is the long term prediction of tumbling rates (e.g. 10 years) for selected targets for the future Active Debris Removal (ADR) missions. Second goal is the attitude state determination in case of contingencies, when a short response time is required between the observations themselves and the attitude determination. One of the project consortium partners, Hypersonic Technology Goettingen (HTG), is developing a highly modular software tool ?OTA to perform short- (days) to long-term (years) propagations of the orbit and the attitude motion of spacecraft in space. Furthermore, ?OTA's post-processing modules will generate synthetic measurements, e.g. light curves, SLR residuals and Inverse Synthetic Aperture Radar (ISAR) images that can be compared with the real measurements. In our work we will present the first attempt to compare real measurements with synthetic measurements in order to estimate the attitude state of tumbling satellite ENVISAT from observations performed by AIUB. We will shortly discuss the ESA project and tOTA software tool. We will present AIUB's ENVISAT attitude state determined from the SLR ranges acquired by the Zimmerwald SLR station. This state was used as the initial conditions within the ?OTA software. Consequently the attitude of satellite was predicted by using ?OTA and compared with the real SLR residuals, as well with the high frame-rate light curves acquired by the Zimmerwald 1 -m telescope.