Spacecraft Attitude Determination using a Combination of GPS Attitude Sensor and Star Sensor Measurements

摘要

The applications of GPS in space, such as orbit andrnattitude determination, offer several advantages, e.g.rncomplete navigation information on board, low weight,rnvolume and power consumption.rnGPS based attitude determination has many importantrnadvantages like the fast and reliable initial acquisition, thernresistance against spin rates and the fact, that at least twornsatellites for deterministic attitude determination arernalways visible during the mission. GPS could also be usedrnas a safe mode sensor. Therefore GPS based attituderndetermination seems very promising. But due to thernachievable accuracy, implied by the baseline length andrnthe signal noise, a GPS attitude sensor cannot be used forrnmissions where high accurate attitude measurements arernneeded and the baseline lengths are restricted.rnFor these missions, a star sensor will be the adequaternattitude sensor. Star sensors are high accurate, robust andrnhave well established algorithms. The disadvantagesrnusing star sensors are e.g. restricted field of view,rnoperation only at low angular rates, sensor performancerndegradation and sometimes problems with the starrnidentification.rnTaking all these individual advantages and disadvantagesrninto account, the combination of a GPS attitude sensorrnand a star sensor seems extremely promising, becausernsuch a sensor combination can be applied to a broad arearnof missions and their requirements of a high accuraternattitude.rnA study project has therefore been initiated atrnDLR/GSOC, which deals with the development of newrnalgorithms for the combination of a GPS attitude sensorrnand a star sensor and the investigation of the variousrnpossibilities to support each other and therefore improvernthe attitude solution and the range of applicability.rnPreliminary results presented in this paper are obtainedrnfrom an experiment on a turn table with a four antennarnGPS attitude sensor and a star sensor on top of it during arnground night experiment.