In-Orbit Status of the Hipparcos Astrometry Mission
The Hipparcos satellite was successfully launched by Ariane 4 flight 33, from French Guyana, on 8 August 1989. However, the apogee boost motor, designed to place the satellite into its intended geostationary orbit, failed to function, and the satellite was left in a highly elliptical transfer orbit. After a perigee raising manoeuvre, using the hydrazine propulsion system, the orbital parameters are approximately: apogee 35900 km, perigee 526 km, eccentricity 0.72, inclination 6.8°, orbital period 10h 40m.
Operational procedures have had to be revised during the first weeks of satellite operations, due to the non-nominal orbit. Commissioning and calibrations have taken longer than foreseen because of the operational difficulties and observational overheads, but routine observations commenced on 27 November. The essential differences between the nominal and the present missions are that observations can only be conducted for about 30–40 per cent of real time in the present mission, and the fact that the actual lifetime of the mission is still rather uncertain, and possibly somewhat shorter than anticipated. This paper gives a summary of the present satellite status, measurement results obtained so far, and in indication of the scientific goals that may be achievable with the present mission.
KeywordsOrbital Period Radiation Belt Solar Array Background Count Rate Reference Star
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