******************************************************* * A V A R U U S U U T I S I A * * April 3, 1990 * * Toimittanut : Kari A. Kuure * ******************************************************* Press Release No 9 Paris, 27 March 1990 Hipparcos satellite survives the long eclipse season The ESA astrometry satellite HIPPARCOS, which attracted great attention in August 1989 when it failed to reach its allocated geostationary orbit after launch, has emerged successfully from a further critical test of its on-board control systems. "Soon after the satellite became trapped in its highly elliptical tranfer orbit, we realised that the power system would face a crucial test around mid-March, when the satellite would experien- ce very long solar eclipses during which Hipparcos remained in the Earth's shadow" says Dr Hamid Hassan, Hipparcos project manager. Indeed during a three week period, the solar arrays were illuminated for a much shorted interval of time than had been foreseen in its nominal circular orbit, and the satellite had to survive long intervals each day solely on its battery power. As the maximum eclipse duration, of about 105 minutes on 16 March, approached, careful contingency plans were at the ESA operations control centre at ESOC, near Darmstadt, FRG, to shut down elements of the payload so that the power drain on the batteries would not be excessive. The power margins on the spacecraft were such that the satellite passed the maximum eclipses with a margin of barely 5 minutes, allowing the scien- tific measurements to proceed without interruption and guarante- eing continued operation of Hipparcos. The same week saw the coming on line of the fourth ground sation to be include into the Hipparcos ground station tracking network. The NASA Goldstone station in the Mohave Desert, California, now supplements the operational sations at Darmstadt, Perth ( Austra- lia) and the CNES station at Kourou, French Guiana. ESA and NASA personnel gave high priority to this task, which improves the amount of useful data that can be collected from the satellite, bringing the Goldstone station into the network two weeks before the original target date. The ESA Project Scientist, Dr Michael Perryman, speaking from the Agency's research centre in the Netherlands, remains cautiously optimistic that the Hipparcos project will be a success. "We have since November that the technology and system concept underlying the Hipparcos mission have been fully demonstrated. With the succesful emergence from the long eclipse season, and good prospects that the satellite can survive for another two and half years, the original scientific goals of the mission may still be within our grasp". For further information, please contact: Beatrice Lacoste Tel: (33.1)42.73.71.55