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7.1. Hipparcos astrometry satellite
7. SCIENTIFIC SPACE MISSIONS 7.1. HIPPARCOS ASTROMETRY SATELLITE”’
The ESA astrometry satellite Hipparcos has now been fully commissioned, and has begun its routine scanning of the sky using a combination of the satellite’s star mapper and primary detectors. On 1 November 1989, the satellites spin axis was manoeuvred from the Sun-pointing direction to an angle of about 43” from the Sun, around which the spin axis will slowly gyrate throughout the satellite’s lifetime. Hipparcos is a scientific mission developed to determine more than 100 000 star positions with an extremely high accuracy, unattainable from ground observations. By making large numbers of measurements over a period of about three years, astronomers will also be able to determine the way in which the stars are moving though our Galaxy, and their distance from our own solar system. This, the scientists working on the Hipparcos project explain, will dramatically improve our knowledge of the Galaxy and the evolution processes of the stars within it. The satellite, launched from Kourou, French Guyana, into a geostationary transfer orbit on 8 August, failed to reach its nominal geostationary orbit after failure of its apogee boost motor. It was therefore decided to use the satellite in its elliptical orbit to the maximum extent possible, and a revised mission was defined. The orbital period of approximately 10.5 h meant that several ground stations were required to obtain full data coverage. Since the start of the revised mission operations, however, all further operations have proceeded smoothly and the on-board instrumentation has performed entirely normally. ‘Apart from the apogee boost motor failure, the performance of the satellite is generally better than specifications” said ESA Project Manager Dr Hamid Hassan. “The satellite subsystems have performed satisfactorily in the unexpected and more severe environmental conditions. In particular, the optical payload performance appears to be well within specifications. As a result, the expected scientific return of the mission looks more promising than the immediate post-launch assessments indicated, although a definitive statement about the results can only be made after the satellite emerges from the long eclipse season which ends in March 1990”. The last three months have been an intensive period for all those involved with the satellite and its operations. The failure of the satellite to re,ach its nominal orbit involved a considerable effort to prepare for the revised mission, while at the same time performing the necessary satellite operations. “This involved the design and implementation of novel and complex interfaces with the satellite which had to be prepared within a very limited time under very (‘)From ESA News Release No. 46,7 November 1989.
85
di~cult conditions” said Dietmar Heger, the Hipparcos Spacecraft Operations Meager at the European Space Operations Centre (ESOC) in the FRG. “The work involved the concentrated efforts of all ESOC Departments as well as project and industry experts. Many ground segment elements required expansion or modification in order to be able to support the demands of the revised mission”. In the revised mission, orbital coverage will be supplied by a combination of the Odenwald (FRG), Perth (Australia) and Kourou ground stations, together bringing the data coverage to about 80%. In addition, use of a NASA ground station at Goldstone in the USA is also being investigated, which would increase the orbital coverage to about 93%. Over the coming months, the data from the satellite will be stored on magnetic tapes at the ESOC Ground Station, and sent out to the European scientific institutes responsible for the reduction of the satellite data and the production of the final Hipparcos Star catalogue. At the same time, any reduction in electricity generation by the solar cells on board the satellite, which has been predicted to occur in the present orbital environment, will be monitored closely, in order to make a reliable prediction of the functional lifetime of the satellite. The satellite lifetime in the revised orbit is likely to be the limiting factor on the positional accuracy achievable by the Hipparcos mission. Professor Jean Kovalevsky, of the CERGE Obsevatory in Grasse (France), leader of one of the scientific teams that will analyse the data from the satellite, has been looking at the first results sent down from the primary detectors. “The data looks very good” he commented, “very close to the behaviour that had been predicted. It will take some weeks before we can assess the full quality of the data, but we can already say that the design and operations concept of the Hipparcos project appear to be largely validated. Because of the concerns about the lifetime of the satellite, however, our excitement about the instrument and first indications of data quality is somewhat tempered by our concern that this important experiment might not yield the full scientific results expected”.
7.2. INF~RED
SPACE OBSERVANCE
Because it is impossible to observe and study dark objects with a telescope which itself radiates light, Europe’s largest astronomy satellite IS0 has become an enormous technological challenge for the world of science and industry. This satellite will be capable of probing into areas of space where there are temperatures as low as -260°C. For this purpose, however, the instrument itself must be cooled to a temperature of -271”C, if it is to remain ‘dark’ enough: The decision making bodies of ESA finally gave the go-ahead for the Infrared (2JFrom German Research Service Special Science Reports, Special Issue Z/89.
86
The ESA astrometry satellite Hipparcos has now been fully commissioned, and has begun its routine scanning of the sky using a combination of the satellite’s star mapper and primary detectors. On 1 November 1989, the satellites spin axis was manoeuvred from the Sun-pointing direction to an angle of about 43” from the Sun, around which the spin axis will slowly gyrate throughout the satellite’s lifetime. Hipparcos is a scientific mission developed to determine more than 100 000 star positions with an extremely high accuracy, unattainable from ground observations. By making large numbers of measurements over a period of about three years, astronomers will also be able to determine the way in which the stars are moving though our Galaxy, and their distance from our own solar system. This, the scientists working on the Hipparcos project explain, will dramatically improve our knowledge of the Galaxy and the evolution processes of the stars within it. The satellite, launched from Kourou, French Guyana, into a geostationary transfer orbit on 8 August, failed to reach its nominal geostationary orbit after failure of its apogee boost motor. It was therefore decided to use the satellite in its elliptical orbit to the maximum extent possible, and a revised mission was defined. The orbital period of approximately 10.5 h meant that several ground stations were required to obtain full data coverage. Since the start of the revised mission operations, however, all further operations have proceeded smoothly and the on-board instrumentation has performed entirely normally. ‘Apart from the apogee boost motor failure, the performance of the satellite is generally better than specifications” said ESA Project Manager Dr Hamid Hassan. “The satellite subsystems have performed satisfactorily in the unexpected and more severe environmental conditions. In particular, the optical payload performance appears to be well within specifications. As a result, the expected scientific return of the mission looks more promising than the immediate post-launch assessments indicated, although a definitive statement about the results can only be made after the satellite emerges from the long eclipse season which ends in March 1990”. The last three months have been an intensive period for all those involved with the satellite and its operations. The failure of the satellite to re,ach its nominal orbit involved a considerable effort to prepare for the revised mission, while at the same time performing the necessary satellite operations. “This involved the design and implementation of novel and complex interfaces with the satellite which had to be prepared within a very limited time under very (‘)From ESA News Release No. 46,7 November 1989.
85
di~cult conditions” said Dietmar Heger, the Hipparcos Spacecraft Operations Meager at the European Space Operations Centre (ESOC) in the FRG. “The work involved the concentrated efforts of all ESOC Departments as well as project and industry experts. Many ground segment elements required expansion or modification in order to be able to support the demands of the revised mission”. In the revised mission, orbital coverage will be supplied by a combination of the Odenwald (FRG), Perth (Australia) and Kourou ground stations, together bringing the data coverage to about 80%. In addition, use of a NASA ground station at Goldstone in the USA is also being investigated, which would increase the orbital coverage to about 93%. Over the coming months, the data from the satellite will be stored on magnetic tapes at the ESOC Ground Station, and sent out to the European scientific institutes responsible for the reduction of the satellite data and the production of the final Hipparcos Star catalogue. At the same time, any reduction in electricity generation by the solar cells on board the satellite, which has been predicted to occur in the present orbital environment, will be monitored closely, in order to make a reliable prediction of the functional lifetime of the satellite. The satellite lifetime in the revised orbit is likely to be the limiting factor on the positional accuracy achievable by the Hipparcos mission. Professor Jean Kovalevsky, of the CERGE Obsevatory in Grasse (France), leader of one of the scientific teams that will analyse the data from the satellite, has been looking at the first results sent down from the primary detectors. “The data looks very good” he commented, “very close to the behaviour that had been predicted. It will take some weeks before we can assess the full quality of the data, but we can already say that the design and operations concept of the Hipparcos project appear to be largely validated. Because of the concerns about the lifetime of the satellite, however, our excitement about the instrument and first indications of data quality is somewhat tempered by our concern that this important experiment might not yield the full scientific results expected”.
7.2. INF~RED
SPACE OBSERVANCE
Because it is impossible to observe and study dark objects with a telescope which itself radiates light, Europe’s largest astronomy satellite IS0 has become an enormous technological challenge for the world of science and industry. This satellite will be capable of probing into areas of space where there are temperatures as low as -260°C. For this purpose, however, the instrument itself must be cooled to a temperature of -271”C, if it is to remain ‘dark’ enough: The decision making bodies of ESA finally gave the go-ahead for the Infrared (2JFrom German Research Service Special Science Reports, Special Issue Z/89.
86