eir standard errors and correlation coefficients were derived in the process;
- since the number of independent geometrical observations per object was large (typically of order 30) compared with the number of unknowns for the standard model (five astrometric unknowns per star) astrometric solutions not complying with this simple five-parameter model, could be expanded to take into account the effects of double or multiple stars, or non-linear photocentric motions ascribed to unresolved astrometric binaries;
- a somewhat larger number of actual observations per object, of order 110, provided accurate and homogeneous photometric information for each star, from which mean magnitudes, variability amplitudes, and in many cases period and variability type classification could be undertaken.
Development, launch and operations
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The Hipparcos satellite was financed and managed under the overall authority of the European Space Agency. The main industrial contractors were Matra Marconi Space (now EADS Astrium) and Alenia Spazio (now Thales Alenia Space).
Other hardware components were supplied as follows: the beam-combining mirror from REOSC at Saint Pierre du Perray; the spherical, folding and relay mirrors from Carl Zeiss AG in Oberkochen; the external straylight baffles from CASA in Madrid; the modulating grid from CSEM in Neuchâtel; the mechanism control system and the thermal control electronics from Dornier Satellite Systems in Friedrichshafen; optical filters, the experiment structures and the attitude and orbit control system from Matra Marconi Space in Vélizy; instrument switching mechanisms from Oerlikon-Contraves in Zurich; the image dissector tube and photomultiplier detectors assembled by the Dutch Space Research Organisation, SRON in The Netherlands; the refocusing assembly mechanism designed by TNO-TPD in Delft; the electrical power subsystem from British Aerospace in Bristol; the structure and reaction control system from Daimler-Benz Aerospace in Bremen; the solar arrays and thermal control system from Fokker Space System in Leiden; the data handling and telecommunications system from Saab Ericsson Space in Gothenburg; and the apogee boost motor from SEP in France. Groups from the Institut d'Astrophysique in Liege and the Laboratoire d'Astronomie Spatiale in Marseille contributed optical performance, calibration and alignment test procedures; Captec in Dublin and Logica in London contributed to the on-board software and calibration.
The Hipparcos satellite was launched (with the direct broadcast satellite TV-SAT2 as co-passenger) on an Ariane 4 launch vehicle, flight V33, from Kourou, French Guiana, on 8 August 1989. Launched into a geostationary transfer orbit, the Mage-2 apogee boost motor failed to fire, and the intended geostationary orbit was never achieved. However, with the addition of further ground stations, in addition to the primary ground station at Odenwald in Germany, the satellite was successfully operated in its geostationary transfer orbit for almost 3.5 years. All of the original mission goals were, eventually, exceeded.
The satellite was operated by the ESA operations control centre at ESOC, Darmstadt (Germany).
Including an estimate for the scientific activities related to the satellite observations and data processing, Hipparcos mission cost some 600 MEuro (2000 economic conditions), and its execution involved some 200 European scientists and more than 2000 individuals in European industry.
Hipparcos Input Catalogue
The satellite observations relied on a pre-defined list of target stars. Stars were observed as the satellite rotated, by a sensitive region of the image dissector tube detector. This pre-defined star list formed the Hipparcos Input Catalogue: each star in the final Hipparcos Catalogue was contained in the Input Catalogue. The Input Catalogue was compiled by the INCA Consortium over the period 1982—89, finalised pre-launch, and published both digitally and in printed form.  Although fully superseded by the sate