Launch of Hipparcos

Hipparcos was a satellite of the European Space Agency, launched on an Ariane 4 rocket, that was the first space mission devoted to astrometry, the precise measurement of the positions and motions of stars. Its name is an acronym for High Precision Parallax Collecting Satellite, and also refers to the ancient Greek astronomer Hipparchus. A failure of its apogee motor left it in an elliptical orbit instead of its planned geostationary one, but engineers adapted the operations and it worked for about three years. The mission produced the Hipparcos Catalogue of more than a hundred thousand stars with unprecedented precision, as well as the larger Tycho Catalogue. The data improved estimates of the distances and ages of stars and of the cosmic distance scale. Its successor is the Gaia mission.

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