Hipparcos

Hipparcos was ESA's pioneering space astrometry mission, measuring stellar positions, distances, motions, and brightness. A slowly rotating telescope repeatedly compared widely separated stars, building a connected framework of angular measurements across the sky. Although its apogee-boost motor failed and left it in an elongated orbit, revised operations recovered a successful observing mission from November 1989 to March 1993. Its observations became the Hipparcos and Tycho catalogues and provided a foundation for later precision mapping by Gaia.