HIPPARCOS and the Space Telescope: Astrophysical implications of two complementary astrometric projects

Hipparcos project (High Precision Parallax Collecting Satellite) is described in reference to its association with the Space Telescope. The astrometric programs of Hipparcos and the Space Telescope are complemenary not only from a purely astrometric point of view, but also for their astrophysical implications. The Space Telescope can perform a limited number of measurements mainly on selected faint stars in narrow fields while the main results of Hipparcos can be a complete survey up to n_B about 9 and very accurate measurements of the brightest stars (m_B 6). The basic set of observations of Hipparcos can be extended by the Space Telescope of fainter and/or more distant stars.