THE HIPPARCOS MISSION - 4 YEARS AFTER LAUNCH

For Hipparcos, launched in August 1989, one setback - the failure of t he apogee boost motor - threatened to obliterate the years of thorough scientific and technical preparations leading up to the launch. Now, following the redesign of the mission operations in 1989, and a contin uous determination to maintain the flow of high-quality scientific obs ervations, ESA's astrometry satellite has completely fulfilled its ori ginal mission objectives, and is close to reaching its fourth year in orbit. The vast on-ground data analysis effort, a collaboration of Eur opean scientists from some 30 institutes, is proceeding well and is pr oviding information that is set to give a remarkable new perspective t o our understanding of the structure, composition, and evolution of ou r Galaxy.