Space Shuttle Atlantis
The European Retrievable Carrier (EURECA) was launched July 31, 1992 by the Space Shuttle Atlantis, and put into an orbit at an altitude of 508 km. It began its scientific mission on August 7, 1992. EURECA was retrieved on July 1, 1993 by the Space Shuttle Endeavour and returned to Earth. On board was the WATCH or Wide Angle Telescope for Cosmic Hard X-rays instrument. The WATCH instrument was sensitive to 6-150 keV photons. The total field of view covered 1/4 of the celestial sphere. During its 11-month lifetime, EURECA tracked the Sun and WATCH gradually scanned across the entire sky. Some 2 dozen known X-ray sources were monitored—some for more than 100 days—and a number of new X-ray transients were discovered.