The Compton Gamma Ray Observatory (CGRO), the second and heaviest of NASA’s Great Observatories was launched. The four instruments onboard were much larger and more sensitive than instruments in the past. A little less than a year into its mission, two tape recorders onboard CGRO failed, which restricted downlinks of scientific data to real time only. CGRO was only able to relay about 50% of its data because the antennas on the GRO could not point to the Tracking and Data Relay Satellite (TDRS) which were in view all of the time and there was still 15% of the GRO orbit that TDRS could not see (known as the Zone of Exclusion).
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