The Gamma-Ray Observatory: An overview

The Gamma-Ray Observatory (GRO) is a 16,000 kg spacecraft containing four instruments which span almost six decades of energy from about 50 keV to about 30 GeV. It will provide the first opportunity to make simultaneous observations over such a broad band of gamma-ray energies. GRO is assembled and undergoing testing prior to its scheduled June 4, 1990 launch aboard the Space Shuttle. The orbit will be circular with an altitude of 450 km and with an inclination of 28 degrees. Data will be recorded at 32 kilobits per second and dumped once per orbit via the Tracking and Data Relay Satellite System (TDRSS). The spacecraft is three-axis stabilized and timing will be maintained to .1 ms. The observing schedule will begin with an all sky survey, consisting of 30 two week pointings, covering the first 15 months of science operations. Following observations will emphasize source studies and deep searches. Originally selected as a Principal Class spacecraft with a two year mission, extension of the mission to six to ten years makes a vigorous Guest Investigator Program both possible and desirable. Such a program will be fully in place by the third year of the mission, with limited opportunities earlier. Each of the four instruments has a capability for observing both gamma-ray bursts and solar flare gamma-rays, and there is some solar neutron capability. Correlated observations with those at other wavelengths is also receiving considerable attention in the mission planning.