Gamma was a Soviet-French gamma-ray observatory launched on 11 July 1990. It circled Earth at an altitude of 375 kilometres and an inclination of 51.6 degrees, operating for about two years. Three telescopes aboard the spacecraft could be pointed together at a single source, allowing observations across different energy ranges.
Gamma-1, the main telescope, used scintillation counters and a gas Cerenkov counter to detect gamma rays from 50 MeV to 6 GeV. A star tracker was intended to improve its pointing accuracy, but a power failure in a spark chamber left the instrument with an angular resolution of about 10 degrees for most of the mission. Disk-M detected radiation from 20 keV to 5 MeV, but stopped working shortly after launch. Pulsar X-2 observed a lower-energy range of 2–25 keV.
The mission examined the Vela Pulsar, the Galactic Center, Cygnus X-1, Hercules X-1 and the Crab Nebula. Its telescopes also measured the Sun during peak solar activity.
Gamma’s origins reached back to 1965, when it was imagined as part of the Soviet Cloud Space Station, later developed into plans for the Multi-module Orbital Complex. Work began in 1972, and the project became a joint venture with France in 1974. As Soviet space-station plans were revised and the original complex was canceled, Gamma’s role changed. By the time its production was authorized in 1979, the observatory had been redesigned as a free-flying spacecraft rather than a station module. A launch planned for 1984 was repeatedly delayed until 1990. Gamma’s story joined ambitious scientific goals to the shifting architecture of Soviet spaceflight.