The observatory featured four main telescopes in one spacecraft, covering X-rays and gamma rays, including various specialized sub-instruments and detectors.

The CGRO was named after Arthur Compton, an American physicist and former chancellor of Washington University in St. Louis who received the Nobel prize for work involved with gamma-ray physics.

Sudden increases in the LAD rates triggered a high-speed data storage mode, the details of the burst being read out to telemetry later.

A strong burst could result in the observation of many thousands of gamma-rays within a time interval ranging from ~0.1 s up to about 100 s. The Oriented Scintillation Spectrometer Experiment (OSSE) by the Naval Research Laboratory detected gamma rays entering the field of view of any of four detector modules, which could be pointed individually, and were effective in the 0.05 to 10 MeV range.

Each detector had a central scintillation spectrometer crystal of NaI(Tl) 12 in (303 mm) in diameter, by 4 in (102 mm) thick, optically coupled at the rear to a 3 in (76.2 mm) thick CsI(Na) crystal of similar diameter, viewed by seven photomultiplier tubes, operated as a phoswich: i.e., particle and gamma-ray events from the rear produced slow-rise time (~1 μs) pulses, which could be electronically distinguished from pure NaI events from the front, which produced faster (~0.25 μs) pulses.

Because of the requirement for a near coincidence between the two interactions, with the correct delay of a few nanoseconds, most modes of background production were strongly suppressed.

EGRET was developed by NASA Goddard Space Flight Center, the Max Planck Institute for Extraterrestrial Physics, and Stanford University.

The tracks of the high-energy electron and positron created were measured within the detector volume, and the axis of the V of the two emerging particles projected to the sky.

This finally convinced the community that GRB afterglows resulted from highly collimated explosions, which strongly reduced the needed energy budget.

With some controversy, NASA decided in the interest of public safety that a controlled crash into an ocean was preferable to letting the craft come down on its own at random.

[4] It entered the Earth's atmosphere on 4 June 2000, with the debris that did not burn up ("six 1,800-pound aluminum I-beams and parts made of titanium, including more than 5,000 bolts") falling into the Pacific Ocean.