Compton Gamma Ray Observatory
The gamma-ray sky's first long-duration eye
Compton was the second of NASA's four Great Observatories, the gamma-ray counterpart to Hubble. At 17 tonnes it was the heaviest astrophysics payload the Space Shuttle had ever lifted, carried to orbit by Atlantis on STS-37 in April 1991.
Its four instruments together covered six orders of magnitude in energy — from 30 keV to 30 GeV — and let astronomers see the universe at wavelengths that never reach the ground. BATSE's all-sky monitor caught a gamma-ray burst roughly once a day for nine years, and proved that those bursts come from cosmological distances, not from inside our own galaxy.
After a gyroscope failed in December 1999, NASA judged the risk of an uncontrolled re-entry of a 17-tonne spacecraft too great, and on 4 June 2000 Compton was deliberately deorbited into the Pacific Ocean — ending nine years of gamma-ray science.
Mission timeline
- 1991 · Apr 5Launch
STS-37 (Atlantis) deploys Compton into a 450 km orbit — the heaviest astrophysics payload ever flown.
- 1991 · AprSpacewalk to free antenna
Astronauts Jay Apt and Jerry Ross perform an unscheduled EVA to manually unjam the high-gain antenna boom.
- 1991 · MayFirst gamma-ray burst detection
BATSE catches its first burst within weeks of activation — and quickly racks up roughly one per day.
- 1992BATSE all-sky distribution
Bursts are isotropic — they come from no preferred direction. This kills the galactic-origin theory and points to cosmological distances.
- 1993 · OctReboost
Orbital altitude raised to 450 km to fight atmospheric drag and extend the mission.
- 1997 · AprFirst EGRET catalog
EGRET's all-sky gamma-ray survey at >100 MeV — the catalog of bright sources still used as the foundation for Fermi today.
- 1999 · Dec 6Gyro failure
One of three gyroscopes fails. NASA decides a controlled deorbit is safer than risking the loss of a second gyro and an uncontrolled re-entry.
- 2000 · Jun 4Controlled deorbit
Four engine burns drop Compton into a remote stretch of the Pacific Ocean — the deliberate end of a Great Observatory.
Active instruments
- Burst and Transient Source Experiment
All-sky monitor for gamma-ray bursts and transients (20–600 keV) — eight detectors, one at each corner
- Oriented Scintillation Spectrometer Experiment
Pointed spectrometer for solar flares and compact sources (50 keV – 10 MeV)
- Imaging Compton Telescope
Mid-energy gamma-ray imager (0.75–30 MeV) — the only instrument to map MeV gamma-rays at high resolution
- Energetic Gamma Ray Experiment Telescope
High-energy survey instrument (20 MeV – 30 GeV) — produced the first all-sky GeV catalog
Headline discoveries
BATSE's all-sky map showed bursts come from every direction equally — ruling out an origin inside our own galaxy and proving they happen across the observable universe.
EGRET produced the first all-sky census of >100 MeV gamma-ray sources — blazars, pulsars, and an unidentified background that took decades to start resolving.
COMPTEL mapped the 1.8 MeV line from radioactive aluminium-26 across the Milky Way — the first direct evidence of ongoing nucleosynthesis in our galaxy.
