# Compton Gamma Ray Observatory

> former NASA space observatory

**Wikidata**: [Q41519](https://www.wikidata.org/wiki/Q41519)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Compton_Gamma_Ray_Observatory)  
**Source**: https://4ort.xyz/entity/compton-gamma-ray-observatory

## Summary
The **Compton Gamma Ray Observatory (CGRO)** was a former NASA space observatory designed to detect gamma rays from celestial sources. Launched in 1991 aboard the Space Shuttle *Atlantis*, it was the second of NASA's Great Observatories program and operated until its controlled deorbit in 2000.

## Key Facts
- **Launch Date**: April 5, 1991, aboard Space Shuttle *Atlantis* (STS-37 mission).
- **Mass**: 15,620 kg at launch.
- **Dimensions**: 9.1 meters long, 4.6 meters wide (spacecraft bus), with a 21.3-meter solar array span.
- **Operator**: Managed by NASA's **Goddard Space Flight Center**.
- **Mission Duration**: Operated from 1991 to 2000, ending with a controlled atmospheric re-entry on June 4, 2000.
- **Named After**: Physicist **Arthur Holly Compton**, a Nobel laureate in physics.
- **Part of**: NASA's **Great Observatories program**, alongside Hubble, Chandra, and Spitzer.
- **Power Source**: Two solar arrays (4,500 watts) and three nickel–cadmium batteries.
- **Wavelength Range**: Sensitive to gamma rays from **60 attometers to 40 picometers**.

## FAQs
### Q: What was the purpose of the Compton Gamma Ray Observatory?
A: CGRO was designed to study gamma rays—high-energy electromagnetic radiation—from cosmic sources like black holes, pulsars, and supernovae. It provided unprecedented insights into violent astrophysical phenomena.

### Q: How was the Compton Gamma Ray Observatory launched?
A: It was deployed by the Space Shuttle *Atlantis* during mission STS-37 on April 5, 1991, from Kennedy Space Center Launch Complex 39B.

### Q: Why was the Compton Gamma Ray Observatory deorbited?
A: Due to a gyroscope failure, NASA opted for a controlled deorbit on June 4, 2000, to ensure safe re-entry over the Pacific Ocean, avoiding populated areas.

### Q: What instruments did the Compton Gamma Ray Observatory carry?
A: It carried four main instruments, including the **Energetic Gamma Ray Experiment Telescope (EGRET)**, which detected high-energy gamma rays.

### Q: What replaced the Compton Gamma Ray Observatory?
A: It was succeeded by the **Chandra X-ray Observatory**, another NASA Great Observatory focused on X-ray astronomy.

## Why It Matters
The Compton Gamma Ray Observatory revolutionized gamma-ray astronomy by providing the first comprehensive survey of the sky in this high-energy spectrum. Before CGRO, gamma-ray observations were limited and often serendipitous. Its discoveries included identifying gamma-ray bursts as extragalactic events, mapping the distribution of cosmic gamma-ray sources, and detecting emissions from supermassive black holes. CGRO's data laid the foundation for later missions like Fermi Gamma-ray Space Telescope, advancing our understanding of the universe's most energetic processes. Its legacy endures in modern astrophysics, shaping theories on dark matter, neutron stars, and the early universe.

## Notable For
- **First dedicated gamma-ray observatory**: CGRO was the first space telescope designed solely for gamma-ray astronomy.
- **Discovery of gamma-ray bursts' cosmic origin**: Proved these bursts originated far beyond the Milky Way.
- **Largest payload deployed by Space Shuttle**: At 15,620 kg, it was one of the heaviest scientific satellites launched at the time.
- **Part of NASA's Great Observatories**: Alongside Hubble, Chandra, and Spitzer, it covered a unique portion of the electromagnetic spectrum.
- **Controlled deorbit**: One of the first large satellites intentionally deorbited to mitigate space debris risks.

## Body
### Overview
The **Compton Gamma Ray Observatory (CGRO)** was a NASA space telescope operational from 1991 to 2000. It was the second of NASA's **Great Observatories program**, following the Hubble Space Telescope, and focused exclusively on gamma-ray astronomy.

### Launch and Deployment
- **Launch**: April 5, 1991, via Space Shuttle *Atlantis* (STS-37).
- **Deployment**: Released into low Earth orbit on April 7, 1991.
- **Orbit**: Circular orbit at ~450 km altitude, inclined at 28.5 degrees.

### Technical Specifications
- **Mass**: 15,620 kg (launch weight).
- **Dimensions**:
  - Length: 9.1 meters.
  - Width: 4.6 meters (spacecraft bus).
  - Solar array span: 21.3 meters.
- **Power**: Two solar arrays generating 4,500 watts, supplemented by three nickel–cadmium batteries.
- **Instruments**:
  - **BATSE (Burst and Transient Source Experiment)**: Detected gamma-ray bursts.
  - **OSSE (Oriented Scintillation Spectrometer Experiment)**: Studied nuclear gamma-ray lines.
  - **COMPTEL (Imaging Compton Telescope)**: Mapped gamma-ray sources.
  - **EGRET (Energetic Gamma Ray Experiment Telescope)**: Observed high-energy gamma rays.

### Scientific Achievements
- **Gamma-Ray Bursts**: Confirmed their extragalactic origin, revolutionizing astrophysics.
- **Black Hole Studies**: Detected gamma-ray emissions from active galactic nuclei.
- **Pulsars and Supernovae**: Identified gamma-ray emissions from neutron stars and stellar explosions.
- **Cosmic Diffuse Gamma-Ray Background**: Mapped the distribution of gamma rays across the universe.

### End of Mission
- **Deorbit**: June 4, 2000, due to gyroscope failure.
- **Re-entry**: Controlled descent over the Pacific Ocean to avoid debris hazards.

### Legacy
CGRO's data remains foundational in gamma-ray astronomy. Its successor, the **Fermi Gamma-ray Space Telescope** (launched 2008), built upon its discoveries. The observatory's name honors **Arthur Holly Compton**, whose work on gamma-ray scattering earned him the 1927 Nobel Prize in Physics.

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## References

1. [Source](https://space.jpl.nasa.gov/msl/QuickLooks/groQL.html)
2. [Source](https://space.skyrocket.de/doc_sdat/cgro.htm)
3. Virtual International Authority File
4. Faceted Application of Subject Terminology
5. Integrated Authority File
6. Jonathan's Space Report
7. [Source](http://cossc.gsfc.nasa.gov/)
8. Freebase Data Dumps. 2013
9. [Source](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1991-027B)