Compton Gamma Ray Observatory
|Compton Gamma Ray Observatory|
NASA's Compton Gamma Ray Observatory takes off from Space Shuttle Atlantis on April 7, 1991, after its use during the STS-37 mission.
|Size:||9.1 m high, 21.3 m span|
|Begin:||April 5, 1991, 14:22 UTC|
|Starting place:||Kennedy Space Center LC-39B|
|Launcher:||Space Shuttle Atlantis|
|Status:||crashed on June 4, 2000|
|Rotation time :||93.6 min|
|Orbit inclination :||28.5 °|
|Apogee height :||453 km|
|Perigee height :||448 km|
The satellite , initially only known as the Gamma Ray Observatory (GRO) , was launched on April 5, 1991 with the STS-37 mission of the Space Shuttle Atlantis . At over 15 tons, it was the heaviest scientific satellite that the space shuttle had ever put into orbit. After a few months it was renamed Compton Gamma Ray Observatory in honor of the physicist and Nobel Prize winner Arthur Holly Compton .
CGRO was the second of four space-based telescopes planned by NASA as part of the “Great Observatory Program”. The other satellites in this program are the Hubble Space Telescope , the Chandra X-Ray Observatory, and the Spitzer Space Telescope .
The CGRO instruments covered a wide range of the electromagnetic spectrum with 20 keV to 30 GeV. The instruments were arranged according to increasing energy:
- Burst and Transient Source Experiment (BATSE)
- This instrument, developed by NASA's Marshall Space Flight Center , searched for gamma-ray flashes in the energy range of 20 to 600 keV . With eight detectors at each corner of the satellite, it could see the entire unobstructed part of the sky.
- Oriented Scintillation Spectrometer Experiment (OSSE)
- Developed by the Naval Research Laboratory , this instrument consisted of four independently movable detectors for the 0.05 to 10 MeV range, optimized for observing rapidly changing sources and the neighboring background.
- Imaging Compton Telescope (COMPTEL)
- This instrument, developed by the Max Planck Institute for Extraterrestrial Physics , SRON Utrecht, ESA and the University of New Hampshire , observed a field of view of one steradian in the energy range from 1 to 30 MeV . Using the Compton effect , the positions of the observed gamma sources could be determined with an accuracy of 5 to 30 arc minutes.
- Energetic Gamma Ray Experiment Telescope (EGRET)
- With this spark chamber developed by the Goddard Space Flight Center , Max Planck Institute for Extraterrestrial Physics and Stanford University for the energy range 20 MeV to 30 GeV, source positions could be determined with an accuracy of about one degree and the energies of the gamma photons with an accuracy of about 15 percent.
Some of the best known results from CGRO include:
- The first sky survey at over 100 MeV energy. With EGRET, 271 sources were discovered.
- A sky map in the emission of radioactive aluminum ( 26 Al) by COMPTEL.
- A total of about 2000 measurements of gamma-ray flashes with BATSE. Their even distribution in the sky indicated that they were not triggered in the Milky Way but in distant galaxies .
- Differentiation of gamma-ray flashes into two classes - long and short.
- Discovery of blazars as the main source of high-energy gamma radiation.
- Detection of weak terrestrial gamma rays from thunderstorms.
The CGRO was well beyond its expected lifespan of five years when on December 6, 1999 one of the gyroscopes for attitude control failed. The loss of another gyroscope would have made the satellite uncontrollable, and in the event of an uncontrolled crash, the risk of death was calculated to be 1: 1000. NASA decided to bring the still functional telescope to a controlled crash over the Pacific , which reduced the risk to about 1:29 million. The mass of CGRO at this point in time was still around 14910 kg. A test ignition of the engines took place on May 28, 2000. On May 31 and June 1, the orbit height was reduced by further braking maneuvers. On June 4, 2000, at 03:56 UTC, a third brake ignition of 21 minutes took place. One orbit later at 05:22 UTC the fourth brake ignition of 30 minutes duration was carried out. This was enough to allow CGRO to enter the earth's atmosphere at around 06:10 UTC. The remaining mass upon reentry was estimated at 14010 kg, of which about 30 to 40 pieces of debris could have reached the water surface. It was the first time that NASA brought down a satellite in a controlled manner.
- GRO in the Encyclopedia Astronautica , accessed on August 1, 2017 (English).
- Richard B. Mrozinski: Entry Debris Field Estimation Methods and Application to Compton Gamma Ray Observatory Disposal. (PDF; 1.1 MB) NASA, accessed on September 24, 2012 (English).
- The Re-Entry of the Compton Gamma Ray Observatory ( Memento of October 15, 2011 in the Internet Archive )
- Justin Ray: Mission Status Center. Spaceflight Now, June 4, 2000, accessed September 24, 2012 .
- William Harwood: NASA space telescope heads for fiery crash into Pacific. Spaceflight Now, May 28, 2000, accessed September 24, 2012 .