Compton Gamma Ray Observatory

  • FLORIDA TODAY Space Online, June 5, 2000: Scientists mourn loss of Compton observatory
  • BBC News, June 4, 2000: Satellite crashes into Pacific
  • ABC NEws, June 4, 2000: Shower of Heavy Metal
  • Spaceflight Now, June 4, 2000: A Fiery Goodbye to Compton Gamma Ray Observatory

    Goddard Space Flight Center

    June 4, 2000


    NASA's Compton Gamma Ray Observatory re-entered the Earth's atmosphere at approximately 2:10 a.m. EDT on June 4, according to calculations made by controllers at NASA's Goddard Space Flight Center, Greenbelt, Md., in coordination with the U.S. Space Command's Control Center.

    As planned, pieces of the observatory that survived the re-entry landed in the Pacific Ocean approximately 2,400 miles (3,862 km) southeast of Hawaii.

    The fourth and final burn needed to re-enter NASA's Compton Gamma Ray Observatory was initiated at 1:22 a.m. EDT on June 4. Compton's Attitude Control thrusters and Orbit Adjust thrusters were fired for 30 minutes.

    After the failure of one of Compton's three gyroscopes, NASA decided to bring the satellite back via a controlled reentry. NASA determined that it was much safer to bring the satellite back now to safe guard against further system failures in the spacecraft that might hinder a controlled reentry.

    "This was a bittersweet day for NASA," said Al Diaz, Director of the Goddard Space Flight Center. "The end of the Compton Gamma Ray

    Observatory mission marks the end of a remarkable spacecraft. Compton left a legacy of outstanding science and revolutionized our knowledge of the gamma ray sky. And while no one at NASA is ever happy to see the end of a science mission, prolonging this mission would have posed an unacceptable and increasing risk to human life. This was an extraordinarily complex task, involving both operations and engineering proficiency. I'm proud of this team and the job they did. They understood the significance of this task, and they performed it flawlessly."

    Compton spent nine productive years in orbit. Engineers began planning for the Observatory's reentry in April 1999 when gyroscope #3 first began experiencing problems. By the time the gyro actually failed in December 1999, engineers had devised a number of deorbit scenarios. Engineers at Goddard, assisted by their counterparts at the Johnson Space Center in Houston, spent the past five months designing a reentry plan to safely deorbit the CGRO spacecraft.

    A total of four burns were used to gradually lower the spacecraft's orbit. The first re-entry burn was conducted on May 30, and a second burn on May 31. At midnight on June 4, controllers fired CGRO's primary thrusters for a third time bringing spacecraft's low point to within 92miles (148 km) of the Earth's surface.

    NASA and international space agencies plan several upcoming missions to continue where Compton left off. The Gamma-ray Large Area Space Telescope (GLAST) is a proposed new high-energy gamma-ray mission to identify and study nature's highest energy particle accelerators. GLAST will be 30 times more sensitive than the Energetic Gamma Ray Experiment Telescope (EGRET) onboard the Compton Gamma Ray Observatory. Swift will be the first mission to focus on studying the newly-discovered afterglow from gamma ray bursts. Swift's rapid repointing capability will enable high-precision X-ray and optical positions to be determined and relayed to the ground for use by a network of dedicated observers at large telescopes.

    The Compton Gamma Ray Observatory was the second of NASA's Great Observatories and the gamma-ray equivalent to the Hubble Space Telescope and the Chandra X-ray Observatory. Compton was launched aboard the Space Shuttle Atlantis in April 1991, and at 17 tons, was the largest astrophysical payload ever flown at that time.

    NEWSALERT: Saturday, June 3, 2000 @ 0851 GMT

    The latest news from Astronomy Now and Spaceflight Now


    On the brink of destruction, NASA's Compton Gamma Ray Observatory is circling Earth for the final times today as controllers prepare to send the crippled craft crashing into Pacific Ocean early Sunday.

    We will provide a live streaming video broadcast of NASA TV coverage:

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    NASA controllers have changed the re-entry time for the Compton Observatory so that it will re-enter the atmosphere 90 minutes earlier than previously planned on Sunday, and drop into a different location in the Pacific Ocean. The de-orbit burn will occur at 1:30am EDT (0530 GMT) and Compton will hit the water at approximately 2:20 EDT (0620 GMT).

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    The Compton Gamma Ray Observatory (CGRO) is now in its final days as an orbiting satellite. The 9-year-old spacecraft is due to reenter the atmosphere Sunday, June 4th, and splash into the Pacific Ocean approximately 4,000 km southeast of Hawaii. CGRO is so large that several dozen large pieces could survive the fiery reentry and strike the water at some 300 kilometers per hour. The probable impact zone is centered on the equator and measures 25 by 1,500 km.

    Flight controllers are bringing down the satellite in steps, using four engine firings to lower the spacecraft's orbit until its closest point is within the atmosphere. The first two burns occurred on May 30th and 31st. The final two will happen on the day of reentry. Impact is expected at 6:20 Universal Time (2:20 a.m. EDT) Sunday.

    The satellite is being destroyed because mission guidelines dictate that, should one of the spacecraft's three gyroscopes fail, as happened last December 19th, the mission would be terminated. The spacecraft could still be controlled with two gyroscopes but would be uncontrollable should a second unit fail. In March, Edward J. Weiler, NASA's Associate Administrator for the Office of Space Science, explained that there was a 10 percent chance that a second gyro would fail during the next three years. If the spacecraft were to plummet to Earth out of control, it would pose a 1-in-1,000 chance of causing a human fatality.

    CGRO's mission was nominally for 5 years, but it has provided valuable data for nearly 9 years. See the July issue of Sky & Telescope (page 48) for an overview of the spacecraft's mission and scientific findings. News

    Friday 02 June 2000

    Compton's Deorbit Puts Jets and Ships at Risk

    If all goes well when NASA deep-sixes its ailing astronomical satellite, the bus-size spacecraft will fall harmlessly into the eastern Pacific Ocean.

    Full story

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    NASA fired the maneuvering rockets of the Compton Observatory to begin its final mission: a fiery descent through the Earth's atmosphere. The firing occurred late Tuesday evening, and dropped the spacecraft's altitude from 510 km down to 350 km. The rockets will fire again early Sunday before dropping the spacecraft into the Pacific Ocean somewhere between Hawaii and Mexico.

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    NASA Headquarters, Washington, DC
    Goddard Space Flight Center, Greenbelt, MD

    May 26, 2000


    On Sunday, June 4, the successful nine-year mission of the Compton Gamma Ray Observatory (CGRO) will end when NASA redirects the spacecraft into Earth's atmosphere. Debris from the controlled re-entry is expected to fall in a remote area of the Pacific Ocean, approximately 2,500 miles southeast of Hawaii.

    NASA controllers will fire CGRO's thrusters four times to lower the observatory's orbit. After each burn, mission trackers at Goddard Space Flight Center, Greenbelt, MD, will determine the observatory's exact position and, if necessary, adjust the descent. The engine burns will occur at:

    Recorded status reports will be available after each burn on the Goddard Audio News Service (301/286-NEWS). Status reports will be posted the following morning to:

    Live coverage on NASA Television of the deorbit activities will begin at 1 a.m. EDT June 4 and conclude at the close of the 6 a.m. briefing.

    NASA Television coverage will include science highlights, re- entry animation and commentary on the re-entry activities by Dr. Neil Gehrels, CGRO project scientist. A NASA fact sheet on the re-entry can be found at:

    Unlike most satellites, Compton is too large to burn up entirely in the atmosphere during re-entry. More than 6 tons (12,400 pounds) of metal debris is expected to fall to the Earth's surface. The debris fragments will range in size from the size of a small stone to several hundred pounds or kilograms.

    To ensure the safety of aircraft and surface vessels in or near the target impact area, Debris Hazard Warning Areas were established well away from land. Shipping and air traffic in the area have been notified to ensure that craft will not be in the vicinity of the impact area.

    NASA decided before Compton was launched that, due to the observatory's size, it would be returned to Earth by controlled re-entry when the mission was over. Extensive research showed that it was significantly safer to perform a controlled re-entry than any other method of dealing with the satellite.

    NASA Television is broadcast on GE-2, transponder 9C located at 85 degrees West longitude, with vertical polarization. Frequency is on 3880.0 MHz, with audio on 6.8 MHz.


    30 mei 2000

    Eervol zeemansgraf voor Nederlands ruimte-instrumentarium

    Zondag 4 juni zal NASA's Compton-observatorium na negen jaar succesvol functioneren terugkeren in de aardse atmosfeer, om in brokstukken in de Stille Oceaan te belanden. Hoewel de wetenschappelijke meetinstrumenten op Compton nog feilloos werken, heeft NASA uit veiligheidsoverwegingen besloten de 17-ton zware satelliet terug te halen. En van de drie voor navigatie belangrijke gyroscopen had het begeven. De Stichting Ruimteonderzoek Nederland (SRON) heeft een belangrijke bijdrage geleverd aan de bouw en het gebruik van COMPTEL, n van de vier telescopen aan boord van de satelliet.

    Het heelal straalt ons toe in een breed spectrum, van de laag energetische radiostraling, tot de hoog energetische Rntgen- en gammastraling. Slechts een deel van de straling dringt door onze dampkring en daar weer een klein deel van kunnen wij detecteren met onze ogen, het zichtbare licht. Om gammastraling uit het heelal waar te nemen moeten we onze toevlucht nemen tot satellieten als het Compton-observatorium.

    COMPTEL is ontworpen voor het waarnemen van gammastraling met een energie van mega-elektronvolts. Deze straling ontstaat bij de meest gewelddadige gebeurtenissen in het universum, zoals supernova's, het verdwijnen van materie in zwarte gaten, de raadselachtige 'gamma-ray bursts' en de vorming van de elementen.

    Tijdens haar dienst op het Compton-observatorium heeft COMPTEL de hemel in kaart gebracht in een voorheen grotendeels onontgonnen deel van het spectrum. Onderzoekers van SRON hebben bijgedragen aan alle facetten van het onderzoek, waaronder het opsporen van gammastralende radioactieve atoomkernen in het heelal, zoals aluminium-26, titanium-44 en kobalt-56. Deze ontstaan in zware sterren en komen vrij bij supernova-explosies. De gammastraling van de radioactieve atoomkernen vormt een directe vingerafdruk van de zogenaamde nucleosynthese, de vorming van de elementen in het heelal.

    Met het in zee storten van het Compton-observatorium eindigen negen jaren vruchtbaar onderzoek in het meest variabele stralingsgebied van het spectrum. Dat is vier jaar langer dan oorspronkelijk gepland. Astrofysici zullen het nu twee jaar moeten stellen zonder 'gamma-ogen'. In 2002 wordt de draad weer opgepakt door de Europese gamma-satelliet Integral.

    Stichting Ruimte Onderzoek Nederland (SRON) is een instituut van de Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) en initieert, ontwikkelt, bouwt en gebruikt instrumenten voor wetenschappelijk onderzoek in en vanuit de ruimte. Today
    25 May 2000

    Scientists Prepare to De-Orbit Compton Satellite

    NASA's ground-control team is expected to decide this week to bring down the spacecraft into the eastern Pacific Ocean.

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    The Compton Gamma Ray Observatory has been working hard for science since it was launched in 1991. But since one of its three gyroscopes failed, NASA has decided to de-orbit the observatory rather than allow another gyroscope to fail - if one does, NASA won't be able to control where the telescope crashes. Scientists who rely on the observatory are trying to get NASA to take the risk anyway.

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