Compton Gamma Ray Observatory Safely Returns to Earth
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.
pieces of the observatory that survived the re-entry landed in the
Pacific Ocean approximately 2,400 miles (3,862 km) southeast of
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.
The predicted CGRO reentry footprint. Pieces which survived re-entry
landed in the Pacific Ocean 3,862 km (2,400 miles) southeast of Hawaii.
"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."
In a message to the team of engineers and scientists who have
worked on Compton, Dr. Neil Gehrels, CGRO project scientist, said
"It is with great sadness that I report the re-entry of the CGRO
mission. The operation was nominal, with our fine spacecraft
performing perfectly to the end. I have tremendously enjoyed working
with all of you on this fantastic mission! After a difficult and
emotional night, I can not find the right words to tell you ...[sic]
The project is not over. We have significant work to do over the
next ~2 years to finish the analysis of the data and complete its
archiving." Scientists anticipate a continued wealth of
information to come from the observations which Compton performed.
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.
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 92 miles
(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
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.
*GLAST launched on June 11, 2008.