U.S. and
French researchers announced the end of an ocean-watching satellite Thursday,
concluding a 13-year mission that transformed their understanding of Earth's
largest bodies of water.
Mission managers
ended the TOPEX/Poseidon mission following the failure of its final reaction
control wheel - used to keep the spacecraft pointed properly - that prevented
future science observations, NASA officials said.
"It's
definitely a happy ending," said Lee-Lueng Fu, the
mission's project scientist at NASA's Jet Propulsion Laboratory (JPL) in
Pasadena, California, in a telephone interview. "The mission launched in 1992
and we specified operation from three to five years, but we got 13. That's more
than anybody could ask for."
A joint
mission between NASA and France's Centre National d'Etudes
Spatial (CNES), the TOPEX/Poseidon spacecraft watched Earth's oceans from an
830-mile (1,335-kilometer) orbit.
"The ocean
is changing all the time," Fu said. "This was the first time we mapped the
elevation of the ocean's surface."
The
satellite used radar altimeters to track changes in sea
level, map ocean tides and study ocean water mixing. Observations from the
spacecraft also helped researchers to better understand global climate
change and weather phenomena such as El Niño, NASA
officials said.
"It was a
revolution for oceanography," Fu said of the TOPEX/Poseidon mission. "It was
the ocean equivalent of a weather map."
TOPEX/Poseidon
also proved that global positioning system (GPS) measurements could be used to
track orbiting satellites. The spacecraft's science mission ended after almost
62,000 orbits around Earth.
But while
the mission is over, the spacecraft won't come crashing into the Earth's
atmosphere any time soon due to the relatively low drag forces in its current
orbit.
"It could
be up to 1,000 years," Fu said of TOPEX/Poseidon's return.
A successor
to TOPEX/Poseidon - dubbed Jason
- launched in December 2001 and worked alongside its predecessor, allowing
flight controllers to verify its function by comparison, added Fu, who also
serves as its project scientist at JPL.
A third
spacecraft, the Ocean Surface Topography Mission, is expected to join Jason in
2008 to continue its ocean-watching task. NASA and CNES are cooperating on both
missions.
"This data
stream, hopefully, will become a permanent asset of the international
community," Fu said.
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