January 01, 2006
After a remarkable 13-year voyage of discovery, TOPEX/Poseidon, the first great oceanographic
Artists concept of TOPEX/Poseidon.
research vessel to sail into space, ended its mission this month.
The spacecraft lost its ability to maneuver when the satellite's pitch reaction wheel, which helps keep the
spacecraft in proper orbital orientation, stalled on October 9. After numerous attempts to recover the instrument,
ground controllers concluded that the wheel was no longer operational.
Launched in 1992 to make precise measurements of the ocean surface, TOPEX/Poseidon was watching
The El Niño in November 1997 and the La Niña in February 1999.
in 1997 when the largest El Niño in 100 years changed weather patterns around the world.
"TOPEX/Poseidon didn't discover El Niño," says mission scientist Dr. Lee-Lueng Fu, a JPL
oceanographer, "but it did give us our first global perspective on this and other short-term
climate events such as La Niña. It allowed us to follow their evolution and showed that these
events weren't limited just to the tropics. It also gave us evidence of even longer-lasting
The mission's most important achievement was to determine the patterns of ocean circulation
- how heat stored in the ocean moves from one place to another. Since the ocean holds most
of the Earth's heat from the Sun, ocean circulation is a driving force of climate.
"TOPEX/Poseidon has given us the longest and most complete observations of surface
circulation in the deep ocean," says Fu. TOPEX/Poseidon made it possible for the first
time to compare computer models of ocean circulation with actual global observations
and use the data to improve climate predictions.
Launch: 10 Aug 1992, 16:08:07 PDT (UTC: 92-222/00:08:07)
Final Command transmitted:
18 Jan 2006, 09:41:18 PST (UTC: 06-018/17:14:18)
Total mission duration:
13 Years 5 Months 7 Days
17 Hours 33 Minutes 11 Seconds
Another of the mission's major accomplishments was to map global tides for the first
time. "Tides are the most visible changes in the ocean on a daily basis," explains Fu.
"They are important for navigation, they have a big role in biological activity, and
they are the major source of mixing in the ocean. The mixing may be small in scale,
but it has a huge effect." Before TOPEX/Poseidon, tides in the open ocean could only
TOPEX/Poseidon was the first mission to demonstrate that the Global Positioning System
could be used to determine a spacecraft's exact location and track it in orbit. Knowing
the satellite's precise position, to within 2 centimeters (less than 1 inch) in altitude,
was a key component in making accurate ocean height measurements possible.
"TOPEX/Poseidon revolutionized oceanography by giving us the first global ocean observing
system," says Massachusetts Institute of Technology oceanographer Dr. Carl Wunsch, one
the mission's architects and early champions. Oceanographer Dr. Walter Munk, Scripps
Institution of Oceanography, described the joint U.S. and French mission as "the most
successful ocean experiment of all times."
The ocean is a different place now than it was when TOPEX/Poseidon first set sail. The
sea is warmer than it was and getting warmer faster. Global sea level is rising. Heat
in the tropics is moving northward more slowly. In some regions, some currents are faster
while others are slower than in the past.
"The biggest lesson from TOPEX/Poseidon is that the ocean is changing all the time," says
Fu, "and it is changing rapidly."
Jason, launched in 2001, now continues the same observations begun by TOPEX/Poseidon. For
the past three years, the two satellites have flown in tandem, providing twice the coverage
of the sea surface and allowing scientists to study smaller features than could be seen by
one satellite. A future mission, the Ocean Surface Topography Mission, is planned for 2008.
After that, scientists propose to make more detailed measurements of ocean surface topography
to study critical issues such as sea level rise.
Wednesday, 18 January 2006, was the final day of the TOPEX/Poseidon era. The spacecraft was terminated
gracefully by a series of commands, and this remarkably successful mission has finally ended.
There are so many people deserving credits for this 13 year run. On behalf of the science community,
I would like to express special thanks to those who have been running the mission on a 24/7/365 basis for all these years.
Your dedication has had a huge impact on the way we have studied the ocean as well as how the future generation will do it.
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