NASAs TOPEX/Poseidon Oceanography Satellite Mission Ends

According to a NASA statement, the joint NASA/Centre National d'Etudes Spatiales TOPEX/Poseidon
oceanography satellite ceased operations after nearly 62,000 orbits
of Earth. The spacecraft lost its ability to maneuver, bringing to a
close a successful 13-year mission.

"TOPEX/Poseidon revolutionized the study of Earth's oceans, providing
the first continuous, global coverage of ocean surface topography and
allowing us to see important week-to-week oceanic variations," said
Mary Cleave, associate administrator for NASA's Science Mission
Directorate. "Its data made a huge difference in our understanding of
the oceans and their affect on global climatic conditions."

TOPEX/Poseidon data have helped in hurricane and El Nino/La Nina
forecasting, ocean and climate research, ship routing, offshore
industries, fisheries management, marine mammals' research,
modernizing global tide models and ocean debris tracking.

"TOPEX/Poseidon was built to fly up to five years, but it became
history's longest Earth-orbiting radar mission," said TOPEX/Poseidon
Project Scientist Lee-Lueng Fu of NASA's Jet Propulsion Laboratory
(JPL), Pasadena, Calif. "It provided, on average, more than 98
percent of the science data it was designed to collect in every
10-day measurement cycle, a remarkable achievement."

The satellite's pitch reaction wheel stalled in October. The wheel
helps keep the spacecraft in proper orbital orientation. Ground
controllers concluded the wheel was not functioning and ended the
mission. The satellite is in orbit 830 miles above the Earth, posing
no threat to the planet.

"TOPEX/Poseidon was a unique mission that attracted users around the
world, including more than 600 scientists in 54 countries," said Yves
Menard, TOPEX/ Poseidon project scientist at Centre National d'Etudes
Spatiales in Toulouse, France.

TOPEX/Poseidon's data have been the subject of more than 2,100
research publications; major science and application achievements
include:

The first decade-long global descriptions of seasonal and yearly ocean
current changes

Refined scientists' estimates of rising global sea level during the
past decade

Provided a new understanding of the role tides play in mixing the deep
ocean

Developed the most accurate ever global ocean tides' models

Provided the first global data set to test ocean general circulation
model performance

Demonstrated global positioning system measurements in space could
determine spacecraft positions with unprecedented accuracy, enabling
rapid delivery of data

Jason, a follow-on oceanography mission launched in December 2001, is
continuing TOPEX/Poseidon's study of ocean circulation affects on the
Earth's climate. Jason precisely maps the surface height, wind speed
and wave height of 95 percent of Earth's ice-free oceans every 10
days. The data provide invaluable input for short-term weather
forecasting, long-term climate forecasting and prediction models.

TOPEX/Poseidon's stellar performance allowed it to fly in tandem with
Jason for nearly three years, doubling data collection. This allowed
the study of smaller-scale ocean phenomena like coastal tides, ocean
eddies and currents. It also improved understanding of how
low-frequency ocean waves transmit signals of climate change.

Beyond Jason, the Ocean Surface Topography Mission is in development
for a scheduled launch in 2008. It will continue providing
high-precision sea surface height data to the oceanographic science
community.

The joint effort had its genesis in 1979, when NASA began developing
the TOPEX mission, while the Centre National d'Etudes Spatiales was
planning a similar one called Poseidon. The agencies formed a single
mission in 1983, and it was launched Aug. 10, 1992.

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