MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEMarch 8, 1999
TOPEX/POSEIDON OCEANOGRAPHIC SATELLITE GETS NEW LEASE ON LIFE
Engineers have given the TOPEX/Poseidon ocean topography
satellite a new lease on life by successfully switching the
principal instrument onboard the satellite to operate on its
backup unit, extending the spacecraft's already unprecedented
lifetime of monitoring ocean circulation patterns worldwide.
With the switch to a fresh altimeter, the highly productive
TOPEX/Poseidon mission, which produced the accurate prediction of
the globally destructive El Niño phenomenon of 1997-98, could
last for months or years to come. The satellite, launched in
August 1992, was originally designed to last three to five years.
Last month, commands were sent to the U.S.-French satellite
to turn off its primary radar altimeter, which was showing signs
of age, and to activate the backup altimeter. Preliminary data
from the satellite analyzed by the TOPEX/Poseidon team at NASA's
Jet Propulsion Laboratory, Pasadena, CA, indicated that the
backup, or "side-B" instrument, is operating smoothly.
"Barring any unforeseen problems with data acquisition, we
will continue to use the spare altimeter to provide global ocean
topography data," said David Hancock III, altimeter instrument
scientist at the Wallops Flight Facility in Virginia, whose team
is monitoring operational data from the joint NASA-Centre
National d'Etudes Spatiales (CNES) satellite.
Dr. Philip Callahan, head of the calibration team at JPL,
said his team is calibrating data from the new altimeter to
extend TOPEX/Poseidon's ability to record global ocean changes as
subtle as 1 millimeter per year (0.04 inches per year) well into
the new millennium. "This work is an excellent testing bed for
cross calibration of TOPEX/Poseidon with its successor, JASON-1,
which is scheduled for launch in May 2000," he said.
From an orbital altitude of 1,336 kilometers (830 miles)
above Earth, TOPEX/Poseidon has successfully acquired data on
sea-surface heights, produced global maps of winds and waves, and
detailed land and ice-sheet topography since 1992. It has
recorded billions of time-specific measurements of ocean and
topography to an accuracy of approximately 3 centimeters (1.2
inches). An international team of scientists has used the data
to study global climate changes and such phenomena as the El Niño
warming pattern in the Pacific Ocean, which occurs about every
two to seven years, and a reverse trend, known as La Niña, which
seems to follow El Niño winters and cools large expanses of ocean
Although the primary altimeter, or "side A," is still
operational, components have started to degrade from wear and
tear on the satellite. The operations team expects to be able to
use side B of the altimeter for the next several years, but will
be able to switch back to side A if necessary, Hancock said.
The Wallops Flight Facility Observational Science Branch,
Wallops Island, VA, which is part of NASA's Goddard Space Flight
Center Laboratory for Hydrospheric Processes, worked with the JPL
science and engineering team to provide specifications for using
the backup altimeter system. The team, in conjunction with
members of Goddard's Applied Engineering and Technology
Directorate, Greenbelt, MD, was responsible for designing the
fully qualified, backup altimeter, built by the Johns Hopkins
Applied Physics Laboratory, Baltimore, MD.
The TOPEX/Poseidon mission is managed by the Jet Propulsion
Laboratory for NASA's Office of Earth Science, Washington, DC.
JPL is a division of the California Institute of Technology,