A
highly successful ocean research satellite jointly operating by NASA and the French space agency CNES (Centre National d'Etudes Spatiales)
was decommissioned this week following the loss of its last remaining
transmitter. Named Jason-1, the satellite provided a massive amount
of data on Earth's oceans for over 11 years.
In
the spring of 2012, based on concern over the limited redundancy of
Jason-1's aging control systems, NASA and CNES moved the satellite
into its planned final "graveyard" orbit, depleted its
extra fuel and reconfigured the mission to make observations that
will improve our knowledge of Earth's gravity field over the ocean,
in addition to delivering its oceanographic data products.
The
first full 406-day marine gravity mission was completed on June 17.
The resulting data have already led to the discovery of numerous
small seamounts, which are underwater mountains that rise above the
deep-sea floor. The data also have significantly increased the
resolution of Earth's gravity field over the ocean, while increasing
our knowledge of ocean bathymetry, which is the underwater depth of
the ocean floor.
Contact
was lost with the Jason-1 satellite on June 21. At the time of the
last contact, Jason-1 and its instruments were healthy with no
indications of any alarms or anomalies. Subsequent attempts to
re-establish spacecraft communications from U.S. and French ground
stations were unsuccessful. Extensive engineering operations
undertaken to recover downlink communications also were unsuccessful.
After
consultation with the spacecraft and transmitter manufacturers, it
was determined a non-recoverable failure with the last remaining
transmitter on Jason-1 was the cause of the loss of contact. The
spacecraft's other transmitter experienced a permanent failure in
September 2005. There now is no remaining capability to retrieve data
from the Jason-1 spacecraft.
On
July 1, mission controllers commanded Jason-1 into a safe hold state
that reinitialized the satellite. After making several more
unsuccessful attempts to locate a signal, mission managers at CNES
and NASA decided to proceed with decommissioning Jason-1. The
satellite was then commanded to turn off its magnetometer and
reaction wheels. Without these attitude control systems, Jason-1 and
its solar panels will slowly drift away from pointing at the sun and
its batteries will discharge, leaving it totally inert within the
next 90 days. The spacecraft will not reenter Earth's atmosphere for
at least 1,000 years.
Mission
review
Launched
Dec. 7, 2001, and designed to last three to five years, Jason-1
helped create a revolutionary 20-plus-year climate data record of
global ocean surface topography that began in 1992 with the launch of
the NASA/CNES TOPEX/Poseidon satellite. For more than 53,500 orbits,
Jason-1 precisely mapped sea level, wind speed and wave height for
more than 95 percent of Earth's ice-free ocean every 10 days. The
mission provided new insights into ocean circulation, tracked our
rising seas and enabled more accurate weather, ocean and climate
forecasts.
“Since
launch, it has charted nearly 1.6 inches (4 centimeters) of rise in
global sea levels, a critical measure of climate change and a direct
result of global warming,” said John Grunsfeld, associate
administrator NASA's Science Mission Directorate in
Washington.
During
parts of its mission, Jason-1 flew in carefully coordinated orbits
with both its predecessor TOPEX/Poseidon and its successor, the Ocean
Surface Topography Mission/Jason-2, launched in 2008. These
coordinated orbit periods, which lasted about three years each,
cross-calibrated the satellites, making possible a 20-plus-year
unbroken climate record of sea level change. These coordination
periods also doubled data coverage.
Combined
with data from the European Space Agency's Envisat mission, which
also measured sea level from space, these data allow scientists to
study smaller-scale ocean circulation phenomena, such as coastal
tides, ocean eddies, currents and fronts. These small-scale features
are thought to be responsible for transporting and mixing heat and
other properties, such as nutrients and dissolved carbon dioxide,
within the ocean.
"Like
its predecessor TOPEX/Poseidon, Jason-1 provided one of the most
comprehensive pictures of changes in the tropical Pacific Ocean,
including the comings and goings of El Nino and La Nina events,"
said Lee-Lueng Fu, Jason-1 project scientist at NASA's Jet PropulsionLaboratory in Pasadena, Calif. "These Pacific Ocean climate
cycles are responsible for major shifts in sea level, ocean
temperatures and rainfall every two to five years and can sometimes
be so large that worldwide weather patterns are affected. Jason-1
data have been instrumental in monitoring and predicting these
ever-changing cycles."
The
Jason-2 mission, operated by the meteorological agencies of the
United States and Europe (the National Oceanic and AtmosphericAdministration and EUMETSAT) in collaboration with NASA and CNES, is
in good health and continues to collect science and operational data.
This same U.S./European team is preparing to launch the next
satellite in the series, Jason-3, in March 2015.
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