The following is an excerpt from a story by Alan Buis, NASA’s Jet Propulsion Laboratory…
The curtain has come down on a superstar of satellite oceanography that played the “Great Blue Way” of the world’s ocean for 11.5 years. The joint NASA and Centre National d’Etudes Spatiales (CNES) Jason-1 ocean altimetry satellite was decommissioned on July 3, 2013, following the loss of its last remaining transmitter.
Launched December 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 of our planet, 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.
“Jason-1 has been a resounding scientific, technical and international success,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate in Washington. “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. The Jason satellite series provides the most accurate measure of this impact, which is felt all over the globe.”
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, 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.
Contact was lost with the Jason-1 satellite on June 21 when it was out of visibility of ground stations. 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.
“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 Propulsion Laboratory. “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.”
For more information on Jason-1, visit: http://sealevel.jpl.nasa.gov and http://www.aviso.oceanobs.com .