Jason was an oceanography mission to monitor global ocean circulation, improve global climate predictions, and monitor events such as El Nino conditions and ocean eddies. The Jason-1 satellite carried a radar altimeter, and it was a follow-on mission to the highly successful TOPEX/Poseidon mission, that measured ocean surface topography to an accuracy of 4.2 cm, enabled scientists to forecast the 1997-1998 El Niño, and improved understanding of ocean circulation and its effect of global climate. Jason-1 altimeter data are part of a suite of data provided by other NASA missions--the GRACE mission uses two satellites to accurately measure Earth's mass distribution, and the QuikSCAT scatterometer mission will measure ocean-surface winds. The Delta vehicle was shared with the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) mission.
Since the oceans are so large, remote sensing from satellites has proved to be the only way to get global information about these vast, hard-to-measure expanses. Spaceborne altimeters, such as the Poseidon 2 instrument that Jason 1 carried, can calculate ocean heights to within centimeters.
The ocean and atmosphere transport heat from the equatorial regions toward the icy poles and the atmosphere sends heat through a complex, worldwide pattern of winds. As these winds blow across the oceans, they help drive the currents and exchange heat, moisture and gases with the water. While winds create daily, short-term weather changes, the oceans have a slower, much longer-lasting effect on climate. The powerful forces of wind and water combine to help regulate our planet's climate.
Accurate observations of sea-surface height and ocean winds provide scientists with information about the speed and direction of ocean currents and about the heat stored in the ocean that, in turn, reveals global climate variations. Jason 1 has helped scientists in their quest to understand these global climate forces.
Weighing about 500 kilograms (about 1,100 pounds), Jason 1 was only one-fifth the weight of TOPEX/Poseidon. After launch, Jason 1 entered orbit about 10 to15 kilometers (6 to 9 miles) below TOPEX/Poseidon's 1,337-kilometer-altitude (830-mile) orbit. During the first few weeks, Jason 1 used its thrusters to raise itself into the same orbital altitude as TOPEX/Poseidon, and then move in close behind its predecessor, trailing by about 500 kilometers (300 miles).
The two spacecraft flew in formation, making nearly simultaneous measurements. The science team compared the data to make sure the instruments were calibrated exactly. This procedure took about six months. Jason 1 will then assumed TOPEX/Poseidon's former flight path, and the older satellite moved into a parallel ground track midway between two Jason 1 ground tracks. This approach to cross-calibration between missions was used again in 2006 when the follow-on OSTM/Jason-2 mission joined the altimetry constellation, after TOPEX/Poseidon was decommissioned.
In 2012, CNES and NASA jointly agreed to a partial passivation of Jason-1 based on the limited redundancy remaining on the spacecraft. In April-May 2012, CNES moved the spacecraft to its ‘graveyard’ orbit, depleted extra fuel, and reconfigured the mission for a geodetic objective, while continuing to meet its original oceanographic requirements. The first full repeat cycle of 406 days in the geodetic orbit, sufficient to satisfy the requirements of the geodetic mission, was completed on June 17, 2013. The resulting data record has enabled the discovery of numerous small seamounts and has significantly increased the spatial resolution of the Earth’s gravity field measurements over the ocean, as well as the knowledge of ocean bathymetry.
Jason 1 carried five instruments: the Poseidon 2 altimeter, the spacecraft's main instrument, to measure altitude; a microwave radiometer to measure atmospheric water vapor; and three precision location-finding instruments.
Jason 1 was a joint project between NASA and France's Centre National d'Etudes Spatiales. The U.S. portion of the mission is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.
Jason 1's mission was designed to last three years, but it lasted over eleven years. Contact with the satellite was lost with the Jason-1 satellite on June 21, 2013. 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, 2013, 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.