Artist's concept depicting the calibration phase of the Jason 1 satellite mission. The spacecraft, shown at right, is now in its operational orbit. Topex/Poseidon, Jason 1's sister satellite, is shown at left. Credit: NASA/JPL

The joint NASA/French Space Agency oceanography satellite Jason 1 has reached its operational orbit and begun six months of instrument calibrations with its sister spacecraft, Topex/Poseidon.

Mission flight controllers at France's Centre National d'Etudes Spatiales' (CNES) Satellite Control Center, Toulouse, France, and NASA's Jet Propulsion Laboratory, Pasadena, Calif., last week commanded Jason 1 to fire its thrusters and lower itself into its operational orbit of 1,337 kilometers (830 miles). Jason 1 is now approximately one minute (approximately 370 kilometers or 230 miles) ahead of the Topex/Poseidon satellite, on an identical ground track.

Launched December 7, 2001 from Vandenberg Air Force Base, Calif., Jason 1 was initially inserted into a 1,327 kilometer (823 mile) orbit 10 kilometers (6 miles) below Topex/Poseidon. A series of thruster maneuvers over the past five weeks gradually placed Jason 1 into its current orbit.

Checkout of the spacecraft and its instrument payload is now complete. All instrument and spacecraft functions and the operations systems at the French space agency and JPL are functioning nominally.

"Jason 1 has begun observations of the same spot of the ocean surface as Topex/Poseidon under nearly identical conditions," said Dr. Lee-Lueng Fu, Jason 1 project scientist at JPL. "These unprecedented observations will allow mission scientists to calibrate and validate the new measurements from Jason 1 with those of Topex/Poseidon. The combined data records will enable us to study long-term changes in the ocean and their effects on climate."

Following completion of the calibration phase, plans are for Topex/Poseidon to be placed in a parallel ground track orbit midway between two adjacent Jason 1 ground tracks. The paired spacecraft operations are expected to produce observations with higher resolution than either satellite could attain alone. This enhanced resolution will improve the detection of ocean eddies, coastal tides and currents and will have both scientific and practical applications.

The French space agency is expected to hand over routine spacecraft operations to JPL in April. JPL will control the satellite and its instruments for the remainder of the mission, expected to last three years. The French control center will continue to monitor the satellite, perform navigation functions and conduct performance analyses.

Jason 1 will continue Topex/Poseidon's observations of ocean surface topography for monitoring world ocean circulation, studying interactions of the oceans and atmosphere, improving climate predictions and observing events like El Nino.

JPL, a division of the California Institute of Technology in Pasadena, manages the U.S. portion of the mission for NASA's Office of Earth Science, Washington, D.C.