New Jason-1 Geodetic Mission
Announcement from the Jason-1 Project on 9 May 2012:
As you have been informed in a previous message on 12 April 2012, the CNES-NASA Joint Steering Group directed the Jason-1 Project to move the satellite to a geodetic orbit. The target orbit was 12+297/406 with a mean altitude at the Equator of 1323.4 km. Jason-1 maneuver operations were started on April 23rd with this baseline, and the first operations to lower the orbit were performed on April 25th. After an initial series of 4 maneuvers were completed, we encountered a serious new propulsion anomaly which resulted in the unexpected overconsumption of hydrazine. A 5th maneuver was designed in order to correct orbital eccentricity. At the time of this new anomaly, Jason-1 was -12.0 km below the reference altimetric orbit with 600m remaining to reach the -12.6 km goal, however there were very few grams of fuel remaining in the tank to continue orbit lowering.
After checking the current orbit carefully, the operational team determined that a geodetic mission was still possible. It was also decided to preserve all remaining fuel for future station keeping maneuvers which is mandatory in a geodetic orbit. Core payloads were switched ON on May 4th and after some POSEIDON2 radar (PRF) adjustments the mission was resumed on May 7th at 15:12:48 UTC.
Below are the characteristics of the new orbit which will be maintained, as before, within +/- 1km control box at the Equator:
• Semi major axis 7702.437 km
• Eccentricity 1.3 to 2.8 E-4
• Altitude equator 1324.0 km
• Orbital period 6730s (1h52’10’’)
• Inclination 66.042°
• Cycle 406 days
• Sub cycles 3.9, 10.9, 47.5, 179.5 days
The ground team is currently preparing for the restart of ground processing operations. For this new phase of the Jason-1 mission, the cycle numbering will restart at 500 and the first OSDRs should be produced within a few hours. Off-line products will be produced once a day for the IGDR, and every 11 days for the GDR's.
We will provide more detailed information as soon as the first science measurements on the new orbit become available.
Thierry Guinle & Glenn Shirtliffe
CNES and JPL Jason-1 Project Managers
Additional Information from PO.DAAC User Services:
Jason-1 has been moved to a lower orbit and began its geodetic mission on 7 May 2012. There is a calibration and validation period that is still occurring. Since cal/val is not complete please use caution when using the new geodetic data. Significant wave height should remain relatively the same since it is on the scale of meters. Measuring mesoscale features will be greatly degraded because the algorithms used by Jason-1 were designed for the older, higher orbit.
The Jason-1 project is still making decisions on the data format and filenaming convention so do not be surprised if these things change all of a sudden. We will try to keep users informed as best we can. Information on the new geodetic orbit will soon be located at http://podaac.jpl.nasa.gov/OceanSurfaceTopography/JASON1
The data from the geodetic mission will be found in folders that end with _geodetic.
You can currently find the new OSDR geodetic data at:
The historical GDR data will become available in a couple of months.
If you have questions please direct them to email@example.com
We apologize if you receive multiple copies of this announcement