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10.05.2012 07:26 Age: 12 yrs

[Jason-1] Start of Geodetic Phase

Category: Operational news

The Cnes-Nasa Joint Steering Group directed the Jason-1 Project to move the satellite to a geodetic orbit.

As mentioned in a previous <link http: www.aviso.oceanobs.com fr actualites _top external-link-new-window>operational news, the Cnes-Nasa Joint Steering Group directed the Jason-1 Project to move the satellite to a geodetic orbit.

Maneuvers

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 23^rd with this baseline, and the first operations to lower the orbit were performed on April 25^th.
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 5^th 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.

Final orbit

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 4^th and after some POSEIDON2 radar (PRF) adjustments the mission was resumed on May 7^th 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 10^-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

Products

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.

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