Wednesday, July 3, 2013

The following message has been forwarded to all registered PO.DAAC users on behalf of the Jason-1 Project Team.

Contact was lost with the Jason-1 spacecraft at some point after the last good downlink at 0114 UTC on 21 June 2013. At the time of the last contact, the spacecraft its payload instruments were in nominal health and there were no indications of any alarms or anomalies. At the beginning of the next contact at 0249 UTC, no downlink signal was detected. 
All attempts to re-establish communications with the Jason-1 spacecraft over the ten days from 21 June to 01 July, from both US and French ground stations, were unsuccessful. 
Tracking and analysis of the spacecraft orbit and attitude from ground assets determined that the Jason-1 spacecraft was in a nominal nadir-pointing attitude, and that there had been no catastrophic breakup or debris event.  There was no unusual change to the Jason-1 orbit preceding this anomaly.  It was concluded that the spacecraft was operating nominally, using the stored on-board sequence and guidance profiles, and that there had been no transition to a Sun-pointing safe hold mode.  There were no significant space weather events at the time of the anomaly.
We wish to extend our sincere appreciation to the emergency support the ILRS, the orbit analysis teams, and the individual laser and radar tracking stations provided invaluable analysis of the Jason-1 anomaly in the absence of any downlink signal.
After consultation with spacecraft, transmitter, and telemetry engineers at Thales Alenia Space (TAS-Cannes) and the transmitter manufacturer TAS-Spain, it was determined that a non-recoverable failure with the A-side transmitter was the cause of the anomaly.  A similar loss of contact with Jason-1 occurred in September 2005, when the B-side transmitter tied to Processor Module B (PMB) failed, resulting in the loss of the half-satellite.  There was no remaining transmitter redundancy on Jason-1 and no other means for the spacecraft to downlink science telemetry. 
A Joint Steering Group teleconference between CNES and NASA senior management was held at  1600 UTC on Friday, 28 June 2013, to discuss the results of the incident investigation and to decide future mission options.  The JSG endorsed the actions detailed below:
-- CNES uplinked commands to the Jason-1 spacecraft to provoke a transition to safe mode on 01 July 2013 at 0810 UTC.
-- Laser stations were able to track and confirm that Jason-1 was in nominal nadir-pointing configuration prior to the entry to SHM.
-- At 0811 UTC, Jason-1 began to drift off nadir and transition toward a Sun-pointing orientation, as expected.
-- At 0907 UTC, intermittent laser returns were received at laser tracking stations, confirming the transition to SHM.
-- Between 1201-1222 UTC, numerous attempts to re-establish downlink communications from a French station in Kourou (South America) were unsuccessful.
-- These events confirmed the loss of the last remaining transmitter and the continued functioning of the onboard receivers.
-- Final "Last Chance" attempts were made to restart the transmitter (over Kourou at 1358 UTC).
-- As agreed by the CNES-NASA Joint Steering Group teleconference, if these final attempts to reestablish downlink were unsuccessful, then commanding to passivate the spacecraft  would begin during a Kerguelen Island (Indian Ocean) pass at 1631 UTC.
-- Commands were sent and resent during this pass to turn off the magnetometer and reaction wheels.  
Without these attitude control systems, the orientation of Jason-1 and its solar panels will now slowly drift away from the Sun and  the batteries will begin to discharge, leaving it totally inert within the next 60 to 90 days.  Jason-1 is currently Sun-pointing and spinning around the main spacecraft axis at about 1.2 degrees per second.
Jason-1 was passivated and decommissioned on 01 July 2013, with the last command sent at 16:37:40 UTC; terminating the Jason-1 mission after 11.5 years of operations.  After 53,535 orbits, the Jason-1 science data mission ended on 21 June 2013 -- four days after the successful completion of the first full 406-day geodetic cycle on 17 June 2013, at sub-cycle 537.  Jason-1 continued to meet all Level 1 mission requirements until its final signal was transmitted.
As Linda Stathoplos of NOAA aptly stated at the JSG meeting last Friday: “Don't be sad because it's over; be happy because it happened!”
From Lee-Lueng Fu:  “It is certainly a sentimental moment for the mission team to mourn the passing of the mission and also celebrate the extraordinary accomplishments of this historic mission.   By passing the baton from TOPEX/Poseidon to OSTM/Jason-2, Jason-1 fulfilled a historic role of demonstrating how a climate data record is to be continued by successive missions with mixed technologies.  The mission has been with us for so long that it has become part of life for many of us.  Now it's time to say goodbye and celebrate the success.  On behalf of the science community of altimetry and sea level studies, I salute the joint NASA/CNES team for their tenacious efforts in keeping the mission running flawlessly to accomplish an invaluable milestone of satellite altimetry.”
From Josh Willis:  “I too have felt incredibly lucky to have been involved with such a successful mission.  I certainly owe my scientific career to this series of missions and I have the joint NASA/CNES team to thank for that.  So I salute you as well, on a job well done.”
From John Lillibridge at NOAA:  “We knew this day was coming, and we can revel in > 11 years of excellent measurements, but it's still kind of sad...”
JPL senior management also send their best regards: “The legacy that Jason 1 leaves all of us is one of an amazing mission that was performed by exceptional  development and operations teams. The continuity of the sea surface height measurement is critical to understanding this changing and restless planet.  There is really no time series that comes close to that of SSH measured by the TOPEX/Jason series of missions. The development team built a bus and a set of instruments that not only met its performance specifications, but they lasted well beyond their planned lifetime. The operations team did an outstanding effort in sustaining the mission, returning the data with minimal outages, and nurturing the spacecraft and its ground system. Job well done. We will miss Jason-1.”  (Jim Graf, on behalf of the Earth Science & Technology Directorate)
“The whole Jason-1 team has done a superb job over more than a decade and the mission has contributed tremendously to our understanding of the oceans dynamic.  Thanks to the whole team.”  (Charles Elachi, Director)
From Jean-Yves Le Gall, (CNES President):  "Jason-1 was an exemplary and multi-faceted altimeter mission. Not only did Jason-1 extend the precise climate record established by TOPEX/Poseidon, it then made invaluable observations for mesoscale ocean studies on his second, interleaved orbit.  Even when  moved to a "graveyard" orbit,  Jason-1 continued to make unprecedented new observations of the Earth's gravity field, with precise measurements right until the end.  Jason-1 contributed so much to so many scientific disciplines.”
The sentiment of the moment was perhaps best summarized in 1915 by the Canadian poet John McCrae:
To you from failing hands we throw
   The torch; be yours to hold it high.
À vous de porter l'oriflamme
   Et de garder au fond de l'âme
We wish a very long life in orbit and many more years of successful science to Jason-2 and SARAL/AltiKa.
Keep the legacy of TOPEX/Poseidon and Jason-1 burning long and bright!
The Jason-1 Project Team
Rosemary, Lee, Josh, Thierry, and Glenn