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Mission Status 2011

Tim Larson, Stardust-NExT Project Manager

March 25, 2011 Final Stardust-NExT Weekly Status Report
When last seen by the ground, Stardust’s subsystems were nominal and trying to complete the Farewell Maneuver. At 18:30 (MDT) the on-board sequence issued the command to place the spacecraft into safe mode and turned the transmitter off for the last time.  At that time the JPL Project Manager, Tim Larson, declared the end of the Stardust and Stardust-NExT missions.

March 18, 2011
The spacecraft continues its post-encounter cruise. The decommissioning review was held on March 18, with the board recommending six actions to be addressed prior to the planned April 7 decommissioning activity. However, a 2 psi pressure drop was observed in the fuel tank over the weekend, leading the propulsion experts to believe that a gas bubble has made its way into the propellant management device, implying the tank might be getting to the end of the propellant. This prompted the team to reconsider the planned date for the decommissioning. With the consent of senior management and NASA HQ, the decommissioning burn will be executed on March 24. This will help the team determine how much fuel is actually left in the tank, providing data that will be valuable to other missions nearing the end of their fuel supply. After this activity, the spacecraft will be commanded into safe mode with the transmitter off. This will mark the end of a wonderful 12 year mission for the Stardust spacecraft. During that time it has flown by an asteroid and two comets, and returned samples of comet dust to earth for detailed study.

March 16, 2011
The spacecraft continues its post-encounter cruise. All subsystems continue to operate as expected. The team is preparing for the decommissioning maneuver, and the decommissioning plan has been prepared and reviewed. The primary date for the decommissioning activity is March 24, with a back-up opportunity on April 7. The Decommissioning Review has been scheduled for March 18 at JPL.

February 24, 2011
The spacecraft continues its departure imaging of comet Tempel 1. This will end with a Navcam calibration that will take place on Friday, February 24. This will be the end of the official Tempel 1 encounter activities. Planning is under way for the decommissioning of the spacecraft.

February 15, 2011 - E+22 Hours
All encounter data was downlinked and verified uncorrupted in the SDC (Science Data Center). PI and DPI gave go to erase images and begin departure imaging. The spacecraft has been reconfigured for post-encounter, FP has been re-enabled, and the heap has been reallocated, enabling new images to be acquired. The departure imaging will start tonight and will continue until PI determines no further useful science is being collected. Thank you all for your help and support. Next report – after decommissioning activities.

February 14, 2011 - E-21 Hours
The spacecraft team has just completed the final commanding prior to encounter. This included the encounter sequence and the supporting files that were built this afternoon with the final trajectory and time of arrival estimates. Most fault protection has now been disabled, and the Mission Phase Bit has been set to ‘Encounter.’ From now on, a safe mode entry will trigger the autorecovery sequence that will attempt to recover the spacecraft autonomously and restart the encounter sequence. The encounter sequence is active. The encounter activity on board the spacecraft will begin at E-9 hours, when the Navcam CCD heater will be turned off to begin the final cooldown. This will be followed by setting the CIDA instrument to encounter mode at E-3 hours.

The telecom analysis for the predicted flyby attitude and locations shows that we will expect to support telemetry after the spacecraft turn to the final encounter attitude at E-1 hour. The supportable telemetry rate will be 504 bps. When the spacecraft executes the final roll for closest approach imaging at E-5 minutes, we may lose the signal, but it will return at E+5 minutes with the roll back.

The spacecraft is now fully configured for encounter and under autonomous control through the encounter. Next planned commanding is after encounter, when the team will command the spacecraft to begin playback of stored telemetry followed by the images and dust data.

February 13, 2011 - E-1 Day
The overnight activities taken by the flight team went very well, and the final OpNavs taken at E-42 hours were successfully acquired and downlinked. The navigation solutions were finished this morning, and they show that the predicted delivery is within the ‘green zone’ of the delivery chart. The nominal flyby point is at 191 km from the surface of the comet with a 11km uncertainty radius. The current Time of Closest Approach estimate is still around 04:40 UTC on February 15 (20:40 February 14 in Pasadena). Based on these discussions and updates, the following decisions were made, with full concurrence between the PM and PI:

- No TCM 34 will be executed
- The nominal imaging sequences for both timing and exposures will be implemented in the flyby sequence

The final Nav and Autonav products will be delivered to DOM slightly ahead of schedule, and these will be used to build the final products. These products will be uplinked to the spacecraft this evening, beginning around 20:00 PST.  Once these products are on board, the next on board activity will begin around E-3 hours.Many thanks to the S/C team, the Nav team, the Science team, and the various ground observers who provided invaluable data.

February 12, 2011 - E-2 Days
The spacecraft continued to perform well today. Optical navigation images continued to be acquired until 16:30 PST today. These images are all on the ground now, thanks to great support by the Deep Space Network. The OpNav images continue to be very good quality with 0.25 pixel uncertainty. These are showing that last night’s pre-TCM 33 decision was correct in that the change in comet position was indeed not part of an oscillating position (e.g. A large rotating jet), but rather the effect of the nucleus signal coming through the coma signal. Today’s solutions show that the comet location is drifting slightly, but on the order of a few kilometers, confirming that the solution selected for the TCM 33 design is appropriate.

The science team has continued to analyze the images to extract photometric data, and a light curve is definitely being extracted. Further analysis is needed, however to see whether there is enough information to predict the expected sub-spacecraft longitude at closest approach. It is likely that this will not be known until after flyby.

An assessment of the Time of Arrival uncertainty was made today, based on both the ground based observations and the OpNav data. The ground observers have provided excellent support with observations coming from Magdalena Ridge in New Mexico, Mauna Kea in Hawaii, the Trappist observatory at La Silla, Chile, and Siding Spring in Australia.  These ground observations have been very important in helping confirm the time of arrival uncertainties. These currently are expected to be in the range of +/- 20 to 30 seconds. Therefore, the final encounter sequence will be built using the nominal image timing sequence. Final confirmation will come after tomorrow’s decision meeting.

TCM 33 was performed this evening. This maneuver was a .9 m/s maneuver with a 50 second burn. This will move the spacecraft approximately 170 km in the b plane. The maneuver execution went as planned, and the overnight tracking data along with the final OpNav image set at E-42 hours ( 02:30 PST Sunday morning) will provide the information needed to calculate the final spacecraft trajectory toward the comet. A decision on whether TCM 34 is needed (selecting between three pre built move out maneuvers) will be made tomorrow (Sunday) at 13:30 PST. The final encounter sequence will be rebuilt with the final TCA estimate and the selected nominal or alternate image timing and exposure sequences. These, along with the final ephemeris and autonav parameter files will be uplinked on Sunday evening.

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