Herschel Status Report - May 2013
The spacecraft continues to be in good health and is operating nominally.
Following the exhaustion of the cooling system's liquid helium coolant on 29 April, a series of post-helium technology tests began on the spacecraft and instruments. Although Herschel no longer is capable of performing science observations, the still fully functional in-orbit spacecraft provides a unique opportunity to test specific spacecraft and subsystem operations, before Herschel is finally switched off. During these tests the performance of various sub-systems is explored over a parameter space, or in modalities, not routinely available during the mission's normal science operations. The test series will conclude in early June and the results will provide valuable input for future missions.
Following conclusion of the post-helium technology tests, measures will be taken to ensure passivation of the spacecraft, leading to a final delta-v manoeuvre to deplete any remaining fuel and the final passivation of Herschel on 17 June 2013.
With the mission's science phase being over, the operations for all three instruments, PACS, SPIRE and HIFI, has concluded, except for activities performed as part of the post-helium technology tests.
Ground segment operations have been nominal and the last of the data from Herschel's scientific observations have been recovered. The final completion percentages of the different programme parts were:
|KPGT||Key Programme Guaranteed Time||:||100%|
|KPOT||Key Programme Open Time||:||100%|
|GT1||First in-flight Guaranteed Time||:||100%|
|OT1p1||First in-flight Open Time, priority 1||:||99.4%|
|GT2||Second in-flight Guaranteed Time||:||100%|
|OT2p1||Second in-flight Open Time, priority 1||:||100%|
|OT1p2 + OT2p2||First and Second in-flight Open Time, priority 2, top 1/3rd||:||98%|
|First and Second in-flight Open Time, priority 2, middle 1/3rd||:||42.5%|
|First and Second in-flight Open Time, priority 2, bottom 1/3rd||:||6.3%|
The remaining 0.6% of the OT1p1 programme part were target-of-opportunity-like observations that were never triggered. The combined completion of all priority 2 observations (top, middle and bottom) is 47.8%. For more details of the different programme parts, see the "overview of Herschel observing" linked from the right-hand menu.
Mission operations were conducted with the support of ESA's New Norcia ground station. Data stored on-board Herschel were received on ground during daily communication passes, each lasting approximately three hours.
A series of final departure manoeuvres in May and June are underway to boost Herschel from its operational orbit around L2 of the Sun-Earth system into its final no-return heliocentric orbit. In this context "no-return" means not returning to the potential well of the Earth-Moon system for at least 300 years.
On 13-14 May the main manoeuvre in the series, the "Disposal Manoeuvre", was executed successfully. For the manoeuvre operations the Cebreros station was used in addition to the New Norcia station. The delta-v manoeuvre had a nominal magnitude of 113.732 m/s. Preliminary assessment of the manoeuvre by Flight Dynamics indicated it slightly over-performed by just +0.19% (+0.216 m/s) and had a direction error of less than 0.15 degrees.
The majority of the spacecraft's remaining fuel was spent during the record 7 hours 46 minutes burn of this manoeuvre, which was initiated at 18:20:35 UT on 13 May 2013. This was the longest delta-v ever applied with the type of thrusters used on-board the Herschel spacecraft (EADS CHT20).
A later "draining" manoeuvre, planned for 17 June, will deplete the little remaining fuel as part of the spacecraft passivation.
The ground segment is now in transition into the mission's post-operations phase, which will extend until the end of December 2017.
Data products are generated routinely and ingested into the Herschel Science Archive (HSA). The sixth bulk reprocessing of the data in the archive is about to begin, upgrading the data products using the latest reduction algorithms and calibration. This will be the first reprocessing to run over the data of the entire mission.
The Herschel Science Centre (HSC), based at ESAC, Madrid, is steadily assimilating refined programme-specific data products from the Herschel Key Programmes, into the HSA.
Over 2475 scientists are now registered as HSA users, about 25 new registrations occurring per month.
During the post-operations phase, the Herschel Science Ground Segment, comprised of the HSC, the three Instrument Control Centres (ICCs) and the NASA Herschel Science Center (NHSC), will continue to support users in the exploitation of the science data. The vast bulk of these data remains to be analysed in depth. Data processing software will continue to be improved, refined data products ingested into the archive, and support documentation enhanced, yielding finally the legacy version of the Herschel output.
- Last of the post-helium engineering tests and wrap-up activities with the spacecraft and the instrument electronics
- 17 June 2013: Final "draining" manoeuvre to deplete all fuel
- 17 June 2013: Switching off the Herschel spacecraft
- 1 July 2013: Start of Post-Operations Phase