Herschel Status Report - February 2013
The spacecraft continues to be in good health and is operating nominally.
At launch, in 2009, Herschel's cryostat was filled with over 2300 litres of superfluid liquid helium, weighing about 335 kg. The helium is steadily used by the spacecraft's active cooling system to cool the payload, so the amount of remaining coolant directly determines Herschel's lifetime for scientific observations. Best estimates for the date of the exhaustion of the liquid helium (LHe) continue to fall in the second-half of March this year.
After Herschel has completed its operational lifetime for scientific observations, the spacecraft will leave its current orbit around L2 and will be injected into a 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. The window for the manoeuvre required to put the spacecraft in its final heliocentric orbit opens on 5 May 2013.
A long period free of big contingencies for any of the three instruments, PACS, SPIRE and HIFI, ended with four anomalies in the last two weeks covered by this report. On 12 February, SPIRE was switched off by autonomous on-board control procedure (OBCP). About thirteen hours later, HIFI too was switched off by autonomous OBCP. SPIRE could be quickly restored to nominal operation. HIFI's recovery to nominal operation took longer and was completed on 21 February.
While the HIFI recovery was progressing PACS was found, through a routine quality check of science data, to have one of its two photometer red bolometer arrays saturated. Later, on 23 February, PACS was found switched off by autonomous OBCP. The PACS spectrometer was fully recovered at the following pass and is again nominal. The PACS photometer is operational again apart from a, most-likely irrecoverable, failure of the one red bolometer array.
The series of apparently unrelated anomalies resulted in extensive round-the-clock recovery actions, involving instrument manual operations and replanning of science schedules, also to minimise the science time lost.
Ground segment operations have been nominal and 100% of the data continues to be recovered. As of 22 February 2013, the approximate completion of the different programme parts was:
|KPGT||Key Programme Guaranteed Time||:||>99%|
|KPOT||Key Programme Open Time||:||>99%|
|GT1||First in-flight Guaranteed Time||:||>99%|
|OT1p1||First in-flight Open Time, priority 1||:||>99%|
|GT2||Second in-flight Guaranteed Time||:||>99%|
|OT2p1||Second in-flight Open Time, priority 1||:||>99%|
|OT1p2 + OT2p2||First and Second in-flight Open Time, priority 2, top||:||73%|
|First and Second in-flight Open Time, priority 2, middle||:||8.5%|
|First and Second in-flight Open Time, priority 2, bottom||:||1.3%|
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 Cebreros ground station for the largest part of the reporting period, from 5 to 26 February. On 26 February the ground station cover returned again to ESA's New Norcia ground station, following completion of repairs to the station's uplink amplifiers. Throughout the reporting period, observational data stored on-board Herschel was received on ground during daily communication passes, each lasting approximately three hours.
The ground segment is operating nominally. Data products are generated routinely and ingested into the Herschel Science Archive (HSA).
A bulk reprocessing of all the science data in the HSA, using the then-latest release of the data processing software (version 9), was started in November 2012 and has been completed in this reporting period.
- March 2013: Predicted end of operational lifetime for scientific observations (exhaustion of the liquid helium for the spacecraft's active cooling system)
- 1 July 2013: Start of Post-Operations Phase