23 Jun 2011 11:39

Spacecraft

The spacecraft continues to be in good health and is operating nominally.

The third Direct Liquid Contents Measurement was performed on 24 May 2011. This measurement assessed the remaining amount of liquid helium for the spacecraft's active cooling system, which directly determines Herschel's lifetime for scientific observations. The inferred mass of liquid helium remaining is about 4 to 5% more than model predictions. The two earlier measurements, performed in November 2009 and November 2010, yielded an estimated mass about 2.3% above and 1.2% below model predictions, respectively. All three measurements are compatible within the uncertainty associated with the model that corresponds to an anticipated lifetime of just under 4 years after launch.

A correction for the star tracker focal length has been uplinked to the spacecraft. This is mainly to reduce the small number of pointings with an unusually large positional error of 6 to 8 arcsec (corresponding to 3-4 σ if the distribution was truly Gaussian). So far, there had been less than 20 such pointings over the mission.

Payload

Operations for all three instruments, PACS, SPIRE and HIFI, have been nominal during the reporting period.

Ground Segment

Ground segment operations have been nominal and 100% of the data continues to be recovered. As of 10 June 2011, the approximate completion of the different programme parts was:

For more details of these different programme parts, see the "overview of Herschel observing" linked from the right-hand menu.

The second, and final, in-flight Announcement of Opportunity (AO2) process is ongoing. Like the previous AOs there are two parts to this final AO: a Call for Guaranteed Time Programmes (GT2) and a Call for Open Time Programmes (OT2).

The first part, the GT2 AO, was issued already on 7 April and closed on 12 May 2011. A total of 32 Guaranteed Time Programmes were proposed and accepted.

The second part, the OT2 AO, was issued during this reporting period on 9 June, and will close on 15 September 2011. After the conclusion of the evaluation process the approved proposals for the OT2 programmes will be announced in late November 2011. There will be no further AOs for Herschel observing time.

Mission Operations
During the reporting period, mission operations have been conducted with the support of ESA's New Norcia and Cebreros ground stations. Observational data stored on-board Herschel was received on ground during daily communication passes, each lasting approximately three hours.

A routine station-keeping manoeuvre, or orbit correction manoeuvre, was performed on 27 May and had a nominal magnitude (delta-v) of 13.3 cm/s. These routine manoeuvres ensure the spacecraft maintains its correct orbit about L2.

Archiving
The ground segment is operating nominally. Data products are generated routinely and ingested into the Herschel Science Archive (HSA).

Future Milestones

• 15 September 2011: Closing date of the OT2 AO.
• Late November 2011: Announcement of approved OT2 proposals.

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Legal disclaimer
This report is based on the Herschel mission manager's report dated 17 June 2011. Please see the copyright section of the legal disclaimer (linked from the home page http://sci.esa.int) for terms of use.