Herschel Status Report - November 2010
The second Direct Liquid Contents Measurement was executed on 2 November 2010 as planned. This measurement assesses the remaining amount of liquid helium (LHe) for the spacecraft's active cooling system, which directly determines Herschel's lifetime for scientific observations. The inferred mass of LHe remaining is 192 kg, about 1.2% less than model predictions. For comparison: the first Direct Liquid Contents Measurement in November 2009 yielded an estimated mass of 283 kg, about 2.3% above the model predictions. Both measurements are compatible with the error bars of ±5% associated with each LHe mass determination and with an anticipated lifetime of just under 4 years after launch.
SPIRE operations have been nominal during the reporting period.
The recent modification of the PACS on-board software - see the previous status report from October 2010 - unveiled as a side-effect a previously undetected feature in the on-board software implementation. This anomaly has been successfully resolved.
On one occasion the HIFI instrument, which was in stand-by mode at the time, continued to send housekeeping telemetry but did not execute any incoming commands. Having excluded all other conceivable causes, HIFI's Instrument Control Unit was rebooted through a cold re-start (power off/power on). This successfully resolved the anomaly and HIFI became responsive again immediately.
The Herschel Observing Time Allocation Committee (HOTAC) has made its recommendation on the proposals that were received in response to the first Open Time Call (OT1) and ESA's Director of Science and Robotic Exploration has awarded observing time to 241 of the 576 proposals received. The Principal Investigators of all OT1 programmes have been informed of this decision and the "proposal refinement" stage has started for programmes that have been awarded observing time. The list of selected OT1 programmes can be found on the Herschel Science Centre website (linked from the right-hand menu).
Several operational days in the reporting period were re-planned, mainly due to two events:
- In the period 24 October to 17 November Herschel participated in a world-wide, coordinated observing programme of comet 103P/Hartley 2, involving NASA's EPOXI mission, other spacecraft, and numerous ground based facilities. End of October this Jupiter class comet made its closest approach to Earth and a few days later reached perihelion. The comet's distance to Herschel was approximately 0.1 AU, which caused the actual ephemeris of this very fast moving object to deviate from the comet's predicted location by as much as 20 arcsec. To keep all planned Herschel observations on target, this positional error had to be compensated for.
- Target of opportunity observations of the quasar 3C454.3 undergoing a massive outburst were requested and considered of sufficient scientific merit to schedule observations of the quasar on short notice.
During the reporting period, mission operations have been conducted with the support of the ESA New Norcia ground station. Observational data stored on-board Herschel was received on ground during communication passes lasting approximately three hours.
The ground segment is operating nominally. Data products are generated routinely and ingested into the Herschel Science Archive (HSA).