Herschel Status Report - June 2010
28 Jun 2010 11:15
Report for period 18 May to 23 June 2010
Mission operations of the Herschel space observatory continued nominally during the reporting period, with the spacecraft and subsystems all performing as expected. Herschel has successfully passed its first In-orbit Performance Review, which was held on 8 June at the European Space Operations Centre (ESOC) in Darmstadt, Germany. No critical issues were identified.
The spacecraft is operating nominally.
Star tracker warm pixels
With the exception of two single event upsets (SEU) in the HIFI memory, all three instruments continue to operate nominally. One of the HIFI SEUs manifested itself in a hitherto unknown way, overloading the spacecraft systems with corrupted telemetry. The only plausible scenario that has been identified to explain the anomaly is that on this occasion it was not the Local Oscillator Control Unit that was affected, but the Instrument Control Unit. The recovery activities were interrupted by another SEU, such that a total of almost three operational days for taking science data were lost.
The statistics of SEUs improve with the increase in elapsed mission time; it is now just over a year since Herschel's launch on 14 May 2009. In the satellite's solid state mass memory (SSMM), which is protected by error detection and correction (EDAC) circuitry, on the order of 1000 bit flips have been detected and reported since launch, none of which had any operational impact. In HIFI we have seen 11 bit flips in five months since operations were resumed using the redundant signal chain. Analysis of the SPIRE data show only 2 bit flips in one year. PACS has not had a single bit flip. All attempts made so far have failed to correlate the observed bit flips to any satellite environmental parameters, or to establish a temporal correlation with the occurrence of bit flips on the Planck spacecraft that also orbits about L2.
The spacecraft's large Lissajous orbit about L2, which is perturbed by the helium outgassing and the daily reaction wheel biasing/unloading, has proven to be extremely stable. The last two planned orbit correction manoeuvres could be skipped because the required delta-v was below the threshold of 5 cm/s.