Published online 14 September 2009 | Nature | doi:10.1038/news.2009.911

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Space telescope suffers instrument delay

Herschel glitch could force a switch to backup electronics.

HerschelHerschel's infrared spectrometer was supposed to study the chemistry of star-forming gas.ESA/AOES Medialab; Background image NASA/ESA/STSci

One of three instruments on board the European Space Agency's Herschel spacecraft has stopped working, impairing the mission's ability to examine the early Universe. After being switched off for more than a month, it is unclear when the instrument will be turned on again.

Launched in May, the spacecraft has three instruments for studying the young, far-infrared Universe, when stars were just beginning to form. The damaged Heterodyne Instrument for the Far Infrared, or HIFI, is a high-resolution infrared spectrometer that is designed to detect elements and molecules in the gas clouds that swirl around between stars and in star-forming regions.

But on 3 August, an unknown event caused HIFI to shut down. A statement on the Herschel Science Centre's blog said on 14 August that the voltage supply for the instrument's control electronics had been damaged. Frank Helmich, principal investigator for HIFI, suggests that a collision with an energetic cosmic ray particle could be the cause. "That really would be a case of bad luck," says Helmich, who is based at the SRON Netherlands Institute for Space Research in Groningen, the Netherlands.

HIFI has a backup system of electronics, but it won't be used until the team is sure the system can be safely activated, says Jürgen Stutzki, co-principal investigator on the HIFI team from the University of Cologne, Germany. A replica of HIFI on the ground at Groningen is being used to try to work out what happened, with the help of engineers from the European Space Agency.

The lowdown on HIFI

A first test of HIFI in July proved that it was working — the instrument produced results that were good enough to be of scientific value straight away, project scientists said at the time.

Peter Roelfsema, HIFI's project manager at the SRON, says that the problems with HIFI now will not have an impact on the total mission except for the delay in making measurements. In the replica HIFI in Groningen, Roelfsema's team is trying out a range of scenarios that might explain why the instrument failed. If they don't identify the specific cause, they will eventually switch to the spare power unit anyway. "It's very clear that HIFI will be switched on," Roelfsema says.

Herschel is currently in a phase known as performance verification, in which the three instruments — HIFI, SPIRE (Spectral and Photometric Imaging Receiver) and PACS (Photoconductor Array Camera and Spectrometer) — are being checked. This phase is due to end in mid-October when initial science tests begin.

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The temporary loss of HIFI hasn't affected the SPIRE and PACS teams, other than giving them extra time on their own instruments now that HIFI's unused time has been shared out. "Our calibration is being accelerated," says Bruce Swinyard, SPIRE instrument scientist at the Rutherford Appleton Laboratory in Didcot, near Oxford, UK.

All three instruments on Herschel act independently, but there is some overlap between HIFI and SPIRE, Swinyard explains. Whereas SPIRE looks at a wide area, HIFI has a much better spectral resolution close up, so it can see the moving gas in star-forming areas. This makes the two instruments complementary: SPIRE finds areas of interest and HIFI dives deeper for the fine detail. "It will be a serious loss of science if they don't get [HIFI] back," Swinyard says. 

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