On 24 May close to 17:00 UT the third and final Herschel science instrument, HIFI, was successfully switched on. In the following 30 hours it has undergone a series of tests that show the functionality of its focal plane units -- the 4 spectrometers, its electronics units and the main moving component its chopper. All items have been shown to be working in similar fashion to on-ground testing and all functional tests have been declared successful.
As HIFI is a heterodyne unit, it also requires the use of a local oscillator unit. HIFI has a sophisticated and complex local oscillator system that allows its spectrometers to obtain high-resolution spectra across a very wide range of frequencies. The local oscillator (LO) unit, with its 14 separate signal-carrying chains,was tested today (26 May at ~14:15 - 17:00 UT). All 14 LO channels are alive and show power levels at the detectors (mixers) consistent with previous on-ground measurements. No icing of the LO windows is apparent, as was considered a possibility from outgassing during launch, and no misalignment of the LO chains is apparent to within 1-2%.
The HIFI instrument is fully functional and will now start to be setup to work optimally for science operations.
[T. Marston from MOC ESOC, posted 26 May 2009]