Depletion of ISO's LHe Supply


I am sorry to have to inform you that ISO's supply of liquid helium ran out on Wednesday 8 April; this is nearly one year more than specified and we have been able to make a total of over 26000 observations, including two visits to the Taurus/Orion region. I attach for your information, the announcement that was released to the Press on 9 April; this has also been posted on this, our ISO WWW, server, 'www.cosmos.esa.int/web/iso'.

We will soon start a short phase of calibrations and technology tests with the satellite. At the end of this -in mid May- we plan to use the remaining hydrazine to lower the perigee so that ISO will re-enter the Earth's atmosphere some time in the first few decades of the next century.

Last September, the ISO OTAC approved a programme, led by Rens Waters NL, of 2.4 - 4 um (band 1) SWS observations to be carried out if (and whenever) possible during this phase. The goal is to extend the MK spectral classification scheme to the infrared by obtaining 2.4 - 4 um scans at full grating resolution (approx. 2000) of as many stars as is possible in the time available. In effect, it is planned to fill gaps in the technology test phase timeline with these observations. As special settings are needed, these observations will be carried out via the 'Calibration Uplink System'.

In preparation, over the Easter weekend, the SWS team at VILSPA has been monitoring the behaviour of its instrument, mainly by manual commanding. However, additionally for test purposes, half a dozen planned SWS observations on bright targets in revolutions 876-879 were executed. The band 1 data look reasonable, thus, confirming the feasibility of the spectral classification programme. As of noon on 13 April, the SWS temperature is around 20K.

When the technology test and calibration phase is over, the focus at VILSPA will shift fully to the post operations phase. We plan to re-process all observations with a new pipeline (version 7), starting in mid-May. When this re-processing is complete, we plan to open the ISO archive some time in early autumn. Some 25% of the ISO data will be in the public domain at that time and will be retrievable.

Further information will be posted as usual on this, the ISO WWW, server.

Best regards,
Martin F. Kessler,
ISO Project Scientist.