Following the tests made each day before the start of the science observations, a sequence of instrument commands has been identified that prevents the P2 detector from entering 'latch-up'. This change has no impact on the execution times of observations. The necessary update to the operational software is currently under test and is expected to become operational on 22 September. This will permit full scheduling of ISOPHOT observations to be resumed. Given that mission planning is usually performed up to three weeks in advance of execution, full use of ISOPHOT (including the stand-alone P2 observations) will be reflected in observing timelines from about mid-October onwards.
Martin F. Kessler,
10 September 1997.
It seems that a P2 observation in conjunction with a P1 observation within the same AOT does not suffer from latch-ups. Thus, the scheduling software has been modified so as to permit such combined observations to get into the timeline.
Currently, each day before the start of the science observations some tests are being made of various methods to prevent latch-ups. Based on the initial results obtained to date, there is hope that full use of the P2 detector may again be posssible in early October.
Martin F. Kessler,
19 August 1997.
As of 11 July and until further notice, no observations with the P2 detector in the ISOPHOT instrument will be scheduled. This affects all observations using the 20um and 25um filters in PHT-P, i.e. a sub-set of the following AOT's: PHT03, PHT04, PHT05 and PHT17/18/19.
Over the last few days there has been a significant increase in the number of events where the read-out electronics for the P2 detector become unstable and noisy. Such an event is referred to as a 'latch-up' and leads to the loss of the observation. About two-thirds of recent P2 observations have suffered from latch-ups. Therefore it has been decided to suspend all P2 observations.
Investigations are continuing on procedures to prevent this phenomenon; further information will be posted here on the ISO WWW as soon as available.
Martin F. Kessler,
ISO Project Scientist,
12 July 1997.