From hnett@jw.estec.esa.nl Tue Oct 22 09:51:13 2002
Date: Fri, 18 Oct 2002 18:54:45 +0200 (MET DST)
From: Herbert Nett
To: mict@jw.estec.esa.nl
Subject: [ENVISAT:mict] MIPAS cooler investigation ongoing
dear all,
This note is to inform you on the status of a recent anomaly of
the MIPAS coolers.
With a similar symptom as encounter during an incident begin August
MIPAS had switched autonomously to its save standby/refuse mode
on 1 Oct, as a result of increased vibration levels measured near the
Stirling cycle coolers beyond the threshold value of 10 mg.
Following a first analysis of the housekeeping data a temporary
malfunction of the vibration cancellation system (VCS) could not be
excluded.
It was therefore decided, following two successful tests of coolers/
displacers and drive electronics, to start a full cool-down cycle,
without activation of the VCS. Since entering measurement mode on 11 Oct.
the MIPAS coolers have been operated in the 'coarse balancing' mode,
which means, without as correction of higher harmonics. The resulting
vibration levels (5-7 mg) are stable but a factor ~2 higher than during
previous operation (2.5-3 mg), with the VCS active.
Following first checks of calibration and scene data acquired this
week no performance degradation due to the changed mode of cooler
operation could be detected. Further checks are planned.
It was decided, during a technical meeting today at ESTEC, not to re-
activate the VCS until a number of ongoing checks on the available
housekeeping have been completed.
We hope that the current anomaly will have no impact on the work of your
teams and that the full quality of currently acquired MIPAS data can
finally be confirmed.
I will keep you informed on this issue.
best regards
Herbert
