Report to the JCMT Board - October 2002

Inclinometry
Measurements of the track very early in this period showed 'spikes' at some track joints - a phenomenon interpreted over the years as being due to underloading of the wheels. A Central Bearing Load adjustment was performed on 15 May, as a result of which the wheels now take 15% of the total antenna load rather than 10%. Although in general the problem disappeared thereafter, spike-afflicted data from 12 August (the second dataset after the July shutdown) show that it cannot be forgotten.

Transit step
Measures of the transit step size were made several times during the period, with all measures bar one showing amplitudes at the horizon of ~3arcsec. The last, discrepant measure was taken with the antenna transitting below the north pole (and hence moving down in elevation before transit and then upwards afterwards), rather than in the south (up then down). The full implication of this discrepancy in under investigation.

Tracking
Tracking of astronomical sources through transit, like those not through transit, show tracking is accurate to ~1" rms in each coordinate over periods of an hour or more.

All-sky pointing
[ All-sky pointing is done in order to maintain the telescope pointing model and is done almost exclusively with SCUBA ]. This period has seen continued disappointing all-sky performance with rms errors in (daz,del) being more typically 2" in each coordinate (or more!) rather than 1.5" seen in previous years. Partly this may be due to the poor weather pertaining during 2002 : there is some noticeable improvement in performance when the weather improves. More than once poor data have, in retrospect, been overinterpreted and the model changed, only to be changed back after acquisition of further data. The pointing department looks forward to the clear, stable weather of winter.

Focus
Default focus positions and elevation- and temperature- dependencies are functioning well, although a review is scheduled.

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