Report to the JCMT Board - April 1997

The last year or so has seen the principal instrument for pointing acquisition change several times. SCUBA was used for the first time in a dedicated pointing run on 11 Oct 1996, and at that time - two months after the most recent track-welding was done - showed the pointing model to be in good shape with rms scatters in azimuth and elevation of 1.1" and 1.5", respectively. SCUBA was not used again in this way, however, until 04 April 1997, but is expected to dominate this role henceforth.

Meanwhile, maintenance of the pointing model has required using the heterodyne receivers with the continuum backend (CBE). The poorer sensistivity of this mode, the loss of the A-band receiver for substantial periods, and poor winter weather, have made this task difficult. Other singular events that impacted pointing occurred during the period and, because of the general difficulties mentioned above, persisted longer than might otherwise have been the case :

• The degradation of the 1MHz clock sometime in February was not properly identified and cured until 10 March 1997, and
• The date of a failure of the central bearing, also eventually noticed in February, is still not known. A software correction for this effect is in place and will remain there until the bearing is fixed or replaced.

Return to POINTING