A Central Bearing Load Adjustment (CBLA) was performed on 15 Dec 2004. Tomas Chylek reported :

   " . . the scheduled central bearing adjustment was successfully
     performed by EMS, JNK and TCH today. The load distribution between
     the central bearing and the rollers has been kept at 85%/15% of the
     total antenna weight. The full results are available
here.

    Datasets  El Dirn     HST     mean leg temperatures   Humidity
                          start     start   middle   end       %
  ( 20041211  90  cw      10:19      4.0      5.2    6.0      25 )
    20041215  90  cw      15:07      8.6      9.5    9.9      25

All data channels look OK; the difference between the model resulting from the new data and the current one (of 11 Dec) is shown below:

• The 2" spike in the F1 difference at azimuth 142 degs was in the 11 Dec dataset.
• The differences in (F1,F2,F3) in the latter case are described by rms scatters of (0.68", 0.26", 0.25") c.f. (0.84", 0.67", 0.55") previously. There are no obvious systematics this time.
• The new CW model was merged with the (CW-CCW) template to create a new hybrid track model, which was installed at HST 18:30 on 15 December 2004.
• The symmetry is OK, and the wheel loads - as judged from strain gauge No.2 only - show an increase of about 10%.

All-sky Pointing
After the new track model was loaded, all-sky pointing was performed using SCUBA. It has just recovered from a warm up and is showing signs of repeating the uncommanded 3.2-day warm-up-cool-down cycle, but its sensitivity is not degraded enough to prevent it being used for pointing on bright sources.

27 pointing measures were recorded in 2.5 hours and the raw residuals w.r.t. the old model are shown below:

The strong systematic in the upper-centre panel reflects a -35" change in the azimuth encoder zero-point : which is the major change expected to result from the CBLA. The raw elevation residuals are gratifyingly small. They data were analyzed using TPOINT. Slight adjustments to the other parameters of the model were allowed to optimize the fit. The rms scatter in (daz,del) of these 27 data about the newly fit model is (1.2",1.2"), and a plot from TPOINT after the fit is shown below:

The new pointing model was enabled just before 22:00 HST 15 December.