New track model installed.

One CW inclinometry run was made Saturday afternoon. (Thanks Ed).

     dataset     Start time     Mean leg temperatures
                     HST        start   middle    end
   inc980214        10:55        7.2      8.6     9.7 C     cf
  (inc980131        12:55        5.2      6.5     7.6       
   inc980124        12:30        8.4      9.6    10.4   
   inc971214        10:55        2.2      3.8     5.0   )

The plot below shows the difference between the model that this new data would generate and the current model, of 971214 :

Whereas a previous difference plot (980124-971214) showed no 'spikes' - and a more recent one (980131-24, and by implication 980131-971214) showed 1-2" spikes at azimuths 13, 38, 64, 193, 218, 244, this new plot shows spikes at these same azimuths, but now of amplitudes typically 3-4". The above azimuths are where wheels 2 and 4 hit some of the track joints (see the table of wheel/joint interactions).

The new model has been installed, but clearly its validity needs regular checking, and I would request that any and every opportunity be taken to get CW inclinometry. If the model is changing so much on such relatively short timescales then we will need equally frequent inclinometry data to keep abreast of it.

Reports of "interesting" pointing on the night of 980215 were received. These data have rms scatters in (daz,del) of (3.3",2.3"), certainly worse than our advertized performance of (1.5",1.5"). The data were inspected to see how many (of the 18 data logged) were taken in the azimuth intervals 8-18, 30-44, 60-70, 188-198, 212-224 and 240-252, which define the large differences seen in the above plot. Only one point did, so the large scatters seen on that night are not attributable to a poor track model. The pointing performance on nights either side of this shows no particular cause for concern regarding the track model, although some odd behaviour of the elevation pointing residuals with time is apparent, usually indicative of uncorrected thermal effects.

Wayne informed me of a change in pointing tactic (from use of the array to 5-pointing with one pixel) that occurred last night. This also seems unconnected with any changes seen in the pointing.

As always, more data seems needed to resolved any of these issues - in particular there is a need for further inclinometry. TSSs : please do inclinometry whenever the opportunity arises.