Bad weather allowed some nighttime inclinometry on the 24th & 25th March :

    Datasets El Dirn     HST     mean leg temperatures   Humidity
                        start      start   middle   end       %
  ( 20020317 90 cw       20:17      3.0      2.8    2.7     100 )
    20020324 60 cw       01:46     -1.0     -1.1   -1.4     100
    20020325 60 cw       01:53      1.7      1.6    1.5     100

The models resulting from the data of the 24th & 25th are compared below with the model from the 17th :

and the difference between the two el=60 runs is shown here :

• On the 24th some event occurred immediately after the first datum at az=10.09. The next demanded azimuth is 11.09, but the second datum was recorded at az=11.54 with crazy values for many if not all tilt channels that took several degrees (~1 minute ?) to disappear. I removed all data with azimuths <20 before reducing the dataset.

• The data of the 24th show distinct structures in both the difference plots in which it's involved, above, particularly at azimuths 37, 64, 217 & 244, corresponding to wheel-joint interactions 4-3/4, 4-4/5, 2-3/4 & 2-4/5, respectively.
  [ The data of the 25th show no such structures.]
  This is a subset of the azimuths involved on 25 Feb that triggered concern of unnaturally low wheel loadings and therefore the unscheduled central bearing load check & adjustment on 05 March. That work was subsequently judged to have been unnecessary, since no change was measured in the CB loading since its previous adjustment.

  The thermal circumstances of the 24th are somewhat colder than usual, although by no means extreme, and may yet provide the explanation for these features. If the answer is not found in the central bearing loading (and therefore wheel loadings ?) then perhaps cold-induced change at some of the track joints listed above is responsible.

• The formal differences in (F1,F2,F3) for these model differences are described by the rms scatters of (0.59", 0.57", 0.60"), (0.59", 0.51", 0.65") and (0.70", 0.38", 0.67"), respectively, cf (0.28", 0.38", 0.32") previously.

• I choose the data of the 25th for the purposes of updating the track model with the reservation that its usefulness may be limited to antenna structure temperatures above zero.

• The updated plot show a deterioration in symmetry at the 24th, but a recovery by the 25th, and . . .

• . . . the updated strain gauge data also show apparent low loading on the 24th, but recovery by the 25th.

  The new model was installed at ~11:35 HST 25 Mar 2002.

Transit Step Amplitude
Transit inclinometry was performed this morning also, and the results are archived. The amplitude remains ~3" and no change is made to the model parameter SCURVE_AMP.