A CW run with the 'fixed' TMU inclinometer was made during the evening :

    Datasets El Dirn     HST     mean leg temperatures   Humidity
                        start      start   middle   end       %
 (  20020327 90 cw       21:56      4.3      3.8    3.3      80 )
    20020424 90 cw       21:00      5.7      4.7    3.7      45

The data were processed into a track model without any temperature corrections, since the temperature channel on the TMU meter is not working. The model resulting is compared below with the model from the 27th of March :

• The blue vertical lines show the locations of the wheel-joint interactions. The 'spikes' are back, in spades ! - see the problem considered fixed in May 1999 by adding 3t of weights to the antenna.

• This is in stark contrast to the previous inclinometry, when all seemed so stable and fine, although lower-level signals of this problem appeared in the data of 25 Feb. On that occasion an adjustment of the central bearing load was requested, but no change in the CB loading was measured.

• Updates to the plots of symmetry and strain gauge data look show low wheel loading as seen most recently on 25 February.

• The track model terms F1 & F2 are affected more than F3, so azimuth pointing is likely to be more affected than elevation : a phenomenon corroborated by pointing data recently.

• Two details of the above diagram are shown below, showing (below left) the azimuth range covered by the recent tracking data (az=140-200), and (below-right) azimuths 200-260.
  

  The locations of these particular 'spikes' would not explain the loss of signal seen in those tracking data, nor the pointing excursion seen at az=180.52, but they are broad enough and widespread enough to cause an average set of pointing data to suffer from excursions up to 5arcsec for 10-20% of the time. And if their appearance and disappearance is irregular then perhaps the above problems are due to other spike patterns being present at that time.

  However, while the 20 SCUBA data recorded during the night had rms residuals in (daz,del) of (2.8",2.0"), removing the (8) data withing 2.5degrees of the suspect trackjoints did not change these rms values by more than 0.1" in each coordinate..

• There are 20 identifiable spikes ocurring where the wheels meet the track joints.
  Wheels (1,2,3,4) (front-right, back-right, back-left, front-left) are involved (5,6,4,5) times, respectively.
  A histogram of the number of times the track joints are involved is shown below :

  Joint

  1/2

  2/3

  3/4

  4/5

  5/6

  6/7

  7/8

  8/9

  9/10

  10/11

  11/12

  12/13

  13/14

  14/1

  Frequency (out of 20)

  -

  - -

  - - - -

  - -

  - - - -

  - - - -

  - - -

  The wheel involvement seems random, but the joint involvement is not. And the thermal component to the problem identified in 1999 seems unlikely here. Is this a new problem, particularly concerning these few joints ?