Tracking 970408

Mars was tracked over the azimuth range 99 - 123. The behaviour of the azimuth residuals show the problems due to the faulty central bearing :

The residuals have the form previously seen now with amplitude 5.2" at (az,el) = (109,58).   The previous algorithm would have suggested an amplitude here of 6.1".

The figure does not correct the data for the time-(az-)lag in the logging process, but thanks to the fairly high resolution of the data (one logged datum each 70 seconds) the location of the bearing problem at this azimuth can be well-established. The logging is the last event in the cycle and Jason reckons that the mid-point of the data-collection occurs at about the mid-point ofthe cycle. The peak and trough occur at (are logged at) uncorrected azimuths of 108.6 and 110.4, the corrected values then being 108.5 and 110.2. TEL_EMPIRICAL.dat currently produces the peak and trough at 108.3 and 109.9.

Conclusions ?

Given

• the scatter elsewhere in the diagram,
• the different (increased) resolution of this new data compared with that used to set up TEL_EMPIRICAL, and
• Justin's (and others') concerns about the noise in the azimuth drives,

The elevation residuals showed a very strong trend with time, which also correlates with temperature differential by the amount of 12.6" for each degree C of difference between the front and back legs. This trend with this size has been seen several times recently and should be correctable by a suitable adjustment to the temp_slope parameter. After correction for this thermal effect the mean rms residual of 75 logged data was 1.0", with no indication of any effect at about azimuth 110 due to the central bearing.

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