Tracking of Uranus with RxB and the fives method was performed for about 2.5 hours between about HST 05:15 and 07:40. Uranus moved from (az,el) = (217,53) to (248,26); the empirical correction was disabled throughout. Pointing residuals are displayed below:

The race defect reveals itself as +ve & -ve excursions in the azimuth residuals. The green line is the current empirical correction (of amplitude 6" at the horizon) and assumes perfect pointing/tracking otherwise. There are clear indications of deteriorating conditions or performance as Uranus passes (az,el) = (242,30) that contaminate a clean extraction of an amplitude at the second event at az=240.

The defect amplitudes (peak-to-peak) at (az,el)=(223,51) and (240,36) are estimated as 2.0" and 2.8", giving amplitudes at the horizon of 3.2" and 3.5", respectively; a mean of 3.3", cf approx 7.0" 6.1" and 5.0" previously. (A trend ? downward ?) This trend might justify changing the amplitude of the correction at this time, but confirmation of this trend will be sought first.

The rms of the elevation tracking errors during this period is 1.1".