Difference: AstrometryThermoelasticDriftCorrection (5 vs. 6)

Revision 62017-01-12 - PilarEsquej

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Astrometry correction due to a thermoelastic drift

Rationale

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Observations performed at the end of the Solar Aspect Angle (SAA) range (the so-called 'warm' attitude range, SAA in the 110 to 119.2 interval) could present a degradation of the pointing performance due to thermo-elastic effects. These would include a larger APE and a pointing drift.
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Observations performed at the end of the Solar Aspect Angle (SAA) range (the so-called 'warm' attitude range, SAA in the 110 to 119.2 interval) could present a degradation of the pointing performance due to thermoelastic effects. These would include a larger APE and a pointing drift.
 
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We have performed a study on this effect by calculating the Z-axis offset for a set calibration observations. While fot STR2 temperatures below -15C the median offset presents a certain scatter around zero, for higher temperatures the behaviour of the Z-axis offset diverges. We have derived a linear correlation between the STR2 temperature and the Z-axis that aims at correcting the effect of such a thermoelastic drift.
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We have performed a study on this effect by calculating the Z-axis offset for a set calibration observations. While for STR2 temperatures below -15C the median offset presents a certain scatter around zero, for higher temperatures the behaviour of the Z-axis offset diverges. We have derived a linear correlation between the STR2 temperature and the Z-axis that aims at correcting the effect of such a thermoelastic drift.
  We have developed a script aimed at correcting the astrometry offset produced by the thermoelastic effect. This should be applied to improve the pointing for observations performed at the 'warm' attitude range (STR2 temperature >-15C). We have applied the script to a set of calibration observations as a test, and checked that the general pointing is improved. The left panel on plot below shows the linear correlation between the STR2 temperature and the Z-axis used to correct this effect. The right panel presents the Z offset distribution before (green) and after (purple) applying the correction, the latter showing an improvement of the APE+ with respect to the original.
 
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