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Image name: Attitude_vs_Temperature.png (click image to enlarge)
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Date submitted: 03-Mar-1995
YOHKOH TEMPERATURE AND POINTING DRIFT L. Acton 3-Mar-95 Since launch the front end of SXT has undergone temperature variations related to orbital parameters plus a long term increase. This variation is illustrated in the LH panel. There are also short and long term variations between the commanded pointing of Yohkoh and the actual pointing as revealed by the position of suncenter on the SXT images and the HXA limb sensors. [These two ways of measuring pointing agree to an accuracy of one or two SXT pixels and, with corrections, are better than one SXT pixel. (J.-P. Wuelser)] The difference between the actual and commanded pointing the N-S and E-W directions are plotted in the lower two panels of the middle section. Note that this attitude discrepancy in the N-S direction is about four times larger than it is in the E_W direction. It is obvious that the sense of the pointing discrepancies are correlated in opposite directions for the 40-day orbital thermal peaks and the annual and long term thermal trends. This accounts for the very great scatter in the correlation diagrams of the RH panel -- although the basic trends can be clearly seen. The solid lines show the effect of smoothing both the temperature and pointing data with a 50 point (roughly 100 days) smoothing width. The dominant periods in the temperature data are close to 25 days 44 days 179 days 323 days although I would not trust the accuracy of these numbers until the power spectrum analysis is more carefully done with more data points than the 632 of this analysis.