Computer Science – Performance
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21530502c&link_type=abstract
American Astronomical Society, AAS Meeting #215, #305.02; Bulletin of the American Astronomical Society, Vol. 42, p.302
Computer Science
Performance
Scientific paper
The Kepler Mission relies on precise differential photometry to detect the 80 parts per million (ppm) signal from an Earth-Sun equivalent transit. Such precision requires superb instrument stability on time scales up to 2 days and systematic error removal to better than 20 ppm. To this end, the spacecraft and photometer underwent 67 days of commissioning, which included several data sets taken to characterize the photometer performance. Because Kepler has no shutter, we took a series of dark images prior to the dust cover ejection, from which we measured the bias levels, dark current, and read noise. These basic detector properties were essentially unchanged from ground-based tests, indicating that the photometer is working as expected. As a result of better thermal stability and illumination from starlight, several image artifacts previously discovered during ground testing have proven more severe on orbit, limiting our ability to detect Earth-size transits over parts of the 112 square degree FOV. Because of Kepler's unprecedented sensitivity and stability, we have seen several unexpected systematics that also affect photometric precision: pointing shifts caused by a variable star used for fine guidance, small focus changes due to outgassing and spacecraft heaters, and shifting bias levels near saturated stars. We are using the first 45 days of science data to characterize these effects and to develop detection and mitigation methods that will be implemented in the calibration pipeline. Based on early testing, we expect to attain Kepler's planned photometric precision over 90% of the FOV.
Kepler was selected as the 10th mission of the Discovery Program. Funding for this mission is provided by NASA, Science Mission Directorate.
Argabright Vic S.
Borucki William. J.
Bryson Steve T.
Caldwell Douglas A.
Dunham Edward
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