Testing immediately before and after flight showed no change in performance for either device. Neither an increase in the number of hot or flickering pixels nor any CTI increase due to radiation exposure was seen.
Pre- and post-flight mean dark current maps for the two test devices
are compared in figures 4.122 and 4.123.
These images are averages of at least ten individual exposures, each of
18 seconds. All except the pre-flight image of w157c1 (the front-illuminated
device) were obtained with the detector temperature at -120C; the preflight
image of w157c1 was obtained at -60C. The front illuminated device w157c1,
which had a small edge glow and a bright defect prior to flight, showed
no evidence of either feature during any post-flight testing. This change
may have been a consequence of handling and may have nothing to do with
the shuttle orbital environment. We conclude that low earth orbit shuttle
cabin environment has no impact upon CCD performance for 1 week exposures.
Figure 1.123:
Dark current for the back-illuminated device w147c3 before (top) and after
(bottom) its flight on STS-85. There is no apparent increase in the dark
current. Both images were obtained at -120C. The same color scale is used
for the two images; the signal level, in electrons per pixel per 18 s,
is shown on the color bar.
