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Hubble Space Telescope
NICMOS Focus During the Second NIC3 Campaign

NICMOS focus during the Second NIC3 campaign (started June 4, 1998)

On June 4th, 1998, the HST Secondary Mirror (SM) was reset to place NIC3 in focus for the second NIC3 campaign. The commanded SM move of 16.6 microns away from the Primary Mirror was expected to result in NIC3 best focus at the nominal NIC3 setting of -9.5 mm in PAM space. The post-move focus results (see the focus history table and plot ) showed that the NIC3 focus moved in the desired direction, although a slight offset from the targeted PAM position remained. The subsequent analysis which involved the attitude breathing model revealed however that the focus measurements were probably impacted by an unusually large breathing anomaly which occured during the post-move focus sweep. This anomaly may account for the offset seen in the latest focus results.