HST Call for Proposals and HST Primer for Cycle 24 . ... The WFC3 IR channel is used to obtain images of a target in filters F110W and F160W. Assume that the ETC has shown that exposure times of 10 minutes for F110W and 20 minutes for F160W are adequate for the science goals. ... Time (minutes) . ... Thus the desired exposures can be accomplished within the two orbits, and there are about seven to eight minutes of unused orbital visibility per orbit that could be used to increase the exposure times. ...