Just an 'in-passing' comment about the accuracy of pointing, and exquisite knowledge of the position of Cassini in the Saturn-system on the part of mission engineers:
This image is a single ISS image (not one of a series) of the star (I think) Vega. It's obviously been timed to capture Vega whilst visible through the Keeler gap.
Keeler gap = 35km wide
Distance of Cassini from Saturn's rings at the time = 830,000km
Cassini's speed: 5-6km per second
The power of mathematics - amazing.