This isn’t the graphic I will finally go with but just a test to see how I would construct such a longer graphic in Orbit. I want to make sure it works before putting in time designing something.
The slides are responsive. This means their width is rounded as near as possible as they grow and shrink. If they images were an exact measurement and not responsive, which you don’t want on a responsive site, they could be made to abut with no gap. But as each browser rounds the fractional widths differently, you will undoubtedly end up with a sliver of a gap. It is beyond your control as well as mine.