You don't need a rotator of doing a mosaic as you want to try to keep the orientation the same between each frame.
I used SGP Mosaic Wizard to create these two mosaics:
Milky Way
Small Magellanic Cloud
The idea is to keep the orientation as close to the same as possible so that no only each sub in each frame is the same from night to night but also so that each frame matches up and overlaps nicely.