Magic in Outer Space — James Hartley

Once upon a time there was a spaceship full of witches ... The witches are rounded up by a religious crusade and exiled on a spaceship for a 190-year trip to another star. The ship has problems, and will run out of air long before they reach their destination, so they are forced to use magic to get there faster. Then, of course, they have a whole new world to cope with and develop. But 190 years later, another Earth ship arrives and tells them that things on Earth are bad and getting worse. So they send an expedition back to Earth to try to fix things ...