Tom Godwin 
Space Prison [EPUB ebook] 

A space ship heading from Earth to Athena, a planet 500 light years away, is suddenly attacked by the Gerns, an alien empire in its expansion phase. People aboard are divided by the invaders into Acceptables and Rejects. The Acceptables are taken as slave labor for the Gerns, and the Rejects are forced ashore on the nearest ‘Earth-like’ barren planet, called Ragnarok. The Gerns say they will return for the Rejects, but the Rejects quickly realise that that isn’t going to happen. How will the stranded humans survive? And will they be able to pay back the Gerns for their cruelty?