Raymond Z. Gallun 
Planet Strappers [EPUB ebook] 

THE PLANET STRAPPERS started out as The Bunch, a group of student-astronauts in the back room of a store in Jarviston, Minnesota. They wanted off Earth, and they begged, borrowed and built what they needed to make it. THE PLANET STRAPPERS got what they wanted — a start on the road to the stars — but no one brought up on Earth could have imagined what was waiting for them Out There! (Goodreads)