I got this from my middle school library back in the 80s but the book seemed to be from the late 50s to mid 70s. This was a young adult targeted novel about a captain who hijacks a military spaceship in protest of nuclear weapons.
He takes school kids as hostages, however he eventually dies from radiation sickness and the children have to figure out how to pilot the ship themselves. I recall a scene where one of the young people succumbs to radiation sickness, and there is a scene where his hair is falling out.