I interpreted that as a question about energy harvesting, not propulsion. Sounds plausible to me. A sort of, cosmic ray greenhouse effect working on a dense in

I interpreted that as a question about energy harvesting, not propulsion. Sounds plausible to me. A sort of, cosmic ray greenhouse effect working on a dense insulated target, producing a heat gradient to a (cosmic ray transparent) radiator. I'm not sure if the material requirements work out, or if it's worth it's mass to bring along.