<font color="yellow">"Actually I was thinking of using the asteroids as shielding for radiation and source of resources etc. "</font><br /><br />That's good thinking! The asteroid 'ship' doesn't help payload's delta-v requirements at all but it does help to <i>sustain</i> it during the trip. There might be working closed carbon cycle for humans, animals, plants with greenhouses, fish ponds etc. Even inanimate payloads might need sustaining like environmental control and electricity.<br /><br />Instead of spending months in crammed, spartan tin cans you'd spend only maybe a few days in a shuttle with limited life support designed to catch up with your asteroid ride and depart it at the destination. Most of the trip would be spent in rather luxurious conditions of a large space station.<br /><br />Now we just need to find a nice asteroid with proper orbit <img src="/images/icons/smile.gif" /> Also it might not be such a bad idea to build a conventional space station to serve similar purpose.