A Cheap Solution for Getting to Mars?
Knight's proposal, which he calls "Mars on a Shoestring," outlines two shuttles going into Earth orbit, hooking them together with a truss and strapping on a powerful enough propulsion system. And that's pretty much it. A pressurized inflatable conduit would connect the two orbiters so the astronauts could go back and forth between the two shuttles.
Then comes the really cool part; a way to provide artificial gravity during the trip to Mars.
More on this inspiring idea here.