Dr. Anthony Zuppero has managed to find a way that we could affordably make the push into outer space and get to inhabit the solar system. A physicist, he’s got the whole thing calculated out, this guy is the real deal. He’s written a very very readable book about his undertaking, which you can download for free in PDF form.
How does he do it? He uses a simple steam rocket which can haul immense loads of water (which is everywhere in the solar system – there are loads of near earth objects (comets / asteroids) and moons – even our own) with a massive crew area made out of water. It’s a serously interesting exploration through one man’s career and the troubles he ran into, as well as the triumphs of discovering that we can actually leave our planet, if we want to.