But I read the Permanent book (www.permanent.com). Both books are probably advocating space colonization, right? The fact is there is no reason for humans to move en-mass into space. And we don't have the launch capacity to do so even if we wanted to. Living & reproducing in space requires both gravity and food production, with millions upon millions of tonnes of infrastructure, maybe billions of tonnes. We can't get that above the atmosphere without high-thrust engines, a skyhook, or a space elevator. Heavy-lift rockets can't be launched in sufficient quantities, and a space elevator will be too vulnerable to micrometeorite impacts due to its long tether. That leaves a Skyhook as the best way to launch mega-payload. Once above the atmosphere we have more options, i.e. low thrust, high-efficiency ion engines, nuclear engines, AIM engines. We can move slowly and methodically. But we need a Skyhook to get there in the first place.

Saw your biomass post. Australia couldn't supply the whole world with electricity because it's too inefficient to transmit electricity over such distances. If you could produce ethanol from seaweed then you've got a transportable fuel that could possibly be transported worldwide. But then, just about anyone could cultivate seaweed, if there were a high-cellulose variety developed, which there isn't yet.