The top two things we should be doing

[JoeStrout]

When we finally get serious about moving into space, we know with certainty that it will have these two features:

1. Habitats (and often ships) will spin to produce artificial gravity.  How much gravity they will produce, we don't know, because we don't have any data on the long-term effects of living between 0 and 1 G.  But we know 0 G is bad (and 1 G is good), so we know they'll spin to produce some amount of gravity.
2. Ships (and maybe habitats) will be nuclear-powered.  That's because accelerating masses in space takes a lot of energy, and the more mass you have, the more energy is required.  So we need something that has a lot of energy for little mass.
   

This cartoon doesn't depict rocket fuel, but its energy density is roughly the same as gasoline.  Uranium is over a million (!) times better.  So this makes it pretty obvious why spacecraft in the future will be nuclear-powered.  (Fusion would be great if we can manage it, but fission will do fine.)

So, given that this is where we're headed, it's frustrating that we've spent five decades going around in space not advancing either of these core technologies.  They're not that hard; the Russians have sent dozens of nuclear reactors into space, including a 10-kW reactor called TOPAZ-II.  I bet we could do better; our nuclear-powered Navy is the best in the world.

And as for artificial gravity, seriously, just spin the thing.  And collect the data today that we need to plan spacecraft and space colonies of tomorrow.

50 years from now, we will look back at the late 20th and early 21st centuries from our spinning, nuclear-powered spacecraft with astonishment.  How could those people have wasted so much time, when the path forward was so clear?

[Sailor Barsoom]

For habitats, solar will work all the way out to the Kuiper Belt, and then some. Just have huge (but low-mass) mirrors. But for stuff that has to move around, especially if there might be unexpected course changes, yeah, go nuclear.

You should have seen the reaction when I suggested nuclear cruise ships here on Earth!

[JoeStrout]

Well, a big part of the problem is that in most peoples minds, all "nuclear" power is pretty much the same.

This would be like mentally lumping all "combustion" engines together, reckoning that a steam engine, a coal plant, a natural gas plant, and a Ferrari F136 engine are all pretty much the same.

In reality, just like "combustion," "nuclear" is a very generic term that encompasses a wide range of designs. I wouldn't want a 1900s-era steam-powered factory in my town any more than I would want a first-generation nuclear plant, but that is no reason to condemn the entire class of power source (in either case).

But I saw a suggestion this week that launching uranium (or, presumably, other fissile materials) just isn't politically acceptable, and that we won't have nuclear power in space until we are mining it from the Moon or other offworld sources. I'm not so sure — it seems to me that the Russians have no qualms about launching it, and will launch pretty much anything for anybody if the price is right. Same for the Chinese (funny how the classically communist countries now epitomize capitalism, eh?). So that's another way to get fuel in orbit... and it's not like it takes very much.

On the other hand, if we're collectively happier getting our uranium from the Moon or NEAs, then I'm all for it. The more commerce and industry we get off-planet, the sooner we'll expand into the solar system in a big way.