The only energy technology that we are going to use and depend upon is nuclear, helped by water, and as a minor contributor – solar, because it’s the only source of energy strategically tolerable to depend upon.
And while teenage boys like to fantasize about star trek technology, adult men only spend vast amounts of money on strategically defensible assets. – That’s Just How It Is.
The way you get to be in charge of money is because people put you in charge of money, and people put you in charge of money largely because they trust what you will do with it. And that means the use of loss aversion, and opportunity cost to make decisions. And expensive, failure-prone, strategically indefensible, and therefore vulnerability-inducing assets are pretty unintelligent investments.
We will explore space when we develop both an extremely light craft big enough for humans to trundle around in, AND an engine capable of efficient conversion of energy to velocity, at constant acceleration of one G or greater. We already have cheap means of flying stuff into orbit. That’s why there is so much in low orbit already. But there appears to be less free ‘stuff’ in space to convert into energy along the way so we are going to have to act like primitive ships and move from mass-port to mass-port, and spending more time traveling because we cannot carry the mass with us to convert into energy.
It is possible that we will discover or invent the interstellar equivalent of hydrocarbons (a very dense store of energy for newtonian scale), but as yet we don’t know of such a thing even though from what precious little we understand about the universe, such a thing should be possible in theory even if in practice we cannot find a means of constructing it.