Physicists are somewhat pessimistic enough about settling Mars in the very, very, very distant future, which requires many orders of magnitudes less energy than the dreamy space ambitions you describe. Additionally, they are far more pessimistic than the general population and physics undergrads.
Fusion-powered ships would require thousands of years to travel to a new earth. Maybe a couple decades to alpha centauri if we really push physics to its limits. You then need to develop materials that won't disintegrate during the trip. You think rubber seals are gonna last? And even then, parts will fail which will need replacement even with really excellent control systems due to the length of the trip. Gases will escape from their containers, requiring a method to replenish on board. Essentially, you'll need a bit of industry on the ship just to deal with long-term maintenance issues that make the upkeep of our infrastructure look like a self-resolving cakewalk. You then need social structures that will endure for the entire voyage, possibly across numerous generations. Then you have the fact that critical failures result in instant death - little pockets of matter that is to small to detect but will destroy everything upon contact at a substantial velocity.
Never mentioned gravity b/c it's almost a non-issue in contrast to everything else. We will probably be able to do fusion before being able to create artificial environments from random materials around us. (we have not been able to artificially create/replicate a our biosphere to date, though this also seems theoretically surmountable, in comparison to the energy problem. however, the notion of taking a chunk of rock which may or may not contain the matter we need and turning it into what we need it to . . . yeah, that's going to take a while)
Essentially, to do even the space travel thing requires a self-sustaining ship capable of traveling for hundreds of years without access to earth with a stable society and an amount of energy completely unfathomable to us now. Oh, and not dying en route due to sh!t in space or bouts of radiation.
But you are talking much, much larger than interstellar travel.
It doesn't look good, and that's under an ideal scenario.
Now, returning to reality, we have not left low-earth orbit in thirty years. We are not putting much of a budget towards developing nuclear fusion. We are quickly burning through fossil fuels that have permitted us to develop as rapidly as we have. Sh!t, we are even content with it, too.
TBH, it's looking to me like we are facing a material development plateau. Other things will improve, but the exponential growth that we saw from the industrial revolution does not seem likely to last. We won't fall back into a dark age or anything, but we're eventually going to have to come to grips with the fact that things mightn't change all that much WRT growth. Of course, I say this independent of the space stuff as it is pertinent to people in general.
coolbeans90
I've never suggested that these things are right around the corner, and in fact said that what we are currently doing now is taking the first 'baby steps' toward this possible future.
I don't forsee such things being possible for a thousand or few years, but I do believe we will get there eventually. Mankind even 100 years ago could not envision the world we live in today, and to write off any future advancements that physics say is possible, just difficult, is short-sighted.
As for the fusion thing, I wasn't suggesting that as a means of propulsion, but rather as an energy source for things like electronics, heat, lighting, growing foodstuffs, etc. The ion engine is probably the best currently known method of propulsion.
Further, avoidance of debris is a non-issue if you have the means to move it with a ram well in advance of the ship arriving at that location. A repulsive electrostatic ram could clear out the smaller particles, followed by larger physical devices. The ship would travel in the envelope behind these devices.
And I'm also not suggesting we take astroid rocks and turn them into something else. Metallic asteroids are a dime a dozen, and there's bound to be such solid debris around any star.
I see these ships as being more a multitude of structures, perhaps not even physically connected but travelling together in such a fashion that it may appear as if they are. This way failure of one structure would not affect the functionality of another.
Also keep in mind that the faster the ship travels, the slower time passes for its occupants. So while a ship bound to Proxima Centauri may from Earths perspective take generations, it could theoretically happen in a single lifetime for those aboard if we can reach sufficient speeds.
Further, all elements originate with hydrogen. If we've got fusion down, we could produce whatever elements we want from it (nucleosynthesis) as this is exactly how stars do it.
And free hydrogen being quite available in space, there's not much we can't do once we get the secrets to fusion down. Again, not in our lifetime, but I do think our species will get there eventually.
Edit: WTH is with GS and the random removal of spaces between words lately?:evil:
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