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Comment by jandrese | Hacker News Reader

This is one thing that I think is underestimated: just how big of a hurdle it is to travel between solar systems. It took the Voyager probes almost 40 years to leave our solar system, which is like taking 40 years to get out your front door on your planned walk across all of Europe and Asia.

By the time we have the technology to do so, we will necessarily have the technology that makes it unnecessary. The primary thing you need is something that can survive effectively indefinitely in deep space where there are no resources available. But if you have that you can build stellar colonies that have unlimited access to solar power and can survive indefinitely just as easily.

It's not like we are short on mass in the solar system either. It will be a long long time until we've used up Jupiter, Saturn, Uranus, the belt, etc...

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We basically have the technology to reach Alpha Centauri in less than 200 years for reasonable amounts of money [1]. I don't find it unlikely that alien civilizations could either do better, or have significantly longer lifespans than us.

[1] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

Say we invent life extending technology or generational ships. What happens when someone gets to Alpha Centauri? What can they do?

Alpha Centauri might not be the best destination, but for suitable systems the travelers could go forth and multiply, eventually sending out ships of their own.

But that makes it a much more costly operation (both in money and risk). Even a nearby star system with a habitable planet would be hard to get going because the settlers that go there would be cut off from their home planet. They would need to take with them everything necessary not only to establish a colony but to thrive (and stave off potential extinction level events which, when your population is small, is far more likely). And there would be little help from homeworld. Even information would take at least the speed of light to get there.

And this is just the tip of the ice berg. I agree with jandrese that people underestimate just how much of a hurdle this is.

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”

― Douglas Adams, The Hitchhiker's Guide to the Galaxy

When talking about interstellar distances people just aren't equipped to think about the scales involved. They're so far outside of the scale of human experience that our brain really struggles to understand the magnitude of the problem.

We're talking about billions of dollars to set up a short term test camp on Mars, and by interstellar standards that is close to nothing.

What could any explorers in the history of mankind do when they got to an unpopulated island or continent? Spread, inhabit, and help ensure the survival of their species.

Whether or not you agree, some people like the idea of humanity surviving as a multi-solar system species.

I'm not sure Alpha Centauri has any inhabitable planets, at least for our biology as it stands today, but what we learn along the way might render that moot.

See my reply to adrianN. Getting there is only a small part of the hurdle to establishing a viable colony, let alone one that can prosper enough to spread further.

This seems to be an exaggeration though to say that we basically have the technology. We have the ability to build a ship that would survive 300,000 one megaton nuclear explosions for 200 years, for a reasonable amount of money? What if this paper spacecraft is actually beyond the realm of material science?

I read a book about the topic. The conclusion seems to be that it was doable with 1960s tech, but the test ban treaty, concerns about fallout and the ban of putting nukes into space killed the project before it could produce a prototype.

Which only makes sense if you ignore all of the details. In 2020 we still don't have any proof of concepts for a self-sustaining biosphere that includes people, much less a spacecraft that can survive for hundreds of years without major maintenance. We don't even have a good solution for absorbing all of those hard gammas from detonating 300,000 fusion bombs in close proximity to the people.

The ship itself offers protection from the radiation. The pusher plate, all those bombs, that's quite a bit of shielding. The life system is of course a problem, but that doesn't change the fact that the ship would be pretty fast.

That's highly speculative and glosses over a lot of the details. The idea that it can be done with today's tech for "reasonable amounts of money" is laughable. The launch costs alone for putting 500,000 tons into orbit already kill that idea.

For a point of reference, SpaceX currently charges about $2,720/kg for LEO. So to get this project off of the ground (literally) you're talking about $1,360,000,000,000. And that's just launch costs. It doesn't include the invention of spacecraft that can survive in deep space indefinitely without resupply, the materials science advances needed to survive 300,000 nuclear explosions (the paper suggests 1mm of stainless steel coated with a thin layer of oil), or the fact that this is only talking about getting to a place we probably don't even want to go.

And this is kind of the point. Once you've invented all of the necessary pre-reqs there's really no point in hitting it with 300,000 nuclear explosions, you already have a self sustaining space colony. You can continue to build those pretty much forever and never ever come close to running out of room. There's no need to travel to some other star system at that point. The sense of adventure has to be weighed against the risk factor of detonating 300,000 nuclear bombs without incident and all of the yet unknown hazards of interstellar travel. Oh, and thanks to the tyranny of the rocket equation it is a one way trip unless you're packing a nuclear bomb factory and enough mining equipment to get the raw materials you need from whatever you happen to find at your destination.

I think the idea was to use the nukes to launch it into space. If you want less fallout you make the project much harder. In that case I'd recommend waiting until you can manufacture things outside the gravity well.

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