Hacker News Reader

Comment by jvanderbot | Hacker News Reader

That's not clear actually. We could, given a religious like motivation, build massive space stations right now with today's rockets, materials, and lifetimes. It's incremental building.

We could not get to the nearest star with today's rockets (or eq.), materials, or lifetimes. There's no incremental engineering there.

View on HN

The star is just 1470 light years from our solar system. So, either a huge coincidence occurred, or there are many stars like this in the Milky Way. In the latter case, you are proposing that every one of the alien civilizations that built each of these things had the same motivational inhibition to colonization. Even more, you are proposing that all such civilizations in the past, and all such civilizations in other galaxies, were similarly inhibited.

A star-spanning civilization would have far more than enough energy to propel interstellar vehicles, for example by laser beaming.

I'm proposing no such thing. GP said that if they had built large structures then it was obvious they could do interstellar travel.

I said that implication was false, it's clear how we might build large orbital structures but not clear how we might to interstellar travel. As a counter example.

The implication is as clearly true as such things could be.

The barrier to interstellar travel is largely economic(*). The resources needed to construct star-spanning structures are many orders of magnitude greater than needed to construct and launch a starship (or a laser with an aperture capable of projecting a beam to interstellar distances).

(*) https://galileo.phys.virginia.edu/classes/109.jvn.spring00/n...

One of the problems with this stuff is most of the problems are analyzed by physicists, who tend to reduce the problem to "can we make the physics work" rather than looking at more practical problems like "do we know if any materials will stand up to getting front-row seats to nuclear explosions?" and the other kinds of engineering problems that have bedeviled rocket science in its entire existence. And that's before getting into more fundamental issues like "what is the effect of space life on human biology?" (to which the answer appears to be somewhere between "maybe unmitigatably harmful" to "catastrophic").

There's a lot of questions that need to be answered before we can truly answer the question "what does it take to make interstellar travel", and the fact that many boosters for space exploration are glibly ignoring those questions is perhaps the biggest barrier of all.

We are getting close to fusion with magnetic containment. So at some point, regular materials won’t be a limit

But materials are improving at a rapid pace. So many orders of scale to co-optimize meta materials. Materials in the future will be magic compared to the limits we have now.

Materials won’t be a barrier to interstellar travel

We are only decades away from being able to do it, for very low mass ships/probes with AI. Long before we will be able to create mega structures

And my point mostly is proven here: We could build a giant space station with spaceX + more iron into space. We could build an interstellar probe in "Some point - we're getting close" or "future" or "a few decades".

Since this whole discussion has been about putative aliens with billions of times our production, not about what we ourselves can do soon, I'm not sure why you're harping on this.

Oh we absolutely could, we could have done it with 1960s technology in fact: https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...

The propulsion may have been theorized to get us up to speed, but there are many other factors, not least of which is shielding from objects while you're going a decent fraction of the speed of light. There's no obstacle avoidance routines with that much momentum.

At 1% of the speed of light, the energy of a proton is 47 keV. This is trivially easy to shield against. The energy of an electron is just 26 eV.

One would need to shield against galactic cosmic radiation, but this really isn't much more of a problem than shielding a vehicle in the solar system.

What about a micrometeoroid?

The risk with these if they are sufficiently large would be an explosion on impact. This is dealt with by placing a thin barrier in front of the vehicle. The particle explodes on impact with the barrier, cutting a small hole. The debris shoots forward, spreading, and is absorbed on a shield. At 0.01 c, a 1 microgram particle deposits 450 joules of energy. This is called a "Whipple Shield".

If necessary, parts of this system could be replaced during the journey.

I just want to be clear that this is all heavily theorized. The density of interstellar space has an assumed ablative rate based on speed of travel, but it wouldn't take much to exceed that. We are at least a few trial runs away from knowing, and that alone makes the prospect of interstellar travel far into the future. (again, repeating my main point)

The technologies within our reach which would be very helpful with building massive space stations are such that they would very much allow for getting to the nearest star within a human lifetime.

The only reason we don't actually reach out for those technologies right now is that many of us have a religious fear of anything nuclear.

This just isn't true. It seems true, because we can treat interstellar travel as a problem of scale, but it doesn't follow that "build big rocket" equates to "go fast and go safe".

The energetics of interstellar dust, radiation, the long timelines of travel. It's not clear at all.

Nuclear energy isn't needed for interstellar travel. Beamed propulsion would likely be faster.

Beamed propulsion is a farther out technology, requiring development of more powerful lasers capable of pushing a crewed vehicle in reasonable amounts of time and has the issue that it is difficult to slow down at the destination.

Nuclear rocket engines were already being developed during the cold war.

Both suffer from the irrationality that the more useful they are capable of being, the more they can be misconstrued as orbital weapons.

I am amused you are objecting to a technology for interstellar travel on the grounds it is "farther out", especially in the context of what hypothetical aliens that are around for millions or billions of years would be using.

We could build a 1% c starship using hydrogen bombs. But it wouldn't make much sense to build it, since in the time it would take to get to even the nearest star we'd likely have something much faster.

I'm not objecting to it, my initial post was trying to emphasize the closeness of technologies capable of reaching the nearest stars, lasers are an option, but imo nuclear propulsion is "closer" in terms of time taken to achieve the energy densities needed to take humans there.

Sure it's only a difference of a couple of decades at worst between the two but in the context of a human lifetime, that's significant.

In what important sense is nuclear closer?

If we sent a nuclear craft today, a future laser or other propulsion craft will still get there much sooner.

Worse, we don’t actually have a nuclear craft design. By the time we worked out a design and built it, the other tech will already be ready.

That is because other tech will require less mass, which will “massively” simplify and reduce cost of the venture.

Given the time the trip will take, it will actually be decades at least, before the optimal time to design and send a ship - even if we had an unlimited budget with the only objective of getting there the soonest we can

Reply on news.ycombinator.com