Hacker News Reader

Comment by api | Hacker News Reader

Look into Project Orion. With thermonuclear bombs you could hit 8% c, which would get you there in "only" 150-200 years including acceleration and deceleration time.

That is still beyond humans with present day life spans, but extend life span to ~1000 years or go full AI and you can totally ride the "devil's pogo stick" to stars <=20ly or so awat.

Fusion rockets would probably be better. I mention Orion because we sort of know how to build it today... at ludicrous cost. No new physics and not that much fundamentally new engineering is needed. Orion is a fabulous and quite valid counter to the folks that seem to like to repeat the canard that interstellar flight is impossible. Hard as hell, sure, but not impossible by any means.

To a fully Kardashev type I civilization it might be around Apollo moon shot difficulty.

View on HN

>Orion is a fabulous and quite valid counter to the folks that seem to like to repeat the canard that interstellar flight is impossible.

I’d never say it’s impossible, if we maintain a civilisation for long enough it might even be inevitable at least at a minimal level.

However, Daedalus/Orion is far from as straightforward as has been suggested by you and others. It’s based on projections of technology made in the 70s, not 70s technology. There are also formidable obstacles, such as obtaining enough Helium3. The authors suggested extracting it from the atmosphere of Jupiter or Uranus. That by itself would be as hard as building the vehicle itself, if not harder. I’d like to see a design for a Jupiter atmospheric scoop and return vehicle.

Also Daedalus couldn’t take people. Staggeringly huge as it was, it was a flyby mission with a 450 ton payload. If it was going to decelerate instead it’s payload was about the size of a washing machine.

Not Daedalus, Orion. It was a 1960s research project involving Freeman Dyson and others. Google it. There is a fantastic documentary that I think is on YouTube.

Orion is kind of shockingly practical. It was forgotten for some time as it was a military research project not NASA or academic.

Do you acknowledge the fact that interstellar travel entails more than just speeding up and slowing down? Because that's what Dyson would be telling you if he were here.

You need a nuclear-powered airtight bunker that can sustain dozens of people, but that's also buildable with 70s technology.

Once you have propulsion and a ship you're pretty well there.

One of the main unsolved problems is the electromagnetic shielding, both front and back (as you need to turn to decelerate). Even at 0.08c every speck of interstellar dust has enormous impact energy, far worse than the radiation of your own bombs. AFAIK this is unsolved.

follow-up: here is what wolfram alpha spits out for a 0.1 grams dust particle hitting you at 0.08c:

https://www.wolframalpha.com/input/?i=1%2F2+*+10%5E-4kg+*+(0...

it's 35% of the fission energy released by totally fissioning 1g of U-235!

i.e. I don't know whether this it's feasible to just have a heavy water & lead shield, as 0.1g is fairly optimistic to be the heaviest particle hitting you. Already at this size we're in range of tactical nuclear weapons.

You will essentially kill dozens of people once they hit an interstellar cloud with anything bigger than a sugar molecule at 2/5c.

Do we actually have navigation technology to travel at 8% c without crashing into deadly space debris?

Or more general: Space travel isn't just about speed.

Space is called space for a reason. Even in real life asteroid rich orbits the odds of hitting something are very low. Pulp sci-fi asteroid fields like the ones depicted in Star Wars are just not a thing. Outside the inner solar system the odds of hitting anything are so low the risk doesn't really rank in comparison with things like major equipment failure in transit.

Nuclear salt water rocket would likely be even faster, but unlike Orion is still just a paper concept at this time.

Is that subjective time for the crew or objective time? Is there much of a difference at 8% c?

Little time dilation at 8%, so not a big difference.

Assuming 200 years for people on earth, the traveler would experience 199.4 years

https://www.wolframalpha.com/input/?i=time+dialation+at+0.08...

Reply on news.ycombinator.com