That was my first thought. Sounds close but is unimaginably far away. I keep flipping back to the difficulties for stone-age man to cross the english channel, and the exponential speed of technological progress, and yet I still can't see it happening for a long, long time. But 100 years ago we couldn't fly the length of a football field, now we do it as a matter of routine.

Thus my mind is a flip-flopping mess of 'can't be done', 'you never know', 'can't be done'... you ge the picture.

Then I start worrying about technological progress being lost through war/politics/religion and having a library of Alexandria moment and having to start all over again.

English Channel: until about 9000 years ago you could walk across. Stone age people had boats too.No historical analogy can come close to interstellar distances.

Fine ; Atlantic Ocean to stone age man. In hindsight, sure, boat development was coming along and it was only a matter of time. But you take the average stone age man, and tell him that you can sail (or fly) across the ocean one day to another land - that's the sort of leap of faith we require now to believe in interstellar travel. Sure the distances are bigger than any analogy, but distances are just a function of speed. At the moment, it can't be done, so we have to rely on some nebulous concept of 'in the future the technology will be developed'. I want to say 'can't be done' but such challenges continually get overcome by the relentless march of technology. So I have to say 'can't say can't'. Thus it messes with my head.

I think it's not technologically unimaginable -- we know basically what we'd need in order to get there. With a nuclear pulse design, plus sufficient life extension to make people willing to go on 200-year voyages, no reason why the Gliese 581 system can't be our second home. (Hopefully we'll think of a catchier name by then).

Taking a really long-term view, Gliese 581g has certain advantages over Earth. Its M-class sun will still be burning many many billions of years after our fuel-hungry sun has burned itself out.

We just need to wait out a bit for YC to fund Zephram Cochrane's warp drive startup.

Theoretically, a nuclear pulse rocket (http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...) could achieve 0.1c, which would make the trip attainable in 200 years. You would need a lot of nuclear bombs though.

And Project Orion is old nuclear pulse tech. The current state of the art thought on that kind of thing is slighty less crude than dropping fission bombs behind a big shield.

I think that once a habitable planet is 99.9% confirmed instead of 90% confirmed, there will be an unprecedented international cooperation in order to build a probe that can get there at .1-.25c.

It's an interesting time to be a human.

Before I came here, I did my own brief (and likely inaccurate) calculations:

Distance to Gliese 581 g: 21 light years Speed of Helios 2 (fastest manmade object in space) = ~ 241350 km/h Time for Helos 2 to reach Gliese 581g ~= 93 907 years

I couldn't help but think of Carl Sagan's "Pale Blue Dot". 93 thousand years is an awful long time. I'm glad I'm wrong.

But the Helios probes aren't constantly accelerating.

Unfortunately the Helios probes can only get up to that sort of speed because they're going downhill (ie towards the sun). Going uphill to get out of the local gravity well is harder.

At Voyager 2 speeds it takes 340,000 years.

Furtunately, once you leave the sun's gravitational pull (enough), you can accelerate at a constant rate. So "even" if you accelerate at 0.1g, you can reach 0.7c in 100 years.

So if we had such an engine and an energy source, we could get to that planet in 200-300 years.

The cool thing is, technology innovations are accelerating as well, so we will develop better engines faster than the old ones will arrive to the destination. It's a cool race.

> The cool thing is, technology innovations are accelerating as well, so we will develop better engines faster than the old ones will arrive to the destination.

So all we have to do is wait long enough, and at some point we will have already gotten there.

You might not need an engine on the craft, just a big reflector and a tightly focused beam on some planetary body that bombarded it with photons.

The problem then would be slowing down at the other end though.

Fire a mirror off ahead of you?

In the book Rocheworld, they do just that. The light sail splits in two, with the outer portion curving to reflect light from the propulsion laser back onto the inner portion to slow down the ship.

> The cool thing is, technology innovations are accelerating as well, so we will develop better engines faster than the old ones will arrive to the destination.

The plot of Lost In Space (1998) contained that premise.

(As did, to a degree, the conclusion of Ender's Game.)

And Robert A. Heinlein's 1956 http://en.wikipedia.org/wiki/Time_for_the_Stars, one of his "juveniles" that I liked as a teenager.

Accounting for time dilation if we can get up to 0.999c(hey i dont know if we can ) it should take less than a year. http://www.1728.com/reltivty.htm

I don't know the exact equation, but accelerating any mass beyond that of a single particle or perhaps molecule to that large a fraction of the speed of light borders on impossible. The energy required to accelerate a mass increases exponentially, so getting any appreciable mass to .999c is pretty much out of the question. Again, no equation (if someone has it I'd love to plug in some numbers) but I'm guessing it would require on the order of the total energy output of the sun to get even a modest spacecraft to that velocity.

"The Physics of Star Trek" by Lawrence Krauss had the equation I believe, but I can't find it!

I'd recommend one of my favorite web sites: http://www.centauri-dreams.org/

It has serious discussions about e.g. http://en.wikipedia.org/wiki/Project_Daedalus

Edit: Recent discussion about Project Icarus from a conference: http://www.centauri-dreams.org/?p=14513