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dbrannan

Feel free to correct my math

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Voyager 2 (man's fastest space craft) is traveling 35,000 miles per hour / 60 = 583 miles per second.

187,000 miles per second equals the speed of light.

Light can travel 57,395,520,000,000 miles in one year (roughly 5.7 trillion miles).

So, in 21 years that would equal 57,395,520,000,000 miles x 21 years, or roughly 120 trillion miles.

Thus, if Voyager 2 was our space craft we'd have 583 miles per second x 60 seconds x 60 minutes x 24 hours x 365 days x 21 years to get 386,095,248,000 billion miles towards our new planet.

There is a huge gap between 386 billion and 120 trillion miles, like 311 times.

That means it would take us roughly 310 x 21 years = 6528 years to get there using current technology.

I just don't see us going there as being very practical.

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If you were born 200 years ago, you would say us being there was impossible.

In a couple centuries, (hopefully) it'll be a non-issue. Who knows? The important thing is that we actually found something only theory foresee.

Assuming this particular news really did it, because I'm certain I've read similar headlines in the past.

At 35,000mph would take 402,000 years. Inter-stellar travel is not for the feint-hearted. It's probably possible to accelerate a space-craft to around 10x this speed using current motor technology. Even so, that's still 40,000 years - and 21 light years is like a nano-meter away on a galactic or cosmological scale.

Really, if you want to cross inter-stellar space in any kind of reasonable time - O(human lifetime) - you need to go faster. Possible solutions are: solar sail or new kinds of ion thruster. Both of these impart a very small force (and hence acceleration) for an exceedingly long time, resulting in very high velocities. Your target speed is about 10% of c. In the case of the solar sail it receives momentum from sun for ~ 50% of distance (assuming similar-sized star to our sun), and then is braked by the momentum from the target star for the rest of the journey.

Problem with solar sail is it needs to be GIGANTIC, and composed of materials stronger and lighter than those available today. Additionally force from sunlight is proportional to 1/r^2 so your acceleration decreases with distance.

So, nuclear powered ion thruster is probably the answer. But, obviously, this kind of project is expensive. And either way, you need living quarters for an entire society to live and reproduce.

Or you can just keep dropping nuclear bombs out the back of your spaceship and blowing them up.

I want to see some math on how fast we could go if we disarmed our militaries and used our nukes as rocket fuel.

back in the 50s there was Project Orion, studying how conventional, explosive nuclear bombs could be used to power inter-stellar spacecraft:

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul...

Why do you limit a reasonable amount of time to a human lifetime? If we're going to colonize interstellar space with anything like our current technology we're probably going to have to ditch that requirement.

There's no reason you can't have a multi-generational ship that takes a thousand years to arrive. You don't have to send thousands of people either, it's enough to send a hundred or so, have them populate on the way, and maybe send some frozen sperm & eggs with them to increase genetic diversity.

Another possibility that'll probably become viable within 50-200 years is to not send any humans at all, but to only send a fast & small ship with human sperm & eggs that can start hatching humans once it gets there. Raising the infants could be done with robots and other infrastructure manufactured once we get there.

A thousand years, yes fine (this is ~ 10 x human lifetime) But to get anywhere in that time you're still going to have to get to some non-infinitesimal fraction of light-speed. Anything less than this you're looking at 10k, 100k, a million years to get to even the closest stars.

I could imagine the feasibility of a multi-generational ship lasting 100 - 1000 years, but not longer. Just think of mechanical and materials fatigue. I doubt anything could be built which would last any longer (if that long).

The length of time is almost beside the point. If one (long-term) goal is to put our eggs (so to speak) in a basket other than that of our sun, then there aren't a lot of alternatives. Other stars are simply very far away.

Ideally we'd be trying a mixture of probes and generational ships, while also experimenting with Moon and Mars bases.

> Just think of mechanical and materials fatigue.

If you're able to bring machines that can construct and repair other machines from raw materials the limitation becomes how much material and energy you can bring with you, not the amount of time you're out there.

Read 'Orphans of the Sky' by Robert Heinlein to get an idea of the many problems with this approach. Human society is not culturally stable enough to utilize a generation-ship method of space exploration.

Heinlein's pessimistic vision of a the population of a generation ship turning into savage illiterates is hardly realistic, or one of the biggest problem with the approach.

Most human societies aren't stable enough for that. But visit most presently isolated communities, and you'll find that they're quite stable.

If you can visit them, they're not isolated.

If you have an ark ship that can handle on the order of hundreds of years of space travel, you'll have an ark ship that can handle essentially indefinite space travel.

At that point: why land?

The reason you're headed for another solar system is to get access to more matter and energy. You can't find that in interstellar space, so eventually your supplies will run out.

In the traditional colony-ship scenario you'll have had to solve the self-sufficiency problem. So additional matter and energy will only be used and run out inasmuch as you're developing and creating new things beyond the originally-conceived equilibrium point of your ship.

As that's likely something an inventive race will always do, I'll grant matter and energy exhaustion even though it wouldn't be in the form of 'running low on food/fuel'.

But even then, matter and energy are far more safely and easily found, harvested and retrieved if you never enter any planet's gravity well.

If you're thinking more along the lines of a hyper-space scenario, where FTL technology is achieved before self-sufficiency is solved, sure, you'd have more-traditional 'supplies' and need to land and colonize Earth-like planets.

We've been referring to different things. Since you referred to "indefinite space travel" I thought you were talking about not going to another solar system at all, i.e. that "land" meant orbiting another sun.

But that was obviously a misreading on my part. Anyway, I completely agree with you that once your ark ship arrives in a new solar system landing on a planet like Gliese 581g would be counterproductive.

Instead of having to deal with a gravity well it would be better to make a home in something like the asteroid belt. You only need energy & resources for manufacturing capacity, a gravity well can only complicate that process.

People might still want to live on planets as a novelty, or for their resources. But I think any society sufficiently advanced to develop a generational ship that can traverse interstellar space would resemble The Culture (i.e. a swarm of migrating ships & habitats) more than they would resemble The Federation (i.e. people mostly living on planets with ships mainly for transport).

> If you want to cross inter-stellar space in any kind of reasonable time - O(human lifetime) - you need to go faster.

Or you can just make people stop dying after this unreasonable short 80 years.

Voyager's goal was to use a number of gravitational maneuvers to sling itself to as many study objects as possible. It was not launched for interstellar travel, otherwise it could be possible to shoot it out a notch faster with the exact same technology.

True. Given a goal of shooting a probe out of the Solar System at the highest possible speed with conventional rockets, we could do a little better. Nothing to bring travel time down below the hundred thousand year mark, though.

Your math must be off if Google's calculator is to be trusted:

http://www.google.com/#q=21+light+years+%2F+35%2C000+miles+p...

(21 light years) / (35 000 miles per hour) = 402 369.978 years

Ah, I should have just Googled it. That being said, 402,370 years makes it sound even more far fetched.

Let me correct your math - there are 3600 seconds in an hour, so the Voyager is actually going <10 miles/sec

It is also more direct to calculate Voyager's speed as a fraction of the speed of light and then divide that into the 21 light years.

  Voyager goes 35,000 miles per hour (given)
           ... 10 miles per second
  Light goes 187,000 miles per second (given)
  Voyager goes 1/2000 the speed of light
  Light takes 21 years to get there (given)
  Voyager takes 42,000 years to get there.

Hopefully I didn't drop too many zeros or use the wrong reciprocal too many (non-canceling) times.

But Voyager was not intended to go fast by interstellar speeds. It just needed to get to all of its planets before its electronics died. Any speed beyond that was a waste and could have been traded off against more data gathering equipment.

When it comes time to send the nanobots with the directions to fabricate exploration gear and giant space arrays to transmit back the results to us, I'm sure we can make them go faster.

Why not just have them assemble the people too?

The google is strong with me today. http://www.kuro5hin.org/story/2002/12/21/17846/757

One of my favorite sci-fi short story trilogies.

With current technology it's probably possible to build a 99%C speed [unmanned] spacecraft but it would cost hundreds of billions and we'd have to get over some politically difficult issues such as shipping tons of weapons-grade plutonium into NEO.

That ship would get there in 25 years or so, so most of us would live to see the reply on its telemetry around the time our grandchildren are our age.

I don't know much about relativistic effects, but people that does told me that that's not practically possible, even with tons of money. But c/2 is not unthinkable if things like http://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magne... keep developing.

What current technology? The energies involved in getting something to 99% of C are insanely high (the kinetic energy of each kilogram at that speed is about the same as the output of a 132Mt bomb).

Then there are the problems of traveling at that speed - which are significant.

"Realistic" designs for interstellar probes generally rely on not carrying the fuel with the probe and having ultralight masses (e.g. Bob Forwards "Starwisp" http://en.wikipedia.org/wiki/Starwisp) - this still requires impressive engineering (a 560km diameter transmitter producing 56GW) for a total probe mass of 1kg and payload of 80g. And that would "only" manage 20% of C.

http://en.wikipedia.org/wiki/Starwisp

Do I believe something like Starwisp will be built - absolutely. In my lifetime? No chance.

I'd be happy if we get people to Mars in my lifetime - something I don't expect to see.

Yeah - it requires a city-sized power station to accelerate mere protons at the LHC to ~c.

In retrospect I think I exaggerated it. But if we would somehow put our effort to it and invest a couple trillion in it, it may be achievable in this century.

FWIW, your math is off you state: "35,000 miles per hour / 60 = 583 miles per second."

Really, this would be: 35,000 mph / (60 minutes per hour) / (60 seconds per minute) = 9.72 miles per second.

Then just decrease the distance traveled by a factor of 60, so instead of 386 billion miles traveled by V2, it would be about 6.4 billion miles.

I think the point is that it exists. We can work on getting there once we figure out whether it exists or not; no point in working on the travel part if we aren't sure the destination exists.

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