The closest exoplanet has been discovered.

[TimothyC]

Nuclear Fission Fragment drives have issues ([urlhttp://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf]even the primary source I have for them says they are probably not feasible[/url]), they do however had the advantage of being able to be be built with modern technology. They also can get ISPs of around 1*10^6 sec, which is better than the Ion drives by a factor of 100.

[Guardsman Bass]

So, a thousand super-tankers (assuming 500 thousand tons per ship) is 500 MILLION tonnes of fuel to get to Alpha Centauri using a theoretical nuclear fusion rocket.

I might've been a little too optimistic about our capability of getting to Alpha Centauri

Can you imagine even building the engines for that nuclear fusion rocket? Or what it would take to hold it together under acceleration and deceleration? It's not pretty. And that's if you're willing to wait 900 years to get it to the Alpha Centauri system! I question whether the electronics in the probe would survive that long in interstellar space.

I think I'd rather spend my money building a colossal array of space telescopes capable of interferometry when you line them up properly.

[Borgholio]

Actually considering the distance to travel, 6 railway tankers isn't all that bad...all things considering. The life of the physical ion exhaust grid is over 3 years already. Just need to get enough thrusters to bring the acceleration to a point where the probe can get there in a reasonable amount of time.

[PeZook]

6 railways tankers is trivial ; A single Saturn V could sent up that amount of tonnage, assuming a 20 ton tanker. But that's for a theoretical superdrive running on antimatter

[Skywalker_T-65]

It would take longer to produce the anti-matter needed than it would for the Fusion rocket to get there wouldn't it?

(note, tounge-in-cheek...I wouldn't know for sure)

[PeZook]

We just need a sufficiently awesome/insane piece of infrastructure to do it. Like covering half the Moon with solar panel farms

[K. A. Pital]

Orions are still quite viable when fired from orbit. And the probe might even get there in time.

[PeZook]

Except for teeny tiny problem of manufacturing enough nukes to load them

But besides that, Orion's only advantage is that the fuel is dense ; But the ISP is only around 3000-4000 so you'll still need an absurd mass of it.

[Borgholio]

6 railways tankers is trivial ; A single Saturn V could sent up that amount of tonnage, assuming a 20 ton tanker. But that's for a theoretical superdrive running on antimatter

Not to nit-pick, the article said super-duper ion OR antimatter. So I'm thinking oversized / overcharged ion drives would do the trick...just need a small nuclear reactor to provide power to them.

[Borgholio]

Just thought of something...when you factor in relativity, would that cause the craft to consume less fuel? Think about humans for instance, at high fractions of lightspeed we age slower, consume less food, etc... Would a mechanical device such as an engine consume less fuel then?

[Simon_Jester]

No.

For a given delta-v, you will need slightly MORE fuel on a slightly relativistic journey to gain that delta-v, not less.

[Boeing 757]

Some of you asking how we might find a way of traveling there someday would likely be interested in this here video: Voyage to Pandora.

I have not watched the whole video just yet, but it seems to be worthwhile if you have a few minutes to kill. It discusses various proposed propulsion systems and spacecraft powered by anti-matter reactors among other things. The narrator is somewhat annoying though.

[Simon_Jester]

If we want to accomplish something within our grandchildren's lifetimes, antimatter is not something we should put on the list of objectives. THere is no remotely cost-effective way to create it, and making it in particle accelerators a particle at a time is so staggeringly inefficient that we'd be at it all century to get anything done.

[Irbis]

They just don't come any closer than this.

What if we find star-less planet closer?

Somebody needs to throw 300 billion dollars at the problem.

You mean, occupy 1/4 of Iraq less?

Sad thing is, if Dubya instead of freedomzing Iraq spent the cash on space elevator-like structure, he could have built several for the kind of money he burned and construction of the probe, no matter how heavy, would have been trivial.

You could alternatively go with a laser-propelled optical sail, but that requires some intense infrastructure.

No, at least not at first. You could get away with slowly raising additional power plants and lasers to orbit over time, you would need full power after the probe would have covered a lot of distance.

Or what it would take to hold it together under acceleration and deceleration? It's not pretty.

Um, we're talking about 1/4 G accel/decel here, it's really not (pardon pun) rocket science...

[Borgholio]

Um, we're talking about 1/4 G accel/decel here, it's really not (pardon pun) rocket science...

Yeah see that's the beauty of slow acceleration. Low stresses on the spaceframe, but over long enough time you can get to a very high rate of speed. As I said earlier, 1/4g acceleration would get you to half the speed of light by the time you got to the midway point. Plus if you send a manned crew, having constant acceleration would eliminate the problems of how to generate gravity to keep the crew healthy.

[LaCroix]

Not to nit-pick, the article said super-duper ion OR antimatter. So I'm thinking oversized / overcharged ion drives would do the trick...just need a small nuclear reactor to provide power to them.

You do know that Ion drives do need a propellant? (Usually Helium.) It's not just electricity driving them. The mass of propellant needed for a ion drive propelling that mass+drive weight+actual probe for about a decade at 1/4g is not trivial.

Which means you need more drives to make it to the 1/4g thrust target.

Also, you would need about 6 equal thruster sections, capable of 1/4 g each, to make that journey before they burn out (2-3 years lifetime). Which means even bigger thruster arrays to generate enough thrust.

It's the same thing as with other rocket drives. at some point, it's a race you only can lose.

Especially, since you can only increase overal thrust if the engines were capable to propel themselves at MORE than the wanted target. No matter of how many 1/10 g max output drives you put together, they will never reach 1/9 g.

[PeZook]

Uh...yes they will. If you use two engines with thrust X, you will get 2X the thrust. So if one engine is capable of accelerating a 0.5kg mass at 1 m/s^2, and itself weighs 0.5kg, then two such engines will accelerate the same payload at 1.33 m/s^2.

[Dass.Kapital]

Also of note with the design of the ship. One can take a page from Atomic Rockets (Which seems to have influenced teh Jungle Smurf's movie) and have the thurst engines mounted a the front of the ship 'pulling' the mass along.

I believe the creator proposed 'Valkyrie as name?

So, instead of a large, solid piece of engineering. You just need a very strong shaft/pole/rope/filament to hold everything together. The creator suggested this would save weight/mass. Mind you, the creator was also proposing an antimatter drive to move the thing along as well...

Much cheers to all.

[Sky Captain]

Fusion rocket engine seems to be only realistic way to propel a space probe so fast it could go to Apha Centauri in 20 - 30 years. According to Atomic Rockets Drive table fusion engine could reach exhaust speed of 30 000 km/s so a cruise speed of some 15 - 20 % c would be possible to reach.
Howewer that would require a lighweight fusion reactor with extreme power to weight ratio.
So in order to send an interstellar probe we would have to at first build self sustaining fusion reactor and then improve the technology until neccesary performance goals are reached.

[Borgholio]

Fusion rocket engine seems to be only realistic way to propel a space probe so fast it could go to Apha Centauri in 20 - 30 years. According to Atomic Rockets Drive table fusion engine could reach exhaust speed of 30 000 km/s so a cruise speed of some 15 - 20 % c would be possible to reach.
Howewer that would require a lighweight fusion reactor with extreme power to weight ratio.
So in order to send an interstellar probe we would have to at first build self sustaining fusion reactor and then improve the technology until neccesary performance goals are reached.

The problem is fuel supply, not thrust. Yes a fusion rocket would leave an ion drive in it's wake while it was burning, but it also uses much more fuel. Ion drives are like the Geo Metros of space propulsion. Slow as hell to start with, but excellent fuel economy once they get going. I can't see anything else capable of accelerating to relativistic speeds...

[RRoan]

I was away from town for a couple of days, and look at how much stuff there is to respond to! It's not often that I get to geek out about interstellar rocketry.

What? Ion drives can have an ISP on the order of 10 000 seconds, which beats VASIMIR by 100% and NERVA by 1000%.

And it's still too low for anything beyond interstellar precursor missions. 100,000 seconds is a good rule-of-thumb minimum ISP for an engine intended for interstellar travel.

NASA thinks that there might be a possibility to use antimatter or some sort of uber ion drive to achieve ISP of 50 000 seconds, but that seems to the physical upper limit of reaction drives.

50,000 seconds for an antimatter rocket sounds like it might be a reference to the AIMStar concept (or something similar), which used antimatter-initiated fusion to heat propellant instead of using the reaction products directly. It's nowhere near the maximum achievable even with fission, let alone fusion or antimatter. An ideal fission drive would, IIRC, have a Ve of ~0.055c (an ISP of ~1.7 million seconds). Fusion maxes out at a Ve of 0.089c, or ~2.7 million seconds. Antimatter? An ideal beam-core antimatter rocket can achieve a Ve of 0.58c (~17.7 million seconds), and if you can also utilize the gamma rays then the Ve maxes out at .96c, or a staggering 29.4 million seconds!

Are you actually going to be able to build rockets that can achieve those velocities with those engine types? No, because this is the real world and you can't make an idealized perfectly efficient rocket. But there's a whole three orders of magnitude of potential improvement beyond 50,000s before you hit the physical upper limit of reaction rockets.

But besides that, Orion's only advantage is that the fuel is dense ; But the ISP is only around 3000-4000 so you'll still need an absurd mass of it.

This is true of the in-depth design studies for an interplanetary orion, but those were relatively small vehicles and 50's-era pure-fission pulse unit designs. The maximum specific impulse for an orion increases with size, since it can survive using more powerful pulse units and yield rises a lot faster than mass until you hit the energy density limits of nuclear weapons. Using thermonuclear pulse unit designs will allow for more powerful pulse units at a given weight, increasing the specific impulse considerably.

For reference, the momentum-limited interstellar orion design concept had a specific impulse of ~710,000 seconds.

Just thought of something...when you factor in relativity, would that cause the craft to consume less fuel? Think about humans for instance, at high fractions of lightspeed we age slower, consume less food, etc... Would a mechanical device such as an engine consume less fuel then?

... no. It means you use more fuel. In fact, as you get into the relativistic velocity regime (past .5c or so) the required amounts of fuel start rising a lot faster than predicted by the regular rocket equation. The idea of using high time dilation factors to get large reductions in apparent trip times is probably not workable without engines based on fantastically high-energy processes unknown to modern physics.

I swear, the relativistic rocket equation hates our guts.

If we want to accomplish something within our grandchildren's lifetimes, antimatter is not something we should put on the list of objectives. THere is no remotely cost-effective way to create it, and making it in particle accelerators a particle at a time is so staggeringly inefficient that we'd be at it all century to get anything done.

A large part of the problem with antimatter is that we currently produce it with ultra-high precision-scientific instruments on the bleeding edge of modern technology and which are optimized for things other than the production of antimatter. Forward estimated that a purpose-built antimatter production facility would be something like 10,000 times more efficient at antimatter production than scientific colliders and would bring the cost of antimatter down to ~10 million dollars per milligram, at which point it is cheap enough to be realistically used for space travel.

The bigger issue is storing antimatter for lengthy periods of time.

You could alternatively go with a laser-propelled optical sail, but that requires some intense infrastructure.

No, at least not at first. You could get away with slowly raising additional power plants and lasers to orbit over time, you would need full power after the probe would have covered a lot of distance.

You're forgetting the lenses.

Forward's original concept used a 1,000-kilometer zone plate, levitated in place by rockets near the orbit of Neptune. While later research has reduced the necessary lens size (mostly by using materials with much higher thermal limits and therefore allowing for much higher acceleration), you still need optical elements of a size such that they cannot be feasibly lifted into orbit; you need to construct them in space, and they should be far enough out that gravitational distortions don't play merry hell with their shape.

Interstellar travel of any sort is hard. If you're still at the point where you build your space infrastructure at the bottom of a gravity well, chances are you won't be able to pull off an interstellar mission with a low enough travel time that it won't get passed by later generations of probes.

[Sky Captain]

Fusion rocket engine seems to be only realistic way to propel a space probe so fast it could go to Apha Centauri in 20 - 30 years. According to Atomic Rockets Drive table fusion engine could reach exhaust speed of 30 000 km/s so a cruise speed of some 15 - 20 % c would be possible to reach.
Howewer that would require a lighweight fusion reactor with extreme power to weight ratio.
So in order to send an interstellar probe we would have to at first build self sustaining fusion reactor and then improve the technology until neccesary performance goals are reached.

The problem is fuel supply, not thrust. Yes a fusion rocket would leave an ion drive in it's wake while it was burning, but it also uses much more fuel. Ion drives are like the Geo Metros of space propulsion. Slow as hell to start with, but excellent fuel economy once they get going. I can't see anything else capable of accelerating to relativistic speeds...

Ion engine has nowhere near exhaust velocity required for fast interstellar travel. Ion engines max out at around 300 km/s exhaust velocity. Even if it is possible to design ion engine with order of magnitude greater exhaust velocity the required electrical power for meaningful thrust levels would quickly go into terawatt range. Fusion engine while providing greater specific impulse also have advantage of producing thrust directly.
Ion thrust = reactor > machinery to convert heat into electricity > ion engine
Fusion thrust = reactor with magnetic nozzle

Obviously a system that produce thrust directly would be capable of much higher performance than a system that involves power conversion steps generating looses and tons of waste heat requiring huge radiators.

[Grumman]

6 railways tankers is trivial ; A single Saturn V could sent up that amount of tonnage, assuming a 20 ton tanker. But that's for a theoretical superdrive running on antimatter

That's about one hundred thousand Tzar Bombas. It's not enough to blow up the Earth ala Alderaan, but I have my concerns about constructing the most powerful weapon in the history of mankind just to send a simple probe.

[PeZook]

Sending ANYTHING over interstellar distances will involve building devices that could sterilize the Earth if misued.

It's a good thing Al-Kaida won't ever be able to produce antimatter and send it into space to act as fuel for interstellar probes, then

[ryacko]

What are the chances that we might find a rogue planet within two light years?