10g will get you ~26 km/sec (~0.1% of c). Not bad. You could then boost that with another propulsion method.
Yep. Relatively speaking, getting up to speed is the “easy” part. I mean, it’s still a gigantic project, but in principle, we could build self-replicating robotic factories and put them on the moon. They would use sunlight as energy and mine the lunar surface for raw materials, replicating themselves.
They would build the components for whatever mega-project we want to build, and then would launch the sub-components via a mass driver on Luna. No friction, everything would be done via solar electricity.
For an engine technology that might actually work, check out this paper : http://arxiv.org/pdf/0908.1803.pdf
Stranger’s going to jump in any moment now and say that everything I say is impossible, of course, and that it won’t happen within 100 years.
Maybe, maybe not. The factor that Stranger is missing is that fundamental physics says we can do it - the reason it takes so darn long and costs so much is it takes ungainly teams of short-lived humans to actually develop the advanced technology required. The actual problem we need to solve in order to have interstellar travel has absolutely nothing to do with spacecraft at all. We need to build a form of artificial intelligence : I think the most straightforward path is to slice human brains and map them, and then emulate them on a large computing system. That’s a task that can be done in 20-30 years.
Emulated minds can probably, based on conservative estimates, think around 1 million times faster than current humans*. Assuming you were emulating a few competent engineers and scientists, they could probably build working starships quite easily.
*This assumes dedicated ASIC chips with the speed of current ICs, but built in 3 dimensions. The chips would be custom fabricated to emulate a specific individual’s mind. Calling them “chips” is a misnomer as they would be shaped more like a cube.
Stranger’s such a stick in the mud. Why can’t he see that self replicating robotic factories building a 10[sup]9[/sup] tonne gamma ray laser to manufacture black holes to power starships through hawking radiation would all be so easy once we simply emulate human brains in silicon.
Oh, news for those just waking up from 1970, fusion is still 50 years away.
Well, Stranger’s attitude seems to basically be “everything we don’t have already is too hard”. I knew a professor like that. Pretty much any idea we don’t already have a working copy of, he would doubt the feasibility of.
As for your second comment : NIF hit net gain a few months back. No one is in any hurry to get fusion working because any rational estimate of the costs for a fusion power reactor would be many times more expensive than other technologies. So the investment into the research is relatively minimal and focused narrowly.
Windmills/Solar/Batteries are all pretty expensive tech, but it’s a lot cheaper than paying for the kinds of exotic components you would need for a fusion generator.
Basically, fusion is not 50 years away if there was a reason to get it. We could probably have it in 5 years if we had a pressing need for it.
I think you miss, or have ignored, my point. It’s *fanciful *to discuss self replicating factories and billion tonne gamma ray lasers producing black holes while casually dismissing their difficulty. Especially given we’ve never built such things and have no idea what the underlying engineering requirements are.
If it make you feel better I have the same objection to space elevators.
Take the LHC - various extensions and developments of existing technology took years to design, test, manufacture and them integrate. Look at the 14 month delay due to a faulty electrical connection. The delay wasn’t simply due to people but the fact that there is a limited supply of 27 tonnes superconducting magnets in the world to use as replacement, they are hard to build despite the fact we’ve been doing it for a while now.
Actually, I think space elevators are a terrible idea. A 29000 mile long cable that is one break away from ruining an entire elevator? Terrible, terrible concept. There’s no way you would ever save money with the precautions you would need to take to run such a thing.
Other concepts seem a lot more tractable, such as :
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Some kind of mass driver for the cargo. A superconducting quench gun or hydrogen gas gun or something.
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Laser abalation from ground based lasers. Isp of 4000 or so, and the heavy and complex stuff (the lasers) stay on the ground.
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When and if we ever have self-replicating and/or fully automated factories, we could just keep recycling spent rocket stages into new rockets and launching them. The reason rockets are so expensive is because thousands of very skilled people are building many of the parts with their hands. If a giant assembly line of robots did the job, and the robots were mostly self repairing, then it would be a lot cheaper.
Technological progress is seems to be exponential until limited by physics and available resources. For something like an interstellar mission, it probably would not really seem any “harder” to wait a few years to make those billion ton black hole generators rather than try to do it using any of the other methods we have discussed here.
There are problems with the black hole starship, just like there are problems with the space elevator and every other starship we’ve discussed so far.
Making a very small black hole would be very difficult, but we’ll gloss over that. Some massive ultratech lasers might suffice; you don’t have to take them with you, so you can make them as big as you like.
Feeding a very small black hole would also be very difficult, since a billion tonne black hole would be a millionth of a nanometre across. You’d need to carry some pretty big black-hole feeder tech with you. This ship is getting more and more massive all the time.
The radiation coming out of the hole is what you want to use to propel the ship; but it would have an effective temperature of about 100,000,000,000 K; the radiation would be very-high-energy gamma rays, fantastically dangerous and penetrating, and fantastically difficult o convert into thrust.
All this to allow a real-world method of converting mass into energy - it seems a lot more complicated than using antimatter, which does the same job but has a much lower mass-penalty.
Research into efficient ways of making AM should have considerably better results than the black hole starship concept, even though antimatter annihilation also emits a lot of nasty high-energy radiation that is tricky to use as thrust.
Using a million tonne hole might be better -except that the radiation would be a thousand times hotter and more dangerous.
One of the things I’ve seen in a few recent Sci-Fi novels is the ability to generate movable micro-black holes. They use them to achieve great speeds in normal space by attraction…the micro-black hole acts as almost a magnet to the ship, and since it moves just ahead of the ship it can allow for incredible speed and maneuverability (of course, you’d need an inertia dampener as well, to keep the pilot from being gravy, which they also magically have). I don’t remember how they addressed the radiation issue, or if they even bothered.
My WAG is that if you could create and sustain a movable black hole, the radiation issue wouldn’t be so hard to overcome. 
This is all wandering a bit far afield of the OP though, which was simply if it’s possible if cost were no object. Stranger seems to think that it’s not, I’m not so sure…I think it’s just possible with current technology to create a mission that lasts a few hundred years and has a non-zero chance of success to get to the closest star using the already mentioned Orion technique. The OP didn’t specify that you had to make the trip in the lifetime of the original crew, and while I think the chances are pretty slim, I disagree that it’s completely impossible, full stop.
Just to expand upon this, the major advantage of a linear accelerator is that the energy accelerating the craft comes from outside the craft. It doesn’t have to be carried by the craft. Things get even better if you can use a gravity assist from a planet or the sun.
It’s worse than that, actually. If it were just gamma rays, we could deal with it… We have materials that can absorb gamma rays. If it takes several meters thick of lead, well, that’s doable. But it won’t be mostly gammas; it’ll be somewhere around 80% neutrinos, and nothing we can build matters a gnat’s fart in a hurricane to them.
I think you’re misunderstanding the concept (or, maybe, the authors you’re reading are). Just using a black hole to pull the ship along doesn’t do anything for you, because then you have to figure out how you’re moving the black hole. You can’t just pull yourself up by your own bootstraps. Rather, the black holes are used as high-efficiency power sources, to power a (relatively) conventional rocket (at least, it’d work by shooting something out the nozzle).
Do you have a cite for that? I know that it’s possible to calculate the temperature for a black hole due to hawking radiation, but how do you characterize the distribution of energy? How do you know it’s not 100% neutrinos or 0%? 80% seems awfully specific for an object we have never observed.
[QUOTE=Chronos]
I think you’re misunderstanding the concept (or, maybe, the authors you’re reading are). Just using a black hole to pull the ship along doesn’t do anything for you, because then you have to figure out how you’re moving the black hole. You can’t just pull yourself up by your own bootstraps. Rather, the black holes are used as high-efficiency power sources, to power a (relatively) conventional rocket (at least, it’d work by shooting something out the nozzle).
[/QUOTE]
It would be the authors then. Of course, this is Sci-Fi so you can do what you like. But they are definitely using the black holes gravity, not the (presumably) Hawking radiation effect you are talking bout. The one story I read talked about using these for fighters to give them extremely high performance (until and unless you lose control of the black hole, in which case it eats the ship).
The calculation depends mostly on the number of modes available to the particles, with some factors to also account for the spin statistics. The first calculation was done by Don Page in 1976, but his information on neutrinos is now outdated-- I updated his work back in 2005. The neutrino dominance is mostly just due to the fact that there are more kinds of neutrinos than there are of photons.
Thanks for this data, Chronos!
Neutrinos seem to be a problem in several ultra-high-powered propulsion systems, including antimatter annihilation. Any workable system would need to minimise the neutrino emissions.
Or figure out how to tweak the processes such that the neutrinos are preferentially emitted in some particular direction in the first place. Given the peculiar way that the Weak Force interacts with chirality, you might be able to pull that off through strong magnetic fields or the like.
Indeed, the ultimate rocket would be one that could convert matter and antimatter into a beam of neutrinos- virtually the same efficiency as a photon rocket and with the side benefit of not being a gigaton weapon of mass destruction.
That would be pretty sweet.
However, even 20% efficiency isn’t bad for a total conversion engine. It would still have acceptable mass ratios for a mission at half the speed of light, and the Bussard Ramjet idea would work in this situation, assuming you can feed the interstellar hydrogen you collect to your black hole engine.
It’s also a lot better than antimatter for the latter reason. Also, a black hole engine would be far safer than having to try to contain antimatter.
I am reading this thread with interest. I particularly like the glib way in which several posters have discussed using antimatter as an energy source. Unless I am grossly misled, the containment issues are not trivial.As I understand it, it is not possible to have antimatter anywhere near matter without spontaneous annihilation. I would consider that to be problematic to the point of being fatal to the concept.
Have we conducted any experiments at all where antimatter has been directly manipulated?. Are there any conceivable ways that this might be done? Because if we have to launch something the size and complexity of the LHC to transport a few hundred antiatoms, it’s just not going to be a feasible route. Fight my ignorance.
You can trap antimatter and recently a team manipulated some
Of course building an industrial scale antimatter generator would involve massive amounts of energy, industrial capacity that beggars the imagination and capabilities we don’t have. Maybe eventually we will, but by that point the available funds for a “cost is no object” project will be staggering compared to what we have available today.