I suppose, since the energy required would go up linearly with mass but exponentially with velocity, you might want to trade off a slower transit time for a larger ship. But that drives the risk factor way up. At 1% of C, you’re talking about 800 years or more to get to Sirius. That’s not a ‘generation ship’ - that’s an entire civilization living inside a spaceship for what might as well be eternity. 800 years ago, Europe was just coming out of the dark ages. We have no way of even guessing what it might take to keep a civilization alive for even a tenth as long. And just for the sake of genetic diversity and specialization, you would need to house tens of thousands of people, and give them enough space that they wouldn’t just destroy themselves fighting for real-estate. I think this is a wholly impractical idea, and flatly impossible to achieve in any time even remotely close to 62 years.
What kind of propulsion system is that?
Just speculating now, if we WERE going to build such a ship, it would be fun to talk about how that might be done. For example, I don’t think we’d haul the mass up from earth. We’d do something like hollow out an asteroid and use the slag as our reaction fuel. Perhaps if we found a nice metallic asterous, we could put a spinning magnetic field around it and let eddie currents melt it. Let the light junk float to the surface, Maybe we first dig into the center and hollow out a big living space, and then coat it in some thick, temperature resistant composite material. Then heat the thing, and let the metals sink down and coat the composite shell. Now you’ve got a big metal-sheathed home covered in dirt. use the dirt for reaction mass, and off you go.
But your timeframe is just way too short. 62 years is really not a very long time at all. Certainly not for engineering on the scale you’re talking about, when you think of all the intermediate steps that would have to be achieved along the way. There’s a certain limiting speed here that you can not get past by just throwing more resources at the problem. It takes time to develop technologies and to engineer large structures. It takes time to do the R&D required.
Your question might be more interesting if we moved the time frame up to 200 years. It would be more interesting sociologically, too. Just how much could you motivate people today to sacrifice to achieve a goal 200 years in the future? How many people alive today would be willing to give up substantial material comfort to benefit not thier kids or grandkids, but their descendents 8 generations away? How much value do people really place on the survival of humanity as a distant, abstract concept?
Depends on which simulation you subscribe to. The first being that the earth breaks up and slowly dissipates into a new asteroid belt. The second being that the bodies merge into a larger mass. Both outcomes change the gravity well sufficiently to destabilize our own moon’s orbit either to the point that it crashes into the earth as well or is released into it’s own new and likely unsurvivable trajectory.
An interesting proposal. I had assumed from the beginning that asteroid and/or lunar mining would play a key role. But melting down an entire metallic asteroid to use as a core is a new twist. How many gigajoules of power would it take to accomplish that? And how much material would be lost to sublimation? Would it be more effective to set up a vast mirror array, rotate the asteroid at the focal point, and melt it down that way using the “free” power of the sun?
Possibly. I was aiming for a time frame long enough to be possible, if challenging, but not so long as to be a shoe-in.
At 200 years it’s pretty much a given that it could be done. I’d even reverse my decision about making a public announcement because there would be time to prepare the populations for the news and to have provisions in place to deal with the repercussions.
I think the point is that you have to heat it all the way through and melt the whole thing. I suppose you could heat it from the surface inwards, but I don’t know if that would be particularly efficient.
I have no idea how much energy it would take. I’m sure you could easily enough calculate it, by looking at the composition of a typical metal-rich asteroid, working out the energy requirements to heat a standard unit of the stuff to the melting point, then scaling it up. It would obviously be a huge amount of energy, but nothing on the scale of moving a moon around. You’d probably need a whole lot of orbiting nuclear reactors powering some big freaking electromagnets if you wanted to try the eddy current thing.
Oh, we can’t agree at all on this. I have no idea if 200 years is a ‘shoe-in’. I suspect not. You might consider that we’ve had supersonic flight for 60 years, and that it’s been almost 40 years since we first set foot on the moon. NASA’s best estimate for a Mars mission is out to 2035 now, I believe.
As engineering projects get bigger and more complex, the time it takes to do them grows dramatically. And a generation ship isn’t one engineering project- it would be the culmination of hundreds of chained projects designed to prove out technologies and perfect manufacturing techniques and such. Consider the International Space Station - the first desigin was approved in 1984. The first modules were actually lifted into space in 1998. Here is 2008, 24 years since it was first started, and it’s still not finished. It’s currently planned to be finished in 2011. If that happens on schedule, that’s 27 years to build a 400 ton orbiting tin shack.
Think about the things that would have to be done to build a generation ship, many which couldn’t even start until you completed designing, building, and testing prerequisite technologies. Assuming we could even figure out how to do it.
I’m sorry to have missed the thrust of this discussion, but I have been unfortunately busy with the more mundane and tedious aspects of putting stuff in orbit. They may say that it is rocket science, but when you have to talk about ground support equipment safety regulations, transportation bureaucracy, and whether or not Madagascar “reasonably close” to Norway in terms of a debris field you end up self-lobotomizing from banging your head against a table.
Here are a few prior threads that may inform the o.p.:
[thread=441422]How do you slow down your colony ship?[/thread]
[thread=477444]Do we have the technology to build a probe to visit another star? [/thread]
[thread=476087]How will humanity react to a habitable world close by?[/thread]
[thread=447180]Why wouldn’t an “atomic rocket” (as in “Rocket Ship Galileo”) work? [/thread]
[thread=398767]Getting to the stars [/thread]
[thread=398234]Stephen Hawking says humanity must go to the stars. Is he right?[/thread]
I have to agree with Sam Stone and Q.E.D.: we simply do not have the propulsion, energy production, materials, or life support technology to build and sustain a spacecraft capable of keeping people alive for the thousands of years it would take to reach even the nearest star systems, nor could it be developed with a reasonable extrapolation of current technologies, including nuclear pulse propulsion. Attempts to make up for the lack of technology by adding complexity (i.e. multiple vessels, staging supplies, et cetera) increases risk and decreases the viability of such plans. One major problem is energy; most people except climatologists simply don’t appreciate how much energy we gain and then waste from the Sun, and how it drives every single ecological process on planet Earth, from growing food to the hydrological cycle that filters and delivers fresh water. Even if we could generate the amount of energy required to maintain some kind of vast ‘space ark’, we’d be left with the problem of radiating away excess heat without any kind of renewable coolant; the larger you make the vessel, the more waste heat is inevitably thermodynamically generated, and you can only radiate with respect to your outer surface to space. Even without consideration to thermodynamic inefficiencies within the system this simply can’t be sustained by a self-contained habitat indefinitely; you’d need a vast radiating surface. The waste energy produced would continue to build up until thermal levels were chokingly high. (There is actually a Fredrick Pohl story about a spacecraft which is caught dead in space, and he gets it absolutely right that their most pressing problem is heat buildup.)
Traveling to another planet in the Solar system or maintaining an artificial habitat is still well beyond current capability, but it is at least plausible given a reasonable extrapolation of current and near-future technologies (nuclear propulsion, extended life support capability, ability to repair radiological damage on the cellular level, et cetera.) I came up with what I think is a [post=9514841]novel large space habitat concept[/post] a while back which would require minimal terrestrial materials and could possibly support tens or even hundreds of thousands of people with a reasonable margin of safety. Trying to build bigger tin cans in space, however, is a doomed effort.
I think that stranger both underestimates Human ingenuity and overestimates our knowledge of science, Physics in particular.
With the threat of total annihilation hanging over our heads,money and resources would be no object,taking previously unacceptable risks with peoples lives would be the norm and investigating any and all scientific theories however improbable would be encouraged.
Science can slowly and surely be investigated by due process but its not that uncommon for startling breakthroughs to be made.
It is not unlikely that with our minds concentrated this way that we could achieve one of those breakthroughs.
So maybe a generation ship would not be necessary.
You need to read The Mythical Man-Month, and take to heart what it says about attempting to speed up projects by just throwing more resources at them. That works fine when your limiting factor is manual labor. It doesn’t work so well when your limiting factors are complexity and knowledge.
Would the Manhatten project have come about if there hadn’t of been a world war going on?
Would the U.S. have gone from a standing start to putting men on the moon in a few short years if it hadn’t had a total shock to the system from their de facto enemies putting a man into space?
Think of all the promising avenues of scientific research TODAY that have to struggle to get any funding at all,let alone adequate funding.
Then you have the promising but less so research areas.
And then you have the obscure research areas and of course those that though they have some scientific merit are considered by cosensus rightly or wrongly to be dead ends.
I dont think that it would be the first time that a blind alley has turned out to be a break through.
And with the extinction of the Human race in the balance I think that people would be prepared to explore five hundred BAs if even only one of them proved worthwhile.
Very often there are no votes in Scientific research,the man in the street cant see any use for,say,Quantum Physics so doesn’t want to pay for it.
As well as that you have the intellectually challenged MITS who is actively against scientific research because it goes against his religious or moral beliefs(stemcell or G.M.,or even Paelontology for example) and also those who think that science will bring about the end of the world as in those who opposed the Large Haydron Collider.
Lets not confuse greedy aerospace companies with lucrative government funding swallowing up vast amounts of money to design ashtrays for Airforce One with people who know that they,their families and everybody they know are all going to die if they dont find a solution FAST.
An extinction event on the horizon would remove ALL financial,political and even moral constraints from the problem solving process.