Anyone who doesn’t understand this point should watch 2001: A Space Odyssey again. In fact, you should watch it again even if you do understand the point :).
Yes, that’s what I meant. But if you need a hard dock and hard air lock with the ship (for large personnel transfers or large cargo transfers), my idea would be a simple cradle. Think of it as a center hub that basically rotates counter to the base ships rotation, and thus is stationary relative to the rotation of the station (at least in the angular plane…obviously you’d need to match vectors and velocity). Ship comes into the hub, docks (something we can and do now, and have done since the early days of Apollo and the Soviets even before that) and is made fast to the center cradle, and then the center cradle/dock is slowly allowed to stop it’s counter rotation and then spun until it’s rotating in synch with the station. Lock it down, open your air lock and climb up into increasingly higher g (you wouldn’t need it to be a full g, even a quarter or half would be enough close to the outer hull). Simple, if you need a hard lock for large transfers of cargo or if you want to not have your people jumping to the hub and using an air lock.
The point is, it’s possible. I can think of several ways you could do it off the top of my head, and I haven’t studied aero-space engineering in longer than some of our posters have been alive. 
And there are a LOT of orders of magnitude smarter folks than me out there who could think of even better ways and methods to do it if you gave them the green light and the resources and turned them loose.
If you go with the Orion idea, while the ship is under thrust you wouldn’t want it to be rotating anyway (for that matter, you wouldn’t want rotation if you used a solar sail or some other continuous thrust system, since you’d have both angular rotation and thrust in a different vector, which would do all sorts of nasty things to the crew I’m thinking, depending on how much thrust we are talking about), so you could do your docking then, and not dock while the ship is coasting and you are using rotation to simulate gravity and keep the crew in decent shape.
None of this stuff is particularly feasible from a cost perspective…but it IS possible. We COULD travel into interstellar space if we really, really wanted too. It’s just engineering…and tremendous, even ruinous costs. And we could do it today, especially if we factor in a low probability of actual success (could does not equal a sure thing, or even more than a minimal chance it would work). In 100 years or a thousand years, it might even make sense and be economically feasible. But the OP is saying it’s impossible, now and forever…and that’s just not correct. We might never do it…but we COULD do it. There is nothing that is a total show stopper for the idea, leaving aside the tremendous cost.
I’m not even convinced the cost will always be tremendous. Kim Stanley Robinson, in Red Mars, suggests the idea of self-replicating machines (I know others have suggested them as well, but I thought this was the best version). If we’re able to create bootstrap factory robots that can seed asteroids, it may just be expensive in terms of time, as we let the robots do their thang.
Gahhh.
Come on people. Do you not think that when they engineer this massive ship the size of a city they are not going to factor in airlock losses? Or random leaks? Or the occasional sector 7G blowing up?
And for that matter, this whole “if thing X breaks down” they are screwed too complaint hasn’t been thought out too well either.
Yes, they might be. But the engineers aren’t just gonna build thing X and say “hope that baby lasts a thousand years”.
If we send a generational ship to a nearby star there is going to be, as shocking as it seems, some actual engineering involved.
You need to read 2312. Seriously.
Yes, we could do it. I was just pointing out some things that we’d need to take into account and overcome for very large, long term, possibly permanent habitats. I WANT for us to do more research in space, at least in the solar system. I think it’s stupid that we aren’t doing more in space, because it pays off in the long run.
We can’t really do interstellar travel now, it’s true. And we never will, as long as we’re too afraid to step out of the front door and into the yard! We can’t run right now, so we have to learn how to crawl and then walk.
As ralph124c suggested, you would be looking at a journey of centuries, perhaps millennia. What would you use for an energy source (life support) that you could rely on for thousands of years in the depths of interstellar space?
Fision reactors. Lots and lots of fision reactors similar to the ones the US Navy uses in most of the capital ships should do the trick.
I agree. I wish we were doing more for manned space exploration. In the long run, it’s the only hope not just for our species but for all life on this planet. We have to walk before we can run, and crawl before we can walk…and right now we aren’t really doing much of anything to advance our experience in difficult and challenging space exploration for humans.
Assuming about a thousand travelers on board (viable breeding population), you might, best-case-scenario based on some quick math, be able to support the ship for a thousand years with about 10 tons of nuclear fuel, which would be in cherry-picked, unrefined form, because it must not lose its energy potential at all, down to the last nugget. How many reactors is rather trivial, you just need one running and several others for back-up/replacement. They do wear out rather quickly though, replacing the working reactor twice a year is probably pushing the limits. The idea lies right at the edge of realistically practical.
Well, the Navy’s been using nuclear reactors for a long, long time, and their reactors last for decades between refueling. I wasn’t a nuclear tech, so no idea how long you can keep the fuel rods…are you saying you can’t store them, unused for long periods of time? That you’d need raw ore? Even assuming that’s the case, I don’t see it as a show stopper, but it definitely changes how I was looking at the problem if that’s the case. My WAG was you’d have multiple redundant reactors similar to what the Navy has, and refuel them every few decades…and jettison them and the spent fuel if they went bad, perhaps recycling the spent rods with a breeder reactor (which would give you weapons grade uranium that could then be used for the Orion I suppose) to stretch things out.
I’m not listening to the content of this thread.
The estimate I put forth for fuel would already be using breeder reactors to squeeze as much energy as possible out of it. Yes, the navy has been using reactors for decades, but we are not talking about decades here, the ship will need to be able to sail for centuries. Fission reactors do not last very long because of the intense radiation the working parts are exposed to, which compromises the metals’ crystal structure. What you really have to consider is that to use a heat engine, you have to recycle the medium (water/steam), so a containment failure in the piping could well release something more important and harder to replace than the fuel, so the reactor components would have to be retired before there might be a risk of this kind of failure.
Nuclear fuel is, by its very nature radioactive, moreso in its refined form, so it will decay on its own, losing some potency. You need to have a large enough quantity to account for natural decay losses, and keeping it in a less pure form is more likely to preserve more of the potent fuel, so you need to carry a lot of fuel mass at the outset. In addition, the fuel mass will be exposed to unmitigated interstellar radiation, which will have some effect on its makeup, probably causing additional decay. Remember, on this long trip, the ship will not be going near any likely sources of energy or fuel, so you need to keep what you have in good condition as you will not be able to replace any losses.
Before we can realistically consider sublight interstellar travel, we need to start with the long round trip Mars mission to at least get some kind of idea what we would dealing with. Right now, the tech for this kind of trip is ridiculously beyond what we are even sort of maybe capable of pulling off. Better, really, to focus on arcane theories of physics that perhaps a smart guy will figure out a way to cheat relativity so that we could make trips instead of expeditions.
I’m holding out for getting abducted by some visiting space aliens that need a drummer. Towards that end, I have been working on a few traitsthat might improve my chances. 
You probably can’t do it for sufficiently large less-than-indefinite periods either - such as the ~1000 years it takes to get where you’re going.
Which is a problem for generation ships, or not at all. By definition, generation ships require us to be able to reproduce in space - if we solve that, why would our great*20 grandchildren need to unsolve it?
We’ve knocked holes in askthepizzaguy’s argument. Let’s pause to consider what he got right.
It won’t be like Star Trek. TOS was based on cultural memories of European westward expansion, submarine movies, with a bit of science worship thrown in. All good fun. But it’s likely that the first interstellar explorers will be robots, better designed to match the rigors of space. Now they may have organic components. But the sort of elaborate life support that humans demand would be a severe waste of resources.
After that, I’d expect genetic engineering to proceed to the point where post-humans are themselves better adapted to outer space. Among the remaining original-bodied humans (relatively speaking) virtual reality will make a lot more sense than some multi-generational project to ship eating and defecating bipeds to another star system. There’s also the seed shipping scenario of iiandy. Or a soma-enabled post-singularity Matrix style Lotus Eater/apocalypse.
Regardless, it looks nothing like Star Wars, Trek or Buck Rogers. A Star Trek scenario assumes not only a number of scientific breakthroughs, but also a very particular technological path. So again, interstellar travel is likely to appear a lot different than typically imagined.
We will figure it out. See this article from 1944, a mere 69 years ago: Can We Ever Fly Faster Than Sound?
I was reading through Popular Science and came across this which I thought some folks might be interested in. Obviously, this is for a theoretical shorter mission than the generation ship, but it shows how some folks are looking at the problem.
What is your people’s obsession with airlocks and airlock losses?
The engineers will factor that in. And for that matter, if its a big deal because they are space walking every darn day (though I would wonder why they needed to be doing so in the first place) you can pump out an airlock till the amount of air you loose would be measured in milligrams if not micrograms.
Again, technologically and engineering wise this is about the smallest problem of a generation ship there is.
Besides what color you paint it.
The color won’t matter if we install a cloaking device.