uh-cuz someday the sun will die in a big hot bad kablooey.
However, if we’re looking for substitute solutions, the technology to collect several brown dwarves and build our own friggin’ brand new star might be less than that required to master interstellar travel.
errr How are you going to collect several brown dwarves without interstellar travel? Just wait for them to come wandering by?
Yes, spinning the ship or habitat is one way of simulating gravity. It might cause other problems, though, which we don’t know about yet. For one thing, it’s going to make docking a lot trickier.
Assuming you mean docking to this theoretical spinning ship, it’s actually fairly easy. If it’s rotating, you dock to the center hub. Problem solved. The only tricky thing I can think of is the crew having to go from zero g to the transition to simulated gravity, but I don’t see it as a show stopper.
That’s the thing. None of this is really very practical or economically viable, so it’s not something we are likely to see in our lifetimes. I can’t even imagine what the costs would be to build a very large generation ship using something like an Orion drive coupled with solar sail and/or ion drive. The word ‘astronomical’ comes to mind. But the OP says it’s impossible, not impractical. It’s not impossible, however…assuming as a species we wanted to spend the resources, it’s certainly possible for us to do with at least a marginal chance of success.
And a 1000 year generational ship won’t be?
My education is in structural engineering, not mechanical. I’m mostly familiar with how to design large objects that never move.
But one thing I remember that even bridges and skyscrapers are subject to is metal fatigue. Turbines, pumps, drive shafts, motors and whatnot cycle. They are subject to fluctuating loads as the operate. At each cycle, they get a bit weaker and weaker until they eventually get small cracks and then they fail. Like bending a paperclip over and over again. I used to watch them test this shit in the engineering lab. They would take a 40 ft I-beam and subject it to tons of stress over and over again, dozens of times a minute until it cracked.
The point is, I think they can make stuff that might last decades. Not centuries. I’d bring a shitload of spare parts if I were you.
Because you can’t maximize every variable in engineering. Many of them are mutually exclusive.
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And a 1000 year generational ship won’t be?
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Obviously they wouldn’t know everything that would factor into such a ship, since one has never been built. But we have been going into space for decades now, and have many advantages in material science and structural engineering and design that the Tacoma Narrows folks didn’t have (yeah, I studied this as well in my aero-engineering classes…I think every engineer got to see that film footage and the analysis at least once).
Obviously the environmental factors would be different than those impacting bridges and skyscrapers. However, the same factors that keep skyscrapers and bridges up would be involved here too. If we are talking generation ships, and not sleeper ships, then there would be lots and lots of trained human crews maintaining these things…same as with those skyscrapers and bridges. Properly maintained, such structures can last indefinitely.
I’m pretty sure they would bring along a ‘shitload’ of spare parts and materials to basically be able to build and fabricate whatever they needed. If they did this, the ships would be massive…larger than the largest supercarrier.
You raise valid points…pretty much the points for why we probably won’t be doing anything like this any time soon (or maybe ever). But the OP is stating that it’s flat out impossible, and I’m not seeing that. It’s certainly possible, even with the technology we have today, to travel in interstellar space. It’s not very practical, and the probability of success is less than assured, but it IS possible. At least, I’ve never seen any real show stoppers to at least the concept in theory.
Bridges and skyscrapers are subject to different weathering forces than would be expected in deep space. Think of the voyager probes, which were launched in 1977 and completed their mission in 1989 and are still going with a their full complement of science instruments available. If they didn’t run out of power/fuel around 2025 I wonder how long they could potentially go. Out in space what is there to stop them really?
But more to the point, if they could be periodically serviced and had been built with a much greater fuel supply how long could they go?
Regarding spare parts, you likely won’t need to bring any. 3-D printers are currently an infant technology but I expect in the future they’ll be models that can produce basically anything. If not, just have a more traditional fabrication shop on board. All you need to bring is the base materials to work with, or perhaps just recycle the ones that need replacing.
No. If we can’t build it well within best engineering practices, then we’ll wait until we can.
Yep. And we can form models for this behavior. Take a look at this graph. You can see that the endurance limit for aluminum increases exponentially as you decrease the stress. For steel, it just goes to infinity under a certain stress level.
No doubt; there will be a lot of spare parts. My opinion is that they’ll have to take the form of “vitamins”; that is, small parts that are difficult to manufacture locally, but where it’s not unreasonable to just carry a huge redundant supply. Microchips would be a good example–we don’t really know how they behave in the very long term. But that’s ok, because microchips are tiny and a cubic meter of them would be enough to supply a huge starship for many centuries.
At any rate, I’m surprised you think a structure could only last decades. We already have steel framed buildings that last many decades and show no noticeable degradation. And these buildings are in a much harsher environment than space–there’s no wind in space, for instance.
Indeed. Sometimes this takes the form of “fast, good, cheap–pick two”. Fortunately, we don’t have to minimize cost (no one ever said this would be cheap). And we have 100k years. So really, we only have to optimize for “good” :).
We aren’t pushing those buildings around the universe with atomic bombs.
Actually, I’m less concerned about the superstructure. Building a giant structural shape out of steel or whatever and making it last a long time is pretty straightforward from an engineering perspective.
It’s really all the small stuff that I’d be worried about. All the computers and motors and pumps and other mundane systems that are critical for life support. How many lightbulbs would the ship need over a thousand years? How many redundant hard drives (or their future equivalent) as they wear out and need to be replaced? How many flicks can a light switch be designed for?
And who even knows what sociological issues they would encounter?
The hub is also rotating, you know. Either you’re going to have to stop the hub while docking, or the ship will have to spin while docking. Stopping the hub means energy loss. Spinning the ship means an awful lot of fiddling with the maneuvering jets. You can’t just dock the ship in a spinning hub, the airlocks have to line up as well.
Why not have a counter-rotating docking boom? Think of it like a helicopter where the blades stay still but the aircraft spins. So you would dock with the boom and travel down a zero-G corridor to the ships core.
I was thinking something on the scale of miles, not office building or large ocean ship scale. Since we’re talking rotating habitats for 10,000 or more people, I’m guessing we would need something like one of the classic theoretical space station designs (O’Neill cylinder, Stanford torus ring or Bernal sphere). Due to the size needed to keep the population from getting motion sickness, they are typically described as having a diameter of from 1 to 10 miles. Plus you would want to have room too. You wouldn’t want generations living Battlestar Galactica style crammed like refugees in the hold of a flying aircraft carrier.
Come on.
We are talking about huge spaceships. Maybe the size of a small town. Lasting hundreds to thousands of years.
And a mildly difficult docking maneuver is a show stopper?
This is like worrying about what colored drapes should go in a newly designed nuclear aircraft carrier.
Missed edit window.
Actually, if you REALLY think about it docking with a large slowly rotating structure is no harder than docking with one that isn’t rotating.
There is nothing special about the number 0 in this case.
How hard wold it be to hollow out a small asteroid, and build living quarters inside? Then, with plasma drive engines, prepare for a 200-400 years trip to a new star system. The living space would be big enough to grow food, recycle wastes, and distill alcohol. Certainly feasible-if we want to do it. But technological advances in the next 100 years will turn the earth into a new Garden of Eden- life will continually improve, no need to leave for millennia, at least.
The center of the hub isn’t rotating though. We are talking about really, really big ships here, so they don’t need to be rotating rapidly. You either have the folks on the ship who would be in zero g simply push off and grab a hold of the rotating hub, or you spin the much smaller ship to a speed where a docking tube can be connected. I’d go with the ‘have them push off and catch a wrung on the spinning hub’ method, personally.
Basically, this would be a fairly minor issue compared to the huge engineering problems that would need to be solved to make something like an Orion function on a ship the size we are talking about…not to mention the other huge hurdles that would need to be jumped to make a ship that could take people from our solar system to some other solar system.
The point though is that there isn’t anything that makes any of this impossible, even with our current technology today. You COULD do it, if you (and a few billion of your fellow humans) really, really wanted too. It’s just not something that’s practical, and so we probably won’t.
[QUOTE=msmith537]
I was thinking something on the scale of miles, not office building or large ocean ship scale. Since we’re talking rotating habitats for 10,000 or more people, I’m guessing we would need something like one of the classic theoretical space station designs (O’Neill cylinder, Stanford torus ring or Bernal sphere). Due to the size needed to keep the population from getting motion sickness, they are typically described as having a diameter of from 1 to 10 miles. Plus you would want to have room too. You wouldn’t want generations living Battlestar Galactica style crammed like refugees in the hold of a flying aircraft carrier.
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Well, a super carrier was the largest mobile object I could think of off the top of my head. Yeah, it would have to be larger than that (which I said)…a LOT larger if you wanted to use an Orion drive. Regardless, in that sort of volume of ship you’d have lots of space for storage, and lots of room for manufacturing and fabrication shops. You’d need storage for food and water (probably you’d create your tanks for water as a jacket around the habitable parts of the ship, thus providing shielding for the crew as well), as well as places to grow food. You’d need HVAC, recycling and treatment for waste, hospital facilities…the whole shebang. It would be incredibly expensive, and a huge technological challenge, and something it’s unlikely we’d ever do…at least not any time soon. But it IS possible, which was my only point in this thread, since the OP seemed to be under the impression it wasn’t possible.
It would also be really cool, and it’s fun to speculate on how you could do it, if you were god king of the world and could command all the planets resources to the goal of getting humans, alive and well, to another solar system. 
*Unpopulated *interstellar travel. Send a robot ship on a ‘multi-generational’ journey to use small gravitational tugs to affect some brown dwarves. Maybe it’ll take 100,000,000 years. We’ve got half a billion years to figure it out.
Besides, there are probably enough brown dwarves closer than Proxima Centauri to make a star. So it could technically be shorter than an interstellar trip.
Even though the ship might not weigh anything in space, it still has mass, and it still has acceleration. Having a few people grab the hub is not going to be enough power to match velocities.
My dad taught me a physics equation when I was about 10 or so, and I still remember it…force equals mass times acceleration. He had me imagine a huge ship, moving in to dock. Then he asked me if I would put my foot between the ship and the dock, even if it was moving very slowly. Even though the acceleration was small, the mass is huge.
[QUOTE=Lynn Bodoni]
Even though the ship might not weigh anything in space, it still has mass, and it still has acceleration. Having a few people grab the hub is not going to be enough power to match velocities.
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Either I’m misunderstanding what you are saying or you are misunderstanding what I am. A person can jump from the (relative) motionless ship to the slowly rotating hub, grab a wrung and basically match velocities and climb in. Why do you think this would be an issue? Are you thinking that these people would have to grab a hold of the hub while still connected to the ship to have the ship match rotational velocity?? That would tear them apart.
Definitely. If someone tried to grab the hub while still connected to the ship it would pull them apart. As you noted, there is still mass. That’s not what I was saying, however. If you wanted to put in some sort of access tube between the ship in the hub and the hub itself you’d need to indeed match rotational velocity in some way…and not by having the crew grab the hub while still in the ship. Not impossible but you could do it. An easier way would be to simply have the crew jump off the ship and grab a hand hold on the hub, however. Remember, this thing wouldn’t be spinning all that fast, especially in the hub.
OK, I think that we didn’t define what we meant by docking…I meant that the docking ship and the station needed to match rotations, so as to match up the airlocks to transfer personnel and cargo. It seems to me that you’re talking about simple personnel transfers, and possibly handheld cargo transfers. Yes, it’s possible for people to jump from the ship to the station, though I’d want them to use safety tethers in case they misjudged the jump, so they could pull themselves back to their launch point and try again. In fact, if it’s just people transferring from ship to station and vice versa, it might be more efficient to jump rather than to match airlocks. However, I think that in most cases, there’s going to be cargo transfer as well, which is why I am concerned about matching airlocks. Each time an airlock is opened and shut, there’s air loss.
