Colony/World/Generation ship Discussion

[Idobox]

It is going to take a LONG TIME before we reach that technology threshold. To imagine such a ship, but using the computer technology, biology, nanotechnology, genetics, and societal norms we know today, is absolutely ludicrous.

We could make a generation ship now, with nuclear pulsed propulsion. At project Orion, they were thinking of sending whole cities to Mars.

Also, if you build machines with the goal of improving themselves, they will always want more energy. It is possible to limit expansion by defining specific rules, but expanding to use all available resources is the default state for self replicating machines.

[-Velocity-]

We could make a generation ship now, with nuclear pulsed propulsion. At project Orion, they were thinking of sending whole cities to Mars.

Also, if you build machines with the goal of improving themselves, they will always want more energy. It is possible to limit expansion by defining specific rules, but expanding to use all available resources is the default state for self replicating machines.

We can't make a colony ship now, because there is no where near enough funding for such a thing. Such a ship will be extremely expensive, and will probably take a well-developed, large-scale space-based manufacturing sector before the cost comes down enough that it becomes economically feasible. It's going to take a long time for that to happen. Space-based manufacturing becomes much easier with machine intelligence running the asteroid mining operations.

[Idobox]

We have the technology to do it, and we don't need any large-scale space-based manufacturing sector.

We could build a giant ship made of steel and concrete and put it in orbit, and the price would not even be that ridiculous. But to put it in orbit, you would need to blast a lot of nukes, which would be terrible for people staying on Earth, and that's a political and social problem.

Faced with an extinction-level event and enough time, that would be a sensible solution.

[Seret]

We have the technology to do it

Looking at what we've put into space in the last 50 or so years, which particular technologies do you think enable the construction of a generation ship? The way I see it's well outside our current capabilities, even considered from a purely technical point of view.

Bear in mind that we have yet to send a human on a long-duration journey to anywhere, even within our own star system, and we've never sent anything to another star. To suggest we're ready to send people on an interstellar journey is wishful thinking. What we're capable of currently is manned flights to Earth orbit and the moon, and sending probes to the rest of our system. At the moment we aren't even sure if we have the tech for a safe manned mission to another planet, let alone an exoplanet.

[Idobox]

Nuclear pulsed propulsion: using nuclear bombs as a propulsion method.

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29

It has massive ISP and TWR, and uses technology from the 50s and 60s, basically a heavy duty plate, a shock absorber, and bombs. Of course, nobody ever tested the concept since it involves detonating a large amount of nukes in the atmosphere, and it doesn't work for small ships, but it is not especially difficult to build once you have nuclear weapons.

[Seret]

uses technology from the 50s and 60s

Sure, it builds on earlier technology (everything does) but there's a big difference between current, viable, mature technology and experimental ideas. People are fiddling about with lots of cool ideas like quantum computers, brain-machine interfaces and nanomachines in labs right now, but they're not technologies we could actually put to use.

it is not especially difficult to build once you have nuclear weapons.

How do you know? Until somebody tries we just don't know. Plenty of technologies look great on paper, but once we try and actually build them we discover they're more difficult than we thought. Fusion power stations would be a good example of this. It's taken us decades longer than we expected, and we're several decades away still.

The technologies we actually have right now are chemical rockets, either solid or liquid fuelled. These are clearly inadequate for interstellar flight on reasonable timescales, and tbh are pretty poor for manned interplanetary flight too. Hence the interest in exotic propulsion like Orion. The lack of interest in manned interplanetary flight however has meant that there's been little actual development in exotic propulsion. The fact we're only interested in sending robots means we can get away with chemical rockets, because low speed isn't a problem.

[nhnifong]

A properly designed ecosystem in a space habitat that is self-contained, recycles all matter, and requires only the input of energy to continue supporting life is the backbone of a generation ship. Anything less than complete self-sustenance and you are going to run out of some precious supply of something, and that means you have to go FAST.

But if the ecosystem only requires the input of energy, then you can take as long as you want to get to the destination, and you may use high-isp low-thrust propulsion. This is the purpose of a generation ship right?

Now the challenge is to create a reliable source of power that can support the ship when outside the vicinity of a star. My personal favorite is simply to not bring any power, just solar and microwave collectors. Beam the power out to the ship from energy-producing satellites in orbit around it's home star. As time goes on, the home civilization upgrades the microwave lasers to higher and higher precision to mitigate dispersion.

The best candidate for propulsion I think would be a pulsed fusion system that ignites small pellets of matter using high energy lasers similar to the ones in the national ignition facility. The resulting neutron energy is used to heat propellant into a plasma where it is directed out of a nozzle.

[Vaebn]

Thats a cute way of doing it, however, I have to say that as a (human) colonist, I'd be scared that the home beam would turn off.

The nice thing with self-contained generation ships is that they also act as lifeboats if something happens to the home system back home (nuclear war, relativistic 99% speed of light missile from another species that didn't like our TV transmissions, apes rising to power etc). On the other a hand, a ship depending on beamed energy has a point of failure at precisely the place they are trying to escape in the first place!

[K^2]

But if the ecosystem only requires the input of energy

I might come off as a bit pedantic on this, but it's not the energy that's required. Energy in needs to be equal to energy out or the crew cooks. What you need is the entropy flow. Any living system is going to increase entropy, so you have to dump it somewhere. Technically, ship is also going to "age", so that's another contribution to entropy.

Easiest way to dump entropy is with waste heat, however, which means that you have to replenish lost energy with low entropy source. But in principle, there can be other ways. Basically, any source of structured anything can be used in lieu of energy source.

[Vaebn]

One propulsion method I've always wondered about but have hardly seen anyone explore, is accelerator based propulsion.

The idea is that in the end, (beamed energy concepts apart) what matters is how fast you can toss your propellant the other way. (Even the Orion thingies are just a trick to accelerate "propellant" really fast). So... what tosses things faster than a particle accelerator?

Now, I know, this is pretty much what an ion drive is but the difference is in scale. The modern idea of an "ion drive" is constrained by the mental image of it having to look like a neat little engines, meant to be go behind something probe sized. Whilst what I am talking about is basically, you know... CERN.

This is not worth imagining for probes. However, if we are talking about generation ships the fact that the vessel is going to be km long is pretty much a given.

Therefore such a vessel could house such a thing running the entire thing length of it (if not wrapped in spirals around it) Accelerating particles to 0.999% the speed of light, which is a far cry from a "normal" ion engine's exhaust of 31 km/s or so.

The real questions to be answered are:

a) Particle accelerators such as CERN are not meant to accelerate great volumes. They just accelerate a handful of particles as opposed to the millions, of millions a "normal" ion thruster does. One question is if someone can ever make an accelerator, able to accelerate much more significant volumes, without the energy requirements and heat losses of the infrastructure doing the accelerating melts everything within a 10 mile radius.

Energy! That's such a thing would need a small city of fission/fusion reactors and a small mountain of fissiles/fusiles for the journey, to power it, is a given.

The question is wither something that, along with the weight and heat losses of all its reactors and reactor turbines and accelerator itself, would still be more "efficient" than, say, nuclear pulse propulsion.

Keep in mind that nuclear pulse propulsion might be super awesome compared to chemical rockets, but not necessarily an efficient use of fissiles itself. Most of the nuke's energy radiates in a big spherical boom to space and the speed of the little bit of gas/plasma that collides with the pusher plate (therefore the "exhaust speed" of it) is of course much much less than the speeds a particle accelerator can archive. (albeit entire kilograms of it) It can also be hard to improve, because the pusher plate has to survive, thus providing a hard limit on how hard you can hit it, but at the same time there is also a hard limit on how small a nuke can be.

Edited October 20, 2013 by Vaebn

[Will Fawkes]

I like the concept of the 'engine' being the outermost layer of the ship because spiraling around and around accelerating the ions about. Sure it's still going to be slow even moving stuff as fast as it is because the thing being pushed is just so bloody massive but I had a thought. Wouldn't that sort of engine configuration also protect from radiation? You have to have shielding anyway for the particle acceleration plus the accelerating particle stream itself.

I have this mental image of a long tube with magnetic funnels at each end. One at the front to hoover up material to be fed into the engines/reactor and another out the back to redirect exhaust for most efficient thrust. Granted this design leaves me wondering how you'll STOP once you find somewhere interesting or if you have enough time to just cut the engines and coast the rest of the way in using the forward magnetic scoop as a drag/bake extending it out so you suddenly are getting velocity loss because you're hitting tons and tons of stuff.

[meve12]

The real questions to be answered are:

a) Particle accelerators such as CERN are not meant to accelerate great volumes. They just accelerate a handful of particles as opposed to the millions, of millions a "normal" ion thruster does. One question is if someone can ever make an accelerator, able to accelerate much more significant volumes, without the energy requirements and heat losses of the infrastructure doing the accelerating melts everything within a 10 mile radius.

Needs some wordsmithing. Can't you dump the heat into the exhaust?

Energy! That's such a thing would need a small city of fission/fusion reactors and a small mountain of fissiles/fusiles for the journey, to power it, is a given.

The question is wither something that, along with the weight and heat losses of all its reactors and reactor turbines and accelerator itself, would still be more "efficient" than, say, nuclear pulse propulsion.

No question there. Might be time for AM/M, or beamed power with AM/M backup

Keep in mind that nuclear pulse propulsion might be super awesome compared to chemical rockets, but not necessarily an efficient use of fissiles itself. Most of the nuke's energy radiates in a big spherical boom to space and the speed of the little bit of gas/plasma that collides with the pusher plate (therefore the "exhaust speed" of it) is of course much much less than the speeds a particle accelerator can archive. (albeit entire kilograms of it) It can also be hard to improve, because the pusher plate has to survive, thus providing a hard limit on how hard you can hit it, but at the same time there is also a hard limit on how small a nuke can be.

Actually, the Orion designers were going to use nuclear 'shaped charges' that would direct the blast in a cone. So 80% efficient instead of a vanilla nuke's 10% efficiency.

Although it makes me wonder if generation ships are worth it in anything but a world-killing emergency(heck, as long as the sun's not gonna blow it could just be a space station.)

[Will Fawkes]

Could be hte original colony/ship started off as a mining vessel that slowly processed the asteroid belt, Kiper belt, and so on into useful productand slowly built more like itself to either continue processing or since enough crowding had happened to cause a large enough population to go 'you know what? we want to move.. Out There'. Though really all a world shi pis is just a colony with propulsion and a means of gathering fuel and materials.

[Vaebn]

For some reason, I instantly write off AM/M due to how difficult it is to make it, at least the ways we make it nowdays. I'd literally call making a kg of anti-matter, a greater project than the generation ship itself. Which in the end, would be carved out of an asteroid or something, so a good part of it is mostly automated digging.

I mean, our production methods are so, so, SO, inefficient... you'd basically have to cover the moon with accelerators or something.

Or space stations sucking the anti-matter created in the van allen belts of every planet. (all these are awesome sci-fi concepts btw)

Worse, anti-matter requires active containment, and we all know from Star Trek what happens if the field blinks even for a moment, (and considering that we are talking about generation ships, this means that those machines will have to operate for hundreds of years, and/or possibly be "hot-swapped", ALWAYS without error, EVER).

However, since we are talking about exotic power/propulsion mechanisms, there is another technology I am annoyed that it never gets mentioned and it might actually be easier and safer than AM to do. Black Hole "reactors"! -> Paper (I have been told that my definition of "easier" and "safer" needs a little work)

The gist of it is that black holes evaporate through hawkings radiation. Therefore, you first make a tiny blackhole (simples), then simply feed it matter at a rate enough for it to neither grow or dissapear, and it will be converting to hawkings radiation, which in turn you capture and have it run... boilers or something. So basically it's like wood stove, only completely different and minus all the wood, the fire, and the lack of singularities. A somewhat different arrangement which would reflect the generated energy one direction, is basically a drive.

It still requires an active system to sustain it, but at least in this case, the penalty for not doing so, would be that your engine would turn off. (black hole evaporates).

But since you don't die every time it screws up, you could the least have 2-3, more as a backups. The evaporation might also be slow enough to have a chance to re-start the matter stream. Have enough of them, and the ship might even be able to re-make one every time it looses one, at which point engine could be considered safely long term sustainable.

Edited October 21, 2013 by Vaebn

[Seret]

It's actually not the propulsion that's the problem with Generation Ships to me. It's the fact they'd have to be closed loop habitats. If you could mange to pull that off propulsion isn't such a big deal, because you can go quite slowly. We've tried to make closed loop experiments and failed. Until we sort that one then it doesn't matter what kind of exotic propulsion you come up with, a generation ship is off the cards.

[Idobox]

Sure, it builds on earlier technology (everything does) but there's a big difference between current, viable, mature technology and experimental ideas. People are fiddling about with lots of cool ideas like quantum computers, brain-machine interfaces and nanomachines in labs right now, but they're not technologies we could actually put to use.

It's a giant dampener and a bunch of thermonuclear weapons. Using explosions to propel stuff is not exactly new technology, and neither are springs. The only difference with what has been built is the scale.

Building a dampener able to support the weight of a generation ship, or a delivery system for thousands of bombs is not trivial, but it is just a scaling problem. It's like going from building a small boat to building a large ship: it will take some work, some good engineering, and some new infrastructure, but not scientific breakthrough.

At the time of project Orion, they thought they could do it in 10 or 20 years.

[nhnifong]

It's actually not the propulsion that's the problem with Generation Ships to me. It's the fact they'd have to be closed loop habitats. If you could mange to pull that off propulsion isn't such a big deal, because you can go quite slowly. We've tried to make closed loop experiments and failed. Until we sort that one then it doesn't matter what kind of exotic propulsion you come up with, a generation ship is off the cards.

That's what I was thinking too. If it's indeed a closed loop habitat (which requires a constant entropy flux) then you can take as long as you please to get to the destination.

I think we need to get started on making simple closed loop habitats in space. For example, How would one of those micro-shrimp, kelp, and bateria systems that you can buy in a glass sphere at Brookstone fare in space? Why have we never launched such an experiment?

On the topic of propulsion, perhaps the best use of antimatter would not be to bring it along in a container on the ship, but to just fire a beam of it at the ship. The ship will capture it with magnets and direct it into a reaction chamber where it will annihilate with a target and heat up propellant.

[Seret]

At the time of project Orion, they thought they could do it in 10 or 20 years.

They thought a lot of eroneous things about nuclear power sources back then. They thought fission power plants would be small, cheap and efficient to operate (and therefore ubiquitous) and they thought fusion power could be developed in a similar timescale.

I reiterate my point though, until someone has tried to build something, you just can't say how easy it is to build. You can take a guess, but you can't have any certainty. Engineers discover unforeseen problems during the design of just about everything. Sometimes those problems are trivial, and easily mitigated during early design work, sometimes they completely derail the whole project. Space vehicles are particularly bad for this, many, many projects have been cancelled during development due to unforeseen problems causing them to take too long and cost too much.

When you say "It's just nukes and springs" you aren't taking into account what that requires. We may have the materials to make one durable and reliable enough for an interplanetary trip, but even then you're talking about immense stresses, temperature fluctuations, vibration, etc. The idea of building one reliable enough for an interstellar journey is a daunting engineering challenge. Remember that if any part of the system fails, the ship is either destroyed or left to drift endlessly in space.

Edited October 22, 2013 by Seret

[Seret]

I think we need to get started on making simple closed loop habitats in space.

I think we are. The ISS recycles a fair bit internally, the only way we're going to build competence in these technologies is building several iterations of manned station as we refine the technology.

The incentive is there. Hauling groceries up to stations and dumping their refuse is expensive. Every resupply trip you save is many millions in the bank. You can bet that space agencies are very interested in that. The trouble is that everything associated with manned flight has to be rigourously tested and certified, and that goes double for life support systems. So development will be slow and conservative.

[Idobox]

Well, the USA have lost a massive piece of steel when testing a nuke in a well. Does that count as a trial?

The temperature and stress involved are not as scary as one might think. Of course building a dampener that will survive several hundreds of nuclear explosions is not trivial, but people build massive structures on dampeners that survive far larger vibrations all the time, to protect buildings from Earthquakes. A push plate can be built of pretty much anything if thick enough.

And keeping the people alive for several hundred years while traveling at a significant fraction of the speed of light are important issues in themselves.

But all in all, it is by far the most mature technology for interstellar travel at reasonable speeds.

It is a sad thing that politics, public opinion and treaties forbid even testing the idea in space.

[MBobrik]

poor man's generation ship - 4 crew, all female ( if males, then altered to have a womb ) and a stockpile preserved eggs and sperm from millions of donors in an extremely well shielded container. the replacement crew members, and several first generations of colonists will be bred from the stored eggs.

[SargeRho]

Would be easier to make a sleeper-ship then.

[nhnifong]

I think we are. The ISS recycles a fair bit internally, the only way we're going to build competence in these technologies is building several iterations of manned station as we refine the technology.

The incentive is there. Hauling groceries up to stations and dumping their refuse is expensive. Every resupply trip you save is many millions in the bank. You can bet that space agencies are very interested in that. The trouble is that everything associated with manned flight has to be rigourously tested and certified, and that goes double for life support systems. So development will be slow and conservative.

I never specified manned flight. I've never even heard of any attempts at small closed-loop aquatic habitats in space, or even just simple <1ton sattelites with nothing inside but insects and plants. Surely we could learn something by starting small.

[JebidiahsBigSister]

Even after 30,000 years of civilization, we haven't changed that much.

It's actually closer to 9000 years

[Seret]

I never specified manned flight. I've never even heard of any attempts at small closed-loop aquatic habitats in space, or even just simple <1ton sattelites with nothing inside but insects and plants. Surely we could learn something by starting small.

There have been some experiments flown that serve as building blocks for larger systems, but obviously the final objective of these is a system for supporting manned flight.