We need to build a generation ship

The Earth is going to be destroyed and there’s nothing we can do about it.

Here’s the deal.

Bob the astronomer and Joe the programmer were working together on a new program for searching the skies for anomolous objects. Mostly by dint of accident they discover a moon sized rock traveling down from above the ecliptic and their calculations show that it’s going to t-bone terra firma in about 62 years. They quietly take their findings to NASA who have some of their big telescopes and computers confirm that yep, it’s going to suck to be us.

The PTBs decide that in this instance, ignorance is bliss and wrap a UV top secret, burn before reading and shoot yourself after reading designation on it.

Coincidentally, about 6 months prior to that, the big boys at NASA discovered that Sirius has an earth-type planet with it’s own nitrox biosphere. Spectroscopy suggests a high probability that there is at least plant life. They hadn’t made an announcement while they were firming up their research and findings.

One bright young soul with realizes that the largest brain pool available on the doomed planet is right here at the SDMB. Bonus points that we work for free.

So can we do it? Can we come up with a workable design for a generation ship that will make an 8.6ly voyage and deliver the cream of humanity to the other end?

The last of the project errata.
It is projected that the existance of the killer rock can be suppressed for 50 years.
Industrialized nations will be advised of the situation because…
Building a generation ship or ships will require global commitment. Obstacles to construction will be dealt with decisively.

The projected cover story when we begin construction will be that there’s a great planet there and we really want to go visit it. We can suggest alternatives prior to the public announcement.

We have one year to have most of a plan together. It’s understood that there will be revisions to cope with unforseen circumstances and developments and technological advancements.

grumble. have to go to work. posting this as a work in progress.

Dude, we can’t even get to the moon. We’re doomed.

I’m not sure.

In terms of building a human inhabitable habitat in space, I think we would be fine. I don’t think that we have yet tried to create artificial gravity (via centrifugal force, for instance), but that doesn’t seem like a particularly difficult task. We would need to construct the ship in space, though, I’d venture to guess.

The main issue I see is power. We don’t have cryogenic sleep perfected, so we’re going to need to feed people for the decades/centuries that it takes to reach Sirius. Farming would be the best bet, except that for that you need light. For most of the trip, you’re going to be pretty far from any stars, so you’re going to have to use batteries or a fuel motor of some sort, pretty continuously. I honestly can’t say how hard that would be to achieve.

62 years? Screw Sirius- Mars is a lot closer, and we’d have more opportunity to make livable biodomes there.


Mostly in stream-of-consoiusness format.

The target is to be prepared to launch in 50 years. It’s expected that at any point after that time the world at large will find out, leading to panic, doomsday cults, economic collapse of some countries and industries.

The early stages will be components that will remain pretty much the same no matter what goes into the final version. Hull framework, cargo holds, system infrastructures such as plumbing, electricity, and data.

While we can freeze and transport thousands of frozen human and animal embryos, if we don’t invent an artificial womb, we’ll have to have livestock to give birth to those.

Plants are less problematical, preparing soil on the far end can be managed if there’s nothing seriously out of balance with what’s on site.

Research on suspended animation should get priority. A sleeping person takes up far less space and resources than an animate one.

Propulsion is going to be a biggie. Starting out today we’re just about limited to using nuclear heat to convert water to steam reaction mass. That’s going to be a whole helluvalot of water.

Two options for artificial gravity right now. Centrifugal as mentioned already. Or constant accelleration at a useful G, flip at midpoint, and decelerate at the same rate. Both with significant technical obstacles.

Probably the most controversial arguments will be the ones about who goes. By what criteria do we decide?

Another will be what of our artifacts will we keep? While it’s a valid argument that they are just things, they are indeed parts of who we are.

The original Constitution and Bill of Rights. The Magna Carta. Original religious texts. The Mona Lisa and other works of art. Fairly lightweight and compact. How about the crown jewels? The statue of David? Tutankhamuns funeral mask and sarcophagus?

Getting these objects won’t be that big of a challenge. We have 50 years to make replacements and swap them in with the cooperation of their governments.

A good point. Don’t put all your eggs in one basket. But how viable is a basket on Mars? Any colonies on Mars will be restricted to domes or underground habitats, probably forever.

While it may have had in the past, Mars has no magnetosphere. Any attempts to create an atmosphere will literally be blasted away by the solar wind. And IIRC, the magnetosphere also shields us from a great deal of the sun’s radiation.

So while we could concievably set up a colony on Mars, I’m not sure we wouldn’t be stepping into a hole we couldn’t get out of again.

50 years from now? Yeah, we’re boned. Not only is energy an issue, but so is reliability. We can make a few relatively simple mechanical devices which can last a few hundred years and even then only if not run continuously. Mission-critical electronic systems? Forget it. We might as well try launching ourselves starward with a giant honking slingshot. Even assuming a reasonably-attainable 10% light speed velocity, we’re looking at nearly 100 years to get there. We couldn’t even keep Biosphere II livable in a fully closed configuration right here on Earth; doing the same thing is space with NO backup is essentially suicide.

Do you remember Biosphere 2? It was an attempt at making a self-contained ecology and was not successful. What you’re proposing would also require a self-contained ecology except that it would have to work.

Actually, on further reflection, 62 years is a lot of time to perfect consciousness uploading- and a computer housing a bunch of human consciousnesses in a simulated world would be a lot easier to move to a safe spot. Heck, you could freeze a bunch of embryos and send them along with the brains-on-a-chip.

About the only viable propulsion system would be a starship-sized Orion nuclear pulse ship. The “small” version was planned to use 1-kiloton yield bombs. The starship version would use 1-megaton bombs for maximum efficiency and use a pusher plate kilometers across. That sounds ambitious but not if you can build an interstellar ark at all. Heck, you would probably need the small Orion just to launch material to build the big one.

A series of launches. The first ones will be slower, as we hope for advanced propulsion systems for later launches. So a mess of (annual?) launches with supplies, birds bees and whatnot until we get the technology right to do a human ship.

At the other end, we can expect to link up with most of the ships, with others arriving over the next couple of years.

Oh, c’mon. Eight whiney, moody, prima-donna scientists? Of course it failed. The key to a successful generation ship is of course, to keep scientists at a minimum.

AFter doing some research on Biosphere 2, that project sounds like the stupidest idea ever. It was never really a serious scientific endeavor. It was an art project. If we’re making a generation ship (or a Lunar/Martian/whatever colony), we’re not going to be trying to keep a sample of each Earthly biome functioning. That was dumb. I have no doubt in my mind that given enough money and resources, a functional habitat could be built. None.

I agree with Paul in Saudi, however. I like the thought of large solar sailed ships being launched towards the target star system, with onboard systems to put them in an orbit. Any orbit, just make sure they aren’t going to hit the star or a planet. Launch them at will, carrying supplies and such for the end colony.

Dump massive research dollars into suspended animation and AI-like systems.

Propulsion is the least of our worries, if we can figure out the suspended animation/hybernation cycle.

Staged launches. With later, faster ships overtaking earlier launches. I think I like that.

Assume we don’t get a handle on suspended animation. How many live people do we need to take to have sufficient genetic diversity? It’s pretty much a given that anyone departing is going to pass some rigorous genetic screening to preemptively eliminate many potential defects. Frozen sperm, eggs, and embryos will give us a huge pool to start over with. Assuming they last that long.

Let me back up and rethink that. Would we be better off with a caretaker crew for the voyage? Artificially inseminating female crew from frozen sperm or embryos to avoid inbreeding. Then later growing out the population from stored materiels for maximum diversity.

I still keep coming back to livestock as a big obstacle. Without an artificial womb we’re going to have to devote big chunks of real estate to maintaining habitat for small families of stock. Artificial insemination eliminates inbreeding issues, and some species can host related breeds through gestation, but damn there’s a lot of stock that’s going to be necessary to provide space and supplies for.

Yeah, the biosphere projects were exercises in futility. But can be used for models on how NOT to do things.

Most people don’t realize how incredibly difficult it would be to get anything to another star, let alone something the size of a generation ship. The energy required is unbelievable. It took a 150 ton Atlas Centaur rocket to launch a 600 lb Pioneer probe to a speed that would get it to our closest star (if it was going in that direction) in… 105,000 years. And if you want it to go faster, the mass of the rocket required goes up exponentially.

To give you an idea, this page gives you some of the math. According to that page, if you had an exotic fusion-powered rocket, to accelerate a 100kg probe to 10% of the speed of light, and then to decelerate it back down at the other end of travel, would require a starting mass of 130,000 tons. That’s a starting mass from orbit.

To give you an idea of what that would take, if we had a Saturn V rocket factory, it would take over 1100 launches to put that much mass in orbit. The energy required would cost many multiples of the entire world’s GDP.

With any of the propulsion technologies we have today or even think we could build in the next few decades, it’s utterly impossible.

So maybe we could do it if we went much, much slower. But then, a ‘generation’ ship implies a mass in the millions of kg, so we’re right back where we started from.

And the risk of failure would be enormously high, because there would be so many unknowns. We simply wouldn’t put humanity’s eggs in such a costly, fragile basket.

I think it’s far more likely that we would engage in multiple crash courses to do the following, in order of likelihood:

  • Figure out how to deflect the rock.
  • Figure out how to build sheltered habitats on Earth that could survive the impact.
  • Try to build sustainable colonies on the moon.
  • Look at building a sustainable colony on Mars.
  • Perhaps look at building in-space sustainable colonies. For example, hollowing out an asteroid.
  • As an outside chance, trying to build small ‘seed’ probes that would send frozen human embryos to other star systems in an attempt to re-start the species.

Is this rock so big that it will shatter the earth? Or heat it up so much that it will be a glowing slag-pile for a few hundred thousand years? Or is it just going to blast the surface, leaving the atmosphere intact? If the latter, then the best plan would be to start two separate crash projects - one to build hardened sustainable environments on earth, and another to build semi-permanent habitats on the moon, to allow people to hide out there for a few years or decades until they could return.

The moon actually has a lot of potential as a permanent habitat. There are huge lava tubes that we might be able to seal and create atmospheres in - we’re talking enclosed, protected environments maybe 100 miles long and thousands of feet in diameter. Big enough for an entire city. If we can find significant water on the moon, this might be an answer. And in the airless environment, a return spaceship could be kept intact for hundreds if not thousands of years if it was sheltered from radiation.

With a crash program to build a space elevator on earth and one on the moon, we could move huge amounts of mass there with relatively low cost. Even with traditional rockets (well, nuclear rockets, but something tells me we’d accept the risk), we could move a lot of mass and people to the moon.

If we could build that space elevator, we could also put a smaller colony on Mars as a backup in case the earth impact took out the moon as well.

I think that’s about all we could realistically hope to accomplish in 62 years, and even that would be an amazing feat.

How about hide in orbit and re-inhabit the Earth after the rock does a damn-damn on it?

That’s why I’m asking how big it is. If it’s truly the size of our moon, then an impact would either shatter the Earth completely, or the two would stick together and the resulting energy absorption would probably raise the temperature so high the Earth would essentially become a molten slag-pile for a long time. Its orbit could change substantially, the atmosphere gone, and in general it would make Mars look like a mighty nice place to live.

Which is why I suggested the nuclear-pulse Orion ships. The main limitation is that you can only get so much delta-V per bomb, so it actually works better for a generation or hibernation ship. 10% lightspeed is impossibly expensive; 1% might be doable if you can wait that long. Within broad limits, making each bomb more powerful is simply a matter of adding more comparitively cheap lithium deuteride and depleted uranium around each fissionable mass. So the potential payload scales up ridiculously- millions of tons. And it wouldn’t require inventing a brand-new technology. You build the “small” version first to test fly it, then use that to boost payload to build the full-scale version.

The first is by FAR the most likely alternative. With 62 years to go getting something, almost ANYTHING there that can apply a delta-v in any direction at all will cause a miss.

Something the size (and presumably the mass) of the Moon? Not a chance in Hell. To get something to move the diameter of the Moon in 62 years requires a velocity of about 1.8 mm per second. Doesn’t sound real fast, but to get a Lunar mass to move that fast requires the application of 67,609,090,842.2 newtons of force over 62 years or 1760 times the thrust of a Saturn V booster. And bear in mind that even a near miss of one Lunar diameter would be disastrous, as tidal forces would rip the Moon to pieces and cause upheavals here on Earth that would pulverize the crust. I’m not sure what would comprise a safe distance, but that ain’t it.