Okay, not literally Krypton style, but let's say some local astronomical event is going to render every rocky surface in our solar system totally uninhabitable. Details aren't terribly important, so let's just say every planet is going to fall into the sun for some reason.

We have... an amount of time before it's going to happen (let's say around ten years), and that before it happens, the earth (and everything else in our solar system) is going to be just as habitable as it currently is.

Also, we have recently received very convincing (and convenient) evidence that there is an earth-like world in a neighboring star system, with, shockingly, an oxygen rich atmosphere and a functioning biosphere (how we got this evidence is also irrelevant, so for fun we'll say an alien robotic probe told us about it before scooting out of the system).

So, the question is, can the human race build a ship capable of restarting the human species (if not the civilization) on that nearby planet?

Some other simplifications/freebies:

  • Human society works out in such a way that at the very least our efforts aren't severely impeded.
  • Only current or very near current technologies are allowed.
  • One "freebie" technology is permitted, with the caveat that it can only be something which theoretically we can probably make, but simply haven't put the effort into making (I have a few candidates in mind, but I don't want to bias your answer).
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    $\begingroup$ This is essentially the plot of When Worlds Collide. Of course, the target planet is a little closer. $\endgroup$ – Spencer Jun 16 '18 at 1:53
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    $\begingroup$ Also reminds me of the book Seveneves, although again, the target is much closer. $\endgroup$ – trevorKirkby Jun 16 '18 at 6:30
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    $\begingroup$ You can land there, but have you considered what the locals might think? For all you know, you might end up in space Australia, without rabbits at that. Where would you get Starship Troopers then? $\endgroup$ – nzaman Jun 16 '18 at 10:39
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    $\begingroup$ @nzaman haha, it's true that we have no guarantee there aren't prohibitively dangerous or even civilized locals on that planet. That's a lot a mass we might want to risk bringing in the form of guns. $\endgroup$ – SomeGuy Jun 16 '18 at 18:36
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    $\begingroup$ @SomeGuy: I was actually thinking in terms of food. They need something to eat once they get there, and they don't know whether the existing stuff is poisonous or thinks of them as manna from heaven $\endgroup$ – nzaman Jun 17 '18 at 10:17

Elon Musk to the Rescue

If you asked this same question 10 years ago, I would be as pessimistic as many of the other answers. But this is 2018. The Faclcon Heavy is in production. The BFR is on the way. Elon Musk has, many times, said that his goal is to establish an outpost on Mars to save humanity.


One "freebie" technology? That would have to be suspended animation (and I don't mean canceling the Flintstones). It is not as far away as you might think. I don't think it could make us live forever, but if we can sleep through the trip and wake up when we get there then we can save a lot of payload otherwise needed for food, water, medicine, etc. If this is a 100-year journey (using Project Longshot as a starting point) and we have sleeper technology that gives us 100:1 metabolic processing then the human bodies will have effectively aged only 1 year (so they are still "young" when they get to the destination) and the nutrients consumed would be equivalent to 1 year - not far off from what a BFR would need to take for a Mars trip. While sleepers would need extra equipment to keep them fed, healthy & safe, they would need essentially crowded bunk space but no common areas, exercise rooms, etc. and all the extra payload space & weight could be devoted to equipment needed on arrival. Unlike one book I read (can't remember the name at the moment), we need to make sure everyone sleeps through - if one person wakes up 1/2-way through and can't go back to sleep then he would eat (in 50 years) 1/2 the food intended to get all 100 people through the first year on the new planet.

How many can we save?

We can't save everyone. But we can easily save thousands. The key is using BFR to get things in orbit and assembling, in a minimalist fashion, in orbit. The main BFR is designed to be fast-reusable, which is a key. Something like:

  • 19 BFR flights for a 3-level hexagonal ship - 1 in center, 6 in 2nd level, 12 in 3rd level. Inner 2 levels have 200 sleepers each = 1,400 people. Outer level filled with food for the first year at the destination and equipment to set up a small colony - water purification, seeds, medicines & medical equipment, computers, tools, solar panels, Teslas, etc. Outer level also provides radiation shielding for the inner levels.
  • 8 BFR flights for a propulsion module. 1 in center to separate this from the main section (not sure this is needed but it is a common style of ship in many sci-fi novels), 7 in 2-level hexagon - center for propulsion (ion? fusion?) and 6 for fuel (reaction mass, not ordinary rocket fuel)

That is a total of 27 BFR flights per 1,400 people. SpaceX, with some BIG government help (remember, so far SpaceX has done the bulk of its development using some government funding but primarily funded by paid commercial, government and military flights and private investment) gets the BFR assembly line running at Liberty Ship speed then we get BFR serial production within 2 years, with ship (sleeper, cargo, propulsion) design running simultaneously. Assuming BFRs can get a weekly refurbish rate and 100 (= 2 years) uses per BFR before retirement (while major overhaul might make sense, I'll assume some occasional damage-beyond-practical repair, plus the production line for new BFRs will make major overhaul less cost-effective), that would mean a total fleet of ~ 60 BFRs but won't have full launch cadence until ~ 30 have been produced. So early production will be key. On the other hand, the starship components will be needed at a steady 2 per day throughout the launch window. Start with the equipment & fuel modules. Sleeper modules would go up last to give those people maximum time on Earth - last 2 years would be almost all sleepers.

With 4 launch pads (2 Florida, 1 Texas, 1 California) running on an alternate-day basis (try for daily but there will always be some days you can't launch due to weather, delays in payload processing, etc.) that would be (2 per day * 365 days * 8 years) / 27 per ship * 1,400 people per ship = 302,814 people. Figure 10% loss due to ships not completing the journey due to mechanical failures, 10% loss of sleepers due to problems "waking up" and you've still got 245,279 - a quarter million people is a nice large genetic pool to restart humanity.

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    $\begingroup$ I think this one gets the checkmark for going so far as to look at the logistics of it, but these were all excellent answers! $\endgroup$ – SomeGuy Jun 17 '18 at 16:03
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    $\begingroup$ One would imagine cost stops mattering when the world is going to end so succinctly. I'm not sure what the mechanisms would be for acquiring goods and services, but using money for anything would surely be moot. Perhaps that leaves open some good story telling opportunities around how they managed to convince people to build, and supply the building of said ships. 8 years is also a lot of time for mischief while these things are being built, I imagine those unable to board will be quite motivated! $\endgroup$ – Ben Jun 18 '18 at 5:19
  • $\begingroup$ @Ben I do agree that mischief would be hard to contain, although, as an idea, they could allow people to send their DNA onboard the ship with the promise of future cloning, plus digital mementoes. That should be able to get a lot of people invested in the success of the project. $\endgroup$ – SomeGuy Jun 19 '18 at 1:20

There is a reasonable chance of success. Definitely not a sure thing.

We need to use the most effective rocket propulsion that we know of and within our capabilities and resurrect Project Orion

Since your propulsion system is a large number of nuclear bombs, this is not generally considered an ideal propulsion system, but if it the only option, it is a dandy system - who cares about the environmental damage and political consequences. BTW, the actual damage from fallout is a lot less than most people would expect.

This system has been studied in surprising detail, and it turns out you need about 800 bombs to obtain earth orbit - mostly independent of the size of your spacecraft. For high speed interstellar flight (133 years to Alpha Centauri), you need quite a lot more bombs (on the order of millions). You can also launch a huge payload - such as a city. A number of different designs to meet different needs have been proposed.

We will need a lot more bombs, as well as the ship itself. But with everything in full-on rush mode, it is conceivable. The United States, and several other countries are already wealthy enough to build such a vehicle.

Given the large mass allotment, you can scale up to add the heavy shielding needed to protect from radiation in space, and possibly an ecosystem complete enough to survive the long trip. Dealing with long-term micro-gravity would also be a major issue, so spinning up your ship needs to be added to the design.

Compared to typical spacecraft, Orion is a simple design which bodes well for a crash program to succeed. There is a lot to do, and much we don't know, but a reasonable chance is better than certain death.

I fear that a reasonable chance in this case may be something like 10% or even 1% -- yeah that's lousy odds. But you should not wait until 10 years left before you start building your interstellar space ship.

Re: the free technology -- I would ask for the ecology package to get the in-flight environment stable and healthy -- we have had no success in doing this well yet..


Maybe. In 10 years? Probably not.

Right, so first off there isn't a lot that can destroy every rocky world. You said don't worry about it but it'd probably affect the answer a bit. I'll do my best to ignore it.

Whatever it is, a catastrophe of this magnitude make humanity quite irrelevant. We for sure can't stop it. The only solution is to leave. This is maybe at the very edge of human possibility. Maybe.

First, we'd need to get people there. This is a lot easier with hibernation technology but I think that's kind of cheating and not as important as shields, so that's my freebie technology. Ion shield technology is in very early stages here on earth but it'll be essential for life.

So, we have a way to protect people from radiation in space. First part done. Next is the ship itself. It'll be big. It'll need to rotate in space to provide gravity; zero-g is too damaging to have people in it for such a long trip. However, to achieve 1g without motion sickness it needs to be a big ring. Inside it'll need hydroponic farms, living quarters, recreational areas, medical facilities, embryo storage, maintenance areas, water purification, power generation, shielding, armour, and a hundred other areas to make this just livable. A small crew raising the next generation of embryos to take over is the best option. Keeps genetic diversity and when they reach the planet, gives them an easy method of populating it again.

Propulsion is difficult. Best option is nuclear propulsion: put simply, you blow up an atomic bomb right behind the ship and it pushes it along. That we have within a reasonable time frame. Best though would be fusion rockets. The fuel is difficult to come by but the trip would be around 40 years. That'd simplify things quite a lot as it would be a single generation ship.

Most importantly of all though, you wouldn't send one ship. You'd send as many as you can, staggered as much as possible to prevent them from being destroyed. Shotgun it. Got nothing to lose.

The problem is the time frame. 10 years, in the scale of such an engineering project, is really really short. 100 I'd say we definitely attempt it a few times. 10? Hard to say. Maybe we get a few cobbled-together ships up there, but it won't be easy.

  • $\begingroup$ why do you think hibernation is cheating? That is one of the technologies I was thinking of for a freebie. $\endgroup$ – SomeGuy Jun 16 '18 at 3:07
  • $\begingroup$ Cause it's fairly out there in terms of possibility; we have nothing like that now. And it kind of removes all the difficulty. A hibernating crew needs nothing. Makes space travel a hell of a lot easier, but not realistic and not in the spirit of the question, I feel. Kind of an auto-win $\endgroup$ – Serenical Jun 16 '18 at 3:25
  • $\begingroup$ Hmm, yeah, I guess that is a fair reason. It's definitely a technology we don't have any real guarantees is actually possible for humans. Although it is interesting that you consider it to be so broken. $\endgroup$ – SomeGuy Jun 16 '18 at 18:17
  • $\begingroup$ well, all you need to do is have landing gear, an onboard computer, some supplies for when they land, the hibernation pods, and some embryo storage. It makes it so vastly easier that I think it really undercuts how difficult this would be IRLv. Because as far as I am aware, nothing close to that tech is here. $\endgroup$ – Serenical Jun 16 '18 at 23:54

10 years? Don't bother trying.

With near-future technology the best we can hope for is a fusion version of Orion. A reasonable estimate of the ISP of a fusion Orion is about 7,500. That's roughly 15 times as good as the best chemical engines. Thus you're looking at roughly 15x the delta-v we have managed to put on a manned rocket--Apollo. It had about 18km/sec, so with the same mass ratio we are looking at 270km/sec. Figure 24km/sec from the surface to solar escape. Another 13km/sec for capture, thus leaving 233km/sec for the trip. That means you're cruising at 116km/sec. That's 116 centuries in flight to Alpha Centauri.


The National Geographic documentary "Evacuate Earth" gave us a doomsday scenario of a Neutron star on its course to hit Earth in 75 years. Even with such an advance to realize ONE generational ship, escapees made it at the last moment, what between riots, defections, suicides, increasing catastrophes, etc.

10 years? In an even more hurry. Orion cannot be built on Earth, you must do it into space. which means USA, Russia, China, EU, India, Japan, Australia, will have to launch and launch and launch materials, keep their austronauts working to an extremely stressful clock, letting them understand that perhaps not all of them or their families will leave Earth.

Riots and wars will spread to get a ticket to safety. Mass exterminations will occur. The candidates will have to be protected 24/7, that is, unless the very guards break down and take the candidates as hostages to get a ticket themselves.

Terrorists and religious zealots will have no trouble convincing hysterical masses to sabotage the efforts by cutting lines of resupplments to the project.

And not to mention plain accidents. You can't do all of this, even in the best conditions and not expect accidents to interfere with the schedule. Two Space Shuttles were destroyed because of...what? A tiny leak in the components, a crack here, and boom! you lose a crew of specialists and a reusable transportation. And you MUST reuse as long as possible since the industries in the world will be under catastrophic pressure to build components for the Ark.

Let's just take the weather: window launches for rockets requires certain meterological conditions, and you can't just come up with innuendo launch stations. Delays will be unavoidable even on that front.

And the more time passes, the more pressure is exerted on the staff and the crew. Medical staff will skip one simple routine procedure with their astronauts, sicknesses set in, more losses. The candidates will start panicking. They are essentially prisoners, they cannot leave the evacuation point's premises -in fact, it would be dangerous even to let them walk around unguarded. Many one candidates will get nervous brackdown or just commit suicide or refuse to leave in order to stay home as doubts creep in deeper and deeper.

Nah, 10 years is not enough.


Since the Ark is a gigantic, untested prototype, and such a complex titan that is supposed to host human survivors, seeds, DNA from at least farm animals and enough human DNA to grant reproduction without inbreeding, is likely to suffer system crashes during its travel. Nuclear propulsion, the only more reliable propulsion technology (and energy generations for the ship's needs) at this point of the story, would use 1,000 years only to reach Proxima Centauri B.

My suggestion is that that convenient planet is located around that sun. It's difficult to imagine the survival of the species in such conditions beyond this limit. In fact, in 1,000 years, arriving to Proxima would be nothing short of a miracle

  • $\begingroup$ I would like to point out that, in this scenario, one of the givens is that a habitable planet is confirmed in an adjacent star system. If we can make it there with enough people we've definitely saved the human race. $\endgroup$ – SomeGuy Jun 16 '18 at 18:21
  • $\begingroup$ I like the greatly improved optimism in your edit ;) $\endgroup$ – SomeGuy Jun 16 '18 at 18:34

Many have highlighted that there is a problem with technology and sociology. I'd like to mention a problem with physics.

We can't flee that fast

So, by definition of the problem, the whole Solar system is scorched off by some kind of a mega Solar flare or something. This means that

  • we cannot run to Mars, as it won't help.

It was not stated in the question for how long the scorching continues and how fast does it advance. But my point is that our current space faring is quite slow and non linear. Assume that the flare takes one year to propagate. (It's a guess, but the radius of the solar system to the edge of the last still-planet is around 4 light hours.)

  • We cannot run away fast enough.

Any kind of propulsion known to us would not accelerate the ship fast enough to outrun the wave, even if we start early. Even worse,

  • We don't run strait.

All space navigation either requires orders of magnitude more energy, or (our option) slides along the gravitational vortices and makes use of cunning (and very curved) transfer orbits. The flare travels linearly, though.

One of better options is research on how deep the flare would burn. Given that it is stated to scorch down stone in every planet in solar system, we would probably loose the atmosphere anyway. But maybe burring few kilometers down would help, who knows?

The second option is to boost research on strong AI and non-quantum teleportation (maybe even using the strong AI), as our only feasible option to live is to warp away.

I also forsee a lot of projects similar to "let's beam our DNA per radio into the space" in a futile attempt to leave some legacy.

  • $\begingroup$ I appreciate your in depth and thoughtful contribution. You're definitely right, if the disaster is going to "reach out" to destroy the planets, whatever ship we send is gonna get caught up in it. It wasn't my intent for that to be the case, but it is definitely worth thinking about. $\endgroup$ – SomeGuy Jun 17 '18 at 15:56

The only way I could see us being able to travel through space for thousands of years with current or near current 'human technology' is for us to turn all of our attention towards creating an Artificial Super Intelligence (ASI) and allow it to figure out and build a ship for us to travel on. Or it would figure out how to stop the impending doom about to befall us all.

As long as we could harness the ASI to do our bidding it would be able to essentially figure everything out (given enough time and computing power - all countries would have to bring their supercomputers together to make it happen - a good way to ensure countries work together.)

It would devise propulsion, shields, food, water, power, etc. It would have to mine the world with robots it created. An ASI would basically be able to figure out and do anything that is physically possible.

Since we're all going to die from the 'event' anyway, the fears of an ASI destroying humanity would be worth the risk and would also make for great suspense. Perhaps the first few AIs were killed before they could get to the ASI state because they became violent or destructive.

The reader wouldn't know which way you're going to take the story. Will we live or die? If we die is it from the ASI or the 'event' because either we couldn't make the ASI in time, or we made it and it couldn't get the ships done in time. Would the ASI be able to come? Would it be too big and consume too much power to make the journey? Would it have a sympathetic personality that makes the audience feel sad that it got left behind after helping us get off the planet?

Other than that, or aliens, I don't see how it is possible to build a sustainable and pilotable biosphere for the thousands of years it would take to get to the new Earth.

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    $\begingroup$ This doesn't sound like a good idea to me - we understand rocket science quite a bit more than we understand how intelligence works. We have no guarantee an ASI is even possible, let alone possible to create in 10 years. Even if the ASI could be built in a year, it wouldn't be able to magically create the infrastructure necessary to build whatever it designs. $\endgroup$ – Rob Watts Jun 16 '18 at 1:44
  • $\begingroup$ @RobWatts, rocket science isn't the hard part. Having a space faring vessel remain viable for human life for at least 100 years is. Handling food and waste alone is huge, let alone electronics. And I think you're underestimating the power of an ASI. Maybe I'm overestimating. But I do believe that once we create a general intelligence, the pace of its progress will be unimaginable. Understanding chemistry will let it create new materials we haven't thought of as well as the robots to build them. "But our computers are so slow." Not when the ASI is designing them and the robots are building them $\endgroup$ – Tracy Cramer Jun 18 '18 at 18:22

@TracyCramer's idea is a good start but with a ten year deadline, even an Artificial Super Intelligence would be hard pressed to save humanity. So the better solution is to NOT save humanity. Just save our genes.

Create Tracy's ASI and ask it to focus on creating a ship capable of carrying itself to the new world. It can take its time getting there and won't need a lot of oxygen or water to survive the trip, so getting it launched on time is reasonably doable. We might even get a few redundant copies of the ASI launched in separate ships just to increase their survival odds.

Then when one of the ships gets to the new world, have the ASI develop artificial womb technology and synthesize fertile human embryos out of spare bits of carbon found on the new world. It might take a billion years for it to get all the bugs worked out but eventually humans would walk on this new world.


10 years is about the time it took to develop the American lunar program, which was far from "let a bunch of humans survive thousands of years in the hostile space and then finally colonize a planet".

The hurdles which will kill this project, requiring more than 10 years to be solved:

  • propulsion: the delta v we can squeeze out of our rocket doesn't allow us to ship large masses into space. We could use gravitational assists from Jupiter and Saturn maybe, but at the price of further lengthening the travel.
  • survival in space: as far as we know now, we are not suited for living in space. Radiation and lack of gravity are serious issues, and again we are mass limited.
  • colonization: all the colonies we set up during our history were heavily reliant on the mother nation during their beginning. Being literally on your own in a hostile environment simply pumps up your chances of failure.

One could say "we can ship frozen embryos with automated life support and hope for the best". Well, aside from consideration on exposing an embryo to cosmic radiation, it is well known that human babies need human contact during their infancy for a proper development, and robotic assistance is way too far from supplying it.


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