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There have been many (many) questions around here about the how, why & even when will man kind become a multi planet society... this is not one of them.

This question in fact goes the other way around, why would humanity fail to become a multi planet society?

Assume for a minute that all of humanity (yes every single one of us, it may be unrealistic but this is world building after all) is all of the sudden willing to put aside religion, consumerism, pride, ethnicity, politics & all the other silly reasons that divide us and we all agree that settling another planet (at least one) is super important and are willing to sacrifice a lot of comforts to get it (let's say around 15% of the total world GDP as well as mass agreements that needed resources and laws are passed to help make the dream a reality).

Starting tomorrow morning (literally tomorrow morning is the starting point of time) every single man & woman alive will work to create a self sustaining colony off world with the undivided attention, desire & resources of the entire world working together to reach that goal before 250 years pass (why 250? because)

Seems great right? now the question is what is a possible realistic reason (which isn't a natural disaster sending us back to the stone age or wiping us out) that will make us fail that goal?

EDL
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cypher
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    Numbers: the USA alone accounts for about 20 to 25% of the world's GDP. – elemtilas Jun 27 '19 at 21:54
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    Do we have to assume that a self-sustaining colony on another planet (like Mars) is theoretically viable at the present tech level? – Alexander Jun 27 '19 at 22:34
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    This seems a bit broad, doesn't it? It could be anything. The colony explodes for some reason. People change their minds 150 years later. There's an ecological collapse on the colony. There's an ecological collapse on Earth and people decide to put resources into that instead. There's a war. Someone sabotages the mission. Aliens destroy the colony. The Sun explodes for some reason. It turns out to be too difficult. A disease wipes out humanity. The singularity happens and only robots end up going to space. Is there something that could make one of these answers better than another? – N. Virgo Jun 28 '19 at 12:29
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    Because there's nowhere to go. – RonJohn Jun 29 '19 at 01:37
  • Some of those "reasons that divide us" can provide an awful lot of motivation to get stuff done – A C Jun 29 '19 at 02:29
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    The ways to fail are legion, the ways to succeed are few. What defines a better answer here? – John Jun 29 '19 at 03:27
  • To answer this question properly, it requires cogent thinking to take into account whatever failure mode(s) prevent our species becoming a multi-planet one, has to deal with whatever it was that unified the world in an attempt to colonize another planet. Maintaining political & cultural unity is never easy. Political & cultural changes are most likely to sabotage multi-planet colonization. – a4android Jun 29 '19 at 04:05
  • Please read our meta posts about high concept questions and open-ended questions. The problem with questions like this is they are broad, not objective and you've provided no criteria for judging a best answer. Please remember that SE is not a discussion forum. VTC OT:POB – JBH Jun 29 '19 at 07:52
  • I think with lots of funding and careful engineering work, we could design and build an extraterrestrial habitat which would provide for all of humanity's known needs. It would still likely fail, though, because it wouldn't be able to provide for all of humanity's needs that we don't realize we have. Humans have evolved in concert with Earth's biosphere, and it's highly likely that there are lots of subtle long-term requirements that we have on services provided by that biosphere that we don't even realize we have (eg gut microbiome maintenance) but would find out about soon enough in space. – Jeremy Friesner Jun 29 '19 at 20:38
  • GDP is a poor metric for how much a person can contribute to a project. An Ethiopian ''worth'' $1/day could work as well as a $1000/day American. – Zdenek Jun 30 '19 at 12:28
  • Suggested readings about interstellar colonies going wrong; Larry Niven's novel Destiny's Road and Frank Herbert's short story "Seed Stock" – Ash Jul 19 '19 at 13:46

15 Answers15

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As every project manager knows, scope creep is the root of all evil.

At the beginning, it was just about sending one ship to another planet. Easy, just a matter of time.

Then someone said something about food diversity, citrus fruits and, for whatever reason, pineapples. So a team was split up to figure out how to grow pineapples on a space ship and in a human colony. Suddenly scientists talked about gene splicing pineapples and strawberries, though no one could figure out why it had to be strawberries. Probably because the wife of the team lead liked them. It took fifty years until someone said "screw pineapples" and stopped the whole thing.

In another meeting another guy talked about how awful dying in space could be, so another team was split off to change the triple redundancies from the current ship design to quadruple redundancies. Just to make sure, they put double redundancies on the quadruple redundancies. The added weight required a redesign of the whole engine system and they had to figure out how to store ten times the previously planned fuel. New propulsion systems were experimented with and abandoned. Eventually someone decided that triple redundancies should be enough after all.

Then someone asked about space pirates, so a team was sent off to develop space weaponry just in case. Nuclear missiles, lasers, railguns, the whole spectrum. They spent forty years just to figure out whether they could build an antimatter bomb. Also armor to defend against all that, which required new materials, so another team was sent off to develop micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating. And don't forget about shields like in star trek, for which another team experimented with em fields for years. At least someone put a stop to the team that was developing synthetic humans to defend against boarders, though that was more for fear of the AI revolution than because of costs.

In another meeting... well, you get the point.

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    Yeah, scope creep was what did in the Soviet moon landing program. They were well on track to blast some brave Heroes of Socialism to the Moon, and to beat the Americans to do it, but then all the sudden someone decided that the cosmonauts had to come back, too... – kingledion Jun 28 '19 at 19:54
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    "So Bob, is your team ready with the micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating for Tuesday?". "No Jack, we'll be ready with the micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating on Wednesday". "That's what you said about the micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating last week". "When attacked by space pirates, do you want faluty micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating or working micro-non-newtonic-carbon-tungsten-fluid-nanotube-reactive-reflective plating??" – Nahshon paz Jun 30 '19 at 13:45
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One problem could be that humanity in fact becomes too committed to the space program and neglects economic sustainability. By concentrating too much on the colonization project, other branches of the economy get neglected and stagnate, which then causes a ripple effect eroding the economic foundation which makes the space program possible in the first place. Examples:

  • Budget cuts in health care and sanitation lead to epidemics in the countries which mine the raw materials for the space program, killing all the miners.
  • Budget cuts in transport infrastructure make the supply chains between the many manufacturing facilities involved in the space program unreliable and result in huge delays. That's really problematic because interplanetary space missions often rely on planetary constellations which only last for a couple days and only happen every couple years. That means a single part which is a week late can delay your whole space program by several years.
  • Budget cuts in education result in a shortage of qualified scientists, engineers and managers to plan the space program and a shortage of qualified workers to execute it. The space program needs to lower their hiring standards. The result of having less competent people in all positions are inefficient solutions which waste resources, unsolved problems which delay project plans and catastrophic accidents which destroy material and cost lifes.
  • Budget cuts in agriculture lead to famines and cause the world population to decline, which amplifies all the problems mentioned before.

So while the space program might move really quick at first, the problems caused by neglecting the economy which supports it make it grind to a halt after a few decades. Humanity realizes that in order for the space program to have any chance to succeed, they need to do a 180° turn and focus on economic development again. But all the problems which affected the space program will also affect these economic stimulus programs. So it might take a very long time to get the economy back to what it needs to be in order to sustain itself and an expensive space program. After they fixed the economy, most parts of the space program will be obsolete, repurposed, forgotten, beyond its shelf-life or ruined by years of neglect. They will basically need to start from square one again.

Philipp
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Well... besides the earth being flat and the literal glass dome preventing anyone from escaping... (jkjkjk)

Given enough time, anything is possible. But if we wanted to do this quickly, we would run into some serious road-blocks.

Finding a planet which is Earthlike enough

First of all, we need to find a planet similar to earth. Colonizing Mars might seem like a good idea, but its mass, nearness to the sun, lack of a moon like ours, and the many other differences between Mars and earth, make it likely that plant life won't grow there easily, and long-term exposure to that environment may have significant negative effects on other organisms. There are hundreds of factors involved in enabling life on earth: mass, density, temperature, atmosphere, nearness to sun, type of sun, mass/density of moon, nearness to moon, magnetic field, mineral contents of ocean, ordering of layers in crust, volcanic activity, shape of mountains affecting wind, etc. etc. etc.. For example, we know that long-term exposure to non-earthlike gravity can cause people's bones to atrophy. Every one of those conditions, if not met well, can lead to other serious health conditions. Given the time it will take to get there, we should get this right the first time, so take a few years thinking about where to go, and maybe send out a few probes. (60 years)

Getting there

There have been some theoretical ideas thrown around for how we can get a probe to fly-by a far planet which we think is earthlike in as little as 60 years using massive solar sails, but the probe was tiny, and we still had a problem where it couldn't decelerate quickly enough to orbit. At best, we would get a few flyby pictures at extremely fast speeds. Stopping in a foreign solar system within one lifetime is a problem we haven't figured out how to solve (and might not be able to solve because of the limits on acceleration which humans can tolerate). So, we'll have to first make a space station which can support plant and human life for several generations, which might be impossible even with spinning stations to simulate gravity, because of the inherent differences those stations will have when compared to earth. (120 years or more)

Generation Ship Planning/Construction

Due to the careful planning of the ship-side ecosystem, population control on the generation ship will have to be strictly regimented. This will represent significant social engineering problems which humanity has never faced before. The few experiments with this kind of small isolated population, which I'm aware of, have been steaming failures. We really don't know how humans will handle spending their entire lives aboard a space ship with only a handful of types of food, their romantic interests potentially having been arranged several generations prior to maximize diversity, and the possibility that a tiny, simple mistake made by some kid on the ship could cause a breach or something and kill everyone. Not to mention, you'll have to have warehouses with new electronic components to constantly maintain your ship in-flight. Electronics don't last all that long. (For this, assuming just one minor failure unaccounted-for, I'm adding an extra 20 years. But realistically, we should expect several failures)

Planetside Resources / Terraforming

If we can land the generation ship on the planet and call that acceptable, then skip this part -- but I think a "planet colony" should actually be interacting with the planet somehow, and not just making physical contact with it via ship struts.

Then, once we get there, we'll have immediate resource issues planetside. Earth represents a very distinct mix of materials favorable to life, and we might not be able to survive off-world without either frequently returning for supplies, or quickly gathering resources from several off-world planets simultaneously. All human colonies depend on transformation of one type of matter into another type of matter in order to produce energy, food, etc. Our plants depend on water with very specific ratios of specific minerals in it to bear fruit, and won't live with too much of this or that other chemical in the water.

Suppose there is too much of Chemical A in the water, so we harvest Chemical B to make filters. When it's time to recycle the filter, we can't recover all the B from the dirty filter, so we have to continually harvest more. Suppose B is not abundant in the soil, so we have to dig deep to find stores of it. To make matters worse, the outer crust of this planet is also dense with Chemical C, which is toxic to humans on contact, but the process of removing that requires lots of time, energy, and maybe even some Chemical D, which just isn't present on this planet at all. So we harvest D from a nearby moon or asteroid, use it to terraform a small portion of the surface, and set up deep and very dangerous mines in the planet to acquire B. In the meantime none of our plants will grow, so now we have to land our generation ship safely on the planet, or be constantly shipping supplies back and forth in orbit. Anyway, all that to say, Tweaking the planet to enable it to support life will take several more generations. (At least another 100-200 years before a small part of the planet becomes self-sufficient.)

The Unknown

Lastly, we don't actually know what's far far out in space yet. We just have a pretty good idea, but there's a chance that we'll just be repeatedly killed by the unknown! (60-120 years setbacks, unpredicted events, compensating for unknown)

Conclusion

Like I said, given enough time, anything is possible. But 250 years might be a bit too aggressive of a timeline. Given my estimates, I'd give us a minimum of 360 years; more realistically 500+ years. 360 is not too far from your window, though, so who knows? Maybe we can do it.

boxcartenant
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    You are in the void of deep space. It's pitch black. You are likely to be eaten by a grue. – dmcontador Jun 28 '19 at 11:57
  • Generation ships, see this comment. TLDR: you'd need 10 pentillion kilograms of fuel to get a colony ship housing 8 people to Alpha Centauri (least-fuel trip) using chemical rockets (other forms of torch-ship are similarly non-viable simply due to the "fuel needed to accelerate the fuel" cascade). – Draco18s no longer trusts SE Jun 28 '19 at 14:30
  • @Draco18s one can imagine a ship with frozen human embryos, that are thawed, raised, nurtured and educated by decent machinery when the ship is about to reach the planet. – stop-cran Jun 28 '19 at 15:23
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    @stop-cran, I mean, we can. But that has its own challenges, such as "how do you raise functional (ie. not psychotic) humans with only robots for mothers?" And you still have to ship enough raw material to feed those kids while you have yet-more-robots set up a habitation on the planet that can support them. Oh, and if something goes wrong, the colony is lost entirely. You have no way to send software updates from Earth. And even that assumes that you can find the fuel to send the robots...each 1kg of ship/payload would need 281,390,211kg of fuel. – Draco18s no longer trusts SE Jun 28 '19 at 15:44
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Cultural shifts: Once your generational ship arrives at the other planet, your descendants look out of their nice, clean space-ship with its hydroponics bays and gravity controls in every room. They see an ugly ball of dirt, all irregularly shaped, where "down" is always the same direction, and you can't turn off the gravity to float in peace.

Then they'll mine the planet via robots to build a second ship to expand to, and head off elsewhere instead of founding a ghastly "colony" of all things...

Chronocidal
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You will not go to space today ever

Balancing a biosphere over the timespan of 100+ years hasn't been shown to be possible. Even Biosphere 2 didn't manage to run its entire originally planned duration, "Both attempts, though heavily publicized, ran into problems including low amounts of food and oxygen, die-offs of many animals and plants included in the experiment, group dynamic tensions among the resident crew, outside politics and a power struggle over management and direction of the project."

But lets assume that Biosphere 2 as a baseline, to get a reasonably close lower-bound on the problem at hand. It really doesn't matter if Biosphere 2 was only sufficient for 1 person, 8, or 80. The numbers get so large here in a minute that a single power of 10 equates to a rounding error.

The amount of mass involved is on the level of "absolutely staggeringly preposterous":

The whole structure contains (for the record) approximately 170,000 metres3 of atmosphere, 1,500,000 liters of freshwater, 3,800,000 liters of saltwater, and 17,000 metres3 of soil.

4 million liters of saltwater. Putting nearly 5 million kg of water into space at \$10,000 a kilogram is not economically viable for any reason, full stop. The soil is even worse. A cubic meter of soil weighs in at about 1.5 metric tons. Or about 25,500,000 kg for the amount in Biosphere 2. And another 220,000 kg for the air gives us $310 billion in launch costs, not including the structure of the ship itself (remember, the space shuttle itself is 75,000 kg for a payload of 4,000-16,000 kg depending on destination), or its fuel. That's already double the total cost of the ISS. And we're not even counting the mass of the plants and animals that will be aboard.

And remember, we're calling Biosphere 2 the bare minimum to maintain 8 people. In order to run a generation ship you need a bare minimum of 200 breeding humans under strict breeding regimens in order to maintain heterozygosity. That is, to prevent inbreeding. So, multiply all these numbers by 25 in your head. More if you want to be safe and allow for the occasional soul lost to accident or disease.

Now, fuel.

Getting to the nearest system to ours, Alpha Centauri involves:

  • 16.8398 km/s of delta-v to leave the solar system from LEO, including a plane change of 9 degrees.
  • 32.935 km/s of delta-v to arrive at, and subsequently not leave, the Alpha Centauri system

Lets round that up to 50 km/s for a bare minimum lowest-fuel trip (and remember that these values do not include launching material into space nor landing on a planetary surface at the other end). And being a generation trip, we don't care if it takes 100 or 100,000 years right now, we just to want to work out the bare minimum needed in order to assess viability: a lowest-fuel-cost trip.

So: 50 km/s, 31 million kg, and 8 people.

8,728,724,371,657,847 (8.7 *1015) kg of fuel using Space-X's Merlin engines. (Feel free to check that yourself; a Merlin engine's exhaust velocity is 2570 m/s).

That's a small moon. No really, its about as massive as Phobos (10.6 *1015kg).

That number is so astronomically large as to make any possible improvements in efficiency meaningless. Even if we improve the Merlin engines by a factor of 10 and use fuel with an energy density 100,000 better (say, nuclear), that still knocks the fuel costs down to a mere 8,728,724,371,657 kg, and we'd have to just multiply back up again once we account for the shell of the space ship, extra fuel for course corrections, obstacle avoidance, a shorter trip, more people, a more habitable system, and so on.

Even if you launch your ship using a fuel-less launch system out of the solar system, so that you only need "half" the delta-v (remember you can't count on a laser station at your destination, and in truth, we can only cut out a third of the delta-v not half of it, but its largely irrelevant), that knocks your fuel down to 0.006%. Or 520,350,872 kg of fuel (after the efficiency improvements and before all the other considerations). This is enough fuel to give an (otherwise empty) space shuttle a delta-v budget of 22.73 km/s using Merlin engines. And that original fuel mass? The 8.7 *1015 kg? The delta-v budget on an empty shuttle is still only 65.48 km/s.

This is the scale of the problem you have.

  • Mass is expensive
  • Delta-v is exponentially expensive
  • Sustaining humans indefinitely requires lots of mass
  • Getting anywhere interesting requires lots and lots of delta-v
  • Getting there in anything less than "infinite time" requires lots and lots and lots of delta-v

The reason the project will fail will be due to the sheer inability of the human race to gather the raw resources necessary and the impossible engineering necessary to build such a megastructure.

Draco18s no longer trusts SE
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  • You can actually use the laser station for deceleration too, in theory - this has been part of old-school hard sci-fi for decades. Mind, "in theory" doesn't cut anywhere close to "feasible engineering" (though to be fair, neither does the actual laser sail concept with near-current technology), not to mention that the approach used would make your trip even longer, and the ship's biosphere (and machinery) even more likely to fail. – Luaan Jun 30 '19 at 09:05
  • @Luaan The whole point of the laser system is that you don't take it with you: you leave the mass of a terrawatt laser and power station back on Earth (or trojan asteroid, wherever you feel like building it). But you're right that its still on the "impractical" end of the feasibility spectrum no matter where you put it. Even Project Longshot only has a payload of 30 tonnes requiring 264 tonnes of nuclear fuel. The payload itself is little more than a sensor suite, fusion reactor, and 250 kW communications laser. – Draco18s no longer trusts SE Jun 30 '19 at 16:11
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    OTOH, there's lots of water in space: just find a handy comet. Likewise, you can grind up a stony asteroid to get the basics of soil. It's not necessary to lift most of the mass out of a significant gravity well. – jamesqf Jun 30 '19 at 18:32
  • @jamesqf On the other other hand, matching orbits with an asteroid or comet has its own set of problems. Second you can't wait to feed, water, and air a crew until after you leave the solar system. Third, you still need to accelerate from wherever you decide to go with whatever mass you pick up out of the solar system. Fourth, you still need to decelerate on arrival. Fifth, the numbers I cited (the 50 km/s of delta-v) are from Low Earth Orbit, not the ground, but sure, lets assume that you don't need to get out of Earth's gravity well; just subtract 4.4 km/s from the required budget. – Draco18s no longer trusts SE Jun 30 '19 at 18:37
  • I wasn't suggesting you take the laser with you :) – Luaan Jun 30 '19 at 19:48
  • @Luaan A laser 4 light years behind you would have a devil of a time (a) focusing on you and (b) pulling. – Draco18s no longer trusts SE Jun 30 '19 at 19:49
  • You're already assuming the laser can keep you in focus for most of the duration of the trip, so that's not a big deal. As for pulling, duh. It will still push you. The trick is coming from the other side, you see. – Luaan Jun 30 '19 at 19:52
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    @Luaan That trick is to dump enough velocity that the solar gravity well captures you so you have the time to do the remainder of the insertion to a planetary orbit. You can't dump that velocity with a laser pointed at your backside. If you're already going slow enough that you're not going to spit out the other side of the system, you don't need the laser. But no, I wasn't assuming the laser can keep you in focus for the whole trip. The back-of-the-envelope math was assuming it can only push you up to transit speed (hence the "half" figure), and highly optimistic. – Draco18s no longer trusts SE Jun 30 '19 at 20:13
  • Just because modern humans cannot maintain a biosphere does not mean that it will not be doable in the future. And you directly took a quote from Wikipedia, but did not mention that "The second closure experiment achieved total food sufficiency and did not require injection of oxygen." In hundreds or thousands years, we will likely have the technology to maintain a biosphere. Also, you do not need to maintain a biosphere anyways, just bring some hydroponically grown plants and algae bioreactors to feed your crew.
    • – Richard Smith Dec 08 '19 at 00:49
  • If you need animals and plants on arrival, you could keep frozen seeds/embryos, or gametes, or just DNA, depending on how advanced your biotechnology is. This can also be used to deal with population bottleneck issues. You could get away with using a tiny (or AI) crew which grows new humans on site. – Richard Smith Dec 08 '19 at 00:55
  • And as there are no physical laws prohibiting extreme life extension and biological immortality, you might not need a generation ship, either. People don't really die of old age, they die because their organs fail and their brain degrades. Even now, many scientists are working towards curing cancer, heart disease, Alzheimer's, etc, so unless humanity gets killed by grey goo or an asteroid or something, clinical immortality will probably emerge at some point, whether through genetic engineering or nanotechnology or cyborgization or organ cloning or stem cell therapy or some combination thereof. – Richard Smith Dec 08 '19 at 00:57
  • You probably would not be launching an interstellar mission just off of Earth's resources. People would expand off the planet at some point, as if they do not, the heat from industry and such would heat the planet faster than it radiates away, cooking everything directly (not relying on greenhouse effect, so source of energy does not really matter for this). Whether through carbon nanotube space elevators or projects such as launch loops/mass drivers, it is possible to greatly reduce launch costs, which would enable mining of asteroids, dwarf planets, and moons.
    • – Richard Smith Dec 08 '19 at 01:01
  • @RichardSmith Alae has been researched (the units are missing from the abstract, so I can't do work with them), but notes that "a number of technical problems need to be solved" first. I used biosphere 2 as a baseline for computing what we could achieve today as per the question's premise. My answer gives a scale to the problem needing to be solved (multiples orders of magnitude of improvements). AI and cryosleep may as well be a fantasy. – Draco18s no longer trusts SE Dec 08 '19 at 01:03
  • You still require a massive fuel budget to slow down at the target system, even if you're only sending a (dry mass, including all infrastructure and engine) 1kg probe (367,756 kg of fuel! That's 60% of the fuel needed to put the space shuttle in orbit). – Draco18s no longer trusts SE Dec 08 '19 at 01:07
  • Your answer states "ever," and "ever," is a really long time, considering how resource rich the entire solar system is. Provided we do not kill ourselves off, (and the chances will drop as we spread throughout the solar system and improve technology) we will have literally millions or billions of years to build infrastructure and develop technology, and a settled solar system with even a partial Dyson swarm will have an economy billions or trillions of time larger than our own. – Richard Smith Dec 08 '19 at 01:11
  • Also, if you launch from the Kuiper Belt or Oort cloud and push yourself out with fusion powered lasers (fuel with water ice from comets), the Sun's gravity will be much weaker and you won't need as much delta V to escape (though that doesn't solve the problem of slowing down). – Richard Smith Dec 08 '19 at 01:16
  • @RichardSmith The primary problem is that physics is a harsh mistress. You need on the order of half a billion kg of fuel per kilogram of payload to get something from one system to another. Even at the theoretical maximum exhaust velocity you need 22,025kg of fuel per kg of payload (the Merlin engine having a mass of 630kg, plus 120 for an astronaut in a space suit). And if you look at my post, starting at the solar edge only saves you ~16k/s of delta-v (costing 1507 kg fuel per kg payload at theoretical maximum thrust). – Draco18s no longer trusts SE Dec 08 '19 at 01:20
  • Not that the kupiter belt really helps: Every gram of fuel you spend slowing down at the construction site in the kupiter belt is two grams you could have spent slowing down at Alpha Centauri. Sure, you can leap frog resources out in smaller trips taking more time, but the overall total cost goes up and the biggest problem is slowing down at Alpha Centauri (remember, this is a Lowest Fuel trip, which will take 1.2 billion years of travel time). – Draco18s no longer trusts SE Dec 08 '19 at 01:24
  • Let us continue this discussion in chat. – Richard Smith Dec 08 '19 at 01:30