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Do Humans Have An Off-World Future?

The views expressed are those of the author and are not necessarily those of Scientific American.

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Optimistic visions of a human future in space seem to have given way to a confusing mix of possibilities, maybes, ifs, and buts. It’s not just the fault of governments and space agencies, basic physics is in part the culprit. Hoisting mass away from Earth is tremendously difficult, and thus far in fifty years we’ve barely managed a total the equivalent of a large oil-tanker. But there’s hope.

“Prediction is very difficult, especially if it’s about the future…”
Neils Bohr

Inside an O'Neill cylinder - life amongst the stars, circa 1970 (NASA)

Back in the 1970′s the physicist Gerard O’Neill and his students investigated concepts of vast orbital structures capable of sustaining entire human populations. It was the tail end of the Apollo era, and despite the looming specter of budget restrictions and terrestrial pessimism there was still a sense of what might be, what could be, and what was truly within reach.

A pair of space habitats on a giant scale (NASA)

The result was a series of blueprints for habitats that solved all manner of problems for space life, from artificial gravity (spin up giant cylinders), to atmospheres, and radiation (let the atmosphere shield you). They’re pretty amazing, and they’ve remained perhaps one of the most optimistic visions of a future where we expand beyond the Earth.

But there’s a lurking problem, and it comes down to basic physics. It is awfully hard to move stuff from the surface of our planet into orbit or beyond. O’Neill knew this, as does anyone else who’s thought of grand space schemes. The solution is to ‘live of the land’, extracting raw materials from either the Moon with its shallower gravity well, or by processing asteroids. To get to that point though we’d still have to loft an awful lot of stuff into space – the basic tools and infrastructure have to start somewhere.

And there’s the rub. To put it into perspective I took a look at the amount of ‘stuff’ we’ve managed to get off Earth in the past 50-60 years. It’s actually pretty hard to evaluate, lots of the mass we send up comes back down in short order – either as spent rocket stages or as short-lived low-altitude satellites. But we can still get a feel for it.

To start with, a lower limit on the mass hoisted to space is the present day artificial satellite population. Altogether there are in excess of about 3,000 satellites up there, plus vast amounts of small debris. Current estimates suggest this amounts to a total of around 6,000 metric tons. The biggest single structure is the International Space Station, currently coming in at about 450 metric tons (about 992,000 lb for reference).

This may look like a lot of stuff....but (NASA, Apollo 11 launch)

These numbers don’t reflect launch mass – the total of a rocket + payload + fuel. To put that into context, a fully loaded Saturn V was about 2,000 metric tons, but most of that was fuel.

When the Space Shuttle flew it amounted to about 115 metric tons (Shuttle + payload) making it into low-Earth orbit. Since there were 135 launches of the Shuttle that amounts to a total hoisted mass of about 15,000 metric tons over a 30 year period.

This begins to sound a bit better right? Hang on though. Take a look at one of these:

Your common or garden supertanker (Credit: US Navy)

This kind of tanker, fully loaded, is about 550,000 metric tons. That’s thirty-six times more mass than the Space Shuttle’s lifetime transfer to orbit. It’s one tanker. Could you build the basic infrastructure to mine and refine a trillion-ton raw asteroid, turn it into metals, materials, tools, and machines with this amount of building material? Perhaps, just. But O’Neill cylinders? A long way off.

By now you may be feeling depressed. Gravity really does suck. But I don’t think realism is a bad thing. In fact what this tells us is a simple, obvious fact. To reach that point of break-even, where what we’ve raised to space is surpassed by what we’ve made in space, we just need to get a little better at step 1. An oil tanker may be some 30 times more massive than 135 Shuttle flights, but that is not a bad factor to overcome. If it were a thousand, or a million, that would be the time to forget it.

So the efforts of space agencies and private launch operations like SpaceX, or Orbital Sciences to drastically reduce the cost of that first step are truly critical. I think there is still hope that an off-world future awaits our species – and it may be vital for our long-term survival.

[Before comments appear about how we shouldn't spend resources on such things until we've resolved our earthly problems: yes, sure, but NASA's entire budget (for example) is at present less than 0.5% of the entire US federal budget. At about $18 billion it is less than the wealth of some individuals on the planet. And other nations don't spend as much, the European Space Agency's budget is about $13 billion. For comparison the National Institutes of Health have a roughly $30 billion annual budget. And the science and technology of space has enabled us to study our home planet in ways that have become central to evaluating and improving the quality of life for all humans, from understanding weather and climate, to population growth and land-use. So there.]

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. kevinrandall 12:17 pm 04/16/2013

    Hello Dr. Scharf,

    I came across your work when I saw the “Evacuate Earth” show. I’ve been really fascinated by the nuclear pulse propulsion concept, and how efficient it is (if we ignore the drawbacks for a moment). It’s interesting that we humanity actually had a propulsion method that would get us to Mars and beyond before we had even put a person into orbit.

    After watching “Evacuate Earth”, I watched a BBC series called “To Mars: By A-bomb” which discussed the history of Project Orion. I’m still confused by one aspect which maybe you can help with.

    Wouldn’t this propulsion method work completely differently in the vacuum of space versus in an atmosphere? I understand how the blast would work on Earth to propel it, but there is no blast in space without an atmosphere as far as I know. From my very, very limited understanding of nuclear weapons, their behaviour in space is very different.

    Could you comment on this please. All the best

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  2. 2. Joshua B 12:28 pm 04/16/2013


    I really lost hope myself. When I was kid I always dreamed of the days that I might be able to hop on a ship and visit the Moon or just even space. You bring up a few valid points, but I think most people alive today won’t see that happen in their life times. I guess we don’t really know where we’ll be in a few decades though, but it’ll probably be a long ways off. I loved your comments there at the end about the budget constraints. I’m sure there will be comments, but in my mind I wish I could take half the defense budget and hand it over to NASA. I think NASA could accomplish a great deal of innovation with a larger budget.

    -Joshua B

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  3. 3. caleb_scharf 12:42 pm 04/16/2013

    Thanks for comments. Re the ‘Project Orion’ style propulsion system – it’s the push of the radiation/particles and mass of the bomb material that provides the impulse to the ship – although that may not amount to much in terms of mass the explosion accelerates it to such a high velocity that the momentum is big.

    I think there’s still reason to be optimistic. There’s a fair chance that the private space industry will continue to scale up and make launch cheaper and cheaper. The other challenges that I didn’t mention here are of course the biological ones – from low-g to radiation, space is a nasty place. But I guess it depends on where you want to go….

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  4. 4. bactbob 12:45 pm 04/16/2013

    It seems that readjustment of our rocket system could solve some of the transport issues: The Hydrogen+Oxygen rocket booster is fundamentally correct, but instead of a large rocket to carry liquid components, use the Hydrogen for lift (very large balloon), add 02 and ignite with a small booster rocket at the balloon apex and use the empty shell as a solar sail.
    more @

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  5. 5. curiouswavefunction 1:02 pm 04/16/2013

    kevinrandall and caleb_scharf: In case of Orion, the propulsion was supposed to be provided by an inexpensive material that would be placed between the exploding hydrogen bomb and the pusher plate on the spaceship (and yes, the radiation pressure would also help). In theory this could be almost anything, from polyethylene foam to rocks and miscellaneous material from planets, comets and asteroids. It was this possibility of using cheap material in space as fuel that partly made Orion so attractive. George Dyson who is the son of Freeman Dyson – one of Orion’s chief scientists – has written a very good book named “Project Orion” describing the project.

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  6. 6. RSchmidt 1:25 pm 04/16/2013

    Where are we with the concept of a space elevator?

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  7. 7. AlexZiegler 2:01 pm 04/16/2013

    What people need to understand is that companies are investing to drill in space. This drilling is for metals that are more common in space but rare here on earth. But guess what… we are also going to get common materials as a result of the drilling… Costs of getting all of that material back to earth is not going to be worth what we can turn it into… The only viable solution is to keep it in space, refine it into different products, that then create the infrastructure needed to build these long term habitable facilaties…..

    All that remains is to design an artificial gravitational device for the system in question….

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  8. 8. jerryd 4:37 pm 04/16/2013

    Other than to see what is there, living off world has little to offer.

    Though it will get reasonably cheap to visit, not much more than a nice cruise lux cabin now. Go SpaceX!! Show them how it’s done.

    Nor will we need it because in 100 yrs there will likely be 1 billion less people than now. And those who are will need little to live on. I doubt we will hit 8.5B people before it reverses at present birth rate drops/woman trends.

    Not to mention countries that aborted girls to have a male. Those girls that survived will be worth far more, liberating them in most cases.

    China and India have this problem bad. And little good comes when men outnumber woman by over a few %. Usually countries like that fail.

    By then, actually by 2050 fossil fuels will be gone in 95% of the countries and that left way too expensive to burn so the GW will start reversing and pollution problem abate.

    If we can get through the next 30 yrs life is going to be nice for the whole world if politics let’s it.

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  9. 9. gmperkins 4:39 pm 04/16/2013

    Solar system, sure, we’ll get out there and do stuff (already have). But beyond that, we’ll need some serious breakthroughs. The holy grail would be anti-gravity. Just don’t see anything happening anytime soon. Can always hope that I’ll be pleasantly shocked in my lifetime.

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  10. 10. sault 5:55 pm 04/16/2013

    If we are to survive long-term as a species, we’ll have to establish sustainable settlements off-world. As soon as we can extract enough materials from the Moon / asteroids to sustain people and make more equipment for extracting resources, then the process will spiral out of control and there will be no telling how far we can go. Getting multiple national governments, corporations and non-profits into the mix helps to keep the temporary political whims of the moment from stalling human history for decades like what happened in the 1970s.

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  11. 11. em_allways_right 8:23 pm 04/16/2013

    Kevin – the explosion pushes you, in the atmosphere or in a vacuum. Newton’s 3rd Law.

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  12. 12. m 9:10 pm 04/16/2013

    It has been researched that we currently over-use our planet by 40%(140%). Meaning we cannot re-use 40% of our usage. At this rate we will need to go to space and get resources because its a finite energy equation. We cannot for instance turn lead back into hydrogen without a lot of energy. So resources can be considered finite on this planet for us, once we turn it into landfill it stays in landfill. Once all the oil is sucked out of the ground its mostly gone and we arent replacing it. Building materials and metals, from mines will eventually run dry in about 200 years, still productive in a minimal sense but dry in a demand sense.

    So yes its space and active resource hunting, there is no question, it is a reality.

    The question of cost will come down as materials become more expensive, but while our materials are at there cheapest right now, we should be putting in all manner of infrastructure…right now.

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  13. 13. jimmybo 9:21 pm 04/16/2013

    Folks as far as going to space, I think using carbon sheets and/or carbon nano tubes to create a space elevator to get to space big time. When you have one up and running then you can use it to start others all over the world at the equator, but the first organization to do this will just about own space so why are we not investing more in R&D to this goal. Once this happens we then will have a manufacturing plants in space, after that it is just matter of advances in tech to go deep space. Space elevators can be used on the moon, mars, ect. for the same usages, if we get into space big time, why would we ever want to go down another gravity well, but to get raw materials.

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  14. 14. Stranger 1:20 am 04/17/2013

    IMHO, Carbon life has nothing to do in outer space except having some fun. Most of space jobs in the future will be done by silicon intelligence – far more robust and cheaper.

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  15. 15. Asteroid Miner 2:06 am 04/17/2013

    6. RSchmidt: See We are crowdsourcing funding for an elevator from the moon. We can’t make good enough carbon nanotubes and we can’t make diamond nanowire yet. The moon’s gravity is low enough to use supermaterials we already have.

    Inventors of diamond nanowire making process: We are interested.

    With an Earth to space elevator, mining gold on asteroids or Mars would be very profitable. Likewise helium3 and some other things.

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  16. 16. stargene 3:17 am 04/17/2013

    Whether we, “..have an off-world future?” can only
    sanely be answered positively if we all begin to
    demand that “We must have an on-world future!”

    State-of-the-art 3-d printers, nano machinery, fusion
    propulsion, O’Neill and Dyson style architectures, AIs
    and more may of course be part of an off-world
    expansion, to name just a few things. But if we, an
    actual present majority of citizens, can’t even manage
    to hold our politicians’ and ceos’ feet to the fire,
    regarding global climate change, real funding of basic
    education, basic science, basic jobs, basic equity
    period… then any ‘Futurism’ talk is just banter. The
    only way to get serious about ‘our future out there’
    is to also get very serious about ‘our future down

    Each action/mind-set can’t help but feed the other.

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  17. 17. Heteromeles 10:27 am 04/17/2013

    As for space elevators, imagine a string 100,000 km long roughly. It’s held by two weights at each end, and the fact that one’s pulled by gravity, while the other one is in orbit, holds it taut.

    What does that string do?

    It twists and vibrates. There’s all sorts of forces acting on it, from the atmosphere to differential heating to the pull of the moon and whatever else. Therefore, I suspect it will vibrate and twist chaotically.

    Now, if the wave heights reach even one part in 100,000, that’s a kilometer-wide swing. I could be wrong, but I think most strings vibrate rather more than this, so the big waves are likely to be tens of kilometers. There will, of course, be small waves as well.

    You want to ride it? For days, if not weeks? Note that the elevator has to travel 100,000 km without melting the cable, so it can’t go too fast. Even at 1,000 km/hr, it will still take 100 hours to reach the top, and 100 km/hr may be more realistic.

    That’s the reality of a space elevator, even if we can build it. I suspect that, if one is built, some crew will ride it up and down, just to demonstrate it’s possible. After they survive the experience, I suspect it will be used predominately for cargo. Very well-padded cargo.

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  18. 18. christinaak 3:59 pm 04/18/2013

    Off-world settlement makes great fiction, and there are a multitude of insurmountable obstacles which guarantee that it will remain nothing more than that.

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  19. 19. verdai 3:59 pm 04/18/2013

    According to the Real amount of energy we have left, mine the space rocks and forget Mars for the moment.
    It is demonic how most waste energy.

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  20. 20. Dr. Strangelove 11:18 pm 04/18/2013


    You have geostationary orbit at 35,786 km altitude. That’s how long the cable of space elevator. So the cable will not snap by centrifugal force, you need a cable with specific strength of 3.4 MN-m/kg. The strongest steel is 0.2 MN-m/kg. The strongest material is carbon nanotube at 45 MN-m/kg. It can withstand the tensile stress of space elevator cable. But we cannot yet manufacture carbon nanotube large scale.

    There’s no problem with heating due to air resistance. The cable is moving at the same speed as earth’s rotation. It will appear stationary from earth and the atmosphere but actually moving at 5,855 mph in space. Going up the space elevator is almost equal to going around the world in distance but saves a lot of energy. Imagine the energy wasted going up the Empire State Building using rocket boosters.

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  21. 21. bucketofsquid 4:25 pm 04/19/2013

    @ Christinaak -Yeh, they said that about the new world too but here we are. I remember learning about the whole “if man were meant to fly we would be born with wings” nonsense too. It is OK that you fear progress but don’t be surprised if the more ambitious pass you by.

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  22. 22. bucketofsquid 4:55 pm 04/19/2013

    Other options are the mountainside rail-gun, the space cannon and the aforementioned hydrogen balloon lift/fuel system. A smaller vessel lifting on the back of an airliner is much cheaper than a rocket as far as fuel costs go. It also would involve a lot less large components plummeting to earth.

    As far as a permanent home, that would be unlikely until we can build a gargantuan ship or station for spin or control gravity. To build the large home in space we could very easily start quite small with a modular design that eventually expands to enclose a large area that could then be built up or simply filled with air and hydroponics or soil and a contained ecosystem. A contained ecosystem in space is another whole set of problems but we wouldn’t need to address it until the modular habitat was under construction.

    Something where each load going up would include a couple of gently curving panels and a few flat connector panels. Each curved panel would connect to an outer or inner curved panel and the flat panels would connect the outer and inner panels to create or expand an enclosed space. First they simply sit in a Lagrange spot. As enough are added you end up with a ring that can rotate. Then you start adding segments to create a cylinder. These would have to be done 2 at a time to avoid throwing the balance of the spin off. You probably have to start with a central docking hub that contains a ring shaped bearing pack of some sort or perhaps magnetic repulsion to allow the outer modules that make up the ring to rotate while the hub doesn’t so ships can dock safely. Power would be mostly solar and the collectors could help protect from radiation if done the right way.

    Many issues to be resolved but the best way to learn is to do a mini test version and see what works. Then scale up and see what new issues you need to solve. The first boat wasn’t an aircraft carrier. It wasn’t even a canoe. I figure another 5 decades to a couple of centuries before we will have anything meaningful going.

    All it takes to justify the effort is 1 dangerous asteroid diverted from the moon or Earth. That, or 1 asteroid captured and mined for rare earths or copper or other strategic elements. An asteroid with a few tons of very large diamonds wouldn’t hurt either.

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  23. 23. christinaak 9:58 pm 04/19/2013

    @ bucketofsquid
    I do not fear progress. I have given the matter a great deal more thought than most people, and came to the conclusion that there are just too many insurmountable problems to overcome. We are limited by the laws of physics after all. The cosmic speed limit set by Special Relativity pretty much guarantees that colonization outside of our solar system is virtually impossible. The development of a fail-safe (with multiple backup systems) would certainly pose quite a problem and if it were even possible to produce one the size of any settlement would be severely restricted in size. Then of course there is the problems of maintenance and fueling, concern for the devastating effects of cosmic rays. Such a settlement would have to be self sustaining for it survive (produce its own food, oxygen-a major fire hazzard, its own fuel etc.)

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  24. 24. Dr. Strangelove 2:05 am 04/22/2013

    The acceleration in space cannon will instantly kill the astronauts. Space gun was first proposed in Jules Verne’s science fiction in 19th century. It was known even then that it was not feasible.

    Three problems with rail gun: 1) If the track is circular, the centrifugal force at escape velocity will break the material unless it’s carbon nanotube.
    2) If the track is straight, to reach escape velocity at 3g acceleration (so as not to kill the astronauts) the track must be 2,133 km long.
    3) The biggest problem is air resistance. It attains escape velocity at ground level where air density is 2.2 million times greater than at 100 km altitude (where rockets reach that speed). The drag force and energy needed overcome air resistance is 2.2 million times greater than rockets.

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  25. 25. Arcturus_Sky 5:58 am 04/23/2013

    To think we can “survive” and thrive in space is a modern-day delusion. You can take the most remote place on this planet and live more comfortably then anywhere off Earth. You’ll more likely see a colony living in the antarctic, inner Greenland, or the top of Mt. Kilimanjaro before we ever see colonies in space or Mars. There is one essential ingredient that the Earth has no matter where you are on the surface- a breathable atmosphere along with a biosphere that has evolved over millions of years to sustain life. To believe that the Earth and all its resources are disposable, that we can just use it up and move on to the next planet, is a very dangerous. It seems to me that any intelligent life form that created technology to travel to other planets and star systems would first and foremost have learned to live on a sustainable home planet. Any life form that thinks that its home planet is disposable is doomed destroy itself long before it would ever have the technology to colonize space.

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  26. 26. blackbird79 6:32 am 04/23/2013

    @ ‘jerryd’ – I DOUBT that you have any meaningful idea what you are talking about. Please cite at minimum one reputable, well-vetted source and/or relevant empirical evidence for the following assertions:

    1. “I doubt that it [world population] will hit 8.5B before it reverses…”

    2. “…by 2050 fossil fuels will be gone in 95% of the countries… so the GW [global warming] will start reversing…”

    Your ideas on women’s liberation are also interesting.

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  27. 27. blackbird79 7:06 am 04/23/2013

    @ ‘Dr. Strangelove’ – You seem to be familiar with the relevant foundation evidence to address my curiosity and maybe further illuminate the issues at hand:

    About two years ago ‘Popular Mechanics’ magazine ran a hidden accelerometer test on packages handled by the usual (suspect) carriers. Their results showed that the tagged packages had reached accelerations up to 6 G’s. Yipes!

    Could you relate such accelerations, under circumstances one might anticipate in such cases, to the ability of humans to maintain consciousness and ensure their bodily safety — for both the proverbial man-on-the-street and for “trained pilots”, if you can? Thank you for your interest. I’m an end user/purchaser of vintage tube electronics and photographic gear from a certain auction site, in case you haven’t already surmised something along those lines!

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