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Could a Balloon Fly in Outer Space?

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Here’s the sort of crazy idea that animates our office conversation at Scientific American. It all started with my colleague Michael Moyer’s joke that a certain politician could build his moon base using a balloon: just capture the hot air and float all the way up. Ha ha, we all know that balloons don’t work in outer space.

But is that really true? Why couldn’t they?

The more I thought about it, the more confused I got, so let me float it as a trial balloon and see whether you can shoot it down. Ground rules: no weaselly appeal to “feasibility” or “practicality” allowed. You have to argue from pure physics.

What makes a space balloon conceivable is that space is not a true vacuum. Even intergalactic space is filled with matter, albeit tenuous; by its standards, Earth’s extended atmosphere is a thick soup. As long as the balloon’s interior density is lower than the ambient density, it should rise—no matter how low the ambient pressure is. Drag force will limit the balloon’s ascent velocity, but shouldn’t stop it altogether and can be minimized by choosing a prolate rather than spherical shape.

As the balloon rises, it will expand in inverse proportion to the ambient pressure and, neglecting temperature, density. At launch, the interior and exterior pressure is equal, and the interior density is lower; during the ascent, the pressure remains equalized, so the interior density will always be less than the ambient. Neglecting temperature is probably not a bad approximation: the absolute temperature will vary at most a couple of orders of magnitude, whereas the pressure and density fall off much more drastically, and in any event we can include a politician to regulate the temperature difference between interior and exterior.

The material tension would rise in proportion to radius. It has units of force, and the maximum possible force in nature, the Planck force, is 1044 newtons, so the balloon could get bigger than the known universe before it absolutely has to pop. The balloon walls would become extremely thin and porous, but because of the scaling of area and volume, they should always remain able to confine the gas.

Bottom line: if you release a helium balloon on the ground, it should rise forever! It will float up until Earth’s atmosphere dovetails with the interplanetary medium, then float up and out of the solar system, then reach interstellar space and float out of the plane of the galaxy like the bubbles blown by supernova, and ultimately settle in one of the voids of large-scale cosmic structure.

Unless I’m missing something, it is a myth that balloons are inherently unable to work in space. The limit is set not by physics, but by trifling engineering problems such as material strength and permeability. Another caveat is that the laws of gas dynamics assume a continuum, an approximation that already fails in Earth’s upper atmosphere.

Now, someone, tell me what I’m missing.

Image credit: NASA/ARCADE/Roen Kelly

George Musser About the Author: is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. He is the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser.

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

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  1. 1. bartonlp 2:55 pm 01/26/2012

    A balloon goes up (rises in the atmosphere)but in space where is up? To where would the balloon rise?

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  2. 2. Nehmo 3:03 pm 01/26/2012

    I don’t understand “…walls would become extremely thin and porous, but because of the scaling of area and volume, they should always remain able to confine the gas”. “Scaling” must mean the relationship between volume and area, but I don’t see how that prevents the walls from becoming permeable to gas. Furthermore, how can you say it’s “porous” but “able to confine”?

    On a separate point, without bothering with calculation, it’s likely the balloon would require more than the age of the universe to escape the galaxy. Even the time required to escape the solar system is incredible.
    `~- Nehmo

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  3. 3. jbrown1114 3:12 pm 01/26/2012

    My guess would be that the gradient pressure across the surface of the balloon in space would be insufficient to cause the buoyant force to act in any particular direction. Therefore, I would expect the balloon to simply expand rather then be propelled. Eventually interaction with other interstellar objects. It is an interesting though experiment though.

    I think an interesting tangent would be whether the transition could be made from balloon to solar sail, there by allowing the balloon to fly in outer space.

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  4. 4. Bart_Hibbs 3:21 pm 01/26/2012

    A few issues. If your balloon does have an elastic skin, then it exerts pressure on the interior gas, increasing its density. At sea level this is minor, but when the ambient pressure is micro-psi it would not take much to compress the gas.

    Lets assume we have a balloon open at the bottom, looking like a hot air balloon, and the bag tension is never enough to push the gas out the bottom. Now at the bottom we are sure the Helium will be of lower pressure than the air.

    The atmospheric density drops by a factor of 2 every 3 miles or so. In Helium, due to its lower density, that distance is 21 miles. As your balloon rises and expands it will become miles in diameter. We get to the point where the Helium density at the bottom of the balloon is less than the air, but at the top the Helium will actually have a higher density than the surrounding air!

    We must start with a balloon that is microscopic at sea level, to insure it never gets too big.

    Then when it gets high enough we watch it blow away in the solar wind. If we stopped the solar wind and all other gas motion, then sure the balloon would continue to move to areas of ever lower gas pressure and density, provided we fill it with hot Hydrogen to insure its always of lower density than the surrounding interstellar medium.

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  5. 5. soundedfury 3:37 pm 01/26/2012

    Perhaps I’m thick, but wouldn’t the accelerating effect of the balloon’s bouyancy be rendered useless without a strong gravitational source and an atmosphere? The balloon is only bouyant due to the fact that the helium is displacing heavier air being pulled towards the gravitational center. With so little gas in space, the accelerating effect is negated and the balloon would continue forward at its slow pace until caught by the gravitational pull of a large object.

    So, really, the balloon doesn’t work in space, but the momentum created by its escape from Earth could carry it into the scenario you suggest.

    I can’t imagine it escapes the solar system, though. I imagine the solar wind would subtly push it towards the outer planets to be gobble up by their gravitational dance.

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  6. 6. GreenTom 3:49 pm 01/26/2012

    Hi–ignoring all the engineering details, I think your right. As support, it’s believed that interstellar bubbles of hot gas on the 10s of light year scale do act like balloons and ‘rise’ relative to galactic gravity, producing fountains of gas into intergalactic space (see pp24-25 of, and Shapiro & Field 1976,

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  7. 7. CrazyIvan 4:14 pm 01/26/2012

    I think the flaw in your arguement is the material is porous and yet it contains the gas?

    The gas that is zipping around will fly off into space and or distribute evenly with the earths atmosphere.
    Meaning you have no more balloon because the material will then collapse on itself from the outside forces.

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  8. 8. Tucker M 4:14 pm 01/26/2012

    Fabulous thought experiment.

    Here’s a thought about where you may have gone wrong: doesn’t your statement “during the ascent, the pressure remains equalized, so the interior density will always be less than the ambient” assume what you’re trying to prove?

    **During the ascent** interior density will always be less than ambient; that’s obvious (since it wouldn’t be ascending anymore, otherwise). But the whole question is whether there’s any such thing as **after** the ascent, right? I think you’re assuming that it won’t, in order to prove that interior density will always be less than ambient…which in turn is what you need to prove in order to show that the ascent won’t end. But it’s certainly possible to imagine a point at which pressure equalization no longer results in a density differential (even neglecting Bart_Hibbs’ point above about elasticity), at which point the ascent should end.

    Now, you may have some other reason to believe that the density differential would persist, and I just missed it. Regardless, I hope you (G. Musser) post a follow-up note about what you’ve learned, and how your thinking has changed about it. Great stuff.

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  9. 9. David N'Gog 4:18 pm 01/26/2012

    AHA! All one needs is a material less dense than aether!

    I’m curious how large a regular helium party-balloon (if we could invent a material strong enough to hold it) would eventually expand to in space. Surely it would become a truly enormous object by the time it got beyond our atmosphere.

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  10. 10. GreenTom 4:20 pm 01/26/2012

    Ignoring engineering details, I think you’re right, and a balloon would rise indefinately.

    As support, hot bubbles of gas on the 10′s of light year scale are believed to rise (relative to the galactic gravatitional field) through the cooler interstellar medium, creating the main mechanisim which ejects gas from the galaxy.

    (See pp24-25 of, or Shapiro & Field 1976,

    (Thought I posted this already, sorry if it’s a duplicate)

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  11. 11. cfaranetta 4:48 pm 01/26/2012

    Here is a related early space experiment that NASA conducted with a balloon in low earth orbit:

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  12. 12. CrazyIvan 5:06 pm 01/26/2012

    It’s the same idea in liquids as it is in gases.
    Gravity versus Buoyancy.

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  13. 13. crcinky 5:25 pm 01/26/2012

    One simple answer. Once it gets to near earth orbit it will be punctured by space junk.

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  14. 14. Autaut 5:58 pm 01/26/2012

    There are two major flaws in the original thoughts.
    First, the membrane becoming porous is real trouble, as we will see later. However i’d consider that an engineering problem, not a basic physics problem, so it is no real gamebraker.
    Second, and more severe, is the thermodynamics problem. Temperature is not some unimportant side-effect, it is a very important factor Avogadro’s law. (which describes state transitions in gas: (p*V)/T = const )
    Common sense tells you, that you need work in order to inflate an elastic balloon. The one we are discussing has to exert a force on gas particles inside to confine them, which means the need of work on inflation holds true. In other words the force per area exerted by the confined gas to the membrane has to increase for higher volumes of our balloon. Furthermore, the pressure inside the balloon is the sum of the pressure of the external atmosphere and the pressure needed to balance the membrane’s elastic force. at some point in the upper atmosphere, the “elastic pressure” will by far outweigh the ambient pressure. This is, where Avogadro strikes:
    To maintain the steady gain in volume AND pressure inside, which is required to climb to higher altitudes, temperature has to rise significantly.
    The simple consequence is that the balloon in our thought experiment really needs a power-source. Moreover the power demand would rise drastically at altitudes over 100km.
    This is also the reason, that a porous mebrane fails to confine the gas, as the internal pressure has to increase.
    You can put this idea to another level, if you assume having a material which would not get porous. Despite that not being possible (limited number of atoms in the membrane) – there still comes a point at which the individual gas particles would have to have so much impulse, that any contact with the membrane inevitably destroys it.
    If you still assume some material that defies this bombardment, you get to quantum physics, where particles start to just tunnle out in the free.
    Despite that, as was mentioned before, above the thermopause, there is no such thing as buoyancy, because solar radiation (light and particles) dominates and air particles are rare enaugh for them to fly on pure ballistic trajectories.
    Furthermore, there are issues with the balloons trajectory, as tidal forces also outweigh buoyant forces at some stage.
    However there is also good news:
    If you somehow manage to overcome all of these issues and watch your balloon leaving our galaxy, it would indeed seem to feel a buoyant force, which is – of course – space inflation

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  15. 15. taomeister 6:57 pm 01/26/2012

    Although there are other issues that need to be addressed, the most important one is escape velocity. Nothing can break the gravitational pull of earth without reaching this velocity. About 40,000 km/hr.

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  16. 16. valenciacjorge 7:14 pm 01/26/2012

    As stated previously with bouyancy, if the balloon is less dense than the air, the force can keep the object afloat. This can occur in our atmosphere. However in deep space, It’s vacuum what prevail’s. As a result, the ballon would experiment the same force that makes our planet movements. Therefore the balloon would proportionally move towards the Body that has more gravity influence on it. That is of course “regardless of all materials and engineering issues”.

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  17. 17. Wazzawazzawoo 7:20 pm 01/26/2012

    The real problem is that your balloon has a payload – the politician. Even as the rest of the balloon is expanding in an ideal way, the politician remains a solid lump of, er, something. Thus the total density of the balloon is the mass of the ideally expanding balloon plus the mass of the politician (an extra seventy kilograms, at the very least) divided by the volume of the whole. Thus the balloon can only rise to the point where its buoyancy is able to hold the politician aloft. A similar situation is often seen with small helium balloons, with enough spare buoyancy to lift only a part of their long strings. They’re held in place by a string that isn’t even tied to anything, just massy enough to hold the balloon down.

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  18. 18. Autaut 7:21 pm 01/26/2012

    That is not true.
    Imagine a spaceship launching from sealevel and – after leaving the atmosphere – reaching escape velocity.
    (Relative to sun’s gravitational field, you get different values, but don’t bother)
    Certainly it will travel an infinite amount of time, but it will get slower and slower and will hardly move anymore after some time.
    Give it some more boost on your initial accelaration, and it will stay faster on it’s whole trip.
    Now image a sister ship, wich just leaves earth orbit, accelerates a little bit and then uses weak thrusters to just accomodate for the gravitational pull. it will never loose speed. as you can easily calculate, it also needs only a finite amount of fuel and energy to completely escape. But it never reaches escape velocity.

    However you are up to something, as there is a fixed amount of energy needed for any one mass to completely escape gravity of another mass. It is called potential. With rockets, it makes sense to express it as escape velocity, but with our balloon this concept does not hold up. If the deep space gas density was higher, you could really escape with a balloon.

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  19. 19. levisque67 7:21 pm 01/26/2012

    What you are missing is that Edgar Allen Poe wrote about this in the 1800s!

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  20. 20. Autaut 7:55 pm 01/26/2012

    The Payload issue is also a misconception.
    Lim v-> +inf ((m+mPay)/(v+vPay)) = 0
    With m/v being density.
    That means you could get infinite small overall density,
    Even with two politicians.
    It is just the otherway round:
    You cant get infinite density by deflating your balloon:
    With v-> 0 you get (m+mPay)/vPay
    But thats

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  21. 21. Houtech 9:13 pm 01/26/2012

    Actually, there has already been a balloon in space. One of the first attempts at a communications satellite was Echo I which was basically a mylar ballon that was inflated in orbit to act as a reflector for radio waves.

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  22. 22. Dr. Strangelove 1:05 am 01/27/2012

    Mr. Musser, a helium balloon cannot fly into space because what makes it fly is the buoyant force governed by Archimedes principle. The difference in density of air and helium produces the buoyant force. Air density is 1.2 kg/m^3 and helium 0.17 kg/m^3. Helium is 0.14 times lighter than air.

    If your balloon has a volume of 1 m^3 the buoyant force is 1.2 – 0.17 = 1.03 x 9.8 = 10 Newtons. However, air density decreases with altitude. At 14 km, it is about 0.14 times the density at sea level. So at that altitude, your balloon will have zero buoyant force and will stop lifting.

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  23. 23. Dr. Strangelove 1:25 am 01/27/2012

    If you allow the balloon to expand to keep the difference in density of air vs. helium, at 14 km altitude the balloon will be 7 times bigger. It will eventually burst.

    Theoretically, it is possible for a balloon to reach space if it reaches escape velocity (neglecting air resistance) before it bursts.

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  24. 24. Dr. Strangelove 3:13 am 01/27/2012

    Let me correct myself. It is theoretically impossible for a balloon to reach space because it is theoretically impossible for it to reach escape velocity.

    On earth’s surface the escape velocity is 11,200 m/s. As the balloon accelerates, the drag force due to air resistance increases following the formula:
    Fd = 1/2 da v^2 Cd A

    where da = air density, v = velocity, Cd = drag coefficient = 0.47 for a sphere, A = cross sectional area of the balloon

    For the balloon to continue accelerating until it reaches escape velocity, the drag force must be less than the buoyant force. A helium balloon with radius 1 m has a buoyant force of 42.28 N.

    Solving the above drag equation, at the velocity of 191 m/s, the drag force will equal the buoyant force. This means the balloon will stop accelerating once it reached 191 m/s. Therefore, it will never reach the escape velocity of 11,200 m/s.

    This limitation is independent of the balloon’s radius. A bigger or smaller balloon will also not reach escape velocity.

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  25. 25. ttheobald 3:29 am 01/27/2012

    From a very simplistic viewpoint, the balloon would be limited by its ability to expand its volume (which is the more practical limitation given current materials) or reduce its internal pressure.

    Eventually, much like a chunk of styrofoam on the sea, the balloon will “float” on the “surface” (defined as the equilibrium point) of the atmosphere. In order to reach escape velocity (enough momentum to carry its weight out of Earth’s gravity), it would have to become neutrally buoyant with space beyond the atmospheric envelope. At that point, it would still be trapped in the backwash generated by the solar wind, and might someday be caught and carried off.

    So from a realistic perspective, it would never get past a certain level in the atmosphere. Hypothetically, it wouldn’t “float” in space so much as drift, at which point the best it could hope for is that it would be affected by the solar wind. Otherwise, it would just become a NEO in its own orbit.


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  26. 26. jcollake 7:31 am 01/27/2012

    This guy says at the end “unless I’m missing something, it is a myth that balloons are inherently unable to work in space”. Indeed, he is missing something I think ;p. Well, several things. First, the balloon would enter, and stay in, high earth orbit where it is blown around by winds indefinitely, until it breaks apart or is punctured (unless it is like one of those floating balloons at a party, that goes down on itself in time ;p). The larger the object, the greater the force of the wind, and so therefore you could not escape this altitude. If you did, you would float back down, since the vacuum of space is lighter than our atmosphere, AND the force of gravity would be exerted on the balloon. Of course, I am not an expert in *any* of this, so what do I know…

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  27. 27. Tucker M 11:04 am 01/27/2012

    Many of the comments above focus on practical issues Musser is aware of, but wasn’t asking about (problems with materials, practicality of lifting a payload), or with misconceptions (like the idea that the balloon would need to reach escape velocity). I understood his question to be: why (in theory) couldn’t a balloon launched from Earth continue to work in space?

    Thinking about that more, I think it depends on what sort of balloon you’re talking about. On Earth, our basic balloons types are twofold: (a) one with a density differential that arises from a gas that is inherently (i.e., ignoring temperature) less dense than the ambient medium (like helium balloons) or (b) one with a density differential that arises from a hotter (and therefore less dense) interior than exterior (like hot air balloons).

    In space, the helium strategy isn’t going to work, since unlike on Earth, helium isn’t less dense than the interstellar medium, which I understand is predominantly hydrogen (and there’s nothing lighter than that). By contrast, the hot-gas balloon is a little more of an interesting question, since we already know that it works in principle, given the motion of heated “bubbles” in space.

    But whether a hot hydrogen balloon launched from Earth could continue to provide lift depends on what temperature the hydrogen would have in space, once expanded to the point of pressure equilibrium. Now, my understanding is that the solar wind and the interstellar medium, though both extremely sparse, are actually fairly hot. If that’s true, the (relatively compact) hydrogen balloon launched from Earth would have to start out at a pretty unimaginable temperature, to have even a hope (after the cooling it would undergo during its dramatic expansion) to be still hot enough to maintain a lower density than the ambient medium of space (and that’s ignoring any inward pressure from the balloon itself). And, of course, it would be cooling rapidly, once expanded.

    So I would guess that while there’s nothing wrong with it in principle, you’d have to start with some awfully super-heated gas (preferably hydrogen), probably significantly hotter than the sun. And I know we promised to put the practical problems aside, but…

    Am I thinking about this correctly?

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  28. 28. deyler 12:46 pm 01/27/2012

    I believe you missed the most important fact: it is not the balloon that rises, it is the surrounding gas that “falls” around the balloon, continuously lifting it. The outside gas will fall around the ballon as long as the specific weight of the ballon remains lower than the specific weight of the surrounding gas. As the balloon rises, the pressure of the gas inside increases the balloon size, because the pressure of the gas outside decreases. The “lifting” force of the gas surrounding the balloon also gets weaker, as the difference between the specific weights approaches zero. At that point, the “lifting” force also disappears and the balloon stops “rising”. The balloon will remain floating forever at the same altitude of equal specific weights for the balloon and the surroundig gas. Well, I guess this is it! Regards, Deyler

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  29. 29. mk1313 1:16 pm 01/27/2012

    Stupid thought experiment. You say to argue only using principles of physics then proceed to throw out those you don’t like by saying ignore tensile strength (a property of physics) etc. Please also explain what material is held together solely by Plancks force such that weakneses would preclude tearing. Furthermore, physics using quantum theory, predicts that even black holes will evapourate and yet we are to believe an infinitely thin membrane will continue to contain the helium. A readily known example is that Hydrogen will escape from a sealed steel container. 1 cm3 of gas at sea level contains approximately 30,000,000,000,000,000,000 atoms so 1 cm3 of helium as it expands into the interstellar space with a density of 1 atom/cm3 would expand to 30,000 trillion litre’s of space. Any material capable of that expansion and still retain sufficient coherince to contain the gas would be far too heavy for the gas to lift from the earths surface so this thought experiemnt is complete BS!

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  30. 30. Bart_Hibbs 1:57 pm 01/27/2012

    At sea level we have 2.5e19 atoms per cc, in interplanetary space, 1 per cc. A 1 foot diameter balloon would have to expand to 556 miles in diameter to accommodate the change. Another factor of 100 increase in diameter would be needed to get to intergalactic space.

    I propose hydrogen plasma in magnetic field generated by currents in the plasma for the “balloon” as that will always be lighter than the surroundings, weights little, can expand forever and already exists in nature, as pointed out above.

    As an aside, the highest any surface launched balloon (the BU60-1) has achieved just by floating up there is 173,900 feet.

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  31. 31. Tucker M 2:02 pm 01/27/2012

    Correction to myself: as I understand it, the absolute temperature of the hydrogen does not drop during expansion (ignoring cooling). So the initial balloon would only have to be as hot as the interplanetary (and then interstellar) medium.

    Still, that’s pretty hot…and I think we can safely say that it’s not true that an unheated “helium balloon…should rise forever,” for the reasons above (i.e., in space the ambient medium is very sparse hydrogen, which at similar temperatures is less dense than helium).

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  32. 32. gmartfin 4:49 pm 01/27/2012

    An appeal to “pure physics” to make a counter argument and then you throw in a politician for temperature regulation…..tsk tsk

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  33. 33. Joseph C Moore, Cpo USN Ret 6:13 pm 01/27/2012

    Simple enough: Helium or any similar gas (including hot air) is lighter than the air at ground level. As the balloon rises in the atmosphere the atmosphere gets thinner (less dense, or lighter. At altitude the balloon gas will equal the atmosphere and stop rising. Outer space is not gaseous being a vacuum, so the balloon’s gas would have to be lighter than a vacuum for it to travel through space. Fersteh?

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  34. 34. Chuck Johnson 6:26 pm 01/27/2012

    The material problem is interesting. A very low modulus material would allow for vast expansion without dramatically increasing the internal pressure required to keep the balloon inflated. Think of soap bubbles that could expand forever.

    Actual materials have been invented that have a negative modulus, they expand under pressure. Perhaps a filmy material could be created with similar properties.

    It seems to me the the bigger problem is the thinning of the membrane as it expands. Again, think of soap bubbles. They burst because as they expand the soapy film becomes to thinned to resist the internal stresses created by the pressure differential.

    I think for buoyancy, all that is required is that the internal density is less than the external density and there is an applied body force. The balloon will move in the opposite direction of the body force.

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  35. 35. none12345 9:46 pm 01/27/2012

    “Although there are other issues that need to be addressed, the most important one is escape velocity. Nothing can break the gravitational pull of earth without reaching this velocity. About 40,000 km/hr.”

    You misunderstand what escape velocity is. It doesn’t necessarily apply in this experiment.

    The wiki definition works. “In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to “break free” from a gravitational field without further propulsion.”

    Its those last 3 words that you are missing. Without further propulsion.

    You do NOT have to reach earth’s escape velocity(calculated at any altitude) to leave the earth’s gravity well. You could move at 1 mile/year and still leave the earths gravity well no problem. Provided you have a constant acceleration just greater then the gravitational force of the earth at whatever altitude you are at.

    In this thought experiment the boyant force exerted upon the balloon provides that acceleration.

    We could engineer a balloon that can sit on top of the earths atmosphere no problem(most of it anyway). But more then that i dont think a material could theoretically exist to take the baloon out of the galaxy. The best you could maybe do is catch the solar wind and then get out to the point where the sun’s pressure balances out with the interstellar medium.

    But you long since ceased being a balloon at that point, and are instead a solar sail.

    I dont think we could engineer such a craft tho that could transition from a balloon to a solar sail….without some kinda of propulsion system to kick it off of the earth’s atmosphere, during the transition from balloon to solar sail.

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  36. 36. sidelight 10:18 pm 01/27/2012

    Um, gas molecules escape the Earth all the time, there at the edge..where do they come from, and where do they go?
    Suppose you had a buch of light like-molecules in a bubble or somehow bound as a group…

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  37. 37. Whammer2 12:26 am 01/28/2012

    Up to a point, yes. High altitude balloons do exist and are used for research. The reason it won’t just “keep going” is because balloons rise in the atmosphere due to the differemce between their internal gas pressure and the outside atmospheric pressure. At some point, high in the atmosphere the balloon will reach a state of equilibrium with the atmospheric pressure outside, and then there is no lift generated; so the ballon stops rising. High altitude ballons fly at heights in excess of 100K feet…ask NASA about that. But all ballons must be made of something, and therefore have mass (weight) so they have a limit to how far they can rise. They need that lift to carry their mass upward, and at equalibrium with the atmosphere, they can’t get any more lift. End result, they just hang there. Now, if they carried a propulsion system to kick in after they reached that equalibrium height…then that’s another matter entirely.

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  38. 38. taomeister 2:32 am 01/28/2012

    I’m afraid I will bow out of further discussion here because it is clear that there are a number of bloggers responding that have only a marginal understanding of physics. It’s simply not worth trying to point out the contradictory statements being made. Once one resorts to out of context wikipedia “facts” to substantiate ones argument, all bets are off.

    I do agree with the comments made by “deyler” and “mk1313″. It is not a very compelling “gedanken experiment”.

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  39. 39. Dr. Strangelove 6:30 am 01/28/2012

    “if you release a helium balloon on the ground, it should rise forever! It will float up until Earth’s atmosphere dovetails with the interplanetary medium, then float up and out of the solar system”

    Absolutely wrong. It will stop rising once it reach the thermosphere 100 km up. There is practically no atmosphere there, no atmospheric pressure, no buoyant force, hence no lift.

    “it is a myth that balloons are inherently unable to work in space.”

    It is not a myth. It is a fact. There’s no air in space. The particles in space don’t behave like fluid. No fluid, no buoyant force.

    “The limit is set not by physics, but by trifling engineering problems such as material strength and permeability”

    Archimedes principle is a law of physics. It is not an engineering problem.

    It may work if your balloon is absurdly big, like 100 km in diameter. Its top is already on the edge of space. If the material is absurdly light, it could reach escape velocity and go to outer space. Unlike balloons in the atmosphere, your space balloon won’t have propulsion in space. It only moves because of inertia due to its kinetic energy.

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  40. 40. Gwyd23 9:04 am 01/28/2012

    if it didn’t get caught by a jet stream and whirled around in the upper atmosphere forever, micrometeorites or even cosmic rays would eventually pop it. but i like the idea. silvering the surface could allow the solar wind to push it to a cosmic void even faster. NASA could call the project Rising Up Squandered Helium, or RUSH.

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  41. 41. mtrphx 9:12 am 01/28/2012

    Odd…a balloon doesn’t rise…it’s pushed. Once the push of the atmospheric pressure is balanced with he mass of the balloon it ceases to be pushed. At that point the only way the balloon could continue to move at all would be if it has somehow reached escape velocity. Am I taking this too seriously?

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  42. 42. kev1337 10:16 am 01/28/2012

    I agree that the balloon could indeed rise indefinitly assuming the correct GOP candidate argued its feasibility with the universe…

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  43. 43. James Brink 12:36 pm 01/28/2012

    A balloon rises when the interior mass/volume is less than the exterior mass/volume and the exterior space has a pressure difference between the top and bottom of the balloon on the outside. Any gas that is lighter than air at the ambient temperature and pressure will float a balloon. Deep space is filled with a gas mixture that is mostly hydrogen (the lightest possible gas) so if the balloon was pure hydrogen and the skin was weightless and infinitely stretchy, the envelope would migrate to the area of lowest gas pressure available. Given the uneven swirly nature of gas in our galaxy, that place would probably be a cul-de-sac of lower pressure somewhere in the Milky Way.

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  44. 44. rfadel12 2:49 pm 01/28/2012

    bartonlp is exactly right. There must be a pressure gradient in order for the balloon to actually move in the direction you state as “up and away”. Sure, the balloon’s density will still be greater than ambient, but space has the same ambient pressure all around, unlike our atmosphere that has a gradient pressure.

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  45. 45. Discovertree 3:22 pm 01/28/2012

    I just cancelled my subscription to Scientific American due to this nonsensical article. I have lost all faith in the editorial and scientific judgement of the publication. Perhaps a more appropriate title for the article would have been; “Could a Special Magical Balloon Fly in Space?”.

    I recommend the management of the organization monitor the office chatter a little more closely if that is in fact representative of the typical water cooler talk.

    I hope there isn’t a raging office argument about how much wood could a wood chuck chuck if a wood chuck could chuck wood? An eternal and equally scientifically perplexing and significant question for sure!

    Best of luck!

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  46. 46. Quinn the Eskimo 11:14 pm 01/28/2012

    Wouldn’t it then float off the surface of the moon, and keep rising — for ever?

    Great space ship. But, it would have to be multi-generational.

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  47. 47. Learo 6:14 am 01/29/2012

    “As long as the balloon’s interior density is lower than ambient, it should rise—no matter how low the ambient pressure is …”
    I do not think this sentence makes sense. All your assumptions are based on the physical fact that ambient is filled with kinds of matters such as Nitrogen, vaper and small particles, which is the agent to “push” the ballon up.
    However, what’s the “agent” in the space? As we all know it is empty in the space.

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  48. 48. Discovertree 11:25 am 01/29/2012

    Folks….space is a vacuum.

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  49. 49. Discovertree 11:29 am 01/29/2012

    Hold on a minute here…so a balloon with a density less than a vacuum could do the trick. What I think I’m hearing here is “So you’re saying there’s a chance….”

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  50. 50. leaf6 3:26 pm 01/29/2012

    Under the supposition that the balloon is indestructible or at least won’t pop:

    As long as the balloon still has an upward velocity as both the force of gravity and air resistance arrive to zero, it will continue to move up forever. If you need an extra boost, you can always expel a stream of air from the balloon.

    Quantum: If all the molecules in the balloon move in the same direction, we know that something very, very… very unlikely just happened.

    By the way, a density less than a pure vacuum will result in a temperature below absolute zero or negative volume or moles.

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  51. 51. ericl 5:16 pm 01/29/2012

    But if the is the air pressure in space, the balloon could expand indefinitely which causes the the aforementioned object to rupture. The material needed to prevent that would negate the use of sending a balloon a into space due to cost effectiveness. You would need to find a material that could resist space and yet be light enough to allow the balloon to continue to ascend.

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  52. 52. Dr. Strangelove 8:04 pm 01/29/2012

    “As long as the balloon’s interior density is lower than ambient, it should rise—no matter how low the ambient pressure is.”

    This is false in space because there is no hydrostatic pressure in space. What you have is dynamic pressure due to the kinetic energy of the particles in space.

    If you put a balloon in space, it will not ‘rise’ or go anywhere (‘rise’ is the wrong term as there is no ‘up’ or ‘down’ in space). But the dynamic pressure of the solar wind can push it. In this case, it acts as a solar sail not as a balloon. A flat sheet can do a better job than a sphere because the former has a higher cross sectional area to mass ratio.

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  53. 53. alan6302 8:08 pm 01/29/2012

    Anyone that believes a balloon could make it to space needs medication. Unless there is some negative mass , anti gravity or some other exotic trick.

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  54. 54. jbroman 9:15 pm 01/29/2012

    It seems that when the balloon rose until the mass of the balloon equaled the mass of the air it displaced the lift of the balloon would be equal to the gravitational attraction and it would stop rising.

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  55. 55. Zou Sir 9:34 pm 01/29/2012

    I do not think the author’s arguments can convince me.
    One of the problems is, “during the ascent, the pressure remains equalized, so the interior density will always be less than the ambient” means the skin of balloon does not have to be forced, this is a very problematic conclusion.
    In my view, the reason why the balloon rises is that the gravity of balloon is less than that of the air which is excluded by the balloon(Archimedes’s law), that is to say, the gravity of the helium in the balloon adds the gravity of the balloon’s skin and body is less than the air which is excluded. At launch, this condition can be satisfied. However, when the balloon becomes higher and higher, the density of air is thiner and thiner, therefore, the gravity of the air is less and less. In the limit of zero gravity of the air, it is impossible for the balloon to be more high because of its own gravity. Here I neglect the resistance, if taking this into account, it is more obvious that the balloon cannot goes to infinity.

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  56. 56. Dr. Strangelove 9:40 pm 01/29/2012


    The Echo 1A satellite balloon reached space because it was carried by a Delta rocket.


    The Local Bubble you are referring to is not a balloon. It is a region in space with low interstellar gas density. Though space contains interstellar gases, it is not a gas that behaves like fluid.

    The density of air in the thermosphere is 10^-10 g/cm^3 while the density of interstellar gas is 10^-24 g/cm^3. That’s 14 orders of magnitude lower than the former. In the thermosphere, air does not behave like fluid. More so for interstellar gases. There’s no hydrostatic pressure in space.

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  57. 57. HotAir 11:09 pm 01/29/2012

    “Bottom line: if you release a helium balloon on the ground, it should rise forever!”

    Nope. Helium is four times denser than hydrogen, so even a balloon with no payload and no structure would be four times too heavy. Next, the balloon would have to be rigid – a normal helium balloon ALWAYS is of higher pressure than the surroundings because the structure of the balloon compresses the helium, and so the gas inside will be heavier than the materials suggest, so a “normal” but massless balloon filled with atomic hydrogen would still be heavier than the surrounding space. So we’re reduced to a rigid massless balloon filled with a true vacuum. That’s a violation of basic physics, and even that will only be lighter than space by perhaps one hydrogen atom per cm3. That’s 1.7 x 10^-27 kg. So to get 1kg worth of “spacelift”, you’d need a massless vacu-balloon about 30,000 kilometers in diameter. (I could be off by an order of magnitude or two, but you get the drift)

    By the way, heating the balloon wouldn’t help as a vacuum is always the lightest possibility and is not affected by temperature.

    So we have a perfectly rigid balloon of zero mass larger than the Earth filled with a true vacuum and all we get is a measly 1kg differential in mass. Since it is true (you do the math) that a structure larger than the Earth will weigh more than 1kg, your balloon won’t fly.

    Finally, space has too low a density to act like a fluid and there is no density differential like there is in our atmosphere, so buoyancy doesn’t work anyway!

    This theory sinks like a lead balloon.

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  58. 58. Daniel35 12:25 am 01/30/2012

    What’s the definition of “fly” here? Does a balloon fly in the atmosphere, or just float? Does a satellite fly? How far out is “outer space”? Where is the edge of the atmosphere? Considering those factors, I think on the average, yes, I think at least black, therefore warm, balloon can fly, at least to the weight of the balloon itself balances the difference in gas densities.

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  59. 59. Dr. Strangelove 8:26 pm 01/31/2012

    Guys. No, a balloon cannot fly in outer space. Float yes. Everything floats in space in the absence of strong gravitational field. A balloon flies in the atmosphere because it has a lift provided by buoyancy. Strictly speaking, a satellite in orbit does not fly. It only moves because of its inertia but it has to accelerate to orbital speed, and therefore fly, before it becomes a satellite.

    Basic physics dictates a balloon cannot have a lift in space. Buoyancy is caused by hydrostatic pressure, which is caused by the weight of a fluid. A lighter material immersed in a fluid is pushed upward by the fluid.

    Interstellar gas in space is neither a fluid nor has weight. It has mass but not weight because there is no strong gravitational field from massive bodies like planets in outer space. The extremely low density of interstellar gas makes its molecules behave like individual particles not like a fluid.

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  60. 60. Dr. Strangelove 12:10 am 02/2/2012

    My detailed calculations show that a gigantic balloon can attain escape velocity (11.2 km/sec) and “fly” into space.

    The balloon is cylindrical 573 km in diameter, 50 km high, filled with hydrogen gas, made of lightweight carbon fiber with areal density 200 g/m^2. It will not burst as the carbon fiber can withstand the shear stress (581 Pa) due to the buoyant force.

    The balloon can move in space only because of its inertia. It has no lift or buoyancy in space.

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  61. 61. Joseph C Moore, Cpo USN Ret 8:49 am 02/4/2012

    The balloon in space forum has to be one of the most inane of concepts to be discussed. Is this the place for grade school “scientific” experiments? The readers of Scientific American deserve a little better than such tripe.

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  62. 62. wrwing 9:24 am 02/4/2012

    An object floats, whether in water, air, or the tenuous gas of outer space because it is less dense than its surroundings. So, to continue the thought experiment – assume the balloon skin has negligible weight and can expand as necessary. What gas must be inside to give it positive buoyancy in comparison to the surrounding (extremely tenuous) gas around it, where ever it is? Helium makes up only around 9% of the interplanetary or interstellar medium – the rest is a mix of neutral and ionized hydrogen atoms. Thus, to make a balloon “float” in that medium it would have to be filled with a “gas” that was ‘lighter’ than atomic hydrogen. There is no such thing unless you hypothesize a “gas” of free electrons, which then would have to be contained. Magnetic fields can trap free electrons, but no balloon skin of any physical material could.

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  63. 63. hybrid 2:59 pm 02/4/2012

    All you have to do is to build a tower high enough that its observation deck is traveling at escape velocity, float your atom sized helium balloon into the elevator and push it out the window at the top. Just get yourself a donald trump of a Real Estate agent and float a loan with a warren buffet money pit. Its all very simple really.

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  64. 64. hybrid 4:14 pm 02/4/2012

    Re write:
    Hire a donald trump of a Real Estate agent, dig up a loan from a warren buffet money pit and build a tower. Then all you have to do is to build the tower high enough so that its observation deck is traveling at escape velocity. Now stick a deflated balloon, a bust of Yuri Gagarin and a small tank of air (or helium if you like) into the elevator. Ride to the top, blow up the balloon as needed, attach it to the bust, and shove it out the penthouse window, —– to escape the surly bonds of Earth and touch the face of ……..
    Its all very simple really.

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  65. 65. hybrid 5:32 pm 02/4/2012

    and again:- Instead of the tower, construct a cylinder from the ground up to the escape altitude.— A cylinder containing air at atmospheric pressure with an airlock at both ends. Release a helium filled balloon through the bottom airlock, to fly up to the escape level. At the top airlock release enough helium to match ambient pressure, attach old Yuri and escape the ……….., and then off we go into the wild black yonder.
    Lighten up folks.

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  66. 66. toothman51 7:36 pm 02/4/2012

    Ok. Ignoring all the problems with material engineering, you are ignoring gravitational pull and density in space. The balloon should rise until it reaches equilibrium and float on top of the atmosphere. I assume there exists some kind of surface tension at the edge of the atmosphere that the balloon would have to cope with. Even after overcoming all of this, in which direction would bouyant forces take the balloon in interstellar space?? Slowly or subtly away from any gravitational pull, in a random, zig-zagging pattern??
    Why don’t you just take it out to space and inflate it there. An inflatable structure may be a practical interplanitary vehicle.. I don’t think it will “self propel” because any gas you use to fill it up will be denser than the surrounding ambient. You will get movement if you just release a little of the inside pressure :)

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  67. 67. Dr. Strangelove 9:55 pm 02/5/2012

    Correction: My more detailed calculations show that even the gigantic 573 km diameter cylindrical balloon cannot attain escape velocity. Its top speed is 2089 m/s at 94 km altitude. Far lower than 11,200 m/s escape velocity.

    It’s not possible. Earth’s atmosphere is so thick that the drag force will overcome the buoyant force before the balloon reaches escape velocity.


    Your “space tower” will not work for the same reason we still don’t have a space elevator. Before you reach orbital speed (which is lower than escape velocity) the centrifugal force will break the material that your space tower or space elevator is made of.

    It’s an engineering problem. The tensile strength of all materials is less than the tensile stress due to centrifugal force. Carbon nanotubes can withstand it but we still cannot manufacture long cables made of carbon nanotubes. Once we have a space elevator, you can send any light object to space, balloon or whatever.

    Your “space cylinder” will not work because the balloon inside it will still encounter drag force.

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  68. 68. Dr. Strangelove 10:07 pm 02/5/2012

    My error. The balloon inside the “space cylinder” doesn’t have to travel at escape velocity relative to the air so no problem with drag force. However, the top of the cylinder is travelling at escape velocity relative to earth. So you have the same problem as in the space elevator. Centrifugal force will break your space cylinder.

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  69. 69. hybrid 4:09 pm 02/6/2012

    Dear Dr Strange …….
    If there would be a centrifugal force acting on the tower of power, then why don’t astronauts in the space station hit the roof. Or are you saying that all tall buildings are subject to centrifugal forces, and in effect that the top stories are trying to fly apart from their base? I hardly think so. You are confused with the space elevator that required a large mass at the top end of a tether, which would cause a tension. But thank you for your critique, which made me google things. I was not aware that:-
    1895 when Konstantin Tsiolkovsky[1] proposed a free-standing “Tsiolkovsky Tower” reaching from the surface of Earth to geostationary orbit 35,786 km (22,236 mi) up. Like all buildings, Tsiolkovsky’s structure would be under compression, supporting its weight from below.

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  70. 70. Dr. Strangelove 9:33 pm 02/6/2012

    Dear hybrid
    No I’m not confused but you need to review Newtonian mechanics. Astronauts don’t hit the roof of the space station because their centrifugal force is balanced by earth’s gravitational pull and they are orbiting at the same speed as the space station.

    Yes all buildings are subject to centrifugal force. Even your body is subjected to it. You don’t notice it because your height of 1.8 m is negligible compared to earth’s radius of 6,300,000 m. Even the height of the tallest building is negligible at 830 m. The increase in centrifugal force is very small.

    BTW you don’t need a mass at the end of the rotating body to produce centrifugal force. The rotating body itself has mass (including your body). The radius of rotation is the distance from the center of mass of the body to the center of the earth.

    Your proposed space tower is 100x higher than the space station. The compressive strength of steel is 440 MPa. A steel tower will collapse under its own weight at 5.75 km high. Your space tower is 35,786 km high. It will be crushed by gravity before centrifugal force breaks it apart.

    IMO using a space tower (with a space elevator) to put a balloon in space is unimaginative. It’s like saying sure we can put a balloon in space, just attach a rocket to it.

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  71. 71. frontierteg 10:37 am 08/28/2012

    Eventually gravity will overtake boyancy.
    This is why aircraft carriers float but do not fly.
    The balloon, regardless of the hyper elastic material, and the contents making it less boyant than the space around it still has mass.
    Gaseous Hydrogen is more boyant than pretty much anything else, and yet it doesn’t float off into space.
    This is a pretty silly question, and I certainly hope it was intended as a joke.

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  72. 72. frontierteg 10:48 am 08/28/2012

    Instead, we should make metal foam in space. That way, the “bubbles” in the foam will be empty (vaccum). This would make the the foam extrememly strong and extrememly light. Then fashion the foam into a large hollow ball, the hollow also being a vaccum. Make it large enough and attach a cable to it and it should be boyant enough to hold several tons of cable. These “metal balloons” could then be used at intervals all the way down to the ground that would relieve the “space tower/elevator” of catostrophic gravitational or centrifugal forces, while allowing them to keep the cables geostationary.

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  73. 73. TweetyBird 1:45 pm 09/17/2012

    Ok, maybe this will help answer some questions.

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  74. 74. hcm1955 7:24 am 06/23/2013

    This is what JP Aerospace is trying to do:

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  75. 75. sesquipedaliman 2:28 pm 08/27/2013

    Well, the best way to deal with this is to get the people on the International Space Station to fill a balloon. they DO have compartments that alternatively have air, and then are evacuated so they can work in space. just bring a balloon in there with some compressed air, and try to fill it up.

    What will that cost? I don’t know, $1 above and beyond the millions we are spending already?

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  76. 76. kaihu 9:40 pm 09/30/2013

    Here is a hybrid balloon design which I believe can go all the way to the edge of the earth’s magnetosphere, and possibly even reaching the moon since the moon is within the range of the earth’s magnetotail.

    The idea is this. Build a large hydrogen balloon with the shape of a torus. A hundred meters in diameter should suffice. Install electrical conductors along the length of the torus to turn it into a giant magnetic coil. Also install solar cells to provide electricity for the coil. Launch this balloon from either the north or south pole and the lifting power from the hydrogen alone should take it to the stratosphere. Next use the electricity gathered from sunlight to generate constant magnetic propulsion against the earth magnetic field and take a polar orbit for maximum propulsion. The device can then use the ‘perigee kick’ technique (see the Wikipedia entry on Magnetic Sail) to reach ever higher altitude.

    Assuming the mass of this vehicle is 500kg then it is going to need 31,360 mega joules (which is 8711 kwh) in order to reach escape velocity (at which point it then does not need the lift from the balloon any more). If the vehicle’s solar cells can generate 10kw from sunlight, then assuming 100% efficiency converting to magnetic propulsion (just for the sake of checking the upperbound) it will then take about one month (8711 kwh / 10kw / 24 hours = 36.3 days) to reach escape velocity and begin to ascend further into space, which is not too bad.

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