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Floating into space

  1. May 18, 2005 #1
    I wondered if you could float into space on a balloon. After a quick search on Google I found an answer that left me with more questions. This is what it said:"Could a helium balloon float all the way up into space?

    A helium filled balloon can float very high up into the atmosphere, however, it cannot float up into outer space. The air in Earth's atmosphere gets thinner the higher up you go. The balloon can only rise up until the atmosphere surrounding it has the same weight as the helium in the balloon. This happens at about a height of 20 miles (32 kilometers) above Earth's surface. So, this is as far as a helium balloon can rise. Outer space starts somewhere around 600 miles (960 kilometers) above Earth's surface
    ."

    The density of the atmosphere changes but the density of the molecules of air stay the same. The Helium molecules are less dense so when the balloon gets high in the atmosphere why cant it just release air to keep it's density less than the surrounding air?

    Then I found another site saying something else "They are amateur scientists and radio operators, and they use weather balloons to send radios, cameras, and scientific experiments high into the stratosphere. The balloons can reach altitudes over 100,000 feet before bursting to shreds and parachuting back to Earth with their payloads. At that altitude, atmospheric pressure is a mere 1 percent of what it is at sea level and the radiation many times greater. Temperatures can reach -90 degrees F. "

    The only thing that limits these flights is the balloon. If a pressure check valve were put on the balloon so ,rather than explode at 100,000 feet ,it just releases helium to maintain pressure at a safe level could it go higher?

    I realize that a balloon could not float into space because once it is in the vaccuum of space it will be denser than it's surroundings. But it should be able to float on top of the atmosphere like a ball floats on the water.

    My Idea is to put a model rocket on a platform. The platform has four or more helium balloons with enough volume to float. Each balloon has a pressure check valve that maintains the balloon's pressure at 5 or more psi. Once the platform foats up to the edge of space a small model rocket can easily launch into space. Perhaps the expiriment could be done on a larger scale.
     
  2. jcsd
  3. May 18, 2005 #2

    russ_watters

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    It could (in fact, it has to to prevent itself from bursting, as implied in your next post), but as it does this, the buoyancy still continues to decrease.
    Yes. There is another way as well - the balloon could start off mostly empty. As it rises the helium inside the envelope expands to eventually fill the envelope. This method is probably better because it results in a roughly constant buoyant force, and its the primary method used by high altitude balloons.

    But again - there's still a limit to how high it can go.
    The atmosphere has no "top" like a container of water. It just keeps getting thinner and thinner. What we call "the edge of space" is an arbitrary definition.
     
  4. May 19, 2005 #3
    Why would the boyancy decrease? If the balloon is fully inflated and it's density remains smaller than the density of the surrounding air, wouldnt the boyancy remain the same?
     
  5. May 20, 2005 #4

    No! The density wouldn't remain less than that of the atmosphere. If the balloon is fully inflated, its density would remain more-or-less constant, however that of the atmosphere is constantly becoming less. At some altitude, a constant pressure balloon would be heavier than the air around it (actually, the balloon would expand and rupture, but here we take the hypothetical case that it couldn't and would remain constant density).

    The best practical solution here would be to use a greatly underinflated balloon, and allow it to expand as it rises into the diminishing pressure upper altitude, thus allowing its density to diminish similarly to that of the atmosphere outside it. At some point, however the weight of the material in the balloon itself would make it heavier than the now much lighter air outside (if it didn't break up first).

    For all practical purposes, however at 20 miles you are already pretty much of the way into space, so to that extent you could declare victory. You'd still fall back as soon as the balloon breaks up, however because you have not attained orbital velocity, in fact you'd be nowhere near it, so you would still need some sort of booster to get you into orbit. Still, a booster from that point (if you could find a balloon platform big enough, sturdy enough and economical enough - - remember, the booster will add to the balloon's weight) would be simpler, easier and cheaper to launch. In my fuzzy memory I seem to recall such an idea being considered.

    KM
     
  6. May 20, 2005 #5

    russ_watters

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    Yes, it has, and iirc it was calculated that they'd need a balloon several miles long to support any decent sized booster. And like you said - velocity is a bigger issue than altitude for achieving orbit.
     
  7. May 20, 2005 #6

    DaveC426913

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    Why use helium? Use the lightest substance: vacuum.

    If you can make a rigid container and "fill" it with vacuum, it will float even higher than He and H.

    Of course... good luck finding a rigid material to hold it...
     
  8. May 20, 2005 #7
    As I stated in my first post the balloon would let air out so the pressure difference between the balloon would remain the same.

    As the balloon goes up and the atmosphere becomes thinner, the balloon's helium would become thinner by releaving pressure. As it goes higher the weight of the air displaced would be less and less but the payload would stay the same. I suppose that would mean the balloon would have to be incredibly large to have lift at the thermosphere.
     
  9. May 20, 2005 #8
    You'd still have the same problem - - - the bag itself. It's not lighter than air, and at some point it would become virtually all of your structure, unless as DaveC426913 says, you could fill it with vacuum.

    KM
     
  10. May 20, 2005 #9
    How high would that limit be?
    Also, what is the density of air at the thermosphere and the stratosphere?
     
    Last edited: May 20, 2005
  11. May 23, 2005 #10
    I want to test the idea just to see if it is feasible. Unfortunatly i'm quite bad at math. I'm trying to come up with an equation to calculate the volume the balloon ( a sphere) would need to be to an object of "x" weight.

    Should the balloon be spherical or tear drop shaped? And what kind of materials should I use? I am thinking of using mylar but I dont know which one has a better strength to weight ratio.
     
    Last edited: May 23, 2005
  12. May 23, 2005 #11

    russ_watters

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    Volume of the balloon is easy: displacement is just mass of air displaced minus mass of helium (or hydrogen) it takes to displace it. From that, for an arbitrary displacement you can get the necessary volume at a specific density/altitude. Ie:

    Halfway down THIS page is the density of air as it changes with altitude. It only goes up to 60,000 feet, but at 60,000 feet, the density of air is about 10% of its sea level density (1.3 kg/m^3). Helium has a sea level pressure density of 0.18 kg/m^3. Therefore every cubic meter of helium can lift 1.1 kg (at sea level). At 60,000 feet, that means it takes ten times the volume (though the same mass), or 10 cubic meters to lift 1 kg.
     
  13. May 23, 2005 #12
    The problem is that equation doesnt include the mass of the balloon which varies with a change in volume.
     
  14. May 24, 2005 #13

    russ_watters

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    No, the mass of the balloon is constant if you use a nearly-empty envelope as if often done. Actually, the only other way to really do it would be to pump helium into a tank as you go higher - if you vented helium as the balloon expanded, you'd end up dropping like a rock when you got back to low altitude.
     
  15. May 24, 2005 #14
    I'm sorry, I was too vague. I meant that in order to make a bigger balloon I would need more balloon material which would increase the weight of the balloon. So the ammount of helium recquired to lift that weight would be more than your equation stated.
     
  16. May 25, 2005 #15

    DaveC426913

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    True but it wouldn't be too hard to turn up some data on the weight of existing hi alt balloons. You want the mass per unit surface area. You can then extrapolate to any size ballooon you want.
     
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