Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Floating Tensegrity Sphere

  1. Mar 18, 2010 #1
    I came across this online the other day:

    I came up with a formula for calculating the mass supported by such a sphere of air (as a function of temperature, height and radius), and just wanted to see if my math checks out.

    http://designbyninjas.com/calculation.jpg [Broken]

    Also, since the air pressure is the same inside as out, would there be any feasible way to pressurize such a system?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 18, 2010 #2
    Do you by chance recall the link to that?
  4. Mar 18, 2010 #3
  5. Mar 19, 2010 #4
    Indeed, a large enough sphere could be used to build a floating city. Also, as a sphere gets bigger the mathematics of heating it up works out to be more and more economical. However, there is the issue of pressure difference. A sphere built to contain even a small pressure difference might need walls so thick it could end up defeating the purpose.

    But you don't really need pressure difference or even temperature difference. Just replace the nitrogen in the air inside the sphere with helium. Helium too expensive? Then replace it with hydrogen; but include safety measures so as to avoid super-Hindenburg scenarios.
  6. Mar 19, 2010 #5
    Not to burst anyone's bubble(pun intended) would anyone really want to live in a floating city that would be an ultimate, and easy, target for terrorists?
  7. Jul 23, 2010 #6
    Alternatively, it could be turned into a miniature Death Star. If fitted with electronic countermeasures and lots of missiles, it could be used to invade enemy territories...
  8. Jul 23, 2010 #7


    User Avatar
    Science Advisor

    The stress on the shell, due to buoyancy, is quadratic in radius. The cross-section area of the shell, however, given constant thickness, increases linearly. That means, at some point, you'll have to start increasing thickness of the shell linearly with the size. If you start scaling thickness linearly with the size, the mass of the shell goes up as a cube of the size, same as the mass of enclosed air.

    In other words, no, it won't work.
  9. Aug 13, 2010 #8
    Love this discussion, I summarized it on my blog, http://lawoftheair.com. While you mention the density and defense issues, you leave out low oxygen and the COLD.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook