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Spider silk and space tethers

  1. Jan 18, 2012 #1
    interested in the news on this this week.
    I am wondering is a single strand of this stronger than a woven number of strands?

    Obviously the woven strand is stronger in that it will bear a greater load but will the single strand stretch further (bearing only its own weight)?
    How long a strand could be drawn until it snapped under its own weight in gravity ( as a space tether)?
    I am thinking that if it could make the distance into space then it could be used to ferry up very small quantities that might eventually add up to a worthwhile amount.
  2. jcsd
  3. Jan 18, 2012 #2
    It is possible to estimate the greatest length that can support it's own weight if you know the Ultimate tensile strength (UTS) and density of the material.
    Carbon fibre has a UTS of 1.7 x 10^9 Pa therefore a fibre of cross sectional area 1mm^2
    ( 1 x 10^-6 m^2) can support a weight of 1.7x10^9 x 1x10^-6 Newtons = 1.7x10^3N
    This is a mass = 1.7x10^2 kg (taking g = 10N/kg).
    If all of this mass is taken to be a fibre then the length can be calculated.
    The density of carbon fibre = 2.3kg/m^3
    So a fibre of cross sectional area = 1x10^-6 m^2 and mass 1.7x10^2 kg would need to have a length given by
    L x 1x10^-6 x 2.3 = 1.7x10^2, which gives L = 74 x 10^6m
    so a carbon fibre 74 million metres long is at the point of breaking under its own weight.
    This is very much an ESTIMATE calculation because I have ignored variation of g with height and probably some other things but at least it gives some idea.
    If you can find data for spider silk then I hope this helps you make some estimates.
  4. Jan 18, 2012 #3
    thanks for that.
    It is a bit academic (I mean above my head) though since I came upon this link


    which seems to fairly definitely say that spider silk is just not strong enough for a space elevator(although carbon nanotubes seems to be a runner according to them =NASA= in 2003).

    But you seem to be calculating 74,000 km length of carbon fibre as an approximation before it would break under its own weight.

    Wouldn't that allow it to carry a load up into space if gravity was all there was to contend with (it seems implausible -have I misunderstood ?)

    I don't have an idea of the UTS of Spider Silk but would I be wrong to assume it would be superior to carbon fibre?
  5. Jan 18, 2012 #4
    thought I would throw this out there. A piece of this long enough to wrap the world at the equator would weigh 2 pounds.

    Best use for this silk so far is to grow replacement skin tendons and nerves growen on this as a structure.

    Space elevator is also a possible use but that will be ages from now. The wind and currents of rising and falling air mixed with water and ice would increase the string to its breaking point. Anything used is going to have to be heated to keep the water off it.
    The company making this is Kraig Biocraft. Stock symbol is KBLB if you are a stockmarket type
  6. Jan 19, 2012 #5
    is it an insane idea that the strands could be made to vibrate along their length at a very short wavelength?
    To stop ice forming and shake of water droplets.
    A bit like a micro tsunami set off from the bottom or the top....
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