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Tethers



Tether Challenge Archive

Welcome to Spaceward's annual tether strength competition.

The single most difficult task in building the Space Elevator is achieving the required tether strength-to-weight ratio -- in other words, developing a material that is both strong enough and light enough to support the 60,000 mile long tether.

Compared to the best commercially available tether, we need a material that is almost 25 times better - about as great a leap as from wood to metal. Quite a tall order!

Luckily for us, about 15 years ago a new material was discovered, one that has the potential of fulfilling these seemingly impossible requirements. The material, Carbon Nanotubes, is only now becoming available from laboratories in its raw form in sufficient quantities.

The task ahead is to weave these raw CNTs into a useful form - a space worthy long tether.

The following chart illustrates quite well how far it is we have to go... We plot the competition results, as well as product spec sheets and published results against a hypothetical 50% yearly improvement curve. Can material strength match this curve? Will progress be steady and linear or will it be characterized by large improvements followed by years of no progress? Time will tell.

In order to encourage CNT laboratories to place greater emphasis on the tensile strength properties of CNTs, we have posted an open dare to industry and academia: We will award up to $2M (in four prize levels), provided by NASA, to the teams that can come up with the best Space Elevator tether sample, provided that they meet the benchmarks shown in the table above.

The rules are simple. The task is not.


A brief history of the challenge:

The challenge was first offered in 2005. The first CNT tether sample was submitted, by MIT's Delta-X team, in 2007. This was the first sample of macroscopic meter-scale tether, composed of billions of nanotubes, each only a fraction of a millimeter long.

In the years that followed, we have seen quite a few additional CNT samples - products of different teams using a wide ranging array of fabrication approaches. As is well known, high tensile strength is the hardest property to achieve in a CNT tether, and all of the samples we have seen to date broke at very low strengths. Some were expected to be weak - they were simply first efforts to put together a macroscopic tether. Some were "buggy" - they showed higher strength at the labs, but failed unexpectedly early in our pull test.

These results do not speak to the fundamental strength of CNTs. As a matter of fact, during these years, lab measurements have confirmed time and again the strength of individual CNTs, and the physics of the interactions between them. It is only a matter of mastering the technique of putting them together that we are waiting for.

The 2011 challenge is drawing near - will this be the year of the CNT tether?


© The Spaceward Foundation 2008 - www.spaceward.org - Mountain View, CA