The other side of the Feasibility Condition is the tether side – the one that corresponds to our Strong Tether challenge.

To recap, we are offering a prize of $0.9M for a tether sample that has a specific strength of 5 MYuri, and an additional prize of $1.1M for a tether sample that has a specific strength of 7.5 MYuri.

For context, today’s materials perform at 2.5 – 3 MYuri at best, and to build a Space Elevator we need material that is 25 – 30 MYuri.  (A MYuri is the name we gave the SI equivalent of N/Tex, or GPa-cc/g)

A visual guide to the task ahead

Actually, we’ll be more comfortable (and the Space Elevator will function a lot better) with a ~35 MYuri material, but this is the bare minimum that we need. Keep in mind that successive 50% improvements in material strength are very large steps, but that we already know that CNT molecules are measured at ~50 MYuri, and fabricated CNT micro-bundles have been produced by several labs at 10 MYuri, so this challenge is not impossible.

It is important to note that while in order to win the prize we require the core metric of specific strength, we do not require the tether samples to be made in a way that is scalable, profitable, repeatable, or durable. We do not care if it took a whole year of undergrads working around the clock, and the sample is the best of 100 samples that were made. This makes the prize very attractive to CNT research labs, since we’re offering a substantial amount of money at a stage where investors are still (rightfully) shy, since the tether is still far far from being a sellable product.

To date, we’ve had two Carbon Nanotube tether samples at the games.

In the 2009 games, the University of Shizuoka team, led by Yoku Inue, entered a CNT tether loop (our second ever).

The tether sample was made out of Carbon Nanotubes that were grown as an aligned nanotube “forest” on a flat substrate, then pulled into a loosely aligned “sliver” and spun into a thread.

The Carbon Nanotubes themselves are short in everyday terms (a tenth of a millimeter) but still represent an aspect ratio of more than 10,000:1. The tether was then looped around to create a closed flat tape, with cross-over lines similar to Brad Edward’s proposed ribbon construction of a Space Elevator.

Being their first effort at a macroscopic tether, it failed very early, pretty much separating between the micro-fibers.

In the 2007 games, team delta-X representing Nanocomp Inc,  presented a tether sample made out of Carbon Nanotubes that were grown in an aerosol-like phase and spun out directly from this “black smoke” in a way reminiscent of a cotton-candy machine. Delta-X’s tether was a very recent result, and so they did not have the ability to form a closed loop just yet. Instead, the tether was tied in a knot to form a closed loop, and as expected, when pulled, the knot slipped.

Both tethers failed at the macroscopic level, very far from the strengths achieved by the individual CNTs or even the CNT micro-bundles that constitute them

On the one hand, just having these samples and talking with the teams gives us a good indication that the challenge is having its desired effect and is drawing research teams to look into tensile strength of CNTs, which is otherwise one of the harder challenges in the field, and one offering longer-terms rewards.

On the other, we’re hoping that in the next games we’ll be able to at least show performance levels comparable to the Kevlar or Zylon type tethers that are out there today.

Spaceward’s next goal is therefore to aggressively pursue the CNT labs out there – we think that the timing is about right, since CNTs are now produced by an ever larger set of universities, and the production of a 2-gram carbon nanotube tether, while incredibly impressive in last year’s terms, will no longer be a novelty in 2010.