Lift cables, skyscrapers, and space

Lifts and skyscrapers: The other mile-high club | The Economist

Here's another interesting piece up at The Economist website:

This week Kone, a Finnish liftmaker, announced that after a decade of development at its laboratory in Lohja, which sits above a 333-metre-deep mineshaft which the firm uses as a test bed, it has devised a system that should be able to raise an elevator a kilometre (3,300 feet) or more. This is twice as far as the things can go at present. Since the effectiveness of lifts is one of the main constraints on the height of buildings, Kone’s technology—which replaces the steel cables from which lift cars are currently suspended with ones made of carbon fibres—could result in buildings truly worthy of the name “skyscraper”.

The problem with steel cables (or “ropes” as they are known in the trade) is that they are heavy. Any given bit of rope has to pull up not only the car and the flexible travelling cables that take electricity and communications to it, but also all the rope beneath it. The job is made easier by counterweights. But even so in a lift 500 metres tall (the maximum effective height at the moment) steel ropes account for up to three-quarters of the moving mass of the machine. Shifting this mass takes energy, so taller lifts are more expensive to run. And adding to the mass, by making the ropes longer, would soon come uncomfortably close to the point where the steel would snap under the load. Kone says it is able to reduce the weight of lift ropes by around 90% with its carbon-fibre replacement, dubbed UltraRope.

The article does note at the end that the development suggests that space elevators may be do-able:

Nor need carbon-fibre lift-cables be confined to buildings. They could eventually make an idea from science fiction a reality too. Space lifts, dreamed up in the late 1950s, are a way of getting into orbit without using a rocket. Building one would mean lowering a cable from a satellite in a geosynchronous orbit above the Earth’s equator while deploying a counterbalancing cable out into space. The cable from Earth to the satellite would not be a classic lift rope because it would not, itself, move. But it would perform a similar function of support as robotic cars crawled up and down it, ferrying people and equipment to and from the satellite—whence they could depart into the cosmos.

I'm guessing that the strength of this new cable has some way to go yet.

But as it happens, I was idly wondering recently about whatever happened to the idea of a "skyhook" system for helping get things into low earth orbit.  

I always thought the idea of space plane catching a ride up at the end of skyhook sounded like a good idea, and I wonder whether the strength of the Kone cable is enough for the job.   (Although a skyhook presumably needs to be rigid, not flexible like a lift cable.  I wonder if that is a problem?)