MIT Technology Review – “Perhaps the biggest hurdle to humankind’s expansion throughout the solar system is the prohibitive cost of escaping Earth’s gravitational pull. So say Zephyr Penoyre from the University of Cambridge in the UK and Emily Sandford at Columbia University in New York. The problem is that rocket engines work by jettisoning mass in one direction to generate thrust for a spacecraft in the other. And that requires huge volumes of propellant, which is ultimately discarded but also has to be accelerated along with the spacecraft. The result is that placing a single kilogram into orbit costs in the region of tens of thousands of dollars. Getting to the moon and beyond is even more expensive. So there is considerable interest in finding cheaper ways into orbit. One idea is to build a space elevator—a cable stretching from Earth to orbit that provides a way to climb into space. The big advantage is that the climbing process can be powered by solar energy and thus would require no onboard fuel. But there is a big problem too. Such a cable would need to be incredibly strong. Carbon nanotubes are a potential material if they can ever be made long enough. But options available today are just too feeble. Enter Penoyre and Sandford, who have revisited the idea with a twist. They say their version of a space elevator, which they call a spaceline, could be built with materials that are commercially available today. First some background. A space elevator as conventionally conceived would consist of a cable anchored on the ground and extending beyond geosynchronous orbit, some 42,000 kilometers (26,098 miles) above Earth…”