Although the concept is simple, the engineering challenges that have to be overcome are awesome. The secret is to find the right material for the ribbon, which has to be light, strong, flexible…oh, and stretch, without breaking, for some 100,000 km (62,000 miles) – higher than geostationary orbit.
The current favoured material for this mega-cable is carbon nanotubes. Made up of interlinking carbon atoms, rolled up into a cylinder, each carbon nanotube is around a millionth of a millimetre in diameter. By sticking a load together you end up with a structure that’s lightweight, strong and flexible.
“This material, or something similar, is the key to making the space elevator a reality,” says Horn. “Carbon nanotubes can be spun into cables and tethers, just like rope is made…theoretically they would be strong enough. We just need to figure out how to manufacture the ribbon out of these materials in large quantities.”
At each annual conference they try to hold a ‘string tether competition’ to see how things are progressing. “No-one has won the competition yet as the bar is pretty high,” Horn says. “Every year we see improvements and better tethers entered.”
“Once the materials aspect is figured out, the rest is just engineering and political problems to solve,” Horn explains. However, the list of these problems is, even for space elevator advocates, rather daunting. It ranges from issues such as how do you operate space elevators (the theme of this year’s conference) to the political treaties required to permanently connect Earth and orbit. From how you go about deploying an enormously long cable (not a job handled by your average scaffolding contractor), to concerns about radiation exposure for human occupants of the climber.
But Horn remains optimistic. Even the proposed length of the space elevator ribbon is not beyond engineering feats, he says, if you consider “there are 80,000 miles of cable in the Golden Gate Bridge”.
Price estimates vary from $10 to $50 billion, which is still cheaper than the cost of the International Space Station (ISS). A space elevator would also take around the same amount of time to build as the ISS and would, arguably, be much more useful.
“Once we have the materials science capability,” says Horn, “we could have the first one built and operational in about a decade with a concerted effort.”
It’s easy to be dismissive of such a grand scheme but the space elevator concept is being taken seriously by a lot of people. The more we use space, the more apparent the limitations of current rocket launchers are becoming. The phenomenal cost is almost certainly holding us back – a point illustrated by the difficulties faced by academics trying to launch small satellites (and covered in my previous column). Space elevators are possible; eventually, I would suggest, they are also inevitable.
“Once we have a big breakthrough, then we can start the clock to build the first Earth space elevator,” says Horn. And if you can’t wait that long, he has another suggestion. “In the meantime, with existing materials, we could build one on the Moon.”
My thanks to BBC Future Facebook followers for the inspiration for this column, there were two people in particular who I should mention but unfortunately, I’ve lost your names…you know who you are. All ideas welcome - Richard.