So the Google X hoverboard was shelved. “When we let it go, it’s a positive thing,” DeVaul says. “We’re saying, ‘This is great: Now we get to work on other things.’”

Like space elevators, something X was widely rumored to be working on but has never confirmed until now. “You know what a space ­elevator is, right?” DeVaul asks. He ticks off the essential facts–a cable attached to a satellite fixed in space, tens of thousands of miles above Earth. To DeVaul, it would no doubt satisfy the X criteria of something straight out of sci-fi. And it would presumably be transformative by reducing space travel to a fraction of its present cost: Transport ships would clip on to the cable and cruise up to a space station. One could go up while another was heading down. “It would be a massive capital investment,” DeVaul says, but after that “it could take you from ground to orbit with a net of basically zero energy. It drives down the space-access costs, operationally, to being incredibly low.”

Not surprisingly, the team encountered a stumbling block. If scaling problems are what brought hoverboards down to earth, material-science issues crashed the space elevator. The team knew the cable would have to be exceptionally strong– “at least a hundred times stronger than the strongest steel that we have,” by ­Piponi’s calculations. He found one material that could do this: carbon nanotubes. But no one has manufactured a perfectly formed carbon nanotube strand longer than a meter. And so elevators “were put in a deep freeze,” as Heinrich says, and the team decided to keep tabs on any advances in the carbon nanotube field.

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