Space Elevator History: Could We Really Reach Space?

A skyscraper stands on its foundations: every floor pushes down on the one below, and the material has to resist compression. Build high enough and the structure crushes itself. That is why Tsiolkovsky’s 1895 tower could never be built.

A space elevator works the other way round. It is centred on geostationary orbit (GEO), 35,786 km above the equator, where an object circles Earth once a day and so appears fixed over one spot. A cable runs from an Earth Port on the equator up through GEO and on to a counterweight far beyond.

Below GEO, each piece of cable is moving slower than orbital speed for its height, so gravity pulls it down. Above GEO, each piece is moving faster than orbital speed, so it pulls outward, like a stone on a string being swung. Balance the two and the cable hangs in tension: it is pulled tight from both ends instead of squashed from above. Tension is greatest at GEO, which is why Pearson showed in 1975 that the cable should be thickest there and taper toward both ends.

A normal cable gets heavier as it gets longer. At some length its own weight snaps it. Engineers call that length the breaking length, and it is the single number that decides whether a space elevator can exist.

For an Earth elevator, the answer is roughly 3,100 to 8,200 km (the higher the figure, the less the cable has to taper). Bradley Edwards’ NASA-funded design assumed a material strength of about 100 gigapascals with very low density. High-strength steel manages about 30 km. Kevlar, Zylon and the best carbon fibre sit around 250-400 km.

Only two materials reach the zone, and only at microscopic scale: carbon nanotubes and graphene. A single nanotube a few nanometres wide can be astonishingly strong; a rope made from billions of them is limited by the weakest joins and defects, and today’s nanotube yarns fall far short of the target. In 2014 Google X reportedly shelved its own look at the idea after finding no one could make a perfect nanotube strand longer than about a metre.

That is the real state of the problem. The challenge is not “can carbon nanotubes be strong?” It is “can anyone manufacture a metre, then a kilometre, then tens of thousands of kilometres of them, with no flaw anywhere?” As of 2026 the answer is no.

Space debris. A rocket crosses the crowded low orbits in minutes. An elevator would sit through every altitude, permanently, in the path of thousands of satellites and fragments. It cannot dodge, so designs rely on tracking and on moving the ocean platform to swing the cable clear. NASA’s studies list collision avoidance as a critical technology.

Weather and lightning. The lowest 20 km face wind, storms and lightning. That is one reason concepts favour an equatorial ocean site away from hurricane tracks, on a platform that can move.

Coriolis forces. A climber going up must gain sideways speed to keep pace with the rotating cable. It borrows that speed from the tether, pulling it slightly westward and setting it swaying. Climb too fast and the swing grows; control systems would have to manage it.

A broken cable. Where it snaps matters. A break low down lets the upper cable, no longer held, swing outward into a higher path. A break high up drops the lower section back toward Earth, where much of it would burn up or wrap around the planet. Designs call for redundancy, monitoring and repair climbers.

Radiation and atomic oxygen. The cable crosses the Van Allen radiation belts, and in low orbit atomic oxygen erodes many materials. That is what the nanotube samples Obayashi put on the ISS from 2015 were testing.

An elevator would not replace rockets. Polar orbits, fast launches and missions away from the equatorial plane would still need them. Its promise is cost: once built, sending cargo up would be a matter of electricity, not a new launch for every payload. A payload released high enough up the rotating cable, above about 47,000 km, would even be flung free of Earth, which is why Obayashi describes its design as a gateway toward the Moon and Mars.

The Moon’s gravity is one-sixth of Earth’s, and it turns once a month instead of once a day. Those two facts shrink the materials problem dramatically. In 2019 Zephyr Penoyre and Emily Sandford proposed the Spaceline, a cable anchored on the Moon and hanging toward Earth, ending deep in Earth’s gravity well near geostationary altitude. Their conclusion: Zylon, a polymer fibre already in mass production, would be strong enough. Earlier lunar tether studies for NASA’s advanced-concepts institute reached similar conclusions. It would still be a colossal project, but it would not need a material that has not been invented.