Could You Ride a Cable Into Orbit? The Material Does Not Exist Yet

The concept is not a tower standing on the ground but a cable held up by rotation. A satellite in geostationary orbit stays above one point on the equator because its orbital period matches the planet's rotation, and a cable extending downwards from such a satellite to the ground would be pulled down by gravity. Extending the cable outwards beyond that point as well produces an outward pull on the far portion, which is greater than the inward pull on the lower portion, so the whole structure is held in tension and stays up. A counterweight at the far end supplies the necessary outward force. Climbers would then ascend the cable mechanically rather than being launched.

The attraction is entirely about the cost of reaching orbit:

• •No propellant, since climbers use power delivered or beamed to them
• •No throwing away of stages, which dominates the cost of rockets
• •Gentle acceleration, so cargo needs no structural strengthening
• •Continuous operation, with many climbers on the cable at once
• •Release at the far end gives a free launch towards other destinations
• •Estimated costs per kilogram orders of magnitude below rockets

The cable must support its own weight over tens of thousands of kilometres, which requires a strength to weight ratio far beyond any existing material. The relevant measure is specific strength, and steel falls short by a factor of many dozens, while the best commercial fibres remain short by a large factor. Carbon nanotubes have theoretical strengths that would suffice, measured on individual tubes a few micrometres long. Producing a cable requires those properties in a continuous structure tens of thousands of kilometres long, and the strength of bulk material made from such tubes has consistently fallen far below the individual figures because defects dominate at scale. A single flaw anywhere in the length is sufficient to fail the whole structure.

The idea has a long history and its origins are more specific than usually reported. Konstantin Tsiolkovsky described a tower to geostationary height in 1895, having been inspired by the Eiffel Tower, and his version was a compression structure that could not work. Yuri Artsutanov published the correct concept in 1960, as a cable in tension deployed downwards from a geostationary satellite, in a Sunday newspaper supplement that went unnoticed outside the Soviet Union for years. Jerome Pearson rediscovered it independently and published in a technical journal in 1975. Arthur C Clarke's novel of 1979 brought it to a wide audience, and Clarke remarked when asked when it would be built that it would happen about fifty years after everybody stopped laughing.

Even with the material, several difficulties are unresolved rather than merely hard. The cable would pass through the orbits of every satellite and every piece of debris, which cross at enormous speed and would sever it, so either the debris must be cleared or the cable must be moved constantly to avoid it. Atmospheric weather at the base and radiation in the belts partway up both degrade materials. The structure would oscillate, and the dynamics of a cable that long under varying loads are not fully characterised. A failure would drop tens of thousands of kilometres of material around the equator. And no existing legal framework covers a structure occupying a fixed position in orbit permanently.

A cable extending from the ground past geostationary orbit is held in tension by the outward pull on its far portion, and climbers ascend mechanically without propellant, which is why the cost per kilogram would fall by orders of magnitude. The cable must support its own weight over tens of thousands of kilometres, which no manufactured material approaches. Debris crossing at orbital speed, oscillation and radiation remain unresolved.