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Let's say that space around earth has no debris. Super elevator is some super durable cable between a space station and earth by which some elevator can travel. Space station is in geostationary orbit, so it never changes its position relative to earth's surface.

What can prevent this kind of technology being invented?

(Only in terms of science, not about its usefulness or bewaring of terrorism etc.)

P.S: If more information needed, please tell me, I will provide.

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  • $\begingroup$ Which space station are you referring to? ISS (usually referred to as "the space station") moves with respect to the surface, completing a roundtrip in about 90 minutes, as anybody spending the night looking at the sky to see it passing by can tell you. $\endgroup$
    – L.Dutch ♦
    Sep 2, 2019 at 12:43
  • $\begingroup$ @L.Dutch any (maybe not existing right now) that does its roundtrip in 24 hours. Impossibility of this kind of station, also might be the answer if so... $\endgroup$
    – えるまる
    Sep 2, 2019 at 12:46
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    $\begingroup$ @Erumaru it is generally a good idea to wait more than a few minutes before accepting an answer; give it at least a day or two to increase the number of people who read your question, as some of them might have better answers for you. $\endgroup$
    – Starfish Prime
    Sep 2, 2019 at 13:12
  • $\begingroup$ @StarfishPrime Thanks for advice! I will try it. $\endgroup$
    – えるまる
    Sep 2, 2019 at 13:13

2 Answers 2

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A space elevator is a well established concept.

Despite being proposed for the first time in 1895, it has not yet found concrete implementation. Why?

Basically we have not yet found any material which is strong enough to withstand all the forces involved in the utilization of a space elevator.

A space elevator cable would need to carry its own weight as well as the additional weight of climbers. The required strength of the cable would vary along its length.

The cable would need to be made of a material with a large tensile strength/density ratio. For example, the Edwards space elevator design assumes a cable material with a tensile strength of at least 100 GPa. Since Edwards consistently assumed the density of his carbon nanotube cable to be 1300 kg/m^3, that implies a specific strength of 77 MPa/(kg/m^3). This value takes into consideration the entire weight of the space elevator. An untapered space elevator cable would need a material capable of sustaining a length of 4,960 kilometers (3,080 mi) of its own weight at sea level to reach a geostationary altitude of 35,786 km (22,236 mi) without yielding. Therefore, a material with very high strength and lightness is needed.

For comparison, metals like titanium, steel or aluminum alloys have breaking lengths of only 20–30 km (0.2 - 0.3 MPa/(kg/m^3)). Modern fibre materials such as kevlar, fibreglass and carbon/graphite fibre have breaking lengths of 100–400 km (1.0 - 4.0 MPa/(kg/m^3)). Nanoengineered materials such as carbon nanotubes and, more recently discovered, graphene ribbons (perfect two-dimensional sheets of carbon) are expected to have breaking lengths of 5000–6000 km (50 - 60 MPa/(kg/m^3)), and also are able to conduct electrical power.

As of today many people are betting on carbon nanotube or graphene as material for building the cable. If they don't manage to satisfy these expectations, well, you have your explanation on why the space elevator cannot be realized.

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Off the top of my head:

  1. Still not yet obvious that suitable materials can be manufactured in bulk. This isn't an absolute restriction on space elevators, but it might be one of those things which is always "50 years away".
  2. Lightning could frazzle your cable and break it or seriously damage it. Dry cables might be ok, but no-one is sure whether wet cables would be safe yet. Good luck stopping lightning, rain or damp clouds around your cable for its entire operational life!
  3. There may be no human-created debris up there, but the earth gets a continuous dusting of micrometerorites all day, every day, forever. That risks abrading or outright snapping your cable.
  4. Higher levels of the atmosphere are very thin, but have non-trivial quantities of things like monatomic oxygen or other radicals that are going to be very effective at chemically damaging your cable, which will obviously have to spend its entire existence in the danger zone.

(personally I suspect that space elevators on earth will always be impractical, but there are other good cheap spacelaunch options out there that have a slightly saner scale and fewer impossible engineering difficulties, and they'll do. save the elevators for every other interesting body in the solar system)

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