# Can we hang a really large rope or wire from space to the Earth? [duplicate]

I have a very simple question that can we hang a really large wire from space to the Earth?

What if we build some turbine kind of thing that can produce electricity in space and we transfer that from space to the Earth? A turbine wouldn't require any force to spin, and produce electricity.

• This has been asked before, the best possible answer you can read is: what-if.xkcd.com/157 (in my personal opinion). Essentially, this boils down to "space isn't just high, it's high and going really, really fast". – Magic Octopus Urn Aug 27 '19 at 17:20
• First paragraph: That's a space elevator. It would be awesome (both in the good and bad sense) if someone made one. Second paragraph: That's a perpetual motion machine. So no. Generating the electricity itself induces resistance on the turbine, and even on Earth, friction is one of the least significant losses during power generation. – Ghedipunk Aug 27 '19 at 17:30
• @MagicOctopusUrn sir i don't see relation of suggested question to my question as im not talking about falling of something instead creating a wire link and specifically producing electricity and transferring it to earth) ! – Rao Hammas Aug 27 '19 at 17:42
• @Ghedipunk ahah yeah elevator is a great idea :D but why friction is least significant factor even on earth ? if so why we need to build so big dams and then store water and force huge turbines to spin and produce electricity ? – Rao Hammas Aug 27 '19 at 17:45
• Cable length is limited by specific strength, a cable from LEO to ground is barely possible (and not in conductive materials) but would be useless. You need to suspend the cable from geostationary orbit which is far beyond our current capabilities. – Hobbes Aug 27 '19 at 18:24

## 1 Answer

can we hang a really large wire from space to earth?

That depends how large that wire is. If it's 500 km long, then no. Gravity will make that wire come down. However, if the wire is long enough to reach an altitude of about 35,000 km, then the wire can be stable through tension as the centrifugal force of the Earth spinning is strong enough for the wire to remain up-right. This is called -- as many others noted -- a Space Elevator. And the space elevator has to be located near the equator because that's where the Earth spins the fastest, thus the centrifugal force is stronger. If it's located near the poles, the wire will come tumbling down as the centrifugal force is less than the force of gravity. If you do put a space elevator at the poles, it will have to be stronger because it can't be stable through tension anymore and it will just spin on it's roll axis and not deliver any payload to orbit (it would be a useless space elevator).

Turbine won't require any force to spin and produce electricity

Turbines simply create electricity by a magnet going past coils of wire, thus producing an AC current (this is called a Dynamo) and then uses a Commutator to convert it to a DC current, but nowadays, Rectifiers such as diodes are used to convert AC to DC. There is a magnetic field in the dynamo which will eventually slow down the turbine until it comes to a complete stop. If you partially spin a dynamo, then it will produce electricity depending on how much you spin it. It's all part of the Law of Energy Conservation. The reason turbines spin here on Earth is because there is a constant force acting on the turbines, whether it's water or wind.

Summary In theory, yes we can "hang a really large wire". That's called a space elevator. Is it possible with today's technology? No. Can we spin a turbine forever in space? No because the magnetic field of the dynamo will decay the turbine's spin.

• That was a really good answer ! i just want to know one more thing will turbine need same amount of force to spin in space that we provide here on earth ? i guess No ! i guess that force will be far less required ? like whenever turbine is about to stop just give it a lil push and here we go again :D ? isn't it ? Also many people and in an article author said because earth is moving (so fast) so it's impossible for a wire or pole to stay hanging at a place ?? – Rao Hammas Aug 28 '19 at 5:04
• @RaoHammasHussain No the energy required to spin the turbine in space will be largely the same as it is on earth - because the way turbines generate electricity is converting the kinetic energy to electrical energy. Key word there converting - this means that for any energy you get out in terms of electricity you lose kinetic energy from the turbine (i.e. it slows down) and you can't get out more than you put in. So give it a "lil push" and it will give you a "lil electricity" - being in space doesn't change that. – motosubatsu Aug 28 '19 at 9:55
• @motosubatsu space is useless than basically :D You are right :) – Rao Hammas Aug 28 '19 at 12:25
• "Turbines simply create electricity by 2 magnets rubbing against each other." What a multitude of errors within such a short sentence! Turbines do not create electricity, they convert hot gas or steam into rotational power. A generator driven by a turbine may produce electrical power. There are no magnets rubbing against each other within a generator. Generators use coils and alternating magnetic fields to create electric power. – Uwe Aug 28 '19 at 14:07
• Why is anybody discussing AC vs. DC here? Last time I checked, Thomas Edison and George Westinghouse were both still dead. – Solomon Slow Aug 28 '19 at 18:40