Why Space Elevators Are Cool

[ErlyRisa]

Space elevators concepts (as written and repeated as a concept , in what feels like eons ago) have not been possible due to material limitation.s

 

Noow

 

We all want 3000km or so worth of perfect nanotube: Sort of possible, but not easy.

 

Once done: You have to errect it (and earth will finally be ready to colonise the galaxy)

 

Once up you supply energy in the form of heat (from the vicinity of Venus)

Ond you can squirt as much junk up into space as you want. Then Earth will be satisfied.

[Moontanman]

A space elevator would be easier on Mars, the fiber known as Kevlar could be used to build it..  

[CraigD]

...

Once done: You have to errect it (and earth will finally be ready to colonise the galaxy)

All proposed space elevators are “lowered” from the top (geostationary orbit) down, not “erected” from the bottom up, as a building is. They rely on the tensile strength of their material, not it’s compressive strength and stiffness.

 

A space elevator would be easier on Mars, the fiber known as Kevlar could be used to build it..

True. Mars is way easier to build a space elevator to that Earth.

 

Using a slightly enhanced version of the program in this 2006 post, I get these numbers for a Martian space elevator made of Kevlar, overengineered by a (pulled completely from my ar… imagination) factor of 2:

u: 42828000000000 m^3/s^2 (Mars's Standard Graviational Parameter)/

r1: 3396200 m (Mars's equatorial radius)/

p: 88642 s (Mars's rotational period)/

M: 25000 kg (initial mass)/

W: 92401.8971071491335 kg (initial weight)

S: 1380000000 N/m^2 (Kevlar strength, 2x safety margin)/

CA: .00003347894822722794692 m^2 (initial cross section area)/

d: 1440 kg/m^3 (density of Kevlar)/

RI: 1000 m increment/

r: 20428200 m (final radius)

CA: 1.352816655387583759 m (final cross section area)

M: 15290230030.74288165 kg (final mass)

W: 1866886984.434865587 N (final weight)

 

Here’s a space elevator massing about 15,300,000 tons (about 1/4th the mass of Earth's largest concrete dam, and not including it’s above stationary orbit “counterweight), with a cross sectional area of about 1.35 m^2 at the top, 33 mm^2 at the bottom, that can lift 25 tons.

 

Reducing the overengineering factor to 1 gives:

S: 2760000000 N/m^2 (tensile strength of Kevlar)/

CA: .0000884480851386102521 m^2 (initial cross section area)/

CA: .004749104852806314991 m (final cross section area)

M: 68206623.08490940054 kg (final mass)

W: 13107529.39374542937 N (final weight)

 

Here the mass is reduced to mere 68,000 tons, but this is the absolute ideal minimum, with no strength margins, which couldn't work in a real application.

 

The real issue with a space elevator, though, isn’t the simple strength calculations, but what sort of complicated effects it might have to withstand. What little actual experience we have with dangling long cables is space shows us that they do complicated, oscillatory things that lead to momentary high forces that break them. To actually build a space elevator, we’d have to understand and manage this complicated behavior, not only in vacuum, but in the more complicated environment of an atmosphere.

 

PS: leaving out the bulk of the program that’s concerned with inputting the parameters, here’s the heart of the MUMPS code I used:

s CC=2*$zpi**2/p/p,r=r1,M=m0,A=u/r/r-(CC*r),W=A*M, CA=W/S

f s r=r+RI,A=u/r/r-(CC*r),CA=W/(S-(d*RI*A)),MI=CA*d*RI,F=A*MI,W=W+F,M=M+MI q:A'>0

Edited December 16, 2014 by CraigD
Fixed major mistakes in program, input, and results

[ErlyRisa]

Don't see the point of the counterweight:

If you can buiild rope to a length: Why not keep building longer - that why we are more satisfied.

 

The knob at the end is not actually needed. - ie. Rotational mass, in order too keep said entity straight, is only there for that...too keep it straight.

 

But Satisfaction can be achieved with a lanky cord...and uses less energy and can keep ejaculating more reliably.

 

The orbital receiving end, does not have to be fixed too the cord: You can "collect" ejaculate material in orbit over time (days -or other dependent on radius)

[CraigD]

First, oops! – I made 2 separate mistakes in my previous post, one an mistake in the formula for centrifugal force, the other an mistake in the strength of Kevlar, the combined effect of which was to reach a result greatly understating the mass of a Martian space elevator. Instead of 6000 tons, with a cross sectional area of about 1 cm^2 at the top, 7 mm^2 at the bottom, and a x4 overstrength factor, it should be something like 15,300,000 tons, 1.35 m^2 at the top, 33 mm^2 at the bottom.

 

I fixed it.

 

Don't see the point of the counterweight:

If you can buiild rope to a length: Why not keep building longer - that why we are more satisfied.

The whole space elevator must have a weight less than zero, or it will fall to the ground, so it must have some mass – a “counterweight” – above geostationary orbit (GEO, about 17032000 above ground level for Mars)

 

The counterweight isn’t required to be very big or close to GEO. Many designs assume that something huge, such as a captured asteroid, will be available, and use it in the design. It’s also possible to extend a cable far above GEO and use a much smaller mass (including the mass of the above GEO cable).

 

If instead of this approach, you minimize the mass of the above GEO part of the elevator and maximize its length (height), because the above GEO parts move faster than the orbital speed for their height. you can get some useful “free trip” capabilities from it, such as launching payloads into Mars escape orbits, or even transfer orbits between Mars and other planets orbits.

 

I worked out a few estimates for this for an Earth Space elevator in this 2010 post, including a “free trip” Earth-Mars transfer orbit. It’s not obvious if a Mars space elevator could manage a Mars-Earth transfer in the same way, though a Mars escape trajectory wouldn’t be difficult, needing just about 5309000 m of cable above GEO.

 

With sufficiently strong materials and clever engineering, space elevators could do much of the “heavy lifting” of putting payloads into interplanetary transfer orbits. They’re very attractive, practically key to a “low energy” approach to large scale interplanetary space travel.

[ErlyRisa]

Yeah I know - I'm saving bitcoins to get a seat (but at this rate it would be easier to mine the material myself, and do the construction myself - as long as right wing know it all rule makers step off and stay out of my way)

Edited December 19, 2014 by ErlyRisa

[Moontanman]

Yeah I know - I'm saving bitcoins to get a seat (but at this rate it would be easier to mine the material myself, and do the construction myself - as long as left wing know it all rule makers step off and stay out of my way)

 

 

Any chance you could leave politics in the politics section?