Sapce Elevator NASA competition winner

[Sky Captain]

Well it`s not like space elevator is the only option to economically lift stuff into orbit at large scale. There is already mentioned magnetic launch possibility that would be good for unmanned payloads. If even that turns to be too difficult to engineer then there is an option to develop a rocket design which is as simple and low tech as possible and easily mass producible perhaps sacrificing some performance and reliability to make it cheaper. The proposed Sea Dragon rocket were supposed to be built at ordinary shipyard from materials used in shipbuilding to cut down on costs and would orbit 550 tons of cargo in single launch. It would be handled and launched from water and thus don`t require elaborate ground handling equipment. A tugboat and fuel tanker would be all what`s needed to launch it.

http://www.astronautix.com/lvs/searagon.htm

Another article describing possibility of big dumb boosters
http://www.optipoint.com/far/farbdb.htm

So it seems that space elevator is not critically necessary to gain cheap access to space. It would be good to have one if it proves to be economically feasible to build but in no way lacking a space elevator is a show stopper to large scale space exploration and resource utilization.

[Gilthan]

question on this

CNT exhibits extraordinary mechanical properties: the Young's modulus is over 1 Tera-Pascal and the estimated tensile strength is 200 Giga-Pascals.

Do we only care what the tensile strength is and not the young's modulus, for the properties of a space elevator use?

High young's modulus is valued in steel cables for suspension bridges, since less elongation under varying load reduces how much parts move around. The same would seem to apply here. I'll skip repeating here prior points about the unlikelihood of getting properties like that on an aggregate scale, rather just pretending they were obtained. With your figures for strength and modulus, the CNT would be elongated 10% if loaded with to half its max tensile strength (a safety factor of 2), like 22000 miles of cable becoming 24000 miles under its working stress. Of course, if in a space elevator, the part of the loading and elongation due to the cable's own weight would be constant, with only the loading from the payload varying in magnitude and position.

The Young's modulus influences the stored elastic energy, since a higher young's modulus would reduce elongation and overall reduce elastic energy stored from a given loading. That's actually an interesting topic.

TNT high explosive is 4000 joules per gram, but a cable with those properties could make something of four times greater instantaneous raw energy release per gram, if stretched near its breaking point and then broken.

That may seem crazy and counter-intuitive, so different from what anybody has experienced with existing metal springs and cables under tension, but this hypothetical cable's properties are so totally different in the magnitude of the figures involved. Pretend we had cable with 200 GPa strength and loaded it to the max. If it had that 1 TPa Young's modulus, strain is 0.2 (20% elongation). The stored elastic energy is 0.5 x 0.2 x 200 GPa = 2E10 joules per cubic meter, like Hooke's Law with a spring. At 1.3 g x cm-3 density, that amounts to 15000 joules per gram.

If loaded to half that with a safety factor, such would be 4000 joules a gram, dropping to only about the energy equivalent of TNT.

In that context, there is the space environment, the periodic localized blasting of an exposed surface, like 1634 miniature impacts on shuttle windows over 54 missions:

Being hit by tiny chips of paint, aluminum, steel, and other types of space garbage is a regular part of Shuttle missions, according to data maintained by Johnson Space Center’s Hypervelocity Impact Technology Facility. In 54 missions from STS-50 through STS-114, space junk and meteoroids hit the Shuttle’s windows 1,634 times necessitating 92 window replacements. In addition, the Shuttle’s radiator was hit 317 times, actually causing holes in the radiator’s facesheet 53 times.

http://www.wired.com/wiredscience/2009/03/shuttledata/

The Shuttle's windows are hard for small impactors to penetrate, being 1.6 to 2.6 inches thickness. Space elevator cable ribbons must be much thinner, though, and can't be much armored, if the elevator's mass over thousands of miles of length is not to be excessive.

That leads to the matter of what happens if one strand in the hypothetical cable is hit, causing an energy release upon breakage like high explosive going off in its vicinity, with blast and miniature shrapnel towards other strands in the cable.

Well it`s not like space elevator is the only option to economically lift stuff into orbit at large scale.

True. Yet, to the degree it gets the most popular press, that fosters waiting for materials technology changes. Fewer people hear about the methods which could be done now (Big Dumb Boosters, mass drivers, etc, or, if really un-PC, Orions).

[Beowulf]

A good hurricane would destroy the cable, and possibly even lightning strikes or other high winds could do the job, and while the Galapagos location minimizes these dangers, it does not eliminate them.

There's this thing about hurricanes: they tend to avoid the equator. Getting too close kills their rotation, which kills them.