A Day On Wikipedia

{{main|Space elevator}}
The ”’construction of a space elevator”’ would be a vast project, requiring advances in engineering, manufacture and physical technology.

== Overview ==
David Smitherman of [[NASA]] has published a paper that identifies ‘Five Key Technologies for Future Space Elevator Development’:<ref>{{cite web | url = http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060000015_2005248072.pdf | title = Critical Technologies for the Development of Future Space Elevator Systems | author = David V. Smitherman, Jr. | accessdate = 2007-11-03 |format=PDF}} NASA Tech Report IAC-05-D4.2.04</ref>

# ”'[[materials science|Material]]”’ for ”cable” (e.g. [[carbon nanotube]] and [[nanotechnology]]) and ”tower”
# ”'[[tether propulsion|Tether]]”’ deployment and control
# ”'[[world’s tallest structures|Tall tower]]”’ construction
# ”'[[Electromagnetic propulsion]]”’ (e.g. [[magnetic levitation]])
# ”’Space infrastructure”’ and the development of [[space-based industry]] and economy

Two different ways to deploy a space elevator have been proposed.

== Traditional way ==
{{Unreferencedsection|date=September 2008}}
One early plan involved lifting the entire mass of the elevator into [[geostationary orbit]], and simultaneously lowering one cable downwards towards the Earth’s surface while another cable is deployed upwards directly away from the Earth’s surface.

[[Tidal force]]s ([[Gravitational force|gravity]] and [[centrifugal force (fictitious)|centrifugal force]]) would naturally pull the cables directly towards and directly away from the Earth and keep the elevator balanced around geostationary orbit.{{Fact|date=September 2008}} As the cable is deployed, [[Coriolis force]]s would pull the upper portion of the cable somewhat to the West and the lower portion of the cable somewhat to the East; this effect can be controlled by varying the deployment speed.{{Fact|date=September 2008}}

However, this approach requires lifting hundreds or even thousands of tons on conventional [[rocket]]s, an expensive proposition.

== Cable seeding design ==
{{Unreferencedsection|date=September 2008}}
[[Bradley C. Edwards]], former Director of Research for the [[Institute for Scientific Research]] (ISR), based in [[Fairmont, West Virginia]] proposed that, if nanotubes with sufficient strength could be made in bulk, a space elevator could be built in little more than a decade, rather than the far future. He proposed that a single hair-like 18-[[tonne|metric ton]] (20 short [[ton]]) ‘seed’ cable be deployed in the traditional way, giving a very lightweight elevator with very little lifting capacity. Then, progressively heavier [[cable]]s would be pulled up from the ground along it, repeatedly strengthening it until the elevator reaches the required [[mass]] and [[Strength of materials|strength]]. This is much the same technique used to build [[suspension bridge]]s.

The 18 tonnes needed for a seed cable may be resonably lightweight; the proposed average mass is about 200 grams per kilometer.{{Fact|date=September 2008}} In comparison, conventional [[copper]] telephone wires running to consumer homes weigh about 4 kg/km {{Fact|date=July 2008}}.

== Loop elevator design ==
This is a less well developed design, but offers some other possibilities.

If the cable provides a useful tensile strength of about 62.5 GPa or above, then it turns out that a constant width cable can reach beyond geostationary orbit without breaking under its own weight. The far end can then be turned around and passed back down to the Earth forming a constant width loop, which would be kept spinning to avoid tangling. The two sides of the loop are naturally kept apart by [[coriolis force]]s due to the rotation of the Earth and the loop. By increasing the thickness of the cable from the ground a very quick (exponential) build-up of a new elevator may be performed (it helps that no active climbers are needed, and power is applied mechanically.) However, because the loop runs at constant speed, joining and leaving the loop may be somewhat challenging, and the carrying capacity of such a loop is lower than a conventional tapered design.<ref>{{cite web
|url=http://gassend.com/publications/ExponentialTethers.pdf
|title=Exponential Tethers for Accelerated Space Elevator Deployment?
|first=Blaise
|last=Gassend
|format=PDF
|accessdate=2006-03-05}}</ref>

==References==
{{reflist}}

==External links==
* [http://www.elevator2010.org/ Elevator:2010] Space elevator prize competitions
* [http://www.spaceelevator.com/ The Space Elevator Reference]
* [http://science.nasa.gov/headlines/y2000/ast07sep_1.htm Audacious & Outrageous: Space Elevators]

[[Category:Exploratory engineering]]
[[Category:Megastructures]]
[[Category:Space colonization]]
[[Category:Space technology]]
[[Category:Vertical transportation devices]]
[[Category:Space access]]