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For example, when an instantaneous force change is applied to one end of a very long cable, the end does not stretch a little, it moves, and keeps moving until the force has had time to propagate to a stationary attachment and back. For a 100km stabilization cable, and a 10km/s speed of sound, that can be 20 seconds, in which time many meters of cable moves.
For example, when an instantaneous force change is applied to one end of a very long cable, the end does not stretch a little, it moves, and keeps moving until the force has had time to propagate to a stationary attachment and back. For a 100km Kevlar 49 stabilization cable, that can be 22 seconds, in which time many meters of cable moves.
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note: Nanotube properties are controversial.  The CTE simulation [[ etd.lib.fsu.edu/theses/available/etd-08262005-003434/.../Thesis.pdf | Prakash ]] is used here, but other simulations differ wildly. note: Nanotube properties are controversial.
The CTE simulation by [[ htp://etd.lib.fsu.edu/theses/available/etd-08262005-003434/.../Thesis.pdf | Prakash ]] is used here, but other simulations differ wildly.

Linear Cables

Stabilization and elevator cables on the launch loop are very long, and propagation delay is a big issue. In most systems people are familiar with, cables are short enough and forces change slowly enough that propagation delay is not a major issue. With a launch loop, forces can change rapidly (milliseconds) while the propagation delays are 10s of seconds.

For example, when an instantaneous force change is applied to one end of a very long cable, the end does not stretch a little, it moves, and keeps moving until the force has had time to propagate to a stationary attachment and back. For a 100km Kevlar 49 stabilization cable, that can be 22 seconds, in which time many meters of cable moves.

Material

density

elastic

strength

CTE

Vsound

Support

100km

Therm exp

notes

modulus

Length

Round Trip

100Km*100K

gm/cm3

GPa

GPa

um/m-K

km/s

km

seconds

m

Steel SAE980x

7.9

200

0.65

12

5.0

8.4

40

120

Pure Kevlar

1.44

124

3.62

-2.7

9.3

250

22

-27

Pure Spectra

0.97

168

2.58

-12

13.2

270

15

-120

continuous creep

Pure Diamond

3.52

1140

>60

1.2

18.0

1700

11

12

Pure nanotube

~1.4

~1000

~60

-9?

26.0

4400

8

-90

composites:

80% Kevlar

80% Spectra

80% nanotube

note: Nanotube properties are controversial. The CTE simulation by Prakash is used here, but other simulations differ wildly.

LinearCables (last edited 2009-08-14 20:56:24 by KeithLofstrom)