Best material for space tethers

Some plastic tethers are very strong but they
may be vulnerable to space radiation and thermal
fatigue. Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.

Characteristic velocity of the strong carbon
fibers is about 2650 m/s. Characteristic velocity
of the strongest plastic fiber, PBO is 2727 m/s.

The aluminum layer can protect the carbon fibers
from oxygen and it can be used as the electrodynamic
tether. A solar powered electrodynamic tether can
replenish the orbital energy of the tether.

It seems possible to use the aluminum as a source
of electric power for a vehicle riding on the
tether. Of course, the aluminum would have to be
hidden inside the tether so that it is not short
circuited by the ionosphere.

More info about strong carbon fibers:
http://www.ias.ac.in/sadhana/Pdf2003Apr/Pe1069.pdf

Andrew Nowicki wrote
Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.

Discover Magazine had a recent article about Dr. Brad Edwards
stationary tether. In that article a researcher from Kentucky was
speculating about carbon nanotubes crosslinked with a "polyester" as a
tether material. I'd sure like like to know what that "polyester" is!
Also I am not sure what the defintion of characteristic velocity is,
but have you looked at M5? The stress displacement curve of M5 dwarfs
HS carbon fiber.

http://www.m5fiber.com/fiber-specs.htm

Andrew Nowicki wrote
Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.

Discover Magazine had a recent article about Dr. Brad Edwards
stationary tether. In that article a researcher from Kentucky was
speculating about carbon nanotubes crosslinked with a "polyester" as a
tether material. I'd sure like like to know what that "polyester" is!
Also I am not sure what the defintion of characteristic velocity is,
but have you looked at M5? The stress displacement curve of M5 dwarfs
HS carbon fiber.

http://www.m5fiber.com/fiber-specs.htm

Tony Rusi wrote:

Discover Magazine had a recent article about Dr. Brad Edwards
stationary tether. In that article a researcher from Kentucky was
speculating about carbon nanotubes crosslinked with a "polyester" as a
tether material. I'd sure like like to know what that "polyester" is!

cyanate ester

Also I am not sure what the defintion of characteristic velocity is,

http://www.islandone.org/LEOBiblio/SPBI1SL.HTM
http://www.islandone.org/LEOBiblio/SPBI1MA.HTM#table

but have you looked at M5? The stress displacement curve of M5 dwarfs
HS carbon fiber.

http://www.m5fiber.com/fiber-specs.htm

Tensile strength and density are the most
important properties of carbon fibers used
in space tether. Stiffness (Young's modulus)
is less important.

Tony Rusi wrote:

Andrew Nowicki wrote
Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.

Discover Magazine had a recent article about Dr. Brad Edwards
stationary tether. In that article a researcher from Kentucky was
speculating about carbon nanotubes crosslinked with a "polyester" as a
tether material. I'd sure like like to know what that "polyester" is!
Also I am not sure what the defintion of characteristic velocity is,
but have you looked at M5? The stress displacement curve of M5 dwarfs
HS carbon fiber.

http://www.m5fiber.com/fiber-specs.htm

Carbon fibre and carbon nanotubes are very different. Carbon nanotubes have
strengths in the hundreds of GPa, carbon fibres have a strength of around 4
Gpa, the better ones more, the worse less.

M5 will be pretty cool stuff if it does what it says, and it's likely to
make the strongest rope known at the moment even at it's present laboratory
5.2 GPa if a rope can be made from it; but even at 9 Gpa, which is still
very theoretical, it's still around 6 times too weak for an elevator with a
reasonable taper.

M5 is quite tough, in the sense that you could abuse it much more than
carbon fibre; but it isn't stronger than the best carbon fibre, and it
doesn't come close to carbon nanotubes in strength; and that ability to take
abuse isn't of any real use in a beanstalk.

Apart from being tough, M5 is also UV-stable, so after climbing ropes it's
probably going to be most useful for making high performance sails. Depends
on creep, stretch, etc.

Spectra is similar-ish in strength (think of the polythene used to keep beer
cans together in six packs. You can stretch it, and it gets thinner and
stronger until it breaks. Do this with polythene that is specially made with
long thin molecules, and stop just before it breaks, and you get Spectra),
as are PBO, Vectran, and even poor old Kevlar.

Another order of magnitude of strength is needed for a beanstalk. Carbon
nanotube is the only known candidate.


--
Peter Fairbrother

Peter Fairbrother wrote:
Tony Rusi wrote:

Andrew Nowicki wrote
Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.

Discover Magazine had a recent article about Dr. Brad Edwards
stationary tether. In that article a researcher from Kentucky was
speculating about carbon nanotubes crosslinked with a "polyester" as a
tether material. I'd sure like like to know what that "polyester" is!
Also I am not sure what the defintion of characteristic velocity is,
but have you looked at M5? The stress displacement curve of M5 dwarfs
HS carbon fiber.

http://www.m5fiber.com/fiber-specs.htm

Carbon fibre and carbon nanotubes are very different. Carbon nanotubes have
strengths in the hundreds of GPa, carbon fibres have a strength of around 4
Gpa, the better ones more, the worse less.

IIRC, single-wall nanotubes, closely packed, defect free get about 230GPa.

Multiwall nanotubes would of course get a bit more, but the density would
be higher.
I looked at theoretical density and strengths of various carbon nanotubes,
and on first inspection, it looked like single-walled tubes of the appropriate
diameter gave the best strength/weight ratio, 230GPa at a density of some
1300Kg/m^3.

Andrew Nowicki wrote in message ...
Some plastic tethers are very strong but they
may be vulnerable to space radiation and thermal
fatigue. Perhaps the best material for the space
tethers is a rope made of strong (6.5 GPa) carbon
fibers coated with a thin layer of aluminum and
fused together in a hot press.
A hybrid composite pultruded rope of Kevlar,M5 and CNT in a tough UV
resistant polymeric matrix.