Levitating geomagnetic buckytubes

Fifteen years ago Richard Moss proposed to
levitate a superconductive cable in the Earth
magnetic field. This idea does not make sense
because no existing superconductor can carry
the required current density. Although very thin
superconductive wires can carry high density
current (tin carries up to 2*10^7 A/cm^2), the
maximum current of thicker wires is limited
by the magnetic field produced by the current.
Strong magnetic field destroys superconductivity.

Richard A. Moss, "Use of a Superconductor Cable
to Levitate an Earth Tethered Platform,"
Journal of the Astronautical Sciences, Vol. 37,
No. 4, October-December 1989, pp. 465-475.

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The good news is that buckytubes (also known as
single wall carbon nanotubes) can levitate in
the Earth magnetic field!

Buckytubes have two kinds of crystallographic
lattice: armchair and zigzag. Drawing:
http://www.islandone.org/LEOBiblio/buckytubes.gif

Armchair buckytubes are ballistic conductors, which
means that their electric resistance is relatively
small (6500 Ohms) and independent of length. If the
armchair buckytubes are free of defects, one millimeter
long buckytube has the same electric resistance as a
buckytube that is one thousand kilometers long! Their
maximum current density is about one billion amperes
per square centimeter -- 3 orders of magnitude more
than the maximum current density of copper! Zigzag
buckytubes are more common, weaker, and behave like
semiconductors.

Geomagnetic field above the magnetic equator is
horizontal. Its average induction is 3*10^-5 tesla.
Let us imagine a buckytube loop levitating above
the magnetic equator. The cross-section area of the
loop is one square centimeter. If the loop carries
electric current equal one billion amperes, the
Lorentz force pulls every lineal meter of the loop
with a force that is the product of magnetic
induction and current: 3*10^-5 * 10^9 = 30,000 newtons.
Buckytube density is 1300 kg/m^3, so the weight of
one lineal meter of the loop is 130*9.8 = 1274 newtons.
The Lorentz force levitating the loop is 24 times
greater that the weight of the loop!

The cheapest implementation of the geomagnetic
levitation is an electromagnetic tether made
of buckytubes. It is not clear if the total weight
of the tether, power supply, and ionospheric
contactors will be smaller than its Lorentz force
thrust. A more practical system of transportation
is a stationary buckytube loop hovering at the
altitude of 100 km above the magnetic equator.
Magnetic trains ride on the loop until they reach
orbital velocity. Unlike the skyhook, the geomagnetic
loop does not fail catastrophically when it is broken.