### GEOMAGNETIC LEVITATION

A superconductive cable anchored in the Earth carries an electric current of great density. The Earth magnetic field generates Lorentz force which levitates the cable. An elevator attached to the middle of the cable transports cargo. Lightning, wind, and icing can break the cable. Geomagnetic levitation of a superconductive cable is impracticable 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.

#### BIBLIOGRAPHY

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. The good news is that armchair buckytubes can levitate in the Earth magnetic field. 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 electrodynamic 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 practicable 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.