The electrowheel combines the abilities of the capture tube and the electrodynamic tether. It is superior to the rotating orbital pipe and bolo. A sounding rocket carries a projectile and its cargo to the electrowheel. The rocket returns to the Earth, while the projectile rides on the electrowheel and is accelerated to the orbital velocity. The electrowheel is made of aluminum foil held against centrifugal force by piano wires. It is very flexible, so the effective speed of sound in the electrowheel is much smaller than the relative velocity of the projectile, and the electrowheel cannot buckle ahead of the projectile. Three sets of double magnets are attached to the projectile. They induce eddy currents in the aluminum foil and generate magnetic drag which accelerates the projectile. Half of the orbital energy of the electrowheel is transferred to the projectile, while the other half is wasted as heat. The momentum of cargo launched from the Earth is balanced by the momentum of Moon dust launched from the Moon.. No bibliography. The minimum mass of the electrowheel (for 1-ton cargo) is about 1000 tons. The maximum diameter of the electrowheel is limited by thickness of the ionosphere to about 1000 km.
The electrowheel orbits the Earth above the equator and rotates about axis parallel to the Earth rotation axis. This rotation generates centrifugal force which ensures round shape of the electrowheel and increases relative velocity between the electrowheel and the projectile. Electronics control electric current flowing through the electrowheel and thereby also control angular velocity of its rotation and shape of its orbit. Perigee of its bottom edge is at the altitude of 200 km, on the sunny side of the Earth. Atomic oxygen erosion is insignificant because the electrowheel is flat and parallel to the flight path.
The electrowheel is very flexible, so it can be easily rolled-up and transported by a rocket to outer space. Linear density of the electrowheel should be small (a fraction of a kilogram per lineal meter) to increase diameter of the electrowheel and reduce cargo acceleration.
The metal electrotube is made of four parts: funnel, elastic tube, solar cells, and electronics. The funnel and elastic tube are made of aluminum alloy. The funnel guides the projectile into the elastic tube. Magnets mounted on both ends of the projectile generate repulsive force which prevents physical contact between the tube and the projectile. A gyro mounted in the projectile helps stabilize it during flight inside the funnel. The elastic tube has a corrugated shape so that it stretches easily. It is kept straight by centrifugal force of slow rotation. The projectile is coated with a silicone rubber (e.g., Dow Corning 3-6077 RTV) which protects it from heat and vibration. The effective speed of sound in the elastic tube is much smaller than the relative velocity of the projectile. This fact prevents buckling of the elastic tube in front of the projectile. As the projectile slows down, its relative velocity slowly drops to zero. To prevent buckling, the last one percent of the tube length must be rigid. At the end of the flight the projectile moves slowly, so the magnetic drag is weak. Argon gas is released from the projectile to bring it to rest.
The metal electrotube is rather rigid and therefore difficult to transport to low Earth orbit unless it is welded in space from helical strips of sheet metal. It is somewhat dangerous because projectile may collide with the funnel. Its cargo is confined to a slender projectile. The only advantage of the metal electrotube is that it can be made very long to reduce acceleration of the cargo.
Although short electrowheel and short electrotube expose projectiles to high acceleration, they can be used as part of a projectile-rocket relay to transport fragile cargo including people. The projectile filled with rocket propellant is accelerated by the electrotube rather than the gun.
The composite electrotube is made of aluminum foil reinforced with carbon fibers and internal hoops. Obsolete satellites are attached to its ends. The electrotube rotates about its center of mass and is held in tension by centrifugal force. Projectile rides on the outside of the tube. A very cheap composite electrotube, called junk electrotube can be made of space junk.
The hoop electrotube is made of rigid aluminum hoops connected with cables. Obsolete satellites are attached to its ends. The electrotube rotates about its center of mass and is held in tension by centrifugal force. Projectile rides on the outside of the hoops. This electrotube is very flexible, so it can be easily transported by a rocket to outer space.
A tube made of silicone rubber which has cavities filled with mercury or gallium is very flexible, but less durable than the electrowheel and it can transport slender cargo only. The metal funnel is made of telescoping pipes. It is too large and too rigid to be transported by the electrotube, so it has to be transported by a rocket. Metal fittings connecting segments of the rubber tube do not fit inside a slender projectile, so they have to be transported by the rocket as well.
When the projectile enters the rubber tube it releases a small amount of argon gas. The gas inflates the rubber tube and thus ensures that the tube is round. At the end of its journey inside the tube, The projectile slows down to about 300 m/s and hits the end of the tube. The last kilometer of the tube must have additional fiber reinforcement to withstand the impact.
Permanent magnets loose their magnetism upon stress. Superconductivity is destroyed by changing external fields. The only kind of magnet suitable for this application is the electromagnet.
The force of magnetic drag depends on the relative velocity of the projectile, resistivity of the aluminum foil, its thickness, and strength of the magnetic field. The magnetic field can be easily adjusted by changing current flowing in the electromagnet.
Dysprosium and Holmium are ferromagnetic materials distinguished by very low Curie temperature (85K for Dy and 20K for Ho) and high saturation fields. Electromagnets utilizing these materials produce maximum field of about 2.5 tesla. These strong electromagnets are so expensive that they would have to be recycled.
R. H. Kropschot, V. Arp, Cryogenics, Vol. 2, No. 1, 1961.
S. H. Autler, Advances in Cryogenics Engineering, Vol. 6, No. 166, 1961.
B. G. Lazarev, L. S. Lazareva, N. A. Chernyak, et al., "Ultimately high magnetic properties of low-temperature ferromagnets - dysprosium and holmium -- produced by hydrostatic extrusion," FIZ MET METALLOVED+ 86: (3)46-57 SEP 1998.