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Magnetic Propulsion of a capsule travelling in a tube is quite simple. It is provided by an Electromagnet, in the basic form of a Coil of Copper Wire wrapped around the tube.
Electricity can be effectively generated by a Solar Panel (or series of Solar Panels) attached to the surface of the Tube (or Solar PAINT applied to the surface). This Solar Panel would generate electricity from daylight. The electricity generated can be stored in a battery, or series of batteries attached to the Tube surface.
A Speed-Sensor would calculate the speed of a passing Capsule. If the speed is below the speed specified for the Tube, the sensor would trigger a switch to allow a pulse of electricity supplied by the Battery to pass through a Coil in front of the Capsule, generating a momentary Magnetic Force that would accelerate the Capsule.
A similar arrangement can be used to slow down a Capsule that happens to be travelling above the prescribed speed.
Of course every Capsule would be initially launched into the Network from a stationary position by means of Magnetic Propulsion, with or without the assistance of Gravity.