One proposed tether system, the Kinetics Interchange Tether (KITE), seems to have more merit than any other. In simple terms, the idea involves towing an aerodynamic payload behind a large subsonic, or low supersonic aircraft with a very long (20 km+) cable.

At high altitude, the aircraft executes a change of direction, and the resulting centripetal action, the intensity of which is dependent on the length of the cable and the rate of turn, will fling the payload into space.

However, no suitable material for the cable exists, but the physics of this method is well-known, and along with mass drivers, offers a simple, and cost effective method of launching payloads into space.

Learn more about Endo-atmospheric Tether on The Alna Space Program & on Tethers Unlimited