the tube is not exactly along the flight path of the shell, but slightly below it, as the shell passes through it the shell will be forced downward, thereby producing an upward force on the tube. To stay aloft, the system would require the shells to be fired continually. The launch loop is essentially a continuous version of this concept. Instead of a cannon firing a shell, a mass driver accelerates a cable into a similar trajectory. The cable is surrounded by an evacuated tube, which is held aloft by pushing down on the cable using electromagnets. When the cable falls back to Earth at the other end of the trajectory, it is captured by a second mass driver, bent through 180 degrees, and sent back up on the opposite trajectory. The result is a single loop that is continually travelling and keeping the tube aloft. To use the system as a space launcher, a launch loop would be about 2,000 km long and 80 km high. The loop would be in the form of a tube, known as the sheath. Floating within the sheath is another continuous tube, known as the rotor which is a sort of belt or chain. The rotor is an iron tube approximately 5 cm (2 inches) in diameter, moving around the loop at 14 km/s (31,000 miles per hour). Keeping the system aloft requires a significant amount of lift, and the resulting path is much flatter than the natural ballistic path of the rotor. Due to the possibility of the loop failing and falling to Earth, it is normally considered as running between two islands outside of heavy shipping routes. Ability to stay aloft When at rest, the loop is at ground level. The rotor is then accelerated up to speed. As the rotor speed increases, it curves to form an arc. The structure is held up by the force from the rotor, which attempts to follow a parabolic trajectory. The ground anchors force it to go parallel to the earth upon reaching the height of 80 kilometers. Once raised, the structure requires continuous power to overcome the energy dissipated. Additional energy would be needed to power any vehicles that are launched. Launching payloads To launch, vehicles are raised up on an 'elevator' cable that hangs down from the West station loading dock at 80 km, and placed on the track. The payload applies