Magnetic levitation trains

[Ruslan Sharipov]

Magnetic levitation trains accelerated in a vacuum tunnel can be used as space vehicles
instead of rockets. Do you know why this idea is not discussed anywhere?

[A_M_Swallow]

The thread you are looking for is called "magnetic propulsion" and is in the "The Lifter" forum.
http://www.liftport.com/forums/index.php?topic=691.0

[neil]

Some problems are: The fastest magnetically levetated trains so far are about 300 MPH = miles per hour, while orbital speed in low Earth orbit is over 17,000 MPH. If t = 2500 seconds and a = 1/3 g = 10 feet per second per second: v = at = 10 times 2500 = 25,000 feet per second, which is about orbital speed. The vacuum tube needs to be s = 1/2 at squared = 5 time 62,500,000 = 312,500,000 feet long. Accelerating at ten g is deadly for humans, plus requires enormous amounts of energy. This reduces the tube length to a bit over ten million feet which is still too long. The vacuum tube needs to allow the space craft to exit at at least 200,000 feet to avoid white hot due to air friction at this speed. Also large amounts of air rush into the vacuum tube when it is opened to allow the space craft to exit. A large cost is needed to pump the tube to high vacuum for the next launch. Major technological advances are needed, however mag lev may work for the first 1000 feet and uses a second stage rocket to get the rest of the altitude and speed.   Neil