Page "Mass driver" Paragraph 14

The 40 megajoules per kilogram or less kinetic energy of projectiles launched at up to 9000 m / s velocity ( if including extra for drag losses ) towards Low Earth Orbit is a few kilowatt-hours per kilogram if efficiencies are relatively high, which accordingly has been hypothesized to be under $ 1 of electrical energy cost per kilogram shipped to LEO, though total costs would be far more than electricity alone.

By being mainly located slightly above, on or beneath the ground, a mass driver may be easier to maintain compared with many other structures of non-rocket spacelaunch.

Whether or not underground, it needs to be housed in a pipe that is vacuum pumped in order to prevent internal air drag, such as with a mechanical shutter kept closed most of the time but a plasma window used during the moments of firing to prevent loss of vacuum.