Why would you want to use a magnetic catapult on earth to get you to 1000kph on earth? You'd still need a lot of rocket to get you the rest of the way to orbit. It probably be simpler and cheaper to just use rocket exhaust to get you to 1000kph. Rocket fuel is not really that expensive, but a shiny new EM Cat could cost many billions in construction including the dedicated power planet before you launch anything. (while we're looking at long term projects we might as well go for a Single-Stage-To-Orbit spaceplane instead of two stages.)

An EM Cat would probably be much more useful on the moon. Besides using it to launch from the moon it might be designed for braking incoming vehicles as well.

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"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau