I see this is no ordinary sled.=20

How about a tesla coil flash along the length of the acceleration
portion of the sled's track and have an inward shaped cone at the back
end of the sled to get the most propulsion from the thrust.

Check with the producers of back-to-the-future if they'll let you have
the flux capacitor. You may need power in the giga-watt range.

On second thought, can the sled's track be vertical? Make a really tall
channel and let the sled free-fall in it.

Shahid

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