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i did that 10 years ago with my EM drive, now BAE Systems are rocking half the speed of light with skylon 8 and the eurofighter 2

https://www.youtube.com/watch?v=IeNJ4qOZsxg

still using the general basics of ring magnets, and compress them to increase the retracting force to get alot more power while using the same amounf of power

https://www.youtube.com/watch?v=W2IKoxt16Ro

turning them off/on like a maglev train for propulsion