re: Discussing Aliens/UFOs on Tucker

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For a spacecraft to acquire a speed of c/10, it would need to acquire kinetic energy, given accurately enough by the non-relativistic formula of 1/2mv2. For a very small unmanned spacecraft of 10 kg, it would require 1/2 x 10 kg x (3 x 107 m/s)2 = 4.5 x 1015 J.

For a manned spacecraft weighing several tons, the energy requirements would exceed the world’s annual electricity consumption. For the city-sized space ships, the energy requirements would be even more staggering. And when the spacecraft slows, it would need to use up almost this amount of energy in braking. If the spacecraft had to accelerate to c/10, slow down and start up many times. It is hard to imagine how enough fuel could be carried. It would probably be impossible without some sort of antimatter drive. If complete conversion of matter to energy (E = mc2)—were possible, 1 ton of antimatter could annihilate 1 ton of ordinary matter to produce. And this is the absolute maximum amount of energy which could be produced even in principle from a given mass of fuel. A spaceship would be nowhere near as efficient.

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