Quote:
Originally Posted by sir_pudding
Not in this case. The straight antimatter rocket probably is better on both counts than the water rocket. It just is really radioactive.
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There is a fundamental physics tradeoff. You can optimize to use less reaction mass per unit thrust, or less energy per unit thrust, but not both. If you optimize for less mass, you necessarily have more energy per unit thrust
Since the reaction mass, and hence its energy content, must be contained in at least some directions to get any thrust out of it, and the energy content of a system is limited by the strength of the materials resisting that energy blowing it apart (the Virial theorem), the maximum thrust to weight ratio you can physically achieve goes down as the energy content per unit thrust goes up.