The trick is not requiring propellant. You can’t carry 90 years worth of water or gas. The Dawn spacecraft launched to Ceres in 2007 used up 425kg of Xenon for only eleven days of thrust for its ion engine.
If you let the fission fragments out the back of the reactor you get more thrust than this. (Even if the EmDrive worked).
You still need tons of fuel for that, in the order of tens of tons per year travelled - unrealistic for travel outside our solar system. Thrust doesn’t really matter at that time scale.
The fuel is the reactor fuel. Literally the fission products of the uranium/plutonium in your reactor, from where the power you want to use for the EmDrive comes from, would beat this.
If the EmDrive actually worked, the correct use is to violate conservation of energy and momentum, not as a straightforward substitute for the engines we have now.
If we can turn mass into energy, why can’t we turn energy into mass?
You can, we’ve been doing that for ages. What’s the rest of your question?
Re:The EmDrive just won't die
by doctor_eval on Sunday September 13, 2020 @05:59PM
(#24464281)
But isn’t it consuming energy? Where is that kilowatt going?
What is the “it” here?
EmDrive looks like an accounting error to me, not something that actually works. Any energy it expends turns into heat, radiating in a predictable but not necessarily isotropic way. This radiation carries momentum, but much less than the EmDrive claims to be capable of.
A rocket or ion drive? The energy goes into the kinetic and gravitational potential of the exhaust.
(Aside: kilowatts are power, not energy).
What this would be useful for is (by no coincidence) also the exact reason why it is considered crank science: you could use it to build a perpetual motion machine because it violates conservation of energy/momentum laws.