> They push mass of gas out the back, when there
> is no more gas (fuel) left they are worthless.
> An ideal solution is to provide thrust from energy
> alone, so thrust can be maintained indefinitely
> provided the vehicle has energy. To date it
> hasn't been done, although many are trying...
> -Roman

Aren't they looking at dark matter or interstellar hydrogen
as fuel ? Suck it in at the front, blow it out the back

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