Doesn't the problem still remain, though, that you're still expelling something from your spacecraft. Sure, it may be more efficient that a chemical rocket, but

Doesn't the problem still remain, though, that you're still expelling something from your spacecraft. Sure, it may be more efficient that a chemical rocket, but are we not still in the conundrum of you have to carry the stuff you're going to expel from your craft to get motive? The article mentions moving a 2600 kg craft with the force of about the weight of 5 quarters, but how much mass of the fuel is expelled to attain that force? How long can that 5-quarter burn last before running out of fuel? Space is pretty empty, but not entirely so, right? Would it be possible to somehow gather the stray atoms & dust that's in a craft's path to "top off the tank"? I know I'm straying into science-fiction area here, but yeah, basically a fuel scoop you might see in say, Elite: Dangerous or Star Gate: Universe (but probably without the part of basically flying into the atmosphere of a star).