I see you are. Unfortunately, there is no such thing as a moving electric field. When you apply charge to your plate, an electromagnetic wave will leave the plate. After it has passed, there will be a field. When you discharge the plate, a new electromagnetic wave will be emitted, terminating the field. The front of a field, so to speak, when it spreads out, is an electromagnetic wave. Likewise the "rear" of a field. Once the field is established, any attractive or repulsive forces will exist between the physical carriers of the field, in your case, the plates. But I'm not saying its not possible to make an electromagnetic propulsion device. A lot of serious reserch is going on in that direction. You must realize, though, that even if you made a device that worked, it would not be any kind of miracle machine; the energy required to take a vehicle to, say, Mars would still be enrmous. The advantage of en EM propulsion device in deep space exploration is that you dont have to bring a physical fuel, and that you can recharge from solar panels. But there are no free rides, you still need lots of energy.