Everything in science starts out impossible. It doesn't even get considered in science unless it has a chance of being impossible. Then it is up to the scientist to demonstrate that it is possible and explain how it is possible.

Edit:

The 1) demonstrate and 2) explain parts are critical and it's not science unless you have 1). Preferably 2) also. EM has neither to match the magnitude of the claims until they can push something across the solar system and back (such that loss of mass is ruled out and the propulsive effect is without a doubt not instrument error).