In this paper, we proposed a totally new mechanism for thrust production, to explain the working of the two reaction-less drives. Namely the EmDrive invented by Roger Shawyer, and the Cannae drive invented by Guido Fetta. The explanation based on a postulated potential or viable momentum deduced from the relativistic momentum energy relation. We assumed that by selectively adding energy to one object of a binary system made of two objects connected by a rigid mass-less rod, a viable momentum would be possessed by this object. We claimed that this will be the inverse of the momentum energy relation. We used the relativistic equivalence of mass and energy to show that the mass of the object where the energy is added will increase. This increase in mass will change the position of the center of mass of the binary system. We postulated that the claimed potential momentum will manifest as a true observable momentum in the direction of center of mass change. The added energy will be absorbed by the object's atoms and manifest as a kinetic energy. And according to the equivalence of all inertial frames of reference dictated by the special theory of relativity the system will be accelerating.