  A propulsion generated without propellent mass and external forces using a
well known physics is possible theoretically. To do that, it is proposed to use
two specific time-varying and constrained distributions of electric charges
which own a symmetry axis and are adequately separated in space. Total charge
of each distribution is zero. With a relative temporal phase-shift between
them, an asymmetry into the far fields momentum variation rate distribution
along the symmetry axis can be induced. Consequently, an electromagnetic
propulsive force is generated and applied over both charge distributions in a
same direction along the axis-say. Magnetic part of this force is dissipative
because closely related to energy lost by radiation. But its electric
counterpart gives a conservative contribution to the propulsive force with no
associated energy losses at zero velocity. Momentum conservation law for the
entire system; the two charge distributions and fields, is respected because
all far fields; radiation ones and relativistic correction one, are taken into
account. If radiation and other energy losses could be minimized, such a
conservative propulsive force could help to realize fast and long space
journeys.
