Procession Drive

The procession engine is by far the most effective means of sub-light travel available. It supercedes the Antimatter-Magnetic Drive, however it is a much more sophisticated technology and remained very expensive, until around 4100. The first such drives were prototyped in 2612, although remained experimental for decades. Production craft using the drive began to appear in the 2680s, but still remained a highly specialist category. They became more common by the 2800s.
The technique produces a generous propulsion of 300 to 600 kG without exaust for most ships. The technique is very simple in words, but very complex in ideas. At the core of design is a mass generator. It produces one enormous, very dense mass in front, and one enormous, very dense antimass behind. The positive mass is attached to the gravhull with a gravity tether, while the negative mass is monitored and modulated to keep it from wavering (some spectacular accidents have resulted from a machine failure to do this). The positive-mass body attracts the negative-mass body, while the negative-mass body repels the positive-mass body. The pair would accelerate itself off to infinity if it were not for a few limiting factors:
1. The masses are not real in the sense of stars and things, they are curvatures in spacetime, and so require energy to maintain. This maintenance energy becomes greater as the ship approaches light speed due to mass dialation.
2. The masses themselves approach lightspeed and so more and more of their energy is devoted to their own mass accretions
3. Higher speeds such as 0.8 and 0.9 of light are near impossible as the space curvature becomes so large in the procession chamber that no engineering materials will prevent the ship from tearing itself apart.
Clearly then, we are left with about 0.75 of light as the fastest conceivable sub light velocities. Such speeds still make most interstellar travel a six-year journey however, most interplanetary travel could be done in a matter of hours.