Antimatter-Magnetic Drive

Toward the turn of the 21st Century, powerful new antimatter reactors were being developed on Lunar research facilities. The new research suggested that fusion power could be largely replaced by pure antimatter annihilation. The radiative exhaust from such a device could conceivably produce thrust of its own. However it was quickly realised that the energy form from the antimatter reaction was exactly the most suitable input for powerful end-fire antennas.

In the simplest form, such an antenna can be considered as being two colinear bar magnets of say an inch long. The north pole of one magnet is placed so that it is closest to the south pole of the other magnet. The two magnets are attracted to each other, but there is no net force on the system as a whole. If magnet A is quickly flipped, so that the poles are reversed, it is now repulsed by magnet B. But magnet B will not feel the effect of magnet A until the effects of the reversal propagate to B’s location. The propagation occurs at the speed of light. While the effect of A is propagating, B is still attracted to A, and there is a net force on the system in the direction of A.

The system is actually a pair of magnetic dipole loop antennas, which are driven 90 degrees out of phase and spaced a quarter of a wavelength apart. Apart from the force, there is another effect: each of the magnetic dipoles is an antenna that emits radio waves, and because of their separation and phasing, the waves on one side along their mutual axis will tend to cancel, while the waves on the other side will tend to reinforce. The system has the property of transmitting radio waves in the opposite direction to the net force, and the force is the radiative reaction to the momentum carried away by radio waves.

In the End-Fire Drive the magnets are actually rapidly fluxing magnetic bottles of plasma. The output of an antimatter reaction is polarised which very rapidly flips one of the magnetic bottles at extremely high frequency. The efficiency of the system is such that the drive overall has no difficulty in converting all the mass input into accelerative power. With the force equal to the net radiative power divided by the speed of light. We get roughly 300 megawatts of power for each Newton of thrust. The output of the antimatter annihilation amounts to about 60 billion megawatts, which amounts to 200 MegaNewtons of thrust for each kilogram of matter consumed.

Prototype ships were developed in 2210s, which had powerful antigrav generators that allowed acceleration to push beyond 15G. In effect the End-Fire drive configurations were capable of 100G acceleration if the entire 1 kilo mass was used up in one second to propel a 200-tonne ship. Instead it was used over a period of 6 seconds. The initial six-second burst could take the 200-tonne ship to a velocity of 2500 km/h. With a roughly 16 hour burst and 10 tonnes of fuel, the ship would approach .176 of the speed of light.

Over the following century, burst times for such a flight were reduced, because of the improvement in inertial dampers. 0.176 of c was achievable in just 4 hours by 2272. It was on the basis of such ships that interstellar travel was becoming possible. It was still impractical as it still left Alpha Centauri at the end of a 24-year journey of 10 tonnes of fuel in a 200-tonne ship. Halving the ship's weight did allow for some fast configurations. These were tweaked to the extent that the same fuel could generate about 0.34 of the speed of light in the fastest vehicles of the time. If however the journey could be one-way then it was conceivable that the rate could be pushed to 0.44 of the speed of light.