The good news is that colliding antimatter with matter can create the amount of energy and thrust that would enable spacecraft to visit the planets of the Solar System in a period of only a few weeks rather than years, and would open up the possibility of manned interstellar missions.
The bad news is that obtaining antimatter for this type of propulsion system is difficult. The main problem is that antimatter is extremely rare. Antiprotons have been discovered in the Van Allen radiation belt that surrounds the Earth. This amounts to 160 nanograms (one nanogram is one billionth of a gram) of antimatter that could be collected by a plasma magnet to power antimatter spacecraft. It would need at least 30 nanograms of these antiprotons to send a ship to Mars in 45 days, so nearby natural supplies would not last very long.
A more long-term solution is to create your own antimatter, to do this you need an ‘atom smasher’, otherwise known as a high-energy particle collider. They consist of linear or circular tunnels (like the CERN’s Large Hadron Collider) lined with supermagnets, that send particles at close to light speed into a target. On hitting the target antiparticles are produced that can be collected by a magnetic field.
The scale of the problem can be gauged by the fact that with today’s technology only a few shortlived nanograms of antimatter can be produced a year, so it would need a dedicated facility to produce antimatter for space missions.
Assuming the production problems are overcome, an antimatter spaceship could be fuelled with pellets made of uranium with a core of deuterium and tritium isotopes. Beams of antiprotons would be fired at the pellets, resulting in the annihilation of the uranium that would generate enough energy to cause the fusion of the isotopes. The resulting release of vast amounts of energy are confined in a chamber and directed out of a nozzle to direct the thrust of the spacecraft, or the energy could be used to heat a propellant to produce the necessary thrust.
Plasma Core drives are just about within the realms of possibility, but Beamed Core drives would eliminate the need for secondary fuel pellets and be much more efficient. The matter and antimatter would be annihilated in a magnetic nozzle and the resulting energy is ejected out of the engine at near light speed. Accelerating the spacecraft up to 40 per cent of the speed of light, it would make trips to the nearest stars a possibility.