Even Farther In the Future
Also between 2020 and 2050, scientists may harness antimatter (matter identical to ordinary matter but opposite in electrical charge) to power spacecraft. The first attempts at this technology will probably involve using small amounts of antiprotons, the antimatter equivalent of protons (positively charged particles in the atomic nucleus), to trigger a tiny fission reaction. This fission reaction could in turn ignite a fusion reaction.
After 2050, scientists may be able to build a type of solar sail powered by laser energy. Instead of using the weak push of sunlight, these “laser sails” would be driven by light from powerful lasers in orbit around the Earth or sun. Using lasers with enough power, laser sails could accelerate to speeds approaching the speed of light.
Scientists will also probably have to wait until after 2050 before making significant progress on the ultimate method of space propulsion: matter-antimatter annihilation. Though still only a theoretical possibility in 2000, matter-antimatter annihilation would provide a much higher exhaust velocity than any other known type of propulsion system. In this type of propulsion, protons would be collided with antiprotons, and the two forms of matter would destroy each other with a tremendous release of energy. The annihilation reactions would also generate positively charged subatomic particles called pions, which could be deflected by magnetic fields to produce thrust with an exhaust velocity of about 33 percent of the speed of light. This is the type of performance required for fast interstellar missions. However, such missions would require tons of protons and antiprotons. In 2000, antiprotons were extremely difficult to produce and store, making this system little more than a future vision.