Antimatter Rockets in Science Fiction

Antimatter is one of the mainstays of science fiction. There are very few self respecting star ships on TV or in the movies that do not power their warp drives with antimatter fuel; Star Trek’s USS Enterprise, for example. While warp drive, another science fiction device that permits fictional star ships to travel faster than the speed of light, may never be built, antimatter is real and is already being considered as a fuel for propelling space craft at rapid velocities.

Antimatter is simply the opposite of normal matter of which the universe is made of. An antimatter atom would have positively charged positrons instead of negatively charged electrons and negatively charged antiprotons instead of positively charged protons. Until recently, the existence of antimatter was considered a theory, developed by British scientist Paul Dirac. But Carl Anderson discovered positrons in 1932, demonstrating that antimatter actually existed. In 1955 researchers created an antiproton at the University of California at Berkley Bevatron. Later, scientists at CERN, the European Organization for Nuclear Research, created the first anti hydrogen atom. Nine were created, each lasting 40 nanoseconds.

When an atom and an anti atom come into contact, both are totally annihilated in an explosion, emitting pure radiation. The explosion would be more powerful than any created by a thermonuclear bomb. If harnessed, such a reaction could prove to be one of the most efficient propulsion methods imaginable. It would be one thousand times more powerful than a fission reaction and three hundred times more powerful than a fusion reaction.

There would be three main components to an antimatter rocket. First, a magnetic storage device would have to contain the antimatter until it is ready for use, since any contact with matter would cause a premature explosion. Then a feed system to introduce the antimatter to a matter target would be needed, to cause the explosion. Finally, a kind of magnetic nozzle would be required to focus the released energy out the stern of the rocket, propelling that vehicle.

In theory, an antimatter rocket with a tiny amount of antimatter fuel could reach Mars in as little as six weeks. This contrasts with trip times of six months to a year using conventional chemical rockets.

There are, of course, a number of problems standing between us and the possible era of interplanetary travel using antimatter rockets. This is besides the obvious technical difficulties of building and operating such a vehicle.

The first impediment is the sheer cost of producing antimatter. Manufacturing anti protons in a particle accelerator costs about 62 trillion dollars a gram. Moreover, such methods produce infinitesimal amounts of antimatter. According to CERN, the amount produced in a particle accelerator in a year would power a 100 watt light bulb for fifteen minutes.

The late scientist and writer Robert Forward suggested building dedicated “factories” for producing antimatter. He theorized that the cost could be brought down to about 10 million dollars a milligram, given proper engineering.

Another problem is that many antimatter/matter reactions result in a great burst of gamma rays. Gamma rays penetrate matter, break apart molecules in human cells, and make the material in one’s engines radioactive. Gamma rays are difficult to shield against and are unhealthy and dangerous to be exposed to.

Fortunately a team of scientists, funded by NASA’s Institute for Advanced Concepts, is designing an antimatter rocket engine that would produce far fewer gamma rays and lower power. It does this by bombarding matter with positrons rather than antiprotons, as is the case in previously considered antimatter engines. Gamma rays produced with positrons have about four hundred times less energy than those produced with antiprotons.

One advantage of an antimatter rocket powered with positrons is that it is safer than other high energy technologies, such as a nuclear powered rockets. If a nuclear powered rocket were to explode in flight, it could release radioactive particles in the atmosphere, possibly contaminating a wide area. An accident involving an antimatter rocket would result in a small burst of gamma rays confined to a small area, about a kilometer, around the vehicle.

Creating positrons to power an antimatter rocket is potentially less expensive as well. It is estimated that with current technology, ten milligrams of positrons would cost about a quarter of a billion dollars. However more research and development should drive that cost down considerably.

Whether the first astronauts to venture to Mars and beyond in an antimatter rocket depends on how promising research and development of such vehicles turn out to be. But it would be ironic if such explorers were to brave the void between the worlds, using the same fuel that powered the star ship Enterprise.

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