However, there are several (major!) technical hurdles to be overcome before an antimatter rocket can be built. The first is that antimatter does not exist in significant amounts in nature – at least, not anywhere near the solar system. It has to be manufactured. Currently the only way to do this is by energetic collisions in giant particle accelerators, such as those at FermiLab, near Chicago, and at CERN, in Switzerland. The process typically involves accelerating protons to almost the speed of light and then slamming them into a target made of a metal such as tungsten. The fast-moving protons are slowed or stopped by collisions with the nuclei of the target atoms, and the protons' kinetic energy converted into matter in the form of various subatomic particles, some of which are antiprotons – the simplest form of antimatter. So efficient is matter-antimatter annihilation that 71 milligrams of antimatter would produce as much energy as that stored by all the fuel in the Space Shuttle External Tank. Unfortunately, the annual amount of antimatter (in the form of antiprotons) presently produced at Fermilab and CERN is only 1-10 nanograms (a nanogram is a million times smaller than a milligram).1 On top of this production shortfall, there is the problem of storage. Antimatter cannot be kept in a normal container because it will annihilate instantly on coming into contact with the container's walls. One solution is the Penning Trap – a supercold, evacuated electromagnetic bottle in which charged particles of antimatter can be suspended. Antielectrons, or positrons, are difficult to store in this way, so antiprotons are stored instead. Penn State and NASA scientists have already built such a device capable of holding 10 million antiprotons for a week. Now they are developing a Penning Trap with a capacity 100 times greater.2 At the same time, FermiLab is installing new equipment that will boost its production of antimatter by a factor of 10-100.
A follow-up to ACMF and ICAN is a spacecraft propelled by AIM (antiproton initiated microfission/fusion) in which a small concentration of antimatter and fissionable material would be used to spark a microfusion reaction with nearby material. Using 30-130 micrograms of antimatter, an unmanned AIM-powered probe – AIMStar – would be able travel to the Oort Cloud in 50 years, while a greater supply of antiprotons might bring Alpha Centauri within reach.
Combining antimatter technology with the concept of the space sail has led to the idea of the antimatter-driven sail.
External siteAntimatter and space propulsion (NASA/JPL)
Related entry• nuclear propulsion
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