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AN antimatter-aided space drive might bring deep-space missions within our
grasp. Engineers at NASA and Pennsylvania State University say that by the end
of the century, spacecraft could reach the edges of the Solar System and
beyond.

They believe an antimatter drive could lead to a one-year round trip to
Jupiter, a five-year trek to the heliopause鈥攖he boundary separating the
Solar System from interstellar space鈥攁nd, in a 50-year trip, the Oort
Cloud, source of the comets.

Antimatter is a mirror image of the matter we see around us. Its particles
are identical in mass but opposite in electrical charge to their normal
counterparts. Antiprotons can be made in a particle accelerator by smashing very
high-energy protons into one another. When antimatter comes into contact with
normal matter both are annihilated, releasing enormous amounts of energy, so it
must be carefully contained in electric and magnetic fields.

Because making antimatter uses up vast amounts of energy only tiny quantities
can be manufactured today鈥攍ess than 10 nanograms per year. So many
scientists have ruled out an antimatter drive as impractical. But George Schmidt
and colleagues at the Propulsion Research Center of NASA鈥檚 Marshall Space Flight
Center in Huntsville, Alabama, think otherwise.

The key, NASA says, is to get away from the idea that you have to annihilate
antimatter to create propulsive power. Schmidt and his colleagues have
calculated that far smaller quantities of antiprotons would be needed if they
were used to initiate a more efficient hybrid fission/fusion drive.

They studied one scheme, pioneered at Penn State, called antimatter initiated
microfusion (AIM), in which an antiproton plasma is repeatedly compressed using
electric and magnetic fields. A droplet of deuterium and helium-3 is mixed with
uranium-238 and injected into the plasma. 鈥淎ntiprotons create a unique type of
fission, producing six times more neutrons in the uranium than normal fission,鈥�
says Schmidt. These neutrons blast the helium-deuterium mixture, making the
nuclei fuse. Hot fusion products create thrust.

An AIM drive needs between 1 and 100 micrograms of antimatter per
mission鈥� depending on the speed required
(see Table). Such quantities seem
huge now, but researchers at the Fermilab accelerator centre near Chicago are
doubling their output of antiprotons every year, says Elvin Harms of Fermilab鈥檚
Antiproton Source. But over the next century, microgram quantities are 鈥減robably
not out of the question,鈥� he says. Schmidt also expects private companies to
start making antiprotons for new types of medical imaging.