AAWSAP DIRD, Aneutronic Fusion Propulsion I, November 2010

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Chapter 4: Antimatter Propulsion
Although the focus of this report is aneutronic fusion propulsion, another possible
propulsion technology involves the use of antimatter. Antimatter is created in certain
nuclear reactions and minute quantities have even been collected from particle
accelerators and stored for a short time in magnetic bottles. Antimatter has the highest
energy density of any material known. When particles of antimatter and matter collide,
they completely annihilate and convert their mass into energy according to Einstein's
famous equation, E = mc2. 10
There are various terrestrial sources of antimatter. Positrons are created
spontaneously from high-energy gamma rays as they decay. Any gamma ray with an
energy of more than 1.022 MeV can decay by pair production where an electron and a
positron are generated. A positron is the antimatter counterpart to an electron and
carries a positive charge. Due to the difference in charge between electrons (13-) and
positrons (13+ ), they can be separated by magnetic fields and the positrons stored.
Certain radionuclides decay through the emission of an antiproton, a negatively charged
antimatter counterpart to a proton. If antiprotons are collected and combined with
positrons, stable atoms of antihydrogen are produced. Antihydrogen has been created
and stored in magnetic bottles. Up to 1012 antiprotons have been successfully stored
for days at a time. Antihydrogen can also be potentially chilled to form liquid
antihydrogen or "ice" to use as a rocket fuel. The specific impulse for antimatter
rockets (Isp/c) are 1 for electron-positron annihilation and 0.60 for proton-antiproton
annihilation. For nuclear fusion, lsp/c is only 0.119, followed by 0.04 for nuclear fission.
Antimatter could be used to heat up a propellant gas and expel it through a Laval
nozzle to generate thrust. If liquid hydrogen is carried onboard the spacecraft, the
electrons and protons in the hydrogen can be annihilated by the antimatter to generate
power. Annihilation products can also be reflected or directed by magnetic fields to be
ejected as exhaust from the rocket to generate thrust. Antimatter is seen as the only
fuel that can potentially accelerate rockets to near the speed of light, providing the
potential for human flight to neighboring star systems.
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