AAWSAP DIRD, Aneutronic Fusion Propulsion I, November 2010

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Appendix C: Antimatter Annihilation Rocket
•'• .
positron
antiproton
stable antihydrogen atom
Figure 16. Antihydrogen Atom.
Using data from Table 3, the only propulsion system that can generate higher l sp than
fusion will be due to antimatter annihilation. By using the Relativistic Rocket Worksheet
in Appendix D, it is possible to decrease the time to reach Proxima Centauri to only
18.5 years by accelerating at 0.05 g to reach 43% of the speed of light. By using
antihydrogen, two annihilation mechanisms are possible:
•
Electron-positron annihilation releases one energetic gamma ray (1.022 MeV) or, in
the presence of a nucleus, two 0.511-MeV gamma rays. There is no effective way
to reflect gamma rays, but they can be absorbed with suitable shielding and their
energy converted into heat.
Research into designs that convert gamma ray heat
into propulsion or electrical power should proceed over the next 10 to 20 years.
•
Proton-antiproton annihilation releases charged and neutral pions, which decay after
about 0.026 microseconds into charged muons and neutrinos. The charged pions
can be used to directly generate thrust or to make electricity if they are directed by
electromagnets. Unfortunately, 40% of the pions will be neutral and quickly decay
into gamma radiation, which are lost from the system or absorbed in the rocket
chamber wall and generate heat. Muons also decay into charged particles (electrons
and positrons), along with neutrinos. Neutrinos and antineutrinos, along with their
energy, are lost from the system.
Novel rocket designs that capture gamma
radiation with a tungsten insert allow the waste heat to be used to accelerate a
propellant, such as hydrogen, to generate additional thrust.
This system was
proposed by Robert Frisbee and Ulrich Walter and deserves further study. 24 Efficient
ways to redirect the energy of gamma rays into thrust should be a major focus of
research.
Antimatter propulsion is fairly straightforward since ignition is not a problem. By
mixing hydrogen with antihydrogen, annihilation begins immediately. Antimatter
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