AAWSAP DIRD, Aneutronic Fusion Propulsion I, November 2010

This Defense Intelligence Reference Document, prepared in fiscal year 2010 by the Defense Intelligence Agency's Defense Warning Office under the Advanced Aerospace Weapon System Applications (AAWSA) Program, reviews aneutronic fusion as a way to propel spacecraft. It compares chemical, ion, fission, fusion and antimatter propulsion, and it also covers radiation shielding and relativistic rocket calculations. It looks at research needs over the next 30 years for missions from low Earth orbit to Mars, Jupiter and Alpha Centauri.

From the source:Release of 2026-09-18 Incident: 11/1/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys aneutronic fusion as a possible advanced space-propulsion method, focusing on fusion reactions that release most of their energy in charged particles rather than neutrons and therefore offer potential advantages over more neutron-intensive fusion concepts, especially in radiation shielding, direct energy conversion, and thrust generation. The report reviews the underlying rocket physics, compares candidate fusion fuels and ignition conditions, and gives particular attention to proton-boron and related schemes, while also discussing Bussard’s concepts and other fusion projects as representative development paths. It also makes clear that the central obstacle remains ignition and sustained net-energy fusion under practical conditions, and it notes additional problems such as x-ray energy losses from the hot plasma, extreme temperature requirements, and the gap between theoretical specific impulse and what proposed systems had demonstrated experimentally. Overall, the document presents aneutronic fusion propulsion as an attractive long-range concept for deep-space travel, but one whose practical realization still depended on major unresolved advances in fusion engineering.

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Chapter 2: Nuclear Fusion Rocket Design
CLASSIC NUCLEAR FUSION SCHEMES
Nuclear fusion, which powers the Sun and the stars, begins with the collision of two
lightweight atomic nuclei to create two new particles with the release of energy. As an
example, if two specific isotopes of hydrogen (tritium and deuterium) were to collide,
the reaction would produce a neutron plus an alpha particle (ionized helium nucleus).
(2.1)
The 17.6 MeV of energy is split between the kinetic energy of the neutron (14.1 MeV)
and the helium nucleus (3.5 MeV) based on conservation of energy and conservation of
momentum. The kinetic energy is eventually converted into heat in a fusion reactor.
The 14.1-MeV neutron will penetrate far into lead or steel shielding and can cause
considerable material damage. The ion ized helium nucleus, however, will not go very
far through any material without being absorbed and dissipating its energy as heat.
There is a novel way to capture the energy from the ionized nucleus. As shown in
Error! Reference source not found., a magnetohydrodynamic (MHD) generator can b
e used to harness the energy from the helium ions and convert it directly into electricity.
The electricity could be used to power an ion drive on a spacecraft or provide power for
life support. Equation 2.2, known as the Lorentz force equation, illustrates which
parameters are involved and how they are related:
F = e (Vx B) (2.2)
Electodes on the Top and
Bottom of the Channel
Carry Electrica l Curre nt
Away
Di rection of the Magnetic Field, B
Path of Ions
Between the
Magnets
Generate the Magnetic Field
Figure 5. Schematic Design of a Magnetohydrodyanamic (MHD)
Generator.
The velocity (V) of the ions interacts with the magnetic field (B) and forces positively
charged ions to move downward in the channel to an electrode where they impart an
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