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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are 800 keV and 300 keV, respectively, much higher t han t he 50 keV required for D-T
neutroni c fu sion.
/H 0 m /He
~ 0 / ffi /H e
/1 B @ / ~ m /He
3x /He+8.7MeV
Figure 10. The Fusion of Hydrogen-1 and Boron-11 Produces Three Alpha Particles
Fortunately, both lithium-6 and boron-11 are readily available, while tritium must be
manufactured due to its 12.6-year halflife. Lithium-6 represents 7.5% of all lithium on
Earth. Lithium is mined at Silverpeak, Nevada.
Another concern in choosing an effective aneutronic fusion scheme is bremmstrahlung,
or "braking radiation." This term refers to the x-rays emitted as electrons pass through
metals and interact with electrons in the outer shells of the metal atoms. In order to
ignite a fusion reaction, the gases must be heated to the point where they ionize and
form a plasma. Electrons stripped from the ions in the plasma will interact with the
walls of the chamber that house the plasma and bremmstrahlung x-rays will result.
Bremmstrahlung is a parasitic process that decreases the temperature of the plasma
and reduces the chance of fusion. While the two favored fusion schemes, p-Li6 and p
B11, can generate significant bremmstrahlung losses, there are techniques proposed
using electromagnets to direct both electrons and ions to minimize x-ray production.
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