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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Specific Impulse
To compare various propulsion systems and their fuel, rocket efficiency can be
represented by the amount of momentum that can be obtained per unit weight of the
propellant that is used. This is defined as the "specific impulse" (lsp ) and is measured
in units of seconds:
I = Li(m v • .,1w 11s,) = v ,x/11111 S/ (1.5)
,.,, ( )• Li ni g earth g ea 1·1/t
Here, earth's gravitational acce leration, gearth, is 9.81 m/s2 . As described earlier, the
best propulsion system is typically one that has the highest possible exhaust or
propellant velocity. High specific impulse, or correspondingly high exhaust velocity,
also produces low energy efficiency.
Table 1: Specific Impulse for Various Rocket Engine Types
En<1ine Tvpe Ve (m/s) Isa (s)
Saturn V Rocket 2nd and 3rd Staqes 4 130 421
LH 2/LOX Liquid Fuel
Solid Rocket 2, 500 255
Best Chemical Rocket Tested 5 320 542
F2/Li/H2 Chem ica l Rocket
Nuclear Therm al Rocket 8 340 850
Ion Thruster 29 000 3 000
VASIMR 290,000 30,000
The efficiency of a rocket can be defined as the ratio of rocket thrust to the power
required to generate the thrust. The resulting equations follow:
Power = dE 2 (1.6)= ½(dm) Vdt 2 dt e
Thrust = (1.7)(dm)V
dt '
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