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.

UNCLASSIFIED//POlt Offl@IAL WS& &NkY
Chapter 1: Theory
ROCKET PRO PU LSION
It is difficult to compare propulsion technology without talking about how objects are
accelerated in space. Within Earth's atmosphere, aircraft use the air to generate lift
and thrust. Propellers or turbofans move a mass of air rearward and Newton's second
and third laws require that the momentum in this exhausted air is equal to a thrust in
the opposite direction. In equation form, the thrust, F, is equal and opposite to the
change in momentum over time.
m d(mv'F =- _ ' / e..x.lrausr ( 1.1)
dt
The momentum of the exhausted air is equal to the mass of air times its velocity and is
provided by the propulsion system. The thrust can be used to accelerate a payload
according to the following equation:
w m
F = m payload a (1.2)
Here, thrust is equal to the payload mass times its acceleration.
This method of momentum transfer works well for aircraft operating within the Earth's
atmosphere; however, operating in space presents special problems. Space is nearly a
complete vacuum, and there is no air mass to accelerate, i.e., no "reaction mass" that
can be accelerated and exhausted at high speeds. In space, the reaction mass is
carried by the rocket in the form of propellant mass, which is expended as the rocket
accelerates.
m m dm m
F = ma +-V (1.3)
dt
In this equation, the thrust is provided by the momentum ejected from the rear of the
rocket, but the total mass of the rocket is decreasing as the fuel is burned up and as
propellant is lost. Examining equation 1.3, we see that there are two ways to increase
rocket thrust. The first is to increase the mass flowrate, dm/dt, typically measured in
kg/s (if mass flowrate is given in kg/s, then thrust, F, is given in newtons to maintain
consistency). Unfortunately, this requires carrying increasing quantities of fuel. For
flights to Mars, the outer planets, or to other star systems, it would not be possible to
carry such large quantities of propellant.
A second choice would be to increase V, i.e., the velocity of the ejected propellant
reaction mass. There is an upper limit, however, to how fast we can eject the propellant.
In his Special Theory of Relativity, Albert Einstein demonstrated that no object that has
any mass when at rest can be accelerated beyond the speed of light or 2. 998 x 108 m/s
in a vacuum. Einstein's relationship between an object's mass (m), its velocity (v), and
the speed of light, (c) is given in equation 1.4:
UNCLASSIFIED/fF&A &FFI&I:.l.k W&li &NkY
1