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This Defense Intelligence Reference Document, dated 1 November 2010, was produced by the Defense Intelligence Agency under its Advanced Aerospace Weapon System Applications (AAWSA) Program. It surveys propulsion technologies that include chemical, ion, and nuclear fission rockets, fusion schemes, aneutronic fusion, and antimatter propulsion. It also covers radiation shielding and speculates on research needs over the next 30 years for missions from low Earth orbit to Mars, Jupiter, Saturn, and Alpha Centauri. The document concludes that aneutronic fusion promises to be an important mechanism for future space propulsion.
UNCLASSIFIED//FIHl 8FFHil.t.k Wfili IH.k\f Long-duration spaceflights will require copious amounts of water for the crew, and water can be used to provide some shielding from neutrons for the astronauts. Shielding material for gamma rays presents a weight problem. Lead is one of the best shielding materials for gamma, but at a cost of about $10,000/lb to launch material into space, lead shielding is expensive to use. The International Space Station and other spacecraft designed for long-term human habitation usually have a small area that is heavily shielded to prevent excessive radiation exposure to the crew during solar events. In addition to the dangers of natural sources of radiation in space that can endanger human health and safety, the propulsion techniques of nuclear fusion and fission generate large fluxes of radiation. Neutron production is of special concern because neutrons can penetrate metals and the structural material of space habitats. The general equations that govern radiation shielding can help develop spacecraft designs that will minimize radiation exposure. The intensity of gamma rays will attenuate according to the following equation: ( 1.17) In equation 1.17, the flux of gamma rays or neutrons, given in particles per unit area per unit time, is represented by ,nrtiat represents the initial flux without the shielding; and μ is the linear attenuation coefficient, a function of the gamma ray or neutron energy and the type of shielding material. The thickness of the material is represented by r. The radiation flux decreases with distance since photons or radioactive particles typically expand outward through a spherical area of 4rrr2 as shown in Figure 3. Equation 1.18 shows the relationship between total attenuation, particle flux, and radiation exposure. Radiation Shielding Material r μ = attenuar,on coefficenl Figure 3. Spherical Radiation Shield Surrounding a Point Source. UNCLASSIFIED//F8A 8FFI&I.«1k Wfi&i a••k>/ 8
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 50 pages are in the text index: search them above, or from the library's search.