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This Defense Intelligence Reference Document, dated 21 November 2010, was prepared by the Defense Intelligence Agency's Defense Warning Office under its Advanced Aerospace Weapons System Applications (AAWSA) Program. It reviews propulsion concepts that use weakly ionized plasmas and magnetohydrodynamics for hypersonic flight and spacecraft. It concludes that the Ajax MHD energy bypass concept is meaningless below Mach 12. A reverse energy bypass with a Virtual Cowl is judged potentially practical, and electric propulsion is expected to become standard for spacecraft.
From the source: Release of 2026-09-18 Incident: 11/21/10, 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 magnetohydrodynamic (MHD) and plasma-based concepts for air-breathing propulsion, onboard power generation, and aerodynamic control, arguing that such systems could in principle extend aerospace performance beyond the limits of conventional chemical propulsion and control surfaces. The report reviews concepts including MHD acceleration, flow control, inlet control, onboard power generation, drag reduction, and plasma-generated “virtual” aerodynamic surfaces, while giving particular attention to hypersonic applications such as scramjet power extraction, reentry vehicles, global-strike gliders, and aero-assisted orbital maneuvers. However, it emphasizes major practical constraints, especially extreme power requirements, system weight and complexity, and the difficulty of achieving useful ionization in colder air at lower hypersonic speeds; on that basis, it argues that Ajax-style MHD bypass concepts, in which energy is extracted from the airflow upstream and reintroduced downstream through an electromagnetic system, are not meaningful below about Mach 12, while treating the “virtual cowl” and related reentry applications as more plausible. The document presents plasma and MHD aerospace systems as a technically serious but highly demanding field whose nearer-term promise lies in specialized hypersonic control, power generation, and reentry applications rather than a fully realized air-breathing propulsion system.
UNCLASSIFIED// FOR OFFICIAL "91! er•tY The average energy cost, W;, of ionization varies greatly depending on the ionization method. For example, in conventiona l glow -like discharges of large volume at moderate or high pressure, the ionization cost is ~10,000 eV (i.e., three orders of magnitude higher than the minimum ionization energy [10-15 eV]). This is due to the low average electron energy ( ~ 1 eV) and to the dominant losses of electron energy in inelastic collisions with air molecules. This is why a highly efficient ionization technique must be used in order to give cold air MHD devices a chance to be viable. High-energy electron beams represent such a technique. Generated in vacuum electron guns and injected into air through either thin foil or a differentially pumped window, energetic (>1-50 keV) electrons produce many more low-energy plasma electrons, so that the average ionization cost is only W; =34 eV. This ionization efficiency is theoretically the best. Of course, electron beam systems are quite difficult to work with due to fragile foils or massive differential pumping facilities; X-ray generation is also not helpful for flight applications. But even putting these important practical problems aside, and even with the lowest possible cost per electron, the requirement that a cold-air nonequilibrium MHD device uses sign ificantly less power for ionization than it extracts from (in the generator case) or adds to (in the accelerator case) the flow imposes a severe constraint on the maximum level of ionization and conductivity. Calculations show that the maximum ionization fraction is on the order of 10-6 and the maximum conductivity is on the order of 1 mho/m. With this low conductivity, substantial (5~0.1 or higher) MHD interaction parameters can only be reached with magnetic fields higher than several Tesla (i.e., 10-20 Tesla). The weight and volume of a magnet then makes such flight devices quite impractical, unless a breakthrough in magnet and materials technologies occurs resulting in ultralightweight magnets with B~l0 Tesla. As an example of potential use of nonequilibrium cold-air MHD devices with ionization by e-beams, we note the studies of MHD scramjet inlet control performed by one of the authors of this survey and his Princeton University colleagues. These theoretical/computational studies showed that indeed, with proper optimization, MHD interaction at the compression ramp upstream of the scramjet inlet can restore the shock-on-lip (SOL) condition at Mach numbers higher than the design Mach number for a given fixed-geometry inlet (Figure 6). During the MHD operation, the generated electrical power would be enough for ionizing e-beams, with a sign ificant percentage of the power left to be stored onboard and used for other purposes. The advantage of MHD inlet control is that it elim in ates the need for a variab le-geometry (movable) cowl that wou ld be associated with a large weig ht and complexity; the disadvantage is that the weight and complexity associated with magnets and e-beam systems may negate the advantages. Systems studies are needed to fully assess the practical ity of this MHD inlet control, and results of such stud ies would strongly depend on the state-of-the-art and future advances in lightweight magnet and e beam technology. 1s, 19, 20, 21, 22 UNCLASSIFIED/,EOP AEEJiGJiPd: ~9E 81\L, 14
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 32 pages are in the text index: search them above, or from the library's search.