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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/ /FOA 8FFI@IAL ~S! 8HL I entropy increase and thus, as can be easily shown, to higher lsp. The lsp increase due to the increase in combustor temperature is made smaller by negative factors such as irreversibilities due to Joule dissipation in both MHD generator and accelerator and by the thermodynamically "wrong" work extraction before the combustor. The lsp increase, however, even in optimal cases, is only several percent. Given the crude assumptions in the paper28 ( 1D flow, no boundary layer and heat losses, uniform plasma, no e-beam energy losses, no losses in electric circuitry), this gain of several percent would turn into a loss of l sp in more realistic analysis. Additionally, the weight and complexity associated with magnet and e-beam systems should be kept in mind. Therefore, one can state with certainty that MHD energy bypass at Mach12). First, stagnation temperatures at these Mach numbers are high enough for significant thermal ionization with reasonable amount of alkali seed (0.01-1% by volume), thus eliminating the need for a heavy, complex, and entropy-generating nonequilibrium ionization system. Second, at static temperatures (>2,000K) reached in the combustor at these Mach numbers, there is no combustion per se, just dissociation of fuel and air molecules followed by full or partial recombination into other molecules that releases heat into the flow downstream of the combustor in the expansion nozzle. For such a regime, the group at NASA Ames showed 29, 30 through modeling that MHD bypass can indeed increase the lsp. Note, however, that materials and structures, as well as fuel development, are currently such that air-breathing flight at Mach> 12 is not realistic. In the future, if air-breathing propulsion at Mach> 12 becomes possible in principle, reexamination of MHD bypass benefits and flaws will be warranted, especially if lightweight magnets also become available by that time. THE REVERSE ENERGY BYPASS Returning to Mach< 12, one of the authors of th is survey, together with his colleagues, has proposed a very different bypass concept, dubbed the reverse energy bypass (Figure 8). 31, 32 The energy (in the form of electricity) is extracted from the flow in an MHD generator placed just downstream of the combustor (or collocated with the combustor). This at least avoids the need fore-beam ionization, since the air mixed with combustion products is sufficiently hot right after the combustor that an acceptable electrical conductivity (on the order of 10 mho/m or higher) can be generated thermally, provided alkali metals are seeded into the fuel and are thus present in the combustor and downstream of it. A part of the electrical energy generated downstream of the combustor could be used upstream of the MHD generator, which is why this is called the reverse energy bypass (the energy being bypassed is moved in the upstream direction) . Plasma-assisted combustion (such as ignition, flameho lding, and mixing) would benefit from this electrica l energy. Plasma heat addition, in steady or transient modes, enabled by this electrical power, would be beneficial for control of shock interaction at the inlet and for drag reduction and/or steering and pitch or yaw control when used in front of the vehicle's nose. UNCLASSIFIED} FOR OPP!e!i!CL tl!JE 8HLY 18
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