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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 8PPl€1A:L l191! t>flt I Similarly, if a voltage source (e.g., a battery) is connected to the electrodes placed on either side of the flow in such a way that the app lied e.m .f . acts against the induced Faraday e.m.f., then the current will flow in the direction opposite to the Faraday current, and the jxB force will be in the direction of the flow. This will be an MHD accelerator that converts the battery-supplied electrical energy partially into enthalpy of the flow and partially into Joule dissipation in the circuit . The correspond ing load factor, k, defined as the ratio of the applied electric field E and the product uB, k = E/uB, is greater than 1 in this accelerator configuration. In generator and accelerator devices, the interaction between the induced motion of electric charges across the B field and that field results in an e.m.f. induced along the flow. Th is secondary e.m.f. is called the "Hall e.m.f., " and the magnitude of Hall effect increases with the ratio of electron-cyclotron frequency, ws= eB/m , and the electron collision frequency, v . This ratio is ca lled the electron Hall parameter, ne. As the Hall parameter approaches 1, the Hall current directed along the flow increases at the expense of the transverse Faraday current, resu lting in reduction of the jxB force. To reduce or eliminate the Hall current, the electrodes placed on either side of the fl ow are normally segmented and thus form multiple pa irs. Each electrode pa ir has a proper resistor and/or battery in its circuit. Theoretically, th is segmented -electrode Faraday configuration enables the performance equa l to that without the parasitic Hall effect. However, as the Hall parameter increases, so does the voltage fall between the adjacent electrode segments, so that eventually arcing between the segments starts, effectively negating the advantage of segmenting. A better (and more "natural") MHD configuration at high values of the Hall parameter is the one where each electrode pa ir (with the electrodes on either sides of the flow and right across each other) is shorted, and the voltage is either extracted (in the generator case) or app lied (in the accelerator case) along the flow, between the first and the last electrode pair. This is called the "Hall configuration ." A usefu l dimensionless parameter reflecting the strength of MHD interaction is called the MHD interaction parameter, or the Stuart number, and it represents the ampere body force effect relative to the flow momentum flux: S= aBL pu In this equation, cr is the electrical conductivity of the fluid, B is the magnetic fi eld strength, L is the characteristic linear dimension, p is the fluid density, and u is the velocity. Therefore, for a significant MHD effect in high-speed, high dynamic pressure flow (e.g., in hypersonics), the conductivity and the B fi eld strength must be high . Herein lies the principal problem for aeronautica l MHD applications. Indeed, normal air is not an electr ical conductor. Air does become ionized and thus electrically conducting as it is heated to very high temperatures (3,000- 10,000K or higher), such as those achieved in shock and boundary layers around reentry veh icles, at Mach numbers M= 12- 25 or so. The ionization fraction then reaches 10·5-10·2, and the conductivity from 100 to about 3,000 mho/m ensues. Seeding UNCLASSIFIED/FAA QFFl&lillt ~9E 8HLI 12
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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.