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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/ /FAA QFFl&IsTiL ~SI! 8flt I electric (plasma) thrusters have been around for decades, their use in space was limited by the electric power available onboard the spacecraft. 2 The advent of high-power solar arrays has made systems from a few kW to tens of kW practical. Chem ical systems will probably always be the primary choice for getting vehicles into space. The thrust levels for electric systems are too low to be practical for that purpose. Chemical and electric (or electromagnetic) propulsion systems have intrinsic differences. For example, chemical propulsion is "energy limited" because the chemical reactants have a finite amount of energy per unit mass (i.e., their enthalpy of combustion or reaction), which ultimately limits their ach ievable exhaust velocity. However, because the propellants are their own energy source, the rate at which energy is supplied to the propellant (which is ultimately limited by the reaction kinetics) is independent of the mass of propellant, so very high powers and thrust levels can be achieved. By contrast, electric propulsion systems are typically not energy limited; an arbitrarily large amount of energy can be delivered (from the external solar, nuclear or chemical power system) to a given mass of propellant so that the exhaust velocity can be an order-of magnitude larger than that of a chem ical system . Instead, electric propulsion systems are "power limited" because the rate at which energy from the external source is supplied to the propellant is proportional to the mass of the power system. This has the result of limiting the thrust of the electric propu lsion system for a given vehicle mass. Because of this, electric propulsion vehicles are typically low thrust-to-weight (T/W) ratio (i.e., low acceleration) vehicles. WEAKLY IONIZED PLASMAS FOR PROPULSION APPLICATIONS This review is devoted to a group of emerging technolog ies centering on weakly ionized plasmas for propulsion and power. 3 Charged particles (ions and electrons) must be present in the flow so that it can interact with applied electric and magnetic fields. Space thrusters operate at very low pressures ( < 100 mTorr or < about 2 psi) with a significant fraction of the working fluid/gas being partiall y ionized (from a few percent to nearly 100 percent) . In contrast, air breathing systems operate at much higher pressures and have low ionization fractions. The ionization fraction of concern (i.e., the fraction of gas molecules that are ionized) ranges from as low as 10-s to 10-2, hence the term " weakly ionized." The gas pressure in the plasmas can take almost any value. In applications to high-altitude flight, the static pressure is on the order of 10-100 Torr, whereas combustion applications demand near-atmospheric ( ~760 Torr) or above-atmospheric pressures. The temperature of the gas can be near-ambient in low-pressure glow discharges, rising to 5,000-10,000K in arc or high-pressure microwave discharges, or even 20,000-30,000K in laser-generated sparks. The plasmas can be generated by electric or electromagnetic fields, from DC to RF, short pulses, microwaves, and optical (laser) beams, or by various combinations of the above. In general, low pressure plasmas tend to be uniform (diffuse) and nonequilibrium. The temperature of electrons and internal molecular modes can be very high, while the gas as a whole stays relatively cold. As the pressure and power loading increase, plasmas tend to become hotter, getting closer to thermal equilibrium, and also break into channels (streamers and arcs). The reality, however, is more complex. In some devices, such as dielectric barrier discharges, nonequilibrium plasmas are generated even at atmospheric pressure, UNCLASSIFIED/FQA &FFIElsllL ~SE et•t I 2
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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.