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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/ /FAR OFFICI Ck W&i 8HLV axis positioning of the plasma region would create steering or pitch/yaw control moments. 42 An attractive application that utilizes this plasma/MHD-enabled increase in L/D is orbit inclination changes for space assets. Even a modest (a few degrees) orbit inclination change requires a very large amount of delta-velocity and energy and thus a very large amount of fuel to be burned. If the space asset dives into the upper atmosphere (to altitudes of 200-300 kft), it can use aerodynamic turning (sim ilar to airplanes), provided the L/D ratio is high enough. Unfortunately, hypersonic L/D, especially in rarefied air at high altitudes, is not much higher than 1. Plasma and MHD technologies hold substantial and realistic promise to achieve hypersonic L/D of 3-10, which would be a game-changer and enable, among other missions, aerodynamically assisted, on-demand orbital inclination changes . We now briefly consider another MHD application : a hybrid chem ical/MHD propu lsion. The nozzle exit velocity of chemical systems (air-breathing and rockets) is limited by the chemical energy available from the fuels/propellants and the temperature limits of the system materials. One method to increase the exit velocity of the system is to add an MHD accelerator system to the nozzle. The flow is first accelerated using a conventional gas dynamic converging diverging nozzle and then the MHD system further accelerates the supersonic flow in the diverging portion of the nozzle. Many ground-based systems have been developed and tested to accelerate flows using MHD systems. These have been primarily either proof-of-concept systems or for hypersonic wind tunnels. 43 • 44 Systems have been proposed for both small in-space systems45 , 46 and for large engines for launch vehicles. 47 While this concept has great potential and the accelerator physics are well established, it has several practical limitations. To be efficient, the energy added to the flow from the MHD system should be on the order of or greater than the energy added by the chemical stage . This requires power levels that are not available on either type of vehicles. For example, for launch vehicles the jet power levels would be in the hundreds of MW to tens of GW range. The low ionization fractions in the flows also severely limit the thrust efficiency of the MHD systems to a few percent. This combined with the large jet powers requires enormous launch -vehicle powers. Similarly for space systems, a better solution would be to use the available power in a more efficient electric thruster. The large powers also require large masses for the MHD system components for reasonable specific mass (kg/kW). To be comparable to pure electric systems on spacecraft, the MHD augmentation system specifi c mass would need to be improved by a factor of 1,000 over state of-the-art technologies. 48 One potential solution around the power issue is to beam the power to the vehicle. 49 Another serious issue is the magnets needed to provide the 2- to 40-Tesla fields required. In many cases, the weight of the magnet and magnet power supply wou ld exceed the veh icle mass usin g existing technology. The magnet system mass will need to be reduced by several orders of magnitude to make flight systems practical. UNCLASSIFIED/FOR OPP!e!ftt tl!E 8HLV 22
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