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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 QFFI@IAL tt91!! 8flt I Chapter 1 : Concept Overview A flight vehicle's speed and altitude limit its available propulsion options. Traditional air-breathing systems (propeller, turbofan, and turbojet) are typ ically limited to altitudes below 80,000 feet. The existing and planned high-altitude vehicles utilize either high-speed propulsion with ramjet and scramjet engines or slow-speed systems with large propellers. Chemical rockets can operate at all altitudes but have limited burn times and require both fuel and oxidizer to be carried onboard. High-speed air-breathing propulsion, based on ram/scramjet engines, have well known difficulties: external and internal flow compression and shock control; shock-shock and shock-boundary layer interactions in the propulsion flowpath; mixing, ignition, and flameholding in the combustor; incomplete combustion and chemical energy release; and very high temperatures and wall heat fluxes in the combustor. There are limits to what can be done about these problems with conventional technologies, which is why the use of plasma (ionized gas) with or without electric and magnetic fields can offer additional opportunities for control and propulsion enhancement. Onboard generation and storage of electric power is one of the main problems encountered with respect to high-altitude, high-speed flight. Hypersonic vehicles, both air-breathing and unpowered reentry "gliders," have no rotating turbomach inery to which an electrical generator could be connected. An attractive power option can be offered by magnetohydrodynamic (MHD) devices. For example, placing an MHD generator immediately downstream of a scramjet combustor can, given the high velocities and temperature of the flow and with metallic additives to the fuel, provide high power (from tens of kW to several MW) with no moving parts. For reentry vehicles, both external (i.e., surface integrated) and internal-duct MHD generators can generate high power also without moving parts. Employing additional equipment like electrical generators imposes a weight penalty that must be optimized with vehicle performance. The use of electric and magnetic systems can open new potential areas for aerospace propulsion. While chemical energy sources are limited by the energy available for particular reactions and are limited to operating conditions that are conducive to combustion, electromagnetic energy can be added to the flow over a much wider range of operating conditions. For example, at very high altitudes (>150 kft), it is difficult to get reliable combustion in hypersonic air-breathing engines. In an electrothermal system, the combustor would be replaced with an electrical heating source that can easily and reliably add enthalpy to the flow even at low pressure. The flow can also be accelerated by manipulating body forces ( electric and magnetic) on charged particles (ion and electrons) within the flow. Outside the atmosphere, we note that operation in space almost always requires rocket propulsion whether it be chemical, electric, or nuclear. The exceptions would be sails and tethers. Spacecraft are rapidly transitioning from chemical rockets to electric (plasma) for most space-based operations.1 The higher specific impulse (lsp) available for electric systems (2 to 100 times that of chemical) has a dramatic impact on the vehicle design and operation. Although UNCLASSIFIED/ FOR OFFICIAL t,91!! 8HLY 1
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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.