AAWSAP DIRD, MHD Air Breathing Propulsion and Power for Aerospace Applications, November 2010

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 OFFICIAL USE ONLY
the temperature range, a moderate seeding with NaK (sodium-potassium)
mixture would be sufficient to produce an electrical conductivity from > 100
mho/m to as high as 1,000-3,000 mho/m. With this level of conductivity, very
modest magnetic field B~0.1-0.2 Tesla would suffice for a strong MHD
performance (Figure 10).
Modeling shows that MW-scale power can be generated in these conditions by a
surface-integrated MHD system from 1 square meter of vehicle surface.
Interestingly, calculations show that the additional weight of the system,
assuming a 1,000-second mission, is determined mostly by the water required to
cool the copper-wire electromagnet and that the additional weight is quite
acceptable, increasing the practicality of the system. 37, 38 , 39 , 4 0
a for virtual
lining and
crease
Figure 10. Reentry Vehicle With Surface-Integrated MHD Device and Plasma
Enabled Virtual Streamlining and L/D Increase.
One good use of such hig h power would be to create a plasma in front of the
vehicle in order to reduce drag (Figure 10). Nonoptimized analysis shows that
the "return" (i.e., the drag power saved divided by the power spent on creating
the plasma) can easily be as high as 40-50 (i.e., the drag power saved is
40-50 times greater than the power spent on the plasma). 41 There are
theoretical and experimental indications that with proper shaping of the plasma
region (specifically, making it long and thin), the "return" can be > 100. Thus,
this "reverse energy bypass" would result in substantial reduction in drag and
increase in L/D (lift-to-drag ratio) by tens of percent. The increase in L/D would
directly translate in increased downrange for an unpowered hypersonic global
"glider" and in increased cross-range for a de-orbiting space asset. Note that off-
UNCLASSIFIEDfFQR &FFIEilslll ~91: 8Hl'I
21