DOW-UAP-D149: MHD Air Breathing Propulsion and Power for Aerospace Applications

Source file: DOW-UAP-D149_AAWSAP-DIRD-MHD-Air-Breathing-Propulsion-and-Power-for-Aerospace-Applications-November-21-2010.pdf Originating agency: Defense Intelligence Agency (DIA), Defense Warning Office, under the AAWSA Program Document type: Defense Intelligence Reference Document (DIRD), "Defense Futures" series; control number DIA-08-1011-006 Date: 21 November 2010 (information cutoff date, ICOD: 20 July 2010) Classification: UNCLASSIFIED//FOR OFFICIAL USE ONLY; the FOUO caveat is struck through on most pages but left intact on a few (for example the contents page and page 25); publicly released in 2026 Page count: 32 VIRIN: 260918-D-D0360-1138 PURSUE Release: 6

Summary

This DIRD is a technical review of plasma and magnetohydrodynamic (MHD) concepts for aircraft and spacecraft. The cover carries the DIA seal, the "Defense Futures" banner, the date 21 November 2010, an information cutoff date of 20 July 2010 and the control number DIA-08-1011-006. The title page names the preparing office as the Technology Warning Division (DWO-4) of the Defense Warning Office, Directorate for Analysis, lists the authors only as "AAP Person 86, AAP Person 87," and calls the paper "one of a series of advanced technology reports produced in FY 2010" under the AAWSA Program, with comments to AAP Person 1, the AAWSA Program Manager.

Unlike many survey papers, this one takes sides. Its one-page summary states that "A well-publicized Ajax concept of MHD energy bypass has been shown to be meaningless below at least Mach 12," promotes an alternative, the "reverse energy bypass" with a plasma "virtual cowl," and identifies reentry vehicles, "global-strike hypersonic gliders" and "aeroassisted orbital maneuvering" as the most promising near-term uses. The text states that one of the authors did some of the research it describes (the inlet-control studies and the reverse energy bypass), so part of the review covers the authors' own work. The paper does not name that author, and neither does this article.

The paper does not mention UAP or UFOs. Among the technical areas of the AAWSAP Statement of Objectives (DOW-UAP-D110) it serves propulsion, power generation and control, and touches on lift through its treatment of lift-to-drag ratio.

Research Article

Structure and sources

After the summary, the body runs 28 numbered pages in five chapters: Concept Overview (weakly ionized plasmas, electric propulsion systems), Aeronautical Applications (MHD principles, nonequilibrium MHD in cold air, the Ajax concept, the reverse energy bypass, reentry and near-orbital flight), Space Applications, Summary and Predictions, and Endnotes. There are 13 figures and no tables. The 55 endnotes are almost entirely peer-reviewed aerospace literature, much of it from the AIAA Journal and the Journal of Propulsion and Power, including the 2008 special section "Weakly Ionized Plasmas for Propulsion Applications," plus a 2002 Jet Propulsion Laboratory internal compendium on advanced space propulsion that the endnotes say "was accessible via internet until 2003 but has since been removed." Photographs show thrusters under test at the Jet Propulsion Laboratory, the University of Michigan and Princeton University, and a proof-of-concept air-breathing MHD engine "being investigated by Lockheed Martin Aeronautics" (Figure 5, page 14). The paper adds that in 2009 the AIAA's first list of top ten emerging aerospace technologies included two plasma technologies.

Plasma, MHD and the cold-air problem

Chapter 1 frames the motivation. Conventional air-breathing engines are "typically limited to altitudes below 80,000 feet"; scramjets struggle with shock control, mixing, ignition and extreme wall heating; and hypersonic vehicles have "no rotating turbomachinery to which an electrical generator could be connected" (page 5). Plasma offers remedies. An MHD generator behind a scramjet combustor, with metal additives in the fuel, could produce "from tens of kW to several MW" with no moving parts. Heated plasma regions can act as "switchable, controllable, and tunable virtual bodies or surfaces" for drag reduction, steering and inlet control (page 7). Among near-term candidates the paper ranks the dielectric barrier discharge actuator, "a remarkably simple device" for controlling flow separation, at "the top of the list" (page 8).

The obstacle is conductivity. MHD works when a conducting fluid crosses a magnetic field: a generator slows the flow and extracts electricity, an accelerator does the reverse, and both waste some energy as Joule heating. (The paper notes that the "Lorentz force" in this setting "should be properly called the ampere force or the ponderomotive force.") Air conducts only when very hot. In reentry shock layers at Mach 12-25 (3,000-10,000 K) the ionization fraction reaches 10⁻⁵ to 10⁻² and conductivity up to about 3,000 mho/m, so a modest 0.1-0.3 tesla field is enough (pages 16-17). In a scramjet combustor at 1,500-2,000 K, even with alkali seeding, conductivity is only 10-30 mho/m and the magnet would need 3-10 tesla. Below about Mach 12 the air is simply too cold, and ionization has to be forced by non-thermal means. Ordinary discharges spend about 10,000 eV per electron-ion pair against a theoretical best of 34 eV for high-energy electron beams, and since a plasma recombines in "~1-10 microseconds" (the flow moves only about 1 cm), ionization must be sustained throughout the MHD channel (pages 17-18). Even under ideal assumptions the paper calculates a maximum conductivity of about 1 mho/m, requiring fields of 10-20 tesla. That makes such devices "quite impractical, unless a breakthrough in magnet and materials technologies occurs." One application survives the arithmetic in principle: electron-beam MHD control of a scramjet inlet (Figure 6), which could restore the "shock-on-lip" condition above the design Mach number, although the authors say systems studies are still needed.

Electric thrusters and the power gap

The electric-propulsion section explains why plasma thrusters fly on spacecraft but not aircraft. Chemical rockets are "energy limited"; electric thrusters are "power limited," because thrust depends on the mass of the power plant (page 6). The paper gives the orders of magnitude (page 11): an SR-71 cruising at Mach 3.2 produces 24,700 lbf of thrust and a jet power of 104 MW, and an RL10 rocket engine 142 MW, against 194 MW for a Nimitz-class carrier's propulsion plant and about 2,000 MW for the Hoover Dam. Spacecraft thrusters handle hundreds of watts to tens of kilowatts. It then describes the three thruster families: electrothermal arcjets, electrostatic ion and Hall thrusters (ion engines reach a specific impulse of 1,000 to more than 20,000 seconds but only 1-5 N/m² thrust density) and electromagnetic magnetoplasmadynamic thrusters (50 kW to tens of MW). It also notes a basic limit: "an air-breathing system can never fly faster than its exhaust velocity."

The Ajax verdict

The longest argument concerns Ajax (Ayaks), which the paper describes as the MHD concept that "has attracted perhaps the most attention over the last decade or two," originating in the 1980s at the Leninetz Scientific & Production Enterprise in Leningrad (page 19). Figure 7 reproduces two published schematics of the vehicle. The paper splits Ajax into three parts and grades each (pages 20-21):

• Endothermic fuel conversion, cracking a kerosene-water mixture into syngas while cooling the vehicle, is "certainly very meaningful and probably viable."
• Plasma drag reduction is real but conventional: claims by "some Russian groups" of an "unknown physical mechanism" were refuted by research in the United States, Europe and Russia showing "that the effects are purely thermal."
• MHD energy bypass, extracting energy upstream of the combustor and returning it downstream, is "perhaps the most controversial part."

On the bypass, the authors referee a published dispute. They accept D. Riggins's point that the cycle runs "in the direction opposite to that dictated by thermodynamics," but say his proof that it always lowers specific impulse contains "a significant mistake," because a scramjet adds heat at static rather than stagnation temperature. They then examine the Ajax group's own calculations (by A. Kuranov and colleagues): the best case gives only "several percent" more specific impulse under crude assumptions, a gain that "would turn into a loss" in a realistic analysis. Hence the conclusion that MHD bypass below Mach 12 "is not a meaningful technology" (page 22). Above Mach 12, where the air ionizes thermally, modelling by a NASA Ames group shows a gain, but air-breathing flight at those speeds "is not realistic" with current materials and fuels.

This verdict sits oddly beside the preceding paper in the series. DOW-UAP-D148, dated one day earlier, describes the Russian AYAKS transport as using lasers, RF generators and an MHD engine to disrupt the bow shock, "doubling the velocity of the vehicle," and treats it as a detection problem. D149 is far more sceptical of the propulsion claims.

Reverse bypass, virtual cowl and reentry

The authors' alternative (pages 22-24) reverses the flow of energy: an MHD generator just behind the combustor, where hot, alkali-seeded exhaust conducts at about 10 mho/m without electron beams, sends power forward to plasma devices for ignition, inlet control, drag reduction and steering. The most promising use is the "virtual cowl" (Figure 9). An inlet designed for Mach 8 spills air at Mach 6; a plasma-heated region ahead of the cowl lip deflects the flow so the inlet captures more cold air. The paper reports that the combination "can actually increase thrust by as much as 20-30%," and that an MHD generator is competitive for "hundreds of kW to 1-10 MW" of onboard power where batteries and fuel cells are not. An onboard nuclear reactor would make these uses "straightforward."

Reentry is where MHD looks strongest (pages 24-26). Shock layers at 10,000-20,000 K, seeded with sodium-potassium (NaK), conduct at up to 1,000-3,000 mho/m, so a 0.1-0.2 tesla field suffices. Modelling indicates "MW-scale power" from a single square metre of surface-integrated MHD panels, with the added weight for a 1,000-second mission dominated by magnet cooling water (Figure 10). Using that power to create a plasma ahead of the nose could save 40-50 times more drag power than it costs, and more than 100 times with a long, thin plasma. That would raise lift-to-drag ratio by tens of percent, extending the downrange of "an unpowered hypersonic global 'glider'" and the cross-range of de-orbiting assets. The most ambitious claim follows: hypersonic L/D is "not much higher than 1," but plasma and MHD could reach 3-10, "a game-changer" enabling on-demand orbital plane changes by dipping into the atmosphere at 200-300 kft (page 26). The paper is much cooler on hybrid chemical/MHD rocket nozzles: launch vehicles would need hundreds of MW to tens of GW, specific mass would have to improve 1,000-fold, and 2-40 tesla magnets would often outweigh the vehicle.

Space applications and predictions

Chapter 3 (pages 27-28) tracks the move of satellites from chemical to electric propulsion: hydrazine resistojets (specific impulse raised from 200 to 300 seconds) and arcjets (600 seconds) on the Lockheed Martin Series 7000 comsat, then xenon ion and Hall thrusters, micro-newton FEEP and colloid thrusters for fine pointing, and air-breathing electric thrusters for drag make-up in very low orbits. It recalls SNAP-10A and the Soviet TOPAZ reactors, the 100 kWe SP-100 tug of the 1990s, the 100 kWe JIMO spacecraft and a 100-MWe piloted Mars vehicle, and notes that a nuclear vehicle in orbit "also enables the beaming of power to air or ground vehicles from orbit or the use of laser and microwave weapons."

Chapter 4 (page 29) lists four flaws: heavy magnets and electron beams, overwhelming power demands for accelerators, entropy losses from Joule heating, and the fact that below Mach 12 non-thermal ionization makes MHD propulsion all but "impossible." Against these it sets the promise of reentry, gliders and aero-assisted orbital manoeuvres, "both feasible and desirable for national defense," and a warning that Russia, China and Japan could develop them "within several years" and deploy them "perhaps within 10 years." It predicts that MHD's prospects would change if hypersonic vehicles carried nuclear power, a question it calls "mostly a political rather than a technological issue," and that electric propulsion will become standard on spacecraft, eventually bringing back fission reactors in space.

One typographical point: the MHD interaction (Stuart) parameter is printed as S = σBL/ρu (page 16), without the square on the magnetic field that the standard definition carries; the surrounding argument is unaffected.

Significance

D149 is one of the most technically rigorous and opinionated papers in the AAWSAP series, written from inside the research field. For readers it does three useful things. It explains in plain physical terms why "magnetic" propulsion of aircraft is so hard: air must be made to conduct, and below Mach 12 that costs more than it returns. It gives a reasoned public verdict on the Ajax concept, rejecting its best-known feature while crediting its fuel-conversion idea. And it points to where plasma and MHD could matter militarily: power generation, drag reduction and manoeuvre for reentry vehicles and hypersonic gliders. Read with DOW-UAP-D148 (detecting hypersonic vehicles) and DOW-UAP-D147 (pulsed power storage), it shows the program looking at the same problem from the sides of propulsion, power and detection. It makes no reference to UAP. Its speculative elements, onboard fusion reactors and L/D of 3-10, are presented as engineering possibilities that depend on breakthroughs in magnets and power sources, not as demonstrated capabilities.

Key People

Locations

Key Concepts

Notable Quotes

"A well-publicized Ajax concept of MHD energy bypass has been shown to be meaningless below at least Mach 12. In contrast, a new 'reverse energy bypass' with Virtual Cowl is potentially practical for air-breathing hypersonic vehicles." -- page 4

"Note that an air-breathing system can never fly faster than its exhaust velocity." -- page 11

"Although there were claims by some Russian groups about 10-15 years ago that weakly ionized plasmas can reduce shock strength via some unknown physical mechanism, extensive research in the United States, Europe, and Russia has conclusively shown that the effects are purely thermal." -- page 21

"Therefore, one can state with certainty that MHD energy bypass at Mach<12 (where nonequilibrium ionization of air is required) is not a meaningful technology." -- page 22

"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." -- page 26

"Having a nuclear vehicle in orbit also enables the beaming of power to air or ground vehicles from orbit or the use of laser and microwave weapons." -- page 28

"These nations have the capability to develop such novel technologies within several years and deploying those technologies perhaps within 10 years." -- page 29

"Since deployment of onboard nuclear power is mostly a political rather than a technological issue, it is difficult to predict if this going to occur and, if yes, when." -- page 29