DOW-UAP-D149, AAWSAP DIRD, MHD Air Breathing Propulsion and Power for Aerospace Applications, November 2010

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MHD Air Breathing Propulsion and Power for Aerospace Applications The Defense Intelligence Reference Document provides nonsubstantive but auLhoritaLive reference information related to intelli ence to ics or methodolo ies. Prepared by: Technology Warning Division (OWO-4) Defense Warning Office Directorate for Analysis Defense Intelligence Agency AAP Person 86, AAP Person 87 (U) COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not This product is one of a series of advanced technology reports produced in FY 2010 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapons System Applications (AAWSA) Program, Comments or gue~tions pertaining to this document should be addressed to._A!_A P_P,.e,,,,r,,s,,,o,,,.n,....1..,,.,..,.,,..,..,,,.__,,,..,,.,.,,..,.,.~J AAWSA Program Manager, Defense Intelligence Agency, ATTN : JUIAF - DI/DW0-3,

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UNCLASSIFIED//FOR OFFICIAL USE ONLY Weakly Ionized Plasmas for Propulsion Applications ....................... 2 Electric Propulsion Systems ......................................................,......5 Basic Principles of Magnetohydrodynamics and Requirements for Nonequilibrium MHD in Cold Air Flows...........................................13 The Ajax Concept: MHD Bypass .................................................,....15 The Reverse Energy Bypass...........................................................18 MHD Applications to Reentry and Near-Orbital Flight ................, . ...20 Chapter 4: SUMMARY AND PREDICTIONS ............................................25 Figure 1. Electrothermal Arcjet Thruster.................................................7 Figure 2. Electrostatic Gridded Ion Thrusters......................................... 8 Figure 3. Field Orientation for Hall Field Systems and PS Hall Figure 4. Electromagnetic Accelerator Field Configuration and Self- Field Electromagnetic Spacecraft Thrusters.......................................9 Figure 6. MHD Control of Scramjet Inlet Using E-Beam Ionization........15 Figure 7. Schematic of Ajax Hypersonic Vehicle Concept......................16 Figure 8. The Reverse Energy Bypass Concept...................................... 19 Figure 9. Schematic of the Virtual Cowl Concept...................................20 Figure 10. Reentry Vehicle with Surface-Integrated MHD Device and Plasma-Enabled Virtual Streamlining and L/D Increase..............., . ...21 Figure 11. Electrothermal Arcjet Thruster on Satellite..........................23 Figure 13. Nuclear Electric Propulsion (NEP) Concept Vehicles.........,....24 UNCLASSIFIED//FOR OFFICIAL USE ONLY

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MHD Air-Breathing Propulsion and Power for Aerospace Applications The paper reviews novel propulsion concepts utilizing plasmas (ionized gases) and magnetohydrodynamics (MHD). These concepts are shown to be attractive due to their potential to achieve propulsion and aerodynamic performance far beyond current conventional technologies. However, significant difficulties impede the development and application of these technologies; these include weight, complexity, higher power, and the need for complex and energy-consuming artificial ionization in "cold" air (at Mach <12). 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. Applications of the Virtual Cowl and other plasma/MHD devices to reentry, global-strike hypersonic gliders, and aeroassisted orbital maneuvering are identified as promising in the near future. The ability of a plasma/MHD system to generate high power onboard and to provide L/D (lift-to-drag ratio) far beyond that possible conventionally makes these applications both feasible and desirable for national defense. However, these applications are also likely to be implemented by nations such as China, Japan, and Russia. The outlook for uses and applications of MHD propulsion could increase dramatically if high-speed (hypersonic) vehicles begin to carry powerful onboard electricity sources, such as nuclear (fission or fusion) reactors. For spacecraft, the current trend of replacing chemical rockets with electric propulsion systems will continue and is likely to become the standard. Electric systems can provide a much wider range of operation (e.g., low-thrust fine positioning/pointing, more frequent or nontraditional maneuvers, and longer times on station) than chemical systems can.

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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 typically 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 turbomachinery 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 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