Ayaks

The Ayaks (Russian: АЯКС, meaning also Ajax) is a hypersonic waverider aircraft program started in the Soviet Union and currently under development by the Hypersonic Systems Research Institute (HSRI) of Leninets Holding Company in Saint Petersburg, Russia.[1][2][3]

Leninetz HLDG Co. small-scale model of the Ayaks aircraft exposed at the 1993 MAKS Air Show, Moscow. The sharp isosceles trapezoid nose, flat top, inclined lower surface and rear SERN are typical of a waverider configuration, similar to the NASA X-43.

Purpose

Ayaks was initially a classified Soviet spaceplane project aimed to design a new kind of global range hypersonic cruise vehicle capable of flying and conducting a variety of military missions in the mesosphere. The original concept revolved around a hypersonic reconnaissance aircraft project, but later was expanded into the wider concept of hypersonic multi-purpose military and civilian jets, as well as a SSTO platform for launching satellites.

The mesosphere is the layer of the Earth's atmosphere from 50 kilometres (160,000 ft) to 85 kilometres (279,000 ft) high, above the stratosphere and below the thermosphere. It is very difficult to fly in the mesosphere — the air is too rarefied for aircraft wings to generate lift, but sufficiently dense to cause aerodynamic drag on satellites. In addition, parts of the mesosphere fall inside the ionosphere, meaning the air is ionized due to solar radiation.

The ability to conduct military activities in the mesosphere gives a country some significant military potential.

History
Layout of the projected Ayaks aircraft

In the late 1970s, Soviet scientists began to explore a novel type of hypersonic propulsion system concept, exposed for the first time in a Russian newspaper with a short interview of Ayaks inventor, Pr. Vladimir L. Fraĭshtadt, who worked at that time at the aero branch of the PKB Nevskoye-Neva Design Bureau in Leningrad.[4] Fraĭshtadt developed the concept around the idea that an efficient hypersonic vehicle cannot afford to lose energy to its surroundings (i.e. to overcome air resistance), but should instead take advantage of the energy carried by the high speed incoming flux. At that time, the whole concept is unknown to the West, although early developments involve the cooperation of Soviet industrial enterprises, technical institutes, the Military-Industrial Commission of the USSR (VPK) and the Russian Academy of Sciences.

In 1990, two articles by defense specialist and writer Nikolai Novichkov give more details about the Ayaks program. The second is the first document available in English.[5][6]

Shortly after the dissolution of the Soviet Union, fundings were cut and the Ayaks program had to evolve, especially as the US government announced the National Aero-Space Plane (NASP) program. At that time, Fraĭshtadt becomes director of the OKB-794 Design Bureau, publicly known as Leninets, a holding company running the open joint-stock company State Hypersonic Systems Research Institute (HSRI) (Russian: НИПГС pr: "NIPGS") in Saint Petersburg.

Early 1993, as an answer to the American announcement of the X-30 NASP demonstrator, the Ayaks project integrates into the wider national ORYOL (Russian: Орёл pr: "Or'yol", Eagle) program, federating all Russian hypersonic works to design a competing spaceplane as a reusable launch system.

In September 1993, the program is unveiled and a first small-scale model of Ayaks is publicly shown for the first time on the Leninetz booth at the 2nd MAKS Air Show in Moscow.

In 1994, Novichkov reveals the Russian Federation is ready to fund the Ayaks program for height years and that a reusable small-scale flight test module has been built by Arsenal Design Bureau. He also states that Ayaks working principles have been validated with an engine test stand in a wind tunnel. The same year, the American NASP project is cancelled, replaced by the Hypersonic Systems Technology Program (HySTP) cancelled as well after three months. In 1995, NASA launches the Advanced Reusable Transportation Technologies (ARTT) program, part of the Highly Reusable Space Transportation (HRST) initiative, but experts from consulting firm ANSER evaluating Ayaks technologies does not believe at first in the performances announced by the Russian and do not recommend to follow the same path.

However, between October 1995 and April 1997, a series of Russian patents covering Ayaks technologies are granted to Leninetz HLDG Co. and consequently available publicly, the oldest having being filed 14 years before.[7][8][9][10]

As the information available out of Russia start to grow, three western academic researchers start to collect the sparse data about Ayaks: Claudio Bruno, professor at the Sapienza University of Rome; Paul A. Czysz, professor at the Parks College of Engineering, Aviation and Technology in Saint Louis University, Missouri; and S. N. B. Murthy, professor at the Purdue University, West Lafayette, Indiana. In September 1996, as part of the Capstone Design Course and the Hypersonic Aero-Propulsion Integration Course at Parks College, Czysz assigns his students to analyze the information gathered, as the ODYSSEUS project.[11] Thereafter the three researchers copublish a conference paper summarizing the Western analysis of Ayaks principles.[12]

With such information, long-time ANSER main expert Ramon L. Chase reviews his former position and assembles a team to evaluate and develop American versions of Ayaks technologies within the HRST program, recruiting H. David Froning Jr., CEO of Flight Unlimited; Leon E. McKinney, world expert in fluid dynamics; Paul A. Czysz; Mark J. Lewis, aerodynamicist at the University of Maryland, College Park, specialist of waveriders and airflows around leading edges and director of the NASA-sponsored Maryland Center for Hypersonic Education and Research; Dr. Robert Boyd of Lockheed Martin Skunk Works able to build real working prototypes with allocated budgets from black projects, whose contractor General Atomics is a world leader in superconducting magnets (that Ayaks uses); and Dr. Daniel Swallow from Textron Systems, one of the few firms that still possess valuable knowledge in magnetohydrodynamic converters, which Ayaks extensively uses.[13][14]

Novel technologies

MHD bypass
See also: Magnetohydrodynamic converter
Layout of Ayaks engines

The Ayaks was projected to employ a novel engine that uses an MHD generator to collect and slow down highly ionized and rarefied air upstream airbreathing jet engines, usually scramjets, although HSRI project lead Vladimir L. Fraĭshtadt told in a 2001 interview that the MHD bypass system of the hypersonic plane Ayaks could decelerate the incoming hypersonic airflow sufficiently to use almost conventional turbomachinery,[15][16] a surprising technical solution considering such hypersonic speeds, yet confirmed as feasible by independent studies using Mach 2.7 turbojets,[17][18][19] or even subsonic ramjets.[20]

The air is mixed with fuel into the mixture that burns in the combustor, while the electricity produced by the inlet MHD generator feeds the MHD accelerator located behind the jet engine near the single expansion ramp nozzle to provide additional thrust and specific impulse. The plasma funnel developed over the air inlet from the Lorentz forces greatly increases the ability of the engine to collect air, increasing the effective diameter of the air inlet up to hundreds of meters. It also extends the Mach regime and altitude the aircraft can cruise to. Thus, it is theorized that the Ayaks' engine can use atmospheric oxygen, even at heights above 35 kilometres (115,000 ft).[21]

A non-equilibrium MHD generator typically produces 1–5 MWe with such parameters (channel cross-section, magnetic field strength, pressure, degree of ionization and velocity of the working fluid) but the increased effective diameter of the air inlet by the virtual plasma funnel greatly increases the power produced to 45–100 MWe per engine.[12][22] As Ayaks may use two to four of such engines, some electrical energy could be diverted to peaceful or military directed-energy devices.[2]

Thermochemical reactors
See also: Thermochemical cycle

The fuel feed system of the Ayaks engine is also novel. At supersonic speeds, air brutally recompress downstream the stagnation point of a shock wave, producing heat. At hypersonic speeds, the heat flux from shock waves and air friction on the body of an aircraft, especially at the nose and leading edges, becomes considerable, as the temperature is proportional to the square of the Mach number. That is why hypersonic speeds are problematic with respect to the strength of materials and are often referred to as the heat barrier.[23]

Ayaks uses thermochemical reactors (TCRs): the heating energy from air friction is used to increase the heat capacity of the fuel, by cracking the fuel with a catalytic chemical reaction. The aircraft has double shielding between which water and ordinary, cheap kerosene circulates in hot parts of the airframe. The energy of surface heating is absorbed through heat exchangers to trigger a series of chemical reactions in presence of a nickel catalyzer, called hydrocarbon steam reforming. Kerosene and water spits into a new fuel reformate: methane (70–80% in volume) and carbon dioxide (20–30%) in a first stage:

CnHm + H2O CH4 + CO2

Then methane and water reform in their turn in a second stage into hydrogen, a new fuel of better quality, in a strong endothermic reaction:

CH4 + H2O CO + 3H2
CO + H2O CO2 + H2

Thus, the heating capacity of the fuel increases, and the surface of the aircraft cools down.[24]

The calorific value of the mixture CO + 3H2 produced from 1 kg of methane through water steam reforming (62,900 kJ) is 25% higher than that of methane only (50,100 kJ).[16]

Besides a more energetic fuel, the mixture is populated by many free radicals that enhance the degree of ionization of the plasma, further increased by the combined use of e-beams that control electron concentration, and HF pulse repetitive discharges (PRDs) that control electron temperature. Such systems create streamer discharges that irrigate the ionized flow with free electrons, increasing combustion effectiveness, a process known as plasma-assisted combustion (PAC).[25][26][27][28]

Such concept was initially named Magneto-Plasma-Chemical Engine (MPCE),[29][30][31] and the working principle referred to as Chemical Heat Regeneration and Fuel Transformation (CHRFT).[32] In subsequent literature, the accent has been put more on magnetohydrodynamics than on the chemical part of these engines, which are now simply referred to as a scramjet with MHD bypass as these concepts intimately require each other to work efficiently.[33]

The idea of thermally shielding the engine is detailed in the fundamental analysis of an ideal turbojet for maximum thrust analysis in the aerothermodynamics literature.[34] That is, putting the turbine (work extraction) upstream and the compressor (work addition) downstream. For a conventional jet engine, the thermodynamics works, however the advanced thermo-fluids analysis shows that in order to add sufficient heat to power the aircraft without thermally choking the flow (and unstarting the engine) the combustor has to grow and the amount of heat added grows as well. It is more "efficient" in using the heat, it just needs a lot of heat. While thermodynamically very sound, the real engine is too large and consumes too much power to ever fly on an aircraft. These issues do no arise in the Ayaks concept as the plasma funnel virtually increases the cross-section of the air inlet while maintaining its limited physical size, and additional energy is taken from the flow itself. As Fraĭshtadt said:[16]

"Since it takes advantage of the CHRFT technology, Ayaks cannot be analyzed as a classical heat engine."

Plasma sheath

As altitude increases, the electrical resistance of air decreases according to Paschen's law. The air at the nose of Ayaks is ionized. Besides e-beams and HF pulse discharges, a high voltage is produced by the Hall effect in the MHD generator that allows a planar glow discharge to be emitted from the sharp nose of the aircraft and the thin leading edges of its wings, by a St. Elmo's fire effect. Such a plasma cushion in front and around the aircraft offers several advantages:[2][35][36]

  • The ionized air becomes electrically conductive, which allows the MHD generator to work and decelerate the flow down to the air-breathing jet engines.
  • The MHD-controlled inlet ramp allows to vector the flow as a shock-on-lip without physical inlet cones.
  • Electric charges mixed with the fuel increase the combustion effectiveness.
  • The bow shock wave is detached further ahead of the aircraft, the energy deposition in this region acting as a virtual blunted nose, although the nose stays physically very sharp. This minimizes the heat flux on materials.[35]
  • The temperature gradient in the air is locally modified, hence the speed of sound value, which mitigates and softens the shock wave. This lowers thermal effects on materials further, as well as the wave drag.[35][37][38]
  • The plasma cocoon surrounding the whole aircraft gives plasma stealth. Combined with hypersonic speeds and maneuverability, such a platform would be very difficult to detect, track and target.

Specifications

According to the data presented at the 2001 MAKS Airshow, the specifications of the Ayaks are:

Parameter Hypersonic Satellite Launcher Multi-purpose Hypersonic Craft Transport Hypersonic Craft
Maximum takeoff weight, tonne 267 200 390
Loaded Weight, tonne 113 85 130
Empty weight, tonne 76
Mass of the second stage, tonne 36
Payload, tonne 10 10
Satellite mass, tonne 6
Turbojet engines 4 4 4
Magneto-plasma-chemical engines 4 6 4
Thrust, turbojet engines, tonne 4×25 4×25 4×40
Thrust, magneto-plasma-chemical engines 4×25 6×14 4×40
Maximal speed, m/s 4000 4000 4600
Service ceiling, km 36 36 36
Practical range at M = 8 ... 10 and height of 30 km, km 14200 10000 12000

Later publications cite even more impressive numbers, with expected performance of service ceiling of 60 km and cruising speed of Mach 10–20, and the ability to reach the orbital speed of 28,440 km/h with the addition of booster rockets, the spaceplane then flying in boost-glide trajectories (successive rebounds or "skips" on the upper layers of the atmosphere, alternating unpowered gliding and powered modes) similarly to the US hypersonic waverider project HyperSoar with a high glide ratio of 40:1.[15][39][40]

Speculation

In 2003, French aeronautical engineer and MHD specialist Jean-Pierre Petit proposed a different explanation about how magnetohydrodynamics is used in this project.[40] His study was based on a paper published in January 2001 in the French magazine Air et Cosmos by Alexandre-David Szamès,[15] and in the same month from information gathered in a small workshop on advanced propulsion in Brighton, England,[41] especially after discussions with David Froning Jr. from Flight Unlimited about his prior work involving electric and electromagnetic discharges in hypersonic flows, presented during the workshop.[35]

Petit wrote about a large and long multipole wall MHD converter on the upper flat surface of the aircraft in contact with the freestream, instead of the linear cross-field Faraday converters located within a channel usually considered. In such a multipole converter, magnetic field is produced by many parallel superconducting thin wires instead of pairs of bigger electromagnets. These wires run below the surface directly in contact with the airflow, their profile following the body of the vehicle. Air is progressively decelerated in the boundary layer in a laminar flow without too much recompression, down to subsonic values as it enters the inlet then the air-breathing jet engines. Such an open wall MHD-controlled inlet will be exposed by two scientists of the Ayaks program in a similar way two years later, although they propose to locate it on the surface of the inclined front ramp underneath the aircraft, to vector the shock wave as a "shock-on-lip" upon the air inlet, whatever the speed and altitude.[42]

As subsonic velocities can be achieved internally while the external flow is still hypersonic, Petit proposes that such platform could use almost conventional turbojets and ramjets instead of scramjets more difficult to control, and such plane would not need vertical stabilizers nor fins anymore, as it would maneuver through locally increasing or reducing drag on particular regions of the wetted area with electromagnetic forces. He then describes a similar multipole MHD accelerator located on the physical surface of the semi-guided ramp nozzle, which accelerates the conductive exhaust gases downstream the jet engines.

Ten years before Petit, Dr. Vladimir I. Krementsov, head of the Nizhny Novgorod Research Institute of Radio Engineering (NIIRT), and Dr Anatoly Klimov, chief of the Moscow Radiotechnical Institute of the Russian Academy of Sciences (MRTI RAS), exposed to William Kaufmann that the MHD bypass system of the Ayaks concept would have been already built in the rumored Aurora secret spaceplane, successor of the Lockheed SR-71 Blackbird.[40][43][44]

  • The Ayaks program is featured prominent in The Broken Sword of the Empire novel by the nationalist author Maxim Kalashnikov.[45]
gollark: A large uptick in VPN usage, perhaps. Who knows.
gollark: How did *that* happen?
gollark: Pythagoras disapproves.
gollark: Both already exist but are sort of meh, but the combination of more advanced versions might work.
gollark: One thing which might take off is some sort of portable phone dock with a monitor/keyboard/mouse and some sort of "cloud gaming" thing.

See also

References
  1. "Hypersonic Systems Research Institute (HSRI) website". hypersonics.ru. Leninetz Holding Company.
  2. Czysz, Paul A. (2006). Future Spacecraft Propulsion Systems: Enabling Technologies for Space. Springer. ISBN 978-3540231615. See pp. 185-195.
  3. "What is the Russian Ayaks aircraft?". North Atlantic Blog. 30 March 2015.
  4. "Nevskoye Planning and Design Bureau". GlobalSecurity.org.
  5. Novichkov, N. (September 1990). "Космические Крылья России И Украины (tr. Space Wings of Russia and the Ukraine)". Эхо планеты (tr. Echo Planet) Аэрокосмос (tr. Aerospace special issue) (in Russian). Vol. 42 no. 237. TASS. pp. 4–8. translated in: Novichkov, N. (1992). At Hypersonic Speeds (Report). Wright-Patterson Air Force Base, Ohio: Foreign Aerospace Science and Technology Center. FASTC-ID(RS)T-0972-92.
  6. Novichkov, N. (6–12 October 1990). Private communication. 41st International Astronautical Congress (IAC). Dresden, Germany.
  7. RU patent 2046203, Freistadt, V. L.; Timofee, G. A. & Isakov, Viktor N. et al., "Method of feeding hydrocarbon fuel in jet engine installation of flying vehicle and jet engine installation of flying vehicle", issued 1995-10-20, assigned to State Hypersonic Systems Research Institute of the Leninetz Holding Company
  8. RU patent 2042577, Freistadt, Vladimir. L.; Isakov, Viktor N. & Korabelnikov, Alexey V. et al., "Method of creating thrust of hypersonic flying vehicle in cruising atmosphere flight conditions", issued 1995-08-27, assigned to State Hypersonic Systems Research Institute of the Leninetz Holding Company
  9. RU patent 2059537, Freistadt, Vladimir. L.; Isakov, Viktor N. & Korabelnikov, Alexey V. et al., "Hypersonic flying vehicle", issued 1996-05-10, assigned to State Hypersonic Systems Research Institute of the Leninetz Holding Company
  10. RU patent 2076829, Kirilkin, V. S.; Leshukov, V. S. & Ushakov, V. M. et al., "Composite ramjet engine", issued 1997-04-10, assigned to State Hypersonic Systems Research Institute of the Leninetz Holding Company
  11. Esteve, Maria Dolores; et al. (May 1997). ODYSSEUS, Technology Integration for a Single Stage to Orbit Space Transport Using MHD Driven Propulsion (Report). Parks College of Aerospace and Aviation, Saint Louis University, St. Louis, MO. Senior Design Study.
  12. Bruno, Claudio; Czysz, Paul A.; Murthy, S. N. B. (July 1997). Electro-magnetic interactions in a hypersonic propulsion system (PDF). 33rd Joint Propulsion Conference and Exhibit. Seattle, WA. doi:10.2514/6.1997-3389.
  13. Chase, R. L.; Boyd, R.; Czysz, P. A.; Froning, Jr., H. D.; Lewis, M.; McKinney, L. E. (September 1997). An Advanced Highly Reusable Space Transportation System: Definition and Assessment Study (Report). ANSER, Arlington, VA. ANSER Technical Report 97-1. Final Report for NASA Cooperative Agreement NCC8-104.
  14. Chase, R. L.; McKinney, L. E.; Froning, Jr., H. D.; Czysz, P. A.; Boyd, R.; Lewis, M. (January 1999). "A comparison of selected air-breathing propulsion choices for an aerospace plane" (PDF). AIP Conference Proceedings. 458: 1133–1138. doi:10.1063/1.57719.
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  16. Szamès, Alexandre-David (October 2001). "Des réacteurs thermochimiques à l'étude" [Thermochemical propulsion under study]. Air & Cosmos (in French). No. 1816. pp. 14–15.
  17. Adamovich, Igor V.; Rich, J. William; Schneider, Steven J.; Blankson, Isaiah M. (June 2003). "Magnetogasdynamic Power Extraction and Flow Conditioning for a Gas Turbine" (PDF). AIAA 2003-4289. 34th AIAA Plasmadynamics and Lasers Conference. Orlando, Florida. doi:10.2514/6.2003-4289.
  18. Blankson, Isaiah M.; Schneider, Stephen J. (December 2003). "Hypersonic Engine using MHD Energy Bypass with a Conventional Turbojet" (PDF). AIAA 2003-6922. 12th AIAA International Space Planes and Hypersonic Systems and Technologies. Norfolk, Virginia. doi:10.2514/6.2003-6922.
  19. Schneider, Stephen J. "Annular MHD Physics for Turbojet Energy Bypas" (PDF). AIAA–2011–2230. 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference. San Francisco, California. doi:10.2514/6.2011-2230.
  20. Chase, R. L.; Boyd, R.; Czysz, P.; Froning, Jr., H. D.; Lewis, Mark; McKinney, L. E. (September 1998). "An AJAX technology advanced SSTO design concept" (PDF). Anaheim, CA. AIAA and SAE, 1998 World Aviation Conference. doi:10.2514/6.1998-5527.
  21. Bityurin, V. A.; Zeigarnik, V. A.; Kuranov, A. L. (June 1996). On a perspective of MHD technology in aerospace applications (PDF). 27th Plasma Dynamics and Lasers Conference. New Orleans, LA. doi:10.2514/6.1996-2355.
  22. Bruno, Claudio; Czysz, Paul A. (April 1998). An electro-magnetic-chemical hypersonic propulsion system (PDF). 8th AIAA International Space Planes and Hypersonic Systems and Technologies Conference. Norfolk, VA. doi:10.2514/6.1998-1582.
  23. Heppenheimer, T. A. (November 2013). Facing the Heat Barrier: A History of Hypersonics. The NASA History Series. National Aeronautics and Space Administration. ISBN 978-1493692569.
  24. KorabeInikov, A. V.; Kuranov, A. L. (June 1999). "Thermochemical Conversion of Hydrocarbon Fuel for the AJAX Concept" (PDF). AIAA 99-3537. 30th Plasmadynamics and Lasers Conference. Norfolk, VA. doi:10.2514/6.1999-3537.
  25. Szamès, Alexandre-David (February 2002). "Combustion exotique : le plasma séduit l'hypersonique" [Hypersonics looks for boost from plasma-assisted combustion]. Air & Cosmos (in French). No. 1829. pp. 16–17.
  26. Klimov, A.; Byturin, V.; Kuznetsov, A.; Tolkunov, B.; Nedospasov, A.; Vyatavkin, N.; Van Wie, D. (January 2002). "Plasma-Assisted Combustion" (PDF). AIAA 2002- 0493. 40th AIAA Aerospace Sciences Meeting & Exhibit. Reno, NV. doi:10.2514/6.2002-493.
  27. Klimov, Anatoli Ivanovich (January 2005). Study of Internal and External Plasma Assisted Combustion in Supersonic Gas Flow (PDF) (Report). IVTAN RAS. Final Technical Report ISTC Project #2127P.
  28. Matveev, Igor B.; Rosocha, Louis A. (December 2010). "Guest Editorial Classification of Plasma Systems for Plasma-Assisted Combustion". IEEE Transactions on Plasma Science. 38 (12): 3257–3264. doi:10.1109/TPS.2010.2091153.
  29. Gurijanov, E. P.; Harsha, P. T. (June 1996). AJAX: new Directions in Hypersonic Technology (PDF). 27th Plasma Dynamics and Lasers Conference. New Orleans, LA. doi:10.2514/6.1996-4609.
  30. Bityurin, V. A.; Lineberry, J.; Potebnia, V.; Alferov, V.; Kuranov, A.; Sheikin, E. G. (June 1997). Assessment of hypersonic MHD concepts (PDF). 28th Plasmadynamics and Lasers Conference. Atlanta, GA. doi:10.2514/6.1997-2393.
  31. Fraĭshtadt, V. L.; Kuranov, A. L.; Sheĭkin, E. G. (November 1998). "Use of MHD systems in hypersonic aircraft" (PDF). Technical Physics. 43 (11): 1309–1313. doi:10.1134/1.1259189.
  32. Leninetz Holding Company - NIPGS (2000). Thermochemical Processes in Plasma Aerodynamics (Report). ASIN B00JBMQ48K.
  33. Sheikin, E. G.; Kuranov, A. L. (October 2003). Analysis of Scramjet with MHD bypass. 3rd workshop on Thermochemical processes in plasma aerodynamics. Saint Petersburg, Russia. S2CID 10143742. The 'Magneto Plasma Chemical Engine' title was used in the paper for designation of the engine. At present the title 'Scramjet with MHD bypass' is frequently used for the engine designation.
  34. Oates, Gordon C. (December 1984). Aerothermodynamics of Gas Turbine and Rocket Propulsion (1st ed.). American Institute of Aeronautics and Astronautics. ISBN 978-0915928873.
  35. Froning, H. D.; Roach, R. L. (November 1999). "Influence of EM discharges on hypersonic vehicle lift, drag, and airbreathing thrust" (PDF). AIAA-99-4878. 9th International Space Planes and Hypersonic Systems and Technologies Conference. Norfolk, VA. doi:10.2514/6.1999-487.
  36. Petit, J.-P.; Geffray, J. (2009). "MHD Flow-Control for Hypersonic Flight". Acta Physica Polonica A. 115 (6): 1149–1151. doi:10.12693/aphyspola.115.1149.
  37. Avramenko, R. F.; Rukhadze, A. A.; Teselkin, S. F. (November 1981). "Structure of a Shock Wave in Weakly Ionized Nonisothermal Plasma" (PDF). JETP Letters. 34 (9): 463–466.
  38. Gordeev, V. P.; Krasil'Nikov, A. V.; Lagutin, V. I.; Otmennikov, V. N. (March 1996). "Experimental study of the possibility of reducing supersonic drag by employing plasma technology" (PDF). Fluid Dynamics. 31 (2): 313–317. doi:10.1007/BF02029693.
  39. United States Air Force Scientific Advisory Board (1996). New World Vistas: Air and Space Power for the 21st Century – Summary Volume (PDF) (Report). Washington, DC: Defense Technical Information Center.
  40. Petit, Jean-Pierre (January 2003). "Le Projet Ajax" [The Ajax Project] (PDF). Ovnis et armes secrètes américaines : L'extraodinaire témoignage d'un scientifique [UFOs and US secret weapons: A Scientist's Extraordinary Evidence] (in French). Éditions Albin Michel. ISBN 978-2226136169.
  41. 1st International Workshop on Field Propulsion and Technology (20–22 January 2001). Institute of Development Studies (IDS), Falmer Campus, University of Sussex, Brighton, UK. Meeting supported by the British National Space Centre (BNSC) and Society of British Aerospace Companies (SBAC).
  42. Sheikin, Evgeniy G.; Kuranov, Alexander L. (2005). "Scramjet with MHD Controlled Inlet" (PDF). AIAA 2005-3223. AIAA/CIRA 13th International Space Planes and Hypersonics Systems and Technologies Conference. Capua, Italy. doi:10.2514/6.2005-3223.
  43. ANSER (8 October 1993). ANSER's Russian Activities Moscow Report #52 (Report).
  44. Mills, Dennis C. (April 2012). "Chapter 5: Ajax" (PDF). Plasma Aerodynamics since the End of the Cold War (Thesis). Florida State University College of Arts and Sciences. pp. 121–157.
  45. Kalashnikov, Maxim (1998). Сломанный меч Империи [The Broken Sword of the Empire] (in Russian). The Great Resistance. ISBN 978-5897470273.
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