The Ayaks (Russian: АЯКС, meaning also 'Ajax') is a hypersonic aircraft program started in the Soviet Union and currently under development in Russia by the Saint Petersburg Institute for the Hypersonic Systems of Leninets Holding Company.
In the early 1980s, Soviet scientists began to explore a new type of aircraft. The Ayaks was to be a new Soviet spaceplane capable of flying and conducting a wide range of missions in the mesosphere, for both military and civilian purposes. 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 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.
Novel "magneto-plasmo-chemical engine"
The Ayaks was projected to employ a novel engine that uses some form of MHD generator to collect and slow down highly ionized and rarefied air. The air is mixed with fuel into the mixture that burns in the combustor, while the electricity produced by the inlet's MHD generator is used in the magnetoplasmadynamic thruster to provide additional thrust. The plasma funnel developed over the air inlet from the magnetohydrodynamics forces greatly increases the ability of the engine to collect air, increasing the effective diameter of the air inlet up to hundreds of meters. Thus, it is theorized that the Ayaks' engine can use atmospheric oxygen, even at heights above 35 kilometres (115,000 ft).
The fuel feed system of the Ayaks engine is also novel. When the aircraft reaches hypersonic speed, it uses the heating energy from air friction to increase the heat capacity of the fuel ("reform" the fuel). The aircraft has double shielding between which water and ordinary, cheap kerosene circulates. The energy of surface heating is used to break up water into hydrogen and oxygen. Thus, the heating capacity of the fuel increases, and the surface of the aircraft cools down. The whole concept is named "Magneto-plasmo-chemical engine" (Магнитоплазмохимический двигатель).
- Energy bypass via coupled MHD generator/accelerator: a portion of the free kinetic energy of air bypasses the combustion chamber, thus reducing entropy rise in the combustion chamber;
- Reforming of the hydrocarbon fuel, increasing its energy concentration;
- Ionization of the air in the nose of the aircraft and the airflow entering the engine;
- Powering the fuel reforming process by the MHD generator in the nose of the engine;
- Increase of the combustion effectiveness of the engine by injecting plasma and/or hydrogen upstream of the main fuel injectors; and
- Diverting some electrical energy produced by the MHD generator to peaceful or military directed-energy devices.
The idea of thermally shielding the engine comes directly from the fundamental analysis of an ideal turboject for maximum thrust analysis in Oates textbook. That is, putting the turbine (work extraction) upstream and the compressor (work addition) downstream. 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.
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|
|Satellite mass, tonne||6|
|Thrust, turbojet engines, tonne||4×25||4×25||4×40|
|Thrust, magneto-plasmo-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|
Earlier publication cited even more impressive expected performance of service ceiling of 60 km and speed of 15..30M 
In 2003, French aeronautical engineer and MHD specialist Jean-Pierre Petit proposed a different explanation about how magnetohydrodynamics is used in this project. His study was based on a paper published in January 2001 in the French magazine Air et Cosmos by Alexandre Szamès and in the same month from information gathered in a small convention about advanced propulsion in Brighton, England. He wrote about a parietal MHD converter, which he believes that Ayaks may both use. He also claimed that the Hall effect induced by this converter would create a plasma in front of the aircraft, and that the resulting plasma cocoon would give the vehicle stealthiness.
References in the popular culture
- The Ayaks program is prominent in The broken sword of the Empire novel by the nationalist author Maxim Kalashnikov.
- Paul A. Czysz Future Spacecraft Propulsion Systems: Enabling Technologies for Space, Springer, 2006, ISBN 3-540-23161-7 pp. 185-195 
- Ovnis et armes secrètes américaines - L'extraodinaire témoignage d'un scientifique, Jean-Pierre Petit, éditions Albin Michel, ISBN 2-226-13616-9
- Maxim Kalashnikov - "The broken sword of the Empire" - ISBN 5-89747-027-8