Hypersonic scramjet research

Most of the SSTO designs studied thus far require the use of air-breathing hypersonic scramjets, thereby limiting the amount of fuel that needs to be carried on board. The Russians did extensive research on such scramjets, which have applications not only in aerospace planes but also in aviation and long-range missiles. They were the first to test hypersonic scramjets in flight under a research program called Kholod (“Cold”). Initiated by the Military Industrial Commission in March 1979, Kholod was actually a wide-ranging research program to study the use of cryogenic fuels such as hydrogen and methane in aviation. This included studies of efficient ways of producing such

propellants, but also the study of hydrogen-fueled scramjets. The latter component of the Kholod program was entrusted to the Baranov Central Institute of Aviation Engine Building (TsIAM), while actual construction of the scramjet took place at the Soyuz design bureau (the former OKB-300), already involved earlier in developing propulsion systems for Spiral’s hypersonic aircraft.

The 1 m long scramjet was configured with an asymmetrical three-shock fixed intake and a coaxial combustion chamber. It was launched by the S200 surface-to-air missile from the Saryshagan test site near Lake Balkhash in Kazakhstan and remained attached to the rocket throughout the flight, although at least some of the vehicles were recovered. Five missions were flown with mixed success between November 1991 and February 1998. The French space agency CNES took part in missions 2 and 3 and NASA was involved in the final two missions. The last mission, using a modified version of the scramjet developed at KBKhA in Voronezh, reached a record velocity of Mach 6.47 [29].

NASA used the acquired experience for its own hypersonic scramjet test program called Hyper-X, in which small X-43A experimental research aircraft with an airframe-integrated scramjet were launched from a B-52 bomber using modified single-stage Pegasus rockets. After an initial launch failure in 2001, the X-43A reached record speeds of Mach 6.83 and Mach 9.6 during two test flights in 2004. In Russia, the Soyuz design bureau also had plans for an air-launched, hydrogen – powered scramjet test bed (GLL-31) capable of reaching Mach 10. This would be launched from the belly of a MiG-31 jet with the help of a modified S-300 surface-to – air missile and be separated from the missile for later parachute recovery (unlike the

non-recoverable X-43A). Soyuz also worked on a ground-launched, kerosene-fueled scramjet capable of reaching Mach 4.5, but the status of the latter two projects is unclear [30].

In 1993 TsIAM together with the Flight Research Institute (LII) and NPO Mashinostroyeniya (the former Chelomey bureau) started work on a new hypersonic scramjet test effort under the Oryol program, more specifically under the propulsion component of the program designated Oryol-2-1. This resulted in a new scramjet test bed called Igla (“Needle”), intended to conduct free-flight tests with the scramjet configured to operate in a usable flight vehicle. Measuring 8 m long, the vehicle has a three-module scramjet engine powered by liquid hydrogen and is launched by a UR-100N (SS-19 “Stiletto”) intercontinental ballistic missile (also used as the basis for the Rokot launch vehicle). Capable of operating up to Mach 14.0, it parachutes down back to Earth after separation from the launch vehicle [31].

There is some speculation that Igla may have made its first test flight as part of a major military exercise staged by Russia’s armed forces on 18 February 2004. This saw the launch of several rockets from Plesetsk and Baykonur, with President Vladimir Putin on hand at Plesetsk to witness the launches there. After the Baykonur launch, which involved a UR-100N, Putin said:

“An experiment has been conducted and successfully concluded. Very soon we will have in service the most up-to-date technical systems, which are able to hit intercontinental targets at hypersonic speed and with great precision and have the ability to carry out a deep maneuver both in altitude and direction.’’

Putin was apparently referring to maneuverable hypersonic warheads that are extremely difficult to counter with missile defense systems. NPO Mashinostroyeniya started work on such a system under the name Albatros in 1987, which was then abandoned at the end of the Cold War but may have been resurrected after the United States’ withdrawal from the Anti Ballistic Missile treaty in 2002 [32].

All indications are that scramjet research in Russia is now mainly being per­formed in the interests of the military, but the experience will still come in handy if Russia ever decides to build an SSTO aerospace plane in the distant future.