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GLL Kholod

Internationally, several countries, such as the United States, Japan, France, Germany, and Russia, conducted air-breathing propulsion technology solutions to efficient, low-cost, point-to-point rapid global access and space transportation. The scramjet, its performance potential, and its design methodology validation were at the center of this quest. Programs sought to address this last major aeronautics frontier.

On March 6, 1979, the Commission of the USSR Council of Ministers Presidium on Military-Industrial Issues adopted a comprehensive plan of research works on the application of cryogenic fuels for aircraft engines. The main objective of this plan was the creation of aircraft power plants operating on liquid hydrogen and liquefied natural gas. It provides for the development and aircraft at supersonic and hypersonic flight speeds. The plan covered the decision of a large range of issues - from the search for the most affective way to the industrial production of cryogenic fuels to create prototypes and models of gas turbine engines and scramjet (scramjet). This connected the USSR Academy of Sciences, Minaviaprom, a number of factories and EDO. The head of the organization in the development and testing of cryogenic fuel engines for high-speed aircraft has been approved by the CIAM. L.I.Baranova.

The most important feature of a scramjet combustion of fuel in a supersonic air stream. Since all the conditions of hypersonic flight essentially undoable on ground test stands, it required flight experiments. The Central Institute of Aviation Motors (CIAM), Moscow, Russia, conducted three rocket- boosted flight tests of its axisymmetric dual-mode Mach 6 design scramjet in the early 1990s. The first was in November 1991, and the second involved a joint project with the French in November 1992. These flights achieved approximately Mach 5.35 and Mach 5.6 respectively. The third attempt was also with the French. In this March 1995 attempt, the engine failed to operate because of some onboard system problems. All scramjet flights were flown captive-carry atop the SA-5 surface-to-air missile that included an experiment flight support unit known as the Hypersonic Flying Laboratory (HFL, GLL in Russian), “Kholod” [Cold].

The Hypersonic Flying Laboratory “Kholod” comprises the entire experimental system including the scramjet engine and the propellant, engine control, engine cooling, instrumentation, and telemetry systems. This laboratory was designed to essentially replace the size and mass of the original SA-5 payload. The hydrogen-fueled axisymmetric scramjet is basically a CIAM Mach 6 design with modifications to the combustor and cooling system to allow testing at Mach 6.5.

Liquid hydrogen direct from the propellant tank circulates through the engine as regenerative coolant before being injected into the engine for combustion. The combustor area cooling system was modified to provide more efficient cooling before injection of the gaseous hydrogen fuel.

In November 1994, NASA contracted with CIAM to continue exploring the scramjet operating envelope from the ram-scram, dual-mode operation below Mach 6 to the full supersonic combustion (scram) mode at Mach 6.5. To accomplish this objective, the higher heat loads required redesign of the combustor and active cooling system; meanwhile, the increase to Mach 6.5 required modifications to the SA-5 booster to improve performance. The contract specifies the building of four identical engines to accomplish all required ground and flight tsts.

Under a contract with NASA, a joint Central Institute of Aviation Motors (CIAM) and NASA team conducted the fourth flight test of the dual-mode scramjet aboard the CIAM Hypersonic Flying Laboratory, “Kholod.” Ground-launch, rocket boosted by a modified Russian SA-5 missile, the redesigned scramjet was accelerated to a new maximum velocity of Mach 6.5. This should allow for the first-time measurement of the fully supersonic combustion mode. The primary program objective is the flight-to-ground correlation of measured data with preflight analysis and wind-tunnel tests in Russia and potentially in the United States.

The first two engines were dedicated to wind- tunnel tests up to Mach 6 simulated flight conditions. The third was designated for flight test, and the fourth will be a backup flight test engine. NASA ground testing of one of the first two engines at the NASA Langley Research Center, Hampton, Virginia, was planned after completion of the flight phase.

Flight launch of the CIAM scramjet took place in the Republic of Kazakstan at the Sary Shagan test range approximately 300 miles north of the city of Almaty on the shores of Lake Balkash. The test range is basically a vast area of flat, semi-arid steppes with large, open launch corridors to the west of the lake toward the Baikonur Space Launch Facility.

Launch preparations began on February 10, 1998. The launch was conducted by Sary Shagan range personnel on February 12 using their mobile launch system consisting of electrical power generators, telemetry, radar, and launch control vehicles. The launch control van also contained real-time telemetry strip charts of selected channels of flight data. The highly trained crew conducted an impressive launch operation under difficult weather conditions.

At 38 sec into the flight, scramjet engine operation and maximum cooling flow rate began as Mach 3.5 was reached. The steam exhaust contrail of the scramjet engine was clearly contrasted with the smaller rocket contrail against the bright blue sky. The contrail and real- time strip chart data confirmed an inlet unstart as the first 1 or 2 sec of fuel injection began. The unstart lasted approximately 10 sec until restart was achieved under continuous fuel injection and remained started for the rest of the flight. Between 56 and 59 sec into the flight, a Mach number of greater than 6.4 was observed at an altitude of approximately 21.3 km. The aim altitude was 24 km.