When work on aerospacecraft began in the West, interest was revived in the USSR. By the mid-1980s the Tupolev OKB with the collaboration of TsAGI, the Kuznetsov OKB and other enterprises and organisations in the military-industrial complex, had prepared a number of proposals for aerospacecraft. These were to be fitted with main and auxiliary liquid-fuel engines, taking off from the ground or being air-launched from carrier aircraft. The next stage was the design of a single-stage aerospacecraft with its main power unit comprising turbojet, ramjet and liquid-fuel rocket motors. In the past few years the OKB has accumulated a wealth of scientific and technological material to enable it to attain its goal, and projects for several single-stage orbiting aerospacecraft with different configurations and engines have been prepared. One of the latest is the ‘2000’ or Tupolev Tu-2000 with a combined power plant comprising turbojet, wide-range ramjet and liquid-fuel rocket engines. (This designation had previously been used for a projected executive aircraft later redesignated Tu-20.)
Faced with the complexity of this task, the engineers decided to begin with a smaller experimental aerospaceplane. This would be used under real flight conditions to test new ideas and new solutions embodied in the aerodynamic layout, powerplant, design and heat shielding of the airframe, onboard systems, engines and equipment. The need for this experimental aerospaceplane is further emphasised by the lack of any full-scale ground simulation facilities for speeds of Mach 6.0-8.0, engine combustion processes and kinetic heating.
The whole uncharted field of the aerospaceplane, the lack of precise information on external factors affecting it, and the present lack of tried and tested answers to questions of design as well as structural materials makes a step-by-step approach to its development and testing essential. For these reasons the whole programme was broken down into two stages: the creation of an experimental hypersonic aircraft with a top speed of around Mach 5.0-6.0, and then of an experimental aerospaceplane to serve as a single-stage reusable prototype for flight testing, including flight beyond the earth’s atmosphere. At present the Tupolev ANTK is working on the second stage, the first stage being effected by using an existing supersonic aircraft.
A tailless layout has been chosen for the aerospaceplane with all its elements structurally integrated around its power package which consists of four turbojets mounted at the rear, a wide-range ramjet under the rear fuselage and two liquid-propellant rocket motors between the turbojets for manoeuvring outside the atmosphere. The aerospaceplane has relatively small, low aspect ratio double-delta wings and a major part in providing lift is played by the flat underside of the fuselage (lifting body). The control surfaces are conventional ones for such a configuration: elevons and a rudder. The main powerplant, the wide-range ramjet, has an air intake with external and internal compression, adjustable combustion chambers with a bevelled exhaust and a multi-channel fuel supply. The primary acceleration is provided by the ramjet. When a speed of Mach 2-2.5 has been reached and the ramjet ignites, the air ducts for the turbojets are closed off. A distinguishing feature of the aerospaceplane’s design is the way in which the airframe and the powerplant are integrated, especially as far as the ramjet is concerned. The underside of the fuselage provides a flow of compressed air for the ramjet and acts as the upper surface of the closed chamber in which the airflow is again compressed internally and burned with fuel while also serving as the upper contoured surface of the bevelled exhaust nozzle.
The large fuselage contains the liquid hydrogen tanks, with the crew of two housed in a cockpit up front. The emergency escape system, in which the nose section and the cockpit is jettisoned, operates from ground level up to maximum altitude. Two versions have been designed: in the first the cockpit descends by parachute and, in the second aircraft-type ejection seats are provided. The experimental aerospaceplane will have ejection seats which will be used after the cockpit has separated. An avionics compartment and the nosewheel well are situated behind the cockpit, while the central and rear fuselage sections are taken up with liquid hydrogen tanks. An oxygen tank in the tail supplies the necessary oxidiser. All the engines use liquefied hydrogen drawn from the single fuel system.
According to preliminary estimates by the OKB, the experimental aerospaceplane will have a take-off weight of 70-90 tonnes and carry 30 tonnes of liquid hydrogen and 5 tonnes of liquid oxygen. In its final form it will have a take-off weight of some 210-280 tonnes. Such an aerospaceplane will be able to place payloads of 6-10 tonnes into earth orbits 200-400 km high. It will resemble the experimental aerospaceplane in layout but will have a bigger wide-range ramjet and up to six turbojets. It will retain the two liquid-propellant rocket motors of the experimental model.
At present the OKB is continuing its research and experimental work on the Tupolev Tu-2000.