THE BURAN AIRFRAME

Buran was a double-delta winged spacecraft capable of putting people and cargo into low Earth orbits and returning them to a controlled gliding landing. Aerodynamic­ally, it was a near-copy of the US Space Shuttle Orbiter. The Soviet orbiter was 36.37m long and had a maximum diameter of 5.50 m. Buran’s airframe consisted of the crew module shell, the forward fuselage, the mid fuselage, the aft fuselage, a body flap, delta wings with elevons, and a vertical tail. The airframe was largely made of aluminum alloys such as D16 (also widely used in aircraft) and 1201 (specifically developed for Buran), designed to withstand temperatures between about — 130°C and +150° C. Other materials used were various titanium alloys for areas experiencing higher stresses as well as a variety of high-temperature and tensile steels. Playing a key role in the development of these materials was the All-Union Institute of Aviation Materials (VIAM). All elements of the airframe were covered by reusable thermal insulation to protect the structure against the wide range of temperatures experienced during ascent, in orbit, and during re-entry.

The forward fuselage (Russian acronym NChF) was 9 m long, 5.5 m wide, and 6 m high. It housed the pressurized crew module and forward reaction control system thrusters. Structurally, it consisted of the nosecap, the forward thruster module, and an upper and lower section. The latter two were manufactured separately to allow the pressurized crew module to be inserted during final assembly.

The mid fuselage (SChF) was 18.5 m long, 6 m wide and 5.5 m high and contained the payload bay, the nose landing gear, the electricity-generating fuel cells, and their fuel tanks, wiring for the power system and flight control system, various tanks for the environmental control system and thermal control system, and also propellant lines connecting the forward and aft thruster sections. Twenty-six frame assemblies provided stabilization of the mid fuselage structure. Longerons on either side absorbed the bending loads of the vehicle and contained the hinges of the payload bay doors. Mounted in the side walls were several doors to vent the vehicle’s unpressurized compartments and to service the fuel cells. The front part of the mid fuselage housed the nose gear wheel well, nose landing gear, and nose gear

doors. The nose gear was situated farther to the back than the Orbiter’s, where it is part of the forward fuselage.

The payload bay doors consisted of port and starboard doors hinged at each side of the mid fuselage. They were 18.5m long and had a gross area of 144 m2. Each door was made up of four segments, each of them resting on 12 hinges. The doors were held closed by a total of 33 latches, consisting of 16 bulkhead latches (eight forward and eight aft) and 17 payload bay door centerline latches. The doors were composed of a lightweight graphite-epoxy composite material (KMU-4E) that was much lighter than the D-16 aluminum alloy used in most of Buran’s airframe. At a later stage it was supposed to have been replaced by an even lighter material called KMU-8. The total mass of Buran’s doors was 1,625 kg, which was 620 kg lighter than the mock-up aluminum doors built for the BTS-002 vehicle that flew the atmospheric approach and landing tests. The doors also served as a strongback for the radiator panels that allowed heat rejection in orbit.

The aft fuselage (KhChF) was 3.6 m long, 5.5 m wide, and 6 m high. It housed the Combined Engine Installation with its orbital maneuvering engines and steering

thrusters, the Auxiliary Power Units, the hydraulic system, and a pressurized equip­ment bay. On the outside were attach points for the tail, the body flap, the wings, and the brake chute.

Buran’s double-delta wings provided aerodynamic lift and control of the vehicle during atmospheric flight. The vehicle’s lift-to-drag ratio was 1.3 during the hyper­sonic phase of re-entry and 5.6 at subsonic speeds. Wingspan was 23.92 m and total area 250 m2 (virtually identical to the values for the Space Shuttle Orbiter). The wings had a 45° degree sweep on the inner leading edge and a 79° sweep on the outer (vs. 45° and 81° on the Shuttle Orbiter). The wings were positioned slightly more forward on the fuselage than those of the Space Shuttle, helping to adjust the vehicle’s center of gravity in the absence of heavy, aft-mounted main engines.

Elevons provided pitch and roll control during atmospheric flight. They were divided into two segments for each wing, with each segment being supported by three hinges. Pitch control was achieved by deflecting all elevons in the same direction (elevator function) and roll control by deflecting the left-wing and right-wing elevons in opposite directions (aileron function). Each elevon traveled 35 degrees up and 20 degrees down (compared with 40° and 25° for the Space Shuttle Orbiter).

The tail (or “vertical stabilizer’’) consisted of a structural fin surface and a two-part rudder/speed brake. Its total area was 39 m2 and that of the rudder/speed brake 10.5 m2. As on a conventional airplane, the rudder provided yaw control when both panels were deflected left or right, but by splitting each of its two panels into two halves it also acted as a speed brake, a feature unique to rapidly descending gliders such as Buran and the Shuttle. The segments could be deflected in the same direction for rudder control of plus or minus 23° (27° on the Orbiter) and the halves could be moved in opposite directions for speed brake control for a maximum of about 43.5° each (49.3° on the Orbiter).

An aerodynamic surface not seen on conventional airplanes is the body flap, attached to the bottom rear of the aft fuselage. With a maximum deflection angle of 30°, it provided pitch control trim to reduce elevon deflections [10].