VENTILATION
Buran had a so-called Airframe Pressurization and Ventilation System (SNVP). Similar to the Orbiter’s Purge, Vent, and Drain System, it served several purposes:
GRAVIMOL material covers Buran’s nosecap (B. Vis files). |
to maintain proper temperature and moisture levels in the vehicle’s unpressurized compartments on the ground, to cool the aluminum skin after landing, to vent the unpressurized compartments during ascent and re-entry, and to prevent big differences in pressure between the mid and aft fuselage. The SNVP consisted of fourteen inward opening 510 x 200 mm vent doors, six on either side of the mid fuselage and one on either side of the aft fuselage, and a series of air ducts with non-return valves. Half of the vent doors were equipped with filters.
Thermal control of Buran’s unpressurized compartments was particularly important in the harsh climate of the Baykonur cosmodrome. The SNVP was used for this purpose whenever the vehicle was not in the hangar, whether it be on the pad or during transportation from the assembly building to the pad or from the runway back to the hangar. After circulating through the vehicle the air was released via the vent doors. Another task of the SNVP on the ground was to prevent accumulation of hazardous gases inside the vehicle.
By cooling Buran’s aluminum skin after landing, the SNVP played an important role in ensuring the ship’s reusability. The aluminum alloy from which the bulk of Buran’s airframe was made (D16) could not be repeatedly exposed to temperatures higher than +150/160°, even though Buran would face the same kind of heating during re-entry as the Shuttle (whose skin can withstand +175°C). Therefore, it was necessary to extensively ventilate the vehicle with cool air (no warmer than +10°C)
Buran’s main systems: 1, crew module; 2, forward thrusters; 3, instrument compartment; 4, flight deck; 5, RM-1 and RM-2 workstations; 6, windows; 7, ejection seats; 8, ejection seat escape hatches; 9, RM-3 workstation; 10, radio altimeter; 11, payload bay; 12, payload bay doors; 13, upper narrow-beam antenna (ONA-I) (stowed); 14, Auxiliary Power Units; 15, drag chute compartment; 16, aft thrusters; 17, propulsion system “base module’’; 18, orbital maneuvering engines; 19, body flap; 20, pressurized instrument compartment; 21, lower narrow-beam antenna (ONA-II) (deployed); 22, gas, water, and ammonia tanks; 23, equipment units; 24, tanks of fire suppression system; 25, fuel cell tanks; 26, fuel cells; 27, electric power system instrument module; 28, entry hatch; 29, mid-deck; 30, lower deck (source: Yuriy Semyonov/Mashinostroyeniye). |
after landing. Ground equipment was hooked up to Buran’s SNVP for this purpose within 8 minutes after touchdown.
The SNVP’s vent doors were primarily used to equalize inside and outside pressure during launch and landing. During launch the doors were opened between altitudes of 200 m and 35 km. In orbit the ventilation doors situated in the mid fuselage were again briefly opened prior to payload bay door opening to dump any residual pressure that might affect the operation of the payload bay door latches. Those same vent doors were opened during the return phase at an altitude of 22.5 km. The ones lacking filters were closed again at 400 m to prevent dust contamination of Buran’s interior. The doors in the aft fuselage remained open throughout the orbital phase of the mission. By creating a near-perfect vacuum in the aft fuselage, it became easier to maintain the liquid oxygen tank of Buran’s propulsion system at cryogenic temperatures.
The SNVP also allowed Buran’s internal compartments to be purged with nitrogen to minimize the fire hazard in both the mid and aft fuselage during the early stages of launch and the final phases of landing. At T — 40 minutes the airflow was stopped, after which the vehicle’s interior was purged with ground-supplied nitrogen until T — 5 minutes. Subsequently, the vent doors were closed to ensure that enough nitrogen remained inside the vehicle during the early phase of launch.
Prior to re-entry the aft fuselage doors were closed until landing, allowing the aft compartment to be purged with nitrogen from an altitude of 30 km. The nitrogen was stored in 15 tanks in the mid fuselage [15].