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|Above: The actual BOR-5 No. 505 space plane, which survived a scorching heat of hypersonic reentry into the Earth atmosphere in 1988, followed by almost two decades of neglect. It is a question which was more damaging. Copyright © 2010 Anatoly Zak|
Previous chapter: Spiral orbiter
Scaled prototypes pave the way to Buran
One of the biggest technical challenges facing Soviet engineers during the development of the Buran reusable space plane was complex aerodynamics and heat loads, which would be encountered by the winged vehicle during its return into the Earth atmosphere.
The task of resolving these problems was first taken by TsNIIMash research institute in Podlipki, the main certification and development center of the rocket industry, and TsAGI institute in Zhukovsky, key organization of the aviation industry. Researchers started their work with extensive wind-tunnel testing of scale models, which represented the entire orbiter or its major components. At the beginning of the 1980s, some 97 models were built for thermal tests, 27 -- for gas-dynamics tests and 16 -- for acoustics tests. New methods of thermal and thermal-vacuum testing had been developed in process.
Ultimately, scaled models of the Buran orbiter would have to be sent either on a ballistic arch beyond the atmosphere or straight into orbit, so it could then simulate conditions of atmospheric reentry. The latest state-of-the art methods for diagnostic of heat flow dynamics would be used during these missions. The USSR's Flight Research Institute, LII, had first conceived such program for Buran's aborted predecessor -- Spiral. A department at LII led by Gennady Vladychin proposed a 1-to-2 model of the Spiral orbiter dubbed BOR-4 -- a Russian abbreviation of "Unpiloted Orbital Spaceplane." The BOR-4 project followed the development of yet smaller models -- BOR-2 and BOR-3 -- which were also used for testing of aerodynamics and thermal protection systems at the altitudes of up to 100 kilometers and velocities up to 13 times the speed of sound (Mach 13). (317)
After the Spiral project was cancelled in favor of Buran, the development of Spiral's scaled prototypes still went ahead for the benefit of the new program. Despite a considerable difference between the design of two space planes, BOR-4's aerodynamic shape still closely matched the profile of the Buran's nose section -- one of the critical areas during the reentry. It was decided to employ BOR-4 to test Buran's heat-resistant tiles during the descent along trajectories closely resembling those of the future orbiter. On BOR-4, tiles intended for Buran were glued on top of the old thermal protection layers originally developed for Spiral. Special thermal indicator paints were used to measure distribution of heat loads on the body of the vehicle. Around 150 different sensors were to gather information on the conditions of the flight, for subsequent recording onboard and following downlink to two telemetry ships and, during the reentry, to a special ground receiving station.
Eight liquid-propellant thrusters would be used to maintain right orientation of the space plane in airless space and asymmetrical movement of the wings would enable to bank the spacecraft.
Following exotic design of the Spiral space plane, BOR-4 could tilt its wings, thus changing their span. During the launch of the model under the payload shroud of a special version of the Kosmos-3 launch vehicle, the prototype's wings would be folded to almost vertical position. Only after the separation from the upper stage of the rocket and the beginning of descent, wings would unfold at the altitude of 70-60 kilometers. In the first mission, wings were opened to the angle of 57 degrees, and, in following launches, the angle of the wing opening was reaching 52-54 degrees.
Upon plunging into the Earth atmosphere, BOR-4 would overcome plasma caused by friction of the ship with the air at hypersonic speed and test thermal protection system in process. Then, at the altitude of 30 kilometers, flight control system would send the vehicle into a steep spiral, in order to slow down the craft as quickly as possible. At the altitude of 7.5 kilometers, the parachute would open, providing a touchdown with the vertical speed of 7-8 meters per second. (106)
BOR-4 flight results
The total of five 1,450-kilogram vehicles in BOR-4 series were launched, four of them into orbit. The fifth orbital launch was planned but was eventually cancelled. BOR-4 missions enabled to obtain critically important experimental data for the development of Buran's heat shield. All major types of thermal protection systems for Buran were tested, including structures designed to protect a nose cap, leading edges of the wing, as well as dark tiles for the bottom and white tiles for side sections of the orbiter and, finally, thermal blankets for the top surfaces. (106)
BOR-5 aerodynamic prototype of Buran
The BOR-4 project was followed by the development of the BOR-5 scaled prototype, which unlike its predecessor, exactly matched the aerodynamic shape of the Buran orbiter, for the exception of being eight times smaller. The 1,450-kilogram BOR-5 glider was designed to try aerodynamic capabilities of Buran, including balance and stability, as well as to measure pressure, heating, and acoustic loads on the ship. Thermal indicator paints, along with melting probes, temperature and other sensors were spread around the vehicle. The information from several accelerometers, angular velocity sensors, gyroscopes, pressure indicators, aerodynamic surface movements would be recorded onboard and transmitted to the ground during the flight. At the same time, BOR-5 was not intended to test heat-resisting shield of Buran.
To control the vehicle in flight, BOR-5 was equipped with a programmable computer, using an inertial navigation system. During the flight in airless space, small thrusters would be used to maintain the correct attitude, while aerodynamic surfaces would later take over to steer the vehicle during its gliding descent through the atmosphere.
BOR-5 flight profile
The BOR-5 gliders would be launched from Kapustin Yar test range by a variation of the Kosmos-3 rocket, dubbed K65M-RB5, on a suborbital ballistic arch in the direction of Lake Balkhash. The descent area was within the range of the Soviet anti-missile test facilities and heavily equipped with radar and other tracking hardware designed to detect high-velocity targets reentering the Earth atmosphere. After a peak of its trajectory at the an altitude of 210 kilometers above the Earth surface, BOR-5 would separate from the upper stage of the rocket and begin a descent with the initial speed of five kilometers per second. Upon hitting the discernable Earth atmosphere at the altitude of around 50 kilometers, BOR-5 would start aerodynamic maneuvering, including bank maneuvers and changing the angle of attack (raising its nose to expose the belly toward the air flow). In order to simulate flight mode of a much bigger Buran, BOR-5 would be programmed to fly much faster. The bird would begin the testing phase of its mission covering 1,070 kilometers per hour and conclude it with the speed of around 850 kilometers per hour. (The actual Buran orbiter was expected to fly 650 kilometer per hour at that point of its trajectory.) A much higher speed led to BOR-5 experiencing heat loads almost 1,000 degrees higher than those expected for Buran. As a result, BOR-5 could not be protected with reusable tiles designed for Buran. Instead, BOR-5 was covered with fiber-plastic-based shield, which would be carried away in layers during the reentry. The most critical area of the nose was made out of heat-resistant alloys. A special fiber-plastic, which would be transparent to radio signals, would also be tested.
At the end of the test phase of the mission, BOR-5 would cover around 2,000 kilometers and descent to the altitude of seven-eight kilometers approaching the western edge of Lake Balkhash. At that point, the flight-control computer would command the vehicle to enter a steep spiral descent, after which the parachute would open at the altitude of three kilometers. The vehicle would hit the ground with the speed of 7-8 meters per second.
Between 1984 and 1988, the total five vehicles in BOR-5 series had been launched. First two flights were conducted primarily for testing of a modified launch vehicle and to try general performance of the BOR-5 prototype. The first test flight had to be repeated due to the failure of the first prototype to separate from its rocket. All further missions were successful and even showed slightly higher aerodynamic performance of the vehicle comparing to estimates. (106)
BOR mission chronology:
1980 Dec. 5: A model of the Spiral space plane, designated BOR-4c, conducted its first suborbital flight in the direction of Lake Balkhash, on top of the K65M-RB5 (Kosmos-3) rocket to test a vehicle for future orbital missions.
1982 June 4: A BOR-4 No. 404, was launched into orbit and splashed down in the Indian Ocean. It was announced under name Kosmos-1374.
1983 March 16: A BOR-4 No. 403, was launched into orbit and splashed down in the Indian Ocean. It was announced under name Kosmos-1445. The recovery of the spacecraft by the Soviet Navy vessel was observed and photographed by a crew of an Australian military plane. The pictures of the top-secret recovery operation were then published around the world, prompting the secrecy-conscious Soviet authorities to re-schedule future missions to conclude in the Black Sea.
1983 Dec. 27: A BOR-4 No. 405, a model of the Spiral space plane was launched into orbit and splashed down in the Black Sea instead of the Indian Ocean to maintain secrecy around the project. It was announced as Kosmos-1517.
1984 July 6: The first suborbital launch of the BOR-5 No. 501 orbiter. Due to an electrical failure, the BOR-5 prototype did not separate from the launch vehicle.
1984 Dec. 19: The last launch of the BOR-4 orbiter concluding a series of four test flights. It was announced as Kosmos-1614. The craft splashed down in the Black Sea.
1985 April 17: The second test launch of the BOR-5 No. 502.
1986 Dec. 27: The third launch of the BOR-5 No. 503.
1987 Aug. 27: The fourth launch of the BOR-5 No. 504.
1988 June 22: The fifth launch of the BOR-5 No. 505.
BOR-5 project development team:
Next chapter: BTS-002/OK GLI test vehicle
Writing and photography by Anatoly Zak
Last update: August 9, 2010
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What was probably set up as a showcase image of the BOR-4 space plane assembly had never been published during the Soviet period.
A fully assembled BOR-4 vehicle, complete with Buran's thermal protection tiles, is apparently shown during pre-launch processing.
The BOR-4 No. 403 space plane, officially known as Kosmos-1445, is being recovered from the Indian Ocean in 1983, as Australian navy crews look on.
The BOR-5 space plane. Note deployed speed brake on the tail's vertical stabilizer. Click to enlarge. Copyright © 2010 Anatoly Zak
Along with heat and time damage, special temperature-indicating paint apparently also left its mark on various parts of the vehicle. Click to enlarge. Copyright © 2010 Anatoly Zak