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Above: The BTS-002 full-scale flying prototype of the Soviet Buran orbiter.
Aerodynamics research showed that adding jet engines to the test version of the orbiter would not significantly alter its flying characteristics. Copyright © 2000 Anatoly Zak
The assembly of the BTS-002 vehicle. Credit: RKK Energia
Four jet engines were the key feature of the BTS-002 vehicle. Click to enlarge. Copyright © 2010 Anatoly Zak
A movable rudder on the vertical stabilizer of the vehicle would "split" during landing to act as a speed brake. Click to enlarge. Copyright © 2010 Anatoly Zak
BTS-002's nose gear had a special extension to enable easier takeoff. Click to enlarge. Copyright © 2010 Anatoly Zak
BTS-002's landing gear was designed to retract in flight. Click to enlarge. Copyright © 2010 Anatoly Zak
BTS-002's cargo bay carried a tank with propellant for the vehicle's jet engines. Click to enlarge. Copyright © 2010 Anatoly Zak
BTS-002's flight controls were very similar to the ones used on the real orbiter. Click to enlarge. Copyright © 2010 Anatoly Zak
Hydraulic system which was used to control horizontal aerodynamic surfaces on the wings of the BTS-002 vehicle. On the background are titanium-made struts, which composed the vehicle's internal structure. Click to enlarge. Copyright © 2010 Anatoly Zak
Rimantas Stankyavichus flew the first mission of BTS-002, along with Igor Volk. Credit: (413)
BTS pilots Aleksandr Shyukin and Anatoly Levchenko. (413)
After almost two decades of abandonment and decay, BTS-002 became a museum exhibit. Click to enlarge. Copyright © 2010 Anatoly Zak
Previous chapter: Buran orbiter
BTS paves the way to the Soviet shuttle
During the development of the US Space Shuttle, a full-scale prototype of the orbiter dubbed Enterprise was carried into the air on the back of a modified Boeing-747 aircraft and then set free in mid-air. With two pilots at the controls, the Enterprise would then glide back to Earth, testing its aerodynamics in process. When the time came for the Soviet Buran to prove its flight capabilities, there was no aircraft, which could support a similar test flight program.
Although a Myasishev VM-T Atlant aircraft was designed to transport elements of the Energia-Buran system, it could not lift a fully assembled vehicle. In the meantime, Antonov-224 Mriya would not appear on the scene until several years later in the program. As a result, Soviet developers chose a totally different approach to atmospheric testing of the winged orbiter than their American colleagues. Instead of lifting a giant glider into the air by another aircraft, a full-scale prototype of Buran was equipped with its own jet engines, so it could take off from the runway under its own power. (413)
Designated BTS-002 or OK GLI (where BTS stands for "big transport vessel" and OK GLI - for "orbiter for horizontal flight tests,") the Buran prototype was almost an exact copy of the actual orbiter. (413) The main difference were four AL-31 engines installed in the tail section of the bird. Two of the engines were equipped with afterburners, like on the Sukhoi-27 fighter aircraft. A propellant tank placed inside the cargo bay of the vehicle would provide the engines with propellant. Although the addition of jet engines did change the aerodynamics of the operational Buran glider, ground testing showed that the impact on flying characteristics would be relatively minor.
Comparing to the operational orbiter, BTS-002 also had an extension on its nose gear, which kept the vehicle under angle of four degrees on the runway for an easier takeoff. (107) The landing gear could be, both, lowered and retracted, while on operational ships, only lowering system would be needed for landing. (106)
Unlike a real Buran, BTS was covered with foam-based equivalents of thermal protection tiles. Nevertheless, all mass and center of gravity characteristics of the real orbiter were preserved on BTS-002.
Specifically, for the BTS program, the ship's digital flight control system was backed up with an analog control system, featuring its own network of sensors, which could handle all aerodynamic surfaces of the vehicle. As it turned out, the back flight controls would never be employed during real flights.
BTS was equipped with ejection seats for two pilots (107) and it was capable of staying in the air up to 30 minutes, instead of three-five-minute glides performed by the unpowered prototype of the US Shuttle.
BTS also had its unique telemetry system, which, unlike operational vehicle, had two sub-systems. One unit, was designed to transmit around 2,300 parameters of the flight control system and its main computers, while, the second would carry 2,200 channels of information from various sensors spread around the ship. In addition, around 450 parameters would be recorded onboard BTS. A special control and measurement station, KIS, was deployed at Myasishev plant to digest telemetry from BTS flights. The actual flight control room was organized at the Zhukovsky airfield. It included a powerful calculation center for real-time tracking of the flight and the transmission of all crucial data to 12 monitors manned by ground controllers. (106)
Test program preparation
To certify systems, which were unique to BTS, special facilities for testing of the propulsion unit, the propellant supply system, the engine fire suppression system, ejection seats and for frequency testing were built at Myasishev Experimental Plant, EMZ. The flight testing itself was conducted at the airfield of the Flight Research Institute, LII in the town of Zhukovsky, near Moscow. Similarly to the Buran's landing facility at Baikonur Cosmodrome in Kazakhstan, the airfield was equipped with landing radar and the Vympel (Banner) microwave landing complex. Existing tracking facilities of the LII landing complex, including the Kama tracking radar and the Opal high-precision optical tracking system, would be used for tracking the vehicle in flight. (106)
Test flight planning
During its real orbital missions, Buran was expected to glide back to Earth without any propulsion. At the altitude of 20 kilometers, the ship's would fly at the speed of 1,870 kilometers per hour or 1.75 faster than a speed of sound. The speed would become subsonic (Mach 0.8) at the altitude of around 10 kilometers. Finally, the touchdown speed was expected to be around 310 kilometers per hour.
It was calculated, that in order to have the projected landing speed, Buran's prototype could have a gliding speed of around 450-470 kilometers per hour. However, after adding possible wind resistance, the gliding speed was increased to 540 kilometers per hour and later adjusted to 520 kilometers per hour. Developers demanded a fixed position of the so-called key point, KT, from which the final approach to the runway would be initiated. For BTS-002 flight planners, it meant that the KT point's coordinates would be pre-programmed and no adjustment based on real-time wind conditions would be possible. For GLI flight tests, the KT point would be located 12.5 kilometers from the end of the runway, at the altitude of four kilometers. Under the circumstances, Buran's descent angles were expected to vary from 17 to 22 degrees and the descent velocity to be 50-60 meters per second. For comparison, the descent speed for a traditional aircraft is normally 4-6 meter per second and the angle of descent is 3-4 degrees.
Only at the altitude of around 500 meters, Buran's steep descent would have to start becoming more gentle and the speed to go down. At the altitude of 100 meters, the pilot was expected to transition to almost an aircraft-like approach. The final landing speed and descent parameters would have to be reached at the altitude of around 15 meters followed by the touchdown with the speed of 300-320 kilometer per hour and the rate of descent of no more than one meter per second.
The crew was expected to pilot BTS-002 manually through a takeoff, ascent and reaching the KT point, as these phases of the flight would not exist in real missions of the Buran orbiter. A two-seat fighter aircraft would accompany the prototype during all tests for visual inspection. Video would also be recorded from the air.
To accumulate plenty of statistics, each flight would include the approach to the runway to the altitude of around 15-20 meters followed by a quick ascent for a second approach and the actual landing. (106) It is clear from pilots' memoirs that during the descent, engines would be put to a low thrust rather then being completely shut down.
Traditionally for the aircraft testing, BTS-002 flying career started with the taxing on the runway, which took place for the first time on Dec. 29, 1984. These test runs were gradually becoming bolder until reaching a takeoff speed and lifting the nose of the vehicle, but without leaving the runway. Finally, on Nov. 10, 1985, OK-GLI took into the air for the first time (52) with Igor Volk and Rimantas Stankyavichus at the controls. There was no attempt to practice the Buran's descent in that flight and the vehicle returned to the runway along a normal aircraft trajectory. The same crew flew three more test missions, which confirmed basic flight capabilities of BTS-002. Later, pilots Anatoly Levchenko, Aleksandr Shyukin, Ivan Bachurin and Aleksei Borodai joined the program.
Beginning with the 4th flight, BTS started practicing Buran's steep descent trajectory. First missions were flown under fully manual control, after which, the auto-pilot started being gradually introduced to control channel by channel -- yaw, pitch and course. During the 6th flight, automated control flew BTS down to the altitude of 100 meters. During the 7th flight, the autopilot was turned off just moments before the touchdown. During the 8th test, the autopilot successfully brought the glider to the runway, even though pilots did take over shortly thereafter. During the 9th mission, the automated system fully controlled the landing, except for the operation of lowering of the nose gear, shortly after the touchdown. Finally, during the 10th flight, on Feb. 16, 1987, all descent and landing operations, beginning with the activation of the autopilot at the KT approach point at the altitude of four kilometers and all the way to stopping of the vehicle on the runway, were performed automatically.
Upon the conclusion of 14 flights, including seven under control of the autopilot, developers considered the automated landing system of the Buran orbiter flight-proven. Nevertheless 10 more BTS missions were ordered to accumulate necessary flight statistics and test the autopilot under less than ideal conditions. The pilots would start the descent with various deviations from the nominal speed, altitude and the direction of flight, often close to allowable limits. However, in all cases, the autopilot reportedly managed to land the glider successfully.
Until April 1988, the vehicle made total of 24 flights, 15 of which concluded with a fully automated landing. (208) Beginning with the 7th flight, the total of 36 approaches to the runway under automated control had been performed. The vehicle always landed well within allowed deviations from expected touchdown point. (106)
The BTS-002's missions allowed to certify both automated and manual flight control of the Buran orbiter and confirmed aerodynamic capabilities of the vehicle. Buran's flight control software was also thoroughly tested. The BTS flight program thus became a major milestone on the way to the first orbital mission of the Buran orbiter in 1988, which concluded with a successful automated landing.
Life after death
The last practical work with the BTS-002 was concluded on Dec. 28, 1989. (208) A flight-processing team of specialists from NPO Molniya, Myasishev experimental team and the Soviet Air Force posed for a group photo in front of the test orbiter in Zhukovsky, after which, the vehicle was retired.
In 1999, a largely neglected BTS-002 was shipped from Russia to Sydney to serve as a tourist attraction during the 2000 Olympic Games. The vehicle was then purchased by an investment group in Singapore, which planned to exhibit the ship around the world. The first destination of the tour was Bahrain, where the ship arrived, only to be seized by authorities due to its owners' financial problems. In the summer of 2003, a private technology museum in the German town of Speyer claimed it purchased the vehicle, however, the ship continued rusting away in the Bahrain harbor until March 2008. Only after all legal battles were settled, the vehicle was transported by sea via Suez Canal to Rotterdam and then up the Rhine River to Speyer. (412)
Next chapter: Buran's spacesuits
Written and illustrated by Anatoly Zak
Last update: November 16, 2013
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