Landing of the Soviet reusable spacecraft Buran remains one of the most impressive episodes in the history of world astronautics. The uniqueness of this event lay not only in the very fact of the device returning to Earth, but also in the fact that the flight and landing took place in a fully automatic mode without the participation of a pilot-cosmonaut.
Engineers had to solve a difficult problem: how to deliver a heavy vehicle weighing more than 80 tons from orbital speed to a complete stop on the runway. The key stage of this process was the final Buran landing maneuver, which was radically different from traditional descent schemes of the time.
Unlike capsules, which use parachutes and jet engines to cushion the impact, Energia-Buran relied solely on the aerodynamic properties of the wing. This required the highest accuracy of calculations on the on-board computer and perfect execution of the underlying algorithms, since the machine had no room for error.
Features of the aerodynamic design
The basis for the successful execution of the landing maneuver was the selected aerodynamic configuration. The device had a load-bearing body and a swept wing, which allowed it to behave like a glider with extremely low aerodynamic quality. lift-to-drag coefficient was only about 1.5, which meant a rapid decrease in speed, but also required a high starting altitude for gliding.
The wing and body design have been optimized to operate over a wide range of speeds, from hypersonic in the upper atmosphere to transonic on approach. Particular attention was paid to the heat resistance of materials, since thermal protection had to withstand colossal air friction temperatures.
An aerodynamic quality of 1.5 means that for every kilometer of altitude reduction, the device flew forward only 1.5 kilometers, which is significantly less than that of conventional aircraft.
Control of the thrust vector during the descent stage was impossible, so maneuvering was carried out solely by changing the roll angle and using rudders. This scheme made the descent trajectory predetermined and strictly dependent on the initial conditions of entry into the atmosphere.
Stages of descent from orbit
The return process began long before entering the dense layers of the atmosphere. Orbital ship Buran switched to orientation braking mode, after which the propulsion system was turned on to dampen the orbital speed. After this, a passive descent began, where the laws of physics played the main role.
At an altitude of about 100 kilometers, the most intense part of the flight began—entry into the atmosphere. The device experienced overloads of up to 3-4 g, and the temperature of the nose cone reached one and a half thousand degrees. At this moment on-board computer continuously adjusted the bank angle so as not to go beyond the safe descent corridor.
Why is entry angle so important?
If the entry angle is too steep, the overloads could destroy the structure or kill the crew (if they were on board). If the angle is too shallow, the device can ricochet from the atmosphere and go into space.
After passing the hottest section and reducing speed to sound, Buran switched to gliding flight mode. It was here that preparations for the final maneuver began, requiring precise positioning relative to the landing strip.
Automatic control algorithm
The heart of the control system was the on-board computer complex, which processed data from gyroscopes, accelerometers and radio altimeters in real time. Algorithms developed by Soviet engineers allowed the system to independently make decisions about trajectory correction without human intervention.
The control system built an optimal descent trajectory, taking into account the current altitude, speed and distance to the airfield. Automatic landing involved performing a complex spatial figure known as an “oblique loop” or a 180-degree turn with a simultaneous decrease.
⚠️ Attention: Unlike manned aircraft, where the pilot can visually assess the situation and make a non-standard decision, automation strictly follows the laid down code, which requires the ideal operation of all sensors.
Particularly difficult was the operation of the system in conditions of turbulence and gusts of wind. The on-board computer had to compensate for external disturbances, changing the position of the rudders and ailerons in a split second in order to keep the device on the glide path.
Approach trajectory
The final part of the flight began at an altitude of about 20 kilometers. The device had to go to the airfield area and take its starting position to perform the landing maneuver. The trajectory was constructed in such a way that by the time the plane touched down the speed and vertical rate of descent were minimal.
The key element was a 180-degree turn, which was performed at a relatively low altitude. At this moment Buran was in the zone of strong winds that could blow the light glider away from the runway. The computer countered these influences by increasing or decreasing the roll.
The approach was carried out on a steep glide path with an inclination angle of about 15-17 degrees, which is significantly steeper than that of a civilian airliner. This allowed the energy to be dissipated more quickly, but required very precise calculation of the starting point of alignment before touching.
| Parameter | Meaning for Buran | Comparison (Airplane) |
|---|---|---|
| Glide angle | 15-17 degrees | 2-3 degrees |
| Landing speed | 300-340 km/h | 200-250 km/h |
| Overload during landing | up to 1.5 g | up to 1.2 g |
| Run length | ~1500-2000 m | ~1000-1500 m |
Sidewind Parry
One of the most critical factors influencing Buran landing maneuver, there was a strong side wind observed on the day of the flight, November 15, 1988. The wind speed near the ground reached 17-20 meters per second, which created a serious threat of demolition of the device.
The onboard control system rebuilt the trajectory in real time, shifting the aiming point against the wind. The device turned its nose against the air flow, compensating for the drift, and only just before touching down it aligned itself along the axis of the runway.
Automatic compensation for strong crosswinds has become one of the main proofs of the reliability of the ship's control system.
Such a maneuver would have required the highest skill from the test pilot, but the machine coped with the task on its own. This demonstrated that algorithms are able to take into account difficult weather conditions more effectively than humans in a stressful situation.
Comparison with the American Shuttle
Although Soviet Buran and American Space Shuttle had similarities in appearance, their landing characteristics and management philosophies differed significantly. The American shuttle was originally designed with manned control in mind, although it had an autopilot.
Control system Burana was designed specifically for full automation, which left its mark on the design of the steering surfaces and algorithms. While the Shuttle pilots could rely on visual contact and intuition, Buran relied only on telemetry.
In addition, the Buran was equipped with air intakes for the propulsion engines (although on the first flight they were not used for reentry), which theoretically gave more room for maneuver in the event of an emergency, although the main scenario always remained glider.
☑️ Criteria for successful landing
Technical details of the final stage
Immediately before touching the strip, at a height of several meters, a leveling maneuver was performed. The rate of descent was dampened by an increase in the angle of attack, which led to a sharp increase in aerodynamic drag.
After touching wheels of a concrete strip at a speed of about 300 km/h, the braking system came into effect. Not only landing gear brakes were used, but also aerodynamic brakes, as well as, if necessary, a parachute system (although they did without it on the first flight).
It is important to note that the chassis Burana was designed with a large margin of strength to withstand the hard landing of a heavy craft. The design of the struts made it possible to effectively absorb impact energy, protecting the fuselage and valuable equipment inside.
⚠️ Attention: Landing at high speed requires a perfectly smooth surface of the runway, as any unevenness can lead to destruction of the landing gear or loss of control.
Results and significance of the flight
Successful completion of a landing maneuver by a ship Buran became a triumph of Soviet engineering. This proved the possibility of creating completely autonomous control systems for complex dynamic objects.
The data obtained on the behavior of the device in the atmosphere, the operation of thermal protection and the effectiveness of control algorithms were unique. They are still of interest to specialists in the field of aerospace engineering and the development of new reusable systems.
Despite the fact that the program was curtailed, the experience gained during testing automatic landing, did not go to waste. Many technological solutions have found application in modern aviation and astronautics, confirming that automation can be more reliable than humans in extreme conditions.
What happened to Buran after landing?
The ship was delivered to Baikonur, where it is still stored. The second flight never took place due to the collapse of the USSR and lack of funding.
FAQ: Frequently asked questions
Why did Buran land automatically and not the pilots?
This was a requirement of the technical specifications to test the operation of the on-board computer and algorithms in a real flight. Additionally, the first flight had no crew on board, making an automatic landing the only option.
Could the pilot intervene during landing?
There were no pilots on board for the first flight. However, the control system was designed so that if a crew were present, they could take control, but priority was given to automation to ensure maximum accuracy.
What was the accuracy of Buran's landing?
The device landed with a deviation of only 1.5 meters from the center line of the runway and 10 meters from the calculated point of contact, which is a phenomenal result even for manned aircraft.
Were engines used during landing?
No, during the final approach and landing itself Buran flew like a glider, using only the aerodynamic properties of the wing. The engines were used only for orbital entry and corrections prior to re-entry.