Buran: The Soviet Space Shuttle

Buran was the first spaceplane to be produced as part of the Soviet/Russian Buran programme. It carried the GRAU index serial number 11F35 K1 and is – depending on the source – also known as OK-1K1, Orbiter K1, OK 1.01 or Shuttle 1.01. Besides describing the first operational Soviet/Russian shuttle orbiter, “Buran” was also the designation for the whole Soviet/Russian space shuttle project. OK-1K1 completed one unmanned spaceflight in 1988, and was destroyed in 2002 when the hangar it was stored in collapsed. It remains the only Soviet reusable spacecraft to be launched into space. The Buran-class orbiters used the expendable Energia rocket, a class of super heavy-lift launch vehicle.

Construction

The construction of the Buran-class space shuttle orbiters began in 1980, and by 1984 the first full-scale orbiter was rolled out. Construction of a second orbiter (OK-1K2, informally known as “Ptichka”) started in 1988. The Buran programme was officially cancelled in 1993.

Operational history

The only orbital launch of a Buran-class orbiter occurred at 03:00:02 UTC on 15 November 1988 from Baikonur Cosmodrome launch pad 110/37. OK-1K1 was lifted into space, on an unmanned mission, by the specially designed Energia rocket. The automated launch sequence performed as specified, and the Energia rocket lifted the vehicle into a temporary orbit before the orbiter separated as programmed. After boosting itself to a higher orbit and completing two orbits around the Earth, the ODU (engine control system) engines fired automatically to begin the descent into the atmosphere, return to the launch site, and horizontal landing on a runway. Exactly 206 minutes into the mission, Orbiter OK-1K1 landed, having lost only eight of its 38,000 thermal tiles over the course of the flight. The automated landing took place on the Yubileyniy airfield runway at Site 251 in Baikonur Cosmodrome where, despite a lateral wind speed of 61.2 kilometres per hour (38.0 mph), it landed only 3 metres (9.8 ft) laterally and 10 metres (33 ft) longitudinally from the target mark. Specifically, as Buran approached Baikonur Cosmodrome and started landing, spacecraft sensors detected the strong crosswind and “the robotic system sent the huge machine for another rectangular traffic pattern approach, successfully landing the spacecraft on a second try.” It was the first space shuttle to perform an unmanned flight, including landing in fully automatic mode. In 1989, it was projected that OK-1K1 would have an unmanned second flight by 1993, with a duration of 15–20 days. Because the Buran programme was cancelled after the dissolution of the Soviet Union, this never took place.

Destruction

On 12 May 2002, the MIK 112 hangar at the Baikonur Cosmodrome housing OK-1K1 collapsed, as a result of poor maintenance, during a massive storm in Kazakhstan. The collapse killed eight workers and destroyed the craft as well as an Energia carrier rocket.

Buran vs Space Shuttle

As a whole the 2 shuttles have the same dimensions, mainly because Buran was made to be a counterpart of the STS Shuttle. But Buran is a little bit lighter than the STS orbiter (62 tons instead of 68 tons). The major difference is the rear of the shuttles, STS have 3 powerful engines SSME for the lift-off whereas Buran has no. This due to an important difference in the design process. Buran was only a payload of the Energia LV so its engines was only for the orbit trajectories. The STS Shuttle has powerful engines because they are used for the putting into orbit, but once there they are useless.

This difference lead to another one, Buran needed a launch vehicle whereas the STS Shuttle is its own launcher. So the engines are on the Energia launcher. The scheme of Energia is nearly the same of STS. A central block (2nd stage) with strap on boosters on its side (1st stage). The 1st stage is made of 4 boosters which are burning fuel and oxygen instead of solid propellant. This is a major difference in design because liquid propellants are more powerful that solid (chemical), and the engines can be easily controlled (increase or decrease the power, or cutting off), so in case of emergency they can be cut-off and prevent the launcher from explosion. The dimensions of the launcher are nearly the same (the Energia’s boosters are smaller), but because Energia uses liquid propellant it is more powerful than STS. The boosters of Energia are also reusable but they use a totally different scheme. Once they burn all their propellant they are ejected from Energia in pair (to avoid damaging the shuttle), then they are separated. A small parachute is deployed to them down, once the atmosphere is more dense a bigger one is deployed. Finally to slow down near touch down retro-rockets are turned on and landing gears are deployed to land them safe. For STS the boosters are ejected after 2 min burn. Then a parachute slow them down until they reach the Ocean where they sea land. Another big difference is that Buran was made to be fully automated or remote controlled, in flight and even in working in orbit (for manipulating payloads). This functionality lead to big differences in the development of the shuttle and the launcher.

The cockpit – Nose

The cabine of the 2 shuttles have some important differences. First, the cockpit of Buran is fixed on shock-absorbers inside the fuselage, to decrease the vibrations during the flight, and the front thrusters block is more voluminous. The front landing gear of the STS orbiter is in the nose under the thrusters block, whereas the Buran’s one is a the junction between the cabin and the payload bay, much more on the back, so the STS orbiter is more tilted during the landing.

On-board computer

The on-board computers are made on the same principle, an important redundancy, to avoid erros in processing and hardware breakdown. The Buran’s computer is cadenced à 4MHz (3 MHz for STS), it is composed of 4 independent units (5 for STS), the dead memory is stored on magnetic tapes, the memory of the Buran’s computer is 819 200 words of 32 bits (106 496 words of 16 bits for STS) which give it a better calculation power. The engineers of the STS computer decided to use well known languages such as FORTRAN for coding the algorithme whereas for Buran new computer science languages were developed (high and down level). It’s more powerful because it uses all the power of the hardware but needs more time to make the language and needs more time for the engineers and technicians to be fully ready to work on it.

The dashboard

The dashboard of Buran was not complete when it flow on November 15, 1988, so it’s not easy to compare it with STS. Due to the automatic functionality it was simpler to the STS one. The Buran’s avionics are clear expression of the Soviets’ general preference for functionality, rather than sophistication, in design. Compared to the advanced digital-fly-by-wire controls system of the U.S. Shuttle, the Buran’s avionics appear

rudimentary. On the Soviet side, the Buran cockpit featured mostly dial instruments, rather than digital displays. The Buran testbed vehicles apparently used an analog version of the flight control system because the digital system was problematic.

The wing

The 2 wings of the orbiter are making a delta wing. It is made of 5 parts, the apex, the middle part with the landing gear, the torque box, the protection of the elevons and the elevons. The wing is light with longerons and lot of strengten pieces. The external coating has also a tighten function like a honeycomb. The lower and upper sides are covered up with heat shields. Each wing measure 18.3 m long and 1.5 m of thickness. The elevons at the end of each wing can move fomr -21.5° to +36.5°. They are from honeycomb structure in aluminium and divided in two parts to minimize the strength on the wings’s hinge.

The payload bay – central part of the fuselage

The payload bays of the two orbiters have the same dimensions and the same function. There is few minors differences in the central part of the fuselage because it’s a part where tanks and antennas are stored, so their locations and nature are differents. In the early design of Buran the payload bay doors were in metal (titanium alloy), which is very heavy, but the use of composites materials made it possible to decrease the mass of the doors of 600 kg compared to the metal model.

The remote manipulator system

The Remote Manipulator System is very different in functionality between the two orbiters, but they have nearly the same dimensions the same liberty degrees, tilts angles and strength (payload of approximately 30 tons). The Buran’s RMS is 360 kg and the STS’s one is 411 kg. Moreover, Buran has two RMS, one on each side of the payload bay, an main RMS and a second in case of failure. The major difference is once again in the automatic functionalities. The Buran’s RMS can execute an automatic sequence stored in the computer or can be remotely piloted from Earth by a technician. Note that the Buran’s RMS was not finished for its first flight in 1988. It was planned to be added few years later.

The vertical stabilizer

The vertical stabilizer is the same for the two orbiters and has the same function, orientating the shuttle during the re-entry phase and aero-brake function. The parachute was introduced later on the Orbiter (after the accident of Challenger), whereas Buran has one from the start.

The engines

The rear part of the two shuttles are very different. The STS orbiter has three different kind of engines at the rear, the SSME (for putting it into orbit), the OMS for orbit insertion and RCS (steering system) for precision movement once in the working orbit. Buran has only two king of engines, the mains (which use liquid oxygen and kerosene) and the steering system with gazeus oxygen. This major difference make the rear of Buran much more lighter and less complicated to maintain. Moreover there is no pods (for the OMS) so the engineers decided to put turbojet at the base of the vertical stabilizer to increase the travel distance during the re-entry phase in case Buran miss the entry window. But they were removed for the first flight because the system was not ready yet.

Energy

The energy systems on the orbiters are similar. There is a fuel cell for electricity and Auxiliary Power Units (APU) for the mechanical systems. The electrical energy is given by a fuel cell, it uses oxygen and hydrogen to generate electricity and produce water for the crew. The americans also used power cells for their Apollo program whereas russians use electrical batteries in that time. But they developed a new fuel cell especially for Buran (from the one they made for their Lunar program). This fuel cell was not installed on the first flight of Buran. The power was given by additional batteries (in the payload bay). The energy used for aerodynamical mechanisms (vertical stabilizer, elevons, landing gears) is produced by an APU. For both shuttles their is three networks and three APUs working in case of a failure (103 kW of power for the Orbiter, 105 kW for Buran). They both use hydrazine as propellant.

Heat shield

The heat shield is a major part of the space shuttle, it protects it during the re-entry in the dense layers of the atmosphere, because the temperature could grow up to 1200°C. The heat shield of Buran is made from three kinds of materials, Reinforced Carbon Carbon plates for the nose and the leading edges of the wings, tiles (38600), black ones mainly of the lower part (where heat is high, they can resist until 1650°C) and white tiles on the other parts of the surface of the fuselage. The thermal protection is mainly ensured by the tiles and also by a coat layer between the tiles and the fuselage. The heat shield of the STS orbiter is composed of 2 types of tiles (black and white) and RCC material for the leading edges of the wings and the nose. The black tiles of the orbiter can resist to 1260°C. The heat shield is the Achilles’ heel of the shuttle. For the STS orbiter the engineers were forced to make another glue to settle the tiles because some of them fell down during the first flight. Moreover, the organisation of the tiles on the surface of the fuselage is very important in comparison of he plasma flow. The engineers working on Buran knew it so developed a very resistive glue (only 7 tiles felt during the first flight) and they assembled the tiles in a particular way. The tile positioning on Buran is different from the American shuttle. On Buran there are no triangular and acute-angled tiles, and all the long slits between the tiles are perpendicular to the plasma flow (see opposite figure). This organization of the tiles makes it possible to reduce aerodynamic turbulences during the flight. As for the nasal part, the elevons and the drift, the tiles are positioned according to a range. For the change of direction of the joints lines pentagonal tiles are introduced, because they do not have acute angles. Later the american engineers developed a new thermal protection named Advanced Flexible Reusable Surface Insulation (AFRSI), it is a thermal coat much more resistive to hits than the tiles. They use it where the heat is not too important (instead of white tiles), it seems that the soviet engineers developed something similar (as we can see on the picture below) but didn’t use it on the fifth shuttles in construction.

Security

The security was an important part of the process during the development of the two orbiters. The major parts of the avionics systems came from aviation (where it was well tested and approved), main circuits, tubes, wiring are doubled, tripled or even quadrupled (for the on-board computer), so that a hardware failure is practically impossible. The main advantage of Buran over STS is that is was made from start to be fully automated. So the computer can take decision more quickly than the crew in case of emergency to save the crew and the payload, by reducing thrust or even eject the shuttle (500 scenaries are stored in the computer). If the shuttle is ejected it will return safely in automatic flight to the landing strip. Moreover, the engines of Energia LV use liquid propellant and can be shutdown if wanted. The pilot and the co-pilot can also be saved by the automatic ejection of their seats during the ascent (from 50 m to 35 km).