Category Energiya-Buran

The new launch vehicle was called RLA-130. While there were still four strap-on boosters with 600-ton RD-123 engines, the three 250-ton thrust RD-0120 engines were now on the “external tank’’ rather than on the orbiter. The overall launch mass was the same as that of the OS-120 (2,380 tons), but the orbiter now weighed just 116.5 tons at launch as compared with 155.35 tons for the OS-120.

Now devoid of main engines, the OK-92 orbiter was to be equipped instead with two kerosene-fueled D-30KP turbojet engines mounted in external pods on either side of the aft fuselage. Widely used on the Ilyushin-62 passenger airliner, these would have to give the orbiter more flexibility in reaching the runway. Also, with a shorter landing roll-out (2.5-3 km vs. 4 km for the OS-120), the vehicle could land on many ordinary runways in the USSR. The engine inlets and outlets would be protected from the vacuum of space and the heat of re-entry by jettisonable covers. The engines were to be activated at an altitude of between 5 and 8 km.

The orbital maneuvering engines and aft reaction control thrusters were now installed in pods adjacent to those housing the D-30KP engines. The nozzles of the forward reaction control thrusters were protected during launch and re-entry by a special cover. As on the OS-120, the propellants to be used by the engines would be hypergolic. The orbital maneuvering engines were to be derived from the 15D619 engine used on the second stage of KB Yuzhnoye’s UR-100 ICBM. The ultimate goal, however, was to replace the toxic propellants by a combination of hydrogen peroxide (H2O2) and kerosene, the latter of which could then be used both by the

D-30KP turbojet engines and the on-orbit propulsion system. For that combination engineers would draw on the experience gained with the RD-510, an H2O2/kerosene engine developed at Energomash for the lunar module of the canceled N-1/L-3M manned lunar project.

OK-92 retained a solid-fuel emergency escape system for early launch aborts, but it now consisted of a single engine installed under the vertical stabilizer. This would be jettisoned 56 seconds into the launch, after which the vehicle would have gained enough speed and altitude to reach the runway with its turbojet engines after an emergency separation from the rocket. In case they were needed in a launch abort, the D-30KP engines could be activated in about 30-50 seconds.

Another feature which set OK-92 apart from the US Orbiter was the use of two remote manipulator arms to deploy payloads from the cargo bay. It was also planned to use the arms in docking operations, pretty much like the Space Shuttle Endeavour used its mechanical arm to dock the Unity module with Zarya during the first Shuttle ISS assembly mission (STS-88) in 1998.

Prior to the maiden orbital mission, the Russians were planning to carry out an extensive series of atmospheric approach and landing tests. In the first stage many on­board systems (such as the propulsion and emergency escape engines, various cabin systems, the remote manipulator arms, etc.) were to be replaced by mock-ups and the vehicle could take off either on its own power or (if its mass was reduced to 60-80 tons) on the back of the An-22 “Antey” aircraft, which would then release it at an altitude of about 2 km. If the mass was reduced to 51-60 tons, the An-22 could also be used to transport the orbiter over a distance of about 2,000 km at an altitude of 2 km. Both for the drop tests and the ferry flights the OK-92’s D-30KP turbojet engines could be used to assist during take-off and the climb to cruise altitude.

For the second stage of the landing tests the OK-92 would be outfitted with most of the systems needed for orbital flight, including the propulsion system and the solid – fuel escape motor. Now too heavy to be carried by the An-22, the OK-92 would fly all the remaining atmospheric test flights on its own power. Plans called for using the combined thrust of the turbojet engines, orbital maneuvering engines, and the solid – fuel motor to take the vehicle to an altitude of 21km and a speed of 1,800 km/h (Mach 1.5) to simulate the final portion of its mission. This was far higher and faster than NASA had been able to do with Enterprise. At this point in time the Russians did not plan a dedicated atmospheric test vehicle, but one that would later be modified into a spaceworthy orbiter. At the time, NASA was planning to do exactly the same with Enterprise, until it was realized in late 1977 that it would be cheaper to turn Structural Test Article STA-099 into the second flight article (what became OV-099 Challenger).

The turbojet engines would also have allowed the OK-92 to fly on its own power to the Baykonur cosmodrome either from the manufacturer or from back-up runways. The range would have been 1,600 km at a cruise altitude of 3 km. However, that could have been increased to 3,000 km by increasing the fuel supply for the engines and using the emergency solid fuel motor as an afterburner on take-off [58].

Thermal protection was definitely one area where the Russians heavily benefited from US experience. Like the Shuttle Orbiter, Buran was largely covered with black and white silica tiles, with reinforced carbon-carbon (RCC) protecting the nosecap and the leading edges of the wings. Ceramic reusable surface insulation was developed in

the 1960s by Lockheed long before the beginning of the Shuttle program, but had to compete with other thermal protection design concepts such as replaceable ablator panels and metallic heat shields before it was eventually chosen for the Shuttle. There was also an alternative idea from Rockwell to use mullite tiles made from aluminum silicate. Therefore, the use of silica tiles on the Shuttle was certainly not a foregone conclusion when research on the Space Shuttle began in the late 1960s. Reinforced carbon-carbon was developed by Ling-Temco-Vought (LTV) for the Dyna-Soar project in the early 1960s.

Although the Myasishchev design bureau did some research on foam ceramic insulation (in cooperation with the All-Union Institute of Aviation Materials) for its spaceplane projects in the early 1960s, there are no indications that the experience gained was passed on to the Buran team. Although the US experience was readily available when work on Buran began in 1976, the Russians still needed to develop their own techniques to process the required raw materials and manufacture the tiles. As Gleb Lozino-Lozinskiy later recalled, it was initially believed that the quartz sand from which the fine quartz fibres for the tiles were made was simply not available in the Soviet Union and would have to be imported from Brazil, but that eventually did not turn out to be necessary [13].

Buran’s thermal protection system (Russian acronym TZP) had an overall mass of 9 tons and was designed to protect the vehicle’s aluminum skin from the very low temperatures in Earth’s shadow (down to — 150°C) to the extremely high temperatures encountered during re-entry (up to +1,600°C). The temperature of the aluminum skin was not allowed to be lower than —120°C or exceed +160°C and shouldn’t be any higher than +50°C prior to the beginning of re-entry. These conditions needed to be met in order for Buran to make a total of 100 missions. Buran had five types of thermal protection: white tiles, black tiles, felt material, carbon-carbon, and thermal barriers.

Buran’s avionics system performed three main functions:

– Guidance, navigation, and control: input of navigational data into the on­board computers, which in turn sent signals to the engines for attitude control and maneuvering functions in orbit and to the aerodynamic surfaces for control during atmospheric re-entry.

– Sending switch-on/switch-off commands to on-board systems and changing their operating modes in keeping with the flight program.

– Monitoring the operation of on-board systems and in case of anomalies ensure the safety of the crew and the completion of the flight program.

Buran’s avionics systems had to meet much higher standards than those of the Soyuz spacecraft because they had to be capable of operating much more independently from ground control stations and needed to ensure a precision landing on a runway rather than a landing in vast stretches of steppe in Kazakhstan. Moreover, they were supposed to enable the vehicle to fly unmanned missions. Buran’s avionics systems consisted of 1,256 instruments of 105 different types installed in 59 electronics boxes in the crew module, the mid and aft fuselage.

In-orbit anomalies posing a serious threat to the crew could have resulted in any of three abort scenarios: “Immediate Return’’, “Early Return’’, or rescue by a Soyuz spacecraft. Buran crews would have had checklists instructing them what to do in each of those situations.

Immediate Return

“Immediate Return’’ was an abort scenario requiring Buran to deorbit between 40 minutes and 3 hours after the occurrence of the anomaly. Forty minutes was considered the minimum time needed to complete all preparations for re-entry such as closing of the payload bay doors, preparing hydraulic systems, donning pressure suits, and loading re-entry software into the on-board computers. One anomaly likely to result in an Immediate Return was considered to be a serious fire in the crew compartment not disabling the vehicle or the crew. After extinguishing the fire with available means, the crew would have donned their Strizh pressure suits to prevent smoke inhalation. If the fire threatened to go out of control after the crew had put on the suits, the crew also had the option of depressurizing the cabin to starve the flames of oxygen. Another such anomaly would be a sudden leak in the ODU propulsion system that within a short period of time would lead to an inability to fire the deorbit engines or position the ship for a Soyuz rescue mission, stranding the crew in orbit.

“Immediate Return’’ could only end with a safe runway landing if the vehicle’s ground track happened to carry it over one of the three available Soviet landing sites within a short time after the occurrence of the anomaly. If this was not the case, the crew would have had to eject from Buran before it crash-landed. Factors to be taken into account here would have been the need to protect public safety and have rescue crews within a reasonable distance of the landing zone (especially if the vehicle had to be ditched in the ocean).

The party/government decree of 17 February 1976 that approved the Energiya – Buran program stipulated that in order to save costs the program should use as much of the N-1 infrastructure at Baykonur as possible. Exactly the same recom­mendation was made by a special commission of the Strategic Rocket Forces that visited the cosmodrome in October 1977. On 1 December 1978 the Central Commit­tee of the Communist Party and the Council of Ministers approved funding for this gargantuan undertaking. However, any cost savings by reusing or adapting N-1 infrastructure must have been relatively small. Both the giant N-1 assembly building and the two N-1 launch pads had to be almost completely rebuilt and several other facilities (most notably the Buran processing building and the runway) had to be built from scratch.

Construction work got underway in 1978 and—as had been the case with the N-1 program in the 1960s—was soon spotted by US photoreconnaissance satellites, providing a clear indication that the Russians were embarking on a major new space initiative. Especially, the construction of the runway was a telltale sign that the Soviet Union was working on a response to the US Space Shuttle program. By the

General location of Energiya-Buran and Soyuz facilities at Baykonur: 1, housing area; 2, MIK OK; 3, MIK RN; 4, SDI; 5, MZK; 6, Energiya-Buran launch pads (nr. 37 and 38); 7, UKSS; 8, landing complex; 9, Soyuz assembly buildings; 10, Soyuz launch pad (source: Aviatsiya i kosmonavtika).

mid-1980s photographs of the Energiya-Buran facilities made by the French SPOT remote sensing satellite were openly available in the West (see Chapter 7).

The Energiya-Buran facilities were located in the central part of the cosmo­drome, some 40 km north of the city of Leninsk and just to the west of the oldest part of the launch site, namely the “Gagarin” launch pad and associated facilities for the Soyuz rocket.

The cosmodrome is divided into so-called “sites”. The most important ones dedicated to Energiya-Buran were:

The Buran processing building (MIK OK) and a platform for test firings of Buran’s propulsion system and Auxiliary Power Units.

The Energiya assembly building (MIK RN).

The Assembly and Fueling Facility (MZK) and the Dynamic Test Stand (SDI).

Energiya-Buran launch pads 37 and 38.

A combined test firing stand and launch pad for Energiya (UKSS).

A landing complex with runway and associated facilities.

Sites 254, 112, and 112a comprised the so-called “Technical Zone’’ (TK) of the Energiya-Buran facilities at Baykonur.

Besides simulator training, a lot of training was conducted by both the LII and GKNII pilots on many types of aircraft. This was mainly in preparation for the atmospheric landing tests on the BTS-002 and also to test the automatic landing systems in preparation for the first flight of Buran in 1988. The training took place both at LII in Zhukovskiy and at the Baykonur cosmodrome.

The most extensively used type of aircraft were Tupolev Tu-154 passenger planes converted as “flying laboratories’’ (Letayushchiye Laboratorii or LL) and therefore also known as Tu-154LL. These were the equivalents of the Shuttle Training Aircraft (STA) in the Space Shuttle program: Gulfstream II business jets which had their cockpit layouts modified to resemble that of the Shuttle. On the STA the left-side instrument panel was modified with a set of Orbiter displays and controls, while the right side contained the normal Gulfstream instruments as a safety measure. The Tu-154LL similarly had a “split-personality” cockpit, but here the Buran displays and controls were in the right side of the cockpit, with the windows draped to simulate the view out of Buran’s cockpit. As on the STA, an on-board computer system translated the pilot’s inputs into control movements largely mimicking those of Buran. In order to match the descent rate and drag profile of Buran, the thrust of the two side-mounted engines was reversed. Opening of the speed brake was simulated by controlling the thrust of the center engine. The Tu-154 flying labs were used to simulate both manned and automatic landings [36].

Although several Tu-154 aircraft were flown in support of the Buran program, only two had the modified cockpits (serial numbers 083 and 119, also known as LL-083 and LL-119, tail numbers CCCP-85083 and CCCP-85119). Other Tu-154 aircraft used by the Buran pilots had serial numbers 024 and 108 [37]. At least one of the aircraft reportedly also had a Buran-type cockpit installed in the front part of the passenger cabin [38].

Also actively used were several MiG-25 jets that simulated landings from much higher altitudes than the Tu-154 (over 20 km compared with about 10 km). One type was a modified version of the MiG-25RBK reconnaissance bomber, which had its standard equipment replaced by communication systems, telemetric equipment, and the like. Special containers with equipment could be mounted on pylons under the wings. Painted under the cockpit of these aircraft was the number 02.

The other was a modified version of the two-seater MiG-25PU training aircraft. It was known as MiG-25-SOTN (SOTN standing for optical/TV surveillance) and served the purpose of escorting other Buran-related training aircraft as well as Buran itself to the runway, with a cameraman seated in the front cockpit shooting video. The MiG-25-SOTN, piloted by Magomed Tolboyev, was in the air both for the launch and landing of Buran on 15 November 1988. Apart from serving as a chase aircraft, the MiG-25-SOTN was also used as a Buran training aircraft in its own right. It had the number 22 painted under the cockpit [39].

LII pilots conducted Buran approach and landing flight profiles on numerous other types of aircraft as well. As a training exercise, unpowered landings were not only performed on the Sukhoy Su-7 and Su-27 fighters, but also on heavy bombers such as the Tupolev Tu-16 and Tu-22M, and the Ilyushin Il-62 passenger plane

(reportedly the most difficult to fly under such conditions). Igor Volk and Anatoliy Levchenko even made unpowered landings from an altitude of 22 km on the super­sonic Tupolev Tu-144 (the twin of Concorde), although it is not entirely clear if this was in support of Buran [40].

When it came to testing the whole stack on the launch pad, NASA and the Russians had different strategies because of the presence vs. absence of main engines on the spaceplane. With the US Orbiter being an integral part of the Space Shuttle stack, all pad-related tests were carried out with the Orbiter in place. In 1979 NASA performed fit checks on the pad of a stack consisting of OV-101 Enterprise and a mock-up External Tank and Solid Rocket Boosters. Pad tests of the main engines were conducted during 20-second “Flight Readiness Firings” several weeks prior to the maiden flight of a new Orbiter (except Endeavour).

Since Buran lacked main engines and was only one of several possible payloads for Energiya, most of the early pad testing at Baykonur focused only on the rocket. Various specially adapted experimental versions of the rocket were rolled out without any payloads attached to undergo dynamic tests, fueling tests, and engine test firings at the Universal Test Stand and Launch Pad (UKSS). Only at a later stage were full-scale mock-ups of Buran used for pad tests of the complete stack.

The 1980 CIA report marked the beginning of a rumor that persisted in the West throughout the 1980s—namely, that the Soviet Union was simultaneously developing two shuttle systems, a small spaceplane orbited by a conventional rocket and a large shuttle similar to its American counterpart. The speculation entered the public domain in the early 1980s via annual Defense Department publications known as Soviet Military Power and America’s leading aerospace magazine Aviation Week & Space Technology (sometimes jokingly called Aviation Leak).

Speculation about the spaceplane was fueled by a series of mysterious test flights in 1977-1979 in which the Proton rocket deployed two heavy objects that re-entered after a single orbit (Kosmos-881/882, 997/998, 1100/1101). Many observers inter­preted these “Double Kosmos’’ missions as re-entry tests of a spaceplane. It wasn’t until the early 1990s that the Russians revealed that these had been test flights of the return capsules of the TKS spacecraft, which were transport ships for the Almaz military space station of the Chelomey design bureau. There are no indications, however, that the missions were linked to the spaceplane program by US intelligence analysts. In fact, the classified 1980 CIA report had correctly identified the missions as re-entry tests of the TKS return vehicles, although it wrongly interpreted the TKS vehicles as successors to the military Almaz space stations rather than transport vehicles serving those stations.

The first irrefutable evidence for the existence of a Soviet shuttle program came in April 1983, when the Australian Air Force publicly released images of the Indian Ocean recovery of the BOR-4 vehicle Kosmos-1445, one of the Spiral scale models that had been modified to test heat shield materials for Buran. Unaware of BOR-4’s roots in the canceled Spiral program, analysts quite logically concluded that the vehicle, which was aerodynamically completely different from the big shuttle, must be a subscale model of the rumored spaceplane.

By the early 1980s US intelligence was aware of the development of the Zenit medium-lift launch vehicle, which it called SL-X-16. The spaceplane was now linked to that booster rather than the Proton, putting it in a somewhat lighter class (roughly 15 tons). Once again a series of mysterious test flights lent credence to this idea. In 1986-1987 the Zenit flew four missions in which it deployed heavy, inert payloads into low Earth orbits (Kosmos-1767, 1820, 1871, 1873), interpreted by some outside the intelligence community as being mass models of the spaceplane. Not until the turn of the century did the Russians reveal that the heavy Zenit payloads had been mass models of the Tselina-2 electronic intelligence satellite with an additional mock payload attached to see how the Zenit would perform when placing heavy payloads into orbit.

This is not to say that there was unanimity among Western observers about the existence of the spaceplane. A report in May 1986 said it was now thought the BOR-4 test flights could have been merely tests of the thermal protection system for the large shuttle [8]. Others interpreted the BOR-4 flights as pure technology development tests analogous to the American PRIME and ASSET programs in the 1960s, not con­nected with any specific follow-on project. It was also noted that the Soviets had never before employed orbital flight tests of subscale models [9].

When Soviet officials finally began disclosing details about the Energiya-Buran system in 1987-1988, there still was no mention of the spaceplane. As preparations for the first flight of Buran were nearing completion and the maiden mission of the

spaceplane had still not materialized, the US intelligence community was beginning to have some doubts as well about the program’s existence. In a classified assessment of the Soviet shuttle program in September 1988, just two months before the flight of Buran, the CIA did not exclude the possibility that BOR-4:

“is only a test vehicle used to gather aerodynamic, aerothermal, and materials

data for the larger shuttle orbiter.’’

However, the overall consensus among CIA experts still was that a separate space – plane program was underway. Unlike the large shuttle, the spaceplane was believed to have significant military potential. It was expected to be able to change its orbital inclination by as much as 15° and change its orbital altitude by about 4,200 km, making it ideal for reconnaissance, inspection, and combat missions. Its expected cross-range capability of up to 2,400 km would provide many additional opportu­nities each day to return to selected military airfields. It was also expected to have limited space station support capability, being used for rapid return of high-priority cargo or crew rescue missions.

The report did acknowledge that the spaceplane had apparently taken a backseat to the large shuttle for several reasons. Two of its primary missions—real-time

reconnaissance of critical targets and post-strike reconnaissance—were by now being fulfilled by newly developed near real-time imaging satellites. Furthermore, resource constraints had possibly forced the Russians to complete the two costly programs sequentially rather than simultaneously. Finally, Soviet attempts to inhibit American anti-satellite and SDI efforts, including a self-imposed moratorium against ASAT testing, were expected to keep the program at a low level at least into the early 1990s. [10].

The Russians elected not to disclose the purpose of the BOR-4 missions until after Buran had flown. One week after the mission, an article in Pravda officially described them as test flights of Buran’s heat shield [11]. However, in February 1989 Scientific American magazine published an article on the Soviet Union’s space pro­gram, which again identified the BOR-4 vehicles as scale models of a small space – plane. With nothing to hide anymore, the Russians were quick to react. Soviet deputy Defense Minister Vitaliy M. Shabanov called the story about the spaceplane a “canard”, not ruling out the possibility that it was just a ploy to obtain funding for a new Dyna-Soar type program. Asked what kind of vehicle was shown in the BOR-4 picture published in the magazine, Shabanov said:

“Well, this is obvious. In order to test the Buran reusable spacecraft four scale models were launched. They were placed into orbit with the designations Kosmos-1374, 1445, 1517, and 1614. The models were used to test elements of the heat shield, control systems, and so on. One of them was photographed by the Australians” [12].

What Shabanov failed to mention, however, was that the vehicles had not been scale models of Buran, but of a spaceplane canceled back in the 1970s.

Even in subsequent years the rumored spaceplane, which some claimed was called Uragan (“Hurricane”), occasionally resurfaced in Western publications. One article in 1995 said that Richard Ward, a noted international technology analyst based with Lockheed, had been told the story of the 1980s space fighter in private discussions with Soviet engineers in May 1990. Ward had been part of an American delegation visiting aerospace centers in Moscow and Kiev, where he talked to several representatives of the aviation industry. He was told that the BOR-4 missions had indeed served as a test series for a full-scale interceptor. Launched by Zenit, the operational vehicle would have had a crew of two and would have been armed with a recoilless gun for on-orbit attacks. The project had reportedly been given impetus after the US announcement that military Shuttle launches from Vandenberg were slated to begin in the autumn of 1986 [13].

Despite the persistent rumors, twenty years on not a single shred of convincing evidence has appeared to counter the notion that the Zenit-launched BOR-4 derived spaceplane was no more than a figment of the imagination of Western analysts. All indications are that BOR-4 was indeed flown for the official reason given by the Russians—namely, to test Buran’s heat shield. It is also known now that there was a parallel effort to convert BOR-4 vehicles into space-to-ground weapons as part of a

Soviet “Star Wars” program (see Chapter 8), but, again, here its role was not that of a subscale model for a piloted spaceplane.

After the cancellation of Spiral in the late 1970s, the Soviet Union did continue conceptual studies of various other small spaceplanes (notably LKS, MAKS, and OK-M), but all of these were aerodynamically different from BOR-4 and its alleged full-scale version. NPO Energiya’s OK-M was intended for launch by Zenit, but primarily seen as a space station support system. However, new evidence shows that NPO Molniya’s air-launched MAKS was supposed to carry out many of the same military tasks that had been eyed for Spiral (see Chapter 9). If there was a need for a military spaceplane in the 1980s, MAKS perfectly fitted the bill. It inherited the military advantages of Spiral, being more flexible and less vulnerable than a Zenit – launched spaceplane. The most plausible conclusion at this stage is that the Russians did consider a military spaceplane in the 1980s, but it was not the one that many Western analysts believed was under development and it was never given the same priority as Buran. Although the BOR-4 missions indirectly provided data applicable to MAKS, they were not seen as precursors to MAKS.

CHANGING SCHEDULES

The original goal for the Buran program was to fly a total of ten test flights using five orbiters. Although considered test flights, most or all of these missions were to be flown to the Mir space station and carry out what would usually be considered operational tasks. All missions would carry 37KB modules in the cargo bay. Three of those were supposed to be built by the Khrunichev factory (serial nrs. 37070, 37071, and 37072). On the early test flights these modules would mainly carry instrumentation and remain in the cargo bay, but eventually at least two of them were to be turned into small scientific laboratories (renamed 37KBI, “I” standing for “research”) that would be left behind at the lateral docking port of Mir’s Kristall module to be picked up on a subsequent mission [1].

In September 1988 officials of the Energiya-Buran program reported to the Council of Ministers that the plan still was to fly ten test flights, with the first two to be flown unmanned [2]. Internal LII planning documents show that by the end of the year the second unmanned flight was scheduled for late 1989, to be followed by the first manned mission in late 1990. There would be one manned flight in 1991 and two in 1992. All missions would be flown by two-man LII crews, except for the first 1992 mission, which was to be piloted by an Air Force GKNII crew. All these initial missions would use either vehicle 1K or 2K [3].

An improvised payload for Energiya 2L

Even as Buran was undergoing initial post-flight servicing at the MIK OK, assembly of Energiya rocket 2L was nearing completion in the nearby MIK RN. Apparently,

this rocket had been configured from the beginning for launching an unmanned payload canister rather than a Buran orbiter. With no Energiya-tailored payloads or upper stages ready to fly at this stage, a plan was devised to launch 2L with two satellites that would usually be orbited separately by the Proton rocket, an unidenti­fied geostationary communications satellite and an Uragan navigation satellite for the Glonass network. Few details have been released about this configuration, known as GK-199: only that the satellites would have been housed in a Polyus-type vehicle with the payload shroud of the Proton rocket. Two Blok-DM type upper stages were probably required to inject the satellites into their proper orbits. One other objective of the launch was to test the parachute recovery of Energiya’s strap-on boosters. A “draft plan’’ for the GK-199 mission was approved at meetings of the Council of Chief Designers in March and May 1989. The 2L vehicle was expected to be ready for roll-out to the pad by March 1990. However, the project received only lukewarm support from the Ministry of General Machine Building, which argued there was no room in its budget for such a flight [4].

The decision to launch Buran as a passive payload on Energiya made it possible to use the same rocket in various configurations to orbit heavy unmanned payloads. Although this was one of the main advantages of the Soviet system as compared with the Space Shuttle, the development of these cargo versions of Energiya always took a backseat to that of the main Energiya-Buran system. One of the main reasons for this must have been that there were few payloads in the given mass range that stood any chance of flying soon. The final go-ahead seems to have been given by the government decree on Buran issued on 21 November 1977.