Category Energiya-Buran

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.

After several years of uncertainty over the status of the Baykonur cosmodrome, the Russian and Kazakh governments agreed in December 1994 that Russia would lease the cosmodrome for 20 years for an annual rent of $115 million. Several months earlier the Russian government had issued a decree calling for the Military Space Forces to transfer authority over a large part of its facilities to the Russian Space Agency. This included all the Energiya-Buran facilities, authority over which was divided by the agency among several design bureaus. While some of the Energiya – Buran facilities stand rusting in the steppes without any prospects for future use, others have been modified for other programs and are once again buzzing with activity.

Another idea for an SSTO spaceplane emerged at the Strategic Rocket Forces’ NII-4 research institute. It was the brainchild of Oleg Gurko, who had been working out ideas for such systems since the late 1940s. The novelty in Gurko’s plan was a hydrogen scramjet that would suck in air heated by the exhaust of a liquid-fuel rocket engine placed in front of it. In the 1960s he approached both Mikoyan and Myasishchev, who both showed interest in building a vehicle using such a propulsion system. However, the barriers between the Strategic Rocket Forces and the Ministry of the Aviation Industry proved too high.

It was not until after the approval of the US Space Shuttle in the early 1970s that Soviet top brass started showing some interest in Gurko’s ideas. On 10 October 1974 the Minister of the Aviation Industry and the Air Force Commander-in-Chief signed an order allowing Myasishchev’s Experimental Machine Building Factory (EMZ) to work out “technical proposals’’ for an SSTO using Gurko’s propulsion system under a program called Kholod-2 (“Cold-2”). Placed in charge of the project within EMZ was A. Tokhunts, one of Myasishchev’s deputies, and the leading engineer was I. Plyusnin. Development of the propulsion system was entrusted to the Kuznetsov design bureau in Kuybyshev, the same bureau that had built the engines for the lower stages of the N-1 rocket. Gurko, now employed by the TsNII-50 R&D institute that had split off from NII-4 in April 1972, continued to provide technical support. Within EMZ the project was known as “Theme 19’’ and the SSTO itself was designated

M-19. It has also been referred to as MG-19 (“G” for Gurko) and was affectionately known as “Gurkolyot”.

In its final design the M-19 was a 69 m long triangular-shaped lifting body with small aft and front-mounted wings and two fins. Having a take-off mass of 500 tons, it was capable of inserting a 40-ton payload into low Earth orbit. There was also an alternative plan for a Buran look-alike vehicle with big delta wings and a single vertical stabilizer. Having the same take-off mass as the primary design, it would have a payload capacity of just 30 tons.

The M-19 had an impressive cross-range capability of 4,500 km and could significantly change its inclination by making dips into the atmosphere down to 50-60 km. Thermal protection was provided by carbon-carbon material and tiles. Situated in the nose was the crew compartment, which could be jettisoned from the vehicle in case of an emergency. It consisted of a flight deck and living compartment and was designed to carry a crew of between three and seven. Behind the crew compartment was a 15 x 4 m payload bay, equipped with an airlock/docking system and a remote manipulator arm.

Installed behind the payload bay was a big, removable tank containing liquid hydrogen for the vehicle’s propulsion system. The latter was made up of a nuclear engine in the aft section of the vehicle, a pair of two-spool turbojet engines, and a set of hypersonic scramjet engines mounted on the underside of the aft fuselage. The propulsion system was adapted from Gurko’s original proposal by the introduction of an on-board nuclear reactor that would heat up the air entering the turbojet and scramjet engines to very high temperatures. This would allow the air to escape from the nozzles at very high speeds with little combustion taking place, making it possible to save hydrogen for later stages of the orbit insertion process. The turbojet and scramjet engines would be used to accelerate the M-19 to a speed of Mach 16 and carry it to an altitude of 50 km. At that point the nuclear engine would kick in to place the ship into orbit.

The M-19 was billed as a multi-purpose system, capable of performing routine space transportation tasks, missions in the interests of science and the national economy, as well as reconnaissance and offensive missions. One big advantage of the SSTO was that it required no staging during launch, meaning that it had an almost unlimited number of launch azimuths.

EMZ was aiming for a step-by-step approach in the development of the M-19. This would include test flights of several “flying laboratories” to test the nuclear and scramjet engines, drop tests and re-entry tests of M-19 models, and the construction of an experimental hypersonic airplane that could act as a long-range bomber with a range of up to 12,000 km or a launch platform to place into orbit 40-ton payloads. The SSTO itself was expected to be ready for its first flight in 1987-1988.

Myasishchev perfectly understood the technical challenges posed by such a system and was well aware it wouldn’t be ready to fly until many years after the Space Shuttle. However, since the Soviet Union was already several years behind in the development of a Space Shuttle response, he reasoned it would be better to start work on a much more advanced and capable system straightaway rather than build a copy that itself would be upstaged by the Space Shuttle by several years.

Despite the futuristic nature of the M-19, Myasishchev was not hampered by his “boss” Pyotr Dementyev, the Minister of the Aviation Industry, albeit more for political reasons than anything else. Just as he did with Spiral, Dementyev seems to have considered the M-19 a convenient tool in his arguments with MOM. Dementyev was wary of getting involved in NPO Energiya’s (read: MOM’s) Space Shuttle “copy”, fearing that if his aviation design bureaus were assigned to the project, some of them would eventually be transferred to MOM. By tacitly support­ing the M-19, he hoped to drag out the decision-making process leading to the approval of a Space Shuttle response.

Work on the project continued even after Myasishchev’s EMZ was absorbed by NPO Molniya to work on Buran in February 1976. On 25 May 1976 the Military Industrial Commission decided to continue basic research on the SSTO spaceplane. Research in support of the M-19 was conducted by leading aviation institutes such as TsAGI, TsIAM, and ITPM. EMZ drew up plans to fly an experimental Lyulka liquid-hydrogen engine on an Ilyushin Il-76 airplane, mainly to test the techniques required to store liquid hydrogen at cryogenic temperatures. After Myasishchev’s death in October 1978, this work was transferred to the Tupolev bureau, where it was successfully completed using the Tu-155.

Myasishchev’s death was a major setback for the Gurkolyot. Nevertheless, work on the project seems to have continued at some level until the collapse of the USSR. Between 1978 and 1988 it was mentioned in three more VPK decisions and even in two government/party decrees. While the M-19 may have been considered a serious contender to counter the Space Shuttle before 1976, it quickly moved into the background once work on Energiya-Buran got underway in earnest. From then on it was probably seen as no more than a promising design for a second-generation shuttle vehicle.

One problem with further research on the M-19 was that it had to be done by organizations already preoccupied with Buran. Although there were government orders for NPO Molniya and TsNIIMash to conduct research on the M-19, there was very little enthusiasm for it. There does seem to have been at least some support for it from Boris Gubanov after he was appointed chief designer of the Energiya – Buran system in 1982. The M-19 was also hampered by interdepartmental squabbling between MOM and MAP, on the one hand, and the Strategic Rocket Forces and the Air Force, on the other hand.

Another problem with the M-19 was the use of a nuclear reactor and propulsion system, which posed safety risks both to the crew and the general public, even though designers went to great lengths to make it as safe as possible. However, the biggest showstopper for the M-19 must have been that few believed it was technically feasible, and perhaps rightly so, because even today, thirty years on, a vehicle of this type remains no more than a distant dream [19].

Early work on the Space Shuttle in the late 1960s did not spark an immediate response from the Soviet side for a number of reasons. The only two design bureaus capable of building manned spacecraft had more pressing concerns. TsKBEM, the former Korolyov design bureau (now headed by Vasiliy Mishin), was preoccupied with Soyuz, the civilian DOS space station, and the N-1/L-3 manned lunar program. TsKBM, the Chelomey design bureau, was busy working on the military Almaz space station and its TKS transport ship, not to mention a variety of unmanned military satellites and anti-ship missile projects.

Not only would the development of a large reusable spacecraft place an extra burden on the already overtaxed design bureaus, there simply was no clear need for such a system in the near future. The Soyuz and TKS spacecraft could perfectly handle transportation tasks for the DOS and Almaz stations and the Soviet Union had a varied fleet of expendable rockets to satisfy satellite launch requirements for many years to come.

Looking at the more distant future, TsKBEM was studying a so-called Multi­purpose Orbital Complex (MOK), an entire orbital infrastructure aimed at lowering space transportation costs. Even here there was no immediate need for a large reusable shuttle system. The centerpiece of the MOK was to be a giant N-1 launched space station called MKBS (Multipurpose Space Base Station) that would serve as an orbiting garage. The idea was that satellites in the constellation would be serviced either at the MKBS or regularly be visited by MKBS-based crews flying light versions of the Soyuz outfitted with a manipulator arm. The satellites themselves would be orbited by expendable rockets or partially reusable rockets based on the N-1. In April 1972 Mishin and Chelomey got approval for a joint proposal to turn Almaz into a combined civilian/military space station serviced by Soyuz spacecraft, allowing TsKBEM to focus on the more distant goal of creating the MOK. The two chief designers agreed that Chelomey’s TKS would be the MOK’s key transportation

system during the program’s experimental phase. Reusable transportation systems were part of the MOK plans, but only at a later stage [2].

There were also other obstacles to the initiation of a Space Shuttle type project. Requiring a blend of aviation, rocket, and space technology, it would be an organ­izational nightmare. The leading missile and space design bureaus, including TsKBEM and TsKBM, came under the “space and missile industry’’ known as the Ministry of General Machine Building (MOM) (headed by Sergey Afanasyev), while the leading aviation design bureaus were under the Ministry of the Aviation Industry (MAP) (headed by Pyotr Dementyev). Although both were willing to participate in such an effort, neither was eager to take on prime responsibility for it, considering it to be “the other ministry’s field of business’’.

Finally, the atmosphere around the turn of the decade may not have been conducive to the start of a totally new program. It was a period marked by many spectacular failures in the Soviet space program, both launch vehicle mishaps (notably the Proton and the N-l) and spacecraft malfunctions (notably lunar and deep-space probes). The string of failures even led to the creation of an investigative commission, which concluded that one of the root causes for the numerous setbacks was the lack of proper ground-testing facilities such as engine test stands, vacuum chambers, and the like. Embarking on a completely new, costly, and technologically advanced project under such conditions would not have been a logical course of action.

However, while any final decision on a Soviet shuttle was still years away, some in the Soviet space community did think it was time to begin preliminary research on such a system. The initiative seems to have come from the Military Industrial Commission (VPK), a body under the Council of Ministers (the Soviet government) that oversaw all defense-related ministries (including MOM and MAP). Among its tasks was to formulate new proposals for military and space projects (with the necessary input from the design bureaus and the military community), which could then be officially approved in the form of joint decrees of the Central Committee of the Communist Party and the Council of Ministers. These decrees would set rough timelines for projects, outline their major goals, and also assign the main organiza­tions that would be involved. It was then again up to the VPK to implement those decrees by dividing the work among the design bureaus, setting concrete timetables, and convening meetings of the people in charge.

In a draft proposal for the Soviet Union’s next five-year space program dated 27 November 1970, the VPK suggested that both MOM and MAP as well as other organizations should work out a so-called “draft plan’’ for a “unified reusable transport ship’’ in 1972. This is the first known written evidence of the Soviet Union’s intention to respond to the Space Shuttle. Essentially, it was an order to produce nothing more than paperwork. The “draft plan’’ is just one of the preliminary stages that Soviet space projects went through before metal was actually cut.

Indications are that the phrase about the reusable transportation system was not included in the final government and party decree describing the country’s goals in space for the next five years. Clearly, the time was not quite ripe enough even for preliminary research on a shuttle system. There may have been opposition from

MOM and MAP but, perhaps more importantly, there was no urgent need to begin this work because the US Space Shuttle had not even been officially approved.

Even President Nixon’s go-ahead for the Space Shuttle project in January 1972 did not set in motion a concerted effort to develop a reusable spacecraft. The first high-level meeting in response to Nixon’s January 1972 announcement was organized by the VPK on 31 March 1972. It was attended by both industry and military officials, more particularly representatives of TsNIIMash (MOM’s leading space test and research facility), the TsNII-30 and TsNII-50 military research institutes, the Chief Directorate of Space Assets or GUKOS (the “space branch’’ of the Strategic Rocket Forces) and the Air Force, but no consensus was reached on the need for a response. At this stage the VPK once again formulated a draft proposal asking MOM, MAP, and other organizations to develop a draft plan for a shuttle system, but it met with stiff opposition from MOM minister Afanasyev and was not accepted.

In late April 1972 another meeting took place at TsNIIMash, attended by some of the chief designers (Mishin, Chelomey, Glushko), officials of MOM and TsNII-50. Their conclusion was that a reusable space transportation system was a less efficient and less cost-effective way of delivering payloads to orbit than expendable boosters. Also, they did not see an immediate need for using such a system to return satellites or other hardware back to Earth, certainly not after Mishin and Chelomey had received approval for the MOK/TKS plan that same month. Moreover, at this point the US Space Shuttle was not considered a military threat to the Soviet Union [3].

Although the decree of 17 February 1976 constituted the formal approval of the Soviet shuttle, it did not stipulate what type of design should be chosen. It merely endorsed the basic requirements for the system laid down earlier by the military (30 tons up, 20 tons down). By the time the decree was passed, the OS-120 and MTKVP concepts had been pretty much abandoned and engineers had settled on the January 1976 OK-92 plan, namely a winged orbiter strapped to the side of a massive launch vehicle consisting of a core stage with three RD-0120 cryogenic engines and four strap-on boosters with one RD-123 LOX/kerosene engine each.

A change made soon afterwards was to increase the number of main engines on the RLA-130 core stage to four and reduce their vacuum thrust from 250 to 190 tons. The additional engine provided extra redundancy in case of a main engine failure during the climb to orbit [59]. At the same time, the sea-level thrust of the LOX/ kerosene engines in the strap-on boosters was increased from 600 to 740 tons, resulting in an improved engine called the RD-170. The RLA-130 had now almost acquired the configuration that would eventually become known as Energiya.

Buran was covered with approximately 38,800 heat-resistant tiles (compared with nearly 31,000 tiles on Columbia for STS-1). Each tile consisted of a substrate and a coating. The substrate came in two types with different densities. One was called TZMK-10 (with a density of 0.15g/cm3) and the other TZMK-25 (density 0.25 g/cm3). These were more or less comparable in characteristics and performance with the two basic types of Shuttle tile substrate (Li-900 and Li-2200). They were used in regions where Buran was exposed to temperatures of anywhere between 700°C and 1,250°C. The tiles were made of high-purity 98-99 percent amorphous silica fibres derived from common sand (SiO2—silica) with minimum amounts of natrium, potassium, and calcium oxides to lower the melting point of the fibers. The thickness of the tiles depended on where they were attached to the aluminum skin and the temperatures and aerodynamic stresses that any particular part of Buran was exposed to.

Both the TZMK-10 and 25 had special 0.3 mm thick glass coatings to reject heat and protect the tiles against wind loads and moisture penetration. This was very

similar to the Reaction-Cured Glass (RCG) coating on the Shuttle’s tiles. Chemicals were added to the coating to give the tiles different colors and heat rejection cap­abilities. Black coating (both for TZMK-10 and 25) was mainly needed to protect the underside of Buran against the high temperatures of re-entry, with the higher-density TZMK-25 only being used in regions exposed to the highest stresses. The black – coated tiles on the belly could not be permanently exposed to sunlight for more than 6 hours. White coating (only applied to TZMK-10) mainly served the purpose of protecting the upper surfaces of the vehicle against solar radiation in orbit.

Although the coating provided some protection against moisture penetration, any cracks in the coating would easily let moisture through. Therefore, additional measures had to be taken to make the tiles waterproof. During manufacture the tiles were treated with a special silicon polymer solution, but that burned out during the first flight in all areas where temperatures exceeded +450° C. Therefore, the tiles would have needed to be rewaterproofed for any subsequent missions (had they been flown). For that purpose the Russians developed a varnish-like coating as well as a technique to permeate the tile with a substance known as hexamethyl disilazane. NASA uses a similar substance (dimethylethoxysilane) for rewaterproofing Shuttle tiles, but injects the material into the tiles, whereas the Russians planned to use a gas diffusion technique.

Since the fragile tiles could not withstand structural deflections and expansions of the aluminum skin, they were not attached directly to the skin, but to 4 mm thick felt

pads, which then in turn were bonded to the actual skin. Similar to the Shuttle’s Strain Isolation Pads, they were attached to the tiles as well as to the skin of Buran with an adhesive based on silicon rubber, ensuring a reliable bond in a temperature range of -130°C to +300°C.

Since the tiles thermally expanded or contracted very little, small gaps were left between them to permit relative motion and allow for the deformation of the alum­inum structure under them due to thermal effects. The gaps were filled with a special felt-type material based on organic fibers and capable of withstanding temperatures of up to 430° C.

Tests showed that, if a tile was lost but the underlying felt pad remained in place, the temperature of the aluminum skin would not reach its 500°C melting point, even in areas where temperatures reached 1,250° C. If the felt pad was also lost, there could be damage to the skin, but only in regions close to where carbon-carbon panels were used.

About 28,000 of the tiles were trapezoidal in shape with sizes ranging from about 150 x 150 mm to 200 x 200 mm. Approximately 6,000 tiles were irregular and formed complex patterns on the hatches, around the nozzles of the engines, and on certain edges. Approximately 4,800 tiles had even more complex shapes. Although the distribution of black and white tiles over Buran’s surface was very similar to that on the Orbiter, there were different layout patterns. A fan-type pattern was used on the nose section, elevons, and the vertical stabilizer to avoid the use of triangular and sharply angular tiles of low strength.

The heart of Buran’s flight control system were two Soviet-built redundant computer sets known as the Central Computing System and the Peripheral Computing System, each consisting of four identical computers called “Biser-4” (“Beads”). The US Space Shuttle has a single redundant set of four computers and a fifth back-up computer using different software. Weighing 33.6 kg and using 270 watts of power, each Biser was made up of a central processing unit to provide the central computational capability and an input-output processor to transmit commands to vehicle systems and validate response data from those systems. The computers ran in sync with each other, with the computations of each computer being verified by the other. If one of the computers failed, it was voted out by the others. Each redundant set remained fully operational with two computers down. If a third one failed, there was still at least a 75 percent chance of maintaining the same capacity as a full set. Rather than using program synchronization as was the case with the Shuttle’s General Purpose Computers, the Biser computers were synchronized by a single quartz clock generator that emitted 4Mhz clock pulses to all eight computers at intervals of 32.8 milli­seconds. The generator had five redundant channels.

Each Biser-4 was equipped with 131,072 32-bit words in random-access memory and 16,384 in read-only memory. The software was divided into system software to operate the computers themselves and applications software to perform the functions required to fly and operate the vehicle. While the operations system software perma­nently resided in the computer, the applications software was too big to fit in the available computer memory space. Therefore, it was divided into several memory groups corresponding to specific flight phases and stored on a magnetic tape mass memory unit with a capacity of 819,200 32-bit words. In that way, applications software needed for a specific phase of the flight could be loaded into the computers’ random-access memory from the mass memory unit when needed. The unit stored two versions of each memory group.

The lead organization for the development of the on-board computers was NPO AP, headed until 1982 by Nikolay Pilyugin, who was subsequently replaced by Vladimir Lapygin. Originally, the software was also to be written at NPO AP, but software development ran into major problems in the early 1980s, which is why several other organizations became involved in 1983. Two new specific software languages known as “PROL-2’’ (used by the on-board computers) and “DIPOL” (used by ground computers during vehicle testing) as well as a software language enabling those two to interact (“FLOKS”) were devised for Buran under the leadership of Mikhail Shura-Bura at the Institute of Applied Mathematics [22].