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The Soviet BOR-4 Spaceplanes and Their Legacy

1. INTRODUCTION

The first two BOR-4 missions splashed down in the IndianOcean and their recoveries were extensively photographed byAustralian Air Force aircraft. The pictures, publicly released in1983, constituted the first solid evidence that the Soviet Unionwas working on some kind of shuttle programme. However,during the 1980s Western analysts wrongly concluded that thevehicles were testbeds of a spaceplane to be launched by theZenit rocket, a programme that was believed to run parallel tothe Energiya/Buran effort. The pictures eventually inspiredNASA engineers to develop a look-alike spaceplane that wasseriously considered as a transportation system for space sta-tion Freedom and is now being eyed to launch paying passen-gers on suborbital and eventually orbital tourist missions.

2. THE SPIRAL PROGRAMME

In a possible response to US work on the Dyna Soar project,several Soviet design bureaus got down to spaceplane studiesin the late 1950s and early 1960s. These were Pavel Tsybin’sOKB-256, Vladimir Myasishchev’s OKB-23, VladimirChelomei’s OKB-52 and Andrei Tupolev’s OKB-156. By themid-1960s none of these projects had moved beyond the draw-ing boards, with the exception of a few subscale suborbital testflights by Chelomei’s bureau.

Despite Dyna Soar’s cancellation in 1963, interest inspaceplanes did not abate. While all aforementioned designbureaus had stuck to the Dyna Soar type technique of launchingspaceplanes with conventional rockets, the Soviet Air Forcedisplayed increasing interest in the early 1960s in air-launchedspaceplanes. Unlike the ground-launched spaceplanes, thesewould not be tied to specific launch sites and could be launchedfrom virtually any place in the world into a wide variety oforbital inclinations. This made the system less vulnerable toattack and gave it far more flexibility in fulfilling key militaryobjectives such as timely reconnaissance of ground-based en-emy targets and inspection and neutralization of enemy satel-lites. Studies conducted in 1964-1965 by the Soviet Air Force

research institute TsNII-30 also concluded that an air-launchedvehicle would best meet the military requirements formulatedfor spaceplanes.

On 30 July 1965 the Ministry of the Aviation Industryassigned the task of building such a system to the OKB-155design bureau of Artyom Mikoyan, which had apparently al-ready worked on an air-launched anti-missile system [1]. Re-named MMZ Zenit in 1966, the bureau was most renowned forits MiG fighter jets. Mikoyan’s team wasted no time in gettingdown to business and by July 1966 had completed a prelimi-nary design for the system, called Spiral. Placed in charge ofthe project was 55-year old Gleb Lozino-Lozinskiy, a deputy ofMikoyan who had played a crucial role in the development ofnumerous MiG jets. As a sign of his dedication to Spiral,Mikoyan set up a special space branch of his design bureau inthe town of Dubna in April 1967 to work on the project.

Spiral was a 115 ton system consisting of a HypersonicBoost Aircraft (GSR or “50-50”), an Orbital Plane (OS) and atwo-stage rocket to place the OS into orbit (Fig. 1). The GSRwas a 38 m long aircraft with a wingspan of 16.5 m and four air-breathing turbojet engines fixed under the main fuselage. Anearly version would burn kerosene and the final one hydrogen.The two-stage rocket mounted on the back of the GSR was tobe propelled by liquid oxygen/liquid hydrogen engines, but thedesigners ultimately wanted to replace the oxygen by fluorine.Although this is a highly toxic substance, it provided a higherspecific impulse and would require smaller tanks than the LOXversion.

When picking the shape of the spaceplane, Mikoyan’s engi-neers may at least partially have been inspired by flight tests ofsuborbital and atmospheric lifting bodies in the United States inthe early 1960s, but in the end they came up with their own,unique design. The spaceplane proper was an 8 m long flat-bottomed lifting body with a large upturned nose, a vertical finand wings that could be rotated to vertical position duringlaunch and the initial portion of re-entry. The vehicle’s aerody-namic design was such that thermal stresses during re-entrywere minimized. The spacecraft’s reusable heatshield was not

THE SOVIET BOR-4 SPACEPLANES AND THEIR LEGACY

BART HENDRICKXMinervastraat 39, 2640 Mortsel, Belgium.

JBIS, Vol. 60, pp.xxx-xxx, 2007

Between 1982 and 1984 the Soviet Union launched four small recoverable lifting bodies designed to test heatshield materialsfor the Soviet space shuttle Buran. Called BOR-4, these vehicles were originally designed to be flown in support of the Spiralmilitary spaceplane programme, but after the cancellation of that project were reoriented towards Buran. They were widelymisinterpreted in the West as subscale versions of a military spaceplane and would later serve as the basis for several Americanspaceplane designs.

Keywords: BOR-4, Spiral, Buran, space shuttle

An abridged version of this paper was presented at the BritishInterplanetary Society "Chinese/Soviet" Symposium on 10 June 2006.

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Bart Hendrickx

solid, but was composed of a set of sheets, much like a fish’sscales. Suspended on ceramic bearings, these sheets couldmove relative to the vehicle’s body as the temperatures onvarious parts of the craft changed during re-entry. The plateswere made of a niobium alloy with a molybdenum disilicidecoating and could withstand temperatures up to about +1500°C.

Situated in the front was the single pilot’s cockpit, which incase of an emergency could be ejected from the spaceplane andland by parachute. The headlight-shaped capsule even had asmall engine and a heatshield to deorbit and re-enter independ-ently if an emergency arose in orbit. The power plant, located inthe back, consisted of a single main engine for changing orbitalinclination and deorbiting, two back-up deorbit engines, six-teen attitude control thrusters and a turbojet engine for sub-sonic propulsion and landing. The landing gear was made up offour skids mounted on the sides of the spaceplane.

In between the cockpit and the engine compartment was a 2m³ payload section stowed full with reconnaissance equipmentor weapons, depending on the mission. There were two recon-naissance versions of the spaceplane, one with optical cameraswith a resolution of up to 1.2 m for detailed photography andanother with an externally mounted radar antenna with a reso-lution of 20-30 m for spotting large objects such as aircraftcarriers. An attack version of the OS was designed to destroysea-based targets with a 1,700 kg nuclear-tipped space-to-surface missile, which required an additional 2 m³ of volume inthe mid-section of the spaceplane (at the expense of fuel).Finally, there were two interceptor versions of the spaceplane.One was supposed to catch up with targets in orbit for closeinspection and had six 25 kg homing missiles on board fordestroying them (if necessary) from a maximum range of 30km. The other was a long-range interceptor outfitted with 170kg homing missiles to neutralize targets from a maximum dis-tance of 350 km. Both interceptor versions had enough fuel onboard to destroy two targets orbiting at altitudes of up to 1,000km. The OS weighed 8.8 tonnes in all configurations, carrying500 kg of payload for reconnaissance and interception mis-sions, and 2,000 kg in its attack configuration.

A typical Spiral mission would begin with the GSR takingoff at a speed of 380-400 km/h using a “launch truck”. Havingaccelerated the system to a hypersonic speed of Mach 6, thecarrier aircraft would release the OS/booster combination at analtitude of 28-30 km and return to its home base. Subsequently,the two-stage rocket would place the spaceplane into a loworbit of approximately 130 x 150 km with inclinations varyingbetween 45 and 135° (if launched from the territory of theUSSR). If equipped with a main engine burning liquid fluorine

Fig. 1 Scale model of the Spiral system.(source: T. Varfolomeyev)

(F2) and amidol (50% N2O4, 50% BH3N2H4), the reconnais-sance and interception versions could change their inclinationby 17° for a second target run and the attack version by 7-8°.The interceptor version could also simultaneously change incli-nation by 12° and ascend to an altitude of up to 1,000 km. Aftera mission of maximum three orbits, the spaceplane would fireits deorbit engine and dive into the atmosphere at a 45-60°angle of attack with the wings folded to near-vertical position,allowing the air stream to flow from the body down to thewings, rather than to the wing leading edges. Cross-range capa-bility was between 1,100 and 1,500 km, offering the pilot muchflexibility in choosing landing sites. After unfolding the wingsto a near-horizontal position and igniting the turbojet engine,the pilot would land the spaceplane on a dirt runway at a speedof no more than 250 km/h.

According to plans formulated in the preliminary design in1966 the Spiral programme was to be conducted in four stages.The first step was to build several full-scale prototypes for avariety of piloted test flights staged from a Tu-95KM aircraft.Subsonic flights were to begin in 1967, followed by X-15 typesupersonic and hypersonic flights in 1968 to altitudes of 120km and speeds of Mach 6-8. In the second stage Soyuz rocketswould be used to launch 6.8 ton versions of the OS (“EPOS” or“50”) into orbit on both unmanned and manned missions in1969 and 1970, with one of the mission objectives being toperform an 8° plane-changing burn. Stage three would see testflights of a kerosene-fuelled version of the GSR in 1970, withthe hydrogen-fuelled version to follow in 1972. That same yearthe fourth stage was to begin with an all-up test of the Spiralcomplex using a kerosene-fuelled GSR and a LOX/liquid hy-drogen rocket booster. In 1973 the hydrogen-fuelled GSR wouldbe used for a manned test of the Spiral system. Later steps werethe introduction of fluorine-based engines for both the rocketand the spaceplane and the development of a reusable rocketbooster with supersonic ramjet engines.

Spiral was by far the largest-scale Soviet spaceplane pro-gramme of the 1960s, although the amount of money investedinto it must still have been dwarfed by what the US Air Forcespent on Dyna Soar. It was also the first for which cosmonautsbegan training. A Spiral training group was set up at Star City in1966 and existed until 1973.

At the beginning of the 1970s Spiral’s fortunes turned forthe worst. Mikoyan, backing the programme with his authority,died in December 1970. Only weeks earlier Soviet DefenceMinister Andrei A.Grechko had denounced the programme as a“fantasy”, refusing to approve a government decree necessaryto provide further funding for Spiral despite having voiced his

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The Soviet BOR-4 Spaceplanes and Their Legacy

support for the project only several months earlier. There wasalso opposition from the new Air Force Commander-in-ChiefPavel S. Kutakhov, who had been assigned to the post in March1969 [2]. One reason for the lukewarm interest in the pro-gramme may have been the challenges involved in masteringadvanced technologies such as the hypersonic carrier aircraftand the reusable metal heatshield. In addition to that, it wasprobably realized by now that at least some of the missionsplanned for Spiral could just as well be performed by unmannedsatellites.

Remarkably enough, the programme continued on what ap-pears to have been a semi-legal basis and did see some hard-ware make it off the ground, even after the Buran programmewas approved in 1976. Why Spiral wasn’t cancelled outrightearlier than that is a fact that remains to be satisfactorily ex-plained by Russian spaceflight historians.

The Gromov Flight Research Institute (LII) built severalscale models of the spaceplane known as Unmanned OrbitalRocket Planes (Bespilotnye orbitalnye raketoplany or BOR) totest its performance during suborbital and orbital missions.These were BOR-1 (a wooden mock-up), BOR-2 (a 1:3 scalemodel) and BOR-3 (a 1:2 scale model), both with ablativeheatshields, several of which were launched on suborbital tra-jectories by R-12 missiles from the Kapustin Yar cosmodromenear Volgograd between 1969 and 1974 (Fig. 2). A full-scaleprototype for subsonic flights (105.11) was ready by the mid-1970s and made several manned autonomous flights as well aspiloted drop tests from the belly of a Tu-95K between June1976 and September 1978 (Figs. 3 and 4). A model for super-sonic tests (105.12) was built but never flown and a model forhypersonic tests (105.13) was partially built. In 1975 planswere drawn up for a 1:2 unmanned scale model called BOR-4that would be launched on orbital test missions. Unlike the realSpiral, this would be equipped with a non reusable ablativeheatshield, but would provide critical data on the spaceplane’saerodynamic characteristics throughout the flight regime [3].

3. THE APPROVAL OF BURAN

The January 1972 decision by President Richard Nixon topress ahead with the development of a reusable Space Shuttledid not elicit an immediate response from the Soviet Union.Soviet design bureaus were preoccupied with several otherpiloted space projects, notably the civilian DOS space station,the military Almaz space station and the N-1/L-3 lunar landingprogramme. Moreover, all the spaceplane work conducted upto that point in the Soviet Union had largely focused on recon-naissance and anti-satellite missions, not the transportationfunctions envisaged for the US Shuttle. The air-launched Spiralwas not suited for the type of missions that America had inmind for the Space Shuttle. Initial studies conducted at variousSoviet research institutes threw doubt on whether a SpaceShuttle type system would be economically more advantageousthan a fleet of expendable rockets, despite the fact that itoffered advantages such as the capability to retrieve and repairorbiting satellites.

Leaving aside the question whether there was a need forsuch a system at all, there was also no consensus on the size ofsuch a vehicle. Some favoured a 20-ton class spaceplane to belaunched by the Proton rocket and others a 100 ton classvehicle akin to the Space Shuttle. Reflecting this uncertainty,the Soviet government decided in December 1973 to investi-gate both concepts at three different design bureaus. Shuttles in

Fig. 2 The BOR-2 suborbital vehicle. (source: B. Hendrickx)

Fig. 4 Aft view of 105.11 Spiral testbed. (source: B. Hendrickx)

Fig. 3 Front view of the Spiral subsonic testbed (105.11) at theMonino Air Force museum outside Moscow.

(source: B. Hendrickx)

the 20-ton class range were to be studied at the design bureausof Chelomei (a concept called Light Spaceplane or LKS) andMikoyan (an enlarged version of the Spiral spaceplane). Stud-ies of a big shuttle were entrusted to the former Korolyovdesign bureau, headed at the time by Vasiliy Mishin. In May1974 Mishin was replaced by Valentin Glushko and the designbureau was reorganized under the name NPO Energiya. Almost

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Bart Hendrickx

overnight, Glushko scrapped the ill-fated N-1/L-3 project andproposed a new family of heavy-lift launch vehicles calledRLA (“Rocket Flying Apparatus”), capable of launching spacestations, space shuttles and manned mission to the Moon andultimately Mars.

Initially, the large shuttle did not figure prominently inGlushko’s RLA plans, which were primarily aimed at establish-ing a permanent base on the Moon. However, in 1975 prioritiesshifted as the Soviet military community became increasinglyconcerned about the military capabilities of the Shuttle. Notcertain of the exact purpose of the Space Shuttle, the Sovietsdecided that the safest thing to do would be to build a systemwith similar capabilities, enabling them to respond to whatevertasks the Shuttle would eventually perform. The official deci-sion came in a government and Communist Party decree dated17 February 1976, which called for the Soviet Union to de-velop a Reusable Space System (MKS) capable of launchingpayloads of 30 tons and returning cargos of 20 tons.

NPO Energiya, subordinate to the “space and missile minis-try” known officially as the Ministry of General Machine Build-ing, was placed in overall charge of the programme. However,it was also decided to set up a new organization under theMinistry of the Aviation Industry to design and build the orbiter’sairframe and various airplane-related components. Called NPOMolniya, it was established on the basis of three existing designbureaus (MKB Molniya, MKB Burevestnik and Myasishchev’sExperimental Machine Building Plant). Also transferred to theorganization were over 100 leading Spiral specialists, bothfrom MMZ Zenit and its former Dubna branch, which in 1972had merged with MKB Raduga (another former branch ofMikoyan’s bureau) to form DPKO Raduga. One of them wasGleb Lozino-Lozinskiy, who became the head of NPO Molniya.

While the February 1976 decree clearly defined the payloadcapacity of the MKS, it did not stipulate what the vehicleshould look like. The NPO Energiya and NPO Molniya peoplehad different ideas. In the weeks leading up to the decree NPOEnergiya specialists had pretty much settled on a delta-wingorbiter called OK-92 which was very similar to its Americancounterpart. Originally, the idea had been to place the mainengines on the orbiter as in the US Space Shuttle configuration,but eventually it was decided to move them to the external tank,turning that into a universal launch vehicle. Flanking the corestage were two pairs of strap-on boosters burning liquid oxygenand kerosene. The Mikoyan contingent within NPO Molniya,well aware that the small air-launched Spiral did not meet therequirements formulated by the government decree, now putforward a giant lifting body (“Product 305-1”) that was essen-tially an enlarged version of the Spiral spaceplane and woulduse the same universal launch vehicle. Finally, in May 1976 thechoice fell on the delta-wing vehicle (“Product 305-2” or Buran),allowing the Russians to benefit from American research anddevelopment on the Space Shuttle.

One area where the Russians drew heavily on US experiencewas in the vehicle’s thermal protection material. Buran wascovered with over 38,000 black and white silica tiles. Each tileconsisted of a substrate and a coating. The substrate came intwo types with different densities. One was called TMZK-10(with a density of 0.15 g/cm³) and the other TMZK-25 (density0.25 g/cm³) These were more or less comparable in characteris-tics and performance to the two basic types of Shuttle tilesubstrate (Li-900 and Li-2200) Both the TMZK-10 and 25 hadspecial 0.3 mm thick glass coatings to reject heat, protect the

tiles against wind loads and moisture penetration. This wasvery similar to the Reaction-Cured Glass (RCG) coating on theShuttle’s tiles. Chemicals were added to the coating to give thetiles different colours and heat rejection capabilities. Blackcoating (both for TMZK-10 and 25) was mainly needed toprotect the underside of Buran against the high temperatures ofre-entry, with the higher-density TMZK-25 only used in re-gions exposed to the highest stresses. White coating (onlyapplied to TMZK-10) mainly served the purpose of protectingthe upper surfaces of the vehicle against solar radiation in orbit.Since the fragile tiles could not withstand structural deflectionsand expansions of the aluminium skin, they were not attacheddirectly to the skin, but to 4 mm thick felt pads, which then inturn were bonded to the actual skin.

For regions exposed to temperatures of up to 370° Buranhad multiple-layer, square-shaped panels of flexible insulation,similar to the Felt Reusable Surface Insulation (FRSI) em-ployed by the Shuttle. Known as ATM-19PKP, the material wassimilar to that used for the felt pads under the tiles and wasinstalled on the upper payload bay doors, portions of the upperwing surfaces and the mid-fuselage. The areas where Buranincurred the highest heating during re-entry (up to 1,650°C)were the nosecap and the leading edges of the wings. As on theShuttle Orbiter, these parts were covered with a reinforcedcarbon-carbon (RCC) material called GRAVIMOL, an acro-nym reflecting the names of the three organizations that devel-oped it (NII Grafit, NPO VIAM and NPO Molniya). Therewere some small differences in the composition of the RCCmaterial used in the nosecap and the wing leading edges(GRAVIMOL-B in the wing leading edges). Each wing leadingedge was covered with 22 RCC panels [4] (Fig. 5).

NASA had no practical way of testing the Shuttle’s ThermalProtection System (TPS) in actual flight conditions prior to themaiden Space Shuttle flight. Although the tiles were flown on F-15Eagle and F-104 Starfighter jets to test their behaviour underaerodynamic load conditions, the first real test for the heatshieldcame on the STS-1 mission of Space Shuttle Columbia in April1981. At that time Buran was still years away from its inauguralflight, with the original launch date of 1983 continuously slippingdue to a variety of factors. Given the similarity of Buran’s heatshieldmaterials, the Russians undoubtedly watched the performance ofthe TPS with more than casual interest as the Space Shuttle wentthrough its test flight programme.

However, rather than just sit back and rely solely on Ameri-can experience, the Russians had worked out their own testprogramme for Buran’s thermal protection system well beforethe Space Shuttle began flying. Besides tests in thermal vacuumchambers, Ilyushin-18D and MiG-25 aircraft were used to testtiles and felt reusable surface insulation at subsonic and super-sonic speeds. The thermal insulation was installed on areas ofthe aircraft that were subjected to the highest dynamic pressureand acoustic loads from the engines. In addition to that, theRussians had the unique opportunity to test the materials inactual re-entry conditions. All they needed to do was to dust offthe old plans for the BOR-4 vehicle and cover it with Buran’sheatshield materials. Even though BOR-4’s shape was not rep-resentative of Buran, the heatshield tests did not require avehicle that exactly mimicked Buran’s shape. The most impor-tant thing was to ensure that the heat-resistant materials wouldbe exposed to the same type of temperatures for about the sameperiod of time. Moreover, the nose section of the BOR-4 testvehicle did more or less match the contours of Buran’s nosesection. In 1977 it was decided to develop two types of scale

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The Soviet BOR-4 Spaceplanes and Their Legacy

Fig. 5 Buran atop the Mriya carrier aircraftat the 1989 Paris Air Show. Note black andwhite tiles and reinforced carbon-carbon onthe nosecap. (source: B. Hendrickx)

models in support of the Buran programme and fly each ofthem five times:

• BOR-4: a 1:2 scale model of the Spiral spaceplane totest Buran’s heatshield materials on orbital missions

• BOR-5: a 1:8 scale model of Buran to test Buran’saerodynamic characteristics on suborbital missions [5].

4. BOR-4 DESIGN AND MISSION PROFILE

Just like the Spiral spaceplane, BOR-4 was a flat-bottomedlifting body with a vertical fin and foldable wings (Fig. 6). Itwas 3.859 m long with a launch mass of about 1,450 kg and alanding mass of 795 kg. The BOR-4 vehicles made it possibleto test the three main types of thermal insulation used on Buran,namely tiles, felt reusable surface insulation and reinforcedcarbon-carbon. Black tiles (using both the TZMK-10 andTZMK-25 substrate) covered the belly, white tiles (with TZMK-10 substrate) were installed on the sides and ATM-19 feltinsulation protected the upper part of the vehicle. Carbon-carbon GRAVIMOL material was used only on the nosecap,with the wing leading edges being too thin for installation ofsuch material (Fig. 7).

The tiles were not attached to BOR’s airframe, but to a thinlayer of aluminium of the same composition as that used inBuran’s airframe. In between this aluminium layer and theactual airframe was an ablative heatshield material (PKT-FL)that had been planned for the original BOR-4 vehicle to beflown in support of the Spiral programme. This provided thenecessary redundancy in case any of the Buran heatshieldmaterial burnt through during re-entry. The area between thenosecap and the airframe was filled with insulating materialmade of heat-resistant fibres. Since the wings were much thin-ner than the rest of the airframe, they were filled with a porousfelt material impregnated with a water-based substance. Evapo-ration of that substance provided enough cooling for the wingduring re-entry in case the Buran heatshield material provedineffective.

BOR-4 was equipped with 150 thermocouples, installedmainly on the airframe and just under the coating of some of thetiles. In addition to that it had accelerometers, angular velocity

sensors, pressure sensors and sensors that indicated the posi-tion of the wings. Information obtained from the sensors wasrecorded on board and sent back to Earth in “packages”.

A typical BOR-4 mission would begin with a launch from theKapustin Yar cosmodrome near Volgograd using a modified two-stage Kosmos-3M booster known as K65M-RB5 (Fig. 8). Baikonurno longer supported that rocket at the time and although Plesetskdid, it was situated too far north to place the spaceplane modelsinto the proper inclination. The rockets used for the BOR-4 mis-sions had originally been earmarked for other missions, but hadalready surpassed their guaranteed “shelf life” and would havebeen used for test launches anyway [6].

The vehicle would be launched with its two wings com-pletely folded so that it fitted under the rocket’s fairing. Afterrelease from the launch vehicle, the wings were moved to aposition that would keep the vehicle stable during re-entry at anangle of attack of between 52° and 57° between altitudes of 70and 60 km. Orientation in orbit was carried out with the help ofeight microthrusters burning hypergolic propellants. After asingle revolution of the Earth BOR-4 initiated its descent backto Earth, firing what is believed to have been a jettisonablesolid-fuel motor mounted on top of the vehicle. At an altitude of30 km the on-board control system sent BOR-4 on a steepspiralling trajectory to decrease speed and at 7.5 km the space-craft deployed a parachute that reduced the vertical landingspeed to 7-8 m/s.

Since the vehicle was not equipped with a landing gear, itneeded to land on water to ensure that its heatshield remainedintact for post-flight analysis. The only major bodies of wateron Soviet territory that would be in the BOR’s flight path werethe Black Sea and Lake Balkhash. However, the Russians hadnever returned a winged vehicle or lifting body from orbit andwere not confident they could aim the spacecraft for precisionsplashdowns in the Soviet Union. Therefore they opted to landthe first vehicles in the Indian Ocean, where they would stillcome down in water even if they fell short of or overshot theplanned landing area. That did, however, significantly increasethe cost of the recovery operations, which, moreover, would behard to conceal from the prying eyes of Western reconnaissanceaircraft.