BURAN Orbital

Spaceship Airframe

Creation

Non-Metallic Structural Materials of the BURAN Orbiter

Vulfovich L.V., Kurochka G.M.
The paper gives a brief data of non-metallic materials of different purpose in the BURAN Orbiter structure, Shows their main properties, fields and efficiency of employment.

The developments of the space vehicles and the stringent requirements to their weight efficiency have lead to a wider use of non-metallic construction materials of various purposes:

• constructional glass- carbon- and acrylic-reinforced plastics;
• industrial rubber products;
• solid-lubricant coatings and greases;
• sealing materials;
• glues paint coating;
• thermal-protective and heat-insulation materials;
• electrical insulating materials.

The BURAN reusable Orbiter is a case in point of wide use of the non-metallic materials of all the listed classes.

To provide the serviceability of BURAN Orbiter’s units and parts specific materials with unique properties were created under the technical specifications of NPO MOLNIYA. They are unique for the ability to retain the desired properties in a wide range of temperatures from – 130˚C to +160˚C (in some cases to + 700...1750˚C), in space vacuum, and besides, when multiply used.

VIAM, NPO MOLNIYA, NPO TECHNOLOGIYA, NIAT, VNIINP, VNIIAeMI, and other chemical enterprises and academic institutes participated in developing new materials and processing technologies.

NPO MOLNIYA, GIPH, TsAGI, TsAGI Novosibirsk office and other organizations carried out the tests of the materials in actual samples and devices.

An important part in creating the new materials and technologies belonged to non-metallic materials department, headed by Mr. Vulfovich L.V. Its tasks included coordination of the work, introducing the new materials and technologies into particular constructions, participating in tests of materials included in the parts and devices, checking and participating in the manufacturing.

Several dozens of new technologies and special equipment were introduced in production at development the BURAN Orbiter. This became the basis of quantity production of the newly designed materials and those designed earlier, but produced only as samples.

The NIKA and NIRA low-temperature plasticity lubricants on the base of perfluoropolymeric for rolling and plain bearings were designed. They had low friction and breakaway factor in both air and vacuum environment. Their main features are as follows:

• operational temperatures range – 120˚C...+150˚C;
• breakaway force -NIRA- 630 kg, -NIKA- 480 kg;
• breakaway moment at –120˚C -NIRA – 0,32 m∙kg∙m, -NIKA – 0,41 m∙kg∙m.

Three-layer solid lubricant coatings on the base of molybdenum disulfide and silver were designed for the unit of dry slide-friction. These coatings are serviceable in vacuum and at temperatures from –130˚C to +700˚C.

The retained elastic at temperatures from –120˚C to +160˚C materials were designed for sealing of the BURAN Orbiter’s airframe.

The UF-7-21, UF-7-21B heat-and-frost resistant sealant on the base of silicon rubber were developed and applied for sealing of surface and permanent joints. They have high adhesion to various primers and contact materials.

Main properties of brush hermetic (at +20˚C):

• density - 1,35 g/cm³;
• specific breaking rupture - 17...30 kg/cm²;
• percent elongation at rupture - 80...160%.

To seal mobile units there was designed the APTS rubberized moisture-air-proof fabric with operational temperatures from –120˚C to +200˚C.

The APTS is arimid fabric with coating on the base of polymethyl silicone rubber.

To seal doors and hatches the 5I-23, 5I-30 heat-and-frost resistant rubbers were developed. They operate at the temperatures from –120˚C to +160˚C. Long-sized (over 5m) ‘horseshoe’ and ‘depressor’ type seals of these rubbers were also developed.

To prevent the seals from sticking a technique of plasmochemical modification of their surfaces was introduced. It allows to lower the rubber-to-metal friction factor by 8…10 times.

To reduce the mass and to meet some special requirement fiberglass reinforced plastics were used in Buran Orbiter’s design.

Radioparent inserts, heat-insulating gaskets, pipe attachment blocks, shaping strip around hatches and doors, thermobridges, pipes of airframe pressurization system, electric insulating parts – are the basic cases of using these materials.

Many of composite materials developed earlier didn’t meet the requirements of BURAN’s operation. This caused the necessity of their modification with additional volume of material studies tests. There are the STAF-1, STP-97K, SK-9HK glass-reinforced plastic used in thermobridges, hatches, doors, pipes, and unit attachment parts.

The STAF-1, STAF-2 fiberglass-reinforced fabric based laminates are serviceable up to the temperature of +700°C. The STP polyamide glass-cloth-base laminates with operational temperature of ~350°C is easy-to-manufacture. It may be produced by vacuum forming at 175°C. The SK-9HK glass-cloth-base laminate is serviceable in amid vapors.

The ORGANIT-5T material allowed to make thin-walled tubes (δ ∼ 0,5 mm). Tubes of this material are strength, lightness, and noncombustible. The layer of the PSK-171 adhesive tape inside provides leak-proofness of tubes, and a layer of metallized polyethylenetereftalate film provides static electricity protection .

The pipe-line of airframe pressurization system consists of a set of tubes from 50 to 300-mm in diameter. They are produced by winding, and connected by adhesive bandages. The use of organic plastic decreased the weight of the pipeline by 30% on average compared to aluminum alloy one.

Another way to reduce the mass is using adhesive honeycomb-filled structures of various types, for example, for parts of the balancing flap, elevons, and brake parachute container. Adhesive aluminum honeycombs and the VK-36 high-strength film-forming adhesive were used in these units.

The VK-36 adhesive provides strong joint of not only aluminum but also of non-metallic composites. Shear strength limit of adhesive joints for aluminum alloy is follows:

• at 70°C – 350 kg/cm²;
• at 160°C – 250 kgf/cm².

The adhesive allows to make three-layer honeycomb panels of most various sizes and shapes.

The three-layer structures using the VK-36 adhesive, the SSP fiberglass honeycomb plastic and skin of glass-cloth-base laminates are applied the material of radioparent inserts, cap of parachute container, etc.

Unlike the three-layer structures using adhesive fiberglass honeycombs, the TZ SPK ablative heat-protection material is fabric glass honeycombs filled with rubber like composition. The TZ SPK-2 re-designed material and its production technology have no analogues. Its composition prevents ablation at high temperatures.

The TZ SPK-2 material was used for heat-protection of BURAN Orbiter’s structural members in high-temperature zones.

The main properties of TZ SPK-2 are as follows:

• density - 0,55...0,66 g/cm³;
• compressive strength at 20°C -20kg/cm²;
• operational temperatures range –150°C ... +1750°C.

The unique design of BURAN Orbiter and variety of technical requirements to devices and units defined the multiplicity of types and properties of the materials in use. For instance, the OM-35 facing material with predefined optical properties was designed and used for shield-vacuum thermal isolation. The OM-35 material is comprises glass- or armid fabric doubled with a metallized film with a layer of adhesive.

In other members, such as mounting points of payload bay’s doors, solar heat-exchanger (SHE), flap, elevons, - heat paint coatings of preset solar radiation absorption and reflection factors were used to control the surface heating. The AK-573, KO-5191 white enamels coating of ‘solar reflector’ class materials with emissivity factor of ε = 0,2...0,3 were used for coating of payload bay interior and outer surfaces of radiation heat-exchanger. The KO-818K and KO-819 black enamels of ‘true absorber’ class with emissivity factor ε = 0.8 and max service temperatures of 600…650°C were used for coating of outer surface of honeycomb elevon flaps, rudder and airbrake casing.

Paint and electroplating coatings formed the basis of the BURAN Orbiter’s corrosion-resistant protection. Other types of metal and non-metal coatings, hermetic materials, lubricants etc. were studied for system of corrosion-resistant protection. Optimal combination of primers, enamels, electroplating coatings, lubricants, and sealant materials provided the protection of the Orbiter under operation conditions, as well as the corresponding of its service life warranties and mass characteristic to the technical specification (paint coating gain in weight 40g/m² for dry retain).

The experience gained in this field of the non-metallic materials was generalized in manual on the BURAN Orbiter’s corrosion-resistant protection, developed by VIAM.

Conclusions

The development of materials and technologies for BURAN Orbiter had a great importance not only for provision of the Orbiter’s serviceability, but also for the advent of material studies and technologies of all sciences and national economy and sciences in the field of chemistry and physical chemistry.

The materials of the BURAN Orbiter may be used and are partially used in aircraft industry, automobile- and ship building, transport, devices of polar areas service, sports goods production etc.

At present moment NPO MOLNIYA works at creating of aerospace systems of next generations. It initiated development of non-metallic construction materials for the aerospace industry of XXI century.