Felt reusable surface insulation

For regions exposed to temperatures of up to 370° Buran had multiple-layer, square­shaped panels of flexible insulation, similar to the Felt Reusable Surface Insulation (FRSI) employed by the Shuttle. Known as ATM-19PKP, the material was similar to that used for the felt pads under the tiles and was applied to the upper payload bay doors, portions of the upper wing surfaces, and portions of the mid fuselage.

Carbon-carbon

The areas where Buran incurred the highest heating during re-entry (up to 1,650°C) were the nosecap and the leading edges of the wings. As on the Orbiter, these parts were covered with a reinforced carbon-carbon (RCC) material. Until 1978 efforts focused on an RCC material known as KUPVM-BS, but despite its high thermal resistance and strength, it turned out to be too difficult to use. Eventually, the choice fell on a material called GRAVIMOL, an acronym reflecting the names of the three organizations that developed it (NII Grafit, VIAM, and NPO Molniya). There were some small differences in the composition of the RCC material used in the nosecap and the wing leading edges (GRAVIMOL-B in the wing leading edges). The material’s density was 1.85 g/cm3. The RCC had a coating of molybdenum disilicide to prevent oxidation. As on the Shuttle Orbiter, each wing leading edge was covered with 22 RCC panels.

Thermal barriers

Flexible thermal seals protected the vehicle in between certain types of thermal protection material and also in areas containing movable parts. Brush-type seals covered small gaps between sections of the payload bay doors and also in the vertical stabilizer, body flap, and elevons. Seals made of quartz fibers protected areas between the thermal protection system and various doors and hatches. Seals composed of silicon carbide fibers were used in areas exposed to extremely high temperatures such as the gaps between the RCC panels on the wing leading edges and areas where the RCC material bordered on the tiles. An ablative material capable of withstanding temperatures up to +1,800°C covered the gaps between the elevons [14].