SPACE WEATHER - AGI

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Section III: Thermal Effects5.2 Launch Vehicles© SSS Educational Series 2012The shuttle developed by United States National Aeronautics and SpaceAdministration (NASA) and recently retired, had a thermal control system for twopurposes, to protect it from the heat during re-entry and against the largefluctuations of thermal energy while in orbit. As the shuttle’s base structure wasconstructed from aluminium it was not able to withstand temperatures over 175 o Cwithout a thermal protective system (TPS) [20]. The outer skin of the shuttle wascomposed of seven different materials that are found on different regions of theshuttle [21].On the shuttle the TPS was divided into a tile based and non-tile based system.There are four different tile types, all of which are very poor conductors in order toprevent heat transfer [20, 22]. The four tile types include high-temperature reusablesurface insulation (HRSI), fibrous refractory composite insulation tiles (FRCI),toughened unipiece fibrous insulation (TUFI) and low-temperature reusable surfaceinsulation (LRSI) [21]. The non-tile materials used on the shuttle as part of the TPSincluded flexible insulation blanket (FIB), reinforced carbon-carbon (RCC), Nomex feltreusable surface insulation (FRSI) and gap fillers [21].On the shuttle, the HRSI tiles were composed of high purity silica fibers and coverthe under-side which are able to withstand temperatures up to 1260 o C [21]. Duringsubsequent repairs of the shuttle, the HRSI tiles were replaced with either FRCI orTUFI tiles, both of which provided increased strength, durability and resistance tocracking. LRSI tiles were originally used on the sides of the craft and the tail wingwhich have been retrofitted with flexible insulation blankets (FIB) composed of awhite low density fibrous silica material that requires less maintenance than theearlier LRSI tiles [21]. The wings of shuttle are lined with reinforced carbon-carbon—acomposite material made from graphite rayon cloth and impregnated phenolic resin[21]. These panels along the wing are between 6 to 13 mm thick and can withstandtemperatures up to 1510 o C [21]. The upper surface and aft fuselage of the shuttlewere coated with FRSI, a white flexible fabric that could withstand temperatures upto 371 o C [21]. Lastly, the gap fillers, composed of alumina fibers, were placed atseveral locations throughout the shuttle (leading edge of foreward fuselage, nosecaps, windshields, side hatch, wings, vertical stabiliser, rudder, speed rake, bodyflaps and on the heat shield around the main engines) to minimise heating bypreventing the formation of vortices in areas where surface pressure gradients wouldresult in a cross-flow of air within the gaps [21].27
Section III: Thermal Effects© SSS Educational Series 2012Figure 12. Shuttle Thermal Protection System (Source: NASA).In addition, at the NASA Ames Research Center in Moffett Field, California, there areadditional studies ongoing to develop Ultra High Temperature Ceramics (UHTC) thatcan be used on future re-entry vehicles [20].The Russian Federal Space Agency (ROSCOSMOS) also has a launch vehicle knownas Soyuz-TMA. This Soyuz launch vehicle is a segmented craft consisting of anforward orbital module (holds crew), a center descent module and an aft servicemodule (contains instruments and engines) [23, 24]. The exterior thermal protectionon a Soyuz-TMA craft involves service module radiators [25], along with a multi-layervacuum-screen thermal insulation [24]. The descent module carries eight thermalblankets held by the apex and base rings which are released when the modules areseparated for re-entry [25].5.3 HumansDue to extreme thermal conditions an astronaut will face during extra-vehicularactivity (EVA), an extravehicular mobility unit is required to withstand the harshconditions. The American spacesuit—Enhanced Extravehicular Mobility Unit (EMU) isjointly developed by Hamilton Sundstrand, International Latex Corporation Doverand NASA [26]. The suit is primarily white, which allows it to reflect a significantportion of the thermal energy from the sun and is able to sustain temperatures from-156 o C to 121 o C [26]. The spacesuit consists of a hard upper torso assembly [27],28
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SPACE WEATHER - AGI

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