Thermal Systems and Design

Abstract

The STS during its entire flight regime is exposed to different thermal environments, causing severe thermal loads to the vehicle, structural elements and several other sensitive elements. All thermal effects such as local heating rate and total heat load are to be analyzed in detail to understand the thermal loads during flight. Thermal environment of the vehicle and subsystems caused by aerodynamic heating depends mainly on their external configuration, vehicle surface material characteristics, flow field characteristics and vehicle trajectory. The thermal load caused by propulsion system depends on the type of propulsion system, vehicle operating altitude, nozzle expansion ratio and the vicinity of the subsystem elements with respect to the propulsion elements. Thermal protection materials and thickness in turn decide the thermal protection system mass depending on thermal environment, type of thermal load, materials used in the system and temperature constraints specified for the various subsystems. Thermal protection systems (TPS) are passive, semi-passive and active depending on the application. While appropriate TPS is used to ensure the normal function of the subsystem to meet the specified functions, the mass of the integrated vehicle has to be minimized. During the initial development phase, an integrated system design approach is required to arrive at optimum structural and thermal designs for the vehicle subsystems. Once the suitable thermal protection materials are chosen based on the detailed analyses, it is essential to carry out thermophysical and mechanical property tests for these materials within the temperature range they are expected to experience in flight. This chapter presents the thermal design aspects of vehicle and subsystems for a launch vehicle. The impact of the thermal environments, on vehicle and subsystems, the need for the integrated design strategy, the requirements of various subsystems which need thermal protection, design constraints and approach for optimum thermal design for each of the subsystems are highlighted. The various aspects of the heating environment due to jet exhaust are described. Thermal response analysis and the methodology for the analysis are covered. Tests for thermal protection systems and their qualification methods are also included.