Active Thermal Protection System for Reusable Launch Vehicle

Abstract

The next step in spaceflight, among others, is the development of a reusable launch vehicle (RLV) suitable for manned missions. All existing designs of re-entry vehicles are either ballistic or low L/D vehicles. In the future, the aim is to develop a high L/D vehicle, because such vehicles experience lower g-loads, making the flight comfortable for manned flights. The development of these vehicles can be useful for both, space (for example, space tourism) and military applications (for example, long-range missiles). Thermal protection system (TPS) is deemed critical to the RLV development, as high L/D vehicles are expected to experience higher thermal loads. Existing TPS solutions are not suitable for this purpose. Therefore, arises the need to find reusable TPS solutions that can sustain the desired thermal loads. Flight testing is a crucial step for developing any hypersonic system, this applies to the TPS design as well. This study aims to investigate the influence of TPS on designing the mission and vehicle for a test flight.
From the various developed and proposed TPS designs in literature, a TPS solution is selected, to meet the requirements identified for future RLVs. The solution is an active cooling concept (cooled metallic TPS), named Enhanced radiation cooling, that uses water as a coolant. Based on a preliminary design investigation, suitable materials are selected and the thickness of the layer is determined. The performance of the proposed TPS design, i.e., the thermal load-bearing ability, is assessed using a transient thermal analysis tool developed for this purpose. The outcome of this analysis proves that the proposed design does not meet the thermal load requirements identified in this study. Nonetheless, the concept shows substantial improvement in performance, it can sustain almost double the heat flux as compared to an uncooled system.
To meet the heat flux requirements, a few modifications in the design are proposed and analysed. These modifications increase the complexity of the system and have other adverse consequences that must be addressed. However, thermal analysis proves that the heat flux requirements, identified at the start of this study, are satisfied. A sensitivity analysis of this modified cooling system shows that the performance of the design is not influenced by material uncertainties. Additionally, the design is found to be robust under varying mission and design parameters, within reasonable bounds. These results can serve as a preliminary input for designing a test vehicle and mission.