Metallic Thermal Protection System Panel Research Articles

Design, Fabrication, and Testing of Metallic Thermal Protection Systems for Spaceplane Vehicles

This study presents the design and testing of a metallic thermal protection system (TPS) for future spaceplane vehicles. A conceptual design of the developed metallic TPS panel consisting of an outer sandwich structure, thermal insulation, inner support brackets, and a base framelike structure was redesigned from the metallic TPS panel developed by NASA. The thermal load was selected from a previous study, which was equivalent to the highest surface temperature of 1050 K. Nine metallic TPS prototype panels and supporting hardware structures made of 304 stainless steel were initially prepared for thermomechanical testing in room conditions. A noncontact thermal–mechanical measurement method was employed to measure full-field temperatures and deformations of the inner base structure and supporting hardware structures. The results indicated that the proposed design satisfied the requirements of temperature and permanent deformation limits. Panel-to-panel gaps showed a significant effect on the temperature rise in the inner base structure. The performance of the prototype proved the feasibility, reusability, and durability of using low-cost 304 stainless steel for TPS structures up to four thermal cycles, and may achieve more in further tests. Results provide valuable data for evaluating designs at the early stage of TPS development and testing in space conditions.

Dynamic Characteristics and Damage Detection of a Metallic Thermal Protection System Panel Using a Three-Dimensional Point Tracking Method and a Modal Assurance Criterion.

A thermal protection system (TPS) is designed and fabricated to protect a hypersonic vehicle from extreme conditions. Good condition of the TPS panels is necessary for the next flight mission. A loose bolted joint is a crucial defect in a metallic TPS panel. This study introduces an experimental method to investigate the dynamic characteristics and state of health of a metallic TPS panel through an operational modal analysis (OMA). Experimental investigations were implemented under free-free supports to account for a healthy state, the insulation effect, and fastener failures. The dynamic deformations resulted from an impulse force were measured using a non-contact three-dimensional point tracking (3DPT) method. Using changes in natural frequencies, the damping ratio, and operational deflection shapes (ODSs) due to the TPS failure, we were able to detect loose bolted joints. Moreover, we also developed an in-house program based on a modal assurance criterion (MAC) to detect the state of damage of test structures. In a damage state, such as a loose bolted joint, the stiffness of the TPS panel was reduced, which resulted in changes in the natural frequency and the damping ratio. The calculated MAC values were less than one, which pointed out possible damage in the test TPS panels. Our results also demonstrated that a combination of the 3DPT-based OMA method and the MAC achieved good robustness and sufficient accuracy in damage identification for complex aerospace structures such as TPS structures.

Thermomechanical Performance of Bio-Inspired Corrugated-Core Sandwich Structure for a Thermal Protection System Panel

A skin structure for thermal protection is one of the most interesting components that needs to be considered in the design of a hypersonic vehicle. The thermal protection structure, if a dense structure is used, is heavy and has a large heat conduction path. Thus, a lightweight, high strength structure is preferable. Currently, for designing a lightweight structure with high strength, natural materials are of great interest for achieving low density, high strength, and toughness. This paper presents bio-inspired lightweight structures that ensure high strength for a thermal protection system (TPS). A sinusoidal shape inspired by the microstructure of the dactyl club of Odontodactylus scyllarus, known as the peacock mantis shrimp, is presented with two different geometries, a unidirectionally corrugated core sandwich structure (UCS) and a bidirectionally corrugated core sandwich structure (BCS). Thermomechanical analysis of the two corrugated core structures is performed under simulated aerodynamic heating, and the total deflection and thermal stress are presented. The maximum deflection of the present sandwich structure throughout a mission flight was 1.74 mm for the UCS and 2.04 mm for the BCS. Compared with the dense structure used for the skin structure of the TPS, the bio-inspired corrugated core sandwich structures achieved about a 65% weight reduction, while the deflections still satisfied the limits for delaying the hypersonic boundary layer transition. Moreover, we first fabricated the BCS to test the thermomechanical behaviors under a thermal load. Finally, we examined the influence of the core thickness, face-sheet thickness, and emittance in the simulation model to identify appropriate structural parameters in the TPS optimization. The present corrugated core sandwich structures could be employed as a skin structure for metallic TPS panels instead of the honeycomb sandwich structure.

A study on metallic thermal protection system panel for Reusable Launch Vehicle

A Ni-based superalloy honeycomb thermal protection system (TPS) panel has been fabricated. And a curved Ni-based superalloy honeycomb sandwich has also been fabricated. The preliminary thermal insulation results of a fabricated Ni-based superalloy honeycomb TPS panel (the areal density of this panel is 6.7kg/m2 and total height is 32mm) indicate that the maximum temperature of the lower surfaces of the panel is lower than 150∘C when the temperature of outer surface is held at 650∘C for 30min. The flatwise tensile strength and compressive properties of a fabricated Ni-based superalloy honeycomb sandwich coupon was studied at room temperature. A multilayered coating has been developed on the surface of the superalloy honeycomb TPS panel for environmental protection and thermal control. The oxidation weight-change results show that the weight change of the Ni-based superalloy honeycomb sandwich with the oxidation resistant coating is extremely small at 1100∘C in air for 10h. The emittance layer of the multilayered coating imparts an emittance in excess of 0.85 during exposure at 850∘C, which was at least 14% greater than that of the substrate with oxidation resistant alone.

Numerical Simulation of Metallic Thermal Protection System Panel Bowing

Numerical simulation of the thermoelastic response of metallic thermal protection panels is presented. The panels, which arebeing designed foruseon the windward surface of theX-33 e ighttest vehicle, deform into convex and concavebowedsurfacesdueto thermalgradientscausedbyaerodynamicheating.Threenumerical models, for the e owe eld, forthein-depth heat transfer, and for the thermoelasticdeformation, are coupled in sequence to yield the transient response of the metallic panel. The aerothermal loads are derived from computational e uid dynamic solutionsandareprescribedasadistributionfunctionwithmaximumbowheightasthegoverningparameter.Finite element models are used to simulate the thermal and structural responses. The coupled simulation is compared to a single-pass uncoupled solution. Results show negligible feedback between the structural deformation and the deformation-induced perturbation of the aerothermal heat load. Nevertheless, signie cant temperature variations on the surface of the panel are produced. The deformations induce lateral temperature gradients that increase the thermal stress within the panel. Finally, it is shown that panel bowing does not appreciably alter the trajectory integrated heat load.