Displacements of Metallic Thermal Protection System Panels During Reentry

Abstract

Bowing of metallic thermal protection systems for reentry of a previously proposed single-stage-to-orbit reusable launch vehicle was studied. The outer layer of current metallic thermal protection system concepts typically consists of a honeycomb panel made of a hightemperature nickel alloy. During portions of reentry when the thermal protection system is exposed to rapidly varying heating rates, a significant temperature gradient develops across the honeycomb panel thickness, resulting in bowing of the honeycomb panel. The deformations of the honeycomb panel increase the roughness of the outer mold line of the vehicle, which could possibly result in premature boundary layer transition, resulting in significantly higher downstream heating rates. The aerothermal loads and parameters for three locations on the centerline of the windward side of this vehicle were calculated using an engineering code. The transient temperature distributions through a metallic thermal protection system were obtained using 1-D finite volume thermal analysis, and the resulting displacements of the thermal protection system were calculated. The maximum deflection of the thermal protection system throughout the reentry trajectory was 6.4 mm. The maximum ratio of deflection to boundary layer thickness was 0.032. Based on previously developed distributed roughness correlations, it was concluded that these defections will not result in tripping the hypersonic boundary layer.

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

“…We were concerned about the bow-out deflection in the heating stage because the vehicle was in the flight path of a mission, and this bowing out into the boundary layer of the external surface of the vehicle could cause flow disturbances and lead to a transition of the boundary layer from laminar to turbulent, thereby greatly increasing the incident heating [7,53]. While the bow-in deflection in the cooling stage had negative values after 2000 s, the vehicle was approaching the ground and the largest deflection was observed when the vehicle was on the ground; thus, the bowing in of the sandwich structures may not cause significant overheating issues related to boundary layer transition, as also reported by the authors of [8,12]. There was some inward permanent deflection of the sandwich structures after one mission.…”

“…Thus, the design of the TPS panel must ensure a safe temperature for the vehicle structure at below the allowable temperature of the internal structure's material [10,11]. It must also provide an acceptable surface deflection to prevent flow transition during flight [12].…”

“…Several studies have focused on the thermomechanical performance of the TPS panel to determine the deflection limit. Daryabeigi et al [12] theoretically calculated the deflection of a honeycomb panel for a TPS panel and evaluated the maximum deflections in terms of the boundary layer transition. Guo et al [13] investigated the thermomechanical performance of a TPS panel with a honeycomb panel at the top surface.…”

“…They also presented an application of the finite element method for TPS panel optimization. Their TPS model followed the design of NASA's TPS panel [1,12]. Most of the research focused on the goal of the temperature limit in the internal structure of the vehicle, and they determined the proper thickness and material for the TPS panel [11,[14][15][16].…”

Thermomechanical Analysis of a Damaged Thermal Protection System

“…Numerical simulation were conducted on superalloy honeycomb TPS to determine its thermoelastic response [21]. The ARMOR TPS concept was evaluated using one-dimensional finite volume thermal analysis to determine the resultant deformations [8], followed by thermal, structural and creep FE analyses [4].…”