Heat flux augmentation caused by surface imperfections in turbulent boundary layers

Aerodynamic heating of hypersonic vehicles is one of the key challenges needed to be overcome in the pursuit of hypersonic ascent, re-entry, or sustained flight. Small, unavoidable imperfections are always present on the surface of aircraft in the form of steps, gaps, and protuberances. These can lead to high levels of localised heat flux augmentation, up to many times the undisturbed level. Flat plate experiments have been carried out in the Oxford High Density Tunnel with the aim of characterising the heating effects caused by small scale protuberances and steps in turbulent boundary layers. The current work presents experimental heat flux augmentation data, an assessment of existing heat flux correlations, and introduces new engineering level correlations to describe heat flux augmentation for a range of surface geometries

DEVELOPING A FLEXIBLE THERMAL PROTECTION SYSTEM FOR MARS ENTRY: THERMAL DESIGN AND TESTING

Flexible Thermal Protection Systems (FTPS) are a key technology needed to enable novel inflatable and deployable aerodynamic decelerators. A development campaign is underway to raise the European FTPS technology readiness level from 2 to 3, advancing design and test capability. An FTPS suitable for a reference Mars landing mission is being designed. The FTPS has three functional layers: outer layers of Nextel 440 BF-20 fabric; insulation layers of SIGRATHERM GFA5 graphite felt and Pyrogel XTE aerogel; and a silicone-coated Kevlar fabric gas barrier. The density, specific heat capacity and thermal diffusivity of candidate materials was measured. Results were then used in thermal simulations to define a baseline layup. The layup thermal conductance was assessed in thermocouple-instrumented layup tests. Layups including joints were also tested and found not to have significantly different conductance. Layup test thermal simulations showed good agreement with the experimental data. Future work will include arc-jet tests and thermal model optimisation

DEVELOPING A FLEXIBLE THERMAL PROTECTION SYSTEM FOR MARS ENTRY: SYSTEMS ENGINEERING, MECHANICAL DESIGN AND MANUFACTURING PROCESSES

A flexible thermal protection system (FTPS) is needed to enable the use of deployable and inflatable hypersonic decelerators. These decelerators could increase entry vehicle drag area beyond that of a conventional rigid heatshield, enabling Mars missions with greater landed masses and higher-elevation landing sites than can be currently achieved. An FTPS is essential to protect the hypersonic decelerator and payload from atmospheric entry aerothermal loads; conventional rigid heatshields are constrained by the available space within the launcher fairing. An ESA technology development is ongoing to raise the European FTPS technology readiness level from 2 to 3 and to define an FTPS that may be integrated with a Mars-entry inflatable hypersonic decelerator. This paper presents the FTPS requirements, material selection, mechanical characterisation and manufacturing technique development

NEW DEMISE TECHNOLOGY CONCEPTS OF SPACECRAFT STRUCTURAL JOINTS

The recently introduced discipline of Design for Demise aims to promote the atmospheric demise of a spacecraft and its respective components during re-entry, to reduce the casualty risk on ground. An earlier opening of spacecraft outer structure improves the overall atmospheric demise of subsystems, units, and components. New technical solutions are therefore needed to achieve a targeted opening / release of external structural components and spacecraft modules. Currently used materials and joining techniques have been investigated within high enthalpy wind tunnel and static heat chamber tests, to better understand the processes at play during their demise. Under consideration of the different failure scenarios observed during testing, the subsequent breadboard testing focused on passively activated demisable joining technologies. Technical design considerations were combined with their potential effects on e.g., the reliability of demise, mechanical performance, system impact, scalability, and potential costs. Based on an elaborated trade-off system various joining concepts then underwent a range of tests in a wind tunnel and re-entry chamber. Testing compared the demise ability with the current state-of-the-art technology and assessed their demise performance. Based on the results the appropriate utilisation of demise technology, can improve the demise of any given spacecraft and by association, reduce the casualty risk on the ground

Methodology and Results of High Enthalpy Wind Tunnel and Static Demisability Tests for Existing Spacecraft Structural Joining Technologies

The recently introduced discipline of design-for-demise (D4D) is looking for technical solutions on different levels to promote the atmospheric demise of spacecraft and respective components in order to reduce the casualty risk on ground. Previously performed studies revealed that opening the outer satellite structure during re-entry as early as possible helps to improve the overall demise. Therefore, technologies to open and/or release external structural elements and spacecraft modules are needed. In order to get a better understanding of the behavior during re-entry of current structural joining technologies, tests have been performed in high enthalpy wind tunnel and static heat chambers. These were setup to be representative of a number of joining configurations utilized within satellite designs. Samples representing a broad range of options were prepared and tested in both chambers. An overview of test procedures and findings are presented here along with early conclusions and future activities. The samples exhibited a broad range of phenomena and it was seen that a number of different failure scenarios are possible dependent upon joining technology used along with heat flux profile and mechanical loads applied, among other influencing factors. The results from these tests will feed into the development of new demisable joining technologies for bread-boarding development and assist in designing similar tests in the near-future. These on-ground activities will help to raise the current understanding of satellite demise and the role that joining technologies play, therefore leading to more informed decisions regarding the ways to increase satellites break-up altitude in the future reducing the on-ground casualty risk