Spacecraft Heat Shield Material Testing in Plasma Flows

背景和潜在影响：该项目的动机是航天器飞行高速进入大气层阶段遇到的工程问题。无论是试图到达另一颗行星的表面，还是在完成使命后返回地球表面，航天器都必须首先穿过大气层，通常速度为10公里/秒。这些高速度在进入的飞行器周围产生高焓等离子体流，这反过来又对飞行器施加极端的热负荷。因此，大气层飞行的这一阶段对空间探索能力的进步构成了主要障碍，热保护系统（也称为隔热屏）用于保护飞行器免受进入大气层的高热负荷的影响。这通常通过使用绝热材料在热表面流和有效载荷之间提供物理屏障来实现。还可以通过利用各种物理和热化学效应来增强屏蔽的耐热性。例如，碳酚醛材料通常用于隔热设计;酚醛树脂的蒸发和随后暴露的碳纤维与流动的相互作用提供了有效的吸热机制。然而，由于这些反应都同时发生并相互作用，它们很难预测，导致这些材料的气动热响应具有很高的不确定性。这就需要在设计过程中考虑较大的安全因素，这就导致了重型运载工具，从而导致发射成本增加和有效载荷重量有限。因此，旨在提高我们对这些材料的理解的研究对于扩大空间探索技术的能力至关重要。该项目福尔斯属于EPSRC工程/流体动力学和空气动力学研究领域。目的和目标：拟议的项目旨在产生高质量的数据，以提高我们对等离子体和隔热材料之间复杂相互作用的理解。实验测试活动将使用牛津大学新的冷膨胀管（CXT）和Osney等离子体发生器（OPG）设施进行。当一起使用时，这允许在代表真实的进入场景期间遇到的空气动力学条件下测试等离子体预热模型。研究方法的新奇：将测试三种不同的材料类型：固体石墨、多孔碳纤维预制件（Calcarb）和软木基酚醛材料（P50）。这种测试顺序首先最大限度地减少与流体相互作用的复杂性，然后逐渐引入孔隙度的复杂性，然后是内部化学反应，允许单独研究各个机制。拟议的测试活动将伴随着新的模拟工具的开发，这些工具将通过收集的实验数据进行验证和校准。其目的是，一旦开发出来，这些工具可以与实验活动一起使用，以更好地了解现有的隔热材料，并帮助开发新技术。参与的公司/合作者：该项目部分由欧洲航天局（ESA）和流体重力工程有限公司资助。

Context and potential impact:This project is motivated by the engineering problems encountered during the high-speed atmospheric entry phase of spacecraft flight. Whether attempting to reach the surface of another planet or returning to the surface of Earth after a mission, a spacecraft must first travel through the atmosphere, typically at velocities on the order of 10 km/s. These high speeds generate high enthalpy plasma flows around the entry vehicle, which in turn impose extreme heat loads on the vehicle. This phase of atmospheric flight therefore provides a major obstacle for advances in space exploration capabilities.Thermal protection systems (also known as heat shields) are used to protect the vehicle from the high heat loads of atmospheric entry. This is typically achieved by using thermally insulating materials to provide a physical barrier between the hot surface flows and the payload. The heat resistance of the shield can also be enhanced by exploiting various physical and thermo-chemical effects. For example, carbon-phenolic materials are commonly used in heat shield design; the vaporisation of the phenolic resin and subsequent interaction of the exposed carbon fibres with the flow provide effective mechanisms for heat absorption. However, since these reactions all occur and interact with each other simultaneously, they are difficult to predict, leading to high uncertainties in the aero-thermal response of these materials. This necessitates large safety factors in the design process, which results in heavy vehicles, thereby resulting in increased launch costs and limited payload weights. Therefore, research aimed at improving our understanding of these materials is crucial for expanding the capabilities of space exploration technology.This project falls within the EPSRC Engineering/Fluid Dynamics and Aerodynamics research areas.Aims and objectives:The proposed project will aim to generate high-quality data to improve our understanding of the complex interactions between plasmas and heat shield materials. Experimental test campaigns will be conducted using the new Cold Expansion Tube (CXT) and Osney Plasma Generator (OPG) facilities at the University of Oxford. When used together, this allows for the testing of plasma pre-heated models at aerodynamic conditions representative of those encountered during real entry scenarios. The combined CXT-OPG facility will be the first of its kind in Europe once commissioned.Novelty of research methodology:Three different material types will be tested: solid graphite, a porous carbon-fibre pre-form (Calcarb) and a cork-based phenolic material (P50). This testing sequence first minimises the complexity of any interactions with the flow, before gradually introducing the complexities of porosity and then internal chemical reactions, allowing for individual mechanisms to be investigated in isolation. The proposed test campaign will be accompanied by the development of new simulation tools, which will be validated and calibrated by the collected experimental data. The aim is that, once developed, these tools can be used alongside experimental campaigns to better understand existing heat shield materials, and aid in the development of new technologies.Companies/collaborators involved:The project is funded in part by the European Space Agency (ESA) and Fluid Gravity Engineering Ltd.