Dynamic Materials Testing for Ultrahigh-Speed Spaceflight

最近的技术发展表明，超高速太空飞行的新时代正在出现，有可能实现快速星际运输和最终星际飞行的路线图。在这样的速度下，当航天器遇到微流星体撞击和高发射加速度时，太空飞行开辟了新的动力学机制。例如，帕克太阳探测器将以300公里/秒的速度遇到尘埃颗粒的撞击，比实验室测试微米级撞击的模拟速度快30多倍。在这些条件下发生的影响将进入以前未曾探索过的高能量密度状态；未来几年，我们将看到更大的航天器速度。目前，最有前途的快速太空旅行技术似乎是定向能，其中地面相控阵激光作为一个单一的，衍射有限的光学能够将能量应用到数百万公里外的目标。光子学革命使这项技术成为可能，光纤激光放大器的成本像摩尔定律一样下降，这使得激光发射器可以以模块化的方式开发。这种能量可以用来为航天器上的高推力电力推进装置提供动力，也可以直接对薄膜施加光子压力。前一种概念是美国宇航局资助的革命性推进快速深空运输研究所的主题，而后一种方法是突破摄星的基础。在直接驱动方法中，动态光子加载到薄（亚微米）薄膜上可以导致100,000 g的加速度。目前还没有测试薄膜对动态载荷响应的测试方法。该研究项目将开拓测试能力的发展，以在这种超高速状态下进行完整的动力学模拟，包括粉尘颗粒撞击问题和薄膜对高动态载荷的响应。气体动力学技术可以将瞬态负载施加到薄膜上，使其在数量上与驱动激光器的条件相匹配，而不必使用10兆瓦级的激光阵列。具体来说，激波管导致的动态载荷被施加到帆上，这与直接激光驱动的光帆所遇到的载荷本质上是相同的。使用我的实验室首创的技术，包括光子多普勒测速，将使薄膜材料在代表性负载下的动态响应能够进行实验研究。利用高能材料内爆薄壁真空圆筒有可能以超过100公里/秒的速度驱动壁材射流向前。该项目将使用现代诊断工具和计算机模拟系统地研究这一现象，目标是能够在实验室中以感兴趣的速度使用这些射流再现撞击事件。

Recent technological developments have signaled that a new era of very high velocity spaceflight is emerging, with the potential to enable rapid interplanetary transport and a roadmap to eventual interstellar flight. Spaceflight at these speeds opens up new regimes of dynamics as the spacecraft encounters micrometeoroid impacts and high launch accelerations. For example, the Parker Solar Probe will encounter dust grain impacts at speeds of 300 km/s, more than 30 times faster than laboratory testing of micron-sized impacts is capable of simulating. The impacts occurring under these conditions will enter previously unexplored regimes of high energy density; the coming years will see even greater spacecraft velocities. At present, the most promising technology for rapid space travel appears to be directed energy, wherein a ground-based phased-array of lasers act as a single, diffraction-limited optic capable of applying energy to a target out to distances of millions of kilometers. This technology has been enabled by the photonics revolution that has seen a Moore's Law-like decrease in the cost of fiber-optic-based laser amplifiers, which permits the beamer to be developed in a modular fashion. The energy can be used to power high-thrust electric propulsion on-board the spacecraft or can apply direct photon pressure onto a thin film. The former concept is the subject of a proposed NASA-funded institute for Revolutionary Propulsion for Rapid Deep Space Transit, while the latter approach is the basis of Breakthrough Starshot. In the direct drive approach, dynamic photon loading onto thin (sub-um) films can result in accelerations of 100,000 g. At present no testing methodologies exist to test the response of the thin films to dynamic loading that would be used. This research program will pioneer the development of testing capabilities for the complete simulation of dynamics in this ultrahigh velocity regime, including the dust grain impact problem and the response of thin films to high dynamic loading. Gasdynamic techniques enable transient loads to be applied to thin films that are quantitatively matched to the conditions of the driving laser, but without having to use a 10 MW-class laser array. Specifically, a shock tube results in dynamic loads being applied to the sail that are essentially identical to those encountered with a direct laser-driven lightsail. Using techniques pioneered in my lab, including Photonic Doppler Velocimetry, would enable the dynamic response of thin film materials under representative loading to be investigated experimentally. The use of energetic materials to implode a thin-walled evacuated cylinder has the potential to drive a jet of wall material forward at velocities greater than 100 km/s. This program will systematically study this phenomenon using modern diagnostic tools and computer simulation, with the goal of being able to use these jets to reproduce impact events at velocities of interest in the laboratory.