Dynamic Materials Testing for Ultrahigh-Speed Spaceflight

最近的技术发展表明，一个非常高速的太空飞行的新时代正在到来，有可能实现快速的星际运输，并最终实现星际飞行的路线图。当航天器遇到微流星体撞击和高发射加速时，以这种速度进行的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/S的速度遇到尘埃颗粒撞击，比实验室测试微米级撞击的速度快30多倍。在这些条件下发生的撞击将进入以前未曾探索过的高能量密度区域；未来几年将看到更大的航天器速度。目前，最有前景的快速太空旅行技术似乎是定向能量，即地面激光相控阵作为一个单一的、衍射受限的光学系统，能够将能量施加到数百万公里外的目标。这项技术得益于光子学革命，基于光纤的激光放大器的成本出现了类似摩尔定律的下降，这使得光束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大推力电力推进提供动力，或者可以对薄膜施加直接的光子压力。前一种概念是NASA资助的快速深空过境革命推进研究所的主题，而后一种方法是突破性星射的基础。在直接驱动方法中，在薄膜(亚微米)上动态加载光子可以导致100000克的加速度。目前还没有测试方法来测试薄膜对将要使用的动态加载的响应。这项研究计划将率先开发测试能力，以完全模拟这种超高速区域的动力学，包括尘埃颗粒撞击问题和薄膜对高动态载荷的响应。气体动力学技术使瞬时负载能够施加到与驱动激光器的条件定量匹配的薄膜上，而不必使用10 mW级的激光阵列。具体地说，激波管导致施加在风帆上的动态载荷与直接激光驱动的光帆所遇到的动态载荷基本相同。使用我的实验室首创的技术，包括光子多普勒测速，将使薄膜材料在典型载荷下的动态响应能够进行实验研究。使用高能材料内爆薄壁真空圆柱体有可能推动壁材射流以高于100公里/S的速度前进。该计划将使用现代诊断工具和计算机模拟对这一现象进行系统研究，目标是能够使用这些射流以实验室中感兴趣的速度重现撞击事件。

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.