美国宇航局超级计算机预测猎户座中止情景的振动如何随高度变化

　　Credits: NASA/Ames Research Center/Timothy Sandstrom, Francois Cadieux, Michael Barad, Cetin Kiris
　　NASA Supercomputers Predict How Vibrations Vary With Altitude for Orion Abort Scenarios
　　作为阿尔忒弥斯任务的一部分，美国宇航局的猎户座宇宙飞船将把第一位女性和第一位有色人种送上月球，并将她们安全送回地球。猎户座将坐在世界上最强大的火箭上，即美国宇航局的太空发射系统，将人类发射到深空。确保宇航员安全的一个组成部分是猎户座的发射中止系统，如果在发射过程中出现紧急情况，该系统可以在瞬间将乘员舱从火箭上拉开。
　　猎户座的发射中止系统位于猎户座太空舱上方，中止功能由中止塔上的固体火箭发动机提供动力。中止操作类似于乘员舱的＂弹出按钮＂动作。中止电机产生热的、湍流的、高速的排气羽流，沿着猎户座的侧面流动。这些羽流会产生强烈的压力波，当猎户座航天器被拉离火箭时，可能会导致发射中止系统与猎户座航天器的组合结构发生振动。 NASA 研究人员分析这些振动，以确保系统在飞行中不会自行摇晃。
　　在发射或升空期间的任何阶段都可以触发中止。火箭的高度、速度、方向和方位在上升过程中不断变化。这些因素会影响电机在中止期间产生的声学振动的强度和程度。中止系统将需要在极其不同的条件下执行。
　　位于加利福尼亚硅谷的美国宇航局艾姆斯研究中心的研究人员正在使用他们称为 LAVA（发射、上升和车辆空气动力学）的尖端计算流体动力学软件来预测和更好地了解不同的中止场景——从发射台到太空边缘——会影响振动水平。 Ames 团队对在 NASA 的 Ascent Abort-2 测试中飞行的发射中止飞行器进行了三个模拟。在每次模拟中，中止都发生在与 NASA 的 Ascent Abort-2 飞行测试不同的情况下。在一种情况下——在飞行早期——中止发生在低空，同时以接近音速的速度飞行，火箭的方向与其飞行方向不对齐。在另一个模拟中，当火箭仍处于低空但飞行速度超过音速时，中止在飞行后期触发。第三种情况研究了在到达太空之前最后一次中止的机会，火箭在非常高的高度以接近五倍音速的稀薄空气飞行。
　　这些模拟是在 NASA 的 Aitken 和 Electra 超级计算机上进行的。这些计算流体动力学预测有助于减少难以测试或测试成本太高的中止场景的不确定性，例如高海拔近超音速中止，进一步有助于降低风险并确保宇航员的安全。该技术能够以更低的成本在超级计算机中运行测试，并在飞行前更快地周转，从而帮助推进 NASA 的任务，最终使 NASA 的探索系统更安全。
　　As part of the Artemis missions, NASA’s Orion spacecraft will carry the first woman and first person of color to the Moon and return them safely back to Earth. Orion will sit atop the most powerful rocket in the world, NASA’s Space Launch System, to launch humans to deep space. An integral part of ensuring astronaut safety is Orion’s launch abort system that can pull the crew module away from the rocket in a split-second if an emergency arises during launch.
　　Orion’s launch abort system sits over the Orion capsule, and the abort function is powered by a solid rocket motor on the abort tower. The abort maneuver resembles the action of an ＂eject button＂ for a crew capsule. The abort motor produces hot, turbulent, high-speed exhaust plumes that flow along the sides of Orion. These plumes create intense pressure waves that can cause vibrations in the combined structure of the launch abort system with the Orion spacecraft as it is pulled away from the rocket. NASA researchers analyze these vibrations to ensure the system doesn’t shake itself apart in flight.
　　An abort could be triggered at any stage during launch or ascent to space. Altitude, speed, direction, and orientation of the rocket constantly change during ascent. These factors affect the strength and extent of the acoustic vibrations the motor’s plumes generate during an abort. The abort system will need to perform under extremely different conditions.
　　Researchers at NASA’s Ames Research Center in California’s Silicon Valley are using their cutting-edge computational fluid dynamics software called LAVA (Launch, Ascent, and Vehicle Aerodynamics) to predict and better understand how different abort scenarios – from the launchpad to the edge of space – will affect vibration levels. The Ames team performed three simulations of the launch abort vehicle that flew on NASA’s Ascent Abort-2 test. In each simulation, abort happened under circumstances different from NASA’s Ascent Abort-2 flight test. In one scenario – early in the flight – abort occurred at low altitude while traveling close to the speed of sound where the rocket’s orientation is misaligned with its direction of flight. In another simulation, the abort triggered later in the flight while the rocket is still at low altitude but traveling faster than the speed of sound. A third scenario studied the last opportunity to abort before reaching space where the rocket was traveling though thin air at very high altitude at nearly five times the speed of sound.
　　These simulations were performed on NASA’s Aitken and Electra supercomputers. These computational fluid dynamics predictions help reduce uncertainty for abort scenarios that are difficult or too expensive to test, like the high altitude near-hypersonic abort, further helping to reduce risk and ensure the safety of astronauts. The technology is helping advance NASA’s missions by making it possible to run tests in a supercomputer at lower cost and with faster turnarounds before flight, ultimately making NASA exploration systems safer.