NASA’s Nancy Grace Roman Space Telescope Has a Hidden Technological Leap
NASA’s Nancy Grace Roman Space Telescope Has a Hidden Technological Leap
美国国家航空航天局（NASA）南希·格雷斯·罗曼太空望远镜隐藏着一项技术飞跃
Two mirrors, each small enough to fit in the palm of your hand, are set to change how we understand the cosmos. 两面镜子，每一面都小到可以放在手掌心，即将改变我们对宇宙的认知。
The launch window for NASA’s Nancy Grace Roman Space Telescope is about to open. The telescope’s primary instrument is due to inform practically every area of astrophysics, but also tucked inside the telescope is a specialized coronagraph, an experimental apparatus that will attempt to directly capture starlight reflected off a planet’s surface for the first time. It’s an ambitious project that NASA hopes will pave the way for a space telescope that can one day provide a glimpse of an Earthlike planet orbiting a sunlike star. NASA南希·格雷斯·罗曼太空望远镜的发射窗口即将开启。该望远镜的主要仪器旨在为天体物理学的几乎所有领域提供信息，但望远镜内部还隐藏着一个特殊的日冕仪——这是一种实验性装置，将首次尝试直接捕捉行星表面反射的星光。这是一个雄心勃勃的项目，NASA希望它能为未来的太空望远镜铺平道路，使其有朝一日能够观测到一颗围绕类太阳恒星运行的类地行星。
That’s a feat far beyond the power of current engineering—hence taking the basic technique for a spin on Roman. “We’ll test them in space for the first time, and we’ll understand what work still is left to go,” says Vanessa Bailey, an astrophysicist at NASA’s Jet Propulsion Laboratory and instrument scientist for the coronagraph. 这是一项远超当前工程能力的壮举，因此需要在罗曼望远镜上对这一基础技术进行测试。“我们将首次在太空中测试它们，并了解还有哪些工作需要完成，”NASA喷气推进实验室的天体物理学家、该日冕仪的仪器科学家凡妮莎·贝利（Vanessa Bailey）表示。
At its core, a coronagraph is just a science-minded sunshade that can block out the light of a bright star and reveal a fainter object otherwise lost in the glare. Such instruments have flown in space before—both the Hubble and James Webb space telescopes carry coronagraphs. But Roman’s is light-years more sophisticated than its predecessors, thanks largely to technology called adaptive optics, which deforms a telescope’s mirror to cancel out these light distortions. It still faces a monumental challenge, though: NASA compares the task of Roman’s coronagraph to photographing a firefly perched next to a floodlight—from across the country. 从本质上讲，日冕仪就是一个科学用途的遮阳板，它可以遮挡明亮恒星的光芒，从而显现出原本会被强光淹没的暗淡天体。此类仪器此前已在太空中使用过——哈勃太空望远镜和詹姆斯·韦伯太空望远镜都携带了日冕仪。但罗曼望远镜的日冕仪比其前辈先进了几个光年，这主要归功于一种名为“自适应光学”的技术，它通过改变望远镜镜面的形状来抵消光线畸变。不过，它仍面临着巨大的挑战：NASA将罗曼望远镜日冕仪的任务比作在全国范围内拍摄一只停在探照灯旁边的萤火虫。
“Any little bit of starlight that gets in the wrong place could just destroy a whole portion of the image,” says Margaret Turnbull, an exoplanet scientist at the SETI Institute, a nonprofit research organization in California, who leads a Roman coronagraph science team. “任何一点进入错误位置的星光都可能毁掉图像的很大一部分，”加州非营利研究机构搜寻地外文明研究所（SETI Institute）的系外行星科学家、罗曼日冕仪科学团队负责人玛格丽特·特恩布尔（Margaret Turnbull）说。
The technology is standard on advanced ground-based telescopes, including the Very Large Telescope in Chile and Hawaii’s twin Keck Observatory. Here, adaptive optics monitors interference from the thick, shifting layers of Earth’s atmosphere that muddy starlight, allowing observatories to capture sharper images. 这项技术在先进的地面望远镜上已是标配，包括智利的甚大望远镜（VLT）和夏威夷的双子凯克天文台。在这些地方，自适应光学系统会监测地球大气层中厚重且不断变化的层流对星光的干扰，从而使天文台能够捕捉到更清晰的图像。
Space telescopes haven’t traditionally needed adaptive optics simply by dint of being beyond the atmosphere’s interference, but they’ve never even tried looking for old, cool planets illuminated solely by reflected starlight. 太空望远镜传统上并不需要自适应光学，因为它们位于大气层干扰之外，但它们此前从未尝试过寻找仅靠反射星光照明的古老、寒冷的行星。
For Roman, the key to its success is those two palm-sized mirrors, each of which is rigged with approximately 2,300 tiny actuators that expand when a small jolt of electricity is applied, infinitesimally reshaping the mirror to reverse interference. It’s the agency’s first time ever flying active deformable mirrors in space. 对于罗曼望远镜来说，成功的关键在于那两面手掌大小的镜子。每一面镜子都配备了大约2300个微型致动器，当施加微小电流时，这些致动器会膨胀，从而对镜面进行微小的形状调整以抵消干扰。这是该机构首次在太空中使用主动变形镜。
But the mirrors can’t do much on their own. The system requires supersensitive detectors to amplify the signal from individual photons—a necessity given how few photons the instrument will catch from any given planet. Then there’s the heart of any coronagraph, the star shades—in Roman’s case, a set of exquisitely detailed masks that Bruce Macintosh, an astronomer who leads the University of California Observatories and a Roman coronagraph science team, calls “beautiful, complicated shapes” unlike anything currently in space. “The Hubble ones are just completely brute force, just literally a little piece of metal that gets in the way of the star,” he says. 但仅靠镜子本身无法发挥太大作用。该系统需要超灵敏的探测器来放大单个光子的信号——考虑到仪器从任何特定行星上捕获的光子数量极少，这是必不可少的。此外，还有日冕仪的核心部件——星光遮罩。在罗曼望远镜的案例中，这是一套极其精细的掩模，加州大学天文台负责人、罗曼日冕仪科学团队负责人布鲁斯·麦金托什（Bruce Macintosh）称其为“美丽而复杂的形状”，与目前太空中现有的任何东西都不同。“哈勃望远镜上的那些只是完全的蛮力设计，实际上只是一小块挡在恒星前面的金属片，”他说。
During the Roman coronagraph’s operations, engineers will gather scads of test data to evaluate how well it works in space and any problems to address before similar technology flies again. Scientists will test the coronagraph by seeing if it can spot a handful of known exoplanets. 在罗曼日冕仪运行期间，工程师们将收集大量的测试数据，以评估其在太空中的工作表现，并找出在类似技术再次应用前需要解决的问题。科学家们将通过观察它是否能发现几颗已知的系外行星来测试该日冕仪。
“If we go through the whole thing and we don’t see them, then we know something is wrong with the coronagraph, because those planets are there,” Turnbull says. The instrument will also target a few stars surrounded by clouds of dust or debris, gathering observations that could reveal gaps caused by planets that scientists can’t yet detect and give scientists a whole new perspective on how normal our solar system’s level of clutter is. “如果我们完成了整个过程却没看到它们，那么我们就知道日冕仪出了问题，因为那些行星确实存在，”特恩布尔说。该仪器还将瞄准一些被尘埃或碎片云包围的恒星，收集到的观测数据可能会揭示由科学家尚未探测到的行星所造成的空隙，并为科学家提供一个全新的视角，去审视我们太阳系的杂乱程度是否处于正常水平。
Everything about Roman’s coronagraph will inform future telescopes seeking ever-smaller planets, including the Habitable Worlds Observatory that NASA hopes to launch, perhaps in the 2040s, that will need a coronagraph up to 100 times more effective; a coronagraph armed with adaptive optics and nearly as sensitive as Roman’s is also due to fly on the planned Lazuli Space Observatory that ex–Google CEO Eric Schmidt’s research institution announced in January. Although seeing alien worlds is the most tantalizing application, coronagraphs could someday show astronomers binary stars or objects hiding near bright quasars. 关于罗曼日冕仪的一切都将为未来寻找更小行星的望远镜提供参考，包括NASA希望在2040年代左右发射的“宜居世界天文台”（Habitable Worlds Observatory），它将需要效能高出100倍的日冕仪；前谷歌CEO埃里克·施密特（Eric Schmidt）的研究机构在一月份宣布的“青金石太空天文台”（Lazuli Space Observatory）计划中，也将搭载配备自适应光学且灵敏度接近罗曼望远镜的日冕仪。虽然观测外星世界是最诱人的应用，但日冕仪有朝一日或许能向天文学家展示双星系统，或隐藏在明亮类星体附近的天体。
Roman is a first, vital step toward this future—and the marvels it may show scientists along the way can support that future too, says Julie McEnery, an astrophysicist at NASA’s Goddard Space Flight Center in Maryland and senior project scientist for Roman. “Obviously, the best way of demonstrating that something works is to do something interesting scientifically,” she says. 罗曼望远镜是迈向这一未来至关重要的第一步，它在此过程中向科学家展示的奇迹也将支持这一未来，NASA马里兰州戈达德太空飞行中心的天体物理学家、罗曼望远镜高级项目科学家朱莉·麦克恩里（Julie McEnery）表示。 “显然，证明某项技术有效的最好方法就是用它做出一些有趣的科学成果，”她说。