We’ve flown a radiation-blocking vest to the Moon and back, and it worked

我们将一件防辐射背心送往月球并返回，实验证明它确实有效

Solar storms, like the one in August 1972 that hit during the gap between the Apollo 16 and Apollo 17 missions, throw bursts of protons intense enough to raise an astronaut’s cancer risk or even cause radiation sickness. Earth’s atmosphere and magnetic field absorb this radiation, but crews heading to the Moon or Mars won’t have that protection, and no spacecraft built so far has enough shielding to stop it. 太阳风暴（例如1972年8月发生在阿波罗16号和17号任务间隙的那场风暴）会释放出强烈的质子流，足以增加宇航员患癌的风险，甚至导致放射病。地球的大气层和磁场能够吸收这些辐射，但前往月球或火星的宇航员将失去这种保护，而目前建造的任何航天器都没有足够的屏蔽层来阻挡它。

A team led by Jordan Houri and Oren Milstein of StemRad, an Israeli-American startup developing personal protective equipment against radiation, proposed that we could solve this by shielding the astronauts instead of shielding the spacecraft. To test this idea, StemRad’s team flew a wearable radiation-shielding vest called AstroRad to the Moon and back aboard NASA’s uncrewed Artemis I mission, then used the flight data to calculate how it would perform during an actual solar storm. It turns out the vest would perform roughly as well as the Orion’s heavily shielded onboard shelter the crew was supposed to hide in to wait out a storm. 由以色列-美国初创公司StemRad的Jordan Houri和Oren Milstein领导的团队提出，我们可以通过保护宇航员个人而非保护航天器来解决这个问题。StemRad公司正在开发个人防辐射装备。为了验证这一想法，该团队将一件名为AstroRad的可穿戴防辐射背心搭载在NASA的“阿尔忒弥斯1号”（Artemis I）无人任务中送往月球并返回，随后利用飞行数据计算了它在实际太阳风暴中的表现。结果显示，这件背心的防护效果与猎户座飞船上宇航员在风暴期间躲避用的重型屏蔽舱大致相当。

Targeted shielding 针对性屏蔽

Spacecraft designers have spent decades weighing shielding options, from aluminum hulls to water-filled walls to superconducting magnets that would deflect charged particles before they reach the crew. All of them run into the same challenge. “The question was how to use mass in a very efficient way,” Milstein says. “Mass is really the bottleneck—every gram counts.” 航天器设计师几十年来一直在权衡各种屏蔽方案，从铝制外壳到注水墙，再到能在带电粒子到达宇航员之前将其偏转的超导磁体。所有这些方案都面临同一个挑战。Milstein说：“问题在于如何以非常有效的方式利用质量。质量确实是瓶颈——每一克都至关重要。”

A shielding garment an astronaut could wear is simultaneously sensible and ridiculous. The ridiculous part was that, for a long time, people thought that a protective garment would need to look like full-plate armor in order to offer meaningful protection. It would presumably need to be made of lead or other high-density materials that would add mass and make moving around nearly impossible. 宇航员穿戴的屏蔽服既合理又荒谬。荒谬之处在于，长期以来人们认为防护服必须看起来像全身板甲才能提供有效的保护。它可能需要由铅或其他高密度材料制成，这会增加重量，使宇航员几乎无法行动。

StemRad engineers, though, figured dressing as a medieval knight doesn’t really get you all that much. The human body, Milstein explains, isn’t uniformly vulnerable to radiation. “Tissues like the bone marrow are a lot more sensitive to radiation compared to the brain,” he says. Following this idea, StemRad developed a belt for nuclear first responders, worn around the hips, which hold roughly half the body’s bone marrow, the tissue that makes blood cells. Protecting even a fraction of the bone marrow lets a person regrow it and survive a high-dose exposure. 然而，StemRad的工程师们发现，打扮得像中世纪骑士并不能带来多少实际好处。Milstein解释说，人体对辐射的敏感度并非均匀分布。“与大脑相比，骨髓等组织对辐射要敏感得多。”基于这一理念，StemRad为核应急响应人员开发了一种佩戴在臀部的腰带，因为人体约一半的骨髓（造血组织）位于此处。保护哪怕一小部分骨髓，也能让人体重新生长出骨髓，从而在遭受高剂量辐射后存活下来。

So, StemRad, working with Lockheed Martin, expanded this idea into a female vest that, aside from the hips, also covered the breasts, stomach, colon, and reproductive organs. These are all less immediately life-threatening when irradiated, but carry a long-term cancer risk. “It still gets people surprised,” Milstein says. “Everybody asks, what about the head? But we’re actually able to reduce the effective dose by 60 percent without protecting the head, the arms, or even the legs.” But choosing where to put shielding was just one part of the problem. Picking the material and making a design that would not hinder the astronaut’s movements was another. 因此，StemRad与洛克希德·马丁公司合作，将这一理念扩展为一件女性背心，除了臀部外，还覆盖了乳房、胃、结肠和生殖器官。这些部位在受到辐射时虽然不会立即危及生命，但存在长期的癌症风险。Milstein说：“这仍然让人们感到惊讶。每个人都会问，头部怎么办？但实际上，即使不保护头部、手臂甚至腿部，我们也能够将有效辐射剂量降低60%。”然而，选择屏蔽位置只是问题的一部分。选择材料并设计出不阻碍宇航员行动的方案则是另一回事。

A division problem 除法难题

“The primary factor in how effective a shielding material is is its atomic number divided by its atomic mass,” Houri says. Hydrogen, which has no neutrons, has roughly double that ratio of any other element, which is why water is often cited as a good space radiation shield. High-density polyethylene (HDPE), an ordinary plastic, packs even more hydrogen by mass than water, and, unlike water, it’s a solid, so you don’t have to worry about leaks. Houri说：“屏蔽材料有效性的主要因素是其原子序数除以原子质量。”氢没有中子，其比例大约是其他任何元素的两倍，这就是为什么水常被认为是良好的空间辐射屏蔽材料。高密度聚乙烯（HDPE）是一种普通塑料，其单位质量所含的氢比水更多，而且与水不同，它是固体，因此不必担心泄漏问题。

The problem with a solid, rather stiff material like HDPE is that when made thick enough to offer good radiation protection, it can compromise comfort. To go around it, StemRad’s team broke it apart into hexagonal rods of varying lengths and cross-sections. “We divided up the shielding panels into thousands of hexagonal tessellated rods of HDPE,” Houri says. These rods, sandwiched between two layers of elastic fabric, made the vest extremely flexible and fluid-like. “It almost behaves the same way that water would, while still remaining solid,” Houri claims. 像HDPE这样坚硬的固体材料的问题在于，当厚度足以提供良好的辐射防护时，会牺牲舒适度。为了解决这个问题，StemRad团队将其分解成不同长度和横截面的六角形棒。Houri说：“我们将屏蔽板分成了数千根六角形镶嵌的HDPE棒。”这些棒夹在两层弹性织物之间，使背心变得极其灵活且具有流动感。Houri声称：“它在保持固态的同时，表现得几乎和水一样。”

The rods run 9 to 60 millimeters long. Engineers calculated their length using the Bethe-Bloch formula, which describes how charged particles lose energy while moving through matter. This way, the team could predict how far a particle with a given energy would travel through their shielding before stopping. Of course, calculations, even highly precise ones, are not enough. To get hard data, StemRad sent its AstroRad vest on a round trip around the Moon. 这些棒的长度在9到60毫米之间。工程师们使用Bethe-Bloch公式计算了它们的长度，该公式描述了带电粒子在穿过物质时如何损失能量。通过这种方式，团队可以预测具有特定能量的粒子在停止前能穿透多厚的屏蔽层。当然，计算即使再精确也不够。为了获得确凿的数据，StemRad将AstroRad背心送往月球进行了一次往返飞行。

Helga and Zohar Helga和Zohar

Because Artemis I flew without a crew, the vest needed stand-ins to wear it. The mission carried two identical torsos, nicknamed Helga and Zohar, adapted from radiotherapy dosimetry phantoms already used in cancer treatment planning. Both were made with tissue-equivalent materials. “They were designed to interact with radiation in pretty much the exact same way that it interacts with human tissue,” Houri explains. 由于“阿尔忒弥斯1号”是无人飞行，背心需要替身来穿戴。任务携带了两个相同的躯干模型，绰号分别为Helga和Zohar，它们改编自癌症治疗计划中使用的放射治疗剂量测定模型。两者均由组织等效材料制成。Houri解释说：“它们的设计初衷就是以与人体组织几乎完全相同的方式与辐射相互作用。”

Zohar was the lucky one wearing the vest. Helga did not have any personal protection. Both phantoms were packed with thousands of dosimeters, tracking radiation dose over specific phases of the flight rather than just a cumulative total. Most of the radiation all these detectors recorded, though, came from the mission’s passage through Earth’s inner Van Allen belt, a region of high-energy trapped protons. There was no solar storm during the Artemis I flight. “If we did have [a solar particle event], that would have been the end of the analysis—we could have just used that data,” Houri said. Instead, the team used the belt crossing as a proxy, since its proton energies roughly overlap with those present during a typical storm. They built Monte Carlo simulations of the spacecraft, phantoms, and vest and checked them against the dosimeters. Zohar是幸运的穿戴者，而Helga没有任何个人防护。两个模型都装满了数千个剂量计，用于追踪飞行特定阶段的辐射剂量，而不仅仅是累积总量。然而，这些探测器记录的大部分辐射来自任务穿过地球内范艾伦辐射带（一个高能捕获质子区域）的过程。“阿尔忒弥斯1号”飞行期间没有发生太阳风暴。Houri说：“如果我们确实遇到了（太阳粒子事件），那分析就简单了——我们直接使用那些数据即可。”相反，团队将穿过辐射带作为替代方案，因为其质子能量与典型风暴期间的能量大致重叠。他们建立了航天器、模型和背心的蒙特卡洛模拟，并根据剂量计的数据进行了验证。