A team led by scientists at Tokyo Metropolitan University has created unprecedentedly lightweight optics for space X-ray telescopes, breaking the traditional trade-off between angular resolution and weight. They used Micro Electro-Mechanical System (MEMS) technology, creating intricate patterns in silicon wafers capable of directing and collecting X-rays. By annealing and polishing, they achieved ultra-sharp features that could rival with the performance of existing telescopes for a fraction of the weight, costing much less to launch.
X-ray astronomy provides an essential tool that helps scientists study and classify the wide range of celestial bodies that emit and interact with X-rays, including our planet. But there’s a catch: Most X-rays are absorbed in our atmosphere, which means telescopes and detectors have to be launched into space. This comes with a whole host of limitations, especially the weight of the device.
One of the key characteristics of all astronomical observing optics is its angular resolution, or the angle that two light sources can make with a detector and still be distinguishable. The problem with conventional X-ray optics is that to achieve higher resolutions the devices become increasingly heavy. This makes launching them into space very expensive. Even for the Hitomi telescope launched in 2016, considered revolutionary light, the effective weight was 600 kg per square meter of useful area.
Now, a team led by Associate Professor Yuichiro Ezoe and Aoto Fukushima has broken that compromise by designing a high-performance unit that weighs just 10kg per square meter. They used Micro Electro-Mechanical Systems (MEMS) technology, a technique designed to make microscopic mechanical actuators, to mold sharp and intricate designs into silicon wafers that can direct and collect X-rays. follows the Wolter I geometry of existing X-ray telescopes, a concentric array of tree-ring shaped slits that can push incoming X-rays through a narrow range of angles and collect them to a point.
What’s unique about the team’s work is how they’ve refined the pattern itself. After etching the slits using a technique called deep reactive ion etching (DRIE), they found that there was a surface roughness to the patterns that could coat the X-ray collection, decreasing resolution. So they “annealed” the pattern, applying heat in a special device for unprecedented lengths of time. With longer and longer annealing, the silicon atoms on the surface of the patterns were able to move more, rounding off any roughness and improving the angular resolution of the telescope. This was followed by grinding and chemical polishing to straighten the rounded edges of the slots themselves.
Importantly, the performance reported by the team matches that of telescopes that are already in action. Its weight makes it particularly suitable for the GEO-X mission, a satellite designed to visualize the Earth’s magnetosphere. The team is aiming for the incredibly low overall weight of 50kg, a technological breakthrough that could see future missions sent into orbit at an incomparably lower cost.