A new telescope technology — measuring just six millimeters in diameter — could improve how future space missions study and monitor the Sun while simplifying onboard hardware and reducing costs.
The technology, developed by engineers at the University of California San Diego in collaboration with BAE Systems Space & Mission Systems, features a special optical component known as a metasurface, which is a device engineered with nanoscale structures that can manipulate light in ways that conventional optical devices cannot.
The work is detailed in a paper published on June 10 in Science Advances.
The researchers say the advance represents one of the first demonstrations of a metasurface being used in a practical scientific application.
"Most academic work on metasurfaces has remained at the proof-of-concept stage," said study senior author Noah Rubin, professor at the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering. "In this case, we fabricated a high-performing metasurface component and had it space-qualified by our industry partners at BAE Systems. We integrated it into a state-of-the-art-telescope that we custom-built with our collaborators who are experts in solar physics, then tested it at an advanced observatory and showed that it can collect scientifically meaningful data from the Sun."
"We're excited for the possibility to deploy our technology in space," Rubin said. "I think this is a very nice example of where fundamental academic research actually can translate to something with real potential for space exploration and science."
New Technology to Measure Solar Magnetic Fields
The technology is a specific type of optical component called a metasurface polarization grating, which Rubin invented while he was a PhD student at Harvard and continued developing at UC San Diego. It measures a property of light known as polarization, which is the specific direction or plane in which light waves vibrate.
In astronomy, measuring polarization is important because it provides information about the Sun's magnetic fields. Having reliable measurements of these magnetic fields, in turn, provides insights into solar events such as coronal mass ejections, which are massive eruptions that can hurl clouds of charged particles toward Earth. These could spell disaster for satellites, electronics infrastructure, communications systems and power grids.
"There's a lot of interest in being able to predict if such events are going to happen," Rubin said.
Today's solar telescopes measure magnetic fields using specialized optical components that analyze different polarization directions — but they generally only do so one at a time. To build a complete picture, the instruments take a series of images while the polarization component rotates between exposures. The process is somewhat like taking several photographs through polarized sunglasses held at different angles and then combining those images to reveal the full information.
But that process creates challenges in space. Because the images are captured one after another, even tiny vibrations on a spacecraft can cause the images to shift slightly between exposures. Those small movements can blur delicate details that need to be captured. To minimize this effect, space missions need sophisticated systems just to stabilize the telescope. "These systems often cost far more than the telescope itself," Rubin said.
The metasurface technology could solve these problems. Instead of measuring one polarization direction at a time, it separates incoming light into several different polarization channels at once. By doing so, all of the information that normally requires multiple images can be captured in just a single snapshot. And with no rotating or moving parts, the result is a simpler and more compact system.
"This could have a significant impact on future space missions," Rubin said.
"The most exciting aspect of this work is that it provides a way forward for fully simultaneous data acquisition in polarization imaging," added study first author Lisa Li, a former postdoctoral researcher in Rubin's group (now an optical engineer at Quantinuum). "The metasurface-enabled imaging technique here allows us to capture images simultaneously through a single, common optical path — and all of that information is from the same moment in time. With these faster frame rates, we can observe phenomena that were too quick for previous instruments to capture."
From Lab to Potential Space Application
The project is the product of roughly five years of innovation by Rubin and his team, with support from NASA. It started with the fabrication of a high-performance metasurface, which presented its own challenges. Afterwards, Rubin teamed up with industry partners at BAE Systems to subject the metasurface to the vibration and temperature tests required for space hardware. These tests demonstrated that the metasurface could potentially survive launch and operation.
Partnering with solar physicists at the National Center for Atmospheric Research (NCAR), the team integrated the metasurface into a custom-built telescope and deployed it at the Dunn Solar Telescope in New Mexico.
Here's how the entire system works: Sunlight first hits a mirror that sits at the top of the Dunn Solar Telescope, which consists of a tower that rises 136 feet above the ground. The light then travels 228 feet underground before being reflected back up to ground level, where it is focused into the team's smaller, custom-built telescope. There, it passes through the metasurface, which is just a tiny fraction of the size of the entire telescope system.
With the metasurface, the system captured simultaneous polarization images of sunspots and measured the magnetic fields embedded within them.
The team compared their data with observations from an instrument aboard NASA's Solar Dynamics Observatory. "We got very, very similar results with our instrument right here on Earth," Rubin said.
Now the team is working toward the next step: space.
Building on the success of their telescope demonstration, the team submitted a proposal to NASA for a mission concept study that will explore how the metasurface could be incorporated into a future space mission dedicated to measuring the Sun's magnetic fields.
If the team is selected, they will have the opportunity to rigorously evaluate whether their technology is suitable for space.
"Watching an idea that started during my PhD grow into something that has passed the proof-of-concept stage and now has the potential to be launched into space — that's a really rewarding experience," Rubin said. "It goes to show what can happen when we invest in promising ideas in academia at an early stage. That's the importance of academic research."
Full study: "Metasurface-Enabled Astronomical Polarimetry"
This work was supported by the Heliophysics Technology and Instrument Development for Science (HTIDeS) program of the Heliophysics Strategic Technology Office (HESTO) of the National Aeronautics and Space Administration (NASA, grant number 80NSSC21K0799).
