Why do sun-observing spacecraft get cloudy vision?

NASA’s Solar Dynamics Observatory captured this image of a solar flare on January 9, 2023.

Earth’s host star can be quite temperamental, forcing astronomers to launch satellites and probes on missions to keep a close eye on the Sun’s massive outburst. But instruments pointed at the Sun tend to get cloudy views as a result of a mysterious layer that has puzzled scientists for years.

Instruments on board NASAs Solar Dynamics Observatory (SDO), which has been observing the Sun since 2010, deteriorated by 40% within five years of launch. Today, a group of scientists may have finally identified the culprit behind the spacecraft’s blurry views: water.

“Degradation of sun-seeing satellites happened before SDO had a problem … but the cause was unclear,” Robert Berg, a researcher at the US National Institute of Standards and Technology (NIST), and one of the authors behind a new examination published in Solar Physics, told Gizmodo in an email. Previous studies “mentioned oxidation as one of several possible causes, but water was not suggested as an oxidant,” he added.

To crack the code, the researchers behind the new study used a space-sized particle accelerator to replicate the conditions imposed by space weather. They found that oxygen atoms from water molecules combined with aluminum from a spacecraft’s instruments to produce a hazy layer of aluminum oxide that blocks incoming rays from the Sun.

In the new research published Thursday, researchers from NIST and the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics detailed these important new findings. “We weren’t able to expose to years of radiation, but together with a model of oxide growth, we show quite convincingly that water vapor with ultraviolet light can cause the observed losses,” Charles Tarrio, a physicist from NIST and lead author. of the new study, explained in an email.

Spacecraft observing the Sun use aluminum filters — each smaller than a postage stamp and thinner than a human hair — to collect extreme ultraviolet light, a wavelength of light emitted by the Sun that is too short for the human eye to see. Although EUV makes up a small fraction of the total amount of light from the Sun, it plays a crucial role in notifying scientists when the star is about to flare.

The sun emits occasional bursts of energy known as coronal mass ejectionsgiant explosions of charged particles that extend away from the Sun like hot whips. These events can affect us here on Earth, resulting in geomagnetic storms that cause disruptions to power grids and navigation systems.

By monitoring the Sun with solar probes and satellites, scientists can get a better handle on its flareup schedule. Unfortunately, spacecraft facing the Sun tend to lose their ability to capture EUV light within a few years of commissioning. A spacecraft’s filter typically transmits about 50% of the EUV light through its detector at the start of its mission, dropping to 25% within a year and 10% within five years, according to NIST. The researchers based this on their study of the SDO, but say other spacecraft suffered the same fate.

Other examples of spacecraft degradation include the LYRA instrument on board the European PROBA2 satellite, the SOLSPEC instrument on board the SOLAR payload to the International Space Station, which was used to measure solar energy, and the Solar Diameter Imager and Surface Mapper telescope on board on the PICARD spacecraft, according to Berg.

For years, scientists believed that the filters developed a layer of carbon, a result of contamination on the spacecraft. But the same group of scientists is behind the new research disproved this theory in 2021 before immediately going back to the drawing board. “The other thing that pointed toward oxidation is that the spacecraft’s instruments have been built to be cleaner and cleaner over the last few decades with the goal of eliminating sources of organic molecules that lead to carbon deposition,” Tarrio said. “But many instruments still show significant decay. This points away from carbon growth.”

Using a particle accelerator to generate EUV light, the researchers deflected this light to the spacecraft’s filters using mirrors while also exposing them to water vapor. After 20 days, the filters developed a layer of aluminum oxide. The layer was not thick enough to hinder the ability of the filters to capture EUV light, but it would likely have gotten even thicker over a longer period of time. The researchers also created theoretical models that matched what happened to the spacecraft in real life.

So how did the oxide layer form in the first place? The researchers believe that water from the spacecraft’s thermal blanket, which is used to control the spacecraft’s temperature, interacts with the filter’s aluminum to produce the oxidized layer that then blocks light from traveling through the detector.

The new research could better inform the design of future solar-observing spacecraft to prevent their rapid degradation. One thing the researchers suggested was adding a layer of carbon to stop the movement of aluminum ions, as well as pipes that block incoming water vapor.

More: Sun-orbiting spacecraft captures fascinating images of a coronal mass ejection

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