Engineers devise a plan to defrost a 'dark universe' telescope a million miles away

The European Space Agency's (ESA) Euclid telescope is gradually losing its vision as layers of water molecules freeze on its mirrors. That's bad news for a mission tasked with observing the dark universe with ultra-sensitive cameras, but the team behind the telescope has come up with a plan to keep Euclid warm in the cold depths of space.

Euclid launches in July 2023 To study the dark universe—the parts of the universe made up of dark energy and dark matter—using the visible-light camera (VIS), near-infrared camera, and spectrometer (NISP). Shortly after launch, the mission's science team began calibrating the telescope's instruments. During this process, team members noticed a gradual decrease in the amount of light measured from stars that were repeatedly observed using VIS.

“Some stars in the universe vary in their luminosity, but the majority are stable for millions of years,” Mischa Shermer, a Euclid calibration scientist, said in his article. statement. “So, when our instruments detected a faint, gradual drop in incoming photons, we knew it wasn't them, it was us.”

After months of investigation, the team now believes that several layers of water molecules were likely frozen onto the mirrors of Euclid's optical instruments. It's a very thin layer of water ice, perhaps a few tens of nanometers thick (about the same width as a DNA strand), but it was enough to affect Euclid's highly sensitive vision.

The telescope likely sucked water from the air while collecting it on Earth, and is now gradually releasing this water from parts of the spacecraft, according to the European Space Agency. In the freezing temperatures of space, the released water molecules will stick to the first surface they land on.

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Euclid is currently located about 1 million miles (1.5 million kilometers) from Earth, where temperatures can drop to about -455 degrees Fahrenheit. Frozen water molecules are a common problem for spacecraft at this distance, but Euclid needed his optical system to be as ice-free as possible to be able to observe the dark universe.

In order to help alleviate the problem of frozen water in the telescope, the team came up with a plan to heat the spacecraft using a decontamination procedure developed before launch. However, turning on the telescope's on-board heaters could affect its mechanical structure, potentially causing expansion that may not allow the spacecraft to return to its original size.

Instead, Mission Control will send commands to heat low-risk optical parts of the spacecraft, starting with two Euclid mirrors that can be heated independently, according to ESA. If this doesn't solve the problem, the team will continue heating other sets of mirrors on Euclid.

“The defrosting process is supposed to restore and preserve Euclid's ability to collect light from these ancient galaxies, but this is the first time we've done this,” VIS instrument scientist Reiko Nakajima said in a statement. “We have pretty good guesses about what surface the ice sticks to, but we won't be sure until we do.”

It's an experimental procedure, but worth the risk because water ice could jeopardize Euclid's ability to scan a third of the sky with unprecedented sensitivity, enough to pick up the smallest galaxies.

Euclid has recovered from a troubling bug before. Shortly after launch, the telescope's precise guidance sensors occasionally lost track of guide stars, a method the telescope uses to pinpoint regions of the universe. the The team on the ground designed a software patch for Euclid, allowing a full recovery.

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