Euclid space telescope’s vision cleared thanks to deicing

The Euclid Space Telescope is back to full operational capabilities after a deicing procedure removed small amounts of water ice from its mirror. As announced last week, some of the instruments on the European Space Agency (ESA) telescope were impeded by the buildup of ice due to water that got into the telescope from the atmosphere during its construction. This water was gradually released over time as the telescope was in space and froze in place.

Even though the ice was less than a nanometer thick, it was enough to impact the highly sensitive VISible instrument (VIS). Now, a mirror on the telescope has been gently warmed and the ice has melted away.

An artist's impression of ESA’s Euclid mission in space.
An artist’s impression of ESA’s Euclid mission in space. ESA. Acknowledgement: Work performed by ATG under contract for ESA.

“It was an enormous team effort over the last months to plan, execute, and analyze the heating of selected mirrors on board Euclid, resulting in the fantastic result we see now,” said Ralf Kohley, Euclid instrument scientist, in a statement. “The mirrors, and the amount of light coming in through VIS, will continue being monitored, and the results from this first test will continue to be analyzed as we turn this experiment into a core part of flying and operating Euclid.”

The telescope has multiple mirrors on board (three curved and three flat), and the team had planned to heat up each mirror one at a time to gradually melt the ice without affecting other parts of the telescope. But as luck would have it, the first mirror they heated turned out to be the one which was causing the majority of the problems.

“Our primary suspect, the coldest mirror behind the main telescope optics, was heated from -147 degrees Celsius to -113 degrees Celsius. It didn’t need to get hot, because in a vacuum, this temperature is enough to quickly evaporate all the ice. And it worked like a charm!” said Mischa Schirmer, a calibration scientist for the Euclid Consortium who was on the deicing team. “Almost immediately, we were receiving 15% more light from the universe. I was certain that we would see a considerable improvement, but not in such a spectacular way.”

The ice will continue to form on the telescope as more water escapes. However, now that the team knows where the ice is forming, it should be a simple matter to repeat the deicing process as required.

“We expect ice to cloud the VIS instrument’s vision again in the future,” said Reiko Nakajima, VIS instrument scientist. “But it will be simple to repeat this selective decontamination procedure every six to 12 months, and with very little cost to science observations or the rest of the mission.”

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