Intricate mission to de-ice a space telescope is go: Euclid's 'eye' is clear

100 minutes of heating to melt a frozen heart... 1.5 million kilometers away from Earth

Boffins at the European Space Agency (ESA) are very pleased with themselves following confirmation that the de-icing process they devised for Euclid's optics has "performed significantly better than hoped."

Launched in 2023, the optics of the Euclid spacecraft have suffered from an accumulation of water ice. While the thickness of the ice was measured in nanometers, scientists could detect its impact through the drop in light observed from distant galaxies.

Due to the finely calibrated instruments onboard, simply heating up the spacecraft to get rid of the ice wasn't an option. Instead, engineers devised an approach in which each mirror would be heated in turn, and observations would be made to see what, if any, impact was made on light coming into the spacecraft.

The team wasn't even sure which of the mirrors was causing the problem but reckoned there was a good chance it was the first mirror they planned to heat.

Showing a flair for the dramatic, Micha Schmidt, Euclid Spacecraft Operations Manager, said, "It was midnight at ESOC mission control when we de-iced the first two mirrors in the procedure."

"We were very careful with our timings, ensuring we had constant contact between the spacecraft and our ground station in Malargüe, Argentina, so we could be ready to react in real time if there were any anomalies."

The team carefully heated the coldest mirror behind the main telescope optics – the prime suspect for the ice build-up – from -147°C to -113°C. "It worked like a charm!" said Mischa Schirmer, calibration scientist for the Euclid Consortium, "Almost immediately, we were receiving 15 percent more light from the Universe. I was certain that we would see a considerable improvement, but not in such a spectacular way."

Schirmer is one of the main designers of the de-icing plan.

The success also means that scientists now know exactly where the ice formed. Although more ice is expected to form over the coming months, the decontamination procedure can be folded into normal operations for the spacecraft.

Reiko Nakajima, VIS instrument scientist, said, "Euclid's 'eye' has been cleared, allowing it to clearly see faint light from distant galaxies, and more of them than would otherwise be possible without this operation." ®

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