Euclid’s Vision Restored: Thanks to a newly devised de-icing procedure

Euclid, the spacecraft on a mission to uncover the secrets of dark matter and dark energy, has had its sight restored thanks to a newly devised de-icing procedure. The process, which involved heating individual mirrors in the spacecraft’s complex optical system, has performed significantly better than anticipated.

Euclid’s mission is to investigate the mysteries of dark matter and dark energy, which are thought to constitute 95% of the universe yet remain unobservable. However, a few nanometers of ice—roughly the width of a large molecule—have been accumulating on the mission’s optics each month, causing a decrease in the light received from distant galaxies.

Teams from the European Space Agency (ESA) across Europe, including ESTEC in the Netherlands, ESOC mission control in Germany, and ESAC science operations center in Spain, collaborated with the Euclid Consortium and industrial partners Thales Alenia Space and Airbus Space to devise a potential solution.

Ralf Kohley, Euclid instrument scientist and head of the anomaly review board, explains, “It was an enormous team effort over the last months to plan, execute and analyze the heating of selected mirrors onboard Euclid, resulting in the fantastic result we see now.”

The teams planned to heat up mirrors in Euclid’s optics one by one, then group by group, and test the effect on the incoming light. They suspected that the first mirror they heated was causing most of the problems.

During ESA Euclid’s first months in space, some water molecules absorbed from the air during assembly on Earth were gradually released. Cold surfaces like the mirrors in Euclid’s instruments attracted these molecules, where they formed a very thin layer of ice. This thin layer began to hinder the satellite’s vision. As a result, operation teams on the ground initiated a de-icing campaign. They sent commands to the satellite to heat the instrument mirrors individually and remove the layer of ice.

Mischa Schirmer, calibration scientist for the Euclid Consortium and one of the main designers of the de-icing plan, explains the results. “Our primary suspect, the coldest mirror behind the main telescope optics, was heated from –147°C to –113°C. 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! 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.”

With Euclid’s vision cleared at the very first stage of the procedure, scientists and engineers could determine where precisely the ice had formed, and where it is likely to form again. “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,” explains Reiko Nakajima, VIS instrument scientist.

“We expect ice to cloud the VIS instrument’s vision again in the future. 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.”

After months of research from scientists and engineers across Europe, late nights at ESA’s ESOC mission control, and 100 minutes of targeted warmth, Euclid’s vision has been protected. These studies, and the incredible result, will also help future satellites likely to face the same, common icy problem.