The ice cloud begins Euclid's optics

Launched on July 1, 2023, by the European Space Agency (ESA). Euclid Laboratory, a mission that would spend the next six years exploring the composition and evolution of the universe. In particular, Euclid We can observe how the universe has expanded over the past 10 billion years to test theories about dark energy. While fine-tuning and calibrating the telescope's instruments in preparation for the mission's first survey, the mission team noticed that a few layers of water ice formed on its mirror after entering the frost of space.

Although common, this is a problem for a highly sensitive task like Euclid's, which requires significant precision to probe cosmic expansion. After months of research, the Euclid team tested a newly designed process to de-ice the mission's optics. On March 20, ESA announced that the team's Ising approach had worked (so far) and that Euclid's vision had been restored. If the method proved successful, it would have confirmed the mission team's plan EuclidThe optical system works for the rest of its mission.

The problem first became apparent when science operations experts noticed a small but progressive decrease in light measured by the telescope. Visible Instrument (VIS). The instrument is responsible for measuring visible light from distant galaxies to determine how the path of light is affected by gravitational fields. Miska Schirmer, a calibration scientist Euclid's confederation and one of the main designers of the new de-icing scheme, explained in an ESA Press release:

„We compared the starlight coming through the VIS instrument to the recorded brightness of the same stars seen by both Euclid and Euclid. That hand task. Some stars in the universe vary in their luminosity, but most remain constant for millions of years. So, when our instruments detected a faint, gradual decline in photons, we knew it wasn't them—it was us.

Artist's impression of Euclid's laboratory. Credit: ESA

Contamination of water was always expected Euclid, which is why there was a „draining campaign” shortly after launch. It heated the telescope with internal heaters and partially exposed to the sun, sublimating most of the water brought in from Earth. However, there was considerable after absorption in the telescope's multi-layer insulation, which slowly began to build up on the glass surfaces of the VIS instrument. After months of research, laboratory studies and calibrations, the team determined the source and began work on a solution.

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The clear solution was warm Euclid Again by running all its internal heaters for days. However, this risked damaging the spacecraft's mechanical structure, which would alter Euclid's optical alignment. Andreas Rudolph, Euclid flight director at ESA's Mission Control, said:

Most other space missions do not have demanding requirements such as Euclid's 'thermo-optical stability'. to complete Euclid's Scientific Objectives By tracking billions of galaxies across more than a third of the sky and creating a 3D map of the universe, we need to keep the mission incredibly stable — including its temperature. Operating the heaters in the payload module should be done with extreme care.

The team began by heating Euclid's two glasses separately, a low-risk approach because they were located in areas where water vapor would not contaminate other instruments. After analyzing the initial results, the team found that Euclid's view had been restored to its previous accuracy. However, this is only a temporary solution, and a long-term strategy for regular de-icing is still being sought. In the meantime, ESA promises to continue to monitor changes to the telescope and share new findings publicly.

The answer to this problem, however, highlights the international collaboration that made this work possible. Euclid Instrument Operations Scientist Ralph Kohli, who coordinated the response, said:

„A complex task requires a united response from teams across Europe, and I am incredibly grateful for the effort and talent that so many have put into it. It has taken work from teams at ESA ESTEC is the technological heart In the Netherlands, the ESAC Science Operations Center Madrid and the Air Traffic Control Board ESOC Mission Control in Darmstadt – but we couldn't have done it without the critical input we received from the Euclid consortium and the spacecraft's prime contractor, Thales Alenia Space, and its industrial partner, Airbus Space.

Additionally, this problem will lead to important research on how to maintain tasks involving highly sensitive optics. Despite how common this problem is for spacecraft, there is very little research on how ice forms on optical mirrors and affects observations. Therefore, the solution developed by the task force and the organization will lead to new procedures for future work. These could come in handy if Euclid joins NASA Nancy Grace Roman Space Telescope (RST) in March 2027 – another mission to explore the „dark universe”.

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read more: ESA

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