Recently the new European space telescope Euclid has started suffering a common issue for spacecraft: the formation of thin layers of water ice. The European Space Agency (ESA) has announced that the Euclid teams are beginning a series of planned operations to de-ice the sensitive optical instruments of the telescope.
Launched in July 2023, the pioneering ESA mission is designed to explore the composition and evolution of the dark Universe. The telescope, now orbiting the L2 Lagrange point, will study the role of gravity and the nature of dark energy and dark matter. Euclid is observing billions of galaxies across more than a third of the sky to create a large-scale map of the Universe’s structure.
Back in November, ESA released the first stunning images captured by the spacecraft.
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A common annoying issue
In recent months during the calibration of the instruments, operations experts noticed a reduction of light measured during star observation with the Visible Instrument (VIS), one of the two main optics of Euclid.
As it happens for other spacecraft, during assembly operations on Earth a small amount of water present in the atmosphere remained stuck inside the telescope. Once exposed to the freezing temperatures of space, water molecules adhered and froze onto the surfaces of the instruments. Despite being as thin as a strand of DNA, the ice layer creates significant issues when it interferes with highly sensitive optics.
Shortly after liftoff Euclid was partially exposed to the Sun and warmed up with on-board heaters, thus sublimating most of the water molecules. However, a considerable fraction has survived, by being absorbed in the multi-layer insulation, and is now being slowly released in the vacuum of space.
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The new plan to restore Euclid’s vision
To mitigate the effect of ice and prevent future issues, Euclid’s teams have come up with a new progressive plan.
By activating all the spacecraft’s heaters for several days, it could be possible to raise the internal temperature from -140 to -3 degrees Celsius, thus getting rid of all the ice present. However, this significant temperature swing would have a notable impact on the mechanical structures, potentially causing irreparable expansions, thereby compromising the optical alignment of Euclid.
In order to observe billions of galaxies over the six years of the mission, scientists require the highest possible sensitivity from Euclid. Furthermore, water accumulations could recur, necessitating a repetition of the thawing maneuver.
To minimize risks, the team will proceed with a gradual heating of only some instruments, starting with the two mirrors that can be heated independently without the released water affecting other components. In this way, they will progressively understand better where the ice accumulations are present, intervening only where strictly necessary to restore Euclid’s observational capabilities. If the light loss persists, other groups of mirrors will be gradually heated.
“Once we have isolated the affected area, the hope is that we can then simply warm up this isolated part of the spacecraft in the future as needed. What we are doing is very complex and fine-grained, so that we can save valuable time in the future.”
— Mischa Schirmer, calibration scientist for the Euclid consortium
If successful, the operations will confirm the mission teams’ strategy to maintain the optical system free from ice throughout its orbital lifespan, considering possible other issues of this kind.
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