Launched on July 1st, 2023, the European Space Agency's (ESA) Euclid Observatory is slated for a six-year mission to explore the Universe's composition evolution and expansion.
During the telescope's instrument calibration phase for its inaugural survey, the mission team encountered an issue with water ice forming on its mirrors upon exposure to the cold vacuum of space, marking the latest in a series of technical challenges for the observatory.
(Photo : VALERY HACHE/AFP via Getty Images)
Euclid Mission Faces Ice Challenge
The problem, though not unusual, presents a significant challenge for the highly sensitive Euclid mission, which demands exceptional precision to explore cosmic expansion. The issue emerged when scientists detected a gradual decrease in the amount of light recorded by Euclid's VISible instrument, tasked with assessing how gravity fields affect visible light from distant galaxies.
Mischa Schirmer, a pivotal member of Euclid's calibration team, explained that the observed decline in starlight was attributed to the telescope itself rather than fluctuations in stellar luminosity.
Despite post-launch efforts to mitigate water contamination through an "outgassing campaign," residual water absorbed in Euclid's insulation persisted, gradually accumulating on the mirror surfaces of the VIS instrument.
After conducting extensive research, laboratory experiments, and calibration exercises, the team identified the source of the problem and devised a solution. Ground-based inspections in November revealed a slight reduction in light captured by Euclid's visible light imager, indicating the presence of a minute layer of ice forming on the telescope's optical surfaces.
Ralf Kohley, Euclid's mission operations scientist, acknowledged the challenge posed by this development but expressed confidence in the team's ability to overcome it and ensure the mission's success.
He emphasized that while preventing water intrusion remains a recurrent challenge for spacecraft, ongoing efforts are underway to address such issues, highlighting the resilience and determination of mission teams in overcoming obstacles encountered during space exploration.
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Euclid Mission's Collaborative Response to Ice Contamination
Kohley emphasizes the coordinated effort of teams across Europe in addressing the issue. The response involved collaboration between ESA's technical heart in the Netherlands, the science operations center in Madrid, and the Flight Control Team in Darmstadt, along with crucial contributions from the Euclid consortium and spacecraft contractors.
The initial solution proposed heating the entire spacecraft, a standard decontamination procedure, but this posed risks of thermal expansion affecting optical alignment. Euclid's demanding requirements on thermo-optical stability necessitated a more meticulous approach, considering even slight temperature changes could impact the mission's precision.
Euclid's Flight Director, Andreas Rudolph, explains the necessity of maintaining thermal stability for the mission's ambitious scientific goals. To minimize thermal changes, the team plans to selectively heat low-risk optical parts, starting with two mirrors independently. They will gradually warm other mirrors, assessing the impact on photon capture as they proceed.
While de-icing should restore Euclid's observational capabilities, the procedure is unprecedented, adding an element of uncertainty. Mischa Schirmer, involved in planning the procedure, expresses excitement and anticipation for the outcome, underscoring the complexity of the task.
Despite being a common issue, there is limited research on how ice formation affects optical mirrors in space. Euclid's investigation could offer insights not only into dark matter but also into addressing longstanding challenges faced by space observation missions, highlighting the significance of its endeavors.
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