Numerical study of water ice and molecular contamination build up during JWST deployment

Brieda, Lubos; Laugharn, Marc; Woronowicz, Michael S.; Henderson-Nelson, Kelly A.; May, Chris P.; Wooldridge, Eve M.

doi:10.1117/12.2635238

Cited by 5 publications

(5 citation statements)

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“…However, Euclid is only 10-20 K below the point of 140-150 K where sublimation and diffusion accelerate rapidly in an exponential fashion. Forecasts of the absolute amount of contamination are therefore hard; they also require full 3D modelling of the emitting and contaminating surfaces, as was done for example for JWST in Brieda et al (2022), which is well beyond the scope of this paper.…”

Section: Discussionmentioning

confidence: 99%

“…Brieda & Laugharn 2020;Zitouni & von Germersheim 2020). They were applied for example to compute the contamination of the JWST during its initial 180 days in flight, accounting for JWST's complex unfolding sequence (Brieda et al 2022). In this section we aim much lower, developing an understanding of the dynamics of molecular contamination to inform our calibration strategy.…”

Section: Contamination and Decontamination Modellingmentioning

confidence: 99%

“…For example, according to our model only 6% of the water molecules evaporating in the telescope cavity escape on direct paths, the rest will undergo numerous redeposition and sublimation cycles before eventually escaping. Furthermore, the high decontamination temperatures result in a decreased sticking coefficient (Kossacki et al 1999;Batista et al 2005;Gibson et al 2011;Brieda et al 2022) and a massively increased evaporation rate. Consequently, the mean free path length might become comparable to -or even smaller than -the size of the spacecraft, in which case pressure effects would have to be taken into account for more accurate evacuation-time estimates.…”

Section: Decontamination Proceduresmentioning

confidence: 99%

“…Accurate contamination forecasts are therefore hard and require considerable effort well beyond the scope of this paper (e.g. Brieda et al 2022, for the James Webb Space Telescope; JWST).…”

Section: Introductionmentioning

confidence: 99%

“…In principle, a code that computes the radiative heat exchange between surfaces can also compute contamination, by replacing the photon flux with the sublimation flux (as e.g. inBrieda et al 2022). A142, page 16 of 34Euclid Collaboration: A&A proofs, manuscript no.…”

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confidence: 99%

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Euclid preparation

Schirmer¹,

al.²

2023

A&A

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Material outgassing in a vacuum leads to molecular contamination, a well-known problem in spaceflight. Water is the most common contaminant in cryogenic spacecraft, altering numerous properties of optical systems. Too much ice means that Euclid’s calibration requirements cannot be met anymore. Euclid must then be thermally decontaminated, which is a month-long risky operation. We need to understand how ice affects our data to build adequate calibration and survey plans. A comprehensive analysis in the context of an astrophysical space survey has not been done before. In this paper we look at other spacecraft with well-documented outgassing records. We then review the formation of thin ice films, and find that for Euclid a mix of amorphous and crystalline ices is expected. Their surface topography – and thus optical properties – depend on the competing energetic needs of the substrate-water and the water-water interfaces, and they are hard to predict with current theories. We illustrate that with scanning-tunnelling and atomic-force microscope images of thin ice films. Sophisticated tools exist to compute contamination rates, and we must understand their underlying physical principles and uncertainties. We find considerable knowledge errors on the diffusion and sublimation coefficients, limiting the accuracy of outgassing estimates. We developed a water transport model to compute contamination rates in Euclid, and find agreement with industry estimates within the uncertainties. Tests of the Euclid flight hardware in space simulators did not pick up significant contamination signals, but they were also not geared towards this purpose; our in-flight calibration observations will be much more sensitive. To derive a calibration and decontamination strategy, we need to understand the link between the amount of ice in the optics and its effect on the data. There is little research about this, possibly because other spacecraft can decontaminate more easily, quenching the need for a deeper understanding. In our second paper, we quantify the impact of iced optics on Euclid’s data.

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Section: Discussionmentioning

confidence: 99%

Section: Contamination and Decontamination Modellingmentioning

confidence: 99%

Section: Decontamination Proceduresmentioning

confidence: 99%

“…Accurate contamination forecasts are therefore hard and require considerable effort well beyond the scope of this paper (e.g. Brieda et al 2022, for the James Webb Space Telescope; JWST).…”

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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