Hygroscopic and thermal stability of high precision replicated epoxy composite mirrors

Zaldivar, Rafael J.; Kim, Hyun I.; Ferrelli, Geena L.

doi:10.1117/1.oe.56.11.117103

Cited by 5 publications

(4 citation statements)

References 19 publications

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“…8 So far, 3D-printed prototype cells have been proven useful to reduce large scale aberrations (see, Bayo et al in this SPIE volume) Another aspect to consider is the degradation over time due to environmental causes. 9 Systematic assessment of mirror degradation in working conditions is critical to establish the potential use of CFRP mirrors in future astronomical telescopes. We have transported a 20cm replica to Paranal observatory and left it exposed to the elements to evaluate its quality degradation over a long period of time.…”

Section: Resultsmentioning

confidence: 99%

Quality control of the CFRP mirror manufacturing process at NPF

Soto

Lobos

Mardones

et al. 2020

Preprint

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The surface quality of replicated CFRP mirrors is ideally expected to be as good as the mandrel from which they are manufactured. In practice, a number of factors produce surface imperfections in the final mirrors at different scales. To understand where this errors come from, and develop improvements to the manufacturing process accordingly, a wide range of metrology techniques and quality control methods must be adopted. Mechanical and optical instruments are employed to characterise glass mandrels and CFRP replicas at different spatial frequency ranges. Modal analysis is used to identify large scale aberrations, complemented with a spectral analysis at medium and small scales. It is seen that astigmatism is the dominant aberration in the CFRP replicas. On the medium and small scales, we have observed that fiber print-through and surface roughness can be improved significantly by an extra resin layer over the replica's surface, but still some residual irregularities are present.

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Section: Resultsmentioning

confidence: 99%

Quality control of the CFRP mirror manufacturing process at NPF

Soto

Lobos

Mardones

et al. 2020

Preprint

View full text Add to dashboard Cite

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“…Furthermore, the glass master can be used an infinite number of times. More details describing this process as well as the critical factors necessary to achieve a high precision mirror have been described in previous publications [9,10,11,12,13].…”

Section: Introductionmentioning

confidence: 99%

“…and then parametric stability studies were performed as a function of time, humidity, and radiation environments. The driving factors of environmental stability were identified, and precision quality and stability were achieved through processing and formulation modifications [9,10,11,12,13].…”

Section: Introductionmentioning

confidence: 99%

Stress mitigation of replicated composite mirrors via multi-layer replication

Ferrelli,

Kim,

Zaldivar

2023

Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems IV

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Replicated composite optics offer a route to manufacture precision mirrors for satellite applications in a fraction of time and with substantial cost and weight savings over conventional glass mirrors. However, the dimensional stability is a critical barrier to entry for utilizing these mirrors in UV/Vis space applications due to the organic nature of the optical surface and its susceptibly to environmentally-induced distortions that can cause deviations greater than SFE λ/20 (~32nm). Recently, advances in this technology have been achieved at The Aerospace Corporation by using UV cured replicating epoxy resins to produce replicated mirrors with relatively zero residual stress and high hygroscopic stability with RT processing. Elevated thermal stability, though, remains a critical issue as CTE mismatch between the composite and resin lead to residual stress formation which immediately degrades the optical quality and then causes further optical drift over time as stress relaxation occurs. In this paper, we demonstrate improved thermal stability of replicated mirrors by utilizing multiple replication layers where buried compliant layers accumulate residual stress and the top layer is an optimized high modulus resin that achieves a high-quality replication. As a result, thermal stresses incurred by elevated temperatures were reduced by more than 60% when measured via laser interferometry. Additionally, due to faster stress relaxation rates of the compliant layers, the CTE mismatch stress was removed in a matter of days versus years of a conventional single layer replication. This stack-up provides a route to mitigate stress and enhance replication stability.

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“…5 Recently, the effects of cure state controlled by thermal processing conditioning on the stability of these mirrors have been investigated. 6 Increasing the cure state of the RL reduces the moisture absorption characteristics as well as increases the thermal stability of the material. However, in bonded structures, performing higher temperature processing to achieve full cure has been shown to also increase interfacial residual stresses, which ultimately negatively affects the flatness of these mirrors.…”

Section: Introductionmentioning

confidence: 99%

Effect of gamma radiation on the stability of UV replicated composite mirrors

2018

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Composite replicated mirrors are gaining increasing attention for space-based applications due to their lower density, tailorable mechanical properties, and rapid manufacturing times over state-of-the-art glass mirrors. Ultraviolet (UV)-cured mirrors provide a route by which high-quality mirrors can be manufactured at relatively low processing temperatures that minimize residual stresses. The successful utilization of these mirrors requires nanometer scale dimensional stability after both thermal cycling and hygrothermal exposure. We investigate the effect of gamma irradiation as a process to improve the stability of UV replicated mirrors. Gamma radiation exposure was shown to increase the cure state of these mirrors as evidenced by an increase in modulus, glass transition temperature, and the thermal degradation behavior with dosage. Gas chromatography-mass spectroscopy also showed evidence of consumption of the primary monomers and initiation of the photosensitive agent with gamma exposure. The gamma-exposed mirrors exhibited significant improvement in stability even after multiple thermal cycling in comparison with nonirradiated composite mirrors. Though improvements in the cure state contribute to the overall stability, the radiation dosage was also shown to reduce the film stress of the mirror by over 80% as evidenced using Stoney replicated specimens. This reduction in residual stress is encouraging considering the utilization of these structures for space applications. This paper shows that replicated composite mirrors are a viable alternative to conventional optical structures. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Hygroscopic and thermal stability of high precision replicated epoxy composite mirrors

Cited by 5 publications

References 19 publications

Quality control of the CFRP mirror manufacturing process at NPF

Quality control of the CFRP mirror manufacturing process at NPF

Stress mitigation of replicated composite mirrors via multi-layer replication

Effect of gamma radiation on the stability of UV replicated composite mirrors

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