Membrane mirrors for large space-based telescopes?

Researches create lightweight flexible mirrors that can be rolled up during launch and reshaped precisely after deployment.

Mirrors are a significant part of telescopes. When it comes to space telescopes, which have complicated procedures for launching and deploying, the primary mirrors add considerable heft, contributing to packaging difficulties.

Researchers have now come up with a novel way of producing and shaping large, high-quality mirrors. These mirrors are not only thinner than the primary mirrors usually employed in space-based telescopes, but are also flexible enough to be rolled up and stored inside a launch vehicle.

Parabolic membrane mirror

The successful fabrication of such parabolic membrane mirror prototypes up to 30 cm in diameter have been reported in the Optica Publishing Group journal Applied Optics in April. Researchers not only believe that these mirrors could be scaled up to the sizes required in future space telescopes, but have also developed a heat-based method to correct imperfections that will occur during the unfolding process.

Using a chemical vapour deposition process that is commonly used to apply coatings (like the ones that make electronics water-resistant), a parabolic membrane mirror was created for the first time. The mirror was built with the optical qualities required for use in telescopes. A rotating container with a small amount of liquid was added to the inside of a vacuum chamber in order to create the exact shape necessary for a telescope mirror. The liquid forms a perfect parabolic shape onto which a polymer can grow during chemical vapour deposition, forming the mirror base. A reflective metal layer is applied to the top when the polymer is thick enough, and the liquid is then washed away.

Thermal technique

The researchers tested their technique by building a 30-cm-diameter membrane mirror in a vacuum deposition chamber. While the thin and lightweight mirror thus constructed can be folded during the trip to space, it would be nearly impossible to get it into perfect parabolic shape after unpacking. The researchers were able to show that their thermal radiative adaptive shaping method worked well to reshape the membrane mirror.

Future research is aimed at applying more sophisticated adaptive control to find out not only how well the final surface can be shaped, but also how much distortion can be tolerated initially. Additionally, there are also plans to create a metre-sized deposition chamber that would enable studying the surface structure along with packaging unfolding processes for a large-scale primary mirror.

Picture Credit : Google 

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