Large, high-quality mirrors that are significantly thinner than the primary mirrors previously used for telescopes placed in space can now be produced and shaped in innovative ways by scientists. The resulting mirrors may be rolled up and placed neatly within a launch vehicle since they are sufficiently flexible.
Sebastian Rabien from Germany’s Max Planck Institute for Extraterrestrial Physics remarked, “Launching and deploying space telescopes is a hard and expensive task.” “This innovative approach, which is quite different from conventional mirror fabrication and polishing procedures, could help resolve weight and packing difficulties for telescope mirrors, allowing for the orbital placement of much larger and consequently more sensitive observatories.”
Rabien reports on the successful manufacture of parabolic membrane mirror prototypes up to 30 cm in diameter in the Optica Publishing Group journal Applied Optics. These mirrors were made by growing membrane mirrors atop a rotating liquid inside a vacuum chamber using chemical vapour deposition. These mirrors may be scaled up to the sizes required in space telescopes. Also, he created a technique that employs heat to adaptively fix any flaws. It might appear once the mirror is unfolded.
Even while this work just proved that the approaches were feasible, it paves the way for more substantial and reasonably priced packable mirror systems, according to Rabien. “It could enable space-based telescopes that are orders of magnitude more sensitive than ones already deployed or being proposed. Permitting lightweight mirrors that are 15 or 20 metres in diameter.”
Using an outdated procedure in a novel way
The COVID-19 epidemic, according to Rabien, provided him some extra time to reflect. And test out novel ideas, which is how the new approach came to be. He explained, “In a long series of tests, we evaluated different liquids to determine their suitability for the process. Also investigated how the homogenous polymer development may be carried out. And worked to optimise the process.
A precursor substance is evaporated and thermally divided into monomeric molecules for chemical vapour deposition. These molecules unite to create a polymer after depositing on the surfaces in a vacuum chamber.
The scientists then added a revolving container containing a little amount of liquid to the interior of the vacuum chamber to give the precise shape required for a telescope mirror. On top of the liquid’s flawless parabolic shape, the polymer can develop to form the mirror foundation. After the polymer is sufficiently thick, evaporation is used to apply a reflective metal layer to the top, and the liquid is then removed.
Altering a folding mirror
This process results in a small, light mirror that may be readily folded or rolled up for space travel. But, after unpacking, it would be quite difficult to restore it to its ideal parabolic shape. The scientists established a thermal technique to reshape the membrane mirror, which leverages a localised temperature change induced by light to provide adaptive shape management and enable the thin membrane to assume the required optical shape.
By fabricating 30-cm diameter membrane mirrors in a vacuum deposition chamber, the researchers tested their strategy. They were able to create premium mirrors with a surface form ideal for telescopes after considerable trial and error. Using a series of radiators and illumination from a digital light projector. They also demonstrated the effectiveness of their thermal radiative adaptive shaping technique.
In order to learn how well the end surface can be moulded. And how much of an initial distortion can be tolerated? The scientists will then use more advanced adaptive control. In order to better understand the surface structure, packaging, and unfolding processes for a large-scale primary mirror. They also intend to build a deposition chamber with a diameter of one metre.
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