Launching and deploying space telescopes is a complicated and costly procedure. Now, researchers have developed a new method to produce and shape large, high-quality mirrors that are much thinner than the primary mirrors previously used for telescopes deployed in space. The resulting mirrors are flexible enough to be rolled up and stored compactly inside a launch vehicle.
“This new approach – which is very different from typical mirror production and polishing procedures – could help solve weight and packaging issues for telescope mirrors, enabling much larger, and thus more sensitive, telescopes to be placed in orbit,” said Sebastian Rabien from Max Planck Institute for Extraterrestrial Physics in Germany.
After much trial and error, researchers successfully created parabolic membrane mirror prototypes up to 30 cm in diameter, which could be scaled up to the sizes needed in space telescopes. These mirrors were created by using chemical vapor deposition to grow membrane mirrors on a rotating liquid inside a vacuum chamber. This allowed them to form a thin parabolic membrane that can be used as the primary mirror of a telescope once coated with a reflecting surface such as aluminum.
For chemical vapor deposition, a precursor material is evaporated and thermally split into monomeric molecules. Those molecules deposit on the surfaces in a vacuum chamber and then combine to form a polymer. This is the first time this process – commonly used to apply coatings such as the ones that make electronics water-resistant – has been used to create parabolic membrane mirrors with the optical qualities necessary for use in telescopes.
Researchers say that using a liquid to form the shape is much more affordable and can be more easily scaled up to large sizes. The thin and lightweight mirror created using this technique can easily be folded or rolled up during the trip to space.
In case of imperfections in the parabolic shape that may occur after the mirror is unpacked, the team developed a thermal method that uses a localized temperature change created with light to enable adaptive shape control that can bring the thin membrane into the desired optical shape.
“Although this work only demonstrated the feasibility of the methods, it lays the groundwork for larger packable mirror systems that are less expensive,” said Rabien. “It could make lightweight mirrors that are 15 or 20 meters in diameter a reality, enabling space-based telescopes that are orders of magnitude more sensitive than ones currently deployed or being planned.”
Researchers next plan to create a meter-sized deposition chamber to better study the surface structure, packaging, and unfolding processes for a large-scale primary mirror.
- Sebastian Rabien. Adaptive Parabolic Membrane Mirrors for Large Deployable Space Telescopes. Applied Optics, 2023; DOI: 10.1364/AO.487262