New Membrane Mirrors for Large Space-Based Telescopes

Max Planck Institute for Extraterrestrial Physics, Garching bei München,Germany

Membrane mirrors made using the new technique are flexible enough to be rolled up. This could be helpful for storing the mirrors inside of a launch vehicle. (Image: Sebastian Rabien, MPE)

Researchers at the Max Planck Institute for Extraterrestrial Physics have developed a new way to produce and shape large, high-quality mirrors that are much thinner than conventional space-telescope mirrors. The final product is even flexible enough to be rolled up and stored compactly inside a launch vehicle.

“Launching and deploying space telescopes is a complicated and costly procedure,” said Sebastian Rabien, MPE. “This new approach — which is very different from typical mirror production and polishing procedures — could help solve weight and packaging issues for telescope mirrors.”

Developed during the COVID-19 pandemic, the new technique works thusly: Mirrors are grown by chemical vapor deposition on a rotating liquid inside a vacuum chamber. While this work demonstrated the feasibility of the method, with the successful fabrication of parabolic membrane mirror prototypes up to 30 cm in diameter, “it lays the groundwork for larger packable mirror systems that are less expensive than usual,” added Rabien.

For the deposition, monomeric molecules are created that deposit on the surfaces in a vacuum chamber and combine to form a polymer. Though it’s commonly used to apply coatings, this is the first time that the process has been used to create parabolic membrane mirrors with optical, telescope-grade qualities. The crucial step is a rotating container filled with a small amount of liquid, which forms a perfect parabolic shape: a “mold” that is affordable and can easily be scaled up to large sizes. When the polymer is thick enough, a reflective metal layer is applied to the top and the liquid is washed away.

The resulting mirror can easily be folded or rolled up for the trip to space. However, it would be nearly impossible to get it back to the perfect parabolic shape after unpacking. So, the researchers developed an adaptive shape control based on a localized temperature change created with spatially variable light projection.

The next step is to apply more sophisticated adaptive control to study how well the final surface can be shaped and how much of an initial distortion can be tolerated. They also plan to create a meter-sized deposition chamber to better study the surface structure and packaging and unfolding processes for a large-scale primary mirror.

For more information, contact Sebastian Rabien at This email address is being protected from spambots. You need JavaScript enabled to view it.; +49 89-30000-3277.