SBIR-STTR Award

The need for very large aperture (>10m) mirrors for space applications is pushing current technology to its limits in providing a material and design that meet required launch restraints. The concept of using a membrane mirror would allow a light-weight and deployable primary to become a viable option in multi-meter sized aperture imaging and High Energy Laser systems. To maintain the required shape yet retain the pliability of a membrane, methods of applying thin-film optical coatings to counteract residual stress in the membrane to maintain a prescribed curvature will be developed using evaporative deposition. This includes metrology techniques to measure the thickness and stress in such coatings, which will be prescribed by finite element analysis. The end result is a coating process to maintain a curvature in a membrane mirror with traceability to large-scale production.

Benefits:
The successful demonstration of the proposed concept of using stress-coatings to maintain a curvature in a membrane mirror will provide an immediate impact on many current and future USAF, NASA, and other DoD space-based large aperture imaging or High Energy Laser (HEL)applications. Many require multi-meter apertures capable of being deployed after launch. The development of this technology would enable such designs to become a reality and also open the door for commercial parties that are interested in the use of very large aperture mirrors. This would not be limited to HEL or imaging applications but also radio frequency and even microwave transmission.

Advanced manufacturing methods have been developed that enable the production of lightweight membrane mirrors from space rated polymer materials (CP1-DE). These materials can be produced with excellent optical quality surface characteristics, ideal for front surface mirrors, and cast into aspherical shapes for imaging applications. These precision cast membrane mirrors have the potential for reducing the aerial density, packaging volume, and cost of space-based optics by an order of magnitude. The optical surface quality of these mirrors is excellent, however, a method is needed to establish and maintain the global figure of these mirrors once deployed. The feasibility of using the intrinsic stress of energetically deposited optical coatings to control the global figure of the membrane mirrors has been demonstrated in previous research on small scale mirrors. This program will demonstrate that method can be applied to manufacture net shape membrane mirrors of large apertures. Recently developed large scale casting and coating facilities will be used to demonstrate the technology for a 1.5 meter net shape membrane mirror. At this scale, membrane mirror technology begins to be beneficial to a large class of applications. Additionally this work will show scalability of the process to much larger sizes.

Keywords:
Lightweight, Mirrors, Membranes, Stress Coatings, Deployable Optics