When it comes to space applications such as satellite communication systems, the optics involved have to navigate a wealth of extreme conditions in order to provide reliable performance.
From the fluctuating temperatures and vacuum of space to the humidity and corrosive chemicals of the launch pad, any degradation can impact the efficiency of the communication systems, leading to potential failures, and in space, there is no such thing as a quick fix or replacement.
High-quality coatings that can withstand these challenging conditions are essential, and advanced protected gold and silver coatings can be an ideal solution for providing this level of protection. As an example, a leading player in the space communications sector to benefit from these types of coatings approached Omega Optical, with a need for a highly specialised optical coating solution. The project required a fast-steering mirror with low surface roughness that would be suitable for use in space. These mirrors are used to direct communication signals between satellites and ground stations, so they need to be extremely robust and reliable.
A vertically integrated solution
The customer selected Omega Optical due to its reputation for vertically integrated manufacturing, as Christopher Harrower, Thin-film Process Engineering Manager at Omega Optical, explains: "Our expertise is in being vertically integrated, meaning we can make the optics and coat them at the same time. This ensures a higher quality product as we understand the entire process from start to finish."
The team at Omega Optical proposed using its advanced protected gold coating for this application. This coating consists of alternating layers of dielectric materials on top of a gold substrate, providing enhanced durability and protection while maintaining the reflective properties of gold. Harrower explains: "The material looks just like gold but has protection. We designed it to satisfy abrasion and environmental tests including moderate abrasion, humidity cycling, and temperature cycling in a vacuum chamber."
Protected gold coating offers a number of benefits over more traditional coatings, such as the ability to withstand harsh environmental conditions, including temperature extremes and humidity, while maintaining the reflective qualities of gold, which is critical for an optical communications system such as this. They also provide protection against moderate abrasion, ensuring longevity and reliability during handling and operation.
In addition to protected gold, Omega Optical has also developed a protected silver coating. Says Harrower: “Protected silver has better reflectivity than gold, but people worry about silver degrading. The silver that we designed can even hold up against acetic acid and ammonium disulfide, substances that are commonly found in harsh environments such as oil fields.” This broadens the application potential of the coatings beyond space to other demanding industries.
The challenges and solutions
The project’s main challenge came at the design stage, when it became apparent that the initial prototype would require some adjustments. Harrower explains: "Initially, we tried a typical design, but it didn't perform quite as we wanted it to. We amended the prototype and performed a series of tests to prove the coating's suitability. These included moderate abrasion, humidity cycling, and temperature cycling in a vacuum chamber, which replicated the conditions the mirror would experience from the launch pad to space."
The results
The testing provided positive results, with the protected gold coating demonstrating consistent performance. Harrower shared a slightly surprising outcome: "After all the testing, the reflection actually increased slightly, about half a percent. This was contrary to the usual expectation of degradation." This improvement in reflectivity post-testing further underscored the robustness of the coating and provided the customer with a high degree of confidence in the product.
The collaboration between Omega Optical and the client resulted in a highly reliable optical coating solution that met the stringent requirements of the space environment. The customer benefitted from the vertically integrated approach, which streamlined the production process and ensured a high-quality, durable end solution.
By addressing the specific needs of the specific customer and project and demonstrating a commitment to rigorous testing and quality assurance, Omega Optical reinforced its position as a leader in advanced optical coatings. Harrower says: "We understand the coatings, we understand the manufacturing. This comprehensive knowledge allows us to deliver exceptional results for our customers, every time.”
