FEATURE OPTICAL COATINGS
Space coat
The development of optical coatings for use beyond Earth is driving innovation, Andrew Williams finds
A
s the use of space-based instruments such as telescopes, satellites and probes increases, a number of companies and
research organisations are busy developing innovative coatings for onboard optical components. So, what are some of the most recent advances in the development and application of optical coatings for space- based devices? And, could advances made in the space sector eventually trickle down to other optical coating markets? Unlike the materials used on Earth, optical coatings for space-based applications need to be extremely stable and durable – largely because maintenance and exchange as a result of wear and tear is not easily possible. These requirements mean that space-based optics must be of the highest quality, and often be tailor- made for specific applications. According to Helmut Kessler, managing director at Manx Precision Optics (MPO), this relentless focus on quality often results in space- related products that are at the forefront of the currently feasible specifications. ‘Space-based applications help to push
forward the boundaries of technology, and therefore make a company more innovative,’ he said. One such company is Colorado-based outfit N-Science, which has created the
24 Electro Optics May 2017
innovative Deep Space Black (DSB) material used to coat a wide variety of instruments, including the Viscam device on the NASA Raven craft. As Dan Scheld, president at N-Science, explained, DSB is essentially the product of a ‘wet chemistry process,’ which results in a highly dentritic ‘space qualified’ surface typical of many optical materials used in space. In tandem with overall optical performance, Scheld believes surface properties such as the ability to provide uniformity over large areas, as well as the ability to deliver this uniformity on complex geometries including internal features, are also ‘critical’ features of space- based coatings. Another important consideration is the overall mechanical stability. ‘The surface must be robust enough
to withstand launch operations and in- orbit operations. In LEO [low Earth orbit] environments the surfaces are exposed to electron radiation and atomic oxygen,’ said Scheld. Alexander Muhr, senior applications engineer at California, US-based Element
Six, agreed that the durability of optics for space-based devices is ‘absolutely critical’ and noted that it can be extremely difficult and expensive – sometimes impossible – to replace components that fail in space. In an effort to face up to these
“Space-based applications help to push forward the boundaries of technology and therefore make a company more innovative”
challenges, the company has developed a novel optical polycrystalline diamond material that Muhr says is ‘incredibly robust mechanically, thermally, and in terms of laser damage threshold’. ‘Optics made from this
material will be able to last longer in the field and survive harsh environments that would cause other solutions to fail. This means less costly repairs and possibly new applications in harsh environments,’ he said. ‘Diamond also has the broadest electro-magnetic
transmission spectrum, from UV to microwave, of any window material. This makes diamond great for spectroscopic and hyperspectral imaging applications,’ he added.
Shelf life Another company very active in this field is UK firm Artemis Optical, which
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