Effective coatings for space technologies are essential for the proper function of a satellite or other spacecraft. This article is an introduction to coatings manufacturer Acktar Ltd, a participant in the satsearch membership program, and was produced in collaboration with the company.
Coatings are an important part of a satellite or space system. They help to minimize the interfering effects of light incident upon the system, or that is created or reflected by equipment on-board.
Coatings also help to improve the efficiency and accuracy of optical payloads and sensors, which typically play a crucial role in a mission’s primary objectives.
Acktar Ltd. is located in Kiryat-Gat, Israel, with subsidiaries in Germany (ACM Coatings GmbH), Japan (Acktar Japan) and Korea. The company was founded in 1993 and has since grown into a multidisciplinary coatings specialist.
Today, Acktar specializes in the manufacture of light-absorbing ‘ultra-black’ coatings for space and other industries, based on vacuum deposition technologies.
Ultra-black coatings have unique optical and surface properties that enable high amounts of light absorption. This can reduce interference for optical applications, improve radiation-shielding, absorb laser power, and provide other benefits for sensitive instruments, as discussed further below.
The company also creates black-coated aluminum and polymer foils in the form of die-cuts, sheets, and rolls, well plates, and microarray slides.
Acktar’s deep black foils and coatings can be applied to many different surfaces (including metal, glass, silicon, ceramic, plastic).
Such products have applicability in a variety of industries, such as aerospace, measurement technology, medical diagnostics, and industrial image processing. And they also have a number of important uses in space.
The importance of effective coatings for space
Space-borne instruments feature several components that can be affected by incident or reflected electromagnetic (EM) radiation. The most heavily impacted classes of equipment are opto-mechanical parts and sub-systems; payloads and sensors that rely on electromagnetic energy to perform their primary function.
A sun sensor, for example, needs to be able to differentiate between incident solar radiation and reflected light from a satellite’s body. Similarly, an Earth Observation (EO) camera includes sections of the optical array coated to limit interference caused by solar radiation, internal reflections, and other stray beams of light.
The main application areas for space-borne coatings are:
- Straylight suppression,
- Laser power absorption,
- Improving signal-to-noise ratio (SNR), and
- High-emissivity coatings.
Suppressing stray light and optimizing optical performance are vital in space applications, to ensure the accuracy and efficiency of both sensing equipment and payloads. This is also known as straylight optimization – where a system is altered to minimize disruption as required.
Virtually every satellite has photonic equipment that must be correctly oriented and shielded for maximum effect. In addition, the growth of optical inter-satellite links and ground-space optical communication has placed more emphasis on straylight management and effective power absorption in these domains.
Of course, in space replacements and maintenance are (currently) virtually impossible. Therefore it is vital that coatings are durable and consistent throughout mission lifetimes. Optimizing coatings for such criteria needs dedicated experience in space.
The space heritage of Acktar’s coatings
Rising in Technology Readiness Level (TRL) and reaching full flight heritage status at TRL 9 is very important for suppliers, in order to demonstrate that their hardware has been tested and proven in space. But it is also important for treatments and materials, such as coatings, to have been fully validated in space.
Acktar has operated in the space industry for many years and has built up experience on a wide range of missions to develop this heritage. Below you can see some examples of space missions that have utilized Acktar’s coatings to improve equipment performance.
Coating hardware for the James Webb Space Telescope
The space-based James Webb Space Telescope (JWST) is the successor to the highly successful Hubble space telescope. It has been in development by NASA, the European Space Agency (ESA), and the Canadian Space Agency since 1996 and is due for launch in 2021.
EADS-Astrium was contracted in the JWST project as prime contractor for an instrument called the Near Infrared Spectrograph (NIRSpec) or ‘Super-Eye.’ This is a €100 million, 200 kg spectrograph that has been built to detect the faintest radiation signals from the most distant galaxies, and also to measure spectra of up to 100 objects simultaneously.
Acktar was chosen in 2007, following an extensive testing and selection process, as the supplier of choice for the design, manufacture, and testing of advanced black infrared (IR) absorbing coatings for the NIRSpec instrument.
Acktar coated and tested an array of parts in its facilities before shipping them to EADS-Astrium, and a range of other European sub-contractors, for integration into the system.
Straylight management in the CHEOPS Mission
The Characterising ExOPlanet Satellite (CHEOPS) mission is ESA’s first initiative to observe exoplanets orbiting nearby bright stars. It uses the transmit method of observation; precision analysis of a star’s dimming while the planet passes between it and the observer.
Acktar’s Fractal Black™ coating was applied to several of the inner surfaces of the optical system, including deflector plates that protect the small telescope against stray light.
The system included various sharp edges that posed a challenge for effective coatings, and also had to be resistant to rapid temperature changes.
Optical qualification and adhesion tests were performed on the edges in order to confirm the adhesion of the coating in thermal environments, and the deflector plate passed all required qualification steps, at both the sub-system and instrument level.
Building for the future
Other missions that the company has taken part in have involved equipment travelling near the Sun or to Mercury, where temperature stability is vital.
Acktar’s FractalBlack™ and MagicBlack™ have also been used in the UV-VIS-NIR (UVN) instrument on Sentinel-4 (part of ESA’s Copernicus program), which observes atmospheric pollutants from outer space.
The challenges of large-scale deep space missions have led to Acktar developing new approaches to managing, applying, and testing coatings optimized for space.
Such lessons bring benefits to NewSpace customers, who may not always have deep experience of engineering for space.
Coatings for NewSpace systems
Building on its heritage and experience in deep space, exploratory, and large-scale missions, Acktar has increasingly focussed on the benefits that its coating and foil technologies can bring to the NewSpace sector.
For teams and missions relying more on commercial-off-the-shelf (COTS) components for small satellites designed for Low Earth Orbit (LEO), effective coatings can bring benefits in terms of efficiency and performance. While radiation protection requirements are lower than in deep space, reducing signal interference is still vital.
Mass, power, and physical volume budgets are limited in NewSpace systems, so straylight suppressing coatings that ensure sensors work better at lower energies, or that focus incident optical signals into the most relevant areas, can significantly impact mission success.
Agility and efficiency are also very important in the NewSpace industry. In many cases, Acktar can build the opto-mechanical part required for a particular sensing system or payload, and deliver it to the customer for integration into the satellite. This can help NewSpace teams better manage their supply chain and focus more resources on the primary innovation in a system.
In addition, Acktar also offers coating as a service. Opto-mechanical parts and other relevant sub-systems may be shipped to the company’s facilities in order for the relevant coating to be applied.
A large amount of qualification work has been undertaken for every coating, foil, and other material that Acktar applies to space-based assets, for both optical and thermal control. Quality control approaches can differ by region or country, but Acktar has invested heavily in meeting all relevant validation requirements.
Providing such services has required Acktar to develop new approaches to scaling supply, in order to meet high volume demands.
An overview of Acktar’s coating portfolio
Acktar™️ produces black-coated optomechanical components and mounts for optical applications that are suitable for reducing noise, unwanted reflections, and increasing the efficiency of the optical system.
A polyimide film designed to deliver low reflectance and high emissivity across the spectrum from UV thru VIS to SWIR, for straylight suppression. The film is a few microns thick, with no particulation, and is vacuum and thermal—vacuum cycling qualified.
A diffusive, abrasion-resistant, polyimide film for straylight suppression. MaxiBlack is currently the blackest polymer that Acktar offers and it has the lowest reflectance across the spectrum from the UV to SWIR. MaxiBlack is manufactured by using roll to roll thin film technology.
An ultra-diffusive, wideband (EUV-FIR), absorbing aluminium foil with 99.9% specular absorptance. The high adhesion, space-qualified material has a long-term operational temperature range of -250°C to +350°C and features low outgassing, with a CVCM < 0.001.
A semi-specular, wideband, absorbing aluminium foil for contaminated environments where the surface needs to be periodically renewed. Spectral Black delivers wideband, low reflectance for FUV, UV, VIS, SWIR, MWIR and LWIR.
Scaling coating services and manufacturing
As mentioned above, Acktar’s coatings are based on vacuum deposition technology. Vacuum deposition involves the application of coating materials onto solid surfaces in thin films, to build up a controlled layer.
Highly specific surface area coatings can be created with tightly controlled morphology to produce materials with low reflectance level.
The coating thickness is just a few microns (typically 3-5 μm) and its density is typically ~1.8 g/cm3. The deposition process is carried out at wide range of temperatures depending on the substrate.
By controlling the composition and morphology of the layer microstructure, the process can be tailored to achieve desired levels of absorption or reflectance over a wide range of wavelengths (EUV-UV, VIS, and NIR-FIR).
As discussed, space is just one sector in which Acktar has applied its expertise, and the experience of working across industries has enabled the company to develop approaches to scaling up production as needed.
Serial production of opto-mechanical space hardware, based on processes developed to meet the needs of demanding deep space missions and industrial throughput in other sectors, can help to ensure large-scale commercial needs are met.
But regardless of manufacturing volume, it helps to ensure that a coatings provider is involved as early in the mission as possible.
Ensuring your coatings benefit the mission
In order to ensure that your mission has the best possible chance of success, particularly if it is reliant on optical payloads, laser communication, and/or solar sensing systems, it is important to consider coatings early in the design. In the worst case scenario an opto-mechanical sub-system may even need to be taken apart in order for the most effective coating to be applied.
Although companies such as Acktar are typically involved from a practical point of view when the mission’s hardware development is at an advanced stage, involving them earlier can help you make better decisions.
Effective coating application processes will help reduce mission complexity, and ensure that the process and staging of the different steps involved in the application can help add value to the system.
Optical designs will also benefit from enhanced simulation. Acktar provides clients with a huge volume of qualification data to help simulate performance, enabling them to, for example, better understand what coating works in what wavelength range.
To find out more about such data, and see further details on Acktar’s products and services, please view Acktar’s supplier hub.