Protective Coatings For Space

Over 20 years ago, a company still known today as AZ Technology of Huntsville, Alabama developed a spray coating system that’s still used by the International Space Station, their innovative spray coating is well known by NASA, ESA, and space satellite manufactures as one of the only space-stable color coatings globally available. Color coatings are important for spacecraft when it comes to identification markings, docking navigational targeting, and craft emblems.

In this new release of the Coatings Talk INSIGHT Newsletter, I'll cover some interesting aspects of protective coatings for space.

Companies like AZ Technology are continuously developing new materials, paints, and coatings for use on spacecraft, satellites and specialized terrestrial applications such as solar panels and observatories which need to meet important and specific customer-driven optical and resistivity requirements. Protective coatings for space application need to be designed to be low out-gassing and extreme space stable and meet toxicity and flammability requirements. Coatings manufacturers all tailor their product properties related to reflectance, emittance, electrostatic charge dissipative, and with a color range to meet specific aerospace industry requirements. As you can imagine the growing market opportunity related to protective coatings for use in space has a limited pool of engineering and professional expertise and production facilities for research and development, production and manufacture coating products that meet strict specifications and technical requirements.

Currently protective coatings for space have a long history of case studies related to exposure with the extremes presented by the environment in space. Many case studies involve coatings that have been applied to: Optical Properties Monitors (OPM) attached to the exterior of the historic Russian MIR space station (approx. 9 months); the MIR MEEP POSA-I experiment (approx. 1 year); the Materials International Space Station Experiment (MISSE) and importantly attached to the outside of the International Space Station (this case study ran approx. 4 years); and on the exterior of the International Space Station (15 years and still ongoing).

Due to the precision surface preparation and coating application required for spacecraft and/or related components, equipment, modules, and more. Prep and paint shops need to have thick film application capability using state-of-the-art equipment. High volume, low pressure (HVLP) turbine type systems are used to deposit paint onto components with complex geometry shapes. Primary paint application facilities need to be capable of handling components up to 100 square feet (~9 m2) specifically depending upon configuration. Facilities need to critically maintain a controlled environment during prep, painting and cure with respect to non coatings particulates, temperature and humidity. In addition, painting facilities typically are equipped with onsite equipment for formulating, compounding and testing coatings to ensure batch-to-batch consistency and quality in the final product. To complement well equipped prep and painting facilities, it’s important that they are staffed with expert craftworkers and inspection personnel all dedicated to quality.

I’ve spent time on protective coatings, additionally spacecraft also use high temperature ceramics with many materials being capable of temperatures of up to 3,000 degrees Fahrenheit. Extensive material testing is important to test protective coatings physical properties, such as adhesion, abrasion resistance, optical properties (solar absorption, emittance, reflectance, and transmittance), density analysis and electrical conductivity determination. This material testing is necessary for future development of tailored advanced technical paints and coatings for use in space and other harsh environments.

Every space mission brings us immense insight, helping us advance human knowledge and our capabilities. But it’s not only the missions themselves that are advancing technology, some of the technology supporting these projects are just as groundbreaking. Materials science is one discipline that underpins successful space projects. Earlier I mentioned the MIR space station, which launched in 1986. MIR, run by the Soviet Union’s space program, used a little-known surface coating technique called plasma electrolytic oxidation (PEO) to increase the life of components. The MIR project ran until 2001 when the project reached its conclusion, the new surface technology protected components for 15 years in the toughest of operating environments: known as extreme space.

Early space missions provided scientists with a lot of interesting answers. But, as is often the case, new discoveries lead to new areas of research. Advancing technologies allowed astrophysicists and scientists to pursue ambitious, formerly considered impossible, space-based missions. For example, in 2018, the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) launched a new mission to the planet Mercury. Using two orbiters, the mission involved a comprehensive study of Mercury, studying the structure and origins of the planet’s magnetic field. Neither agency had ever undertaken a mission of this magnitude before, the extremes of temperatures, particles (which are highly abrasive due to the solar wind), and radiation.

As with almost every spacecraft, lightweight materials, chiefly aluminum were used throughout the two orbiters. The alloys’ light weight helps to minimize launch costs, making missions more feasible, while their strength provides a stable platform for the multitude of scientific instruments housed onboard. However, with today’s very innovative spacecraft designs the boundaries are being stretched of what is possible. Engineers are faced with a number of issues with light alloys as they push the use of these materials to their absolute tested limits.

Light alloy coatings for space

Light alloys have a range of hugely attractive characteristics for spacecraft applications. However, the extreme conditions encountered in space mean they still require advanced surface modification technologies in order to protect them and enable their widest possible use.

To successfully combat the elements, surface coatings need to offer complete protection from a range of challenges:

Cold welding. Many of the mechanical problems found in early satellites were caused by cold welding. Even in the absence of heat, metals in contact fuse together in vacuums. Coatings are necessary to reduce contact adhesion in order to defend against cold welding.

UV degradation. Externally facing components are prone to solar photon damage, the effects are clearly visible in returning spacecraft. UV rays can change the micro-structure of aluminum alloys resulting in negative impacts such as reducing their tensile strength.

Thermal shocks. Materials in space applications frequently suffer severe thermal shocks, either during launch or when they are subjected to highly variable temperatures in orbit or solar system transit. Materials therefore require coatings with good thermal shock resistance and insulation so as to protect thermally electronics and scientific instruments. Since aluminum is three times more conductive than steel, surface coatings are so vital.

Solar absorbance & thermal emittance. Coatings designed to reflect solar radiation will reduce the deterioration impact on spacecraft systems. Coatings with a high level of emittance and low levels of absorption reduces the temperature of materials and electrical systems.

In essence, advanced technical surface coatings are needed to reduce light alloys’ exposure to the hostile environments of space. As a result, coatings had to be found that offered complete, comprehensive protection against any and all forms of space environmental damage to mitigate risks of further consequences caused by other potential means of light-weight alloy failures.

White silicone paints and ‘clear’ anodizing solutions have long been deployed in thermal-controlling coatings for space. However, those two options provide limited performance within extreme space environments, especially over the periods of time required in long-orbit and deep space exploration missions.

Some of the benefits include:

• High infrared region optimization.
• High stability dealing with harsh space environmental conditions, related to extreme UV, high temperatures and thermal shock.
• Extremely good surface adhesion.
• Very low out-gassing.
• Environmentally friendly applications.
• Ability with coating application on complex shapes.
• Provide best current technology thermal shielding of exterior spacecraft surfaces.

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