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Researchers say they have developed a coating that can protect spacecraft and satellites from solar radiation while also allowing possible harvesting of heat energy from sunlight.
The research team working with Airbus at the University of Surrey's Advanced Technology Institute claims its nano-coating, referred to as a Multifunctional Nanobarrier Structure (MFNS), can be applied to the surfaces of equipment, including antennas, and it has been shown to be able to reduce the operating temperature of such surfaces from 120°C to 60°C (248°F to 140°F).
In its study published online, the team explains that thermal control is essential for most spaceborne equipment as heating from sunlight can cause large temperature differences across satellites that would result in mechanical stresses and possible misalignment of scientific instruments such as optical components. Paradoxically, space systems also require heat pipes to ensure minimal heating so that payloads can withstand the coldest space conditions.
To address this, thermal control systems often comprise a combination of both active and passive techniques, but these can eat into the weight and power budgets for the mission payload itself.
"While solutions already on the market offer protection, they are bulky and can be restrictive when it comes to thermal control," said Professor Ravi Silva, Director of the Advanced Technology Institute at the University of Surrey and one of the authors of the study.
The solution the team developed is a multilayer protection nanobarrier, which it says is comprised of a buffer layer made of poly(p-xylylene) and a diamond-like carbon superlattice layer that gives it a mechanically and environmentally ultra-stable platform.
The MFNS is deposited onto surfaces using a custom plasma-enhanced chemical vapor deposition (PECVD) system, which operates at room temperature and so can be applied to heat-sensitive substrates.
The combined layer is a dielectric and therefore electromagnetically transparent across a wide range of radio frequencies, the study states, allowing it to be used to coat antenna structures without adding "significant interference" to the signal.
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According to the team, the MFNS can be modulated to provide adjustable solar absorptivity in the ultraviolet to visible part of the spectrum, while at the same time exhibiting high and stable infrared emissivity. This is achieved by controlling the optical gap of individual layers.
This extends to self-reconfiguration in orbit, if the report can be believed, by means of balancing the UV and atomic oxygen (AO) exposure of the MFNS coating. AO is created from molecular oxygen in the upper atmosphere by UV radiation, forming AO radicals commonly found in low Earth orbit, the research adds.
As to the harvesting of heat energy, this can be achieved through the creation of highly absorbing structures with a photothermal conversion efficiency as high as 96.66 percent, according to the team. This is aided by the deposition of a nitrogen-doped DLC superlattice layer in the coating which gives rise to enhanced optical absorption across a wide spectral range.
These enhanced properties, along with advanced manufacturing methods, demonstrate that the MFNS can be a candidate for many thermal applications such as photodetectors, emitters, smart radiators, and energy harvesting used in satellite systems and beyond, the study states.
Professor Silva paid tribute to the help the University of Surrey received from Airbus Defence and Space in developing the new coating. ®