Low Earth orbit may seem like empty space, but for the thousands of satellites orbiting our planet at altitudes between 95 and 1,900 km, it is actually a surprisingly hostile environment. At every moment, these spacecraft are bombarded by highly reactive oxygen atoms that corrode their surfaces, while collisions with atmospheric molecules create drag that gradually pulls them back toward Earth. Most satellites only last about five years before these unrelenting forces take their toll and the spacecraft falls back through the atmosphere. Now a team at the University of Texas at Dallas is developing a protective coating that could fundamentally change how satellites survive in orbit.
Earth’s atmosphere from space shows a blue layer in the stratosphere. It is a hostile environment for any satellite launched into low Earth orbit (Source: NASA)
The main cause of damage to spacecraft in low Earth orbit is atomic oxygen. When ultraviolet radiation from the sun hits molecular oxygen in the thin upper atmosphere, it splits the molecules into individual atoms. These individual atoms are far more reactive than the stable O₂ molecules we breathe, and they are the most common particles encountered by satellites in low-Earth orbit. When these atoms collide with spacecraft surfaces, they don’t simply bounce off but bind to the material, causing oxidation. Essentially, satellites slowly rust away in space.
Beyond the corrosion problem, satellites also face the challenge of air resistance. Any collision with particles in the atmosphere, be they oxygen atoms or other molecules, slows the satellite slightly. Over time, these countless small impacts cause the spacecraft to lose altitude and eventually fall back to Earth. It’s a dual threat that engineers must contend with: materials must withstand both chemical erosion and the physical forces of air resistance.
The team, led by materials scientist Rafik Addou, is tackling this challenge by adopting techniques from other industries and applying them in novel ways. One approach uses atomic layer deposition, a method originally developed for making microelectronics. In this process, protective layers are built up atomically, layer by layer, providing unprecedented control over the structure and properties of the material. Precision is extremely important when trying to create a surface that can withstand the unique conditions of space.
Schematic representation of a reaction cycle of the ALD process, using the example of the trimethylaluminum (TMA)-water process for producing thin aluminum oxide films (Source: By Véronique Cremers, Riikka Puurunen, Jolien Dendooven)
Their second technique, called sol-gel processing, creates solid materials from liquid solutions. This method, commonly used to create optical coatings like the anti-reflective layers on eyeglasses, allows researchers to design surfaces smooth enough to minimize drag while maintaining protective properties. By combining these approaches, the team has developed a coating that independent tests show can withstand even more extreme atomic oxygen conditions than those actually found in space.
Addou and his colleagues hope their work will allow spacecraft to operate in very low Earth orbit, where the environment is significantly harsher due to higher concentrations of atomic oxygen and nitrogen. This area offers advantages for certain applications, but has so far been largely unusable because the materials there decompose so quickly. If successful, their protective coatings could open up new opportunities for satellite operations in this challenging but potentially valuable orbital zone.
Source: Engineers develop new protective coating for spacecraft
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