What comes to mind when you think of the word corrosion? Is it the rust on a bicycle left out in the rain, or maybe the white powder that forms after an alkaline battery is inside an electronic device for too long? On Earth, corrosion is a part of having oxygen in our atmosphere — the process of rusting is even called oxidation — so what happens when you take oxygen out of the equation? Can spacecraft corrode once they leave the Earth’s atmosphere behind?
Oxygen plays a massive role in corrosion here on Earth. If you’ve ever seen a rusty piece of metal, you’ve seen the result of this chemical reaction. Iron, in particular, reacts with oxygen and water to form iron oxide — the scientific name for rust.
Even in space, engineers have to contend with oxygen. There is still oxygen up to about 700km above the surface of the planet, but it’s not the O2 that we see at sea level. For comparison, the International Space Station sits in a low earth orbit at about 400km above sea level. At those altitudes, the element exists as atomic oxygen — a single atom instead of the molecules that we’re used to. This makes it even more reactive and more likely to cause oxidation if it comes into contact with anything that will react with it.
Atomic oxygen tends to destroy anything that it comes into contact with. Iron will corrode quickly, but other more common materials like stainless steel and aluminum form an oxide layer once they come into contact with atomic oxygen. This oxide layer acts as a protective coating that prevents the material from eroding further.
Once you get outside of the planet’s atmospheric envelope, above 700km, oxygen is no longer a problem, but that doesn’t mean that you’re home free when it comes to spacecraft corrosion. Ships in deep space experience another type of corrosion known as cold welding. If you put two pieces of metal together on Earth, the thin layers of oxidation keep them from exchanging electrons and bonding. Once you’re outside of the planet’s atmosphere, you no longer have that layer of oxidation protecting the materials and keeping them separate. If you place those same two pieces of metal together in a vacuum, they’ll fuse without needing to heat them like you’d have to do at home.
Exposure to charged particles and radiation can also cause materials to degrade both outside and inside the spacecraft, depending on the level of exposure. Most of these energy waves contain enough power to remove electrons from affected atoms, which causes the materials to fall apart over time.
Corrosion costs businesses a lot of money here at home — upwards of $2.5 trillion every year, according to a 2016 study by the National Association of Corrosion Engineers. In outer space, corrosion isn’t just an expensive proposition. If left unchecked, it could put the lives of astronauts and eventual colonists at risk. If equipment fails far from home, there’s not much we can do from here.
Engineers are still working on developing materials that are better able to resist the corrosive forces of atomic oxygen within the Earth’s atmospheric envelope, and the even harsher conditions once we start reaching deep space.
So, can spacecraft corrode in outer space? With modern materials, the answer is definitely yes. Close to the planet, atomic oxygen is more reactive than the molecular oxygen that we encounter down here at sea level, which causes even usually non-reactive materials like aluminum and stainless steel to corrode a little bit. Once you get outside of that atmospheric envelope, charged particles and radiation steal electrons from materials, making them degrade over time. The answer is yes — at least for now.
We may develop materials or alloys in the future that are corrosion-proof for long-distance space travel, but for the moment, with the elements, we have now, corrosion is something that we’ll have to contend with as we start to explore the cosmos.