While designing anything for operation in space has its challenges, there is at least one thing that is more of a problem for objects in Earth orbit than for deep-space probes: atomic oxygen. We like oxygen because we need it to live, but it is also highly reactive as a single atom. Luckily, on Earth, most of what we breathe is O2. [Space Daily] talks about the challenges of the International Space Station dealing with the “space weather” of atomic oxygen in low Earth orbit.
Part of the problem is that even when we know better, we tend to think of the atmosphere coming to an abrupt end and space being a hard vacuum. But in reality, the atmosphere gradually dissipates, and at “only” 400 km above the Earth, the Space Station is really flying through a very thin atmosphere.
To compound the problem, this is above the ozone layer, so the Sun’s UV light rips O2 into single oxygen atoms. Over time, these free oxygen atoms can affect many parts of a spacecraft exposed to them. Engineers first noticed that materials recovered from spacecraft had more damage and changes to material properties on the pieces facing the direction of travel. NASA has spent years testing different materials by mounting trays of different material samples outside the ISS.
