Astronauts recently cleaned windows on the International Space Station after they noticed that it had become cloudy from the exhaust residue of visiting spacecraft.

Astronauts may conduct advanced experiments in space, but they also need to do simpler maintenance tasks.

One such chore was completed this week when two Russian cosmonauts wiped down windows on the International Space Station. 

One was a porthole that had been coated with the residue of fumes left by visiting spacecrafts' exhaust systems. 

According to Devan Bolch, a NASA analyst, the astronauts had noticed one of the windows looked hazy on a previous spacewalk, and when they swiped across it