system
Given the following post, respond as if you're commenting on Reddit:
human
How do astronauts keep their helmets from fogging up?

I remember my dad asking that when Apollo 11 came out when I was a kid, and now I still don't have a definite answer.
gpt
The box on the back of the suit isn't just air supply. It's called the personal life support system and it constantly circulates air through the suit, regulating gas content, temperature and humidity. It's essentially a portable HVAC system. The constant circulation removes excess humidity that could cause fogging.