system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we briefly lose connection with spacecrafts upon reentry?

When a space craft is reentering the atmosphere, their connection with the guys back on the ground is cut off for a few minutes. I've been told "ionized plasma around the craft" is the reason, but that doesn't tell me much of anything. IF that's correct, why would the ionized plasma prevent the signals from reaching each other? If that's not the case, please explain :) Thanks!
gpt
Plasma (ionized gas) consists partly of free electrons. So the electrons will respond freely to any signal whose frequency is below the plasma frequency (a function only of electron density; typically in the far IR for reentry, signals are in the microwave-radio). Electrons that oscillate back and forth re-radiate at the same frequency: the net result being reflection, with some absorptive losses due to collisions. Any transmitted signal is exponentially decayed through the plasma.

It's the same reason metals reflect visible light. The plasma frequency of metals is typically in the ultraviolet.

The only reason regular gas like air doesn't reflect like a plasma is because the electrons are tightly bound to their atoms and can only change energy is large discrete jumps. When electrons are free in a plasma, their energy states are much closer together, so they behave approximately classically when there aren't too many of them (the subtlety comes when you consider metals, which though there are many possible states for the electrons, there about as many electrons to fill them, so you have to worry about things like Fermi statistics).