Why do astronauts use walkie talkies to communicate?

Answer 1

When they're inside their spacecraft, in the "shirtsleeve" environment, and the spacecraft

is full of air, they don't need walkie-talkies, and are able to communicate in the usual way,

using only mouths and ears.

But if they're operating in an environment without air, such as during a "space-walk"

or on the moon, then they need to use radio.

The reason for the difference is the fact that sound needs a substance to travel through.

If there is no air between the speaker's mouth and the listener's ear, then sound cannot

make the trip, and another means of communication is required.