how come there is a blackout period when the space shuttle goes behind the moon? Is it because radio waves can be transmitted through a solid object or through a vacuum or why?
Radio waves do not go through a solid object like the moon, hence the other side of the moon from the Earth is a radio shadow area.
Interestingly the moon can act as a radio reflector and it is possible to bounce radio signals sent from Earth off the moon, and receive them back on Earth. This is not just done by those with huge dishes like NASA, it can be done with modest equipment and relatively low power.