"They're machines that stay up in the sky and fly around the earth."
We read the placard:
"Tracking and relay data satellites."
That didn't help.
"They orbit the earth. They just keep going around and around."
"And we send signals up to them and they send them back down."
Finally, I think of something that Sam knows about. I say, "Signals are things like your voice on the phone. You can talk on the phone and your voice goes way up high to the satellite and then it comes back down to another phone so someone else can hear you."
Sam looks up at the satellite and yells, "ECHO!!!"