Satellite geodesy is like when someone is trying to find out how big and where things are on planet Earth.
They use satellites - which are like big metal balls that orbit around the Earth in space - to help them do this.
These satellites have special equipment that can measure things like the Earth's gravity and the way it rotates. They also have cameras that take pictures of the Earth from really high up!
Scientists use all of this information to make maps and models of the planet Earth. They can tell us where different things are on Earth (like cities, mountains, and oceans) and how tall they are.
Satellite geodesy is really important because it helps us understand our planet better and how it's changing over time. It also helps us make important decisions, like where to build things and how to keep our planet healthy.