Stay above the same place on Earth "forever" ... thus they stay in the same place in our sky.
The five major types of artificial satellites are: research, communications, weather, navigational, and applications. Please see the related links.
There are no known satellites of Mercury.
Communication satellites orbit around the Earth.Communication satellites orbit around the Earth.Communication satellites orbit around the Earth.Communication satellites orbit around the Earth.
Mercury has no satellites.
Those are called planetary satellites or natural satellites. Each planet has its own set of natural satellites that orbit around it.
Triangulation of satellites requires three satellites that bank of one another simultaneously.
It has 3 satellites!
Elliptical satellites don't have a constant speed, but circular satellites do
Applications satellites, like weather satellites, communications satellites (TV, Cell phone, internet), military observation birds, reconnaissance satellites and other "useful" things predominate. Purely scientific satellites such as the Hubble Space Telescope are in the minority.
All the satellites, communications, exploratory, military etc. are artificial satellites of Earth.
If each ring can hold 3 satellites, you can accommodate all 24 satellites with 8 rings. Each ring would hold 3 satellites, for a total of 24 satellites.
Mercury has no natural satellites.