Question

What keeps a satellite up in its orbit about the Earth?

Answer 1

Its tangential velocity

Explanation:

Ideally the orbit of a satellite perfectly balances tangential velocity with the effect of gravity so gravity provides exactly the required centripetal force to prevent the satellite leaving orbit.

If the satellite is high enough above the Earth's surface, then the drag of the Earth's atmosphere will be quite small, so there will be little to prevent the satellite from remaining in orbit.

Small adjustments to attitutde and position of satellites are typically made using thrusters that eject gas or ion streams.