Conservation of energy tells us that the sum of KE and PE remains constant. When a satellite is in a circular orbit, the satellite's distance from the center of the attracting body doesn't change, so its PE is constant. Therefore, its KE is also constant. When a satellite is in an elliptical orbit, the distance changes. As the satellite moves farther away from the Earth, PE increases and KE decreases (it slows down), and as it moves closer to the Earth, PE decreases and KE increases (it speeds up). The total energy remains constant, i.e., it is conserved.
Work Step by Step
This is discussed on pages 197-198.