When a satellite is in an elliptical orbit, at all times (with the exception of the apogee and perigee), there is a component of gravitational force in the direction of motion, doing work and changing the satellite's KE. As it moves farther away from the Earth, it slows down, and as it moves closer to the Earth, it regains that speed. In a circular orbit, gravity is always perpendicular to the direction of the satellite’s motion. No work is done, and no change in KE results. This is discussed on page 194 and shown in Figure 10.27.