The magnitude of gravitational potential energy of the earth-satellite system is U with zero potential energy at infinite separation. The kinetic energy of satellite is K. Mass of satellite << mass of the earth. Then

K = 2U

Kinetic energy of the satellite K = $\frac{GMm}{2r}$ while magnitude of the potential energy U = $\frac{GMm}{r}$

Hence K = $\frac{U}{2}$