Hint for a noncircular orbit

Assume that the mass of the central body is much larger than the mass of the satellite. We may then neglect the acceleration and kinetic energy of the central body.

The sum of the kinetic and potential energy has the same value in two different points on the orbit, i.e. the total energy is conserved.

The expression for the potential energy is

           

Remember that the proper unit for r is meter.