altitude of the apogee or of the perigee

The altitude of the apogee or perigee above a specified reference surface serving to represent the surface of the Earth. [NTIA] [RR] Note: In technical usage, the definite article is not used with the term apogee or perigee alone. A body orbiting the Earth is said simply to be "at apogee" or "at perigee."It may, however, properly be said to be "at the point of apogee" or "at the point of perigee."