A New Value for the Earth's Flattening, derived from Measurements of Satellite Orbits

Abstract

IN a recent article¹ in Nature, we described how the Earth's gravitational field could be explored with the aid of satellites, and gave some results obtained from analysis of kinetheodolite observations of Sputnik 2 (1957β), the orbit of which was inclined to the equator at an angle near 65°. From observations of a single satellite, the coefficient J of the second harmonic in the Earth's gravitational potential could only be evaluated if the coefficient D of the fourth harmonic were given its conventional value of 10.6 × 10⁻⁶. On this assumption the value derived¹ for J was 1626 × 10⁻⁶, corresponding to a value of 1/298.1 for the Earth's flattening (defined as the difference between equatorial and polar radii, divided by the equatorial radius), as compared with the previously accepted value² of 1/297.1. To obtain J, and D independently, results from two satellites, of substantially different orbital inclinations, are required.