Astrodynamics/The Kepler Problem
The Kepler Problem[edit | edit source]
While Kepler's equation is easy to solve for time, there is no general solution for the reverse problem. To determine eccentric anomaly (and thus spacecraft position) at a given time, generally an iterative numerical method is used, such as Newton's method:
The iteration takes the form
For most elliptical orbits an initial guess of E0 = M is sufficient; for orbits with eccentricities greater than 0.8, E0 = π may be used. Better initial guesses are possible, but are not generally required. The iterative process is repeated until required accuracy conditions are achieved, for example:
Where δ is the desired accuracy.