There are several forms of Kepler's equation. Each form is associated with a specific type of orbit. The standard Kepler equation is used for elliptic orbits ( 0 ≤ ≤ e < 1 ). The hyperbolic Kepler equation is used for hyperbolic trajectories ( e > 1 ). The radial Kepler equation is used for linear (radial) trajectories ( e = 1 ). Barker's equation is used for parabolic trajectories ( e = 1 ).