For parabolic orbits, in place of the semi-major axis of the ellipse a, we use the perihelion distance q, and in place of the epoch time we use the time of perihelion passage Tp. In the...For parabolic orbits, in place of the semi-major axis of the ellipse a, we use the perihelion distance q, and in place of the epoch time we use the time of perihelion passage Tp. In the case of a body orbiting the Sun, GM is the graviational constant of the Sun, equal to 1.32712440041×1020m3s−2.
