Wolfram|Alpha has astrodynamic calculators. Solve problems related to circular orbit velocity, Earth satellite period in a circular orbit; the elliptic orbit formula; energy to launch; escape velocity; Hohmann angular alignment, entrance Δv, exit Δv, total Δv or transfer time; Kepler's equation; Kepler's first or third law; the rocket or vis‐viva equation; and the Bussard ramjet.
