Characteristic energy
In astrodynamics, the characteristic energy (formula_1) is a measure of the excess specific energy over that required to just barely escape from a massive body. The units are length time, i.e. velocity squared, or energy per mass. Every object in a 2-body ballistic trajectory has a constant specific orbital energy formula_2 equal to the sum of its specific kinetic and specific potential energy: formula_3 where formula_4 is the standard gravitational parameter of the massive body with mass formula_5, and formula_6 is the radial distance from its center. As an object in an escape trajectory moves outward, its  kinetic energy decreases as its potential energy (which is always negative) increases, maintaining a constant sum. Note that "C" is "twice" the specific orbital energy formula_2 of the escaping object. Non-escape trajectory. A spacecraft with insufficient energy to escape will remain in a closed orbit (unless it intersects the central body), with formula_8 where If the orbit is circular, of radius "r", then formula_11 Parabolic trajectory. A spacecraft leaving the central body on a parabolic trajectory has exactly the energy needed to escape and no more: formula_12 Hyperbolic trajectory. A spacecraft that is leaving the central body on a  hyperbolic trajectory has more than enough energy to escape: formula_13 where Also, formula_16 where formula_17 is the asymptotic velocity at infinite distance. Spacecraft's velocity approaches formula_17 as it is further away from the central object's gravity. Examples. MAVEN, a Mars-bound spacecraft, was launched into a trajectory with a characteristic energy of 12.2 km/s with respect to the Earth. When simplified to a two-body problem, this would mean the MAVEN escaped Earth on a hyperbolic trajectory slowly decreasing its speed towards formula_19. However, since the Sun's gravitational field is much stronger than Earth's, the  two-body solution is insufficient. The characteristic energy with respect to Sun was negative, and MAVEN – instead of heading to infinity – entered an elliptical orbit around the Sun. But the maximal velocity on the new orbit could be approximated to 33.5 km/s by assuming that it reached practical "infinity" at 3.5 km/s and that such Earth-bound "infinity" also moves with Earth's orbital velocity of about 30 km/s. The InSight mission to Mars launched with a C of 8.19 km/s. The Parker Solar Probe (via Venus) plans a maximum C of 154 km/s. C  (km/s) to get from Earth to various planets: Mars 12, Jupiter 80, Saturn or Uranus 147. To Pluto (with its orbital inclination) needs about 160–164 km/s.