In astrodynamics the characteristic energy () is a measure of the excess specific energy over that required to just barely escape from a massive body. The units are length2time-2, i.e., energy per mass.
where is the standard gravitational parameter of the massive body with mass and 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.
Characteristic energy can be computed as:
A spacecraft with insufficient energy to escape will remain in a closed orbit (unless it intersects the central body) with:
- Wie, Bong (1998). "Orbital Dynamics". Space Vehicle Dynamics and Control. AIAA Education Series. Reston, Virginia: American Institute of Aeronautics and Astronautics. ISBN 1-56347-261-9.