Escape Velocity
The minimum speed an object must reach to break free from a celestial body's gravitational pull without further propulsion.
Explanation
Escape velocity on Earth's surface is approximately 11.2 km/s (about 25,000 mph). It is derived from equating kinetic energy to gravitational potential energy — meaning an object with that speed has enough energy to reach infinite distance. In practice, spacecraft do not need to reach full escape velocity at the surface because they gain altitude while under thrust. Escape velocity decreases with altitude: at LEO altitudes it is about 10.9 km/s. To leave Earth entirely, a spacecraft must achieve at least escape velocity relative to Earth, though to reach another planet requires additional energy for a Hohmann transfer. The concept also applies to other bodies: the Moon's escape velocity is 2.38 km/s, Mars' is 5.03 km/s, and the Sun's at Earth's orbit is about 42 km/s.
Why It Matters
Escape velocity sets the fundamental energy requirement for interplanetary missions. Any spacecraft leaving Earth must be accelerated to at least this speed, which directly determines launch vehicle size and propellant needs.
Concept Map
How Escape Velocity connects to other glossary terms:
Frequently Asked Questions
Do all rockets need to reach escape velocity to leave Earth?
Not exactly. Rockets can coast after engine cutoff and still escape if total energy (velocity plus altitude) is sufficient. Continuous thrust is not required.
Is escape velocity the same everywhere?
No. It depends on the mass and radius of the celestial body. It is highest on the Sun and lowest on small asteroids.
Sources
Last updated: July 1, 2026