Glossary — L
18 terms
LEO
Low Earth Orbit: an orbit with an altitude between roughly 160 and 2,000 kilometers above Earth's surface.
Example: Most crewed space stations, including the ISS, operate in low Earth orbit.
Launch
The act of sending a vehicle into space, beginning with liftoff.
Example: The launch lifted off on schedule at dawn.
Launch vehicle
A rocket system that carries payloads to space.
Example: The launch vehicle stood ready on the pad.
Launch pad
The ground facility from which a rocket lifts off.
Example: Crews cleared the launch pad before fueling.
Launch complex
A site including pads, integration, and support facilities.
Example: The launch complex hosted multiple pads and towers.
Liquid propellant
Rocket propellant stored as a liquid, enabling throttling and restart.
Example: Liquid-propellant engines can be throttled and shut down mid-flight.
Lander
A spacecraft designed to touch down on a planet or moon's surface.
Example: The lander touched down near the lunar south pole.
Launch tower
The structure supporting a rocket and its connections before liftoff.
Example: The launch tower retracted its arms at T-30 seconds.
Lifting reentry
A reentry using aerodynamic lift to steer and reduce peak loads.
Example: A lifting reentry let the shuttle target its runway precisely.
Liftoff
The instant a vehicle leaves the pad under its own thrust.
Example: Liftoff occurred at T+0 after the hold-down clamps released.
Launch window
The interval of time during which launch must occur to reach a target.
Example: The mission had a two-hour launch window to hit the station.
Low-gain antenna
A wide-beam antenna used for near-omnidirectional, low-rate links.
Example: The low-gain antenna provided an emergency command link.
Launch abort system
A system that pulls a crew vehicle away from a failing rocket.
Example: The launch abort system test validated astronaut escape.
Landing guidance
The guidance algorithm steering a vehicle to a precise touchdown.
Example: Landing guidance targeted the drone ship's deck center.
Lift-to-drag ratio
A measure of aerodynamic efficiency, lift divided by drag.
Example: A high lift-to-drag ratio gave the shuttle crossrange.
Lunar mission
A mission whose destination is the Moon.
Example: The lunar mission landed near the south pole.
Low lunar orbit
An orbit around the Moon at low altitude, typically a few tens of kilometers.
Example: Artemis landers descend from low lunar orbit to the surface.
Lagrange point
One of five equilibrium points where the gravity of two large bodies balances orbital motion.
Example: JWST orbits the Sun-Earth L2 Lagrange point, 1.5 million km away.