Glossary of Space Exploration Terminology

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L
L-band
A range of microwave radio frequencies in the neighborhood of 1 to 2 GHz.
Lander spacecraft
A spacecraft designed to reach the surface of a planet or moon and survive long enough to telemeter data back to Earth.
Langrangian point
In a system dominated by two attracting bodies (such as Sun and Earth), a point at which a third, much smaller body (such as a satellite) keeps the same position relative to the other two. Theoretically, the Sun-Earth system has 5 Lagrangian points, but only two are important: L1, on the sunward side of Earth, about 4 times the distance of the Moon, and L2 at approximately the same distance on the midnight side. The only two lagrangian stable points, L4 and L5, lie in the orbit of the primary body, leading and trailing it by a 60-degree arc. Jupiter's trojan asteroids can be found orbiting around the Jupiter-Sun L4 and L5 points.
Lanyard
Small rope or cord.
Laser
Light Amplification by the Stimulated Emission of Radiation. A device for producing a coherent monochromatic high-intensity beam of light.
Latitude
Circles in parallel planes to that of the equator defining north-south measurements, also called parallels.
Launch complex
The complex of site, facilities and equipment used to launch a missile or space rocket.
Launch pad
The load-bearing base from which a rocket or spacecraft positioned on its launcher is fired.
Launch window
An interval of time during which a space vehicle can be launched to accomplish a given mission, e.g. a flight to Venus or Mars.
LC
Launch Center.
Leading side
For a satellite that keeps the same face toward the planet, the hemisphere that faces forward, into the direction of motion.
Leap year
Every fourth year, in which a 366th day is added since the Earth's revolution takes 365 days 5 hr 49 min.
LEO
Low Earth Orbit.
LGA
Low-Gain Antenna.
LH2
Liquid Hydrogen.
Liftoff
The start of a rocket's flight from its launch pad. Colloquially, "blast-off".
Light
Electromagnetic radiation that is visible to the eye, in the neighbourhood of 1 nanometer wavelength.
Light speed
299,792,458 meters per second +/- 1.2 m/sec (186,282.39 miles/sec). U.S. National Bureau of Standards, 1971.
Light time
The amount of time it takes light or radio signals to travel a certain distance at light speed.
Light year
The distance light travels in one year, approximately 9.46 trillion km (5.88 trillion miles).
LiOH
Lithium Hydroxide.
Liquid hydrogen
A cryogenic rocket fuel which becomes liquid at -423oF.
Liquid oxygen
A cryogenic oxidizer which becomes liquid at -279oF.
Lithosphere
The crust of a planet.
LM
Lunar Module.
LO2
Liquid Oxygen. Also abbreviated LOX.
Local time
Time adjusted for location around the Earth or other planets in time zones.
LOI
Lunar Orbit Insertion.
Longitude
Great circles that pass through both the north and south poles, also called meridians.
Longitude of ascending node
In an orbit, the celestial longitude of the ascending node.
Longitudinal axis
The fore-and-aft line through the center of a space vehicle.
Low Earth Orbit
An orbit in the region of space extending from the Earth's surface to an altitude of 2,000 kilometers. Given the rapid orbital decay of objects close to Earth, the commonly accepted definition is between 160-2,000 km above the Earth's surface.
Low-energy charged particle detector
A device designed to characterize the composition, energies, and angular distributions of charged particles in interplanetary space and within planetary systems.
Low-gain antenna
An omni-directional spacecraft antenna that provides relatively low data rates at close range, several AU for example.
LOX
Liquid Oxygen. Also abbreviated LO2.
LRBM
Long Range Ballistic Missile.
LRV
Lunar Roving Vehicle.
LT
Launch Time.
Lunar
Of or pertaining to the Moon.
Lunar module
The craft used by Apollo missions for Moon landings. The lunar module consisted of a descent stage, used to land on the Moon and as a platform for liftoff, and an ascent stage, used as crew quarters and for returning to the orbiting command module.
Lunar roving vehicle
A battery powered wheeled vehicle used by Apollo astronauts to explore the lunar surface.
LV
Launch Vehicle.

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Rocketry & Space Technology

Glossary courtesy of Robert Braeunig's
Rocketry & Space Technology website.