| Acronym | Meaning |
 | ISZ | Iskusstvenniy Sputnik Zemli |
| IUE | International Ultraviolet Explorer |
| IUS | Inertial Upper Stage |
| IVT | Interface Verification Test |
| JAEL | JSC Avionics Engineering Laboratory |
| JCMT | James Clerk Maxwell Telescope |
| JD | Julian Date; Julian Day (Number) |
| JEM | Japanese Experiment Module |
| JERS | Japanese Earth Resources Satellite |
| JGR | Journal Of Geophysical Research |
| JILA | Joint Institute For Laboratory Astrophysics |
| JPL | Jet Propulsion Laboratory |
| JSC | Johnson Space Center |
| KAO | Kuiper Airborne Observatory |
| KB | Construction Bureau |
| KPM | Kometen |
| KPNO | Kitt Peak National Observatory |
| KSC | Kennedy Space Center |
| KTB | Cretaceous-Tertiary Boundary |
| LAGEOS | Laser Geodynamics Satellite |
| LANL | Los Alamos National Laboratory |
| LARC | Langley Research Center |
| LASCO | Large Angle Spectrometric Coronograph |
| LC | Launch Complex |
| LDEF | Long Duration Exposure Facility |
| LEDA | On-line Earthnet Data Access |
| LEM | Lunar Excursion Module |
| LEO | Low Earth Orbit |
| LERC | Lewis Research Center |
| LEST | Large Earth-based Solar Telescope |
| LFC | Large Format Camera |
| LGA | Low Gain Antenna |
| LGM | Little Green Men |
| LH | Liquid Hydrogen |
| LHA | Local Hour Angle |
| LIS | Lightning Imaging Sensor |
| LLNL | Lawrence-Livermore National Laboratory |
| LM | Lunar Module |
| LMC | Large Magellanic Cloud |
| LN2 | Liquid Nitrogen |
| LOX | Liquid OXygen |
| LPO | La Palma Observatory |
| LPV | Long Period Variable |
| LRB | Liquid Rocket Booster |
| LRSI | Low-temperature Reusable Surface Insulation |
| LSR | Local Standard Of Rest |
| LST | Local Sidereal Time |
| LTP | Lunar Transient Phenomenon |
| LY | Light Year (usu. Ly) |
| M | Messier |
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