| A&A | Astronomy And Astrophysics | - | Atmospheric Research Center |
| AACS | Attitude And Articulation Control Subsystem | - | Atmospheric Research Center |
| AAO | Anglo-Australian Observatory | - | Atmospheric Research Center |
| AAS | American Astronomical Society | - | Atmospheric Research Center |
| AAS | American Astronautical Society | - | Atmospheric Research Center |
| AAVSO | American Association Of Variable Star Observers | - | Atmospheric Research Center |
| AC | Atlas Centaur | - | Atmospheric Research Center |
| ACE | Advanced Composition Explorer | - | Atmospheric Research Center |
| ACF | Automated Control Function | - | Atmospheric Research Center |
| ACR | Active Cavity Radiometer | - | Atmospheric Research Center |
| ACRIM | ACR Irradiance Monitor | - | Atmospheric Research Center |
| ACRV | Assured Crew Return Vehicle | - | Atmospheric Research Center |
| ACRV | Astronaut Crew Rescue Vehicle | - | Atmospheric Research Center |
| ACTS | Advanced Communications Technology Satellite | - | Atmospheric Research Center |
| ADEOS | Advanced Earth Observing Satellite | - | Atmospheric Research Center |
| ADFRF | Ames-Dryden Flight Research Facility | - | Atmospheric Research Center |
| ADS | Astrophysical Data System (at Havard-Smithsonian CfA) | - | Atmospheric Research Center |
| ADS | Aitken Double Star Catalog | - | Atmospheric Research Center |
| AE | Arianespace SA | - | Atmospheric Research Center |
| AEPI | Atmospheric Emissions Photometric Imaging | - | Atmospheric Research Center |
| AF | Air Force | - | Atmospheric Research Center |
| AFETR | USAF's ETR | - | Atmospheric Research Center |
| AFGWC | Air Force Global Weather Center | - | Atmospheric Research Center |
| AFP | Air Force Program | - | Atmospheric Research Center |
| AFPRO | Air Force Plan Representative Office | - | Atmospheric Research Center |
| AFRSI | Advanced FRSI | - | Atmospheric Research Center |
| AFWTR | USAF's WTR | - | Atmospheric Research Center |
| AGB | Asymptotic Giant Branch | - | Atmospheric Research Center |
| AGE | Auxiliary Ground Equipment | - | Atmospheric Research Center |
| AGN | Active Galactic Nucleus | - | Atmospheric Research Center |
| AGU | American Geophysical Union | - | Atmospheric Research Center |
| AIAA | American Institute Of Aeronautics And Astronautics | - | Atmospheric Research Center |
| AIPS | Astronomical Image Processing System | - | Atmospheric Research Center |
| AIRS | Atmospheric Infrared Sounder | - | Atmospheric Research Center |
| AJ | Astronomical Journal | - | Atmospheric Research Center |
| ALAE | Atmospheric Lyman-Alpha Emissions | - | Atmospheric Research Center |
| ALDP | Advanced Launch Development Program | - | Atmospheric Research Center |
| ALEXIS | Array Of Low Energy X-ray Imaging Sensors | - | Atmospheric Research Center |
| ALPO | Association Of Lunar And Planetary Observers | - | Atmospheric Research Center |
| ALS | Advanced Launch System | - | Atmospheric Research Center |
| AMOS | Air Force Maui Optical System | - | Atmospheric Research Center |
| AMSR | Advanced Microwave Sounding Radiometer | - | Atmospheric Research Center |
| ANSI | American National Standards Institute | - | Atmospheric Research Center |
| AOA | Abort Once Around (shuttle Abort Plan) | - | Atmospheric Research Center |
| AOA | Angle Of Attack | - | Atmospheric Research Center |
| AOCS | Attitude And Orbit Control System | - | Atmospheric Research Center |
| APE | Auroral Photography Experiment | - | Atmospheric Research Center |
| APJ | Astrophysical Journal | - | Atmospheric Research Center |
| APL | Applied Physics Laboratory (at Johns Hopkins) | - | Atmospheric Research Center |
| APM | Attached Pressurized Module (a.k.a. Columbus) | - | Atmospheric Research Center |
| APM | Atmospheric Particle Monitor | - | Atmospheric Research Center |
| APT | Automatic Picture Transmission | - | Atmospheric Research Center |
| APT | Automatic Photoelectric Telescope | - | Atmospheric Research Center |
| APU | Auxiliary Power Unit | - | Atmospheric Research Center |
| ARC | Ames Research Center (NASA) | - | Atmospheric Research Center |
| ARC | Astrophysical Research Consortium | - | Atmospheric Research Center |
| ARISTOTELES | Applications And Research Involving Space Technologies Observing The Earth's Field From Low Earth Orbiting Satellite | - | Atmospheric Research Center |
| ARRL | American Radio Relay League | - | Atmospheric Research Center |
| ARTEMIS | Advanced Relay TEchnology MISsion | - | Atmospheric Research Center |
| ASA | Astronomical Society Of The Atlantic | - | Atmospheric Research Center |
| ASCO | Arab Satellite Communications Organization | - | Atmospheric Research Center |
| ASE | Advanced Space Engine | - | Atmospheric Research Center |
| ASEM | Assembly Of Station By EVA Methods | - | Atmospheric Research Center |
| ASI | Agenzia Spaziale Italiano | - | Atmospheric Research Center |
| ASP | Astronomical Society Of The Pacific | - | Atmospheric Research Center |
| ASRM | Advanced Solid Rocket Motor | - | Atmospheric Research Center |
| ASS | Antenna Support Structure | - | Atmospheric Research Center |
| ASTER | Advanced Spaceborne Thermal Emission And Reflection | - | Atmospheric Research Center |
| ASTRO | Space Astrophysics Laboratory | - | Atmospheric Research Center |
| ATAL | Alternate Transoceanic Abort Landing | - | Atmospheric Research Center |
| ATCS | Active Thermal Control System | - | Atmospheric Research Center |
| ATDRS | Advanced Tracking And Data Relay Satellite | - | Atmospheric Research Center |
| ATLAS | Atmospheric Laboratory For Applications And Science | - | Atmospheric Research Center |
| ATM | Amateur Telescope Maker | - | Atmospheric Research Center |
| ATM | Apollo Telescope Mount (on Skylab) | - | Atmospheric Research Center |
| ATMOS | Atmospheric Trace Molecule Spectroscopy | - | Atmospheric Research Center |
| ATO | Abort To Orbit | - | Atmospheric Research Center |
| ATSR | Along Track Scanning Radiometer | - | Atmospheric Research Center |
| AU | Astronomical Unit | - | Atmospheric Research Center |
| AURA | Association Of Universities For Research In Astronomy | - | Atmospheric Research Center |
| AVHRR | Advanced Very High Resolution Radiometer | - | Atmospheric Research Center |
| AW&ST | Aviation Week And Space Technology | - | Atmospheric Research Center |
| AXAF | Advanced X-ray Astrophysics Facility | - | Atmospheric Research Center |
