| U3P | Union Pour La Promotion De La Propulsion Photonique | - | Atmospheric Research Center |
| UARS | Upper Atmosphere Research Satellite | - | Atmospheric Research Center |
| UBM | Unpressurized Berthing Mechanism | - | Atmospheric Research Center |
| UDMH | Unsymmetrical DiMethyl Hydrazine | - | Atmospheric Research Center |
| UFO | Unidentified Flying Object | - | Atmospheric Research Center |
| UGC | Uppsala General Catalog | - | Atmospheric Research Center |
| UHF | Ultra High Frequency | - | Atmospheric Research Center |
| UIT | Ultraviolet Imaging Telescope | - | Atmospheric Research Center |
| UKST | United Kingdom Schmidt Telescope | - | Atmospheric Research Center |
| UOSAT | University Of Surrey Satellite | - | Atmospheric Research Center |
| UPPP | Union Pour La Promotion De La Propulsion Photonique | - | Atmospheric Research Center |
| USA/RC | Universities Space Automation/Robotics Consortium | - | Atmospheric Research Center |
| USAF | United States Air Force | - | Atmospheric Research Center |
| USMC | United States Marine Corps | - | Atmospheric Research Center |
| USML | United States Microgravity Laboratory | - | Atmospheric Research Center |
| USMP | United States Microgravity Payload | - | Atmospheric Research Center |
| USN | United States Navy | - | Atmospheric Research Center |
| USO | Ultra-Stable Oscillator | - | Atmospheric Research Center |
| UT | Universal Time | - | Atmospheric Research Center |
| UTC | Coordinated Universal Time | - | Atmospheric Research Center |
| UV | Ultraviolet | - | Atmospheric Research Center |
| UVPI | Ultraviolet Plume Instrument | - | Atmospheric Research Center |
| UVS | Ultraviolet Spectrometer | - | Atmospheric Research Center |
