| Abbreviation | Definition |
|---|---|
| UI | Ariel ( Uranus satellite number 1) |
| UI | Ultraviolet Imaging |
| UI | User Interface |
| UIC | User Identification Code |
| UII | Umbriel ( Uranus satellite number 2) |
| UIII | Titania ( Uranus satellite number 3) |
| UIO | User Integration Office |
| UIR | Unidentified Infrared |
| UIT | Ultraviolet Imaging Telescope |
| UIV | Oberon ( Uranus satellite number 4) |
| UKIRT | United Kingdom Infrared Telescope |
| UKIRT | United Kingdom Infra-Red Telescope |
| UL | UnderLoad |
| UL | UpLink |
| UL | Upper Left |
| UL | Upper Limit |
| ULA | Fairbanks, Alaska (Spaceflight Tracking and Data Network Site) |
| ULA | United Launch Alliance |
| ULC | Unpressurized Logistics Center |
| ULD | Ultra Low Drag |