| Acronym | Meaning |
 | UNBAL | Unbalance |
| UNDK | Undock |
| UNDV | Undervoltage |
| UNIV | Universal |
| UNLCH | Unlatch |
| UNLK | Unlock |
| UP | Upper |
| UPLK | Uplink |
| UPP | User Parameter Processing |
| UPS | Uninterruptible Power Supply |
| UPS | Uninterruptible Power System |
| UPS | Upright Perigee Stage |
| UPTLM | UPlink Telemetry |
| UR | Unsatisfactory Report |
| UR | Upper Right |
| URA | Urine Receptacle Assembly |
| URN | Urine |
| URT | Upright |
| US | United States |
| US | Upper Stage |
| USA | United States Of America |
| USAF | United States Air Force |
| USB | Unified S-Band |
| USB | Upper Side Band |
| USBE | Unified S-Band Equipment |
| USBI | United Space Booster |
| USBS | Unified S-Band System (Subsystem) |
| USEC | Microsecond |
| USI | Update Software Identity |
| USN | United States Navy |
| USNS | United States Navy Ship |
| USRA | Universities Space Research Association |
| USS | United States Ship |
| USS | United States Standard |
| USS | Utility Support Structure |
| UST | United States Testing (Company) |
| UST | Universal Servicing Tool |
| UT | Umbilical Tower |
| UT | Unit Tester |
| UT | Universal Time |
| UT&GS | Uplink Text And Graphics System |
| UTC | Coordinated Universal Time |
| UTC | Unit Test Cases |
| UTC | United Technology Center |
| UTC | Universal Test Console |
| UTE | Universal Test Equipment |
| UTI | LUtility |
| UTLM | Up Telemetry |
| UTS | Urine Transfer System |
| UU | Micromicron |
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