| 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 |