| Acronym | Meaning |
| OSP | Operations Support Plan |
| OSR | Operations Support Room |
| OSS | OEX SuPport System |
| OSS | Office Of Space Science |
| OSS | OPtics Subsystems |
| OSS | Orbiting Space Station |
| OSSA | Office Of Space Science And Applications |
| OSSRH | Orbiter Subsystem(s) Requirements Handbook |
| OST | Operations Support Team (GSFC) |
| OST | Orbiter SuPport Trolley |
| OSTA | Office Of Space And Terrestrial Application(s) |
| OSTDS | Office Of Space Tracking And Data Systems |
| OSTO | Office Of Space Transportation Operations |
| OSTP | Orbiting System Test Plan |
| OSTS | Office Of Space Transportation Systems |
| OT | Operating Time |
| OT | Operational Instrumentation MDM-Tank |
| OT | Operational Test |
| OT | Operational Trajectory |
| OT | Optical Tracker |
| OT | Out Temperature |
| OT | Overti Me |
| OT&E | Operational Test And Evaluation |
| OTA | Optical Telescope Assembly |
| OTB | Orbiting Tanker Base |
| OTBD | Outboard |
| OTC | Orbiter Test Conductor |
| OTD | Operational Technical Documentation |
| OTD | Orbiter Test Director |
| OTDA | Office Of Tracking And Data Acquisition (now OSTDS) |
| OTEMP | Overtemperature |
| OTH | Over-the-Horizon (.Radar) |
| OTK | Oxidizer Tank |
| OTL | Ordnance Test Laboratory |
| OTLC | Orbiter Timeline Constraints |
| OTO | One-Time-Only |
| OTOS | Orbit-to-Orbit Stage |
| OTP | OPerational Test Procedure |
| OTP | Operations Test Plan |
| OTP | Operations Turnaround Plan |
| OTR | Operating Time Record |
| OTR | Outer |
| OTS | Off-the-Shelf |
| OTS | Orbiter Test Conductor |
| OTT | Optional Team Targeting |
| OTV | Operational Television |
| OTV | Orbital Transfer Vehicle |
| OTV | Orbiter Transfer Vehicle |
| OTY | Quantity |
| OUI | Quito |