| OSM | On-Orbit Spares Model | In English | |
| OSM | Orbiter Service Module | In English | |
| OSO | Orbiting Solar Observatory | In English | → Observatories |
| OSOP | Orbiter Systems Operating Procedure | In English | |
| OSS | Office of Space Sciences | In English | → Astronomy |
| OSS | Orbiting Space Station | In English | |
| OSSA | Office of Space Sciences and Applications | In English | → Astronomy |
| OSSA | Office of Space Science and Applications | In English | → Astronomy |
| OSSIU | Orbiter-Space Station Interface Unit | In English | |
| OSSRH | Orbiter Subsystem Requirements Handbook | In English | |
| OST | Orbiter Support Trolley | In English | |
| OSTA | Office of Space and Terrestrial Applications | In English | → Astronomy |
| OSTDS | Office of Space Tracking and Data Systems | In English | → Data |
| OSTO | Office of Space Transportation Operations | In English | |
| OSTP | Orbiting System Test Plan | In English | |
| OSTS | Office of Space Transportation Systems | In English | |
| OTA | Operational Trajectory Analysis | In English | → Aeronautics, aircraft |
| OTB | Orbiting Tanker Base | In English | |
| OTC | Orbiter Test Conductor | In English | |
| OTD | Orbiter Test Director | In English | |
| OTE | Orbital Transfer Equipment | In English | |
| OTLC | Orbiter Time Line Constraint | In English | |
| OTOS | Orbit-To-Orbit Stage | In English | |
| OTS | Orbital Test System | In English | |
| OTS | Orbital/Orbital Transfer System | In English | |
| OTV | Orbit Test Vehicle | In English | |
| OTV | Orbital Transfer Vehicle | In English | |
| OUT | Orbiter Utility Tray | In English | |
| OV | Orbiter Vehicle | In English | |
| OV | Orbital Vehicle | In English | |
| OVEI | Orbiter Vehicle End Item | In English | |
| OVNI | Objeto Volador No Identificado = OVNI | Objet Volant Non Identifié | In French = OVNI | Objecte Volador No Identificat | In Catalan = НЛО | Неидентифициран летящ обект | In Bulgarian = UFO | Unidentifiziertes Flugobjekt | In German = UFO | Unidentified Flying Object | In English = UFO | Unknown Flying Object | In English = UFO | Uidentificeret flyvende objekt | In Danish = NIFO | Neidentigita Fluganta Objekto | In Esperanto = UFO | Unbekend fleanend objekt | In Frisian = עב"מ | עצם בלתי מזוהה | In Hebrew = OVNI | Oggetto Volante Non Identificato | In Italian = NLO | Neidentificēts lidojošs objekts | In Latvian = UFO | Uidentifisert flygende objekt | In Norwegian = UFO | Uidentifisert flygande objekt | In Nynorsk = NOL | Niezidentyfikowany Obiekt Latający | In Polish = OVNI | Objeto Voador Não Identificado | In Portuguese = OZN | Obiect Zburător Neidentificat | In Romanian = НЛО | Неопознанный летающий объект | In Russian = NLO | Neidentifikovani leteći objekat | In Serbo-Croatian |
In Spanish | |
| OVNI | Oggetto Volante Non Identificato = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Italian | |
| OVNI | Objecte Volador No Identificat = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Catalan | |
| OVNI | Objeto Voador Não Identificado = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Portuguese | |
| OVNI | Objet Volant Non Identifié = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In French | |
| OZN | Obiect Zburător Neidentificat = OVNI, НЛО, UFO, NIFO, עב"מ, NLO, NOL (look above) |
In Romanian | |
| P&E | Propellant and Explosive | In English | → Chemical technology |
| PACRUSS | Passive and Active Control of Space Structures | In English | |
| PACS | Pointing and Attitude Control System | In English | |
| PAD | Propellant Acquisition Device | In English | |
| PADSIM | Precision Attitude Determination Simulation | In English | |
| PALS | Precision Approach and Landing System | In English | → Aeronautics, aircraft |
| PATH | Postflight Attitude and Trajectory History | In English | → Aeronautics, aircraft |
| PCIL | Pilot-Controlled Instrument Landing | In English | → Aeronautics, aircraft |
| PCS | Probability of Crew Safety | In English | → Aeronautics, aircraft |
| PCVL | Pilot-Controlled Visual Landing | In English | → Aeronautics, aircraft |
| PDA | Propellant Drain Area | In English | |
| PDP | Postinsertion Deorbit Preparation | In English | → Astronomy |
| PDS | Pathfinder Demonstration Satellite | In English | |
| PF | Powered Flight | In English | → Aeronautics, aircraft |
| PFC | Preliminary Flight Configuration | In English | → Aeronautics, aircraft |
| PFC | Postflight Checklist | In English | → Aeronautics, aircraft |
| PFC | Performance Flight Certification | In English | → Aeronautics, aircraft |
| PFCF | Payload Flight Control Facility | In English | → Aeronautics, aircraft |
| PFCS | Primary Flight Control System | In English | → Aeronautics, aircraft |
| PFL | Propulsion Field Laboratory | In English | → Research institutes → Aeronautics, aircraft |
| PFP | Powered Flight Program | In English | → Aeronautics, aircraft |
| PFRT | Preliminary Flight Rating Test | In English | → Aeronautics, aircraft |
| PFS | Primary Flight System | In English | → Aeronautics, aircraft |
| PFS | Primary Flight Software | In English | → Software → Aeronautics, aircraft |
| PFT | Postflight Testing | In English | → Aeronautics, aircraft |
| PFTA | Payload Flight Test Article | In English | → Aeronautics, aircraft |
| PhASp | Physics and Astrophysics from Spacelab | In English | → Serial publications, periodicals → Astronomy |
| PHP | Planetary Horizontal Platform | In English | → Astronomy |
| PIO | Pilot-Induced Oscillation | In English | → Aeronautics, aircraft |
| PL | Postlanding | In English | → Aeronautics, aircraft |
| PL | Propellant Loading | In English | |
| PL | Prelaunch | In English | |
| PLA | Parachute Location Aid | In English | → Aeronautics, aircraft |
| PLC | Propellant Loading Console | In English | |
| PLI | Propellant-Level Indicator | In English | |
| PLIM | Propellant Linear Insulation Matrix | In English | |
| PLPS | Propellant Loading and Pressurization System | In English | |
| PLS | Primary Landing Site | In English | → Aeronautics, aircraft |
| PLS | Personnel Launch System | In English | → Aeronautics, aircraft |
| PLS | Propellant Loading System | In English | |
| PLS | Postlanding and Safing | In English | → Aeronautics, aircraft |
| PLSL | Propellants and Life Support Laboratory | In English | → Research institutes |
| PLSR | Postlaunch Service Review | In English | |
| PLV | Postlanding Ventilation | In English | → Aeronautics, aircraft |
| PLV | Postlanding Valve | In English | → Aeronautics, aircraft |
| PLVC | Postlanding Vent Control | In English | → Aeronautics, aircraft |
| PMALS | Preliminary Miniature Air-Launched System | In English | → Aeronautics, aircraft |
| PMC | Permanently Manned Capability | In English | |
| PMD | Propellant Management Device | In English | |
| PMM | Planetary Mission Module | In English | |
| PMP | Prelaunch Monitor Program | In English | → Human-computer interaction |
| PMV | Permanent Manned Vehicle | In English | |
| POD | Precision Orbit Determination | In English | |
| PODTG | Precision Orbit Determination Task Group | In English | |
| POE | Pilot Operational Equipment | In English | → Aeronautics, aircraft |
| POEM | Polar Orbiting Earth Mission | In English | → Astronomy → Earth sciences |
| POGO | Polar Orbiting Geophysical Observatory | In English | → Geophysics |
| POGS | Polar-Orbiting Geomagnetic Survey | In English | → Geophysics |
| POP | Preflight Operations Procedure | In English | → Aeronautics, aircraft |
| POP | Prelaunch Operations Plan | In English | → Aeronautics, aircraft |
| POP | Perpendicular to Orbit Plane | In English | |
| POP | Polar-Orbiting Platform | In English | |
| POST | Program to Ootimize Simulated Trajectories | In English | → Aeronautics, aircraft |
| POWG | Payload Orbital Working Group | In English | |
| PPS | Partial-Pressure Suit | In English | |
| PQGS | Propellant Quantity Gauging System | In English | |
| PrAA | Progress in Astronautics and Aeronautics | In English | → Serial publications, periodicals → Aeronautics, aircraft |
| PRB | Parachute Refurbishment Building | In English | → Aeronautics, aircraft |
| PRM | Posigrade Rocket Motor | In English | |
| PRR | Preflight Readiness Review | In English | → Aeronautics, aircraft |
| PRTLS | Powered Return To Launch Site | In English | |
| PS | Parachute System | In English | → Aeronautics, aircraft |
| PSBLS | Permanent Space-Based Logistics System | In English | → Maintenance and logistics |
| PSC | Planetary Spacecraft | In English | |
| PSCL | Propellant Systems Cleaning Laboratory | In English | → Research institutes |
| PSF | Propellant Servicing Facility | In English | |
| PSIG | Propulsion Systems Integration Group | In English | |
| PSM | Propellant Storage Module | In English | |
| PSP | Planetary Scan Probe | In English | |
| PSP | Planetary Scan Platform | In English | |
| PSS | Propellant Supply Subsystem | In English | → Aeronautics, aircraft |
| PSTL | Pressure Model Static and Transient Launch Configuration | In English | |
| PSV | Probability of Vehicle Success | In English | |
| PSV | Planetary Space Vehicle | In English | |
| PTCC | Propulsion Test Control Center | In English | |
| PTCS | Propellant Tanking Computer System | In English | |
| PTV | Pathfinder Test Vehicle | In English | |
| PU | Propellant Utilization | In English | |
| PU | Propellant Unit | In English | |
| PUCS | Propellant Utilization Control System | In English | |
| PUGS | Propellant Utilization and Gauging System | In English | |
| PUV | Propellant Utilization Valve | In English | |
| PVA | Preburner Valve Actuator | In English | |
| PVA | Propellant Valve Actuator | In English | |
| PVDS | Propellant Vent and Drain System | In English | |
| PVO | Pioneer Venus Orbiter | In English | → Astronomy |
| PVT | Pyrotechnic Verification Test | In English | |
| PVT | Preflight Verification Test | In English | → Aeronautics, aircraft |
| QMS | Qualification Model Spacecraft | In English | |
| QRSL | Quick-Reaction Space Laboratory | In English | → Research institutes |
| QTV | Qualification Test Vehicle | In English | |
| RAE | Royal Aerospace Establishment | In English | → Aeronautics, aircraft |
| RAI | Radar Altimeter Indicator | In English | → Aeronautics, aircraft |
| RALPH | Reduction and Acquisition Of Lunar Pulse Heights | In English | → Astronomy |
| RALT | Radar Altimeter | In English | → Aeronautics, aircraft |
| RAPCON | Radar Approach and Control | In English | → Aeronautics, aircraft |
| RATO | Rocket-Assisted Takeoff | In English | |
| RCS | Reentry Control System | In English | |
| RDS | Rocketdyne Digital Simulator | In English | |
| REA | Rocket Engine Assembly | In English | |
| REAM | Rocket Engine Assembly Module | In English | |
| REM | Rocket Engine Module | In English | |
| RFHA | Reusable Flight Hardware Authorization | In English | → Hardware → Aeronautics, aircraft |
| RIMSS | Rockwell International Modular Satellite System | In English | |
| RISEC | Rockwell International Shuttle Equipment Cradle | In English | |
| RJ/EC | Reaction Jet/Engine Control | In English | → Aeronautics, aircraft |
| RJC | Reaction Jet Control | In English | → Aeronautics, aircraft |
| RJD | Reaction Jet Device | In English | → Aeronautics, aircraft |
| RJD | Reaction Jet Driver | In English | → Aeronautics, aircraft |
| RJDA | Reaction Jet Driver Aft | In English | → Aeronautics, aircraft |
| RJDF | Reaction Jet Driver Forward | In English | → Aeronautics, aircraft |
| RJOD | Reaction Jet/OMS Driver | In English | → Aeronautics, aircraft |
| RKA | Rossiskoye Kosmicheskoye Agentsvo | In Russian | |
| RM | Rendezvous Maneuver | In English | → Aeronautics, aircraft |
| ROCES | Ranger Orbiter Crew Escape System | In English | |
| ROEU | Remotely Operated Electrical Umbilical | In English | |
| RORSAT | Radar Ocean Reconnaissance Satellite | In English | → Marine research, oceanography |
| ROSA | Romanian Space Agency | In English | → Astronomy |
| ROSAT | ROentgen SATellite | In English | → Astronomy |
| ROTV | Returnable Orbital Transfer Vehicle | In English | |
| RP | Rocket Propellant | In English | |
| RPL | Rocket Propulsion Laboratory | In English | → Research institutes |
| RR | Rendezvous Radar | In English | → Aeronautics, aircraft |
| RRDA | Rendezvous Radar Deployment Actuator | In English | → Aeronautics, aircraft |
| RREA | Rendezvous Radar Electronics Assembly | In English | → Electronics |
| RREU | Rendezvous Radar Electronics Unit | In English | → Electronics |
| RRS | Retrorocket System | In English | |
| RRT | Rendezvous Radar Transducer | In English | |
| RRT | Rendezvous Radar Transfer | In English | |
| RRT | Rendezvous Radar Transponder | In English | |
| RSLS | Redundant Set Launch Sequence | In English | |
| RSO | Resident Space Object | In English | → Astronomy |
| RSOC | Rockwell Space Operations Company | In English | |
| RSRB | Redesigned Solid Rocket Booster | In English | |
| RSRM | Redesigned Solid Rocket Motor | In English | |
| RSSPO | Resident Space Shuttle Project Office | In English | |
| RTF | Return To Flight | In English | → Aeronautics, aircraft |
| RTFSS | Real-Time Flight Safety Software | In English | → Software → Aeronautics, aircraft |
| RTLS | Return To Launch Site | In English | → Aeronautics, aircraft |
| RV | Reentry Vehicle | In English | |
| RVAO | Reentry Vehicle Associated Object | In English | |
| S&MST | Space and Missile System Test | In English | → Military engineering |
| S&SED | Satellite and Space Electronics Division | In English | → Electronics |
| SAAS | Shuttle Aerospace Actuator Simulator | In English | |
| SAB | Satellite Assembly Building | In English | |
| SAB | Shuttle Assembly Building | In English | |
| SAB | Spacecraft Assembly Building | In English | |
| SABIR | Space-Based Interceptor | In English | → Military engineering |
| SAC | Space Applications Corporation | In English | |
| SAD | Spacecraft Attitude Display | In English | |
| SAD | Shuttle Authorized Document | In English | |
| SAEF | Spacecraft Assembly and Encapsulation Facility | In English | → Mechanical engineering |
| SAF | Spacecraft Assembly Facility | In English |