| O&C | operations and checkout |
| O&C | operations and control |
| O&FS | operations and flight support |
| O&M | operations and maintenance |
| O&P | operations and procedures |
| O&R | overhaul and repair |
| O&S | operational and support |
| O&S | operations and support |
| O/B | on board |
| O/B | operational base |
| O/C | operations critical |
| O/D | on dock |
| O/D | outside diameter |
| O/F | oxidizer-to-fuel ratio |
| O/L | overload |
| O/L-RC | overload reverse current |
| O/R | outside radius |
| O/R | oxygen relief |
| O/V | overvoltage |
| O/V-U/V | overvoltage/undervoltage |
| OA | Office of Applications |
| OA | omnidirectional antenna |
| OA | operational aft |
| OA | operational instrumentation MDM aft |
| OA | orbit adjust (telemetry) |
| OA | orbiter assembly |
| OA | output axis |
| OA | overall |
| OAA | ORU alternative analysis |
| OAA | orbiter access arm |
| OAA | orbiter alternate airfield |
| OAB | Ordnance and Assembly Building |
| OAFD | orbiter aft flight deck |
| OAFTO | Orbiter Atmospheric Flight Test Office |
| OAHTS | orbiter avionics hardware tracking system |
| OAL | overall level |
| OALC | Ogden Air Logistics Center |
| OAME | orbital attitude and maneuvering electronics |
| OAMP | Optical Airborne Measurements Program |
| OAMS | orbital attitude and maneuvering system |
| OAO | orbital astronomical observatory |
| OAR | off-axis rejection |
| OARE | Orbital Acceleration Research Experiment |
| OARME | Oxygen Atom Reaction Materials Experiment |
| OARS | Orbiter Avionics Radiation Specification |
| OAS | office automation system |
| OAS | optical assembly simulator |
| OAS | orbiter aeroflight simulator |
| OAS | orbiter atmospheric simulator |
| OAS | orbiter avionics simulator |
| OAS | orbiter avionics system |
| OASCB | Orbiter Avionics Software Control Board |
| OASIS | Orbit Avionics Software Integration Study (IBM's) |
| OASIS | oceanic and atmospheric scientific information system |
| OASIS | orbiter experiment autonomous supporting instrumentation |
| OASM | Office of Aerospace Medicine (NASA) |
| OASPL | overall sound pressure level |
| OAST | Office of Aeronautics and Space Technology |
| OAT | operational acceptance test |
| OAT | overall test |
| OATS | orbiter avionics tracking system |
| OB | on board |
| OB | operational base |
| OB | outboard |
| OBC | on-board checkout |
| OBC | on-board computer |
| OBCO | on-board checkout |
| OBCP | on-board computer program |
| OBCS | on-board checkout subsystem |
| OBDU | on-board diagnostic unit |
| OBS | operational bioinstrumentation system |
| OBS | operational biomed sensor |
| OBS | operational biomedical system |
| OBV | oxidizer bleed valve |
| OC | on center |
| OC | on condition |
| OC | open circuit |
| OC | orbital check |
| OC | over center |
| OC | overcurrent |
| OCA | orbiter capability analysis |
| OCA | orbiter capability assessment |
| OCAC | orbiter cabin air cleaner |
| OCALC | Oklahoma City Air Logistics Center |
| OCB | operational configuration baseline |
| OCC | Office of Contract Compliance |
| OCC | Operations Control Center |
| OCCP | orbit command computer program |
| OCCS | operator control console subsystem |
| OCD | operational concept document |
| OCD | operations concept documentation |
| OCDR | orbiter critical design review |
| OCDU | optics coupling data unit (G&N) |
| OCE | Ocean Color Experiment |
| OCF | on-board computational facility |
| OCF | orbiter computational facilities |
| OCH | orbiter common hardware |
| OCI | organizational conflict of interest |
| OCM | optical countermeasure |
| OCN | operation control number |
| OCN | order change number |
| OCN | order control number |
| OCO | OMS cutoff |
| OCO | open-close-open |
| OCP | Office of Commercial Programs |
| OCP | operations checkout procedure |
| OCP | output control pulse |
| OCR | operational capability readiness |
| OCR | operational concept review |
| OCR | optical character reader |
| OCR | optical character recognition |
| OCS | on-board checkout system |
| OCS | operational control segment |
| OCU | ordnance control unit |
| OD | observational data (telemetry) |
| OD | operational downlink |
| OD | operations directive |
| OD | operations director |
| OD | outside diameter |
| OD | oxygen drain |
| OD&E | operational demonstration and evaluation |
| ODA | optical diagnostic assembly |
| ODB | operational data base |
| ODB | operational data book |
| ODC | other direct costs |
| ODCDR | orbiter delta CDR |
| ODDL | on-board digital data load |
| ODDP | object-dependent data processor |
| ODDS | operational data delivery services |
| ODDTE | Office of the Director, Defense Test and Evaluation |
| ODE | operational demonstration and evaluation |
| ODES | Optical Discrimination Evaluation Study |
| ODF | orbit determination facility |
| ODF | output data formatter |
| ODIN | orbital design integration system |
| ODM | orbiter disconnect mechanism |
| ODOP | offset Doppler (tracking system) |
| ODP | operational display procedure |
| ODR | output data redundancy |
| ODRAN | operational drawing revision advance notice |
| ODRC | Orbiter Data Reduction Center |
| ODU | output display unit |
| OEAS | orbital emergency arresting system |
| OEC | other early capability |
| OECO | outboard engine cutoff |
| OEM | original equipment manufacturer |
| OEPS | operationally efficient propulsion system |
| OES | orbiter emergency site |
| OESS | orbiter/ET separation system |
| OET | orbiter engineering and test |
| OEX | orbiter experiment |
| OEXP | Office of Exploration |
| OF | operational forward DSC or MDM |
| OF | operational instrumentation MDM forward |
| OF | orbital flight |
| OF | outside face |
| OF | oxygen fill |
| OFCC | Office of Federal Contract Compliance |
| OFCCP | Office of Federal Contract Compliance Programs |
| OFDS | orbiter flight dynamic simulator |
| OFDS | oxygen fluid distribution system |
| OFI | operational flight instrumentation |
| OFK | optical flight kit |
| OFP | operational flight profile |
| OFP | operational flight program |
| OFP | orbiter flight program |
| OFS | orbital flight system |
| OFS | orbiter flight simulator |
| OFS | orbiter flight system |
| OFS | orbiter functional simulator |
| OFT | operational flight test |
| OFT | orbital flight test |
| OFT | orbital flight training |
| OFTDS | orbital flight test data system |
| OFVR | out-of-field-of-view rejection |
| OG | outer gimbal (roll) |
| OG | oxygen gage |
| OGA | outer gimbal angle |
| OGA | outer gimbal axis |
| OGE | operating ground equipment |
| OGMT | orbiter Greenwich mean time |
| OGTM | one-g trainer and mockup |
| OGV | oxygen gage valve |
| OH | overhaul |
| OH | overhead |
| OHA | operating hazard analysis |
| OHA | orbital height adjustment maneuver |
| OHC | optics hand controller |
| OHF | occupational health facility |
| OHGVT | orbital horizontal ground vibration test |
| OI | operating instruction |
| OI | operational increment (software) |
| OI | operational instrumentation |
| OI | operations interface |
| OI | orbiter insertion |
| OI | orbiter instrumentation |
| OIA | Office of Internal Affairs |
| OIA | Office of International Affairs |
| OIA | orbiter interface adapter |
| OIB | Operating Improvement Board |
| OIC | orbital integrated checkout |
| OIDB | OI data base |
| OIE | orbiter integration engineering |
| OII | operations integration instruction |
| OIO | operations integration officer |
| OIR | open item report |
| OIR | operations integration review |
| OIS | Optical Imager Study |
| OIS | operational intercommunication system |
| OIS | orbit injection subsystem |
| OIS | orbit inserting system |
| OIS | orbit insertion subsystem |
| OIS | orbiter insertion system |
| OIS | orbiter instrumentation systems |
| OISAR | optical inverse synthetic-aperture radar |
| OISR | open item status report |
| OISS | open item status subsystem |
| OISTP | Oxygen-Iodine Supersonic Technology Program |
| OIT | orbiter integrated test |
| OIT | orbiter integration test |
| OIT | orbiter interface test |
| OIV | oxidizer isolation valve |
| OIVS | orbiter interface verification set |
| OJT | on-the-job training |
| OL | open loop |
| OL | operational left DSC or MDM |
| OL | overlay |
| OL | overload |
| OLDB | on-line data bank |
| OLERD | orbiter landing emergency rescue data |
| OLF | orbiter lifting frame |
| OLIF | Orbiter Landing Instrumentation Facility |
| OLOW | orbiter lift-off weight |
| OLSA | orbiter/LPS signal adapter |
| OLSP | Orbiter Logistics Support Plan |
| OM | office management |
| OM | operational mid DSC or MDM |
| OM | operations manager |
| OM | optical master |
| OM | outer marker (ILS) |
| OMA | operations maintenance area |
| OMA | operations management application |
| OMA | orbiter maintenance area |
| OMAS | operations management application software |
| OMB | Office of Management and Budget |
| OMBUU | orbiter midbody umbilical unit |
| OMCF | Orbiter Maintenance and Checkout Facility |
| OMCF | operations and maintenance control file |
| OMCS | operations and maintenance communications system |
| OMD | operations and maintenance documentation |
| OMDR | operations and maintenance data record |
| OME | orbital maneuvering engine |
| OME | orbiter main engine |
| OMET | orbiter mission elapsed time |
| OMEWG | Orbiter Maintenance Engineering Working Group |
| OMGA | operations management ground application |
| OMI | operations and maintenance instruction |
| OMIJC | operations and maintenance instruction job card |
| OMISS | operation and maintenance instruction summary sheet |
| OMK | orbiter mission kit |
| OML | orbiter mold line |
| OML | outer mold line |
| OMMH | orbiter maintenance man-hour |
| OMP | operating maintenance plan |
| OMP | operations and maintenance plan |
| OMPR | operational maintainability problem reporting |
| OMPT | observed mass point trajectory |
| OMR | operations and maintenance requirement |
| OMR | operations management room |
| OMR | orbiter management review |
| OMRB | Operating Material Review Board |
| OMRC | operational maintenance requirements catalog |
| OMRF | Orbiter Maintenance and Refurbishment Facility |
| OMRF | Orbiter Modification and Refurbishment Facility |
| OMRP | operations and maintenance requirements plan |
| OMRS | operations and maintenance requirements and |
| OMRS | operations and maintenance requirements system |
| OMRSCB | Operations and Maintenance Requirements and Control Board |
| OMRSD | operations and maintenance requirements and specifications document |
| OMS | operations management system |
| OMS | orbital maneuvering system (subsystem) |
| OMSP | operational maintenance support plan |
| OMU | optical measuring unit |
| OMV | orbital maneuvering vehicle |
| OMV | oxygen manual valve |
| ONBT | orbiter neutral buoyancy trainer |
| OND | operator need date |
| ONR | Office of Naval Research |
| ONSCOSTS | operation and support costs model |
| OOD | object-oriented data base |
| OOD | object-oriented design |
| OOD | orbiter on dock |
| OODP | out-of-detent pitch |
| OODR | out-of-detent roll |
| OOH | Orbital Operations Handbook |
| OOMM | Organizational Operations and Maintenance Manual |
| OOP | out of position |
| OOR | on-orbit review |
| OOS | on-orbit station |
| OOS | orbit-to-orbit Shuttle |
| OOS | orbit-to-orbit stage |
| OOSD | on-orbit support document |
| OOSD | orbital operations support document |
| OOSDP | on-orbit station distribution panel |
| OOSS | on-orbit support system |
| OOT | out of tolerance |
| OP | operating procedure |
| OP | oxygen purge |
| OP&R | operations planning and requirements |
| OPA | operations planning analysis |
| OPB | oxidizer preburner |
| OPBOV | oxidizer preburner oxidizer valve |
| OPBS | orbiter payload bay simulator |
| OPD | optical path difference |
| OPDAR | optical detection and ranging |
| OPE | operational processing equipment |
| OPE | other project element |
| OPEIU | Office and Professional Employees International Union |
| OPF | Orbiter Processing Facility |
| OPGUID | optimum guidance technique |
| OPI | operations procedure instruction |
| OPI | orbiter payload interrogator |
| OPIDF | operational planning identification file |
| OPIS | orbiter prime item specification |
| OPL | open problem list |
| OPL | orbiter project parts list |
| OPLF | Orbiter Processing and Landing Facility |
| OPM | Operations Procedure Manual |
| OPM | outer planet mission |
| OPO | Orbiter Project Office |
| OPOV | oxidizer preburner oxidizer valve |
| OPP | other physical principles |
| OPPAR | orbiter project parts authorization request |
| OPPG | operating program (DIU) |
| OPPS | operations planning and project support |
| OPR | office of primary responsibility |
| OPR | operations planning review |
| OPR | orbiter payload recorder |
| OPR | oxygen pressure regulator |
| OPRV | oxygen pressure relief valve |
| OPS | operational sequence |
| OPS | orbiter project schedule |
| OPS | oxygen purge system |
| OPSDB | operations data base |
| OPSDBA | operations data base administrator |
| OPSS | orbital propellant storage subsystem |
| OPT | operational pressure transducer |
| OPTB | operational program time base |
| OPWS | orbital payload work station |
| OR | operational right DSC or MDM |
| OR | operations requirement |
| OR | operations review |
| OR | operations room |
| OR | outer roll |
| OR | oxygen relief |
| ORA | operational requirements analysis |
| ORACLES | optical regulator algorithms for the control |
| ORAM | output random access memory |
| ORB | Operations Review Board |
| ORC | operations request card |
| ORCHIS | Oak Ridge computerized hierarchical information system |
| ORCUS | orbital recording capability and update system |
| ORD | operational readiness data |
| ORD | operational ready data |
| ORD | operations requirements document |
| ORD | orbital requirements document |
| ORE | output request element |
| OREO | OMS/RCS engineering officer |
| ORI | operational readiness inspection |
| ORLA | optimum repair level analysis |
| ORP | OFS retransmission processor |
| ORR | Orroval Valley, Australia (STDN) |
| ORR | operational readiness review |
| ORR | operations requirements review |
| ORS | orbital refueling system |
| ORS | orbital reservicing system |
| ORS | orbital resupply system |
| ORSDI | Oak Ridge selective dissemination of information |
| ORT | operational readiness test |
| ORT | orbit readiness test |
| ORU | orbital replaceable unit |
| ORU | orbital replacement unit |
| ORV | orbital research vehicle |
| OS | on-orbit station |
| OS | operating software |
| OS | operating system |
| OS | orbiter CEI specification |
| OSA | operational support area |
| OSC | Operations Support Center |
| OSC | Operations Support Contract |
| OSC | optical signatures code |
| OSCF | Operations Support Computing Facility |
| OSCN | orbiter specification change notice |
| OSCR | orbiter software change request |
| OSCRS | orbital spacecraft consumables resupply system |
| OSD | Office of the Secretary of Defense |
| OSDH | Orbiter System Definition Handbook |
| OSE | operating support equipment |
| OSE | orbital support equipment |
| OSE | orbiter support equipment |
| OSE | other support equipment |
| OSEC | operations security |
| OSES | operation support equipment/software |
| OSF | orbiter simulation facility |
| OSF | ordnance storage facility |
| OSHA | Occupational Safety and Health Act |
| OSHA | Occupational Safety and Health Administration |
| OSHA | operating and support hazard analysis |
| OSI | open system interconnect |
| OSI | open systems interconnection |
| OSID | operating system interface definition |
| OSLM | operations shop or lab manager |
| OSM | on-orbit spares model |
| OSM | operational status monitoring |
| OSM | orbiter service module |
| OSMP | operational support maintenance plan |
| OSO | ocean systems operation |
| OSO | orbiting solar observatory |
| OSOP | orbiter systems operating procedure |
| OSR | operations support room |
| OSR | optical surface reflector |
| OSRBD | operational software reliability benchmark development |
| OSS | Office of Space Sciences |
| OSS | operational SDI system |
| OSS | optics subsystem |
| OSS | orbiting space station |
| OSSA | Office of Space Sciences and Applications |
| OSSIU | orbiter-Space Station interface unit |
| OSSRH | Orbiter Subsystem Requirements Handbook |
| OST | Operations Support Team (GSFC) |
| OST | orbiter support trolley |
| OSTA | Office of Space and Terrestrial Applications |
| OSTDS | Office of Space Tracking and Data Systems |
| OSTF | off-site test facility |
| OSTO | Office of Space Transportation Operations |
| OSTP | orbiting system test plan |
| OSTS | Office of Space Transportation Systems |
| OT | offensive threat |
| OT | operating time |
| OT | operational instrumentation MDM tank |
| OT | operational test |
| OT | operational trajectory |
| OT | optical tracker |
| OT | out temperature |
| OT | overtime |
| OT&E | operational test and evaluation |
| OT&E | optical test and evaluation |
| OTA | operational trajectory analysis |
| OTA | optical telescope assembly |
| OTB | orbiting tanker base |
| OTC | optical test chamber |
| OTC | orbiter test conductor |
| OTD | operational technical documentation |
| OTD | orbiter test director |
| OTDA | Office of Tracking and Data Acquisition |
| OTE | optical test and evaluation |
| OTE | orbital transfer equipment |
| OTEC | Operational Test and Evaluation Center |
| OTF | operational time fraction |
| OTF | optical transfer function |
| OTH | over the horizon (radar) |
| OTH-B | over-the-horizon backscatter |
| OTK | oxidizer tank |
| OTL | ordnance test laboratory |
| OTLC | orbiter time line constraint |
| OTM | output transformation matrix |
| OTO | one time only |
| OTOS | orbit-to-orbit stage |
| OTP | operational test procedure |
| OTP | operations turnaround plan |
| OTR | operating time record |
| OTS | off the shelf |
| OTS | orbital test system |
| OTS | orbital transfer system |
| OTS | orbiter transfer system |
| OTT | optional team targeting |
| OTV | operational television |
| OTV | orbit test vehicle |
| OTV | orbital transfer vehicle |
| OUP | OFS uplink processor |
| OUSDR&E | Office of the Undersecretary of Defense, Engineering |
| OUT | orbiter utility tray |
| OV | orbiter vehicle |
| OV | oxygen vent |
| OVCO | Operational Voice Communication Office |
| OVDS | oxidizer vent drain system |
| OVEI | orbiter vehicle end item |
| OVI | operational validation inspection |
| OW | optical window |
| OW | order wire |
| OWD | one-way Doppler |
| OWDE | one-way Doppler extraction |
| OWF | optimum working frequency |
| Orion | communications satellite for service over the Atlantic Ocean |