TypeFewer LettersMore Letters
Acronym A-train [Afternoon Train satellite constellation](https://en.wikipedia.org/wiki/A-train_%28satellite_constellation%29)
Acronym ABS [Acrylonitrile Butadiene Styrene](https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene), hard plastic
Asia Broadcast Satellite, commsat operator
Acronym ACES [Advanced Cryogenic Evolved Stage](https://en.wikipedia.org/wiki/Advanced_Cryogenic_Evolved_Stage)
[Advanced Crew Escape Suit](https://en.wikipedia.org/wiki/Advanced_Crew_Escape_Suit)
Acronym ACS Attitude Control System
Acronym ACST Australian Central Standard Time (UTC+9.5), Northern Territory and South Australia
Acronym ADCS Attitude Determination and Control System
Acronym ADELINE [Advanced Expendable Launcher with Innovative Engine Economy](https://en.wikipedia.org/wiki/Adeline_\(rocket_stage\)), Airbus Safran's returnable-engine first stage
Acronym ADEPT Adaptive Deployable Entry and Placement Technology carbon-fiber heatshield
Acronym AEB Agencia Espaciale Brasileira
Acronym AFB [Air Force Base](https://en.wikipedia.org/wiki/Military_airbase)
Acronym AFSS Automated Flight Safety System
Acronym AFTS Autonomous Flight Termination System, see FTS
Acronym AGL Above Ground Level
Acronym AHRS Attitude and Heading Reference System
Acronym AIS [Automatic Identification System](https://en.wikipedia.org/wiki/Automatic_Identification_System)
Acronym AIT Assembly, Integration and Testing
Acronym AJR Aerojet Rocketdyne
Acronym AoA Angle of Attack
Acronym AoE Area of Effect
Acronym AOS Acquisition of Signal
Acronym AR Area Ratio (between rocket engine nozzle and bell)
Aerojet Rocketdyne
Acronym AR-1 AR's [RP-1/LOX engine](https://en.wikipedia.org/wiki/Aerojet_Rocketdyne#AR1) proposed to replace RD-180
Acronym ARM Asteroid Redirect Mission
Advanced RISC Machines, embedded processor architecture
Acronym ARMD Aeronautics Research Mission Directorate, NASA
Acronym ASAP Aerospace Safety Advisory Panel, NASA
Arianespace System for Auxiliary Payloads
Acronym ASAT [Anti-Satellite weapon](https://en.wikipedia.org/wiki/Anti-satellite_weapon)
Acronym ASDBC Autonomous Spaceport Drone Bouncy Castle, for soft landings
Acronym ASDS Autonomous Spaceport Drone Ship (landing platform)
Acronym ASIC Application-Specific Integrated Circuit
Acronym ASL [Airbus Safran Launchers](https://en.wikipedia.org/wiki/Airbus_Safran_Launchers), builders of the Ariane 6
Acronym ASS Acronyms Seriously Suck
Acronym ATP Acceptance Test Procedure
Acronym ATV Advanced Technology Vehicle, a launcher for sub-orbital experiments
Acronym ATV [Automated Transfer Vehicle](https://en.wikipedia.org/wiki/Automated_Transfer_Vehicle), ESA cargo craft
Acronym AVI Avionics Operator
Acronym BARGE [Big-Ass Remote Grin Enhancer](https://twitter.com/IridiumBoss/status/864579184483590144) coined by @IridiumBoss, see ASDS
Acronym BCC (Iron/steel) [Body-Centered Cubic](https://en.wikipedia.org/wiki/Allotropes_of_iron) crystalline structure
Backup Control Center, MSFC (for ISS operations if Houston is inoperative)
Acronym BE-3 Blue Engine 3 hydrolox rocket engine, developed by Blue Origin (2015), 490kN
Acronym BE-4 Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN
Acronym BE-4U Blue Engine 4 methalox rocket engine, Blue Origin (2018), vacuum-optimized
Acronym BEAM [Bigelow Expandable Activity Module](https://en.wikipedia.org/wiki/Bigelow_Expandable_Activity_Module)
Acronym BECO Booster Engine Cut-Off
Acronym BEO Beyond Earth Orbit
Acronym BFR Big Falcon Rocket (2017 enshrinkened edition)
Yes, the F stands for something else; no, you're not the first to notice
Acronym BFS Big Falcon Spaceship (see BFR)
Acronym BFT Big Falcon Tanker (see BFS)
Acronym BO Blue Origin (*Bezos Rocketry*)
Acronym BPC BFR/ITS/MCT Planetary Colonizer, 2017 design
Acronym BSS Back-Shell Separation, event during Curiosity EDL
Acronym CAA Crew Access Arm, for transfer of crew on a launchpad
Acronym CAP [Combat Air Patrol](https://en.wikipedia.org/wiki/Combat_air_patrol)
Acronym CARE Crew module Atmospheric Re-entry Experiment
Acronym CBC Common Booster Core
Canadian Broadcasting Corporation
Acronym CBM [Common Berthing Mechanism](https://en.wikipedia.org/wiki/Common_Berthing_Mechanism)
Acronym CC Commercial Crew program
Capsule Communicator (ground support)
Acronym CCAFS Cape Canaveral Air Force Station
Acronym CCAM Collision and Contaminance Avoidance Maneuver
Acronym CCDEV [Commercial Crew DEVelopment](https://en.wikipedia.org/wiki/Commercial_Crew_Development)
Acronym CCiCap [Commercial Crew Integrated Capability](https://en.wikipedia.org/wiki/Commercial_Crew_Development#Commercial_Crew_integrated_Capability)
Acronym CCtCap [Commercial Crew Transportation Capability](https://en.wikipedia.org/wiki/Commercial_Crew_Development#Commercial_Crew_Transportation_Capability_.28CCtCap.29)
Acronym Cd [Coefficient of Drag](https://en.wikipedia.org/wiki/Drag_coefficient)
Acronym CDR Critical Design Review
(As 'Cdr') Commander
Acronym CF Carbon Fiber (Carbon Fibre) composite material
CompactFlash memory storage for digital cameras
Acronym CFD Computational Fluid Dynamics
Acronym CLCDr Central Launch Command Director
Acronym CME Coronal Mass Ejection
Acronym CMG Control Moment Gyroscope, RCS for the Station
Acronym CMP Command Module Pilot (especially for Apollo)
Acronym CNC Computerized Numerical Control, for precise machining or measuring
Acronym CNES Centre National d'Etudes Spatiales, space agency of France
Acronym CNSA Chinese National Space Administration
Acronym CoG Center of Gravity (see CoM)
Acronym CoM Center of Mass
Acronym CONUS [Contiguous United States](https://en.wikipedia.org/wiki/Contiguous_United_States)
Acronym COPV [Composite Overwrapped Pressure Vessel](https://en.wikipedia.org/wiki/Composite_overwrapped_pressure_vessel)
Acronym COSPAR Committee for Space Research
Acronym COTS [Commercial Orbital Transportation Services contract](https://www.nasa.gov/cots)
Commercial/Off The Shelf
Acronym CREAM Cosmic Radiation Effects and Activation Monitor, Station experiment slated for CRS-12
Acronym CRS [Commercial Resupply Services contract with NASA](http://www.nasa.gov/mission_pages/station/structure/launch/)
Acronym CRS2 Commercial Resupply Services, second round contract; expected to start 2019
Acronym CRYOTE Cryogenic Orbital Test Environment
Acronym CSA Canadian Space Agency
Acronym CST (Boeing) Crew Space Transportation capsules
Central Standard Time (UTC-6)
Acronym CUCU COTS UHF Communications Unit (ISS-to-Dragon radio)
Acronym C^(3)PO Commercial Crew and Cargo Program Office, NASA
Acronym DCS Decompression Sickness
*Digital Combat Simulator*, the flight simulator
Acronym DCSS Delta Cryogenic Second Stage
Acronym DIVH Delta IV Heavy
Acronym DLR Deutsches Zentrum fuer Luft und Raumfahrt (German Aerospace Center), Cologne
Acronym DoD US Department of Defense
Acronym DPL Downrange Propulsive Landing (on an ocean barge/ASDS)
Acronym DRL Downrange Landing
Acronym DRO [Distant Retrograde Orbit](http://ccar.colorado.edu/asen5050/projects/projects_2013/Johnson_Kirstyn/finalorbit.html)
Acronym DRRPL Down-Range Retro-Propulsive Landing
Acronym DRRRPL Down-Range Re-entry and Retro-Propulsive Landing
Acronym DRRRRPL Down-Range Retrograde, Re-entry, and Retro-Propulsive Landing maneuver
Acronym DRRRRRRPL Down-Range Retrograde RCS Rotation, Re-entry, and Retro-Propulsive Landing maneuver
Acronym DSG NASA [Deep Space Gateway](https://www.nasa.gov/feature/deep-space-gateway-to-open-opportunities-for-distant-destinations), proposed for lunar orbit
Acronym DSN Deep Space Network
Acronym DST NASA Deep Space Transport operating from the proposed DSG
Acronym DTN Delay/Disruption Tolerant Networking
Acronym DVIC Digital Voice Inter-Communications subsystem between consoles in launch/mission control
Acronym EAR Export Administration Regulations, covering technologies that are not solely military
Acronym ECLSS Environment Control and Life Support System
Acronym EDAC Error Detection And Correction in integrated circuits
Acronym EDL Entry/Descent/Landing
Acronym EDRS European Data Relay System
Acronym EELV [Evolved Expendable Launch Vehicle](https://en.wikipedia.org/wiki/Evolved_Expendable_Launch_Vehicle)
Acronym EGSE Electrical Ground Support Equipment
Acronym ELC EELV Launch Capability contract ("assured access to space")
Acronym ELDRS Enhanced Low Dose Rate Sensitivity (lower-intensity radiation causing more damage)
Acronym ELE [Extinction-Level Event](http://www.imdb.com/title/tt0120647/)
Acronym ELT Extremely Large Telescope, under construction in Chile
Acronym EM-1 [Exploration Mission 1](https://en.wikipedia.org/wiki/Exploration_Mission_1), first flight of SLS
Acronym EML1 Earth-Moon Lagrange point 1
Acronym EOI Earth Orbital Insertion maneuver
Acronym EOL End Of Life
Acronym ERV Earth Return Vehicle
Acronym ESA European Space Agency
Acronym ESO [European Southern Observatory](https://en.wikipedia.org/wiki/European_Southern_Observatory), builders of the VLT and EELT
Acronym ESPA EELV Secondary Payload Adapter standard for attaching to a second stage
Acronym ETLA Extended Three Letter Acronym (4+ letters)
Acronym ETO Earth-To-Orbit transport of materials
Acronym ETOV Earth To Orbit Vehicle (common parlance: "rocket")
Acronym EUS Exploration Upper Stage
Acronym EVA Extra-Vehicular Activity
Acronym EVS Extra-Vehicular Suit (see EVA)
Acronym F1 Rocketdyne-developed rocket engine used for Saturn V
SpaceX Falcon 1 (obsolete medium-lift vehicle)
Acronym F9EFT Falcon 9 v1.2.1, Even Fuller Thrust (uprated, 2016)
Acronym F9FT Falcon 9 Full Thrust *or* Upgraded Falcon 9 *or* v1.2
Acronym F9R Falcon 9 Reusable, test vehicles for development of landing technology
Acronym FAA Federal Aviation Administration
Acronym FAA-AST Federal Aviation Administration [Administrator for Space Transportation](http://www.faa.gov/about/office_org/headquarters_offices/ast/)
Acronym FAP Fairing Acoustic Protection
Acronym FCC Federal Communications Commission
(Iron/steel) [Face-Centered Cubic](https://en.wikipedia.org/wiki/Allotropes_of_iron) crystalline structure
Acronym FFSC Full-Flow Staged Combustion
Acronym FFSCC Full Flow Staged Combustion Cycle
Acronym FFSS Firefly Space Systems
Acronym FISO [Future In-Space Operations teleconferences](http://spirit.as.utexas.edu/%7Efiso/archivelist.htm)
Acronym FLEA Four Letter Extended Acronym (see ETLA)
Acronym FLP First Launch Pad at Satish Dhawan Space Centre, operational since 1990s
Acronym FLW The Following (as found on NOTAMs)
Acronym FMEA [Failure-Mode-and-Effects Analysis](https://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis)
Acronym FOD [Foreign Object Damage](https://en.wikipedia.org/wiki/Foreign_object_damage) / Debris
Acronym FoS Factor of Safety for design of high-stress components (see COPV)
Acronym FRAM Flight Releasable Attachment Mechanism
Acronym FRL Fire-Retardant Latex (White rocket paint)
Acronym FRSC Fuel-Rich Staged Combustion
Acronym FSW [Friction-Stir Welding](https://en.wikipedia.org/wiki/Friction_stir_welding)
Acronym FTBA "Flip This ~~Bi-~~ Booster Around" boostback burn, part of first-stage landing procedure
Acronym FTS Flight Termination System
Acronym G-LOC G-force-induced Loss Of Consciousness
Acronym GCR Galactic Cosmic Rays, incident from outside the star system
Acronym GEO Geostationary Earth Orbit (35786km)
Acronym GeV Giga-Electron-Volts, measure of energy for particles
Acronym GNC Guidance/Navigation/Control
Acronym GOX Gaseous Oxygen (contrast LOX)
Acronym GPC General-Purpose Computer (the [IBM AP-101](https://en.wikipedia.org/wiki/IBM_AP-101) on Shuttle)
Acronym GRB Gamma-Ray Burst
Acronym GSE Ground Support Equipment
Acronym GSFC Goddard Space Flight Center, Maryland
Acronym GSLV Geosynchronous Satellite Launch Vehicle
Acronym GSLV (India's) Geostationary Launch Vehicle
Acronym GSO Geosynchronous Orbit (any Earth orbit with a 24-hour period)
Acronym GTE Ground Test Equipment (as opposed to Ground Support Equipment, which would support a launch)
Acronym GTO [Geosynchronous Transfer Orbit](http://www.planetary.org/blogs/jason-davis/20140116-how-to-get-a-satellite-to-gto.html)
Acronym GTO-1500 Geosynchronous Transfer Orbit (185 x 35786km, 0 inclination), requires 1500m/s to reach GEO
Acronym GTO-1800 Geosynchronous Transfer Orbit (185 x 35786km, 27-degree inclination), requires 1800m/s to reach GEO
Acronym H1 First half of the year/month
Acronym H2 Molecular hydrogen
Second half of the year/month
Acronym HASC (US) House (of Representatives) Armed Services Committee
Acronym HDEV High Definition Earth Viewing experiment, fitted to ISS
Acronym HEEO Highly Elliptical Earth Orbit
Acronym HEMO Highly Elliptical Mars Orbit
Acronym HEO High Earth Orbit (above 35780km)
Human Exploration and Operations (see HEOMD)
Acronym HEOMD Human Exploration and Operations Mission Directorate, NASA
Acronym HERA [Human Exploration Research Analog](https://www.nasa.gov/analogs/hera)
Acronym HEU Highly-Enriched Uranium, fissile material with a high percentage of U-235 ("boom stuff")
Acronym HIAD Hypersonic Inflatable Aerodynamic Decelerator (derived from LDSD)
Acronym HIF Horizontal Integration Facility
Acronym HIL Hardware in the Loop, see HITL
Acronym HITL Hardware in the Loop
Human in the Loop
Acronym HLC-39A **Historic** Launch Complex 39A, Kennedy (Saturn V, Shuttle, SpaceX F9/Heavy)
Acronym HLLV Heavy Lift Launch Vehicle (20-50 tons to LEO)
Acronym HLV Heavy Lift Launch Vehicle (20-50 tons to LEO)
Acronym HPFTP High Pressure Fuel Turbopump
Acronym HPOTP High Pressure Oxidiser Turbopump
Acronym HPTP High Pressure Turbopump
Acronym HSF Human Space Flight
Acronym HST Hubble Space Telescope
Acronym HTPB Hydroxyl-terminated polybutadiene, solid propellant
Acronym HTS Horizontal Test Stand
Acronym HUD Head(s)-Up Display, often implemented as a projection
Acronym IAC International Astronautical Congress, annual meeting of IAF members
Acronym IAF [International Astronautical Federation](http://www.iafastro.org/)
Indian Air Force
Acronym IANARS I Am Not A Rocket Scientist, but...
Acronym ICBM Intercontinental Ballistic Missile
Acronym ICPS Interim Cryogenic Propulsion Stage
Acronym ICT Interplanetary Colonial Transport (see ITS)
Acronym IDA [International Docking Adapter](https://en.wikipedia.org/wiki/International_Docking_Adapter)
Acronym IDSN Indian Deep Space Network
Acronym IDSS [International Docking System Standard](https://en.wikipedia.org/wiki/International_Docking_System_Standard)
Acronym IFR [Instrument Flight Rules](https://en.wikipedia.org/wiki/Instrument_flight_rules)
Acronym IIP Instantaneous Impact Point (where a payload would land if Stage 2 failed)
Acronym ILC Initial Launch Capability
Acronym ILS [International Launch Services](https://en.wikipedia.org/wiki/International_Launch_Services)
[Instrument Landing System](https://en.wikipedia.org/wiki/Instrument_landing_system)
Acronym IM Initial Mass deliverable to a given orbit, without accounting for fuel
Acronym IMGTO Initial Mass deliverable to GTO, see IM
Acronym IMLEO Initial Mass deliverable to LEO, see IM
Acronym IMRS International Mars Research Station (proposed by Blue Mars)
Acronym IMU Inertial Measurement Unit
Acronym INS [Inertial Navigation System](https://en.wikipedia.org/wiki/Inertial_navigation_system)
Acronym IRFNA Inhibited Red Fuming Nitric Acid, mixed with hydrogen fluoride for stability
Acronym IRNSS Indian Regional Navigation Satellite System
Acronym ISAP In-Situ Air Production
Acronym ISC Institutional Services Contract, under which a private company provides support services to NASA/USAF
Acronym ISECG International Space Exploration Coordinating Group
Acronym ISEP In-Situ Electricity/Energy Production
Acronym ISFP In-Situ Food Production
Acronym ISL Inter-Satellite Link communication between satellites in orbit
Acronym Isp Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)
Acronym ISPP In-Situ Propellant Production
Acronym ISRO Indian Space Research Organisation
Acronym ISRU [In-Situ Resource Utilization](https://en.wikipedia.org/wiki/In_situ_resource_utilization)
Acronym ISSP [International Space Station Program](https://en.wikipedia.org/wiki/International_Space_Station_program), the legal framework for ISS maintenance
Acronym ISTRAC ISRO Telemetry, Tracking and Command Network
Acronym ISW (US) Institute for the Study of War
Acronym ISWP In-Situ Water Production
Acronym ITAR (US) International Traffic in Arms Regulations
Acronym ITN Interplanetary Transport Network
Acronym ITS Interplanetary Transport System (2016 oversized edition) (see MCT)
[Integrated Truss Structure](https://en.wikipedia.org/wiki/Integrated_Truss_Structure)
Acronym ITU International Telecommunications Union, responsible for GEO slot allocation
Acronym IVA Intra-Vehicular Activity
Acronym IVF [Integrated Vehicle Fluids ^PDF](http://www.ulalaunch.com/uploads/docs/Published_Papers/Supporting_Technologies/Space_Access_Society_2012.pdf)
Acronym IVS Intra-Vehicular Suit (see IVA)
Acronym JAXA Japan Aerospace eXploration Agency
Acronym JCSAT Japan Communications Satellite series, by JSAT Corp
Acronym JOI Jovian Orbital Insertion maneuver
Acronym JPADS Air Force [Joint Precision Air Drop System](https://en.wikipedia.org/wiki/Joint_Precision_Airdrop_System), possible parafoils for fairing recovery
Acronym JPL Jet Propulsion Lab, California
Acronym JRTI Just Read The Instructions, Pacific landing ~~barge~~ ship
Acronym JSC Johnson Space Center, Houston
Acronym JWST James Webb infra-red Space Telescope
Acronym KARI Korean Aerospace Research Institute
Acronym KOS Keep Out Sphere, 200m radius from ISS
Kerbal Operating System, the KSP in-game rocket OS
Acronym KSC Kennedy Space Center, Florida
Acronym KSP *Kerbal Space Program*, the rocketry simulator
Acronym L1 [Lagrange Point](https://en.wikipedia.org/wiki/Lagrangian_point) 1 of a two-body system, between the bodies
Acronym L2 Paywalled section of the NasaSpaceFlight forum
[Lagrange Point](https://en.wikipedia.org/wiki/Lagrangian_point) 2 of a two-body system, beyond the smaller body ([Sixty Symbols](https://www.youtube.com/watch?v=mxpVbU5FH0s) video explanation)
Acronym L3 [Lagrange Point](https://en.wikipedia.org/wiki/Lagrangian_point) 3 of a two-body system, opposite L2
Acronym L4 "Trojan" [Lagrange Point](https://en.wikipedia.org/wiki/Lagrangian_point) 4 of a two-body system, 60 degrees ahead of the smaller body
Acronym L5 "Trojan" [Lagrange Point](https://en.wikipedia.org/wiki/Lagrangian_point) 5 of a two-body system, 60 degrees behind the smaller body
Acronym LAS Launch Abort System
Acronym LC-13 Launch Complex 13, Canaveral (SpaceX Landing Zone 1)
Acronym LC-39A Launch Complex 39A, Kennedy (SpaceX F9/Heavy)
Acronym LCC Launch Control Center
Acronym LCH4 Liquid Methane
Acronym LDSD Low-Density Supersonic Decelerator test vehicle
Acronym LEM (Apollo) [Lunar Excursion Module](https://en.wikipedia.org/wiki/Apollo_Lunar_Module) (also Lunar Module)
Acronym LEO Low Earth Orbit (180-2000km)
Law Enforcement Officer (most often mentioned during transport operations)
Acronym LES Launch Escape System
Acronym LEU Low-Enriched Uranium, fissile material that's not explosively so
Acronym LH2 Liquid Hydrogen
Acronym LIDAR [Light Detection and Ranging](https://en.wikipedia.org/wiki/Lidar)
Acronym LIGO Laser Interferometer Gravitational-wave Observatory
Acronym LLCC (SpaceX) Launch and Landing Control Center, Port Canaveral
Acronym LLO Low Lunar Orbit (below 100km)
Acronym LMO Low Mars Orbit
Acronym LMP (Apollo) Lunar Module Pilot
Acronym LN2 Liquid Nitrogen
Acronym LNG Liquefied Natural Gas
Acronym LO2 Liquid Oxygen (more commonly LOX)
Acronym LOC Loss of Crew
Acronym LOLI Limited-Operational-Life Item (lasts a number of cycles before needing replacement)
Acronym LOM Loss of Mission
Acronym LOS Loss of Signal | |Line of Sight
Acronym LOV Loss Of Vehicle
Acronym LOX Liquid Oxygen
Acronym LPFTP Low Pressure Fuel Turbopump
Acronym LPG Liquified Petroleum Gas
[Liquified Pigeon Guts](https://www.reddit.com/r/SpaceXLounge/comments/6to7zk/how_many_pigeons_can_a_falcon_9_launch_into_leo/dlmmcg3/)
Acronym LPOTP Low Pressure Oxidiser Turbopump
Acronym LPSC Liquid Propulsion Systems Centre
Acronym LPTP Low Pressure Turbopump
Acronym LRR Launch Readiness Review
Acronym LV Launch Vehicle (common parlance: "rocket"), see ETOV
Acronym LZ Landing Zone
Acronym LZ-1 Landing Zone 1, Cape Canaveral (see LC-13)
Acronym MAF Michoud Assembly Facility, Louisiana
Acronym MAV *Mars Ascent Vehicle* ([possibly fictional](https://en.wikipedia.org/wiki/The_Martian_\(Weir_novel\)))
Acronym MaxQ Maximum aerodynamic pressure
Acronym MBA ~~Moonba-~~ Mars Base Alpha
Acronym MCC Mission Control Center
Mars Colour Camera
Acronym MCP Mechanical Counterpressure spacesuit
Acronym MCT Mars Colonial Transporter (see ITS)
Acronym MDA [Missile Defense Agency](https://en.wikipedia.org/wiki/Missile_Defense_Agency)
[MacDonald, Dettwiler and Associates](https://en.wikipedia.org/wiki/MacDonald,_Dettwiler_and_Associates), owner of SSL, builder of Canadarm
Acronym MECO Main Engine Cut-Off
[MainEngineCutOff](https://mainenginecutoff.com/) podcast
Acronym MegaROSA Multi-element Roll-Out Solar Array
Acronym MENA Middle East and North Africa, Morocco to Iran
Acronym MEO Medium Earth Orbit (2000-35780km)
Acronym MEOP Maximum Expected Operating Pressure
Acronym MER Mars Exploration Rover (Spirit/Opportunity)
Acronym MES Main Engine Start
Acronym MET [Mission Elapsed Time](https://en.wikipedia.org/wiki/Mission_Elapsed_Time)
Acronym MeV Mega-Electron-Volts, measure of energy for particles
Acronym MFR Medium ~~Fu-~~ Falcon Rocket (Falcon 9/Heavy), contrast BFR
Manipulator Foot Restraint, support equipment for Hubble servicing
Acronym MGS Mars Global Surveyor satellite
Acronym MHI Mitsubishi Heavy Industries, builder of the H-IIA
Acronym MLLV Medium Lift Launch Vehicle (2-20 tons to LEO)
Acronym MLP Mobile Launcher Platform
Acronym MLV Medium Lift Launch Vehicle (2-20 tons to LEO)
Acronym MMH Monomethylhydrazine, liquid hypergolic propellant
Acronym MMH Mono-Methyl Hydrazine, HCH3N=NH2; part of NTO/MMH hypergolic mix
Acronym MMOD Micro-Meteoroids and Orbital Debris
Acronym MMSEV [Multi-Mission Space Exploration Vehicle](https://www.nasa.gov/exploration/technology/space_exploration_vehicle/index.html)
Acronym MMU [Manned Maneuvering Unit](https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit), untethered spacesuit propulsion equipment
Acronym MOI Mars Orbital Insertion maneuver
Acronym MOM Mars Orbiter Mission
Acronym MON Mixed Oxides of Nitrogen
Acronym MPLM [Multi-Purpose Logistics Module](https://en.wikipedia.org/wiki/Multi-Purpose_Logistics_Module) formerly used to supply ISS
Acronym MRO Mars Reconnaisance Orbiter
Acronym MSFC Marshall Space Flight Center, Alabama
Acronym MSL Mars Science Laboratory (Curiosity)
Acronym mT ~~Milli-~~ *Metric* Tonnes
Acronym NA New Armstrong, super-heavy lifter proposed by Blue Origin
Acronym NAC NASA Advisory Council
Acronym NAS National Airspace System
[Naval Air Station](https://en.wikipedia.org/wiki/Naval_air_station)
Acronym NAVIC Navigation with Indian Constellation
Acronym NDA Non-Disclosure Agreement
Acronym NDE Non-Destructive Examination
Acronym NdGT Neil deGrasse Tyson
Acronym NDS [NASA Docking System](https://en.wikipedia.org/wiki/NASA_Docking_System), implementation of the international standard
Acronym NDT Non-Destructive Testing
Acronym NEO Near-Earth Object
Acronym NERVA Nuclear Engine for Rocket Vehicle Application (proposed engine design)
Acronym NET No Earlier Than
Acronym NEV Nuclear Electric Vehicle propulsion
Acronym NG New Glenn, two/three-stage orbital vehicle by Blue Origin
Natural Gas (as opposed to pure methane)
Northrop Grumman, aerospace manufacturer
Acronym NGLLC Northrop-Grumman [Lunar Lander Challenge](https://en.wikipedia.org/wiki/Lunar_Lander_Challenge), 2006-09
Acronym NGSO Non-Geostationary Orbit
Acronym NOAA National Oceanic and Atmospheric Administration, responsible for US ~~generation~~ monitoring of the climate
Acronym NORAD North American Aerospace Defense command
Acronym NOTAM [Notice to Airmen](https://en.wikipedia.org/wiki/NOTAM) of flight hazards
Acronym NPT Nuclear (Non-)Proliferation Treaty
Acronym NRO (US) National Reconnaissance Office
Acronym NROL Launch for the (US) National Reconnaissance Office
Acronym NS New Shepard suborbital launch vehicle, by Blue Origin
Nova Scotia, Canada
Neutron Star
Acronym NSF [NasaSpaceFlight forum](http://forum.nasaspaceflight.com)
National Science Foundation
Acronym NTO diNitrogen TetrOxide, N2O4; part of NTO/MMH hypergolic mix
Acronym NTP Nuclear Thermal Propulsion
Network Time Protocol
Acronym NTR Nuclear Thermal Rocket
Acronym OATK Orbital Sciences / Alliant Techsystems merger, launch provider
Acronym OCISLY Of Course I Still Love You, Atlantic landing ~~barge~~ ship
Acronym OECD Organisation for Economic Cooperation and Development
Acronym OG2 Orbcomm's Generation 2 17-satellite network (see OG2-2 for first successful F9 landing)
Acronym OML Outer Mold Line, outer profile of an aircraft/aeroshell
Acronym OMS Orbital Maneuvering System
Acronym OOA Orbit Once Around launch maneuver
Acronym OPTEMPO Operating/Operational Tempo
Acronym ORSC Oxidizer-Rich Staged Combustion
Acronym OSM Operations Safety Manager
Acronym OWL [Overwhelmingly Large Telescope](https://en.wikipedia.org/wiki/Overwhelmingly_Large_Telescope) project, abandoned in favor of ELT
Acronym PAF Payload Attach Fitting
Acronym PAO Public Affairs Officer
Acronym PAZ Formerly [SEOSAR-PAZ](https://directory.eoportal.org/web/eoportal/satellite-missions/p/paz), an X-band SAR from Spain
Acronym PCV Port Canaveral
Acronym PDV Powered Descent Vehicle for retro-propulsive landing
Acronym PLF Payload Fairing
Acronym PLSS Personal Life Support System
Acronym PMA ISS Pressurized Mating Adapter
Acronym PMD Propellant Management Device
Acronym PMF Propellant Mass Fraction
Acronym PPF SpaceX Payload Processing Facility, Cape Canaveral
Acronym PSLV Polar Satellite Launch Vehicle
Acronym PSLV [Polar Satellite Launch Vehicle](https://en.wikipedia.org/wiki/Polar_Satellite_Launch_Vehicle)
Acronym PSLV-CA Polar Satellite Launch Vehicle - Core Alone (without strap-on boosters)
Acronym PSLV-G Polar Satellite Launch Vehicle, with six 1 m diameter, 10 m long strap-on boosters
Acronym PSLV-XL Polar Satellite Launch Vehicle, with six 1 m diameter, 13.5 m long strap-on boosters
Acronym PSOM Solid Propellant Strap-On Motor, used in the PSLV
Acronym PTC Passive Thermal Control
Acronym PTK-NP Roscosmos [Piloted Transport Ship, New Generation](https://en.wikipedia.org/wiki/Prospective_Piloted_Transport_System)
Acronym QA Quality Assurance/Assessment
Acronym QAM Quality Assurance Manager
[Quadrature Amplitude Modulation](https://en.wikipedia.org/wiki/QAM)
Acronym QD Quick-Disconnect
Acronym RAAN [Right Ascension of the Ascending Node](https://en.wikipedia.org/wiki/Longitude_of_the_ascending_node)
Acronym RAL Rutherford Appleton Laboratory, UK
Acronym RCO Range Control Officer
Acronym RCS Reaction Control System
Acronym RD-180 [RD-series Russian-built rocket engine](https://en.wikipedia.org/wiki/RD-180), used in the Atlas V first stage
Acronym RFNA Red Fuming Nitric Acid, hypergolic oxidiser
Acronym RFP Request for Proposal
Acronym RIO [Radar Intercept Officer](https://en.wikipedia.org/wiki/Naval_flight_officer)
Acronym RLV Reusable Launch Vehicle
Acronym RLV-TD Reusable Launch Vehicle - Technology Demonstrator
Acronym RNTLS Return Near To Launch Site (ASDS in port)
Acronym ROC Range Operations Coordinator
Radius of Curvature
Acronym Roomba [Remotely-Operated Orientation and Mass Balance Adjuster](https://www.reddit.com/r/spacex/comments/6k8gzg//djk5g68/), used to hold down a stage on the ASDS
Acronym ROSA Roll-Out Solar Array (designed by Deployable Space Systems)
Acronym Roscosmos [State Corporation for Space Activities, Russia](https://en.wikipedia.org/wiki/Roscosmos_State_Corporation)
Acronym RP-1 Rocket Propellant 1 (enhanced kerosene)
Acronym RPA ["Rocket Propulsion Analysis"](http://www.propulsion-analysis.com/index.htm) computational tool
Acronym RPY Roll/Pitch/Yaw
Acronym RS-25 Rocketdyne-developed rocket engine used for Shuttle; see SSME, SLS
Acronym RSS Realscale Solar System mod for KSP
Acronym RTF Return to Flight
Acronym RTG Radioisotope Thermoelectric Generator
Acronym RTLS Return to Launch Site
Acronym RUD Rapid Unplanned Disassembly
Rapid Unscheduled Disassembly
Rapid Unintended Disassembly
Acronym s/c Spacecraft
Acronym SAA [Space Act Agreement](https://en.wikipedia.org/wiki/Space_Act_Agreement), formal authorization of 'other transactions'
Acronym SABRE Synergistic Air-Breathing Rocket Engine, hybrid design by Reaction Engines
Acronym SAFER [Simplified Aid For EVA Rescue](https://en.wikipedia.org/wiki/Simplified_Aid_For_EVA_Rescue)
Acronym SAS [Stability Augmentation System](http://wiki.kerbalspaceprogram.com/wiki/SAS), available when launching craft in KSP
Acronym SBSP Space-Based Solar Power generation
Acronym SCADA [Supervisory Control And Data Acquisition](https://en.wikipedia.org/wiki/SCADA) remote monitoring and control
Acronym SDS [Satellite Data System](https://en.wikipedia.org/wiki/Satellite_Data_System)
Acronym SDSC Satish Dhawan Space Centre
Acronym SEB Single-Event induced Burnout, radiation damage causing destructively high current
Acronym SECO Second-stage Engine Cut-Off
Acronym SEE Single-Event Effect of radiation impact
Acronym SEGR Single-Event Gate Rupture, transistor gate destroyed by radiation impact
Acronym SEL Single-Event Latchup, transistor stuck high due to radiation damage
Sun-Earth Lagrange point
Acronym SEP Solar Electric Propulsion
Acronym SES Formerly Société Européenne des Satellites, comsat operator
Acronym SET Single-Event Transient, spurious radiation discharge through a circuit
Acronym SFNA Stable Fuming Nitric Acid, hypergolic oxidizer
Acronym SHAR Sriharikota High Altitude Range
Acronym SHLLV Super-Heavy Lift Launch Vehicle (over 50 tons to LEO)
Acronym SHLV Super-Heavy Lift Launch Vehicle (over 50 tons to LEO)
Acronym SITVC Secondary Injection Thrust Vector Control
Acronym SLC-37 Space Launch Complex 37, Canaveral (ULA Delta IV)
Acronym SLC-40 Space Launch Complex 40, Canaveral (SpaceX F9)
Acronym SLC-41 Space Launch Complex 41, Canaveral (ULA Atlas V)
Acronym SLC-4E Space Launch Complex 4-East, Vandenberg (SpaceX F9)
Acronym SLC-4W Space Launch Complex 4-West, Vandenberg (SpaceX F9, landing)
Acronym SLCH4 Slush/Supercooled Liquid Methane
Acronym SLP Second Launch Pad at Satish Dhawan Space Centre, operational since 2005
Acronym SLS Space Launch System heavy-lift
Acronym SMAB (Former) Solid Motor Assembly Building, Cape Canaveral
Acronym SMART "Sensible Modular Autonomous Return Technology", ULA's engine reuse philosophy
Acronym SMAW [Shielded Metal Arc Welding](https://en.wikipedia.org/wiki/Shielded_metal_arc_welding)
Acronym SMD Science Mission Directorate, NASA
Acronym SNC Sierra Nevada Corporation
Acronym SoI Saturnian Orbital Insertion maneuver
Sphere of Influence
Acronym SOMD Space Operations Mission Directorate, NASA
Acronym SOP Standard Operating Procedure
Acronym SOX Solid Oxygen, generally not desirable
Acronym SPICE SPectral Imaging of the Coronal Environment, instrument on ESA's Solar Orbiter
Acronym SPIF Spacecraft Processing and Integration Facility, Cape Canaveral (now PPF)
Acronym SRB Solid Rocket Booster
Acronym SRP Supersonic Retro-Propulsion
Acronym SSAU State Space Agency of Ukraine
Acronym SSBA Space Situational Based Awareness
Acronym SSC Stennis Space Center, Mississippi
Acronym SSL Space Systems/Loral, satellite builder
Acronym SSME [Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)
Acronym SSO Sun-Synchronous Orbit
Acronym SSP Space-based Solar Power
Acronym SSRMS Space Station Remote Manipulator System (*Canadarm*)
Acronym SSTO Single Stage to Orbit
Acronym SSVP Sistema Stykovki i Vnutrennego Perekhoda, Russian docking standard
Acronym STA Special Temporary Authorization (issued by FCC for up to 6 months)
Structural Test Article
Acronym STEREO Solar TErrestrial RElations Observatory, GSFC
Acronym STP [Standard Temperature and Pressure](https://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure)
[Space Test Program](https://en.wikipedia.org/wiki/Space_Test_Program), see STP-2
Acronym STP-2 [Space Test Program 2](https://en.wikipedia.org/wiki/Space_Test_Program#Upcoming_Activities), DoD programme, second round
Acronym STS Space Transportation System (*Shuttle*)
Acronym SUFR Straighten Up and Fly Right, weight jettison event during Curiosity EDL
Acronym SV Space Vehicle
Acronym T/E Transporter/Erector launch pad support equipment
Acronym TAL [Transoceanic Abort Landing](https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Transoceanic_abort_landing)
Acronym TAN [Thrust Augmented Nozzle](http://selenianboondocks.com/2007/11/thrust-augmented-nozzles/)
Acronym TCM Trajectory Correction Maneuver
Acronym TDRSS (US) Tracking and Data Relay Satellite System
Acronym TE Transporter/Erector launch pad support equipment
Acronym TEA-TEB [Triethylaluminium](https://en.wikipedia.org/wiki/Triethylaluminium)-[Triethylborane](https://en.wikipedia.org/wiki/Triethylborane), igniter for Merlin engines; spontaneously burns, green flame
Acronym TEI Trans-Earth Injection maneuver
Acronym TEL Transporter/Erector/Launcher, ground support equipment (see TE)
Acronym TFR Temporary Flight Restriction
Acronym TID Total Ionizing Dose of radiation
Acronym TIG [Gas Tungsten Arc Welding](https://en.wikipedia.org/wiki/Gas_tungsten_arc_welding) (or Tungsten Inert Gas)
Acronym TLA Three Letter Acronym
Acronym TLE Two-Line Element dataset issued by NORAD
Acronym TLI Trans-Lunar Injection maneuver
Acronym TLP Third Launch Pad at Satish Dhawan Space Centre, under construction
Acronym TMI Trans-Mars Injection maneuver
Acronym TOSC Test and Operations Support Contract
Acronym TPA TurboPump Assembly, feeds fuel to a rocket engine
Acronym TPS Thermal Protection System for a spacecraft (on the Falcon 9 first stage, the engine "Dance floor")
Acronym TRL Technology Readiness Level
Acronym TSFC Thrust Specific Fuel Consumption (fuel used per unit thrust)
Acronym TSM Tail Service Mast, holding lines/cables for servicing a rocket first stage on the pad
Acronym TSTO Two Stage To Orbit rocket
Acronym TT&C Telemetry, Tracking and Control communications with a satellite
Acronym TVC Thrust Vector Control
Acronym TWR Thrust-to-Weight Ratio
Acronym UDMH Unsymmetrical dimethylhydrazine, liquid hypergolic propellant
Acronym UDMH [Unsymmetrical DiMethylHydrazine](https://en.wikipedia.org/wiki/Unsymmetrical_dimethylhydrazine), used in hypergolic fuel mixes
Acronym UHF Ultra-High Frequency radio
Acronym USAF United States Air Force
Acronym USOS United States Orbital Segment
Acronym VAB Vehicle Assembly Building
Acronym VAFB Vandenberg Air Force Base, California
Acronym VBB Very Big Brother (Blue Origin's proposed VTVL vehicle, unknown payload to LEO)
Acronym VFR [Visual Flight Rules](https://en.wikipedia.org/wiki/Visual_flight_rules)
Acronym VIF Vertical Integration Facility
Acronym VLEO V-band constellation in LEO
Very Low Earth Orbit
Acronym VSAT Very Small Aperture Terminal antenna (minimally-sized antenna, wide beam width, high power requirement)
Acronym VSSC Vikram Sarabhai Space Centre
Acronym VTOL Vertical Take-Off and Landing
Acronym VTS Vertical Test Stand
Acronym VTVL Vertical Takeoff, Vertical Landing
Acronym VV Visiting Vehicle (visitor to the Station)
Acronym WDR Wet Dress Rehearsal (with fuel onboard)
Acronym WFNA White Fuming Nitric Acid, hypergolic oxidiser
Acronym WSO [Weapons Systems Officer](https://en.wikipedia.org/wiki/Weapon_systems_officer)
Acronym XEUS [eXperimental Enhanced Upper Stage](https://en.wikipedia.org/wiki/Masten_Space_Systems#Xeus)
Acronym XIPS-25 [25cm Xenon Ion Propulsion System](https://en.wikipedia.org/wiki/XIPS-25) used on Boeing 702 satellites
Acronym ZBP Zero Pre-Breathe (spacesuit and habitat at same pressure
Acronym ZPS Zero Prebreathe Spacesuit
Jargon ablative Material which is intentionally destroyed in use (for example, heatshields which burn away to dissipate heat)
Jargon apoapsis Highest point in an elliptical orbit (when the orbiter is slowest)
Jargon apogee Highest point in an elliptical orbit around Earth (when the orbiter is slowest)
Jargon apohelion Highest point in an elliptical orbit around the Sun (when the orbiter is slowest)
Jargon autogenous (Of a propellant tank) Pressurising the tank using boil-off of the contents, instead of a separate gas like helium
Jargon bipropellant Rocket propellant that requires oxidizer (eg. RP-1 and liquid oxygen)
Jargon crossfeed Using the propellant tank of a side booster to fuel the main stage, or vice versa
Jargon cryogenic Very low temperature fluid; materials that would be gaseous at room temperature/pressure
Jargon dancefloor Attachment structure for the Falcon 9 first stage engines, below the tanks
Jargon deep throttling Operating an engine at much lower thrust than normal
Jargon electrolysis Application of DC current to separate a solution into its constituents (for example, water to hydrogen and oxygen)
Jargon EMdrive Prototype-stage reactionless propulsion drive, using an asymmetrical resonant chamber and microwaves
Jargon granularity (In re: rocket engines) Allowing for engine-out capability when determining minimum engine count
Jargon grid-fin Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large
Jargon high beta Times of year when the Earth-Sun line and the plane of orbit are nearly perpendicular
Jargon hydrolox Portmanteau: liquid hydrogen/liquid oxygen mixture
Jargon hypergolic A set of two substances that ignite when in contact
Jargon kerolox Portmanteau: kerosene/liquid oxygen mixture
Jargon lithobraking "Braking" by hitting the [ground](https://en.wiktionary.org/wiki/lith-)
Jargon methalox Portmanteau: methane/liquid oxygen mixture
Jargon milspec Military Specification
Jargon monopropellant Rocket propellant that requires no oxidizer (eg. hydrazine)
Jargon periapsis Lowest point in an elliptical orbit (when the orbiter is fastest)
Jargon perigee Lowest point in an elliptical orbit around the Earth (when the orbiter is fastest)
Jargon perihelion Lowest point in an elliptical orbit around the Sun (when the orbiter is fastest)
Jargon powerpack Pre-combustion power/flow generation assembly (turbopump etc.)
Jargon prepreg [Pre-impregnated composite fibers](https://en.wikipedia.org/wiki/Pre-preg) where the matrix/binding resin is applied before wrapping, instead of injected later
Jargon pyrophoric A substance which ignites spontaneously on contact with air
Jargon quess Portmanteau: Qualified Guess (common parlance: "estimate")
Jargon Raptor [Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX, see ITS
Jargon regenerative A method for cooling a rocket engine, by [passing the cryogenic fuel through channels in the bell or chamber wall](https://en.wikipedia.org/wiki/Regenerative_cooling_\(rocket\))
Jargon retropropulsion Thrust in the opposite direction to current motion, reducing speed
Jargon Sabatier Reaction between hydrogen and carbon dioxide at high temperature and pressure, with nickel as catalyst, yielding methane and water
Jargon scrub Launch postponement for any reason (commonly GSE issues)
Jargon Starlink SpaceX's world-wide satellite broadband constellation
Jargon tripropellant Rocket propellant in three parts (eg. lithium/hydrogen/fluorine)
Jargon turbopump High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust
Jargon ullage motor Small rocket motor that fires to push propellant to the bottom of the tank, when in zero-g
Event CRS-10 2017-02-19|F9-032 Full Thrust, core B1031, Dragon cargo; first daytime RTLS
Event DM-1 Scheduled|SpaceX CCtCap Demo Mission 1
Event DM-2 Scheduled|SpaceX CCtCap Demo Mission 2
Event Inmarsat-5 F4 2017-05-16|F9-034 Full Thrust, core B1034, GTO comsat; expended
Event NROL-76 2017-05-01|F9-033 Full Thrust, core B1032, ^(classified payload); landed at LZ-1
Event TGO 2016-03-14|(Launch of) Trace Gas Orbiter at Mars, an ESA mission