This list of Gaia acronyms is actively maintained by Jos de Bruijne (jdbruijn@rssd.esa.int). It was last updated on Wed Dec 16 13:29:20 CET 2009 Other web-based archives include: http://tla.surly.org/ http://www.astro.umd.edu/~marshall/ast_acro.html http://www.spacetoday.org/NASA/SpaceAcronyms/SpaceAcronyms.html http://www.stsci.edu/hst/HST_overview/documents/acronymList http://science.ksc.nasa.gov/facts/acronyms.html 1B2S : 1 Big (or) 2 Small (window options for resolved double-star sampling; obsolete) 1D : One-dimensional 2D : Two-dimensional 2MASS : Two-Micron All Sky Survey 3D : Three-dimensional 3F : Old baseline for MBP photometric system (UB-PWG-016) 4B : Old baseline for BBP photometric system (GAIA-LL-051) A : {\AA}ngstrom; non-SI unit of length, to be avoided AAD : Attitude Anomaly Detector AAE : Austrian AErospace A : Amp\`ere; SI unit of electric current AAS : Alcatel Alenia Space (now Thales-Alenia Space) AB : Anti-Blooming AB : Astrometric Binary ABB : Avionic BreadBoard ABCL : As-Built Configuration List ABD : Anti-Blooming Drain ABF : Adjacent Best Fit ABI : Application Binary Interface ABS : Astrometric Binary Star AC : ACross scan (direction) AC : Alternating Current AC : Auto Collimation ACC : Attitude Control Computer ACF : ACross-Scan Following (FoV) ACFLAT : Auto-Collimation FLAT mirror ACI : Concerted Inciting Action (French acronym) ACK : Acknowledgement ACL : Access Control List ACMS : Attitude Control and Measurement Sub-system ACN : Attitude Control and Navigation ACP : Acquisition Command Packet ACP : Across-Scan Preceding (FoV) ACP : Astro Coarse Phase ACS : Advanced Camera for Surveys (HST) ACS : Attitude Control Sub-system ACSM : Apply Calibration Software Module ACTEL : Micro-electronics supplier A/D : Analogue-to-Digital (converter) AD : Applicable Document ADASS : Astronomical Data Analysis Software and Systems ADC : Analogue-to-Digital Converter ADCM : Attitude Data Collection Module ADD : Architectural Design Document ADE : Adaptive Differential Encoding ADP : Acceptance Data Package ADR : Average Data Rate ADSD : Asiago Database of Spectroscopic Databases AD : Sequence-Controlled Service ADU : Analogue-to-Digital Unit AE : Astro Elementary AEF : Actual Event File AF : Astrometric Field (in Astro) AFMA : AC-Flat Mechanical Assembly AFM : AC-Flat Mirror AFMM : AC-Flat Mirror Mechanism AFMM AFR : Annualised Failure Rate AGB : Asymptotic Giant Branch (star) AGI : Applications Graphics Interface AGIS : Astrometric Global Iterative Solution AGN : Active Galactic Nucleus AGP : Astro Gate Phase Ag : Silver AHB : Advanced High-speed Bus AHFD : See HFAD AI : Action Item AI : Assembly and Integration AIDA : Astronomical Infrastructure for Data Access AIM : Astrometric Instrument Model AIP : Astrophysikalisches Institut Potsdam AIRF : AGIS-Internal Reference Frame AIT : Assembly, Integration, and Test AIV : Assembly, Integration, and Verification AIX : Advanced Interactive eXecutive (proprietary operating system developed by IBM based on UNIX System V) AL : Acceptance Load AL : ALong scan (direction) Al : Aluminium ALMA : Atacama Large Millimeter Array (ESO) ALPT : ALong-scan Phasing Table ALTEC : Advanced Logistic Technology Engineering Centre AMAP : As Much As Possible AME : Absolute Measurement Error AMFIN : Advanced Modular Facility for Interplanetary Navigation AMOS : Air Force Maui Optical and Supercomputing Site AMR : Age-Metallicity Relation ANN : Artificial Neural Network ANoVA : ANalysis of VAriance ANP : Astro Normal Phase ANSI : American National Standards Institute AO : Announcement of Opportunity AOCS : Attitude and Orbit Control Sub-system AoS : Acquisition of Signal AP : Antenna Panel AP : Application Process AP : Astrophysical Parameter APB : Advanced Peripheral Bus APC : Along-scan Pixel Coordinate APE : Absolute Pointing Error APE : Astrophysical Parameter Estimation APH : Attitude Pointing History API : Application Programming Interface APID : Application Process IDentifier APM : Assistant Project Manager APM : Automatic Plate Measuring APR : Array Power Regulator APS : Active Pixel Sensor APU : AOCS Processing Unit APU : Astro Processing Unit (obsolete) AR : Acceptance Review AR : Anti-Reflection coating (CCD) ARB : Anomaly Review Board arcmin : Arcminute, minute of arc (unit of angle) arcsec : Arcsecond, second of arc (unit of angle) ARE : Absolute Rate Error ARG : Astrophysics Research Group (Antwerpen) ARI : Astronomisches Rechen-Institut (part of ZAH, Zentrum f\"ur Astronomie, Heidelberg) ARO : Automatic Reconfiguration Order ARP : Antenna Reference Point ARW : Angle Random Walk AS : Action Sp\'ecifique AS : Adjacent Sample ASAP : As Soon As Possible ASAS : All-Sky Automated Survey ASC : Attitude Star Catalogue ASCII : American Standard Code for Information Interchange ASD : AeroSpace and Defence Industries Association of Europe ASD : AStrium Deutschland ASD : Auxiliary Science Data ASE : Automatic Scheduling Execution ASF : AStrium France ASF : Nominal effective `filter (band) profile' for ASM (Astro) (obsolete) ASI : Agenzia Spaziale Italiana ASIC : Application-Specific Integrated Circuit ASM : Astrometric Sky Mapper (obsolete) ASM : Attached Sync Marker ASM : Automatic Storage Management ASP : Alcatel SPace A : Specific project phase (feasibility; concluded by PRR) ASR : Average Star Rate AST : Autonomous Star Tracker ASTP : ASTrometric Parameters Astro : Astrometric Instrument (obsolete) ASU : AStrium United Kingdom ASU : Astronomical Server URL AT : Average Tilt ATC : Active Thermal Control ATOX : ATomic OXygen ATP : Authorisation To Proceed ATP : Automatic Test Procedure ATXE : Attitude Error in the X-direction ATXU : Attitude Update in the X-direction ATYE : Attitude Error in the Y-direction ATYU : Attitude Update in the Y-direction ATZE : Attitude Error in the Z-direction ATZU : Attitude Update in the Z-direction AU : Astronomical Unit AUT : AUTomated AUT : AUTonomy AV : Astrometric Verification AVD : AVoiDance (file) AVM : Avionics Model AVM : Avionics Verification Model AVO : Astrophysical Virtual Observatory AVU : Astrometric Verification Unit AWG : American Wire Gauge AWG : Astronomy Working Group (ESA) AWT : Advanced Window Toolkit AXD : AuXiliary Data AZP : Astrophysical Zero Point BA : Basic Angle BAL : Broad Absorption Line (galaxies) BAM : Basic-Angle Monitoring (Device) BAMD : Basic-Angle Monitoring Device BAM-N : Nominal BAM (CCD) BAM-R : Redundant BAM (CCD) BAS : Basic-Angle Stability BAT : Bandwidth Allocation Table BAT : Battery BAV : Basic-Angle Variation BAVS : Basic-Angle Variation Stability BAVSWG : BAVS Working Group BAVWG : BAV Working Group BB : Bread-Board BBF : Broad-Band Filter (in BBP; obsolete) BBFH : Burbidge, Burbidge, Fowler, Hoyle (star) b : Bit BBM : BreadBoard Module (Model) BBP : Broad-Band Photometer (obsolete) B : Byte (8 bit) BC : Beam-Combiner BC : Best Case BCC : Blank Carbon Copy BCDR : Battery Charge-Discharge Regulator BCM : Bad Column Map BCR : Battery Charge Regulator BCRS : Barycentric Celestial Reference System BDA : BAM Density Assembly (ND filter) BD : Brown Dwarf (star) BDD : Beam Direction Deviation BDE : Basic Differential Encoding BDL : Bureau Des Longitudes (IMCCE) BDR : Battery Discharge Regulator BDR : Bread-board Design Report BDT : Bulk Data Transfer BER : Bit Error Rate BFW : Bloomed Full Well BG : Background BGBC : BackGround and Bias Calibration BGD : BackGround Determination BGM : Besan{\c{c}}on Galaxy Model BGM : Besancon Galaxy Model BHB : Blue Horizontal Branch (star) BID : Battery Integration Device BIL : Back(side)-ILluminated (CCD) BIPM : Bureau International des Poids et Mesures BIT : Built-In Test B : Johnson photometric B band BLAS : Basic Linear Algebra Subprogrammes BLOB : Binary Large OBject BLS : Battery and Load Simulator BM : Beam Map BM : Butler Matrix BM : (MIL-STD-1553B) Bus Monitor BNF : Backus-Naur Form BoL : Beginning of Life (also denoted BOL) BoT : Beginning of Track BP : Blue Photometer BPC : Barcelona Processing Centre BPP : Blue-Photometer Prism bps : Bits per second Bps : Bytes per second BRDF : Bi-directional Reflectance Distribution Function BRF : Boresight Reference Frame BRM : Bipod Release Mechanism BRP : BP/RP BRS : Barycentric Reference System BSA : Beam Steering Algorithm BS : Bright Star BSC : Barcelona Supercomputing Centre BSD : Berkeley Software Distribution BSE : Binary-Star Evolution BSM : Bright-Star Mapper (Monitor) B : Specific project phase (system definition and design; concluded by SRR and PDR) BT : Bandwidth Symbol Duration BU : Brunel University BVC : Barycentric Velocity Correction BW : Baade's Window (special, high-density area on the sky) BW : BandWidth C1B : First common baseline (C1) for BBP photometric system, based on F4B photometric system (UB-PWG-028) C1M : First common baseline (C1) for MBP photometric system, based on S5M photometric system (UB-PWG-029) CAA : Conformal Array Antenna CAB : Contract Appeal Board CA : Calar Alto observatory Ca : Calcium CaC : Cost at Completion CA : Construction Analysis CADC : Canadian Astronomical Data Centre CAD : Computer Aided Design CADM : Configuration And Data Management CAG : Calibration, Attitude, Global (AGIS) CALDATA : CALibration DATA CAMCAO : Infrared Camera for the VLT CaU : Calibration Unit CB : Configuration Baseline CB : Connector Bracket CBS : Cost Breakdown Structure CCB : Configuration Control Board CC : Carbon Copy CCC : Computer Control Centre CC : Change Control CCCP : Cleanliness and Contamination Control Plan CCD : Charge-Coupled Device CCDRS : CCD Reference System CCE : Charge Collection Efficiency CCG : Country/Company Grouping CCLRC : Council for the Central Laboratory of the Research Councils (UK, obsolete and now STFC) CCN : Contract Change Notice CCP : Configuration Command Package CCR : Configuration Change Request CCS : Central Check-out System CCS : Centralised Control Software CCSDS : Consultative Committee for Space Data Systems cd : Candela, SI unit of luminous intensity CD : Compact Disc CD : Cumulative Distribution CDD : Configuration Data Document CDF : Calibration Data File C&DH : Command and Data Handling CDM : Charge Device Model CDM : Charge Distortion Model CDM : Clock Distribution Module CDMS : Command and Data Management Sub-system CDMU : Command and Data Management Unit CDMWG : Common Data Management Working Group (obsolete) CDR : Critical Design Review CDROM : Compact Disc Read-Only Memory (also known as CD-ROM) CDS : Concatenated Decoding System CDS : Correlated Double Sampling CDU : Clock Distribution Unit CDWG : Common Data Working Group (obsolete) CEA : Commissariat \`a l'Energie Atomique (France) CEB : CEBreros (ground station near Madrid, Spain) CE : Conducted Emission CE : Conformit\'e Europ\'eenne CELT : California Extremely Large Telescope CEMGA : CTI Effects Models for GAia CEO : Celestial Ephemeris Origin (obsolete) CEO : Chief Executive Officer CEP : Celestial Ephemeris Pole CEPF : Core Ecliptic Pole Field CERN : Centre Europ\'enne pour la Recherche Nucl\'eaire CESCA : CEntre de Supercomputac\'io de CAtalunya CeSiC : Carbon-SiC (also known as CeSIC, CSiC, CSIC, C-SiC, and C-SIC) CET : Central European Time CfA : (Harvard-Smithsonian) Center for Astrophysics CFA : Harvard-Smithsonian Center for Astrophysics (USA) CF : Conversion Factor [e- per ADU] CFE : Customer-Furnished Equipment CFHT : Canada-France Hawaii Telescope CFITSIO : C-FITS-IO (library of C and Fortran subroutines for reading and writing [input-output] data files in FITS) CFRP : Carbon Fibre Reinforced Polymer CFS : Calibration Faint Star CG : Conjugate Gradient CGH : Compressed Gaseous Hydrogen CGM : Constants of Gaia Motion CHC : Charge Handling Capacity (CCD) CHORIZOS : CHi-square cOde for parameteRixed modelIng and characteriZation of phOtometry and Spectrophotometry CIC : Clock-Induced Charge CI : Charge Injection CI : Configuration Item CID : CCD Injection Delay CID : Charge-Injection Device (CCD) CIDL : Configuration Item Data List CIF : Community InterFace CIL : Critical Items List CIO : Celestial Intermediate Origin CIP : Celestial Intermediate Pole (obsolete) CIPM : Comit\'e International des Poids et Mesures CIR : Central Invoice Registration (office; ESA) CIS : Charge-Injection Structure (CCD; avoid this name in Gaia) CITI : Corporate ICT Infrastructure CKDR : ClocK DriveR CLASS : CLASSification CLC : Large-scale Calibration in the AC direction (also denoted CLAC) CL : Closed Loop CLCW : Command Link Control Word CLL : Large-scale Calibration in the AL direction (also denoted CLAL) CLTU : Command Link Transfer Unit CM : Calibration Model CM : Common Mode CM : Configuration Management CMDB : Configuration Management DataBase CME : Coronal Mass Ejection CMP : Configuration Management Plan CN : Change Notice CNES : Centre National d'Etudes Spatiales (France) CNO : Carbon-Nitrogen-Oxygen cycle (star) CNR : Carrier to Noise Ratio (C/N) CoC : Certificate of Conformance CO : Check-Out (also denoted C/O) CO : Complete Observation (of object in AF) CODATA : Committee on Data for Science and Technology COD : Catastrophic Optical Damage CODC : CCD One-Day Calibration (FL) CODEC : COder/DECoder CoG : Centre of Gravity CoM : Centre of Mass COMPASS : Catalogues of Objects and Measured Parameters from All Sky Surveys CoMRS : Centre of Mass Reference System CONF : Confirmed (in Gaia Parameter Database status field) CoP : Center of Pressure COP : Command Operation Procedure CORBA : Common Object Request Broker Architecture CORTEX : Command, Ranging, and Telemetry Unit COTS : Commercial-Off-The-Shelf cPCI : Compact PCI CP : Commissioning Phase CP : Conference Proceeding CPD : Calibration Products Database CPDU : Command Pulse Distribution Unit CPG : Chebyshev Polynomial Guidance CPI : Customer Precap Inspection CPM : Chemical Propulsion Module CPM : Common Proper Motion CPM : Cross Pointing Mode CPS : Chemical Propulsion Sub-system CPU : Central Processing Unit CPV : Commissioning and Performance Verification CQ : Certificate of Qualification CQG : Chebyshev Quaternion Guidance CRB : Change Review Board CRB : Charge-Release Background CRC : Charge-Release Curve CRC : Cyclic Redundancy Code CR : Change Request CR : Charge Release CR : Cold Radiator CR : Commissioning Review CR : Cosmic Ray CR : Cram\'er-Rao (bound/limit) CReMA : Consolidated Report on Mission Analysis CREME : Cosmic-Ray Effects on Micro-Electronics CRF : Celestial Reference Frame CRG : Contingency and Recovery Procedure CRID : Command Request Interface Document CRNU : (CCD) Column Response Non Uniformity CRP : Contingency Recovery Procedure CRR : Command Request Response CRT : Central Reference Time CS : Conducted Susceptibility CS : Contract Structure CSC : Small-scale Calibration in the AC direction (also denoted CSAC) CSF : Command Stack File CSG : Centre Spatial Guyanais (Gaia launch site) CSI : Customer Source Inspection CSL : Centre Spatial de Li\`ege CSL : Small-scale Calibration in the AL direction (also denoted CSAL) CSM : CPS Scanning Mode C++ : Specific programming language C : Specific programming language (also called ANSI-C) C : Specific project phase (detailed definition; concluded by CDR) CSS : CCD Support Structure CSV : Comma-Separated Value (database output format, e.g., for MS Excel) CSW : Central SoftWare CTB : Common ToolBox CTC : Cost To Completion CT : Central Tube CTE : Charge Transfer Efficiency CTE : Coefficient of Thermal Expansion CTF : Charge Transfer Function CTI : Charge Transfer Inefficiency CTQP : Critical Technology Qualification Plan CTR : Central Time Reference CTR : ConTRol CTS : Concept and Technology Study CTSR : Concept and Technology Study Report CUC : CCSDS Unsegmented (time) Code CUC : CCSDS Unsegmented time Code CU : Coordination Unit (in DPAC) CUO : Copenhagen University Observatory (Denmark) CUX-L : (Scientific) Leader of CUX (also denoted CUL) CUX-Q : Quality assurance leader of CUX (also denoted CUQ) CUX-T : Technical manager of CUX (also denoted CUT) CVCM : Collected Volatile Condensable Material CV : ConVerter CV : Cosmic Vision CV : Curriculum Vitae CVD : Chemical Vapour Deposition CVS : Concurrent Versions System (obsolete) CW : Calender Week CWG : Calibration Working Group CY : Calender Year DACC : Data Analysis Coordination Committee (obsolete) DAC : Data Analysis Consortium (obsolete; superseded by DPAC) DAC : Digital-to-Analogue Converter DACE : Data Analysis Consortium Executive (obsolete) DA : Detection Algorithm DAG : Data Analysis Group DAL : Data Access Layer DAO : Data Access Object DAQ : Data AcQuisition (system) DAS : Data Archive Subsystem DASS : Data Analysis Software System DB : DataBase Db : Decibel DBMS : DataBase Management System DBT : DataBase Testing DC : Date Code DC : Direct Current DC : Direction Cosine DCI : Data Conversion Interface DCL : Declared Components List DCM : Direction Cosine Matrix DCN : Document Change Notice DCR : Dedicated Control Room DCR : Document Change Request DCT : Defered Charge Trail DCT : Discovery Channel Telescope DDD : Detailed Design Document DDEF : Displacement Damage Equivalent Fluence D : Deutschland (Germany) DDI : Data Display Interface DDID : Data Delivery Interface Document DDL : Deliverable Document List DDOR : Delta DOR (ranging) DDP : Delivered Duty Paid DDP : DPC Development Plan DDR : Detailed Design Review DDS : Data Disposition System DDT : Definition, Development, and Testing DD&V : Design, Development, and Validation (Verification) DDV : Design, Development, and Verification DEC : Declination DE : Developmental Ephemerides (from JPL/NASA) deg : Degree (unit of angle) DEI : Data Exchange Interface DEMUX : DE-MUltipleXer DFB : Distributed FeedBack (laser) DF : Dark Fibre DF : Data Flow DFL : Detailed First Look DFLE : Detailed First Look Evaluator DFLM : Detailed First Look Monitor DFT : Discrete Fourier Transform DGL : Diffuse Galactic Light DGS : Dresden Gaia Simulator DH&C : Data Handling and Compression DHM : Deployment Hinge Mechanism DHS : Data Handling Sub-system DHU : Data Handling Unit DIB : Diffuse Interstellar Band DIE : Digital Interface Electronics DIL : Deliverable Item List DIP : Dual Inline Package DIVA : Deutsches Interferometer f\"ur Vielkanalphotometrie und Astrometrie (cancelled) DIV : Integer division DL : Design Load DL : DownLink DLR : Deutsches Zentrum f{\"u}r Luft und Raumfahrt DLTS : Deep-Level Transient Spectroscopy DMA : Direct Memory Access DM : Data Model DM : DeMonstrator (Model) DM : Development Model DM : Differential Mode DML : Declared Material List DMP : Document Management Procedure DMPL : Declared Mechanical Parts List DMSA : Double and Multiple Systems Annex (Hipparcos Catalogue) DMS : Data Management Sub-system DMS : Document Management System (ESA) DMS : Double and Multiple Star(s) DMSWG : Double and Multiple Stars Working Group (obsolete) DMT : Dark Matter Telescope DMWG : Data Management Working Group DMZ : De-Militarised Zone DNEL : Discharge Non-Essential Loads DNL : Differential Non Linearity DNS : Domain Name System DOB : Diffuse Optical Background DoC : Department of Commerce (USA) DoD : Department of Defense (USA) DoD : Depth of Discharge DoF : Degree(s) of Freedom (also known as DOF) DoF : Depth of Focus DOM : Document Object Model DOP : DPC Operations Plan DOR : Differential One-way Range DOR : Direct Operation Request DoS : Department of State (USA) DoY : Day of Year DPAC : Data Processing and Analysis Consortium DPACE : Data Processing and Analysis Consortium Executive DPA : Destructive Physical Analysis DPCB : Data Processing Centre Barcelona DPCC : Data Processing Centre CNES DPC-C : DPC Configuration manager DPC : Data Processing Centre DPCE : Data Processing Centre ESAC DPCG : Data Processing Centre (ObsGE/ISDC) Geneva DPCI : Data Processing Centre (Institute of Astronomy) Cambridge DPC-M : DPC Manager DPCOM : Data Processing Centre Operations Manager DPC-Q : DPC Quality assurance manager DPCT : Data Processing Centre (INAF-OATo) Torino DP : Data Processing DPGS : Data Processing Ground Segment DPH : DPC Procedures Handbook DPL : Declared Process List DPS : Data Processing Software DPWG : Data Processing Working Group (dissolved) DQE : Detected Quantum Efficiency DRAM : Dynamic RAM DRB : Delivery Review Board DRC : Data Reduction Cycle DRC : DPAC Risk Code DR : Data Release DRD : Document Requirements Definition DR : Design Report DR : Dynamic Range DS9 : Deep Space 9 (specific astronomical data visualisation application; SAOImage) DSA : Deep Space Antenna DSA : Deployable Sunshield Assembly DSC : Discrete Source Classification (Classifier) D/SCI : ESA Scientific Directorate (or ESA Director of Science) DS : Data Set DS : Data Structure DS : Definition Study DS : Differential Signal DSG : Deployable Solar Generator DSIT : Definition Study Industrial Teams DSN : Deep Space Network DSNU : (CCD) Dark Signal Non Uniformity DSNU : Dark Signal Non Uniformity DSP : Deployable Solar Panel DSP : Digital Signal Processor D : Specific project phase (production; concluded by QR and FAR) DSR : Data Storage and Retrieval DSS : Digital Sun Sensor DSV : Dummy Sample Value DTCP : Daily Telecommunications Contact Period DTD : Document Type Definition DTP : DPC Test Plan DTR : DPC Test Report DTT : Detected Transit Time DU : Detection Unit DU : Development Unit (in DPAC) DUX-L : Leader of DUX DVC : Device Commanding DVD : Digital Video (Versatile) Disc DWI : Deviation Work Item DX : DipleXer E2ES1 : End-to-End Stage 1 E2ES2 : End-to-End Stage 2 E2ES3 : End-to-End Stage 3 E2ES4 : End-to-End Stage 4 e2v : UK-based Gaia CCD manufacturer (e2v technologies) EaC : Estimate at Completion EAD : EADS Astrium Deutschland EAD : Effective Average Deviation EADS : European Aeronautic Defence and Space company (EADS Astrium is the Gaia prime contractor) EAF : EADS Astrium France EAR : Export Administration Regulation EAU : EADS Astrium United Kingdom EB : Eclipsing Binary EBL : Extra-galactic Background Light Eb/N0 : Energy per bit/Noise Power density ECC : ESTRACK Control Centre EC : Economic Conditions ECI : Earth-Centred Inertial ECLS : Environmental Control and Life Support ECOS : ESA Costing Software ECSS : European Cooperation for Space Standardisation EDAC : Error Detection And Correction EDDS : EGOS Data Dissemination System EED : Electro-Explosive Device EEE : Electronic, Electrical, and Electro-mechanical EEPROM : Electrically Erasable Programmable Read-Only Memory E : Espa\~na (Spain) EFIS : ESA Financial and Invoicing System EFM : Electrical Functional Model EFR : Early Failure Rate EFRL : Exponential Failure-Rate Law EGOS : ESA Ground Operations System EGRS : Electrical Ground Reference Structure EGSE : Electrical Ground Support Equipment EICD : Electrical Interface Control Document EID : Equivalent Injection Delay EID : Event Identifier EIDP : End-Item Data Package EIH : Einstein-Infeld-Hoffmann (equations) EIRP : Equivalent Isotropic Radiated Power EIU : Electrical Interface Unit ELDR : Extremely Low Dose Rate ELR : Environmental Lapse Rate ELSA : European Leadership in Space Astrometry ELT : Extremely Large Telescope EMBC : Earth-Moon BaryCentre EMC : Electro-Magnetic Compatibility EME2000 : Earth Mean Equator and equinox at epoch J2000 EM : Engineering Model EMF : Electro-Motive Force EMF : Event Monitoring Function EMI : Electro-Magnetic Interference EMS : ESTRACK Management System ENOB : Effective Number Of Bits EODM : Electro-Optical Demonstrator Model EO : Electro-Optical EO : Extended Object EoF : End of File EoI : Expression of Interest EoL : End of Life (also denoted EOL) EOP : Early Orbit Phase EOP : Earth Orientation Parameters EoT : End of Track EPC : Ecliptic Pole Catalogue EPER : Extended Pixel Edge Response EPF : Ecliptic Pole Field EPG : Earth-station Position Generator (AOCS) EPIC : Electrical Power and Interface Controller EPIC : Electronic Power and Interface Controller EPM : Ephemerides of Planets and the Moon EPPL : European Prefered Parts List EPS : Electrical Power Sub-system EPSL : Ecliptic Pole Scanning Law EQM : Engineering Qualification Model EQSR : Equipment Qualification Status Review (also known as ESR) EQT : EQuipmenT ERA : Earth Rotation Angle ERC : Early-Release Catalogue ERE : Extended Red Emission ER : Experienced Researcher (ELSA) ERS : Early-Stage Researcher (ELSA) ERT : Earth Reception Time ESAC : European Space Astronomy Centre (VilSpa) ESA : European Space Agency ESAM : Emergency Sun Acquisition Mode (AOCS) ESARAD : European Software tool for Analysis of spacecraft RADiation environment ESATAN : European Software tool for Analysis of spacecraft Thermal ANalysis ESCC : European Space Components Coordination ESD : Electro-Static Discharge ES : Emergency Surveillance Es : Espa\~na (Spain) ESF : European Science Foundation ESH : Equivalent Sun Hours ESOC : European Space Operations Centre (ESA) ESO : European Southern Observatory E : Specific project phase (utilisation, including LEOP and in-orbit testing; concluded by MIOCR) ESP : Extended Stellar Parametriser ESP : Extra-Solar Planet ESR : Early-Stage Researcher ESR : Equipment Suitability Review ESRIN : European Space Research INstitute (ESA) ESTEC : European Space research and TEchnology Centre (ESA) ESTRACK : ESA Tracking Stations Network E-SVM : Electrical SerVice Module ESVM : E-SVM ESY : Equivalent Sun Years ETB : Engineering Test Bed ETCA : Etudes Techniques et Constructions A\'erospatiales ETH : ETHernet ETM : Electrical Test Model ETS : EMC Test Stand EUICD : External User Interface Control Document eV : Electron-Volt EVF : EVent File EVN : European VLBI Network EVRP : EVent RePorting EW : Equivalent Width (spectroscopy) EXT : EXTernal Interface EXTR : EXTRactor EY : EagleYard F4B : BBP photometric system (see C1B) FADE : Fully Adaptive Differential Encoding FAE : Fully Adaptive Encoding FA : Field Angle FA : Functional Analysis FAMbE : Fully Adaptive Model-based Encoding FAME : Fast Algorithm for Median Evaluation FAME : Fizeau (Fast) Astrometric Mapping Explorer (cancelled) FAMOUS : Frequency Analysis Mapping On Unusual Sampling FAR : Flight Acceptance Review FAST : Fundamental Astronomy by Space Techniques (Hipparcos) FAV : FAVourable FC : Fibre Channel FCL : Foldback Current Limiter FCP : Flight Control Procedure FCR : Flight Control Room FCT : Flight Control Team FCT : Function FCV : Flow Control Valve FDA : Fully-Dynamic Approach (Hipparcos attitude modeling) FDDB : Flight-Dynamics DataBase FDDC : Flight-Dynamics Database Content FDDD : Flight-Dynamics Database Delivery FD : False Detection FD : Flight Dynamics FDH : FrieDrichsHafen FDIA : Flight Dynamics Implementation Analysis FDI : Field Density Index FDIR : Failure Detection, Isolation, and Recovery FDRC : Flight Dynamics Requirements Compilation FDR : Final Design Review FDR : Flight-Dynamics Room FDROR : Flight-Dynamics Routine Operations Room FDS : Flight-Dynamics System (at MOC) FDV : Fill and Drain Valve FEC : Front-End Controller FEE : Front-End Electronics FEEP : Field-Emission (or Field-Effect) Electric Propulsion FELICS : Fast, Efficient, and Lossless Image Compression System FEM : Finite-Element Model FEM : FOG Electronics Module FET : Field-Effect Transistor FF : Feed Forward FF : Field-Free (CCD area) FFP : Firm Fixed Price F : France FFT : Fast Fourier Transform FGSE : Fluidic Ground Support Equipment FHT : File Header Table FID : Failure IDentification FID : Function IDentifier FIFO : First In, First Out FIL : Front(side)-ILluminated (CCD) FIR : Finite Impulse Response (filter) FIR : Full IDV Report FIT : Failures In Time (failures per billion hours) FITRAS : FIle TRAnsfer System (also denoted GFTS) FITS : Flexible Image Transport System FK5 : Fifth Fundamental Catalogue FLAME : Final Luminosity And Mass Estimator FLAMES : Fiber Large Array Multi-Element Spectrograph (VLT) FLAMES : Fibre Large Array Multi Element Spectrograph FL : First Look FLOP : FLoating-point OPeration FLOPS : FLoating-point OPerations per Second FLP : First-Look (pre-)Processing FLP : Frame-Loss Probability FLREAD : FormatLess READing FLS : First-Look Scientist FLWG : First-Look Working Group FMA : Final Mission Analysis FMECA : Failure Modes, Effects, and Criticality Analysis FM : Flat Mirror FM : Flight Model FMMR : Flight-Model Manufacturing Review FMRR : Flight-Model Readiness Review FMSS : Folding Mirror Support Structure FNRS : Fonds National de la Recherche Scientifique (Belgium) FOD : Flight Operations Director FOG : Fiber Optical Gyro FOG : Fibre Optic Gyro FoM : Figure of Merit FOM : Flight Operation Mode FOP : Flight Operation Procedure (Plan) FoSd : Design Factor of Safety FoS : Factor of Safety FoSu : Ultimate Factor of Safety FoSy : Yield Factor of Safety FoV : Field of View (also denoted FOV) FoVRS : Field-of-View Reference System FP7 : Seventh Research Framework Programme FPA : Focal Plane Assembly (Focal Plane Array) FPAG : Fundamental Physics Advisory Group (ESA) FPASS : Focal-Plane-Assembly Static Simulator FPER : First-Pixel Edge Response FP : Final Presentation FP : Focal Plane FPGA : Field-Programmable Gate Array FPR : First-Pixel Response (also denoted FPER) FPRS : Focal Plane Reference System FPSM : Focal Plane to Sky Mapping FPU : Floating-Point Unit FR : Final Review FSB : Front Side Bus FSE : Flight Support Equipment FS : File System FS : Flight Spare FSG : Faint Star polluted by a TDI Gate FSG : Fixed Solar Generator FSI : Faint Star polluted by charge Injection F : Specific project phase (disposal/re-entry; not applicable to Gaia) FSS : Fine Sun Sensor FTA : Fault Tree Analysis FTE : Full-Time Equivalent FTP : File Transfer Protocol FUMO : FUnctional MOdel FVB : Functional Validation Bench FV : Flight Vehicle FVP : Full Video Package FVV : Fill and Vent Valve FWC : Full Well Capacity (CCD) FWHM : Full Width at Half-Maximum FXML : Fortran XML library G1 : CCD-PEM Gain 1 (SM, AF, BP, RP) G2 : CCD-PEM Gain 2 (RVS) GaAs : Gallium-Arsenide GAAT : Gaia Accuracy Analysis Tool GAIA : Global Astrometric Interferometer for Astrophysics (obsolete; now spelled as Gaia) GaiaTools : Gaia software toolbox GALEX : GALaxy Evolution eXplorer GAM : Gaia Attitude Model GAP : Gate Astro Phase (sub-mode of AOCS Normal Mode) GAREQ : GAia Relativistic Experiment on Quadrupole light deflection GAREX : GAia Relativity EXperiment GASS : GAia System-level Simulator GassVal : GASS Validation software tool GAT : Gaia Astronomical Tools GATT : Gaia Algorithm Tracking Tool (GDAAS, obsolete) GB : Giant Branch (star) Gb : Gigabit GB : GigaByte GBnnn : Gaia BBP magnitude, with nnn the `central' wavelength in nm (obsolete) GBOG : Ground-Based Observations for Gaia (DPAC) GBOT : Ground-Based Optical Tracking GC3 : Great-Circle Cell Count GCC : General Clauses and Conditions gcc : Specific C and C++ compiler (GNU) GCDMWG : Gaia Common Data Management Working Group (obsolete) GC : Great Circle GCN : GRB Coordinates Network GCP : Ground Communication Plan GCRF : Gaia Celestial Reference Frame GCR : Galactic Cosmic Ray (avoid this name in Gaia) GCR : Great-Circle Reduction (Hipparcos) GCRS : Geocentric Celestial Reference System GcRS : Geocentric Reference System GCS : Geneva - Copenhagen Survey GCVS : General Catalogue of Variable Stars GCWG : Gaia Calibration Working Group GDAAS : Gaia Data Access and Analysis Study (obsolete) GDAC : Gaia Data Analysis Consortium (obsolete; superseded by GDPAC) GDA : Gaia Detection Algorithm GDB : Gaia DataBase (obsolete; superseded by MDB) GDD : General Design Description GD : Gaia Detection GDIR : General Design and Interface Requirements GDMWG : Gaia Data Management Working Group (obsolete) GDPAC : Gaia Data Processing and Analysis Consortium GDRN : Gaia Data Reduction Network (obsolete) GEN : GENeral GEN : Observatoire de Gen\`eve GEO : Geostationary Earth Orbit GEPI : Galaxies Etoiles Physique et Instrumentation (OdP) GERF : Gaia Extra-galactic Reference Frame GFCC : Ground-Facilities Control Centre GF : Nominal effective `filter (band) profile' for AF (Astro) (obsolete) GFRP : Graphite Fiber-Reinforced Polymer GFTS : Generic File Transfer System (also denoted FITRAS) G : Gaia photometric white-light magnitude (SM and AF) GGG : Galician Group for Gaia (Universidad de La Coru\~na and University of Vigo) G : Giga; SI units prefix for 1E9 GGSSEG : Gaia Ground-Segment System Engineering Group G&H : G&H Technology, Inc. (US space industry company) GHOST : Gaia HOt Stars Team GIBIS : Gaia Instrument and Basic Image Simulator GIC : Gaia Input Catalogue (obsolete) GIDE : Generic Interface Data Exchange Gi : Gigabinary, Gibi; units prefix for 2^{30} = 1024 * 1024 * 1024 GIGO : Garbage In, Garbage Out GIS : (Astrometric) Global Iterative Solution GL : Gravitational Lensing GLIMPSE : Galactic Legacy Mid-Plane Survey Extraordinaire GLONASS : GLObal NAvigation Satellite System GmbH : Gesellschaft mit beschr\"ankter Haftung (German for company with limited liability) GM : Body-centric gravitational constant GMC : Giant Molecular Cloud GMF : Global Mapping Function GM : Galaxy Model GMM : Geometrical Mathematical Model GMnnn : Gaia MBP magnitude, with nnn the `central' wavelength in nm (obsolete) GMSK : Gaussian Minimum Shift Keying GMST : Greenwich Mean Sidereal Time GMV : Spanish `business solutions' company GN2 : Gaseous Nitrogen GNC : Guidance, Navigation, and Control GNM : Gaia Numerical Methods GNU : GNU is Not Unix GOES : Geosynchronous Operational Environmental Satellite(s) GOG : Gaia Object Generator GOM : Ground Operation Mode GOM : Ground Operations Mode GOP : Ground Operations Procedure GPA : Gravity Probe A GPB : Gravity Probe B GPDB : Gaia Parameter DataBase GP : Galactic Plane GPL : GNU Public License GPS : Galactic-Plane Scan GPS : Global Positioning System GPU : Gaia Processing Unit GRA : Gravity Reduction Action (risk management) GRB : Gamma-Ray Burst GRC : Global Reference Curve GREAT : Gaia Research for European Astronomy Training GREM : Gaia RElativity Model GR : General Relativity GRM : General Relativistic Model GRS : Geocentryc Reference System GRVOS : Gaia Radial Velocity Optimisation Study GSC : Guide Star Catalogue GSC-II : Guide Star Catalogue version 2 (also denoted as GSC-2) GSCMP : Ground-Segment Configuration Management Plan GSDD : Ground-Segment Design Document GSDM : Gaia SOC Development Manager GSDR : Ground-Segment Design Review GSDT : Gaia SOC Development Team GSE : Ground Support Equipment GSE : Gyro Stellar Estimator GSFC : Goddard Space Flight Centre (NASA) GSF : Nominal effective `filter (band) profile' for SSM (Spectro) (obsolete) GS : Gaia photometric white-light magnitude in Spectro (SSM; obsolete) GS : Ground Segment (also denoted G/S) GS : Ground Station (also denoted G/S) GSIR : Ground-Segment Implementation Review GSM : Ground-Segment Manager GSMT : Giant Segmented Mirror Telescope GSOE : Gaia SOC Operations Engineer GSOM : Gaia SOC Operations Manager GSOT : Gaia SOC Operations Team GSPAP : Ground-Segment Product Assurance Plan GSP : Generalised Star Parametrisation (Parametriser) GSPPHOT : Generalised Stellar Parametriser PHOTometry GSPSPEC : Generalised Stellar Parametriser SPECtroscopy GSR : Gaia Sphere Reconstruction GSRQR : Ground-Segment Requirements Review GSRR : Ground-Segment Readiness Review GSSE : Ground-Segment System Engineering GSTB : Galileo System Test Bed GST : Gaia Science Team GST : Greenwich Sidereal Time GST : Ground-Segment Team GSTV : Ground-System Test and Validation GTC : Ground Configuration Table GTD : Geometric Theory of Diffraction GT : GaiaTools G/T : Gain divided by (noise) Temperature GTK : Globus ToolKit GTP : Generic Telemetry Processor GTS : Gaia Transfer System GUI : Graphical User Interface GUM : Gaia User Manual GUMS : Gaia Universe Model Snapshot GVS : Global Variability Studies GWP : Gaia Work Package GYR : GYRoscope Gyro : GYROscope HAL : Hardware Abstraction Library (software) HBA : Host Bus Adapter HCO : Harvard College Observatory HCRS : Hipparcos Catalogue Reference System HCSS : Herschel Common Science Software HDA : High-Density Area HD : Historical Duration HDM : High-Density Mode HDRM : Hold Down and Release Mechanisms HEALPix : Hierarchical Equal-Area iso-Latitude Pixelisation HEMT : High Electron Mobility Transistor HEP : High-Energy Physics HFAD : High-Frequency Attitude Disturbances (also denoted AHFD) HFA : History File Archive HFE : Human Factor Engineering HF : Host Framework HGA : High-Gain Antenna HiPr : High Priority HKDCM : Housekeeping Data Collection Module HK : Housekeeping (also denoted H/K) HPA : High-Power Amplifier HPC : High-Performance Computing HPC : High-Priority Command H/P : Herschel/Planck (ESA missions) HPLV : High-Pressure Latch Valve HPR : Hardware Platform Review HPSRM : Hardware Processing System-C Reference Model (VPU) HPT : High-Pressure Transducer HRC : High-Resolution Channel (HST ACS) HRD : Hertzsprung-Russell Ddiagram HR : Hertzsprung-Russell (diagram) HR : High Resolution HRTF : High-Rate Telemetry Formatter HRVC : High-Rate Video Chain HSIA : Hardware/Software Interaction Analysis HSOB : High-Stability Optical Bench HSP : High System Priority HSSL : High-Speed Serial Link HST : Hipparcos Science Team HST : Hubble Space Telescope HTM : Hierarchical Triangular Mesh HTML : HyperText Markup Language HTS : High-Temperature Storage HTTP : HyperText Transfer Protocol HVLD : Horizontal and Vertical Lifting Device HW : Hardware (also denoted H/W) Hz : Hertz; SI unit of frequency I3 : Integrated Infrastructure Initiatives IAA : Institut d'Astronomie et d'Astrophysique (Bruxelles) IAD : Intermediate Astrometric Data (Hipparcos) IAD : Ion-Assisted Deposition IAE : Inertial Attitude Estimator IAG : International Association of Geodesy IAGL : Institut d'Astrophysique et de G\'eophysique de Li\`ege IAR : Implementation Acceptance Review IAR : Implementation and Acceptance Review IAUC : IAU Circular IAU : International Astronomical Union IBAS : INTEGRAL Burst Alert System IBE : Ion-Beam Etching IBF : Ion-Beam Figuring IB : Interconnection Board ICAP : Identification, Classification, and Astrophysical Parametrisation ICD : Interface Control Document IC : Initial Conditions IC : Integrated Circuit IC : Irradiated Configuration I : Cousins photometric I band ICP : Interconnection-module Configuration Package ICPOES : Inductive Coupled Plasma Optical Emission Spectroscopy ICRF : International Celestial Reference Frame ICRS : International Celestial Reference System IDA : IDT/IDU Algorithms IDA : Intermediate Data Algorithm (library) IDA : Intermediate Data Algorithms IDDMP : Information, Documentation, and Data Management Plan IDE : Integrated Development Environment IDFI : Integrated FDI IDFT : Inverse Discrete Fourier Transform ID : Identifier (Identification) ID : Injection Delay IDL : Interactive Data Language IDM : Interface and Data Manager IDMP : Information, Documentation, and Data Management Plan IDT : Initial Data Treatment (Image Dissector Tube in Hipparcos scope) IDU : Intermediate Data Update IDV : Intermediate Data Validation IEEC : Institut d'Estudis Espacials de Catalunya (Barcelona) IEEE : Institute of Electrical and Electronic Engineers IERS : International Earth Rotation Service IFA : Institute for Astronomy (Edinburgh) IFCP : Instrument Flight Control Procedure IFDI : Integrated Field Density Index IF : InterFace (also denoted I/F) IF : Intermediate Frequency IFMS : Intermediate Frequency and Modem System IFOP : Instrument Flight Operations Plan IFoV : Instantaneous FoV IGM : Inertial Guidance Mode IGSL : Initial Gaia Source List I : Implemented IIR : Infinite Impulse Response (filter) I : Italia (Italy) IIT : IDT Ingestion Task IKSSO : Identification of Known Solar-System Objects ILSA : Improved Least-Squares Approach IMCCE : Institut de M\'ecanique C\'eleste et de Calcul des Eph\'em\'erides IMF : Initial Mass Function IMHO : In My Humble Opinion IM : Instrument Model IM : Integration Model IM : Interconnection Module (FPA/CCD) IMT : Information Management Tool (a database used by the DPAC Project Office to administrate the status of requirements traceability, software documentation, etc.) IMU : Inertial Measurement Unit (Honeywell) INAF : Instituto Nazionale di Astrofisica (Italy) INFRA : INFRAstructure INFT : In-Flight Testing ING : INGestor INL : Integral Non Linearity INPOP : Int\'egrateur Num\'erique Plan\'etaire de l'Observatoire de Paris INTA : Laboratorio de Astrof\'isica Espacial y F\'isica Fundamental (LAEFF-INTA) INTEGRAL : INTErnational Gamma-Ray Astrophysics Laboratory (ESA) INT : Initial Training Network INT : INTterferogram (Code V format) IoA : Institute of Astronomy (Cambridge; also denoted IOA) IOC : Infinite Overlapping Circles IOC : In-Orbit Commissioning IOCR : In-Orbit Commissioning Review IOF : Institut fuer angewandte Optik und Feinmechanik (Fraunhofer Institut, Jena, Germany) IOGA : Initial On-Ground Attitude IO : Input-Output (also denoted I/O) IOM : Inter-Office Memorandum (JPL/NASA) IPC : Industrial Policy Committee (ESA) IPD : Image Parameter Updating IPD : Image Products Database IPFD : Isotropic Path Flux Density IP : Image Processing IP : Internet Protocol IPLM : Integrated Payload Module IPR : Intellectual Property Right IPU : Image Parameter Updating (in IDU) IRAF : Image Reduction and Analysis Facility (NOAO) IRD : Interface Requirements Document IRIG : Inter-Range Instrumentation Group IRQ : Interrupt ReQuest ISA : Initial Spectrum Analyser ISC : Integrated System Check ISCL : Indexed Statically Chained List ISDC : INTEGRAL Science Data Centre ISM : InterStellar Medium ISO : International Organisation for Standardisation (Geneva, Switzerland) Isp : SPecific Impulse (thruster) ISS : International Space Station ISS : Internet Service System ISST : Integrated Sub-System Test IST : Integrated SVM Test IST : Integrated System Test ISV : Independent Software Verification ISVT : Independent Software Verification Team ISVV : Independent Software Verification and Validation ITAR : International Traffic in Arms Regulations ITG : InTerroGator IT : Information Technology I&T : Integration and Test ITMC : Integrated TeleMetry Curve ITO : Indium Tin Oxide ITPA : Institute of Theoretical Physics and Astronomy (Vilnius) ITRF : International Terrestrial Reference Frame ITRS : International Terrestrial Reference System ITS : InTeSpace ITT : Integration and Test Team ITT : Invitation To Tender ITU : International Telecommunications Union IUGG : International Union for Geodesy and Geophysics IVA : Intra-Vehicular Activity IVOA : International Virtual Observatory Alliance IvS : Institute of Astronomy (Instituut voor Sterrenkunde; Catholic University of Leuven) JAS : Java Analysis Studio JASMINE : Japanese Astrometry Satellite Mission for INfrared Exploration JAXA : Japanese Aerospace Exploration Agency JBLAS : Java BLAS JDBC : Java DataBase Connectivity JD : Julian Date JDK : Java Development Kit JED : Julian Ephemeris Date (to be avoided; see also JD) JFET : Junction Field-Effect Transistor JHU : Johns Hopkins University JJPF : Java/Jini Parallel Framework JLAPACK : Java LAPACK JMAPS : Joint Milliarcsecond Astrometric Pathfinder Survey JMX : Java Management eXtensions JNI : Java Native Interface JOMP : prototype OpenMP implementation for Java JPB : Joint Procurement Board JPIP : Joint Project Implementation Plan JPL : Jet Propulsion Laboratory (DE ephemerides) JQL : Java Query language JRE : Java Runtime Environment JSP : Java Server Page JUREX : JUpiter RElativity Experiment JVAS : Jodrell Bank-VLA Astrometric Survey (catalogue) JVM : Java Virtual Machine JWST : James Webb Space Telescope (formerly known as NGST) KA : Acceptance Factor KAL : Keep-Alive Line KBO : Kuiper-Belt Object kbps : Kilobits per second KE : Kinetic Energy KF : Kalman Filter kg : Kilogram; SI unit of mass Ki : Kilobinary, kibi; units prefix for 2^{10} = 1024 KIP : Key Inspection Point K : Kelvin; SI unit of temperature k : Kilo; SI units prefix for 1E3 KM : Model Factor KO : Kick-Off KOM : Kick-Off Meeting KON : Konkoly Observatory of the Hungarian Academy of Sciences (Budapest) KP : Project Factor KQY : Qualification Factor krad : Kilorad (radiation dose unit) KRV : Kinematic Radial Velocity kSPS : KiloSamples Per Second KTC : Multiplication of k, T, and C (k: Boltzmann's constant; T: temperature; C: sense node capacitance); KTC noise is also known as reset noise L1 : First cache layer (cache RAM inside the CPU) L1 : First Lagrange point of the Sun and Earth-Moon system (not applicable to Gaia) L2I : L2 (orbit) Insertion L2 : Second cache layer (small SRAM chips on the motherboard) L2 : Second Lagrange point of the Sun and Earth-Moon system (applicable to Gaia) L3CCD : Low-Light-Level CCD (obsolete) LAB : Laboratoire d'Astrophysique de Bordeaux LAB : Lateral Anti-Blooming LA : License Agreement LAME : Luminosity, Age, and Mass Estimator LAM : Launch and Initial Acquisition Mode LAM : Launch & initial Acquisition Mode LAN : Local Area Network LAOB : Laboratoire d'Astrophysique de l'Observatoire de Besan{\c{c}}on LAPACK : Linear Algebra PACKage LASER : Light Amplification by Stimulated Emission of Radiation LaTeX : (Leslie) Lamport TeX (document markup language and document preparation system) LAT : Lot Acceptance Test L_B : Average value of 1-d(TT)/d(TCB) L_C : Average value of 1-d(TCG)/d(TCB) LCDA : Launcher Coupled Dynamic Analysis LCDM : Lambda Cold Dark Matter LCI : Launch-Critical Item LCLA : Launcher Coupled Loads Analysis LCL : Latch(ing) Current Limiter LCTA : Launcher Coupled Thermal Analysis LDAP : Lightweight Directory Access Protocol LED : Light-Emitting Diode LEI : Leiden Observatory (Sterrewacht Leiden) LEO : Low Earth Orbit LEON : Space-qualified processor LEOP : Launch and Early Orbit Phase LET : Linear Energy Transfer LFA : Lead Funding Agencies LFA : Local Funding Authority LGA : Low-Gain Antenna LGPL : Lesser General Public License L_G : Value of 1-d(TT)/d(TCG) (defining physical constant) LHC : Large Hadron Collider (at CERN) LHC : Left-Hand Circular LIC : Launcher Injection (dispersion) Correction (manoeuvre) LINEAR : The Lincoln Near-Earth Asteroid Research LISN : Line Impedance Stabilisation Network LIT : Listen-In Test LLI : Local Lorentz Invariance LLI : Long Lead Item LL : Limit Load LL : LiveLink LL : Lower Level LLR : Lunar Laser Ranging LLS : Linear Least Squares LMC : Large Magellanice Cloud (special, high-density area on the sky) LM : Laser Metrology LM : Levenberg-Marquardt LN2 : Liquid Nitrogen LNA : Laborat\'orio Nacional de Astrof\'isica (Brazil) LNA : Low-Noise Amplifier LOCO : LOssless COmpression LODC : LSF/PSF One-Day Calibration (FL) LoI : Letter of Intent LO : Lohrmann Observatory (Dresden Technical University) LoPr : Low Priority LoS : Line of Sight (also denoted LOS) LoS : Loss of Signal LPC : Local Plane Coordinates LPGL : Lesser Public GNU general License LPLV : Low-Pressure Latch Valve LPT : Low-Pressure Transducer LRR : Launch Readiness Review LRVC : Low-Rate Video Chain LSA : Launch Service Agreement LSA : Least-Squares Approach LSB : Least Significant Bit LSB : Linux Standard Base LSB : Low Surface Brightness (galaxy) LSF : Line Spread Function LS : Learning Set LS : Lommel-Seeliger (scattering law) LSM : Large-scale SiC Mirror (Gaia M1 demonstrator) LSP : Low System Priority LSS : Large-Scale Simulation (GASS) LSST : Large-aperture Synoptic Survey Telescope LSW : Landessternwarte (part of ZAH, Zentrum f\"ur Astronomie, Heidelberg) LTA : Long-Term Archive LTE : Local Thermal Equilibrium LTI : Linear Time Invariant LTOL : Local Trap-Occupancy Level LTP : Long-Term Plan(ning) LTT : Light Travel Time LTT : Line Transfer Time LU : Leicester University (UK) LU : Lund Observatory (Sweden) LUN : Logical Unit Number LUT : Look-Up Table LVA : Launch Vehicle Adaptor (Authority) LVDS : Low-Voltage Differential Signal LV : Latch Valve LV : Launch Vehicle L-X : Launch minus X (months, days, hours, minutes, ...) LZW : Lempel-Ziv-Welch (specific data compression scheme) M1 : First mirror M2M : M2 Mechanism M2MM : M2 Mirror Mechanism M2 : Second mirror M3 : Third mirror M4 : Fourth mirror M5 : Fifth mirror M6 : Sixth mirror MAAP : Motherhood And ApplePie MAD : Mission Assumptions Document MAE : Modified `Adaptive' Encoding MAINDB : MAIN DataBase MAIT : Manufacturing, Assembly, Integration, and Test MAN : MANual MAP : Multiplexed Access Point mas : Milliarcsecond (1E-3 arcsec) MAS : Mission Automation System MATISSE : Next-generation data management products that offer native object storage and support for SQL MBA : Main-Belt Asteroid MBEAN : Managed BEAN from JMX MbE : Model-based Encoding MBF : Medium-Band Filter (in MBP; obsolete) Mb : Megabit (1,000,000 bit) MB : MegaByte MBO : Main-Belt Object (asteroid) MBP : Medium-Band Photometer (obsolete) MBPM : Medium-Band Photometer Module (obsolete) Mbps : Megabits per second MBps : Megabits per second MBSM : Medium-Band photometer Sky Mapper (obsolete) MCC : Mission Control Centre MCDM : Multiple Criteria Decision Making MCEP : Mean Celestial Ephemeris Pole (obsolete) MC : Master Clock MCMC : Monte Carlo Markov Chain MCM : Monitor and Control Module MCM : MultiChip Module MC : Monte-Carlo (simulation/process) MCR : Main Control Room MCS : Mission Control System MCU : Main Computing Unit MDB : Main DataBase MDC : Mapped Diagnostic Contexts MDE : Mirror Drive Electronics MDR : Mission Definition Review MDVE : Model-based Development and Verification Environment MDW : Model Damaged Window MEA : Main Error Amplifier MEGACAM : Instrument at CFHT MEOP : Maximum-Expected Operating Pressure MeV : Mega-electron-Volt MFD : Mirror Fixation Device MFG : ManuFacturinG MF : Master Function MF : Minor Frame MFN : Master Function Number MGA : Medium-Gain Antenna MGR : ManaGeR MGSE : Mechanical Ground Support Equipment MIB : Minimum Impulse Bit MIB : Mission Information Base MICD : Mechanical Interface Control Document MIDAS : Munich Image Data Analysis System (ESO) MIFC : Manufacturing and Inspection Flow Chart Mi : Megabinary, Mibi; units prefix for 2^{20} = 1024 * 1024 MIMO : Multiple Input - Multiple Output MIOCR : Mission In-Orbit Commissioning Review MIP : Mandatory Inspection Point MIP : Mission Implementation Plan MIPS : Million Instructions Per Second Mips : Million instructions per second (also denoted MIPS) MIRD : Mission Implementation Requirements Document MIR : Management Information Report MIT : MOC Interface Task MJD : Modified Julian Date (to be avoided; see also JD) MLA : Multi-Lateral Agreement MLI : Multi-Layer Insulation M-L : Mass-Luminosity (relationship) M : Mega; SI units prefix for 1E6 m : Meter; SI unit of length MMH : Mono-Methyl Hydrazine MMIC : Monolithics Microwave Integrated Circuit m : Milli; SI units prefix for 1E-3 MM : Man Month MM : Mirror Mechanism (M2 mirror) MM : Mission Manager MMS : Matra Marconi Space (now EADS Astrium) MMU : Mechanical Mock-Up MNEM : MNEMonic MN : Meeting Minutes MOC : Mission Operations Centre MOD : Mission Operations Department MOD : Modulus of integer division MoI : Moment of Inertia MOIS : Mission Operations Information System MoM : Minutes of Meeting MOM : Mission Operations Manager MOND : MOdified Newtonian Dynamics MOSFET : Metal-Oxide Semiconductor Field-Electric Transistor MoS : Margin of Safety MOST : Micro-variability and Oscillations of STars MPA : Micro-Propulsion Assembly MPCB : Material and Process Control Board MPC : Minor Planet Centre MPE : Micro-Propulsion Electronics MPFM : Micro-Propulsion Feed Module MPHF : Mass Properties History File MPHF : Mass Property History File MPIA : Max Planck Institute for Astronomy (Heidelberg) MPI : Message Passing Interface MPLS : Multi-Protocol Label Switching MP : Management Plan MP : Metal-Poor (star) MPP : Message Passing Package MPP : Message Processing Programme MPPT : Maximum Power Point Tracker MPR : Monthly Progress Review MPSK : M-Phase Shift Keying MPS : Micro-Propulsion Sub-system MPS : Mission Planning System (at MOC) MPT : Multi Purpose Trolly MPTS : Multi-Purpose Tracking System MRB : Material Review Board MRC : Master Reference Cube MRD : Mission Requirements Document MRE : Mean Rate Error MR : Metal-Rich (star) MR : Modified Relativity MRR : Manufacturing (Mission) Readiness Review MRS : Mechanical Reference System (obsolete; replaced by SCRS) MRT : Mission Readiness Test MRU : Main Regulator Unit MSB : Most Significant Bit MSCB : Management and Schedule Control Board MSC : Multiple-Star Classifier MSC/NASTRAN: Software for finite-element analysis MSE : Mean Standard Error MSG : Meteosat Second Generation MSL : Modified Scanning Law MS : Main Sequence (star) MS : MicroSoft (software company) MSOO : Mission Scheduling and Optical Observations MSRR : Mission SRR MSSL : Mullard Space Science Laboratories (UK) MST : Minimal Spanning Tree M-SVM : Mechanical SerVice Module MSVM : M-SVM MTA : Micro(-Propulsion) Thruster Assembly MTA : Micro-Thruster Assembly MTBF : Mean Time Between Failure MTF : Modulation Transfer Function MTJ : Matrix Toolkits for Java MTL : Mission Time Line MTM : MPS Thrust Modulator MTO : Maximum Time slot marker Offset MTP : Medium-Term Plan(ning) MTP : Mid-Term Presentation MTR : Mid-Term Review MTS : Maximum TS Sources MTS : Mission Timeline Summary muas : Microarcsecond (1E-6 arcsec) mu : Micro; SI units prefix for 1E-6 MU : Mock-Up muP : Micro Processor mus : Microsecond MUX : MUltipleXer MY : Man Year NACK : Negative Acknowledgement NA : Neutraliser Assembly NA : Not Applicable (also denoted as N/A) NAOJ : National Astronomical Observatory of Japan NAP : Normal Astro Phase (sub-mode of AOCS Normal Mode) NASA : National Aeronautics and Space Administration (USA) NAS : Network Attached Storage NBI : Niels Bohr Institute (Copenhagen, Denmark) NCD : Network Configuration Document NCR : Non-Conformance Report NCTRS : Network Control and Routing System NCTSR : Network Control and Telemetry Routing System NDAC : Northern Data Analysis Consortium (Hipparcos) NDA : Non-Disclosure Agreement NDB : Network DataBase NDI : Non-Destructive Inspection NDIU : Network Data Interface Unit ND : Neutral Density (filter) NEA : Near-Earth Asteroid NEA : Non-Explosive Actuator NEC : Near-Earth Comet NEE : Noise Equivalent Error NEO : Near-Earth Object NEP : North Ecliptic Pole NER : Normal-Equation Residual NES : Non-Emergency Surveillance NFS : Network File System NGST : Next Generation Space Telescope (obsolete; now called JWST) NIEL : Non-Ionising Energy Loss NIMO : Non-Inverted Mode Operation NI : Non-Irradiated NI : Not Implemented NIS : Network Interface Server NIST : National Institute of Standards and Technology (USA) NL : NetherLands NLTE : Non-LTE NM : Normal Mode (AOCS) n : Nano; SI units prefix for 1E-9 N : Newton; SI unit of force NNI : Native Numerical Interface NN : Nearest Neighbour NNO : New NOrcia (ESA ground station near Perth, Australia) NNR : No-Net-Rotation NOA : National Observatory of Athens (Greece) NOAO : National Optical Astronomy Observatories (USA) NOMC : Normal Operation Mode with Chemical thrusters NOME : Nominal (scientific) Operational ModE NOM : NOMinal NOP : Network Operations Procedures NOVAS : Naval Observatory Vector Astrometry Subroutines (USNO) NRB : Non-conformance Review Board (previously known as MRB) NRD : Numerical Requirements Document NRT : Near Real-Time NRZ-L : Non-Return to Zero-Level NSDC : Natural Satellites Data Centre NSFA : Numerical Standards in Fundamental Astronomy NSI : NASA Standard Initiator NSL : Nominal Scanning Law NSS : Non-Single Star NST : Nitrogen Storage Tank NSVF : Numerical Software Validation Facility NTO : (di-)Nitrogen TetrOxide NTO : Nitrogen TetrOxide NTT : New Technology Telescope (ESO) NTUA : National Technical University of Athens (Greece) NVO : National Virtual Observatory (USA) NWO : Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands) OABO : Osservatorio Astronomico di Bologna OACN : Osservatorio Astronomico di Capodimonte (Napoli) OACT : Osservatorio Astrofisico di Catania OA : Outlier Analysis OAPD : Osservatorio Astronomico di Padova OARM : Osservatorio Astronomico di Roma OASIS : Organisation for the Advancement of Structured Information Standards OATE : Osservatorio Astronomico di Teramo OATO : Osservatorio Astronomico di Torino OBA : Optical-Bench Assembly OBCD : On-Board-Computed Data OBCP : On-Board Control Procedure (not applicable to Gaia) OBDH : On-Board Data Handling OBD : On-Board Detection OBDWG : On-Board Detection Working Group (obsolete) OBJ : OBJect processing OBMF : On-Board Monitoring Function OBMT : On-Board Mission Timeline OB : On-Board OB : Optical Bench ObsGE : Observatory of GEneva (Switzerland) OBSM : On-Board-Software Maintenance OBS : On-Board Storage OBS : On-Board time broadcasting Signal OBS : Organisation Breakdown Structure OBSR : On-Board Storage and Retrieval OBSS : Origins Billion Star Survey (NASA) OBSW : On-Board Software OBTM : On-Board Time Management OBT : On-Board Time (realised in CDU) OCA : Object Cluster Analysis OCA : Observatoire de la C\hat{o}te d'Azur (Nice) OCC : Operations Control Centre OCMC : Orbit Control Mode with Chemical thrusters OCM : Orbit Control Mode OCMS : ORATOS Configuration Management System O-C : Observed minus Computed OC : Open Centre ODAS : One-Day Astrometric Solution ODB : Operational DataBase ODC : One-Day Calibration ODE : Ordinary Differential Equation ODF : Opacity Distribution Function ODIS : One-Day Iterative Solution OD : Object Data (source packet) OD : Operational Day OdP : Observatoire de Paris (France) ODP : Optical Data Processor OEM : Orbital Ephemeris Message OEM : Orbit Ephemeris Message OF : Object Feature (source packet) OFT : Orbital Flight Test OFW : Optimum Full Well OGA1 : First On-Ground Attitude determination (in IDT) OGA2 : Second (and improved) On-Ground Attitude determination (in ODAS/FL) OGA : On-Ground Attitude OGLE : Optical Gravitational Lensing Experiment OGSE : Optical Ground Support Equipment OGS : Operations Ground Segment OHP : Observatoire de Haute Provence (France) OIRD : Operations Interface Requirements Document OITF : Offset-Instability Task Force OJDBC : Oracle JDBC OJS : ORATOS Job Scheduler OL : Open Loop OMA : Opto-Mechanical Assembly OM : Object Matching OM : Operational Manual OM : Operations Manager ONU : Offset Non-Uniformity OOC : On-Orbit Control OoL : Out of Limit OO : Object Oriented OPAL : On-board software Process Assets Library OPD : Optical Path Difference OPM : Observatoire de Paris Meudon (France) OPSNET : OPErations NETwork OPS : Object Processing System OPS : OPerationS OPTO : OPTical observations - spacecraft Observation file OPTT : OPTical observations - Telescope list file OPUS : Operational Pipeline Unified Systems ORATOS : ORbit and ATtitude Operations System OR : Observation Report OR : Offner Relay (RVS; obsolete) ORR : Operations Readiness Review ORU : Orbital Replaceable Unit OSA : Overall System Architecture OSE : Optical Sources and Electronics OSF : Operations Schedule File OS : Observatoire de Strasbourg (France) OS : Operating System OTS : Off-The-Shelf OWL : OverWhelmingly Large Telescope OWLT : One-Way Light Time PAA : Phased-Array Antenna PACK : PACKet (Telecommand or Telemetry) PAD : Part Approval Document PAED : Project Assurance and Engineering Disposition Pan-STARRS : Panoramic Survey Telescope and Rapid Response System PAP : Product Assurance Plan PA : Product Assurance PAR : Performance Assessment Report PAS : Payload Adapter System PATP : Preliminary Authorisation To Proceed PBK : Parameter BookKeeping PB : PetaByte PB : Play-Back PCA : Pressure Control Assembly PCA : Principal Component Analysis PCAT : Packet CATegory PCB : Parts Control Board PCB : Printed Circuit Board PC : (DPAC Project Office) Project Coordinator PCDU : Power Control (Conditioning) and Distribution Unit PCG : Pre-conditioned Conjugate Gradient PCGS : Proportional Cold-Gas Sub-system PCI : Peripheral Component Interface PCM : Pulse Code Modulation PC : Personal Computer PCP : Project Closure Plan PC : Prime Contractor PCU : Power Control Unit PDA : Percentage Defects Allowance PDA : Photometric Data Analysis PDB : (Gaia) Parameter DataBase PDF : Portable Document Format PDF : Probability Density Function PDHE : Payload Data Handling Electronics PDHS : Payload Data Handling Sub-system PDHS : Payload Data Handling Support PDHU : Payload Data Handling Unit PDMS : Prototype Data Management System PD : Parasite Detection (in IDU) PD : Partial Derivative PDP : Project Development Plan PD : Proportional plus Derivative controller PDR : Preliminary Design Review PDS : PLM Deployment Stand PDU : Power Distribution Unit PEGASE : Projet d'Etude des Galaxies par Synth\`ese Evolutive PEM2 : (Maxwell) Prototype Engineering Model #2 (VPU) PEM : Prototype Engineering Module PEM : Proximity Electronics Module PERP : PEriodic RePorting PFCI : Potential Fracture-Control Item PFC : Parameter Format Code PFL : Probability of Frame Loss (also known as FLP) PFM : Proto Flight Model PFS : Point Spread Function PGIS : Photometric Global Iterative Solution PGSE : Propulsion Ground-Support Equipment PhD : Doctorate in Philosophy PHOT : PHOTometric processing PIA : Propellant Isolation Assembly PID : PAA Integration Device PID : Process IDentifier PID : Proportional plus Integral plus Derivative controller PIND : Particle-Induced Noise Detection PI : Partially Implemented PIP : Project Implementation Plan PI : Principal Investigator PISA : Principal Investigator Support Area PJM : Plasma Jet Machining PK : Pimary Key PLASTIC : PLatform for AStronomy Tool InterConnection PLC : Period-Luminosity-Colour (star) PLL : Phase-Locked Loop PLM : PayLoad Module PL : Payload (also denoted P/L) PL : Period-Luminosity (star) PMAC : Payment Milestone Achievement Certificate PMA : Preliminary Mission Analysis PMD : Propellant Management Device PMD : Software tool to detect software problems PMIS : Project Management Information System PMO : Project Management Officer PM : Phase Modulation PM : Polarisation Maintaining PMP : Parts, Materials, and Processes PMP : Planning Management Plan PM : Progress Meeting PM : Project Manager PNG : Portable Network Graphics PODC : Photometric One-Day Calibration (FL) PO : (DPAC) Project Office POD : Predicted Orbit Data PO : Partial Observation (of object in AF) POR : Payload Operations Request POSIX : Portable Operating System Interface POS : Payload Operations System PoS : Plane-of-Sky PPARC : Particle Physics and Astronomy Research Council (UK, obsolete and now STFC) PPBI : Post-Programming Burn-In PPC : Power PC PPCU : Power Processing and Conditioning Unit (FEEP) PPE : Prompt Particle Event p : Pico; SI units prefix for 1E-12 PPL : Probability of Packet Loss ppm : Parts per million PPMX : PPM-eXtended (extended version of PPM catalogue) PPN : Parametrised Post-Newtonian (formalism in General Relativity) PP : Propulsion Panel PPS : Pulses Per Second PRA : Preliminary Risk Assessment PRA : Probability Reduction Action (risk management) PRD : Performance Report Document PREF : Parameter REFerence (number) PRiSM : Parall\`elisme, des R\'eseaux, des Syst\`emes, et de la Mod\'elisation (UVSQ) PRNL : Pixel-Response Non-Linearity PRNU : Photo-Response Non-Uniformity PROC : PROCedure PROM : Programmable Read-Only Memory PR : Progress Report PRR : Preliminary Requirement Review PRS : Pixel Reference System PRS : Precessing Reference System PRT : Packet Routing Table PRT : Platinum Resistance Thermometer PRU : Pyrotechnic Release Unit PSA : Parts Stress Analysis PSD : Power Spectral Density PSF : Point Spread Function PS-ICD : Packet Structure Interface Control Document PSI : Paul Scherrer Institut (Switzerland) PSK : Phase Shift Keying PS : Photometric System PS : Project Scientist PSR : Project Support Room PSS : PEM Support Structure PSS : Portable Satellite (Spacecraft) Simulator PSS : Procedures, Specifications, and Standards PSST : Project Scientist Support Team PSU : Power Supply Unit PSV : Phase State Vector PTC : Parameter Type Code PTC : Passive Thermal Control PTC : Photon Transfer Curve PTFE : PolyTetraFluoroEthylene PT : Pressure Transducer PT : Product Tree PTR : Post Test Review PtV : Peak-to-Valley PTXC : Packet Transmission Control PUS : Packet Utilisation Standard PVA : Photo Voltage Assembly PVA : Photo-Voltaic Assembly PVA : Pressurised Vessal Assembly PVCF : Partial Virtual-Channel Frame PV : Performance Verification PVS : Procedure Variation Model PWG : Photometry Working Group (obsolete) PWM : Pulse Width Modulation PWR : PoWeR PYXIS : PYXel Instrument Software (PDHE) (also known as Pyxis; obsolete) QA : Quality Assurance QAR : Qualification Acceptance Review QA&V : Quality Assurance and Validation QA&VU : Quality Assurance and Validation Unit QCI : Quality Conformance Inspection QC : Quality Control QEH : Quantum Efficiency Hysteresis QE : Quantum Efficiency (CCD) QL : Qualification Load QL : Quick Look QML : Qualified Manufacturers List QM : Qualification Model QMS : Quality Management System QPL : Qualified Products List QR : Qualification Review QRS : Quartz Rate Sensor QSL : Qualification Status List QSOC : QSO Classifier QSO : Quasi-Stellar Object QTH : Quartz Tungsten Halogen QTR : Qualification Test Review RAA : RUAG Aerospace Austria RACM : Rubidium Atomic Clock Module RAC : Real Application Cluster RAF : Return All Frame RAFS : Rubidium Atomic Frequency Standard RAID : Redundant Array of Inexpensive Disks RAL : Rutherford Appleton Laboratory (UK) RAMOD : Relativistic Astrometric MODel RAM : Random Access Memory RAMS : Reliability, Availability, Maintainability, and Safety RA : Right Ascension RAR : RAMS Analysis Report RAS : Rien \`a Signaler (nothing special to be noted) RAVE : RAdial Velocity Experiment RBD : Reliability Block Diagram RB : Requirements Baseline Rb : Rubidium RCD : Requirements Control Document RCF : Return Channel Frame R : Cousins photometric R band RC : Reference Configuration RC : Requirements Compilation RCR : Requirements and Conceptual Design Review RCS : Reaction Control Sub-system RCWG : Radiation-Calibration Working Group RDB : Raw DataBase RDM : Reference Data Manager RDP : Radiation-Damage Parameter RD : Reference Document R&D : Research and Development REMAT : RElativistic Models And Tests (DU in CU3) REN : Rigid Earth Nutation REOSC : Optronic Systems Department of SAGEM REP : Radial Equipment Panel RE : Radiated Emission REU : Remote Electronics Unit (not applicable for Gaia) RFA : Request for Approval RFC : Request for Comments RFCT : Radio Frequency Compatibility Test RFDN : Radio Frequency Distribution Network RFD : Request For Deviation RFDU : Radio Frequency Distribution Unit RFI : Request For Information RFLV : Relative Focal Length Variation RFQ : Request For Quotation RF : Radio Frequency RF : Reference Frame RFSR : RF Suitcase Requirements RFW : Request For Waiver RGB : Red Giant Branch (star) RGC : Reference Great Circle RGCS : Reference Great-Circle System RHC : Right-Hand Circular RIC : Radiation-Induced Conductivity RID : Review Item Discrepancy RIDT : RVS Initial Data Treatment (FL) RIFA : Relativity In Fundamental Astronomy RKP : Requirement Key Point RLPD : Rate-Limited Proportional-Derivative attitude controler RME : Rate Measurement Error RMI : Remote Method Invocation RMP : Risk Management Plan RM : Reconfiguration Module RMS : Root-Mean-Square RMT : Risk Management Team RMU : Rate Measurement Unit RNP : Research Network Programme roAp : Rapidly oscillating Ap star ROA : Read-Out Amplifier (CCD) ROB : Royal Observatory of Belgium ROD1 : Reconstructed Orbit Data 1 ROD2 : Reconstructed Orbit Data 2 RODC : RVS One-Day Calibration (FL) ROD : Restituted Orbit Data RoD : Review of Definition RoD : Review of Design ROEMER : Proposal for the Third Medium-Size ESA Mission (M3; not approved) ROFT : Read-Out Finishing Time ROM : Read-Only Memory ROM : Rough Order of Magnitude RON : Read-Out Noise (CCD) ROOT : Object-oriented data analysis framework developed at CERN RO : Read-Out (sample coordinate) ROR : Read-Out Register (also known as Serial Register) RPE : Relative Pointing Error RPM : Revolutions Per Minute RPP : Red-Photometer Prism RPPU : RVS Pre-Processing Unit (obsolete) RP : Red Photometer RP : Resolving Power RRFWG : Relativity and Reference Frame Working Group (obsolete) R : Row (CCD chip across-scan coordinate identifier in focal plane) RR : Rate Reduction RS232C : Standard 25-pin serial connection between computers and modems RSA : RUAG Space Austria RSD : Reference Sampling Delay RSE : Robust Scatter Estimate (measure of distribution width in AGIS) RSLI : Reference Scanning Law schedule - ICRF attitudes RSLO : Reference Scanning Law schedule - initial spin phase (Omega) RSLQ : Reference Scanning Law schedule - Quaternion attitudes RSL : Reference Scanning Law RSLS : Reference Scanning Law Schedule RS : Radiated Susceptibility R-S : Reed-Solomon (encoding) RS : Reference System RSSD : Research and Scientific Support Department (ESA) RSS : Really Simple Syndication RSS : Reference Sky Scene RSS : Root-Sum-Square RTB : Real-time TestBed RTC : Real-Time Clock RTDB : Run-Time DataBase RTD : Resistance Temperature Detector RTEMS : Real-Time Executive for Multiprocessor System (software) RTF : Radiation Task Force (DPAC internal) RTN : Research Training Network (EU) RTO : Recovery Time Objective RTOS : Real-Time Operating Software RTP : Real-Time Prototype RT : Real-Time RT : Remote Terminal R&T : Research and Technology RT : Room Temperature RTS : Real-Time Simulator RTU : Remote Terminal Unit RUG : RijksUniversiteit Groningen (Kapteyn Astronomical Institute) RUP : Rational Unified Process RVF : Radial Velocity Filter (special filter in MBP; obsolete) RV : Radial Velocity RVSM : Radial Velocity spectrometer Sky Mapper (obsolete) RVS : Radial Velocity Spectrometer RVSWG : RVS Working Group (obsolete) RVT : Radiation Verification Test RVZP : Radial Velocity Zero Point RW : Random Walk S3R : Sequential Switching Shunt Regulator S5M : MBP photometric system (see C1M; obsolete) SAAC : Software for Analysing Astrometric CCD (data) SAA : Solar Aspect Angle SAA : South Atlantic Anomaly SADT : Structured (System) Analysis and Design Technique SAFLIM : Semi-analytical Approach Functions to LIssajous Motion SAGA : System of Accommodation for Gaia Algorithms (CNES) SAGA : System of Accomodation of Gaia algorithms SAGEM : Specific company for design, development, and manufacturing of opto-mechanical equipment SAG : Science Advisory Group (obsolete; superseded by GST) SAG : Sun Acquisition Gyrometer SaH : Sample and Hold SAM : Sun Acquisition Mode (AOCS) SAN : Storage Area Network SAO : Smithsonian Astrophysical Observatory SAP : Solar-Array Panel SAPS : Solar-Array Power Simulator SAR : Specification (System) and Architecture Review SARV : Small-Amplitude Regular Variable (star) SA : Science Alert(s) SA : Solar Array SAS : Science Analysis System (XMM) SAS : Soci\'et\'e par Actions Simplifi/'ee SAS : Solar Array Simulator SAS : Sun Acquisition Sensor SAT : Satellite Archive Team SaW : Stand-alone Worker SAW : Stand-Alone Worker SBC : Single Board Computer SBC : Supplementary Buried Channel (CCD) SBM : Stand-By Mode SBN : Small Bodies Nomenclature SB : Spectroscopic Binary (star) SBT : Satellite Base Time (the practical representation of OBT) SC3 : Special Commission number 3 on Fundamental Constants (IAG) SCAG : Source, Calibration, Attitude, Global (AGIS) SCA : Software Criticality Analysis SCCS : Standard Cubic Centimeters per Second SCET : SpaceCraft Event Time (realised in CDMU, SCET is slaved to OBT) SCI : Schedule-Critical Item SCL : Static Change List SC : (MLA) Steering Committee SCMP : Software Configuration Management Plan SCM : Software Configuration Managment SCN : SCeNe SCOE : Special Check-Out Equipment SCOM : SCience Operations Manager SCOS2000 : Default ESA SCOS (also known as SCOS2K and S2K) SCOS : Spacecraft Control and Operations System SCOT : Special Conditions Of Tender SCP : Satellite Commissioning Plan ScQL : Science Quick Look (obsolete) SCR : Simulations Control Room SCR : Software Change Request SCRS : SpaceCraft Reference System SCS750FX : Specific PPC board (Maxwell) SCSI : Small Computer System Interface SC : Spacecraft (also denoted S/C) SCS : Spacecraft Common Simulator SDA : Specific Development Activity SDBC : Satellite DataBase Content SDBD : Satellite DataBase Delivery SDB : Satellite DataBase SDB : Spacecraft DataBase SDCM : Source Data Collection Module SDD : Software Design Document SDE : Software Development Environment SDID : Starv Density Injection Delay SDK : Software Development Kit SDPC : Spectroscopic Data Processing Centre SDPM : Source Data Processing Module SDP : Software Development Plan SDP : Supplementary Data Pattern SDR : System Design Review SDS : Science Data Server SDSS : Sloan Digital Sky Survey SD : Standard Deviation SE2ET : System End-to-End Test (also denoted (SETET) SEB : Single-Event Burn-out (also denoted SEBO) SECDEC : Single Error Correction and Double Detection SED : Spectral Energy Distribution SEE : Single-Event Effect SEF : Science Event File SEF : Standard Exchange Format SEGR : Single-Event Gate Rapture SEG : Software Engineering Guidelines SEL : Single-Event Latch-up SEM : Space Environment Monitor (GOES) SEPE : Solar Energetic Particle Event SEPM : Solar Electrical Propulsion Module SEP : South Ecliptic Pole SEP : Strong Equivalence Principle SE : Standard Edition SE : Standard Error SETET : System End-To-End Test (also denoted SE2ET) SET : Single-Event Transient SEU : Single-Event Upset SFCG : Space Frequency Coordination Group SFH : Star Formation History SFIRD : Stations and Facilities Implementation Requirements Document SFM : Stations and Facilities Manager SFR : Star Formation Rate SF : Scale Factor SF : Soyuz-Fregat SFT : Short Functional Test SFW : Surface Full Well SGA : Stellar and Galactic Astronomy group SGICD : Space to Ground Interface Control Document SGIS : Spectroscopic Global Iterative Solution SGM : Safe Guard Memory Sgr : Sagittarius (constellation with high average star density) SGSDD : Science Ground-Segment Design Description SGS : Science Ground Segment SGS : Symmetric Gauss-Seidel SIA : Sagnac Interferometer Assembly SiC : Silicon-Carbide (material for PLM torus, mirrors, etc.) SID : Structure Identifier SID : System Identifier (Oracle) SIF : Service Interface Function (spacewire link for S/W load/troubleshooting) SILOGIC : French IT company SIMDATA : SIMulation DATA SIMSAT : Software Infrastructure for Modeling Satellites SIM : SIMulation (SIMulator) SIM : Space Interferometry Mission SiNAD : Signal-to-Noise Detection Ratio SIP : Science Implementation Plan SIRD : Science Implementation Requirements Document SIR : Specifications and Interfaces Review Si : Silicon SISO : Single Input - Single Output SISO : Single Input, Single Output SISPA : Small Instantaneous Sub-Pupil Area SIS : Spacecraft Information System SIS : Spacecraft Interface Simulator SIS : Spectroscopic Iterative Solution (superseded by SGIS) SI : Syst\`eme International (International System of units, defined by ISO) SIT : System Integration Test SIXE : Spanish-Italian X-ray Experiment SKEL : Spacecraft Key Event Log SK : Spare Kit SLED : Super LED SLE : Space Link Extension SLG : Scanning-Law Guidance SLM : Scanning-Law Monitor SLRS : System-Level Reassessment Study SLTA&DS : System-Level Technical Assistance and Definition Study SLTRS : System-Level Technical Reassessment Study SLT : Sector Link Table SMA : Shape Memory Alloy SMA : Star Mapper(-based) Attitude (Hipparcos) SMC : Small Magellanice Cloud (special, high-density area on the sky) SMD : Surface Mount Device SME : Small- and Medium-sized Enterprises SME : Software Maintenance Environment SMO : Suspect Moving Object SMP : Science Management Plan SMR : Software Modification Request SM : Sky Mapper SM : Software Module SM : Structural Model SMTP : Small-Message Transfer Protocol SMT : Surface Mounted Technologies SNAP : Supernova-Acceleration Probe SNR : Science News Release (ESA) SNR : Signal-to-Noise Ratio (also denoted SN and S/N) SNR : SuperNova Remnant SN : Serial Number (also denoted S/N) SN : SuperNova SOAD : Science Operations Assumptions Document SOAP : Simple Object Access Protocol SOC : Science Operations Centre SoC : Status of Compliance SOC : System On a Chip SODA : SCOS ORATOS Distributed Access SOFA : Standards Of Fundamental Astronomy (IAU) SOF : Spacecraft Observations File SOGS : Science Operations Ground Segment SOIA : Science Operation Implementation Agreement SOM : Self-Organising Map SOM : Spacecraft Operations Manager SOM : Spacecraft Safe Mode SoM : Space of Measurements SOR : Science Operations Request SOSD : Science Operations Scenario Document SOS : Specific Object Studies SOT : Science Operations Team SOT : Science Operations Tool SOVP : System Operations Validation Plan SoW : Statement of Work SOW : Statement Of Work SPACON : SPAcecraft CONtroller SPAE : Source PArallax Error SPAP : Software Product Assurance Plan SPaP : Stream Pre-compression and Partitioning SPAR : Software Product Assurance Report SPA : Software Product Assurance SPAU : Source PArallax Update SPB : Senior Procurement Board SPB : Slowly Pulsating B-star SPC : Science Programme Committee (ESA) SPD : Spectral Products Database SPEC : SPECtroscopic processing Spectro : Spectrometer instrument (obsolete) SPENVIS : SPace ENVironment Information System SPE : Solar Particle (Proton) Event SPF : Single-Point Failure SPGRID : SPectral GRIDS (grids of synthetic spectra) SPG : Sun Position Generator (AOCS) SPID : SCOS-2000 Packet Identifier SPLIB : SPectral LIBraries (synthetic spectral data) SP-L : Split Phase-Level SPME : Source Proper-Motion Error SPMP : Software Project Management Plan SPMU : Source Proper-Motion Update SPOE : Source POsition Error SPOU : Source POsition Update SPR : Software Problem Report SP : Software Product SP : Source Packet SP : SPecification SPS : Samples Per Second SPSS : Spectro-Photometric Standard Star SPSS : Statistical Package for the Social Sciences (now, more generally, a leading worldwide provider of predictive analytics software and solutions) SP : Star Packet SP : Static Parameter SP : Sub Pupil SPU : Spectro Processing Unit (obsolete) SPV : Supervisor (module) SpW : Space Wire SQAP : Software Quality Assurance Plan SQL : Structured Query Language SQMP : System Quality Management Plan SRaD : Stream Restoration and Decoding SRAM : Static RAM SRC : Spacecraft Reference Configuration SRD : Software Requirements Document SRD : System Requirements Document SREM : Space Radiation Environment Meter (obsolete) SRE : Science and Robotic Exploration (ESA directorate) SRF : Software Re-use File SRH : Shockley-Read-Hall SRIF : Square-Root Information Filter SRIM : Stopping Range of Ions in Matter SRM : Separation Release Mechanism SRN : Software Release Note SRP : Solar Radiation Pressure SRR : System Requirements Review SR : Semi-Regular (variable star) SRS : Scanning Reference System SRS : Software Requirements Specification SRS : Spacecraft Reference System (obsolete) SRS : Spacecraft Requirements Specification SR : Status Report SR : Summing Register (also known as Summing Well) SRV : Semi-Regular Variable (star) SRV : Spectroscopic Radial Velocity SSAC : Space Science Advisory Committee (ESA) SSA : Software Support Area SSAS : Single-Star Astrometric Solution SSCB : Station-Spacecraft oCculting Body angle SSCH : Science SCHedule SSC : Source Sequence Count SSC : Spectrum Shape Coefficient SSC : Spitzer Science Centre (NASA) s : Second; SI unit of time SSLC : Single-Sided Limit Cycle SSL : Secure Socket Layer SSMM : Solid-State Mass Memory SSM : Second Surface Mirror SSM : Spacecraft Safe Mode SSM : Spectro Sky Mapper (obsolete) SSOC : Solar-System-Object Classifier SSO : Solar-System Object SSPA : Solid-State Power Amplifier SSR : Science Support Room SSR : Software Support Room SSR : Solid-State Recorder SSSB : Small Solar-System Body SS : Solar System SSSO : Small Solar-System Object SSS : Software and System Specification SSS : Software System Specification SSS : System Software Specification SS : Sub-System (also denoted S/S) SS : Sun Search SS : SunShield (also denoted SSH) S : Strip (CCD chip along-scan coordinate identifier in focal plane) SST : Space Surveillance Telescope SSU : Specific Source Unit SSWG : Solar-System Working Group (obsolete) STAF : File Archive and Transfer Service (implemented at CNES) STB : Software Test Bench STC : STation Computer stdin : Standard input STDM : Spacecraft Trajectory Data Message stdout : Standard output STD : STandarD STE : Special Test Equipment STES : Star Tracker Electronics Stimulator STE : Star-Tracker Electronics STFC : Science and Technology Facilities Council (UK, formed on 1 April 2007 by merging PPARC and CCLRC) STH : Star-Tracker Head STI : Shield Thermal Insulator STI : Sunshield Thermal Insulator STI : Sunshield Thermal Isolator STK : Software ToolKit STM : Structural and Thermal Model (Structural-Thermal Mode, Structure Test Model) STP : Software Test Plan STR-E : Star Tracker Electronics STR-OH : Star Tracker Optical Head STRP : STatistic RePorting STR : Software Test Report STR : Star TRacker ST : Satellite Time ST : Scientific Target STSP : Standard Time Source Packet STS : Star Tracker System STS : System Test Specification STUFF : Computer code to generate mock catalogues of astronomical sources (E. Bertin) STVR : Software Test and Validation (Verification) Report STV : STeVenage (UK) SubCo : Sub-Contractor SUM : Software User Manual SUM : Spacecraft (or Satellite) User Manual SUPER : Supervised classification SuROM : Start-up ROM SuSW : Start-up SoftWare SVD : Singular Value Decomposition SVD : Special Variability Detection SVF : Software Validation (Verification) Facility SVM : SerVice Module SVM : Support Vector Machine SVN : SubVersioN SVO : Spanish Virtual Observatory SVP : Sample Video Package SVP : Software Validation Plan SVP : System Verification Plan SVS : Software Validation Specification SVTP : Software Verification Test Plan SVT : System Validation Test SVVP : SVV Plan SVVR : SVV Report SVV : Software Verification and Validation SWA : Sliding Window Algorithm (obsolete) SWG : Simulation Working Group (obsolete) SWR : Equipment software resource SWRI : Southwest Research Institute (USA) SWR : Software Resource SW : Software (also denoted S/W) SW : Space Wire SWS : Sampling and Windowing Strategy SYNTH : Specific spectrum synthesis software (Nikolai Piskunov) TAA : Technical Assistance Agreement TADS : Technical Assistance and Definition Study (also denoted TA&DS) TAI : International Atomic Time TAR : Test Acceptance Review TAS : Thales-Alenia Space TAT : Telescope Alignment Tool TBA : To Be Announced TBA : To Be Assigned TBC : To Be Confirmed TBD : To Be Defined (Determined) TBR : To Be Resolved TB : TeraByte TB : Thermal Balance TBTV : Thermal Balance/Thermal Vacuum (Test) TBW : To Be Written TBW : Tukey Bi-Weighted (centroiding) TCB : Barycentric Coordinate Time TCDS : Telemetry Concatenated Decoding System TCE : TeleCommand Encoder TCG : Geocentric Coordinate Time TCI : Technology Conformance Inspection TCL : Test Configuration List TCO : Transparent Conductive Oxide TCP-IP : Transfer Control Protocol - Internet Protocol TCR : True Comment Ratio TCSEQ : TeleCommand Sequence Manager (software) TCS : Thermal Control Sub-system TC : TeleCommand (Packet) TC : Thermal Control TC : Time Correlation TCV : TeleCommand Verification TCXO : Temperature-Controlled Crystal Oscillator TDAC : Tycho Data Analysis Consortium (Hipparcos) TDA : Technological Demonstrator (Development) Activity TDB : Barycentric Dynamical Time (obsolete) TDC : Time Data Codification TDI : Time-Delayed Integration (CCD) TDN : Total Detection Noise TDS : Test Data Set TD : Test Design TD : Theoretical Deviation TD : Total Dose TEB : Tender Evaluation Board TEC : Thermo-Electric Cooler TEDN : Total Electronic Detection Noise TEO : Terrestrial Ephemeris Origin (obsolete) TEP : Tangential Equipment Panel TFG : Transfer-Frame Generator TFGTS : TFG Time Strobe TFM : TransFer Mode TF : Test Field TF : Transfer Frame TG : Gaia (proper) Time TG : Gaia proper Time TG : Transfer Gate THD : ThresHolD THR : THRuster TICTI : Technical ICT Infrastructure TID : Total Ionising Dose TIM : TIMing TIO : Terrestrial Intermediate Origin TIS : Total Integrated Scattering TI : Test Item TI : Thermal Inertia TLF : Telescope List File TLS : TouLouSe (Fr) TLV : Thruster Latch Valve TMA : Three-Mirror Anastigmatic (telescope) TMcodec : Telemetry CODEC TMC : Telemetry Curve TMDM : Thermal-Mechanical Demonstrator Model TMF : Telecommand Master Function TMI : Image Telemetry TML : Total Mass Load TMM : Thermal-Mathematical Model TMP : TeleMetry Processor TMR : Triple Modular Redundancy TMS : Telemetry Master Schedule TMTC : TeleMetry and TeleCommand (also denoted TM/TC) TM : Telemetry (Packet) TM : Test Manager TM : Thermal-Mechanical TM : Thermal Model TM : Trace Matrix TMV : Triple Majority Voting TNID : Total Non-Ionising Dose TNO : (Nederlandse Organisatie voor) Toegepast-Natuurwetenschappelijk Onderzoek TNO-TPD : Physics Department of Netherlands Organisation for Applied Scientific Research TNO : Trans-Neptunian Object TN : Technical Note TOB : Tender Opening Board ToC : Table of Contents TOM : Time-Out Monitor ToR : Terms of Reference TPF : Task Parameter File TPF : Terrestrial Planet Finder TPN : Telemetry Packet Number TPS : Thermal Protection Sub-system TP : Temperature Probe TRB : Test Review Board TRC : Tycho Reference Catalogue TrES : Trans-atlantic Exoplanet Survey TRM : TRansition Mode (AOCS) TRP : Technology Research Programme (ESA) TRR : Test Readiness Review TRSP : TRanSPonder TRS : Topocentric Reference System TR : Test Report TR : Transmitted (sample coordinate) TSC : Transport and Storage Container TSM : Time Slot Marker TSM : TranSition Mode (AOCS) TS : Test Set TS : Test Specification TS : Time Slot TTAS : Thermal Test Adapter Spacer TTA : Thermal Test Adapter TT&C : Telemetry, Tracking, and Commanding TTL : Through-The-Lens TTMT : Thermal Tent Mating Tool TTR : Telemetry, Telecommand, and Reconfiguration TT : Terrestrial Time TT : Thermal Tent TUM : Technical User Manual TVAC : Thermal Vacuum (also denoted TV) TVT : Thermal Vacuum Test TWP : Top-level Work Package TWTA : Traveling WaveTube Amplifier UAO : Uppsala Astronomical Observatory (Sweden) UART : Universal Asynchronous Receiver Transmitter UBGS : Universitat de Barcelona Gaia Simulator UB : University of Barcelona (Spain) UCAC : USNO CCD Astrograph Catalogue UCL : University College London (UK) UGC : Unresolved Galaxy Classifier UH : University of Helsinki (Finland) UI : User Interface U : Johnson photometric U band UK : United Kingdom ULB : Universit\'e Libre de Bruxelles (Belgium) ULP : User Loading Profile UL : Ultimate Load UL : University of Ljubljana UM2 : Universit\'e Montpellier 2 (France) UML : Unified Modeling Language UM : User Manual UNAU : University of Aarhus (Denmark) UNCT : Dipartimento di Fisica e Astronomia (Universit\`a di Catania, Italy) UNDP : Facult\'es Universitaires de Notre-Dame de la Paix (Namur, Belgium) UNIPD : University of Padova (Italy) UNSUP : UNSUPervised Classification UOA : University Of Athens (Greece) UOL : University of Leicester (UK) UPC : Universitat Polit\`ecnica de Catalunya (Spain) URAT : USNO star catalogue URD : User Requirements Document URL : Uniform Resource Locator USA : United States of America us : Microsecond (avoid this notation in Gaia) USML : U.S. Munitions List USNO : United States Naval Observatory US : United States UT1 : Universal Time 1 UTC : Coordinated Universal Time UTKP : Unit Test Key Point UT : Universal Time UVES : UV-Visual Echelle Spectrograph (VLT) UVIE : University of Vienna (Austria) UVSQ : University of Versailles - St Quentin-en-Yvelines (France) UV : UltraViolet UWE : Unit-Weight Error UXPECT : UneXPECTed Features VALD : Vienna Atomic Line Database VARI : VARIability processing VAT : Value Added Tax VBS : Very Bright Star VBS : Virtual Bright Star VCA : Virtual-Channel Assembler VCB : Verification Control Board VCD : Verification Control Document VCM : Virtual-Channel Multiplexer VCS : VLBA Calibrator Survey (Catalogue) VC : Virtual Channel VDA : Vapour-Deposited Aluminium VFS : Virtual Faint Star VGA : Video Graphics Array VGTT : Vacuum Ground Thermal Tent VHDL : VHSIC Hardware Description Language VHSIC : Very High-Speed Integrated Circuit VIM : Variability-Induced Mover VIM : Variability-Induced Mover (DMSA, Hipparcos Catalogue) VIP : Virtual Internet Protocol VISTA : Visible and Infrared Survey Telescope for Astronomy VIS : Vertical Integration Stand V : Johnson photometric V band VLA : Very Large Array (NRAO) VLBA : Very Long Baseline Array VLBI : Very Long Baseline Interferometry VLTI : Very Large Telescope Interferometer (ESO) VLT : Very Large Telescope (ESO) VM : Virtual Machine VO : Virtual Object VO : Virtual Observatory VoV : Volumes of Variation (technique) VPA : Video Processing Algorithms VPHG : Volume Phase Holographic Grating VPU : Video Processing Unit VRD : Voltage of the Reset Drain Vr : Radial Velocity VSDS : Video Selection and Distribution System VSD : Video Sampling Delay Vsini : Rotational velocity (in projection) VSOP : Variations S\'eculaires de l'Orbite des Plan\`etes VST : VLT Survey Telescope (ESO) VS : Virtual Star VSWG : Variable Star Working Group (obsolete) VTC : Validation Test Case V : Volt; SI unit of voltage VV : Verification and Validation VxWorks : Specific OS WAM : Window Acquisition Manager WAP : Single-pixel (unbinned) WA window (obsolete) WA : Specific window designation in AF (obsolete) WB : BBP window designation (obsolete) WBS : Work Breakdown Structure WB : Weight Balancing WCA : Worst-Case Analysis WCSM : Wavelength (scale) Calibration Software Module WC : Worst Case WD : White Dwarf (star) WD : WinDow WEP : Weak Equivalence Principle WER : Word-Error Rate WFC : Wide-Field Channel (HST ACS) WFE : WaveFront Error WFI : Wide-Field Imager (ESO 2.2-m telescope) WFM : Wave-Front Map WFPC2 : Wide-Field and Planetary Camera 2 (HST) WFRL : Weibul Failure-Rate Law WFST : Wide-Field Star Tracker WFS : WaveFront Sensor WGAS : Working Group on Astronomical Standards (IAU) WG : Working Group WISE : Wide-field Survey Explorer WL : Wedged Lens WM : MBP window designation (obsolete) WN : White Noise WP : Work Package wrt : With reference to (also denoted w.r.t.) wrt : With respect to (also denoted w.r.t.) WR : Window in RVS (covering a star spectrum; obsolete) WSDL : Web Services Description Language WSP : Single-pixel (unbinned) window (obsolete) WSS : Weather Station System Wtn : WiTNess W : Watt; SI unit of power WY : Bright-star window designation in Astro (obsolete) XDF : eXtensible Data Format XE : eXpress Edition XEUS : X-Ray Evolving Universe Spectrometer (ESA) XLP : eXtremely Large Programme XM : Cross-Matching XML : eXtensible Markup Language XMM : X-ray Multi-mirror Mission (ESA; officially known as XMM-Newton) XP : eXtreme Programming XPND : Transponder XP : operating system for MicroSoft XP : Shortcut for BP and/or RP (generic name for Blue or Red Photometer) XSD : XML Schema Definition XSL : eXtensible Stylesheet Language XSLT : eXtensible Stylesheet Language Transformation X : Telecommunication band used for Gaia YL : Yield Load ZAH : Zentrum f\"ur Astronomie (Heidelberg, comprising LSW and ARI) ZAMS : Zero-Age Main Sequence (star) ZAP : Zoom Astro Phase (sub-mode of AOCS Normal Mode) ZARM : Centre for Applied Space Dynamics and Microgravity, Bremen (Germany) ZL : Zodiacal Light Z : Metallicity (star)