This list of Gaia acronyms is actively maintained by Jos de Bruijne (jos.de.bruijne @ esa.int). It was last updated on Fri Apr 5 13:53:19 CEST 2024 Other web-based archives include: http://tla.surly.org/ http://www.spacetoday.org/NASA/SpaceAcronyms/SpaceAcronyms.html https://asd.gsfc.nasa.gov/archive/hubble/overview/glossary.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 : Amp\`ere; SI unit of electric current A : Specific project phase (feasibility; concluded by PRR) A : {\AA}ngstrom; non-SI unit of length, to be avoided A/D : Analogue-to-Digital (converter) AAD : Attitude Anomaly Detector AAE : Austrian AErospace AAS : Alcatel Alenia Space (now Thales-Alenia Space) AB : Anti-Blooming AB : Astrometric Binary AB : Astrophysical Background ABB : Avionic BreadBoard ABC : Approximate Bayesian Computation ABCL : As-Built Configuration List ABD : Anti-Blooming Drain ABF : Abbreviated Functional Test ABF : Adjacent Best Fit ABG : Attitude - Basic angle - Global (calibration in AGIS) ABI : Application Binary Interface ABL : Astrometry-Based Luminosity ABS : Astrometric Binary Star AC : ACross scan (direction) AC : Alternating Current AC : Auto Collimation ACC : Attitude Control Computer ACEP : Anomalous Cepheid 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 : Advanced Customer Support ACS : Attitude Control Sub-system ACSM : Across-Scan Scan Motion ACSM : Apply Calibration Software Module ACTEL : Micro-electronics supplier AD : Applicable Document AD : Sequence-Controlled Service 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 ADQL : Astronomical Data Query Language ADR : Average Data Rate ADS : Airbus Defence and Space (formerly known as EADS-Astrium) ADSD : Asiago Database of Spectroscopic Databases ADU : Analogue-to-Digital Unit AE : Astro Elementary AE : AstroElementary AEF : Actual Event File AEF : Actual Events File (conceptually described in JSH-010) AF : Astrometric Field (in Astro) AFM : AC-Flat Mirror AFMA : AC-Flat Mechanical Assembly AFMM : AC-Flat Mirror Mechanism AFMM AFR : Annualised Failure Rate Ag : Silver AGB : Asymptotic Giant Branch (star) AGBB : Asymptotic Giant Branch Bump AGI : Applications Graphics Interface AGIS : Astrometric Global Iterative Solution AGISPY : AGIS PYthon (Jupyter notebook) AGN : Active Galactic Nucleus AGP : Astro Gate Phase AHB : Advanced High-speed Bus AHFD : See HFAD AI : Action Item AI : Activity Index 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 AlertPipe : Alerts Pipeline (CU5 / DPCI) 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 : Advanced Mechanical and Optical Systems 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 AO : AstroObservation AOB : Any Other Business AOCS : Attitude and Orbit Control Sub-system AoS : Acquisition of Signal AP : AlertPipe AP : Antenna Panel AP : Application Process AP : Astro-Photo job (IDT) AP : Astro-Photo(meter) 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 APIS : Astrometric Primitive non-Iterative Solution (HTPM) APM : Assistant Project Manager APM : Automatic Plate Measuring APR : Auxiliary (Array) Power Regulator APS : Active Pixel Sensor APSIS : Astrophysical ParameterS Inference System (CU8) APU : AOCS Processing Unit APU : Astro Processing Unit (obsolete) AR : Acceptance Review AR : Anomaly 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 ARES : Analysis and Reporting System ARG : Astrophysics Research Group (Antwerpen) ARI : Astronomisches Rechen-Institut (part of ZAH, Zentrum f\"ur Astronomie der Universit\"at Heidelberg) ARO : Automatic Reconfiguration Order ARP : Antenna Reference Point ARTS : Anomaly Report Tracking System ARV : Absolute Radial Velocity ARW : Angle Random Walk AS : Action Sp\'ecifique AS : Adjacent Sample AS : Attitude–Source (constraint) ASA : Astrometric Science Alert 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 ASDC : ASI Science Data Centre ASE : Astro-Stellar Estimator (fusion of Astro rate and STR measurements) ASE : Automatic Scheduling Execution ASF : AStrium France ASF : Nominal effective `filter (band) profile' for ASM (Astro) (obsolete) ASI : Accelerated Simple Iteration 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 ASP : Astro Source Prob(ability) ASR : Average Star Rate AST : Astro Source Table AST : Autonomous Star Tracker ASTP : ASTrometric Parameters ASTRA : Advanced Systems Transforming Research Astronomy Astro : Astrometric Instrument (obsolete) ASU : AStrium Uk ASU : AStrium United Kingdom ASU : Astronomical Server URL ASW : Application S/W AT : Astrophysical Transient 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 AU : deprecated acronym for astronomical unit, use au instead AUS : Archive Usage Scenario AUT : AUTomated AUT : AUTonomy AV : Astrometric Verification AV : Automated Verification AVD : AVoiDance (file) AVI : Added-Value Interface (CU9) 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 b : bit B : Byte (8 bit) B : Johnson photometric B band B : Specific project phase (system definition and design; concluded by SRR and PDR) BA : Basic Angle BAC : Basic-Angle Calibration BAL : Broad Absorption Line (galaxies) BAM : Basic-Angle Monitor BAM-N : Nominal BAM (CCD) BAM-R : Redundant BAM (CCD) BAMD : Basic-Angle Monitor Device 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 BBCR : Bias, Background, and Charge Release (task) BBF : Broad-Band Filter (in BBP; obsolete) BBFH : Burbidge, Burbidge, Fowler, Hoyle (star) BBM : BreadBoard Module (Model) BBP : Broad-Band Photometer (obsolete) 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 BD : Brown Dwarf (star) BDA : BAM Density Assembly (ND filter) 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 BE : Big Endian BEER : BEaming Ellipsoidal Reflection BER : Bit Error Rate BFW : Bloomed Full Well BG : Background BGBC : BackGround and Bias Calibration BGD : BackGround Determination BGL : Base GLobal BGM : Besan{\c{c}}on Galaxy Model BGP : Base Global Parameter 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 BLAS : Basic Linear Algebra Subprogrammes BLOB : Binary Large OBject BLS : Battery and Load Simulator BLS : Box-fitting Least Squares (method / algorithm) BLS : Box-Least-Squares (method) BM : (MIL-STD-1553B) Bus Monitor BM : Beam Map BM : Butler Matrix BN : Bayesian Network BNF : Backus-Naur Form BNSL : Back to NSL BoL : Beginning of Life (also denoted BOL) BOT : Beginning Of Track BoT : Beginning of Track BP : Blue Photometer BP : Bonus Priority BPC : Barcelona Processing Centre BPP : Blue-Photometer Prism bps : bit(s) 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 BS : Bright Star BSA : Beam Steering Algorithm BSC : Barcelona Supercomputing Centre BSD : Berkeley Software Distribution BSE : Binary-Star Evolution BSM : Bright-Star Mapper (Monitor) BT : Bandwidth Symbol Duration BTG : Beta Test Group (CU9) BTG : Beta Testing Group BU : Brunel University BV : French spelling of Visual Binary BVC : Barycentric Velocity Correction BW : Baade's Window (special, high-density area on the sky) BW : BandWidth BWD : BackWarD transition (i.e., NAP to GAP, GAP to ZAP, or NAP to TSM) C : Specific programming language (also called ANSI-C) C : Specific project phase (detailed definition; concluded by CDR) C&DH : Command and Data Handling C++ : Specific programming language C1 : Cycle 01 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) C2 : Cycle 02 C3 : Cycle 03 CA : Calar Alto observatory Ca : Calcium CA : Calibration-Attitude (constraint) CA : Construction Analysis CAA : Conformal Array Antenna CAB : Contract Appeal Board CaC : Cost at Completion CAD : Computer Aided Design CADC : Canadian Astronomical Data Centre CADM : Configuration And Data Management CAG : Calibration, Attitude, Global (AGIS) CALDATA : CALibration DATA CAMCAO : Infrared Camera for the VLT CAP : Configurable Algorithm Parameter CAS : Calibration-Attitude-Source (constraint) CaU : Calibration Unit CB : Configuration Baseline CB : Connector Bracket CBAM : calibration parameter C_{BAM} from LL-091 CBAT : Central Bureau for Astronomical Telegrams (IAU) CBS : Cost Breakdown Structure CC : Calibration-Calibration (constraint) CC : Carbon Copy CC : Change Control CCB : Configuration Control Board CCC : Computer Control Centre CCCP : Cleanliness and Contamination Control Plan CCD : Charge-Coupled Device CCD : Contract Closure Documentation 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 ccSN : core-collapse SuperNova cd : candela; SI unit of luminous intensity CD : Compact Disc CD : Cumulative Distribution CDB : Configuration DataBase (formerly known as Calibration DataBase) CDCI : Common Data Centre Infrastructure (ISDC) CDD : Configuration Data Document CDF : Calibration Data File 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 CDUPA : CDU Phase Analyser CDWG : Common Data Working Group (obsolete) CE : Conducted Emission CE : Conformit\'e Europ\'eenne CEA : Commissariat \`a l'Energie Atomique (France) CEB : CEBreros (35-m ESA ground station near Madrid, Spain) CEI : e2v Centre for Electronic Imaging CELT : California Extremely Large Telescope CEMGA : CTI Effects Models for GAia CEMP : Carbon-Enhanced Metal-Poor (star) CentOS : Community Enterprise Operating System 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 Serveis Cient\'ifics i Acad\`emics de Catalunya CeSiC : Carbon-SiC (also known as CeSIC, CSiC, CSIC, C-SiC, and C-SIC) CET : Central European Time CEU : Current Ephemeris Uncertainty CF : Conversion Factor [e- per ADU] CF : Crowded Field CfA : (Harvard-Smithsonian) Center for Astrophysics CFA : Harvard-Smithsonian Center for Astrophysics (USA) 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 CGL : Constrained GLobal CGM : Constants of Gaia Motion CGP : Consider Global Parameter CH : CCD Health (calibration) CHC : Charge Handling Capacity (CCD) CHF : Swiss Franc CHORIZOS : CHi-square cOde for parameteRixed modelIng and characteriZation of phOtometry and Spectrophotometry CI : Charge Injection CI : Colour Index CI : Configuration Item CIC : Clock-Induced Charge 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 CL : Charge Loss CL : Closed Loop CLASS : CLASSification CLC : Large-scale Calibration in the AC direction (also denoted CLAC) 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) CO : Check-Out (also denoted C/O) CO : Complete Observation (of object in AF) CoC : Certificate of Conformance COD : Catastrophic Optical Damage CODATA : Committee on Data for Science and Technology CODC : CCD One-Day Calibration (FL) CODEC : COder/DECoder CoG : Centre of Gravity COIN : Consolidation Integrator CoM : Centre of Mass COMA : COlour-MAgnitude COMARA : COlour-MAgnitude-RAte 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 COST : European COoperation in Science and Technology COTS : Commercial-Off-The-Shelf COVID : COrona VIrus Disease COWG : Calibration and Operation Working Group CP : Characterisation Point CP : Commissioning Phase CP : Conference Proceeding cPCI : compact PCI CPD : Calibration Products Database CPDU : Command Pulse Distribution Unit CPG : Chebyshev Polynomial Guidance CPG : Compressed Packet Group CPI : Customer Precap Inspection CPM : Chemical Propulsion Module CPM : Common Proper Motion CPM : Cross Pointing Mode CPMP : Common-Proper-Motion Pair CPS : Chemical Propulsion Sub-system (thrusters used in SAM, IGM, OCM) CPU : Central Processing Unit CPV : Commissioning and Performance Verification CQ : Certificate of Qualification CQG : Chebyshev Quaternion Guidance CR : Change Request CR : Charge Release CR : Cold Radiator CR : Commissioning Review CR : Cosmic Ray CR : Cram\'er-Rao (bound/limit) CRB : Change Review Board CRB : Charge-Release Background CRC : Charge-Release Curve CRC : Cyclic Redundancy Code CReMA : Consolidated Report on Mission Analysis CREME : Cosmic-Ray Effects on Micro-Electronics CRF : Celestial Reference Frame CRF : Command Request File CRF : Contingency Recovery File CRG : Contingency and Recovery Procedure CRID : Command Request Interface Document CRISA : Computadores Redes e Ingenería SA CRLB : Cram\'er-Rao Lower Bound CRNU : (CCD) Column Response Non Uniformity CRP : Contingency Recovery Procedure CRR : Command Request Response CRT : Central Reference Time CS : Calibration-Source (constraint) CS : CCD Saturation CS : CCD Saturation (calibration) CS : CheckSum CS : Complete Source CS : Conducted Susceptibility CS : Contract Structure CS : Cool Star CSC : Small-scale Calibration in the AC direction (also denoted CSAC) CSEQ : Command SEQuence 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 CSS : Catalina Sky Survey CSS : CCD Support Structure CSV : Comma-Separated Value (database output format, e.g., for MS Excel) CSW : Central SoftWare CT : Central Tube CTB : Common ToolBox CTC : Cost To Completion 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 CU : Coordination Unit (in DPAC) CUC : CCSDS Unsegmented (time) Code CUC : CCSDS Unsegmented time Code CUO : Copenhagen University Observatory (Denmark) CURM : CPS Usage Rate Management CURM : CPS-Usage-Rate Monitor CUX-L : (Scientific) Leader of CUX (also denoted CUL) CUX-Q : Quality assurance leader of CUX (also denoted CUQ) CUX-ST : Technical Support (Support Technique) for CUX processing at DPCC CUX-T : Technical manager of CUX (also denoted CUT) CV : Code V CV : ConVerter CV : Cosmic Vision CV : Curriculum Vitae CVCM : Collected Volatile Condensable Material CVD : Chemical Vapour Deposition CVS : Concurrent Versions System (obsolete) CW : Calender Week CWG : Calibration Working Group CY : Calender Year D : Deutschland (Germany) D : Specific project phase (production; concluded by QR and FAR) D/SCI : ESA Scientific Directorate (or ESA Director of Science) DA : Detection Algorithm DAC : Data Analysis Consortium (obsolete; superseded by DPAC) DAC : Digital-to-Analogue Converter DACC : Data Analysis Coordination Committee (obsolete) DACE : Data Analysis Consortium Executive (obsolete) DAF : Data Analysis Framework DAG : Data Analysis Group DAL : Data Access Layer DAM : Dynamical Attitude Model (formerly known as Gaia Attitude Model - GAM) 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 : Data Centre DC : Date Code DC : Direct Current DC : Direction Cosine DCEP : classical (\delta) Cepheid DCI : Data Conversion Interface DCL : Declared Components List DCM : Direction Cosine Matrix DCN : Document Change Notice DCR : Dedicated Control Room DCR : Differential Chromatic Refraction DCR : Document Change Request DCS : De-compression and Calibration Services DCT : Defered Charge Trail DCT : Discovery Channel Telescope DD&V : Design, Development, and Validation (Verification) DDC : Data Device Corporation DDD : Detailed Design Document DDEF : Displacement Damage Equivalent Fluence DDI : Data Display Interface DDID : Data Delivery Interface Document DDL : Deliverable Document List DDM : Data-Delivery Manager 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 DDV : Design, Development, and Verification DE : Developmental Ephemerides (from JPL/NASA) DEC : Declination deg : degree; unit of angle DEI : Data Exchange Interface DEMUX : DE-MUltipleXer DENAP : DpcE Nss Astrometric Pipeline DEPR : Deprecated (in Gaia Parameter Database status field) DF : Dark Fibre DF : Data Flow DF : Dispersion Function DFB : Distributed FeedBack (laser) DFL : Detailed First Look DFLE : Detailed First Look Evaluator DFLM : Detailed First Look Monitor DFT : Discrete Fourier Transform DFU : Direct Follow-Up DGL : Diffuse Galactic Light DGS : Dresden Gaia Simulator DH&C : Data Handling and Compression DHM : Deployment Hinge Mechanism DHS : Data Handling Sub-system DHS : Data-Handling sub-System DHU : Data Handling Unit DIAC : Data Integrity and Accountability Checks DIB : Diffuse Interstellar Band DIE : Digital Interface Electronics DIL : Deliverable Item List DIP : Dual Inline Package DIPD : Detection + IPD DIPD : Detection and Image Parameter Determination DIPD : Double-peak IPD DIV : Integer division DIVA : Deutsches Interferometer f\"ur Vielkanalphotometrie und Astrometrie (cancelled) DL : Design Load DL : DownLink DLA : Damped Lyman-Alpha (system) DLR : Deutsches Zentrum f\"ur Luft und Raumfahrt DLTS : Deep-Level Transient Spectroscopy DM : Data Model DM : DeMonstrator (Model) DM : Development Model DM : Differential Mode DMA : Direct Memory Access DML : Declared Material List DMP : Document Management Procedure DMPL : Declared Mechanical Parts List DMS : Data Management Sub-system DMS : Document Management System (ESA) DMS : Double and Multiple Star(s) DMSA : Double and Multiple Systems Annex (Hipparcos Catalogue) 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) DOCh : Daily Operations Chat 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 DoNM : Date of Next Meeting DOP : DPC Operations Plan DOR : Differential One-way Range DOR : Direct Operation Request DoS : Department of State (USA) DoY : Day of Year DP : Data Processing DPA : Destructive Physical Analysis DPAC : Data Processing and Analysis Consortium DPACE : Data Processing and Analysis Consortium Executive DPC : Data Processing Centre DPC-C : DPC Configuration manager DPC-M : DPC Manager DPC-Q : DPC Quality assurance manager DPCB : Data Processing Centre Barcelona DPCC : Data Processing Centre CNES DPCE : Data Processing Centre ESAC DPCG : Data Processing Centre (ObsGE/ISDC) Geneva DPCI : Data Processing Centre (Institute of Astronomy) Cambridge DPCOM : Data Processing Centre Operations Manager DPCT : Data Processing Centre Torino (ALTEC) DPGS : Data Processing Ground Segment DPH : DPC Procedures Handbook DPL : Daily PipeLine (at SOC) DPL : Declared Process List DPS : Data Processing Software DPWG : Data Processing Working Group (dissolved) DQE : Detected Quantum Efficiency DR : Data Release DR : Design Report DR : Dynamic Range DR1 : Gaia Data Release 1 DR2 : Gaia Data Release 2 DR3 : Gaia Data Release 3 DR4 : Gaia Data Release 4 DR5 : Gaia Data Release 5 DRAM : Dynamic RAM DRB : Delivery Review Board DRC : Data Reduction Cycle DRC : DPAC Risk Code DRCD : Data Release Contents Definition DRD : Data Release Documentation DRD : Document Requirements Definition DRI : Data Release Item DRV : Differential Radial Velocity DS : Data Segment DS : Data Selection DS : Data Set DS : Data Structure DS : Definition Study DS : Differential Signal DS9 : Deep Space 9 (specific astronomical data visualisation application; SAOImage) DSA : Deep Space Antenna DSA : Deployable Solar Array DSA : Deployable Sunshield Assembly DSC : Discrete Source Classification (Classifier) DSG : Deployable Solar Generator DSIT : Definition Study Industrial Teams DSL : Domain Specific Language DSN : Deep Space Network DSNU : (CCD) Dark Signal Non Uniformity DSNU : Dark Signal Non Uniformity DSP : Deployable Solar Panel DSP : Digital Signal Processor DSR : Data Storage and Retrieval DSS : Digital Sun Sensor DSV : Dummy Sample Value DT : Dictionary Tool DTCP : Daily Telecommunications Contact Period DTD : Document Type Definition DTP : DPC Test Plan DTR : DPC Test Report DTS : Data Transfer Subsystem DTT : Detected Transit Time DTU : Dumb Terminal Unit 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 E : Espa\~na (Spain) E : Specific project phase (utilisation, including LEOP and in-orbit testing; concluded by MIOCR) E-SVM : Electrical SerVice Module 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 EAM : Eclipse Avoidance Manoeuvre EAR : Event Anomaly Report EAR : Export Administration Regulation EAU : EADS Astrium United Kingdom EB : Eclipsing Binary Eb/N0 : Energy per bit/Noise Power density EBL : Extra-galactic Background Light EC : Economic Conditions EC : Erasure Coding EC : European Commission ECC : ESTRACK Control Centre ECE : EADS CASA Espacio ECI : Earth-Centred Inertial ECLS : Environmental Control and Life Support ECOS : ESA Costing Software ECSS : European Cooperation for Space Standardisation ECSV : Enhanced Character-Separated Values EDAC : Error Detection And Correction EDC : External Data Centre EDDS : EGOS Data Dissemination System EDSD : Exponentially Decreasing Space Density EED : Electro-Explosive Device EEE : Electronic, Electrical, and Electro-mechanical EEPROM : Electrically Erasable Programmable Read-Only Memory 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 EGSE : Extra-Galactic Science with Gaia EGSG : Extra-Galactic Science with Gaia EHB : Extreme Horizontal Branch 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 ELS : Emission-Line Star ELS : l'Ensemble de Lancement Soyouz ELSA : European Leadership in Space Astrometry ELSF : Empirical LSF ("option 4") ELT : Extremely Large Telescope EM : Engineering Model EMBC : Earth-Moon BaryCentre EMC : Electro-Magnetic Compatibility EME2000 : Earth Mean Equator and equinox at epoch J2000 EMF : Electro-Motive Force EMF : Event Monitoring Function EMI : Electro-Magnetic Interference EMS : ESTRACK Management System ENOB : Effective Number Of Bits EO : Electro-Optical EO : Extended Object EODM : Electro-Optical Demonstrator Model EoF : End of File EoI : Expression of Interest EoL : End of Life (also denoted EOL) EOP : Early Orbit Phase EOP : Earth Orientation Parameters EOR : Extended Operations Request EOT : End Of Track EoT : End of Track EP : Ecliptic Pole EPC : Ecliptic Pole Catalogue EPCN : Ecliptic-Pole Catalogue North EPCS : Ecliptic-Pole Catalogue South 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 EPUB : Electronic PUBlication EQM : Engineering Qualification Model EQSR : Equipment Qualification Status Review (also known as ESR) EQT : EQuipmenT ER : Experienced Researcher (ELSA) ERA : Earth Rotation Angle ERC : Early-Release Catalogue ERE : Extended Red Emission ERIC : European Research Infrastructure Consortium ERS : Early-Stage Researcher (ELSA) ERT : Earth Reception Time ES : Emergency Surveillance Es : Espa\~na (Spain) ESA : European Space Agency ESAC : European Space Astronomy Centre (VilSpa) 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 ESDC : ESAC Science Data Centre ESF : European Science Foundation ESH : Equivalent Sun Hours ESLB : ESA(C) Software Licensing Board ESO : European Southern Observatory ESOC : European Space Operations Centre (ESA) ESP : Extended Stellar Parametrizer ESP : Extra-Solar Planet ESP-CS : Extended Stellar Parametrizer Cool Stars ESP-ELS : Extended Stellar Parametrizer Emission-Line Stars ESP-HS : Extended Stellar Parametrizer Hot Stars ESP-UCD : Extended Stellar Parametrizer Ultra Cool Dwarfs ESQ : Extended Sequential Quantile 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 ESVM : E-SVM ESY : Equivalent Sun Years ETA : Earth-Trojan Asteroid 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 EUTF : ESTRACK User Task Force eV : electron-Volt EVF : EVent File EVN : European VLBI Network EVRP : EVent RePorting EW : Equivalent Width (spectroscopy) EWS : Early Warning System EXT : EXTernal Interface EXTR : EXTRactor EY : EagleYard F : France F : Specific project phase (disposal/re-entry; not applicable to Gaia) F4B : BBP photometric system (see C1B) FA : Field Angle FA : Functional Analysis FAAD : Fine Attitude-Anomaly Detector FAC : Field-Angle Calculator FADE : Fully Adaptive Differential Encoding FAE : Fully Adaptive Encoding FAIM : Functional AnalytIc Model (for the calibration of XP data) FAMbE : Fully Adaptive Model-based Encoding FAME : Fast Algorithm for Median Evaluation FAME : Fizeau (Fast) Astrometric Mapping Explorer (cancelled) FAMOUS : Frequency Analysis Mapping On Unequal Sampling FAO : Field-Angle Offset FAOC : Field-Angle-Offset Calculator FAP : False-Alarm Probability FAQ : Frequently Asked Question FAR : Flight Acceptance Review FAST : Fundamental Astronomy by Space Techniques (Hipparcos) FAV : FAVourable FBVS : Flat-Band Voltage Shift 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 FD : False Detection FD : Flight Dynamics FDA : Fully-Dynamic Approach (Hipparcos attitude modeling) FDDB : Flight-Dynamics DataBase FDDC : Flight-Dynamics Database Content FDDD : Flight-Dynamics Database Delivery FDH : FrieDrichsHafen FDI : Field Density Index FDIA : Flight Dynamics Implementation Analysis FDIR : Failure Detection, Isolation, and Recovery FDR : Final Data Release FDR : Final Design Review FDR : Flight-Dynamics Room FDRC : Flight Dynamics Requirements Compilation FDROR : Flight-Dynamics Routine Operations Room FDS : Flight-Dynamics System (at MOC) FDV : Fill and Drain Valve FE : Full Extraction (CU6) 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) FFoV : Following FoV FFP : Firm Fixed Price FFT : Fast Fourier Transform FGSE : Fluidic Ground Support Equipment FHNW : University of Applied Sciences and Arts Northwestern Switzerland FHT : File Header Table FID : Failure IDentification FID : Function IDentifier FIFO : First In, First Out FIL : Front(side)-ILluminated (CCD) FIR : Financial Information Report 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 FL : First Look FLAME : Final Luminosity, Age, and Mass Estimator FLAMES : Fiber Large Array Multi-Element Spectrograph (VLT) FLC : Full Light Curve 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 FM : Flat Mirror FM : Flight Model FM : Full Moon FMA : Final Mission Analysis FMAR : Final Mission Analysis Review FMECA : Failure Modes, Effects, and Criticality Analysis FMMR : Flight-Model Manufacturing Review FMRR : Flight-Model Readiness Review FMSS : Folding Mirror Support Structure FNRS : Fonds National de la Recherche Scientifique (Belgium) FOC : Focal-length and Optical-distortion Calibration FOC : Full Operational Capability (Galileo) 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) FOPPP : FOP Production Plan FoS : Factor of Safety FOS : Folding Optics Structure (supporting M4/M5/M6 and RVS OMA) FoSd : Design 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 FP : Final Presentation FP : Focal Plane FP7 : Seventh Research Framework Programme FPA : Focal Plane Assembly (Focal Plane Array) FPA : Fractional Pixel Allocation FPAG : Fundamental Physics Advisory Group (ESA) FPASS : Focal-Plane-Assembly Static Simulator FPER : First-Pixel Edge Response FPG : Failed Packet Group FPGA : Field-Programmable Gate Array FPR : First-Pixel Response (also denoted FPER) FPR : Focused Product Release FPRS : Focal Plane Reference System FPSM : Focal Plane to Sky Mapping FPU : Floating-Point Unit FR : Final Review FRAD : Fine Rate-Anomaly Detector FS : File System FS : Flight Spare FSA : Fixed (non-deployable) Solar Array FSB : Front Side Bus FSE : Flight Support Equipment FSG : Faint Star polluted by a TDI Gate FSG : Fixed Solar Generator FSI : Faint Star polluted by charge Injection FSS : Fine Sun Sensor FSW : Flight SoftWare FTA : Fault Tree Analysis FTE : Full-Time Equivalent FTN : Faulkes Telescope North FTP : File Transfer Protocol FTS : Faulkes Telescope South FTT : Frame Transmission Time FUMO : FUnctional MOdel FUN-SSO : Follow-Up Network for Solar-System Objects FV : Flight Vehicle FVB : Functional Validation Bench FVP : Full Video Package FVU : Fraction of Variance Unexplained FVV : Fill and Vent Valve FWC : Full Well Capacity (CCD) FWD : ForWarD transition (i.e., from ZAP to GAP or GAP to NAP) FWHM : Full Width at Half-Maximum FXML : Fortran XML library G : Gaia photometric white-light magnitude (SM and AF) G : Giga; SI units prefix for 1E9 G&H : G&H Technology, Inc. (US space industry company) G/T : Gain divided by (noise) Temperature G1 : CCD-PEM Gain 1 (SM, AF, BP, RP) G2 : CCD-PEM Gain 2 (RVS) GA : (IAU) General Assembly GA : Genetic Algorithm GaAs : Gallium-Arsenide GAAT : Gaia Accuracy Analysis Tool GACS : Gaia Archive Core Systems GAGNES : Gaia for AGN and Extragalactic Science GAIA : Global Astrometric Interferometer for Astrophysics (obsolete; now spelled as Gaia) GAIA : Great Advances In Astronomy GAIA : GREAT Astrometry Innovation Alliance Gaia-ASOI : Gaia AStrometric Object of Interest (exoplanet candidate) GAIA-ESO : Galactic Astrophysics via VISTA Imaging, Gaia Astrometry, and ESO SpectrOscopy GAIA-ITN : GREAT Astrometry Innovation Alliance - Innovative Training Network Gaia-RVOI : Gaia Radial-Velocity Object of Interest (exoplanet candidate) Gaia-TROI : Gaia photometric-TRansit Object of Interest (exoplanet candidate) GaiaTools : Gaia software toolbox GALEX : GALaxy Evolution eXplorer GAM : Gaia Attitude Model (superseded by DAM) GAP : Gaia Archive Preparations (DPAC WG) GAP : Gate Astro Phase (AOCS normal-mode submode with VPUs in Gate mode; GAP = medium submode of NM) GAPG : Gaia Archive Preparation Group GAPS : Gaia Andromeda Photometric Survey GAREQ : GAia Relativistic Experiment on Quadrupole light deflection GAREX : GAia Relativity EXperiment GARP : GBOT Astrometric Reduction Pipeline GASS : GAia System-level Simulator GassVal : GASS Validation software tool GAT : Gaia Analysis Tool GAT : Gaia Astronomical Tools GAT : GOG Analysis Tool GATE : GAia Transiting Exoplanet GATT : Gaia Algorithm Tracking Tool (GDAAS, obsolete) GAVIDAV : Gaia Added Value Interface for Data Visualisation GAVIDAV : Gaia Added-Value-Interface Doing Advanced Visualisation GAVIDAV : Gaia AVI DAta Visualisation GAVIP : Gaia Added Value Interfaces Portal GAVIP : Gaia Added-Value-Interface Platform GAVISC : Gaia Added Value Interface Spectral Classification GAVISC : Gaia Added-Value-Interface for Spectral Classification GAVITA : Gaia Added Value Interface for Transient Analysis GAVITA : Gaia Added-Value-Interface for Transient Alerts GAVITEA : Gaia Added-Value-Interface for TEmporal Analysis GAVS : Gaia Archive Visualisation Service 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 GC : Great Circle 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) GCDS : GREAT Chemo-Dynamical Survey GCN : Galactic Coordinates Network (system) GCN : GRB Coordinates Network GCP : Ground Communication Plan GCR : Galactic Cosmic Ray (avoid this name in Gaia) GCR : Great-Circle Reduction (Hipparcos) GCRF : Gaia Celestial Reference Frame GCRS : Geocentric Celestial Reference System GcRS : Geocentric Reference System GCS : Geneva - Copenhagen Survey GCVS : General Catalogue of Variable Stars GCWG : Gaia Calibration Working Group GD : Gaia Detection GDA : Gaia Detection Algorithm GDAAS : Gaia Data Access and Analysis Study (obsolete) GDAC : Gaia Data Analysis Consortium (obsolete; superseded by GDPAC) GDAF : Gaia Data Analytics Platform GDAS : Gaia Data Access Scenario(s) GDAS : Gaia Data-Access Scenario GDB : Gaia DataBase (obsolete; superseded by MDB) GDD : General Design Description GDE : Gaia Discovery Engine (Vaex) GDIR : General Design and Interface Requirements GDMWG : Gaia Data Management Working Group (obsolete) GDPAC : Gaia Data Processing and Analysis Consortium GDR1 : Shortcut for Gaia DR1 (avoid usage) GDRN : Gaia Data Reduction Network (obsolete) GEA : Gaia ESA Archive GEN : GENeral GEN : Observatoire de Gen\`eve GENIUS : Gaia European Network for Improved User Services GEO : Geostationary Earth Orbit GEPC : Gaia Ecliptic-Poles Catalogue (formerly known as EPC) GEPI : Galaxies Etoiles Physique et Instrumentation (OdP) GEQ20 : Number of sources with light curves with a number of transits greater than or equal to 20 GERF : Gaia Extra-galactic Reference Frame GF : Nominal effective `filter (band) profile' for AF (Astro) (obsolete) GFCC : Ground-Facilities Control Centre GFRP : Graphite Fiber-Reinforced Polymer GFTS : Generic File Transfer System (also denoted FITRAS) GG : Generic Global (parameter) GGB : Generic Global Block (formerly known as GGU) GGG : Galician Gaia Group GGG : Galician Group for Gaia (Universidad de La Coru\~na and University of Vigo) GGSSEG : Gaia Ground-Segment System Engineering Group GGU : Global Generic Update GHOST : Gaia HOt Stars Team GHY : GoonHillY ground station Gi : Gigabinary, Gibi; units prefix for 2^{30} = 1024 * 1024 * 1024 GIBIS : Gaia Instrument and Basic Image Simulator GIC : Gaia Input Catalogue (obsolete) GIDE : Generic Interface Data Exchange GIGO : Garbage In, Garbage Out GInHeTS : Gaia INtegration HElper Tools for Saga GINO : Gaia Italian National Outreach GIS : (Astrometric) Global Iterative Solution GL : Gravitational Lensing GLIMPSE : Galactic Legacy Mid-Plane Survey Extraordinaire GLONASS : GLObal NAvigation Satellite System GM : Body-centric gravitational constant GM : Galaxy Model GM : Gaussian Mixture GM : Gaussian Mixture(s) GmbH : Gesellschaft mit beschr\"ankter Haftung (German for company with limited liability) GMC : Giant Molecular Cloud GMF : Global Mapping Function 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 GN : Gauss-Newton GN2 : Gaseous Nitrogen GNC : Guidance, Navigation, and Control GNM : Gaia Numerical Methods GNU : GNU is Not Unix GOES : Geosynchronous Operational Environmental Satellite(s) GOFT : Gaia Observation Forecast Tool (formerly known as GOST) GOG : Gaia Object Generator GOM : Ground Operations Mode GOP : Ground Operations Procedure GOSA : Gaia ground-based Observational Service for Asteroids GOSA : Ground-based Observation Service for Asteroids GOST : Gaia Observation Scheduling Tool GP : Gaia Perturber (asteroid) GP : Galactic Plane GPA : Gaia Photometric Alert (deprecated, use GSA instead) GPA : Gaia Precursor Archive GPA : Gravity Probe A GPB : Gravity Probe B GPDB : Gaia Parameter DataBase GPFS : General Parallel File System GPL : GNU Public License GPS : Galactic-Plane Scan GPS : Global Positioning System GPU : Gaia Processing Unit GR : General Relativity GRA : Gravity Reduction Action (risk management) GRB : Gamma-Ray Burst GRC : Global Reference Curve GREAT : Gaia Research for European Astronomy Training GREAT2Net : GREAT 2nd Network GREM : Gaia RElativity Model GRM : General Relativistic Model GROND : Gamma-Ray-burst Optical/Near-infrared Detector (ESO) GRS : Geocentryc Reference System GRVOS : Gaia Radial Velocity Optimisation Study GS : Gaia photometric white-light magnitude in Spectro (SSM; obsolete) GS : GaiaSource GS : Ground Segment (also denoted G/S) GS : Ground Station (also denoted G/S) GSA : Gaia (photometric) Science Alerts GSA-P : GSA-Publication (system) GSAWG : Gaia Science-Alerts Working Group (GREAT) GSC : Guide Star Catalogue GSC-II : Guide Star Catalogue version 2 (also denoted as GSC-2) GSCMP : Ground-Segment Configuration Management Plan GSCP : Gaia System Calibration 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 GSF : Nominal effective `filter (band) profile' for SSM (Spectro) (obsolete) GSFC : Goddard Space Flight Centre (NASA) 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 GSP : General Stellar Parameteriser GSP : Generalised Star Parametrization (Parametrizer) GSPAP : Ground-Segment Product Assurance Plan GSPC : Gaia Synthetic Photometry Catalogue GSPPHOT : Generalised Stellar Parametrizer PHOTometry GSPSPEC : Generalised Stellar Parametrizer SPECtroscopy GSR : Gaia Sphere Reconstruction GSRQR : Ground-Segment Requirements Review GSRR : Ground-Segment Readiness Review GSSE : Ground-Segment System Engineering GSSEWG : Ground-Segment System-Engineering Working Group GST : Gaia Science Team GST : Greenwich Sidereal Time GST : Ground-Segment Team GSTB : Galileo System Test Bed GSTV : Ground-System Test and Validation GT : GaiaTools GTC : Ground Configuration Table GTD : Geometric Theory of Diffraction GTK : Globus ToolKit GTP : Generic Telemetry Processor GTS : Gaia Transfer System GTSC : Gaia Transport and Storage Container GUASOM : Gaia Utility for Analysis and knowledge discovery based on Self-Organising Maps GUCDS : Gaia Ultra-Cool Dwarf Sample GUI : Graphical User Interface GUM : Gaia User Manual GUMS : Gaia Universe Model Snapshot GVD : General Variability Detection GVS : Global Variability Studies GWP : Gaia Work Package GYR : GYRoscope Gyro : GYROscope H/P : Herschel/Planck (ESA missions) HAC : Hercules-Aquila Cloud HADS : High-Amplitude Delta Scuti (star) HAL : Hardware Abstraction Library (software) HATT : High-Accuracy Time Transformation HBA : Host Bus Adapter HCO : Harvard College Observatory HCRS : Hipparcos Catalogue Reference System HCSS : Herschel Common Science Software HD : Historical Duration HDA : High-Density Area HDF : Hierarchical Data Format HDF5 : Hierarchical Data Format version 5 HDFS : Hadoop Distributed File System 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 HF : Host Framework HFA : History File Archive HFAD : High-Frequency Attitude Disturbances (also denoted AHFD) HFE : Human Factor Engineering HGA : High-Gain Antenna HiPr : High Priority HiPS : Hierarchical Progressive Surveys HK : Housekeeping (also denoted H/K) HKDCM : Housekeeping Data Collection Module HMM : Hidden Markov Model HP : Heliotropic Phase HP : High Priority HPA : High-Power Amplifier HPC : High-Performance Computing HPC : High-Priority Command HPLV : High-Pressure Latch Valve HPM : High Proper Motion (star) HPR : Hardware Platform Review HPSRM : Hardware Processing System-C Reference Model (VPU) HPT : High-Pressure Transducer HR : Hertzsprung-Russell (diagram) HR : High Resolution HRC : High-Resolution Channel (HST ACS) HRD : Hertzsprung-Russell Diagram HRTF : High-Rate Telemetry Formatter HRVC : High-Rate Video Chain HS : Hot Star HS : Hybrid Solver 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 HTPM : Hundred-Thousand Proper Motion catalogue/project 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 I : Cousins photometric I band I : Implemented I : Italia (Italy) I&T : Integration and Test 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 IAU : International Astronomical Union IAUC : IAU Circular iaw : in agreement with IB : Interconnection Board IBAS : INTEGRAL Burst Alert System IBE : Ion-Beam Etching IBF : Ion-Beam Figuring IC : Initial Conditions IC : Integrated Circuit IC : Internal Calibrator(s) IC : Irradiated Configuration ICAP : Identification, Classification, and Astrophysical Parametrization ICCUB : Institut de Ci\`encies del Cosmos Universitat de Barcelona ICD : Interface Control Document ICN : Inverse Condition Number ICP : Interconnection-module Configuration Package ICPOES : Inductive Coupled Plasma Optical Emission Spectroscopy ICRF : International Celestial Reference Frame ICRS : International Celestial Reference System ID : Identifier (Identification) ID : Injection Delay IDA : IDT/IDU Algorithms IDA : Intermediate Data Algorithm (library) IDA : Intermediate Data Algorithms IDDMP : Information, Documentation, and Data Management Plan IDE : Integrated Development Environment IDE : Interactive Data Exploitation IDFI : Integrated FDI IDFT : Inverse Discrete Fourier Transform IDL : Interactive Data Language IDM : Interface and Data Manager IDMP : Information, Documentation, and Data Management Plan IDR : Intermediate Data Release IDT : Initial Data Treatment (Image Dissector Tube in Hipparcos scope) IDTDe : IDT Developer edition IDU : Intermediate Data Update IDV : Intermediate Data Validation IEEC : Institut d'Estudis Espacials de Catalunya (Barcelona) IEEE : Institute of Electrical and Electronic Engineers IEL : Integrated Energy Level IERS : International Earth Rotation Service IF : InterFace (also denoted I/F) IF : Intermediate Frequency IFA : Institute for Astronomy (Edinburgh) IFCP : Instrument Flight Control Procedure IFDI : Integrated Field Density Index IFMR : Initial-Final Mass Relation IFMS : Intermediate Frequency and Modem System IFOP : Instrument Flight Operations Plan IFoV : Instantaneous FoV IGM : Inertial Guidance Mode IGQC : Initial Gaia QSO Catalogue IGSL : Initial Gaia Source List IIOC : Initial In-Orbit Calibration IIR : Infinite Impulse Response (filter) IIT : IDT Ingestion Task IKSSO : Identification of Known Solar-System Objects ILSA : Improved Least-Squares Approach IM : Instrument Model IM : Integration Model IM : Interconnection Module (FPA/CCD) IMCCE : Institut de M\'ecanique C\'eleste et de Calcul des Eph\'em\'erides IMF : Initial Mass Function IMHO : In My Humble Opinion IMT : Information Management Tool (DPAC Project Office database) 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 INT : Initial Training Network INT : INTterferogram (Code V format) INTA : Laboratorio de Astrof\'isica Espacial y F\'isica Fundamental (LAEFF-INTA) INTEGRAL : INTErnational Gamma-Ray Astrophysics Laboratory (ESA) IO : Input-Output (also denoted I/O) IoA : Institute of Astronomy (Cambridge; also denoted IOA) IOC : In-Orbit Commissioning IOC : Infinite Overlapping Circles IOCA : In-Orbit Calibration Activity IOCP : In-Orbit Calibration Procedure IOCR : In-Orbit Commissioning Review IOF : Institut fuer angewandte Optik und Feinmechanik (Fraunhofer Institut, Jena, Germany) IOGA : Initial On-Ground Attitude IOM : Inter-Office Memorandum (JPL/NASA) IOPR : In-Orbit Performance Review IOS : In-Orbit Strut IP : Image Processing IP : Internet Protocol IPC : Industrial Policy Committee (ESA) IPD : Image Parameter Determination IPD : Image Products Database IPFD : Isotropic Path Flux Density IPLM : Integrated Payload Module IPR : Intellectual Property Right IPU : Image Parameter Updating (in IDU) IQT : IDT Quick Tracking IRAF : Image Reduction and Analysis Facility (NOAO) IRD : Interface Requirements Document IRIG : Inter-Range Instrumentation Group IRQ : Interrupt ReQuest IRR : Integration Readiness Review IRT : InfraRed Triplet ISA : Initial Spectrum Analyser ISAM : Interactive Service for Asteroid Models 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 IT : Information Technology IT : Integration Test ITAR : International Traffic in Arms Regulations ITG : InTerroGator ITMC : Integrated TeleMetry Curve ITN : (EC Marie Sk\l{}odowska-Curie) Initial Training Network ITO : Indium Tin Oxide ITPA : Institute of Theoretical Physics and Astronomy (Vilnius) ITPA : Intra-TDI1 Phase Anomaly 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 IVELA : Interactive Visualisation Environment for Large Archives IVOA : International Virtual-Observatory Alliance IVP : Integrated Variability Pipeline 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 JD : Julian Date JDBC : Java DataBase Connectivity JDK : Java Development Kit JED : Julian Ephemeris Date (to be avoided; see also JD) JFET : Junction Field-Effect Transistor JHU : Johns Hopkins University JIRA : issue tracking product (not an acronym, but a truncation of Gojira, the Japanese name for Godzilla) 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) K : Kelvin; SI unit of temperature k : kilo; SI units prefix for 1E3 KA : Acceptance Factor KAL : Keep-Alive Line KBO : Kuiper-Belt Object kbps : kilobits per second KDE : Kernel Density Estimator KE : Kinetic Energy KEF : Knife-Edge Function KF : Kalman Filter kg : kilogram; SI unit of mass Ki : Kilobinary, kibi; units prefix for 2^{10} = 1024 KIP : Key Inspection Point KL : Kullback-Leibler KLD : Kullback-Leibler Divergence KM : Model Factor KO : Kick-Off KOM : Kick-Off Meeting KON : Konkoly Observatory of the Hungarian Academy of Sciences (Budapest) KP : Project Factor KPI : Key Performance Indicator KQY : Qualification Factor krad : kilorad; radiation dose unit KRU : Kourou 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 L-X : Launch minus X (months, days, hours, minutes, ...) L1 : First cache layer (cache RAM inside the CPU) L1 : First Lagrange point of the Sun and Earth-Moon system (not applicable to Gaia) L2 : Second cache layer (small SRAM chips on the motherboard) L2 : Second Lagrange point of the Sun and Earth-Moon system (applicable to Gaia) L2I : L2 (orbit) Insertion L3CCD : Low-Light-Level CCD (obsolete) LA : License Agreement LAB : Laboratoire d'Astrophysique de Bordeaux LAB : Lateral Anti-Blooming LAM : Launch & initial Acquisition Mode LAM : Launch and (Sun-)Acquisition Mode LAM : Launch and Initial Acquisition Mode LAME : Luminosity, Age, and Mass Estimator 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 LAT : Lot Acceptance Test LaTeX : (Leslie) Lamport TeX (document markup language and document preparation system) LATT : Low-Accuracy Time Transformation LCDA : Launcher Coupled Dynamic Analysis LCDM : Lambda Cold Dark Matter LCI : Launch-Critical Item LCL : Latch(ing) Current Limiter LCLA : Launcher Coupled Loads Analysis LCO : Las Cumbres Observatories LCTA : Launcher Coupled Thermal Analysis LDAP : Lightweight Directory Access Protocol LDM : Light Data Management LE : Little Endian 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 LGPL : Lesser GNU Public License LHC : Large Hadron Collider (at CERN) LHC : Left-Hand Circular LHS : Left-Hand Side LHS : Luyten Half-Second catalogue LIC : Launcher Injection (dispersion) Correction (manoeuvre) LIC : Line Integral Convolution LINEAR : The Lincoln Near-Earth Asteroid Research LIR : Launcher-Interface Ring LISN : Line Impedance Stabilisation Network LIT : Listen-In Test LL : Limit Load LL : LiveLink LL : Lower Level LLI : Local Lorentz Invariance LLI : Long Lead Item LLR : Lunar Laser Ranging LLS : Linear Least Squares LM : Laser Metrology LM : Levenberg-Marquardt LMC : Large Magellanic Cloud (special, high-density area on the sky) LMS : Light-weight Monitoring System LN2 : Liquid Nitrogen LNA : Laborat\'orio Nacional de Astrof\'isica (Brazil) LNA : Low-Noise Amplifier LO : Lohrmann Observatory (Dresden Technical University) LoC : Loss of Convergence LOCKSS : Lots Of Copies Keeps Stuff Safe LOCO : LOssless COmpression LODC : LSF/PSF One-Day Calibration (FL) LoI : Letter of Intent LoPr : Low Priority LoS : Line of Sight (also denoted LOS) LoS : Loss of Signal LOWESS : LOcally WEighted Scatterplot Smoothing LP : Low Priority LPC : Local Plane Coordinates LPGL : Lesser Public GNU general License LPLV : Low-Pressure Latch Valve LPT : Low-Pressure Transducer LPV : Long-Period Variable (star) LRR : Launch Readiness Review LRVC : Low-Rate Video Chain LS : Large Scale LS : Learning Set LS : Lommel-Seeliger (scattering law) LSA : Launch Service Agreement LSA : Least-Squares Approach LSACP : Large-Scale Astrometric Calibration Parameter LSB : Least Significant Bit LSB : Linux Standard Base LSB : Low Surface Brightness (galaxy) LSCP : Large-Scale Calibration Parameter LSF : Line Spread Function LSM : Large-scale SiC Mirror (Gaia M1 demonstrator) LSP : Low System Priority LSS : Large-Scale Simulation (GASS) LSST : Legacy Survey of Space and Time of the Rubin Observatory (formerly known as Large-aperture Synoptic Survey Telescope) LSW : Landessternwarte (part of ZAH, Zentrum f\"ur Astronomie der Universit\"at Heidelberg) LT : Liverpool Telescope LT : Long-Term 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 LV : Latch Valve LV : Launch Vehicle LVA : Launch Vehicle Adaptor (Authority) LVDS : Low-Voltage Differential Signal LZW : Lempel-Ziv-Welch (specific data compression scheme) L_B : Average value of 1-d(TT)/d(TCB) L_C : Average value of 1-d(TCG)/d(TCB) L_G : Value of 1-d(TT)/d(TCG) (defining physical constant) M : Mega; SI units prefix for 1E6 m : meter; SI unit of length m : milli; SI units prefix for 1E-3 M-L : Mass-Luminosity (relationship) M-SVM : Mechanical SerVice Module M1 : First mirror M2 : Second mirror M2M : M2 Mechanism M2MM : M2 Mirror Mechanism M3 : Third mirror M4 : Fourth mirror M5 : Fifth mirror M6 : Sixth mirror MAAP : Motherhood And ApplePie MAD : Mission Assumptions Document MAE : Modified `Adaptive' Encoding MAGIL : MAnager of the Gaia Image Library MAINDB : MAIN DataBase MAIT : Manufacturing, Assembly, Integration, and Test MAN : MANual MAP : Maximum A Posteriori (estimate) MAP : Multiplexed Access Point MAR : Mean Absolute Residual MariaDB : open-source relational database management system (Maria is the second daughter of the creator, Michael Widenius) mas : milliarcsecond (1E-3 arcsec) MAS : Mission Automation System MATISSE : MATrix Inversion for Spectral SynthEsis MATISSE : Next-generation data management products that offer native object storage and support for SQL Mb : Megabit (1,000,000 bit) MB : MegaByte MBA : Main-Belt Asteroid MbE : Model-based Encoding MBEAN : Managed BEAN from JMX MBF : Medium-Band Filter (in MBP; obsolete) 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) MC : Master Clock MC : Monte-Carlo (simulation/process) MCC : Mission Control Centre MCDM : Multiple Criteria Decision Making MCEP : Mean Celestial Ephemeris Pole (obsolete) MCG : Match-Candidate Group MCM : Monitor and Control Module MCM : MultiChip Module MCMC : Monte-Carlo Markov Chain MCR : Main Control Room MCS : Mission Control System MCU : Main Computing Unit MDB : Main DataBase MDC : Mapped Diagnostic Contexts MDD : Multi-Dimensional Data 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 MEOR : Mission Extended-Operations Review MEOR : Mission Extension Operations Review MeV : Mega-electron-Volt MF : Master Function MF : Minor Frame MFD : Mirror Fixation Device MFG : ManuFacturinG MFN : Master Function Number MFS : Mass-Flow Sensor MGA : Medium-Gain Antenna MGR : ManaGeR MGSE : Mechanical Ground Support Equipment MI : Mantis Issue Mi : Megabinary, Mibi; units prefix for 2^{20} = 1024 * 1024 MI : Modulation Index 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 MIKS : Multiple Independent Keplerian Solutions MIM : Minimum Injection Method (for charge injection) MIM : Minimum-Injection Method MIMO : Multiple Input - Multiple Output MIOCR : Mission In-Orbit Commissioning Review MIOG : Mean Instrument Object Generator MIP : Mandatory Inspection Point MIP : Mission Implementation Plan MIPS : Million Instructions Per Second Mips : Million instructions per second (also denoted MIPS) MIR : Management Information Report MIRAD : Micro-particle Impact Related Attitude Disturbance MIRD : Mission Implementation Requirements Document MISE : Mean Integrated Square Error MIT : MOC Interface Task MJD : Modified Julian Date (to be avoided; see also JD) ML : Machine Learning ML : Maximum Likelihood MLA : Multi-Lateral Agreement MLE : Maximum-Likelihood Estimate MLG : MaLarG\"ue ground station (35-m ESA ground station in Argentina) MLI : Multi-Layer Insulation MM : Man Month MM : Mirror Mechanism (M2 mirror) MM : Mission Manager MMaaS : Multi-Mission as a Service MMaaS : Multi-mission Management-as-a-Service MME : Model-Mismatch Error MMH : Mono-Methyl Hydrazine MMIC : Monolithics Microwave Integrated Circuit MMM : Mock-MOC MIT = Mock-Mission-Operations-Centre MOC Interface Task = Mock-Mission-Operations-Centre Mission-Operations-Centre Interface Task MMS : Matra Marconi Space (now EADS Astrium) MMU : Mass Memory Unit MMU : Mechanical Mock-Up MN : Meeting Minutes MNEM : MNEMonic MOC : Mission Operations Centre MOD : Mission Operations Department MOD : Modulus of integer division MoG : Moving Gaussian MoI : Moment of Inertia MOI-IT : Mission Operations IT MOIS : Mission Operations Information System MoM : Minutes of Meeting MOM : Mission Operations Manager MOND : MOdified Newtonian Dynamics MORO : Multi-band Outlier Removal Operator MoS : Margin of Safety MOSFET : Metal-Oxide Semiconductor Field-Electric Transistor MOST : Micro-variability and Oscillations of STars MP : Management Plan MP : Metal-Poor (star) MPA : Micro-Propulsion Assembly MPA : Multi-Parameter Analysis MPC : Minor Planet Center MPCB : Material and Process Control Board MPE : Micro-Propulsion Electronics MPEB : MPE-B branch MPFM : Micro-Propulsion Feed Module MPHF : Mass Properties History File MPHF : Mass Property History File MPI : Message Passing Interface MPIA : Max Planck Institute f\"ur Astronomy (Heidelberg) MPLS : Multi-Protocol Label Switching MPP : Message Passing Package MPP : Message Processing Programme MPP : Multi Purpose Project model in JIRA MPP : Multi-Pinned Phase (CCD) MPPT : Maximum Power Point Tracker MPR : Monthly Progress Review MPS : Micro-Propulsion Sub-system MPS : Mission Planning System (at MOC) MPSK : M-Phase Shift Keying MPT : Multi Purpose Trolley MPTS : Multi-Purpose Tracking System MR : Mean Residual MR : Metal-Rich (star) MR : Modified Relativity MRB : Material Review Board MRC : Master Reference Cube MRD : Mission Requirements Document MRE : Mean Rate Error MRR : Manufacturing (Mission) Readiness Review MRS : Mechanical Reference System (obsolete; replaced by SCRS) MRT : Mission Readiness Test MRU : Main Regulator Unit MS : Main Sequence (star) MS : MicroSoft (software company) MSB : Most Significant Bit MSC : Multiple-Star Classifier MSC/NASTRAN: Software for finite-element analysis MSCA : Marie Sk\l{}odowska-Curie Action MSCB : Management and Schedule Control Board MSE : Mean Standard Error MSG : Meteosat Second Generation MSL : Modified Scanning Law MSO : Master Switch Off MSOO : Mission Scheduling and Optical Observations MSPA : Multiple Spacecraft Per Aperture MSRR : Mission SRR MSSL : Mullard Space Science Laboratories (UK) MST : Minimal Spanning Tree 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 mu : micro; SI units prefix for 1E-6 MU : Mock-Up muas : microarcsecond (1E-6 arcsec) MUM : Michael (Biermann), Uli (Bastian), and Marcus (Hauser) (the FL scientists team) muP : micro Processor MUPA : Multiple Uplink Per Aperture MURM : MPS Usage Rate Management mus : microsecond MUX : MUltipleXer MWSC : Milky-Way Star Cluster MY : Man Year n : nano; SI units prefix for 1E-9 N : Newton; SI unit of force NA : Neutraliser Assembly NA : Not Applicable (also denoted as N/A) NACK : Negative Acknowledgement NAOJ : National Astronomical Observatory of Japan NAP : Normal Astro Phase (AOCS normal-mode submode with VPUs in Operational mode; NAP = finest submode = science-operations mode) NAS : Network Attached Storage NASA : National Aeronautics and Space Administration (USA) 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 ND : Neutral Density (filter) NDA : Non-Disclosure Agreement NDAC : Northern Data Analysis Consortium (Hipparcos) NDB : Network DataBase NDI : Non-Destructive Inspection NDIU : Network Data Interface Unit 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 NET : Not Earlier Than NFS : Network File System NG : Next Generation NGC : North Galactic Cap NGST : Next Generation Space Telescope (obsolete; now called JWST) NI : Non-Irradiated NI : Not Implemented NIEL : Non-Ionising Energy Loss NIMO : Non-Inverted Mode Operation NIS : Network Interface Server NIST : National Institute of Standards and Technology (USA) NL : NetherLands NLTE : Non-LTE NM : Normal Mode (AOCS) NN : Nearest Neighbour NNI : Native Numerical Interface NNO : New NOrcia (35-m ESA ground station near Perth, Australia) NNR : No Net Rotation (constraint) NNR : No-Net-Rotation NOA : National Observatory of Athens (Greece) NOAO : National Optical Astronomy Observatories (USA) NOM : NOMinal NOMC : Normal Operation Mode with Chemical thrusters NOME : Nominal (scientific) Operational ModE NOP : Network Operations Plan NOP : Network Operations Procedures NOVAS : Naval Observatory Vector Astrometry Subroutines (USNO) NR : Nightly Run NRB : Non-conformance Review Board (previously known as MRB) NRD : Numerical Requirements Document NRT : Near Real-Time NRZ-L : Non-Return to Zero-Level NS : New Source NSDC : Natural Satellites Data Centre NSF : Null-Space Function 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 NTF : Noisy Transit Fraction NTO : (di-)Nitrogen TetrOxide NTO : Nitrogen TetrOxide NTP : Network Time Protocol NTT : New Technology Telescope (ESO) NTUA : National Technical University of Athens (Greece) NU : Non-Uniformity NVO : National Virtual Observatory (USA) NWO : Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands) O-C : Observed minus Computed OA : Outlier Analysis OAAD : Operational Attitude-Anomaly Detector OABO : Osservatorio Astronomico di Bologna OACN : Osservatorio Astronomico di Capodimonte (Napoli) OACT : Osservatorio Astrofisico di Catania OAI : Open Archives Initiative 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 OB : On-Board OB : Optical Bench OBA : Optical-Bench Assembly OBCD : On-Board-Computed Data OBCP : On-Board Control Procedure OBD : On-Board Detection OBDH : On-Board Data Handling OBDWG : On-Board Detection Working Group (obsolete) OBJ : OBJect processing OBMF : On-Board Monitoring Function OBMT : On-Board Mission Timeline OBS : On-Board Storage OBS : On-Board time broadcasting Signal OBS : Organisation Breakdown Structure ObsGE : Observatory of GEneva (Switzerland) OBSM : On-Board-Software Maintenance OBSR : On-Board Storage and Retrieval OBSS : Origins Billion Star Survey (NASA) OBSW : On-Board Software OBT : On-Board Time (realised in CDU) OBTM : On-Board Time Management OC : Open Centre OCA : Object Clustering Analysis OCA : Observatoire de la C\^{o}te d'Azur (Nice) OCC : Operations Control Centre OCCASO : Open Cluster Chemical Abundances from Spanish Observatories survey OCM : Orbit Control Mode OCMC : Orbit Control Mode with Chemical thrusters OCMS : ORATOS Configuration Management System OD : Object Data (source packet) OD : Operational Day 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 OdP : Observatoire de Paris (France) ODP : Optical Data Processor OEM : Orbital Ephemeris Message OF : Object Feature (source packet) OFT : Orbital Flight Test OFW : Optimum Full Well OGA : On-Ground Attitude OGA1 : First On-Ground Attitude determination (in IDT) OGA2 : Second (and improved) On-Ground Attitude determination (in ODAS/FL) OGA3 : On-Ground Attitude from AGIS OGAR : On-Ground Attitude Reconstruction OGCP : On-Ground Control Procedure OGLE : Optical Gravitational Lensing Experiment OGS : Operations Ground Segment OGSE : Optical Ground Support Equipment 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 OM : Object Matching OM : Operational Manual OM : Operations Manager OMA : Opto-Mechanical Assembly ONU : Offset Non-Uniformity OO : Object Oriented OOC : On-Orbit Control OoL : Out of Limit OPAL : On-board software Process Assets Library OPD : Optical Path Difference OPM : Observatoire de Paris Meudon (France) OPS : Object Processing System OPS : OPerationS (environment) OPSNET : OPErations NETwork OPTICS : Ordering Points To Identify the Clustering Structure OPTO : OPTical observations - spacecraft Observation file OPTT : OPTical observations - Telescope list file OPUS : Operational Pipeline Unified Systems OR : Observation Report OR : Offner Relay (RVS; obsolete) OR : Operations Rehearsal ORATOS : ORbit and ATtitude Operations System ORB1 : (reconstructed) ORBit 1 ORB2 : (reconstructed) ORBit 2 ORCT : Operations Rehearsal Coordination Team ORR : Operations Readiness Review ORU : Orbital Replaceable Unit OS : Observatoire de Strasbourg (France) OS : Operating System OSA : Overall System Architecture OSARG : OGLE Small-Amplitude Red Giant OSE : Optical Sources and Electronics OSF : Operations Schedule File OSG : Operations Support Group (formerly known as Operations Steering Group) OSR : Optical Solar Reflector OST : Observation Schedule Tool OTS : Off-The-Shelf OWL : OverWhelmingly Large Telescope OWLT : One-Way Light Time p : pico; SI units prefix for 1E-12 PA : Product Assurance 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 PAR : Performance Assessment Report PARC : Packet ARChive PARSEC : PAdova and TRieste Stellar Evolution Code PAS : Payload Adapter System PATP : Preliminary Authorisation To Proceed PB : PetaByte PB : Play-Back PBK : Parameter BookKeeping PC : (DPAC Project Office) Project Coordinator PC : Personal Computer PC : Prime Contractor PC : Pseudo Colour PCA : Pressure Control Assembly PCA : Principal Component Analysis PCAT : Packet CATegory PCB : Parts Control Board PCB : Printed Circuit Board 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 PCP : Project Closure Plan PCU : Power Control Unit PD : Parasite Detection (in IDU) PD : Partial Derivative PD : Proportional plus Derivative controller 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 PDM : Phase-Dispersion Minimisation PDMS : Prototype Data Management System PDP : Project Development Plan PDR : Preliminary Design Review PDS : PLM Deployment Stand PDU : Power Distribution Unit PE : Payload Expert PE : PhotoElementary PE : Processing Element PEG : Payload Experts Group PEG : Post-Newtonian Gravity PEGASE : Projet d'Etude des Galaxies par Synth\`ese Evolutive PEM : Prototype Engineering Module PEM : Proximity Electronics Module PEM2 : (Maxwell) Prototype Engineering Model #2 (VPU) PER : Perth PERP : PEriodic RePorting PET : Procedure Editor Tool PFC : Parameter Format Code PfC : Proposed for Closure PFCI : Potential Fracture-Control Item PFL : Probability of Frame Loss (also known as FLP) PFM : Proto Flight Model PFO : Particle Fall-Out (detector) PFoV : Preceding FoV PFS : Point Spread Function PG : Packet Group PG : Postgres PGIS : Photometric Global Iterative Solution PGSE : Propulsion Ground-Support Equipment PGW : Plane Gravitational Wave PhD : Doctorate in Philosophy PHOT : PHOTometric processing PhotPipe : Photometric Pipeline (CU5 / DPCI) PI : Partially Implemented PI : Principal Investigator PIA : Propellant Isolation Assembly PID : PAA Integration Device PID : Process IDentifier PID : Proportional plus Integral plus Derivative controller PIND : Particle-Induced Noise Detection PIP : Project Implementation Plan PISA : Principal Investigator Support Area PJM : Plasma Jet Machining PK : Pimary Key PL : PayLoad (also denoted P/L) PL : Period-Luminosity (star) PLASTIC : PLatform for AStronomy Tool InterConnection PLC : Period-Luminosity-Colour (star) PLL : Phase-Locked Loop PLM : PayLoad Module PM : Phase Modulation PM : Polarisation Maintaining PM : Processor Module PM : Progress Meeting PM : Project Manager PMA : Preliminary Mission Analysis PMAC : Payment Milestone Achievement Certificate PMAR : Preliminary Mission-Analysis Review PMD : Propellant Management Device PMD : Software tool to detect software problems PMIS : Project Management Information System PMO : Project Management Officer PMP : Parts, Materials, and Processes PMP : Planning Management Plan PMTS : Permanent Mounted Transducer System PNG : Portable Network Graphics PO : (DPAC) Project Office PO : Partial Observation (of object in AF) PO : PhotoObservation PoC : Point of Contact POD : Predicted Orbit Data PODC : Photometric One-Day Calibration (FL) POI : Plan d'Op\'erations Imbriqu\'ees (Interleaved Operations Plan) POR : Payload Operations Request POS : Payload Operations System PoS : Plane-of-Sky POSIX : Portable Operating System Interface PP : Photometric Processing (PhotPipe) PP : PhotPipe PP : Pre-Processor PP : Propulsion Panel 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 PPL : Probability of Packet Loss ppm : parts per million PPMX : PPM-eXtended (extended version of PPM catalogue) PPN : Parametrized Post-Newtonian (formalism in gravitational physics) PPS : Pulses Per Second PR : Pressure Regulator PR : Progress Report PRA : Preliminary Risk Assessment PRA : Probability Reduction Action (risk management) PRD : Performance Report Document PREF : Parameter REFerence (number) PRIMAL : PaRtIcle-by-particle M2M ALgorithm PRIMASS : PRImitive Asteroids Spectroscopic Survey 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 PRODEX : PROgramme de D\'eveloppement d'EXp\'eriences scientifiques PROM : Programmable Read-Only Memory PRR : Preliminary Requirement Review PRS : Pixel Reference System PRS : Precessing Reference System PRT : Packet Routing Table PRT : Platinum Resistance Thermometer PRU : Pyrotechnic Release Unit PS : Packet Store PS : Photometric System PS : Pre-Scan PS : Project Scientist PS-ICD : Packet Structure Interface Control Document PSA : Parts Stress Analysis PSA : Photometric Science Alert (deprecated, use GSA instead) PSD : Power Spectral Density PSF : Point Spread Function PSI : Paul Scherrer Institut (Switzerland) PSK : Phase Shift Keying PSR : Project Support Room PSS : PEM Support Structure PSS : Portable Spacecraft Simulator PSS : Primary-Source Selection PSS : Procedures, Specifications, and Standards PSST : Project Scientist Support Team PST : Processing Support Tool PSU : Power Supply Unit PSV : Phase State Vector PT : Pressure Transducer PT : Product Tree PTC : Parameter Type Code PTC : Passive Thermal Control PTC : Photon Transfer Curve PTF : Palomar Transient Factory PTFE : PolyTetraFluoroEthylene PTR : Post Test Review PtV : Peak-to-Valley PTXC : Packet Transmission Control PUS : Packet Utilisation Standard PV : Performance Verification PVA : Photo Voltage Assembly PVA : Photo-Voltaic Assembly PVA : Pressurised Vessal Assembly PVCF : Partial Virtual-Channel Frame PVL : Passband Validation Library PVNO : Pyro Valve Normally Open PVP : Performance Verification Paper 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 QA&V : Quality Assurance and Validation QA&VU : Quality Assurance and Validation Unit QAR : Qualification Acceptance Review QC : Quality Control QCG : Quality Control Group QCI : Quality Conformance Inspection QE : Quantum Efficiency (CCD) QEF : Quadrupole Efficiency Factor QEH : Quantum Efficiency Hysteresis QL : Qualification Load QL : Quick Look QM : Qualification Model QML : Qualified Manufacturers List QMS : Quality Management System QPL : Qualified Products List QPRE : Quasi-Periodic Rate-Excursion (Event) QR : Qualification Review QRS : Quartz Rate Sensor QSL : Qualification Status List QSO : Quasi-Stellar Object QSOC : QSO Classifier QTH : Quartz Tungsten Halogen QTR : Qualification Test Review QUAM : Quadri-Module R : Cousins photometric R band R : Row (CCD chip across-scan coordinate identifier in focal plane) R&D : Research and Development R&T : Research and Technology R-S : Reed-Solomon (encoding) RA : Right Ascension RAA : RUAG Aerospace Austria RAC : Real Application Cluster RACM : Rubidium Atomic Clock Module RAF : Return All Frame RAFS : Rubidium Atomic Frequency Standard RAID : Redundant Array of Inexpensive Disks RAL : Rutherford Appleton Laboratory (UK) RAM : Random Access Memory RAMOD : Relativistic Astrometric MODel RAMS : Reliability, Availability, Maintainability, and Safety RAPID : Raw Archive Packet Interceptor and Dumper RAR : RAMS Analysis Report RAS : Rien \`a Signaler (nothing special to be noted) RAVE : RAdial Velocity Experiment RB : Requirements Baseline Rb : Rubidium RBD : Reliability Block Diagram RC : Reference Configuration RC : Requirements Compilation RC : Root Cause RCCC : Real-time Capturing Circuit Converter RCD : Requirements Control Document RCF : Return Channel Frame RCIs : Release-Critical Items RCR : Requirements and Conceptual Design Review RCS : Reaction Control Sub-system RCWG : Radiation-Calibration Working Group RD : Reference Document RDB : Raw DataBase RDM : Reference Data Manager RDP : Radiation-Damage Parameter RDP : Raw-Data Processing RE : Radiated Emission RECONS : REsearch Consortium On Nearby Stars RELAX : REgular LAnguage for XML Next Generation REMAT : RElativistic Models And Tests (DU in CU3) REN : Rigid Earth Nutation REOSC : Optronic Systems Department of SAGEM REP : Radial Equipment Panel REP : RE-Processing (environment) REST : REpresentational State Transfer RETEX : RETurn-of-EXperience REU : Remote Electronics Unit (not applicable for Gaia) RF : Radio Frequency RF : Random Forest RF : Reference Frame RFA : Request for Approval RFC : Random Forest Classifier RFC : Request for Comments RFCT : Radio Frequency Compatibility Test RFD : Request For Deviation RFDN : Radio Frequency Distribution Network RFDU : Radio Frequency Distribution Unit RFI : Request For Information RFLV : Relative Focal Length Variation RFQ : Request For Quotation RFSR : RF Suitcase Requirements RFW : Request For Waiver RGB : Red Giant Branch (star) RGBB : Red Giant Branch Bump RGC : Reference Great Circle RGCS : Reference Great-Circle System RHC : Right-Hand Circular RHEL : Red Hat Enterprise Linux RHS : Right-Hand Side RIC : Radiation-Induced Conductivity RICH : (charge) Release, Injection, and CCD Health (calibration) 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 RM : Reconfiguration Module RME : Rate Measurement Error RMI : Remote Method Invocation RMP : Risk Management Plan RMS : Root-Mean-Square RMT : Risk Management Team RMU : Rate Measurement Unit RNP : Research Network Programme RNP : Residual Normal Point RNP : Residual Normal Point(s) RO : Read-Out (sample coordinate) ROA : Read-Out Amplifier (CCD) roAp : rapidly oscillating Ap star ROB : Royal Observatory of Belgium ROD : Restituted Orbit Data RoD : Review of Definition RoD : Review of Design ROD1 : Reconstructed Orbit Data 1 ROD2 : Reconstructed Orbit Data 2 RODC : RVS One-Day Calibration (FL) ROE : Regular Operations Exercise ROEMER : Proposal for the Third Medium-Size ESA Mission (M3; not approved) ROFABO : Remove Outliers Faint And Bright Operator 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 ROR : Read-Out Register (also known as Serial Register) ROU : Reporting Operation Utility ROWLT : Relativistic One-Way Light Time ROWLT : Relativistically corrected One-Way Light (travel) Time ROWLT : Relativistically-corrected OWLT (file) RP : Red Photometer RP : Resolving Power RPE : Relative Pointing Error RPM : Revolutions Per Minute RPP : Red-Photometer Prism RPPU : RVS Pre-Processing Unit (obsolete) RR : Rate Reduction RR : Risk Register RRD : Round-Robin Database RRFWG : Relativity and Reference Frame Working Group (obsolete) RRM : Rate-Reduction Monitor RRT : Receiver, Tracking, and Telemetry RS : Radiated Susceptibility RS : Reference System RS232C : Standard 25-pin serial connection between computers and modems RSA : RUAG Space Austria RSD : Reference Sampling Delay RSE : Robust Scatter Estimator (measure of distribution width in AGIS) RSL : Reference Scanning Law RSLI : Reference Scan Law ICRS spin-axis orientation file RSLI : Reference Scanning Law schedule - ICRF attitudes RSLO : Reference Scanning Law schedule - initial spin phase (Omega) RSLP : Reference Scan Law initial-spin-Phase file RSLQ : Reference Scan Law attitude Quaternion file RSLQ : Reference Scanning Law schedule - Quaternion attitudes RSLS : Reference Scanning Law Schedule RSS : Really Simple Syndication RSS : Reference Sky Scene RSS : Root-Sum-Square RSSD : Research and Scientific Support Department (ESA) RT : Real-Time RT : Remote Terminal RT : Room Temperature RTB : Real-time TestBed RTC : Real-Time Clock RTC : Release Time Constant RTD : Resistance Temperature Detector RTDB : Run-Time DataBase 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 RTS : Real-Time Simulator RTU : Remote Terminal Unit RUG : RijksUniversiteit Groningen (Kapteyn Astronomical Institute) RUP : Rational Unified Process RUWE : Re-normalised UWE RV : Radial Velocity RVF : Radial Velocity Filter (special filter in MBP; obsolete) RVS : Radial Velocity Spectrometer RVSM : Radial Velocity spectrometer Sky Mapper (obsolete) RVSWG : RVS Working Group (obsolete) RVT : Radiation Verification Test RVZP : Radial-Velocity Zero Point RW : Random Walk s : second; SI unit of time S : Strip (CCD chip along-scan coordinate identifier in focal plane) S12/S19 : Service 12 / Service 19, i.e., definition of on-board autonomy in FDIR S2E2 : (ESA) SCI-S System Engineering Environment (replacement of SOCCI) S2LGA : Switch to LGA S3R : Sequential Switching Shunt Regulator S5M : MBP photometric system (see C1M; obsolete) S6 : Service-6 (Bulk Data Transfer) SA : Science Alert(s) SA : Secular Acceleration SA : Solar Array SAA : Solar Aspect Angle SAA : South Atlantic Anomaly SAAC : Software for Analysing Astrometric CCD (data) SaaS : Software as a Service SAD : System Assurance Document SADT : Structured (System) Analysis and Design Technique SAFLIM : Semi-analytical Approach Functions to LIssajous Motion SAG : Science Advisory Group (obsolete; superseded by GST) SAG : Sun Acquisition Gyrometer SAGA : System of Accommodation for Gaia Algorithms (CNES) SAGA : System of Accommodation of Gaia Algorithms SAGA : System of Accommodation of the Gaia Algorithms SAGA : System of Accomodation of Gaia algorithms SAGEM : Specific company for design, development, and manufacturing of opto-mechanical equipment SaH : Sample and Hold SAM : Statistical Analysis Module 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) SAS : Science Analysis System (XMM) SAS : Soci\'et\'e par Actions Simplifi/'ee SAS : Solar Array Simulator SAS : Sun Acquisition Sensor SAT : Science Archives Team (at ESAC) SAW : Stand-Alone Worker SaW : Stand-alone Worker SB : Spectroscopic Binary (star) SB2 : Double-lined Spectroscopic Binary SBC : Single Board Computer SBC : Supplementary Buried Channel (CCD) SBM : Stand-By Mode SBN : Small Bodies Nomenclature SBNAF : Small Bodies: Near and Far SBT : Satellite Base Time (the practical representation of OBT) SC : (MLA) Steering Committee SC : Spacecraft (also denoted S/C) SC3 : Special Commission number 3 on Fundamental Constants (IAG) SCA : Software Criticality Analysis SCAG : Source, Calibration, Attitude, Global (AGIS) 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 SCLO : Scan Law Change Operation SCM : Software Configuration Managment SCMP : Software Configuration Management Plan SCN : SCeNe SCOE : Special Check-Out Equipment SCOM : SCience Operations Manager SCON : Source CONsolidator SCOS : Spacecraft Control and Operations System SCOS2000 : Default ESA SCOS (also known as SCOS2K and S2K) SCOT : Special Conditions Of Tender SCP : Satellite Commissioning Plan SCP : SOC Calibration Procedure ScQL : Science Quick Look (obsolete) SCR : Simulations Control Room SCR : Software Change Request SCRS : SpaceCraft Reference System SCS : Spacecraft Common Simulator SCS : Super Computer for Space SCS750FX : Specific PPC board (Maxwell) SCSI : Small Computer System Interface SCT : SOC Calibration Team SD : Standard Deviation SDA : Specific Development Activity SDB : Satellite DataBase SDB : Spacecraft DataBase SDB : System DataBase SDBC : Satellite DataBase Content SDBD : Satellite DataBase Delivery SDCM : Source Data Collection Module SDD : Software Design Document SDE : Signal Detection Efficiency SDE : Software Development Environment SDE : Sunshield Drive Electronics SDID : Starv Density Injection Delay SDK : Software Development Kit SDM : SOC Development Manager SDM : Source, Detection-classifier, and cross-Match SDP : Software Development Plan SDP : Supplementary Data Pattern SDPC : Spectroscopic Data Processing Centre SDPM : Source Data Processing Module SDR : System Design Review SDS : Science Data Server SDSS : Sloan Digital Sky Survey SDT : Spacecraft Dynamical Time SE : Standard Edition SE : Standard Error SE2ET : System End-to-End Test (also denoted (SETET) SEA : Source Environment Analysis (CU5) SeaPipe : Source Environment Analysis Pipeline (CU5 / DPCI) 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 SEG : Software Engineering Guidelines SEGR : Single-Event Gate Rapture SEL : Single-Event Latch-up SEL2 : Sun-Earth Libration point number 2 (also known as L2) SEM : Space Environment Monitor (GOES) SEP : South Ecliptic Pole SEP : Strong Equivalence Principle SEPE : Solar Energetic Particle Event SEPM : Solar Electrical Propulsion Module SET : Single-Event Transient SETET : System End-To-End Test (also denoted SE2ET) SEU : Single-Event Upset SF : Scale Factor SF : Soyuz-Fregat SFCG : Space Frequency Coordination Group SFE : Surface-Figure Error SFH : Star Formation History SFIRD : Stations and Facilities Implementation Requirements Document SFM : Stations and Facilities Manager SFR : Star Formation Rate SFT : Short Functional Test SFW : Surface Full Well SG : Selex Galileo SG : Super Giant SGA : Stellar and Galactic Astronomy group SGC : South Galactic Cap SGE : Sun Grid Engine SGICD : Space to Ground Interface Control Document SGIS : Spectroscopic Global Iterative Solution SGM : Safe Guard Memory Sgr : Sagittarius (constellation with high average star density) SGS : Science Ground Segment SGS : Symmetric Gauss-Seidel SGSDD : Science Ground-Segment Design Description Si : Silicon SI : Simple Iteration SI : Syst\`eme International (International System of units, defined by ISO) SIA : Sagnac Interferometer Assembly SIAM : Spacecraft/Instrument Alignment Matrix 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) SIG : Scientific Interfaces Group SIG : Scientific Interfaces Group (DPAC) SILO : Societ\`a Italiana Lavorazione Oro SILOGIC : French IT company SILSO : Sunspot Index and Long-term Solar Observations SIM : SIMulation (SIMulator) SIM : Space Interferometry Mission SIMDATA : SIMulation DATA SIMSAT : Software Infrastructure for Modeling Satellites SiNAD : Signal-to-Noise Detection Ratio SIP : Science Implementation Plan SIR : Specifications and Interfaces Review SIRD : Science Implementation Requirements Document SIS : Spacecraft Information System SIS : Spacecraft Interface Simulator SIS : Spectroscopic Iterative Solution (superseded by SGIS) SISO : Single Input - Single Output SISO : Single Input, Single Output SISPA : Small Instantaneous Sub-Pupil Area SIT : System Integration Test SIXE : Spanish-Italian X-ray Experiment SJ : Small JASMINE SK : Spare Kit SKEL : Spacecraft Key Event Log SL : Scanning Law SLE : Space Link Extension SLED : Super LED SLG : Scanning-Law Guidance SLM : Scanning-Law Monitor SLRS : System-Level Reassessment Study SLT : Sector Link Table SLTA&DS : System-Level Technical Assistance and Definition Study SLTRS : System-Level Technical Reassessment Study SM : Sky Mapper SM : Software Module SM : Structural Model SMA : Shape Memory Alloy SMA : Star Mapper(-based) Attitude (Hipparcos) SMC : Small Magellanic Cloud (special, high-density area on the sky) SMD : Surface Mount Device SME : Small- and Medium-sized Enterprises SME : Software Maintenance Environment SME : Standard-Model Extension SMO : Suspect Moving Object SMOK : Scaled Model Of Kinematics SMP : Science Management Plan SMR : Software Modification Request SMSGEN : Sampled Mean Spectrum GENerator SMT : Surface Mounted Technologies SMTP : Small-Message Transfer Protocol SN : Serial Number (also denoted as S/N) SN : Serial Number (also denoted S/N) SN : SuperNova SNAP : Supernova-Acceleration Probe SNR : Science News Release (ESA) SNR : Signal-to-Noise Ratio (also denoted SN and S/N) SNR : SuperNova Remnant SOAD : Science Operations Assumptions Document SOAP : Simple Object Access Protocol SOC : Science Operations Centre SoC : Status of Compliance SOC : System On a Chip SOCCI : (ESA) Science Operations Configuration Control Infrastructure (replaced by S2E2) SODA : SCOS ORATOS Distributed Access SOF : Spacecraft Observations File SOFA : Standards Of Fundamental Astronomy (IAU) SOGAR : Scanning-law Optimisation for GAREQ SOGS : Science Operations Ground Segment SOIA : Science Operation Implementation Agreement SOM : Self-Organising Map SoM : Space of Measurements SOM : Spacecraft Operations Manager SOP : Script Offline Processing SOR : Science Operations Request SOS : Specific Object Studies SOSD : Science Operations Scenario Document SOT : Science Operations Team SOT : Science Operations Tool SOVP : System Operations Validation Plan SOVT : System Operations Validation Test SOW : Statement Of Work SoW : Statement of Work SP : Software Product SP : Source Packet SP : SPecification SP : Star Packet SP : Static Parameter SP : Sub Pupil SP-L : Split Phase-Level SPA : Software Product Assurance SPACON : SPAcecraft CONtroller SPAE : Source PArallax Error SPAP : Software Product Assurance Plan SPaP : Stream Pre-compression and Partitioning SPAR : Software Product Assurance Report SPAU : Source PArallax Update SPB : Senior Procurement Board SPB : Slowly Pulsating B-star SPC : Science Programme Committee (ESA) SPD : Spectral Products Database SPD : Stellar Photon Distribution SPE : Solar Particle (Proton) Event SPEC : SPECtroscopic processing Spectro : Spectrometer instrument (obsolete) SPENVIS : SPace ENVironment Information System SPF : Single-Point Failure SPF : Star Param(eter)s FLAME SPG : Sun Position Generator (AOCS) SPGRID : SPectral GRIDS (grids of synthetic spectra) SPID : SCOS-2000 Packet Identifier SPL : Split Phase-Level SPLIB : SPectral LIBraries (synthetic spectral data) SPME : Source Proper-Motion Error SPMP : Software Project Management Plan SPMU : Source Proper-Motion Update SPOE : Source POsition Error SPOP : Standard Public Outreach Plan SPOU : Source POsition Update SPR : Software Problem Report 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) 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 SR : Semi-Regular (variable star) SR : Status Report SR : Summary Report SR : Summing Register (also known as Summing Well) SRaD : Stream Restoration and Decoding SRAM : Static RAM SRC : Secondary Red Clump SRC : Spacecraft Reference Configuration SRD : Software Requirements Document SRD : System Requirements Document SRE : Science and Robotic Exploration (ESA directorate) SREC : S-RECord (Motorola text format to code binary files) SREM : Space Radiation Environment Meter (obsolete) 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 SRP : Sun Rotation Phase SRR : System Requirements Review SRS : Scanning Reference System SRS : Software Requirements Specification SRS : Spacecraft Reference System (obsolete) SRS : Spacecraft Requirements Specification SRV : Semi-Regular Variable (star) SRV : Spectroscopic Radial Velocity SS : Small Scale SS : Solar System SS : Sub-System (also denoted S/S) SS : Sun Search SS : SunShield (also denoted SSH) SSA : Software Support Area SSA : Spectroscopic Science Alert SSAC : Space Science Advisory Committee (ESA) SSAS : Single-Star Astrometric Solution SSB : Solar-System Barycentre SSC : Source Sequence Count SSC : Spectrum Shape Coefficient SSC : Spitzer Science Centre (NASA) SSCB : Station-Spacecraft oCculting Body angle SSCH : Science SCHedule SSCP : Small-Scale Calibration Parameter SSD : Solid-State Disk SSH : Secure SHell SSL : Secure Socket Layer SSLC : Single-Sided Limit Cycle SSM : Second Surface Mirror SSM : Spacecraft Safe Mode SSM : Spectro Sky Mapper (obsolete) SSMC : Stellar Source Main Characteristics SSMM : Solid-State Mass Memory SSO : Solar-System Object SSOC : Solar-System-Object Classifier SSPA : Single Star with Perspective Acceleration SSPA : Solid-State Power Amplifier SSR : Science Support Room SSR : Software Support Room SSR : Solid-State Recorder SSR : Sum of Squared Residuals SSS : Software and System Specification SSS : Software System Specification SSS : System Software Specification SSSB : Small Solar-System Body SSSO : Small Solar-System Object SST : Space Surveillance Telescope SSU : Specific Source Unit SSWG : Solar-System Working Group (obsolete) ST : Satellite Time ST : Scientific Target ST : Short Term STAF : File Archive and Transfer Service (implemented at CNES) STAMTA : Single-Transit Analysis / Multi-Transit Analysis STB : Software Test Bench STC : STation Computer STD : STandarD stdin : standard input STDM : Spacecraft Trajectory Data Message stdout : standard output STE : Special Test Equipment STE : Star-Tracker Electronics STES : Star Tracker Electronics Stimulator 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 STIL : Starlink Tables Infrastructure Library STILTS : STIL Tool Set STK : Software ToolKit STM : Structural and Thermal Model (Structural-Thermal Mode, Structure Test Model) STP : Software Test Plan STR : Software Test Report STR : Star TRacker STR : System (Software) Test Report STR-E : Star Tracker Electronics STR-OH : Star Tracker Optical Head STRP : STatistic RePorting STS : Short Time Scale STS : Star Tracker System STS : System Test Specification STSM : Short-Term Science Mission STSP : Standard Time Source Packet STUFF : Computer code to generate mock catalogues of astronomical sources (E. Bertin) STV : STeVenage (UK) STVR : Software Test and Validation (Verification) Report 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 SVOP : Scientific Validation Offline Processing SVP : Sample Video Package SVP : Software Validation Plan SVP : System Verification Plan SVS : Software Validation Specification SVT : Scientific Validation Team SVT : System Validation Test SVTP : Software Verification Test Plan SVV : Software Verification and Validation SVV : STR Velocity Vector SVVP : SVV Plan SVVR : SVV Report SW : Science Window SW : Software (also denoted S/W) SW : Space Wire SWA : Sliding Window Algorithm (obsolete) SWG : Simulation Working Group (obsolete) SWR : Equipment software resource SWR : Software Resource SWRI : Southwest Research Institute (USA) SWS : Sampling and Windowing Strategy SY : Staff Year SYNTH : Specific spectrum synthesis software (Nikolai Piskunov) T2CEP : Type-II Cepheid TAA : Technical Assistance Agreement TADS : Technical Assistance and Definition Study (also denoted TA&DS) TAI : International Atomic Time TAMS : Terminal Age Main Sequence TAP : Table Access Protocol TAR : Test Acceptance Review TAS : Thales-Alenia Space TASC : Tool for Auxiliary Scientific Calculations (https://www.fd-tasc.info/roscmd/) TAT : Telescope Alignment Tool TB : TeraByte TB : Thermal Balance TBA : To Be Announced TBA : To Be Assigned TBC : To Be Confirmed TBD : To Be Defined (Determined) TBO : Two-Body Orbit TBR : To Be Resolved TBT : To Be Tested TBTV : Thermal Balance/Thermal Vacuum (Test) TBW : To Be Written TBW : Tukey Bi-Weighted (centroiding) TBW : Tukey BiWeight TC : TeleCommand (Packet) TC : Thermal Control TC : Time Correlation TCB : Barycentric Coordinate Time TCDS : Telemetry Concatenated Decoding System TCE : TeleCommand Encoder TCG : Geocentric Coordinate Time TCI : Technology Conformance Inspection TCI : Time since Charge Injection TCL : Test Configuration List TCo : Time Correlation TCO : Transparent Conductive Oxide TCORR : Time CORRelation TCP : Transmission Control Protocol TCP-IP : Transfer Control Protocol - Internet Protocol TCR : True Comment Ratio TCS : Thermal Control Sub-system TCSEQ : TeleCommand Sequence Manager (software) TCV : TeleCommand Verification TCXO : Temperature-Controlled Crystal Oscillator TD : Test Design TD : Theoretical Deviation TD : Total Dose TD : Transit Description TDA : Technological Demonstrator (Development) Activity TDAC : Tycho Data Analysis Consortium (Hipparcos) TDB : Barycentric Dynamical Time (obsolete) TDC : Time Data Codification TDI : Time-Delayed Integration (CCD) TDN : Total Detection Noise TDP : Technical Data Package TDS : Spacecraft Dynamical Time TDS : Test Data Set TDS : Transit Depth Significance TE : Trending Epoch TEB : Tender Evaluation Board TEC : Thermo-Electric Cooler TED : Thermo-Elastic Distortion TEDN : Total Electronic Detection Noise TEO : Terrestrial Ephemeris Origin (obsolete) TEP : Tangential Equipment Panel TF : Test Field TF : Transfer Frame TFG : Transfer-Frame Generator TFGTS : TFG Time Strobe TFLOP : Tera FLOP TFM : TransFer Mode TG : Gaia (proper) Time TG : Gaia proper Time TG : Transfer Gate TGAS : Tycho-Gaia Astrometric Solution TGE : Total Galactic Extinction THD : ThresHolD THR : THRuster TI : Test Item TI : Thermal Inertia TICTI : Technical ICT Infrastructure TID : Total Ionising Dose TIM : TIMing TIO : Terrestrial Intermediate Origin TIS : Total Integrated Scattering TLC : Time-Link Calibration TLF : Telescope List File TLG : Titov-Lambert-Gontier (catalogue of QSOs; http://adsabs.harvard.edu/abs/2011A%26A...529A..91T) TLS : TouLouSe (Fr) TLV : Thruster Latch Valve TM : Telemetry (Packet) TM : Test Manager TM : Thermal Model TM : Thermal-Mechanical TM : Trace Matrix TMA : Three-Mirror Anastigmatic (telescope) TMA : TM Arranger TMC : Telemetry Curve TMcodec : Telemetry CODEC TMDM : Thermal-Mechanical Demonstrator Model TME : Template-Mismatch Error 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 TMSO : Tc file for Master Switch Off TMT : Thermal Limit Trigger TMT : Thermal Monitoring Table TMTC : TeleMetry and TeleCommand (also denoted TM/TC) TMV : Triple Majority Voting TN : Technical Note TNID : Total Non-Ionising Dose TNO : (Nederlandse Organisatie voor) Toegepast-Natuurwetenschappelijk Onderzoek TNO : Trans-Neptunian Object TNO-TPD : Physics Department of Netherlands Organisation for Applied Scientific Research TNS : Transient Name Server TOB : Tender Opening Board ToC : Table of Contents TOM : Time-Out Monitor TOPCAT : Tool for OPerations on Catalogues And Tables ToR : Terms of Reference TP : Temperature Probe TP : Twin Peaks (in BAM signal) TPF : Task Parameter File TPF : Terrestrial Planet Finder TPN : Telemetry Packet Number TPS : Thermal Protection Sub-system TR : Test Report TR : Transmitted (sample coordinate) 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 TRS : Topocentric Reference System TRSP : TRanSPonder TS : Test Set TS : Test Specification TS : Time Series TS : Time Slot TSAF : Tc file for SAFe mode TSC : SpaceCraft proper Time (“inverted”, French style) TSC : Transport and Storage Container TsCI : Time since Charge Injection TSE : Total System Error TSM : Time Slot Marker TSM : TranSition Mode (AOCS) TSST : Tc file for Separation Sequence TSUR : Tc file for SURvival mode TT : Terrestrial Time TT : Thermal Tent TT&C : Telemetry, Tracking, and Commanding TTA : Thermal Test Adapter TTAS : Thermal Test Adapter Spacer TTC : Telemetry and TeleCommand TTCP : Telemetry and TeleCommand Processor TTCP : Telemetry, Telecommand, and Control Processor (replaced IFMS) TTH : Thermal-Tent Housing TTL : Through-The-Lens TTMT : Thermal Tent Mating Tool TTR : Telemetry, Telecommand, and Reconfiguration TUM : Technical User Manual TV : Testing and Validation TVAC : Thermal Vacuum (also denoted TV) TVT : Thermal Vacuum Test TWP : Top-level Work Package TWTA : Traveling WaveTube Amplifier U : Johnson photometric U band UAO : Uppsala Astronomical Observatory (Sweden) UART : Universal Asynchronous Receiver Transmitter UB : University of Barcelona (Spain) UBGS : Universitat de Barcelona Gaia Simulator UC : Use Case UCAC : USNO CCD Astrograph Catalogue UCD : Ultra-Cool Dwarf UCD : Unified Content Descriptor UCL : University College London (UK) UDP : User Datagram Protocol UGC : Unresolved-Galaxy Classifier UH : University of Helsinki (Finland) UI : User Interface UK : United Kingdom UL : Ultimate Load UL : University of Ljubljana ULB : Universit\'e Libre de Bruxelles (Belgium) ULP : User Loading Profile UM : User Manual UM2 : Universit\'e Montpellier 2 (France) UML : Unified Modeling Language UMM : University of Montpellier Masterlist (of radial-velocity zero points) 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) UR : Unavailability Report URAT : USNO star catalogue URD : User Requirements Document URL : Uniform Resource Locator us : microsecond (avoid this notation in Gaia) US : United States USA : United States of America USML : U.S. Munitions List USNO : United States Naval Observatory UT : Universal Time UT1 : Universal Time 1 UTC : Coordinated Universal Time UTKP : Unit Test Key Point UV : UltraViolet UVES : UV-Visual Echelle Spectrograph (VLT) UVIE : University of Vienna (Austria) UVSQ : University of Versailles - St Quentin-en-Yvelines (France) UWE : Unit-Weight Error UWU : Unit-Weight Uncertainty UXPECT : UneXPECTed Features V : Johnson photometric V band V : Volt; SI unit of voltage VAEX : Visualisation And (interactive) EXploration VAL : VALidation (environment) VALD : Vienna Atomic Line Database VAM : Validation Analysis Module VARI : VARIability processing VariPipe : Variability Pipeline (CU7 / DPCG) VAT : Value Added Tax VB : Visual Binary VBAC : Velocity and Basic-Angle Calibration (also known as VEEBAC) VBS : Very Bright Star VBS : Virtual Bright Star VC : Virtual Channel VCA : Virtual-Channel Assembler VCB : Verification Control Board VCD : Verification Control Document VCM : Virtual-Channel Multiplexer VCS : VLBA Calibrator Survey (Catalogue) VD : Viterbi Decoder VDA : Vapour-Deposited Aluminium VDB : Validation DataBase VDS : Validation Data Set VDT : Validation Data Table VEEBAC : Velocity-Error and Effective-Basic-Angle Calibration VFS : Virtual Faint Star VG : ViewGraph VGA : Video Graphics Array VGTT : Vacuum Ground Thermal Tent VHDL : VHSIC Hardware Description Language VHSIC : Very High-Speed Integrated Circuit VIM : Variability-Induced Mover (DMSA, Hipparcos Catalogue) VIMF : Variability-Induced Mover with Fixed configuration VIMO : Variability-Induced Moving Objects VIP : Virtual Internet Protocol VIS : Vertical Integration Stand VISTA : Visible and Infrared Survey Telescope for Astronomy VLA : Very Large Array (NRAO) VLBA : Very Long Baseline Array VLBI : Very Long Baseline Interferometry VLT : Very Large Telescope (ESO) VLTI : Very Large Telescope Interferometer (ESO) VM : Virtual Machine VO : Virtual Object VO : Virtual Observatory VoV : Volumes of Variation (technique) voxel : VOlume piXEL (box in ra, dec, distance) VPA : Video Processing Algorithms VPHG : Volume Phase Holographic Grating VPU : Video Processing Unit VPU : Visibility Periods Used Vr : Radial Velocity VRC : Vertical Red Clump VRD : Voltage of the Reset Drain VRF : Velocity Reference Frame VS : Virtual Star VSD : Video Sampling Delay VSDS : Video Selection and Distribution System VSH : Vector Spherical Harmonic(s) VSH : Vector Spherical Harmonics Vsini : Rotational velocity (in projection) VSOP : Variations S\'eculaires de l'Orbite des Plan\`etes VST : Validation Source Table VST : VLT Survey Telescope (ESO) VSWG : Variable Star Working Group (obsolete) VTC : Validation Test Case VTM : Voltage-Tunable Method (for charge injection) VTR : Validation Test Report (CU9) VTS : Validation Test Specification (CU9) VV : Verification and Validation VxWorks : Specific OS W : Watt; SI unit of power W3 : World Wide Web Consortium WA : Specific window designation in AF (obsolete) WAM : Window Acquisition Manager WAP : Single-pixel (unbinned) WA window (obsolete) WB : BBP window designation (obsolete) WB : Weight Balancing WBS : Work Breakdown Structure WC : Worst Case WCA : Worst-Case Analysis WCSM : Wavelength (scale) Calibration Software Module WD : Watch Dog WD : White Dwarf (star) WD : WinDow WEAM : Whitehead Eclipse Avoidance Manoeuvre 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 WFMOS : Wide-Field Multi-Object Spectrograph WFPC2 : Wide-Field and Planetary Camera 2 (HST) WFRL : Weibul Failure-Rate Law WFS : WaveFront Sensor WFST : Wide-Field Star Tracker WG : Working Group WGAS : Working Group on Astronomical Standards (IAU) WIMPY : World Map Print Out WISE : Wide-field Survey Explorer WL : Wedged Lens WM : MBP window designation (obsolete) WMR : Window Model Record WN : Warning Notice WN : White Noise WP : Work Package WR : Window in RVS (covering a star spectrum; obsolete) WRS : Window Reference System wrt : with reference to (also denoted w.r.t.) wrt : with respect to (also denoted w.r.t.) WSDL : Web Services Description Language WSP : Single-pixel (unbinned) window (obsolete) WSS : Weather Station System Wtn : WiTNess WY : Bright-star window designation in Astro (obsolete) X : Telecommunication band used for Gaia XAA : X-band Acquisition Aid XDF : eXtensible Data Format XE : eXpress Edition XELSF : eXtended ELSF (also known as EELSF) XELSF : eXtended Empirical Line Spread Function XEUS : X-Ray Evolving Universe Spectrometer (ESA) XHPA : X-Band High-Power Amplifier XHTML : eXtensible HyperText Markup Language 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 XP : operating system for MicroSoft XP : Shortcut for BP and/or RP (generic name for Blue or Red Photometer) XPND : Transponder XSD : XML Schema Definition XSL : eXtensible Stylesheet Language XSLT : eXtensible Stylesheet Language Transformation YaJaHs : Yet another Java Help system (Herschel) YL : Yield Load Z : Metallicity (star) Z : Zulu, meaning UTC Z+G : Zoom + Gate mode (VPU mode) ZAH : Zentrum f\"ur Astronomie der Universit\"at Heidelberg ZAMS : Zero-Age Main Sequence (star) ZAP : Zoom Astro Phase (AOCS normal-mode submode with VPUs in Zoom + Gate mode; ZAP = coarsest submode of NM) ZARM : Centre for Applied Space Dynamics and Microgravity, Bremen (Germany) ZL : Zodiacal Light