MESSENGER EXPERIMENT DATA RECORD SOFTWARE INTERFACE SPECIFICATION FOR THE X-RAY SPECTROMETER Revision 3.7 07/01/2015 Prepared by Raymond Espiritu Erick Malaret Applied Coherent Technology Corporation DOCUMENT REVIEW This document and the archive it describes have been through PDS Peer Review and have been accepted into the PDS archive. Richard Starr, MESSENGER XRS Instrument Scientist, has reviewed and approved this document. Susan Slavney, PDS Geosciences Node Representative, has reviewed and approved this document. Susan Ensor, MESSENGER Science Operations Center Lead, has reviewed and approved this document. Revision History Version Number Date Changes 2I 4/24/2008 * Start of revision history: version included in MESSENGER PDS Release 4. 3 12/10/2009 * Added documentation for XRS Command Echo EDR. Command Echo EDRs contain a daily history of command echoes produced by the instrument. 3.1 12/11/2009 * Minor editorial changes, mostly for typos, by Richard Starr. 3.2 12/29/2009 * Minor edits to sec. 6.5.1 to include missing REF.CAT, PERSON.CAT, MD5.TAB, XRSINDEX.TAB and XRS_CMDECHO.FMT files. * Sec. 5.3.4: Replaced cmd echo file label example which had incorrect INTERCHANGE_FORMAT with a new correct one from the M3 Flyby. 3.3 01/07/2010 * Added N/A values for SC_RANGE and SC_ANGLE 3.4 06/16/2011 * Added Document Review information 3.4 06/16/2011 * Added info to Section 3 headers and footers 3.4 06/16/2011 * Changed "periherm" to "apoherm" in orbit start time description 3.4 08/25/2011 * Removed references to XRSINDEX.TAB/LBL 3.5 05/25/2012 * Change document title from MESSENGER Data Management and Science Analysis Plan to MESSENGER Data Management and Archiving Plan. Update references. * Reference MESSENGER Data Management and Archiving Plan for release schedule and remove release schedule, table B-1, from this document. 3.6 03/10/2014 * Corrected sec. 8.6: APPENDIX: XRS Engineering Parameter Conversion Equations footnote. 3.7 07/01/2015 * Change "Experimental Data Record" to "Experiment Data Record" in text. * Note use of clock partitions in time tags in product labels following January 8, 2013 S/C clock reset (Section 5.4.2). Table of Contents 1 Purpose and Scope of Document 5 1.1 Purpose 5 1.2 Scope 5 2 Applicable Documents 5 3 Relationships with Other Interfaces 5 4 Roles and Responsibilities 6 5 Data Product Characteristics and Environment 6 5.1 Instrument Overview 6 5.2 Data Product Overview 7 5.3 Data Processing 8 5.3.1 Data Processing Level 8 5.3.2 Data Product Generation 8 5.3.3 Data Flow 8 5.3.4 Labeling and Identification 10 5.4 Standards Used in Generating Data Products 12 5.4.1 PDS Standards 12 5.4.2 Time Standards 12 5.4.3 Coordinate Systems 13 5.4.4 Data Storage Conventions 13 5.5 Data Validation 13 6 Detailed Data Product Specifications 13 6.1 Data Product Structure and Organization 13 6.1.1 Handling Errors 13 6.1.2 Geometric Elements 14 6.2 Data Format Description 14 6.3 File Naming Conventions 14 6.4 Label and Header Description 14 6.4.1 PDS Label File Format 14 6.4.2 Binary Table File Formats 16 6.4.3 ASCII Table File Formats 16 6.4.4 Format File Keyword Definitions 16 6.5 Directory Structure and Contents for XRS EDR Data Archive Volume 17 6.5.1 Directory Contents 17 7 Release of Archives to PDS 19 8 Appendicies 20 8.1 APPENDIX: XCOLUMN.FMT File 20 8.2 APPENDIX: XRS_CMDECHO.FMT File 43 8.3 APPENDIX: SPICE Kernel Files Used in MESSENGER Data Products 45 8.4 APPENDIX: CODMAC/NASA Definition of Processing Levels 46 8.5 APPENDIX: MESSENGER XRS Glossary and Acronym List 47 8.6 APPENDIX: XRS Engineering Parameter Conversion Equations 48 1 Purpose and Scope of Document 1.1 Purpose This document will serve to provide users of the MESSENGER X-Ray Spectrometer (XRS) Experiment Data Record (EDR) data product with a detailed description of the XRS instrument, data product generation, validation and storage. The XRS EDR consists of an X-ray spectrometer measurement over a given area of the Mercury surface and a simultaneous measurement of the solar X-ray spectrum. Measurements are grouped together into a PDS binary table which consists of all measurements obtained over one earth day. Only XRS EDRs are addressed by this document. Higher level products, such as Calibrated Data Records (CDRs) or Reduced Data Records (RDRs) are addressed by the XRS RDR SIS document. This SIS will address the XRS EDR data product, the file transfer method from the MESSENGER Science Operations Center to PDS, and the format and content of the XRS EDR Volume Archive. The document is thus both an EDR data product SIS and an EDR archive volume SIS. 1.2 Scope This Software Interface Specification (SIS) is useful to those who wish to understand the format and content of the XRS EDR data products. Typically, these individuals include scientists, data analysts, and software engineers. The SIS applies to EDR data products produced during the course of MESSENGER mission operations. Reduced Data Records and Calibrated Data Records (RDR and CDRs) are outside the scope of this SIS and are described in a separate SIS document - the XRS RDR SIS. RDRs and CDRs are also archived in their own, separate PDS archive volume. 2 Applicable Documents The Messenger XRS SIS is responsive to the following Documents: * MESSENGER Mercury: Surface, Space Environment, Geochemistry, Ranging; A mission to Orbit and Explore the Planet Mercury, Concept Study, March 1999. Document ID number FG632/ 99-0479 * Planetary Data System Standards Reference, Aug 1, 2003, Version 3.6. JPL D-7669, Part-2. * MESSENGER Data Management and Archiving Plan. The Johns Hopkins University, APL. Document ID number 7384-9019 * [PLR] Appendix 7 to the discovery program Plan; Program Level Requirement for the MESSENGER Discovery project; June 20, 2001. * Instrument Calibration Report X-Ray Spectrometer 3 Relationships with Other Interfaces The XRS EDR data products are stored on Hard Disk and in an SQL (Structured Query Language) relational databases for rapid mission access during mission operations. The data products will be electronically delivered to the PDS Geosciences Node according to the delivery schedule in the MESSENGER Data Management and Archiving Plan. The data in the EDR files themselves will be stored in a PDS BINARY TABLE object. 4 Roles and Responsibilities The roles and responsibilities of the instrument teams, Applied Physics Lab (APL), Applied Coherent Technology (ACT), and the Planetary Data System (PDS) are defined in the MESSENGER Data Management and Archiving Plan. 5 Data Product Characteristics and Environment 5.1 Instrument Overview The Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission is designed to orbit Mercury following one Earth flyby, two flybys of Venus and three of Mercury. It launched in August 2004 and will use these flybys to achieve an orbit insertion around Mercury in March 2011. Initial data collection will begin during the three flybys of Mercury, and will primarily consist of global mapping and measurements of the surface, atmosphere and magnetosphere composition. MESSENGER will remain in orbit for the rest of the nominal mission, which is scheduled to end in March 2012 [see the MESSENGER Data Management and Archiving Plan for extended mission updates]. Once in orbit around Mercury it will begin a series of observations using multiple instruments. These observations will provide data to answer questions about the nature and composition of Mercury's crust, tectonic history, the structure of the atmosphere and magnetosphere, and the nature of the polar caps. The X-Ray Spectrometer (XRS) experiment is comprised of three identical gas proportional counters (GPC) that measure X-rays emitted from the surface of Mercury in the energy range from about 1 to 10 keV. X-rays in this energy range sample the planetary surface to depths of a few tens of microns. The GPCs each have a 10-cm2 active area and use both anti-coincidence wires and pulse shape discrimination to minimize background. Balanced filters are used to resolve the lower energy X-ray lines from Mg, Al, and Si. This technique has been used previously on other orbital X-ray experiments flown on the Apollo 15, 16 and NEAR-Shoemaker missions. One GPC has a thin aluminum filter, which filters out Si photons, one has a thin Mg filter, which filters out Al and Si photons, and the third GPC has no filter. The energy resolution of the gas counters is sufficient to resolve the higher energy lines from S, Ca, Ti, and Fe. A small Si-PIN detector is used as a solar monitor, because the Sun is the source of the planetary X-ray fluorescence. The field-of-view (FOV) of the GPCs is 12 degrees. Both the GPCs and the Si-PIN detector count individual photons, producing an electronic pulse that is proportional to the energy of the absorbed photon. Each valid count is stored in energy histograms (spectra) that are 244 channels for the GPC and 231 channels for the Si-PIN. The accumulation time for these histograms will vary depending upon proximity to the planet. At periapsis the accumulation time will be 40 seconds and at apoapsis 450 seconds. The XRS is comprised of three physical units. The GPCs make up the Mercury X-ray Unit (MXU). The Solar Assembly for X-rays (SAX) includes the Si-PIN diode, preamplifier, shaping electronics and thermal electric cooler (TEC). The analog and digital electronics are contained in the Main Electronics for X-rays (MEX) unit. The SAX is located at the "top center" edge of the solar shield (see Figure 1). The MXU and MEX are co-located within the payload adapter ring. Figure 1 XRS Configuration on MESSENGER 5.2 Data Product Overview This SIS document only contains information on the XRS Experiment Data Record (EDR) data product. Please refer to the Calibrated Data Record (CDR) SIS and Reduced Data Record (RDR) SIS for documentation on higher level XRS products. There are two data products for the XRS EDR archive. One is the MESSENGER X-Ray Spectrometer EDR. This is the primary data product. The other is the XRS Command Echo EDR. This document will refer to the two types by their standard data product id. "XRSEDR" for the XRS spectral data and "XRS COMMAND ECHO" for the command echo data. Each EDR product consists of 2 files. One file contains the data itself. The XRSEDR data are arranged in binary table format while the XRS COMMAND ECHO data are stored in ASCII table format. The other file is a label file, which describes the content of the data file. The label file defines the start time and end of the observation, product creation time, etc. The PDS label file contains a reference pointer to a separate format file. The format file describes the structure of the table in the data file and each of the different fields within the table. This format file resides in LABEL directory of the data archive volume. Each EDR data product will contain all observations collected or command echos generated by the instrument on a given Earth day. 5.3 Data Processing 5.3.1 Data Processing Level There will be one XRS EDR data volume archive. The volume archive will contain CODMAC (Committee on Data Management and Computation) level 2 data products, also known as EDRs. Each product will have a unique file name and conform to the file naming convention in section 6.3. All EDR products will be stored at the APL Science Operations Center (SOC). Data downlink is telemetered through NASA's Deep Space Network (DSN) managed by the Jet Propulsion Laboratory in Pasadena, CA, and then forwarded to the APL Mission Operations Center (MOC). The MOC then sends telemetry in the form of CCSDS packets to the SOC. Level 1 CODMAC XRS data is extracted from the CCSDS packets and stored in a database and file system at the SOC. Periodic automatic execution of the 'PIPE-XRS2EDR' software will then generate the EDRs. 5.3.2 Data Product Generation The X-Ray Spectrometer EDR files will be produced by the MESSENGER Science Operations Center (SOC) operated jointly by APL and ACT. The 'PIPE-XRS2EDR' software creates EDR data in the PDS labeled format specified by this SIS. The EDR data products are made available to the MESSENGER Science Team for initial evaluation and validation. At the end of the evaluation and validation period, the data are organized and stored in the directory structure described in section 6.5 for transmittal to the PDS Geosciences node. The transmittal process is described in the following section, Data Flow. The initial and subsequent releases to PDS are according to the schedule table in the MESSENGER Data Management and Archiving Plan. PDS will then provide public access to the data products via its online distribution system. 5.3.3 Data Flow The MESSENGER SOC operates under the auspices of the MESSENGER Project Scientist to plan data acquisition and generate and validate data archives. The SOC supports and works with the MOC, The Science Team, instrument scientists, and the PDS. Figure 2 MESSENGER Data Flow shows the flow of data within the MESSENGER project and out to PDS. The MOC handles raw data flow to and from the MESSENGER spacecraft and the SOC converts the raw telemetry into EDRs. The Science Team validates the EDRs and notifies the SOC if corrections are needed. Documentation and EDRs are delivered to the PDS Geosciences node. SPICE Kernels are delivered to the PDS Navigation and Ancillary Information (NAIF) node. The MESSENGER SOC will deliver data for the XRS EDR data volume in standard product packages. Each package will comprise data and ancillary data files, organized into directory structures consistent with the volume design described in section 6.5. Figure 2 MESSENGER Data Flow The following describes the electronic transfer process of releasing data to PDS for the first PDS delivery. Future data deliveries will be assumed to follow the same process unless otherwise noted in an update of this document. Given the long duration of the mission the project is reserving the option of exploring alternate data delivery methods for subsequent deliveries. As such, the method of electronic transfer may change and will be revised accordingly in the SIS. Any changes to the delivery process will be noted in an update to the SIS document and will include the specific dates which will use the new delivery process. The delivery of products to the data volume will follow the schedule in the MESSENGER Data Management and Archiving Plan In the week prior to the delivery date the directory structure will be compressed into a single "zip archive" file for transmittal to the PDS node. The zip archive preserves the directory structure internally so that it can be recreated after electronic delivery to the PDS node. The zip archive file is transmitted to the PDS node via FTP to an account set up by the receiving node. Also transmitted will be a checksum file created using the MD5 algorithm. This provides an independent method of verifying the integrity of the zip file after it has been sent. Within days of transmittal the PDS node will acknowledge receipt of the archive and checksum file. If acknowledgement is not received, or if problems are reported, the MESSENGER SOC will immediately take corrective action to effect successful transmittal. After transmittal the PDS node will uncompress the zip archive file and check for data integrity using the checksum file. The node will then perform any additional verification and validation of the data provided and will report any discrepancies or problems to the MESSENGER SOC. It is expected that the node will perform these checks in about two weeks. After inspection has been completed to the satisfaction of the PDS node, the node will issue to the MESSENGER SOC acknowledgement of successful receipt of the data. Following receipt of a data delivery the PDS node will organize the data into a PDS volume archive structure within its online data system. Newly delivered data will be made available publicly from PDS once accompanying labels and other documentation have been validated. 5.3.4 Labeling and Identification For every X-Ray data file there exists a PDS Label file. The label file conforms to PDS version 3.6 standards. Consult the PDS Standards Reference Document for more information on this standard. The PDS label describes the data product and provides ancillary information about the data product. The label file is detached and separate from the data file which contains the data in a PDS binary table. The following is an example of the contents of the XRSEDR PDS label file. Details about the label format are specified later in section 6.4. PDS_VERSION_ID = "PDS3" /*** FILE FORMAT ***/ FILE_RECORDS = 130 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 2258 /*** GENERAL DATA DESCRIPTION PARAMETERS ***/ PRODUCT_ID = "XRS2006018_DAT" PRODUCT_VERSION_ID = "V1" PRODUCT_CREATION_TIME = 2006-08-30T21:26:05 PRODUCT_TYPE = "DATA" STANDARD_DATA_PRODUCT_ID = "XRSEDR" SOFTWARE_NAME = "PIPE-XRS2EDR" SOFTWARE_VERSION_ID = "1.0" INSTRUMENT_HOST_NAME = "MESSENGER" INSTRUMENT_NAME = "XRAY SPECTROMETER" INSTRUMENT_ID = "XRS" DATA_SET_ID = "MESS-E/V/H-XRS-2-EDR-RAWDATA-V1.0" MISSION_PHASE_NAME = "VENUS 1 CRUISE" TARGET_NAME = "CALIBRATION" START_TIME = 2006-01-18T13:13:57 STOP_TIME = 2006-01-18T23:58:56 SPACECRAFT_CLOCK_START_COUNT = "46077252" SPACECRAFT_CLOCK_STOP_COUNT = "46115952" ^TABLE = "XRS2006018.DAT" OBJECT = TABLE COLUMNS = 175 INTERCHANGE_FORMAT = BINARY ROW_BYTES = 2258 ROWS = 130 DESCRIPTION = " This table contains X-ray spectra and associated instrument parameters, as observed by the MESSENGER X-Ray Spectrometer (XRS). Detailed descriptions for the parameters defined below are contained in the EDR SIS document. The complete column definitions are contained in an external file found in the LABEL directory of the archive volume. " ^STRUCTURE = "XCOLUMN.FMT" END_OBJECT = TABLE END Notice that the external format file, "XCOLUMN.FMT", defines the structure of the binary table. The table structure is detailed in APPENDIX: XCOLUMN.FMT File. The following is an example of the XRS Command Echo label file. PDS_VERSION_ID = "PDS3" /*** FILE FORMAT ***/ FILE_RECORDS = 20 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 125 /*** GENERAL DATA DESCRIPTION PARAMETERS ***/ PRODUCT_ID = "XRS_CMD2009274_TAB" PRODUCT_VERSION_ID = "V1" PRODUCT_CREATION_TIME = 2009-10-01T20:47:23 PRODUCT_TYPE = "ANCILLARY" STANDARD_DATA_PRODUCT_ID = "XRS_COMMAND_ECHO" SOFTWARE_NAME = "PIPE-XRS2EDR" SOFTWARE_VERSION_ID = "1.1" INSTRUMENT_HOST_NAME = "MESSENGER" INSTRUMENT_NAME = "XRAY SPECTROMETER" INSTRUMENT_ID = "XRS" DATA_SET_ID = "MESS-E/V/H-XRS-2-EDR-RAWDATA-V1.0" MISSION_PHASE_NAME = "MERCURY 3 FLYBY" TARGET_NAME = "MERCURY" START_TIME = 2009-10-01T13:09:18 STOP_TIME = 2009-10-01T13:10:58 SPACECRAFT_CLOCK_START_COUNT = 162890024 SPACECRAFT_CLOCK_STOP_COUNT = 162890124 ^TABLE = "XRS_CMD2009274.TAB" OBJECT = TABLE COLUMNS = 7 INTERCHANGE_FORMAT = ASCII ROW_BYTES = 125 ROWS = 20 DESCRIPTION = " This table contains one set of the commands executed by the MESSENGER X-Ray Spectrometer (XRS). A set is defined as all data with timestamps corresponding to a given Earth day. The complete column definitions are contained in an external structure file found in the LABEL directory of the archive volume. Additional details are contained in the EDR SIS document. " ^STRUCTURE = "XRS_CMDECHO.FMT" END_OBJECT = TABLE END Notice that the external format file, "XRS_CMDECHO.FMT", defines the structure of the ASCII table. The table structure is detailed in APPENDIX: XRS_CMDECHO.FMT file. 5.4 Standards Used in Generating Data Products 5.4.1 PDS Standards The XRS EDR data products comply with the Planetary Data System standards for file formats and labels, as specified in the PDS Standards Reference. The EDR data products include: * A Binary or ASCII Table object (the primary data), * Label File - serves as a high-level description of the parameters of which correspond to the Table object. * a pointer to a FORMAT file which describes the structure of the table 5.4.2 Time Standards The MET field in the XRS EDR binary table matches the spacecraft time in integer seconds that is transmitted to MESSENGER subsystems by the Integrated Electronics Module (IEM). This is referred to by the MESSENGER project as Mission Elapsed Time (MET). MET = 0 is August 3, 2004, at 05:59:16 UTC, which is 1000 seconds prior to the MESSENGER launch. Relativistic effects and circumstances occurring during the mission would result in MET not being a true account of seconds since launch. Following a planned spacecraft clock reset1 on January 8, 2013, partition numbers (1/, or 2/) were added to product labels to disambiguate MET seconds after the spacecraft clock reset (if partition number is not present, SPICE defaults to partition 1/). For this reason the MESSENGER spacecraft clock coefficients file is archived at the PDS Navigation and Ancillary Information Facility (NAIF) Node. This file is used in conjunction with the leapseconds kernel file in order to calculate the conversion between MET and UTC. The conversion is easily done through the use of SPICE kernels and the CHRONOS Utility. CHRONOS is a utility included with the SPICE package that is distributed by the PDS NAIF node. The SPICE kernels are files that contain the information needed to perform the conversion. Two SPICE kernels are required. One is the Leapseconds Kernel (LSK) and the other is the MESSENGER Spacecraft Clock Kernel (SCLK). The SCLK file is used by CHRONOS to convert between spacecraft clock time and ephemeris time, while the LSK file is used to convert from ephemeris time to UTC time. The CHRONOS utility is self-documenting and the SPICE package itself contains full documentation on each of the utilities (including CHRONOS) and how they are used. 5.4.3 Coordinate Systems The following lists the computational assumptions for the geometric and viewing data provided in the PDS label. There are two coordinate systems in use: 1) the celestial reference system used for target and spacecraft position and velocity vectors, and camera pointing; and 2) the planetary coordinate system for geometry vectors and target location. The celestial coordinate system is J2000 (Mean of Earth equator and equinox of J2000). The planetary coordinate system is planetocentric. COMPUTATIONAL ASSUMPTIONS * The mid-point time of observation is used for the geometric element computations. * Label parameters reflect observed, not true, geometry. Therefore light-time and stellar aberration corrections are used as appropriate. * The intertial reference frame is J2000 (also called EME2000). * Latitudes and longitudes are planetocentric. * Distances are in km, speeds are in km/sec, angles are in degrees, angular rates are in degrees/sec, unless otherwise noted. * Angle ranges are 0 to 360 degrees for azimuths and local hour angle. Longitudes range from 0 to 360 degrees (positive to the East). Latitudes range from -90 to 90 degrees. 5.4.4 Data Storage Conventions The data are organized following PDS standards and stored on hard disk and in a SQL (Structured Query Language) database for rapid access during mission operations. The MESSENGER SOC will transfer data to PDS via electronic transfer and delivery methods as detailed in section 5.3.3. After verification of the data transfer PDS will provide public access to MESSENGER science data products through its online data distribution system. 5.5 Data Validation The XRS EDR data products will be validated by the XRS Instrument scientist for science content and for compliance with PDS archive standards [MESSENGER Data Management and Archiving Plan]. 6 Detailed Data Product Specifications 6.1 Data Product Structure and Organization The MESSENGER XRS EDR data set will be archived at the PDS Geosciences node as a data archive volume. The XRS EDR products in the data archive volume are intended to store the data in a form closest to the raw telemetry data received from the spacecraft. The automated production and release of the EDRs will follow the release schedule in the MESSENGER Data Management and Archiving Plan. If errors are discovered the data will be replaced with corrected EDRs on the next scheduled delivery date. 6.1.1 Handling Errors The possibility exists that errors may be introduced into the archive even with validation procedures applied to the archive volumes. An ERRATA report file is maintained to track and document all discovered uncorrectable errors that may occur during the mission. Correctable errors, such as revised EDRs or EDRs that were missing from a previous PDS delivery will be provided at the next scheduled PDS delivery or at the final delivery date (see schedule in the MESSENGER Data Management and Archiving Plan). PDS will then replace the outdated files with the revised EDR files in the data directories of the archive volume. The ERRATA report file is archived in the ROOT directory of the XRS EDR data volume. 6.1.2 Geometric Elements The geometric elements are an essential part of the archive; they contain the data and information to characterize the geometric properties of the sensor, and to fully describe the viewing geometry of an observation. These data are essential to geodetic, cartographic, and photometric applications. The geometric elements are organized according to the SPICE kernel concepts adopted by the Navigational Ancillary Information Facility (NAIF) at the Jet Propulsion Laboratory. SPICE is an acronym for Spacecraft, Planet, Instrument, C-matrix, and Event kernels. The SPICE kernel data set will be stored in ancillary data volumes at the PDS NAIF Node. 6.2 Data Format Description Data is stored in binary table format. A detached PDS format file will provide a detailed description of the structure of the binary table. 6.3 File Naming Conventions The general form of the XRSEDR file name is "XRSYYYYDOY.DAT", where: XRS instrument identifier: represents the XRS instrument YYYY The four digit year corresponding to the MET for each record in the EDR. DOY The three digit day of year corresponding to the MET for each record in the EDR. .DAT the file extension will always be the three character mnemonic 'DAT', indicating data stored in binary format. The PDS label will have the same naming convention but with the file extension .LBL. The command echo EDRs will have a separate file naming convention to distinguish themselves from the science data. The general form of the XRS Command Echo EDRs is "XRS_CMDYYYYDOY.TAB" where: XRS_CMD indicates the file contains XRS command echo data. YYYY The four digit year corresponding to the MET for each record in the EDR. DOY The three digit day of year corresponding to the MET for each record in the EDR. .TAB the file extension indicating the data is stored in ASCII format. 6.4 Label and Header Description 6.4.1 PDS Label File Format The following are the keyword definitions for the detached PDS label file. The detached PDS label file has the same name as the data file it describes, except for the extension .LBL to distinguish it as a label file. PDS_VERSION_ID Represents the version number of the PDS standards documents that is valid when a data product label is created. PDS3 is used for the Messenger Data products. FILE_RECORDS The file_records element indicates the number of physical file records, including both label records and data records. RECORD_TYPE The record_type element indicates the record format of a file. The FIXED_LENGTH value is appropriate for the BINARY table object used for the MESSENGER XRS EDR data products. RECORD_BYTES This element indicates the number of bytes in a physical file record, including record terminators and separators. PRODUCT_ID The product_id data element represents a permanent, unique identifier assigned to a data product by its producer. See also: source_product_id. Note: In the PDS, the value assigned to product_id must be unique within its data set. PRODUCT_VERSION_ID Identifies the version of the product, represented initially by "V1". The version number will be incremented if the product needs to be regenerated as a result of a correction of the data or as a result of a change in the method used to create the product. PRODUCT_CREATION_TIME Stores the time that the data product was created, in UTC time. PRODUCT_TYPE The XRS EDR contains science data, hence the value is always "DATA". STANDARD_DATA_PRODUCT_ID The XRS EDR files are identified as belonging to the same standard data product via this ID. SOFTWARE_NAME Identifies the name of the software system creating the data products. SOFTWARE_VERSION_ID The version number of program or program library used by the instrument to collect observations. INSTRUMENT_HOST_NAME Identifies the MESSENGER spacecraft on which the instrument is located. INSTRUMENT_NAME The full, unabbreviated name of the instrument. INSTRUMENT_ID The project abbreviation of the instrument. DATA_SET_ID Uniquely identifies the EDR file as part of a volume collection. MISSION_PHASE_NAME Identifies the project designation of the mission phase associated with the data product. TARGET_NAME The target of the observation. START_TIME The start time of the observation. STOP_TIME The time when the instrument stopped collecting measurements. SPACECRAFT_CLOCK_START_COUNT Clock count of the spacecraft computer at the start of the observation. SPACECRAFT_CLOCK_STOP_COUNT Clock count of the spacecraft computer at the end of the observation. ^TABLE Identifies the name of the EDR file which contains the data in BINARY table format. The structure of the data file is defined in a referenced format file. ^STRUCTURE This is a pointer to the external file which provides the structure definition for the table object. 6.4.2 Binary Table File Formats Each XRS PDS label will contain a pointer to the XCOLUMN.FMT file. This file describes the structure of the XRS binary table. This includes column name, byte size, data type, applicable units, and a description of the value assigned to the column. The full XCOLUMN.FMT file is shown in section 8.1 Appendix: XCOLUMN.FMT file. 6.4.3 ASCII Table File Formats Each XRS COMMAND ECHO PDS label will contain a pointer to the XRS_CMDECHO.FMT file. This file describes the structure of the XRS ASCII table. This includes column name, byte size, data type, applicable units, and a description of the value assigned to the column. The full XRS_CMDECHO.FMT file is shown in the Appendix. 6.4.4 Format File Keyword Definitions The following describes the keywords used in the format files: OBJECT Identifies the object as a column field within a binary table. NAME Indicates a literal value representing the common term used to identify an element or object. NOTE: in the PDS data dictionary, name is restricted to 30 characters and must conform to PDS nomenclature standards. COLUMN_NUMBER Identifies the location of the column within the larger table data object. For tables consisting of rows (I= 1, N) and columns (j = 1, M) the column_number is the j-th index of any row. BYTES Specifies the total number of bytes allocated for this particular column element. DATA_TYPE Specifies the internal representation and/or mathematical properties of the value being stored in this column. START_BYTE Identifies the location of the first byte of the particular column, counting from 1. DESCRIPTION Describes the value(s) stored in the column object. ITEMS This keyword is used for columns containing spectra values, such as column 175 in the XRS EDR binary table. Defines the number of multiple, identical occurrences of a single data item. For example, in column 175 there are 244 items which correspond to channels 10-253 in the detector. ITEM_BYTES This keyword is used for columns containing spectra values, such as column 175 in the XRS EDR binary table. Represents the size of each individual item within the column field. For example, in column 175 each item is a 2-byte integer. 6.5 Directory Structure and Contents for XRS EDR Data Archive Volume The following illustration shows the directory structure overview for the XRS EDR Data Archive Volume. This volume contains the XRS EDR data products, supporting documentation, and any additional files required for the volume to be compliant with PDS standards. The content of the volume is expected to be updated with periodic releases according to the schedule in the MESSENGER Data Management and Archiving Plan. Revised EDRs (if needed) will also be delivered according to the same schedule. Revised EDRs will have an incremented version number in the PDS label. Directory Structure Overview ___________________________________|____________________ | | | | | |