Data Set Information
DATA_SET_NAME GRAIL MOON LGRS RAW SCIENCE V1.0
DATA_SET_ID GRAIL-L-LGRS-2-EDR-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The Gravity Recovery and Interior Laboratory (GRAIL) Lunar Gravity Ranging System (LGRS) Experimental Data Record Archive is a time-ordered collection of raw and partially processed data collected during the GRAIL mission to the Moon. The DATA_SET_ID 'GRAIL-L-LGRS-2-EDR-V1.0' includes the following components: Instrument host (i.e., 'GRAIL') Target (i.e., 'L' for Lunar) Instrument (i.e., 'LGRS' for Lunar Gravity Ranging System) CODMAC Data processing level number (i.e., '2') Description (i.e., 'EDR' for Experiment Data Record) Version number (i.e., 'V1.0') This data set was collected between March and December 2012. Most of the data were extracted from spacecraft telemetry (packet data) [ROGSTAD2012]. They were corrected for telemetry errors and have been split or decommutated. Data are tagged with time and location of acquisition within the spacecraft frame. Each telemetry packet generated by the LGRS flight software was wrapped inside a packet called a BlackJack Protocol Frame, which ensured the integrity of the data; Blackjack was inherited from the predecessor Gravity Recovery and Climate Experiment (GRACE) terrestrial gravity mission. The documents GPA_TD_D_71987_REVE.TXT and BLACKJACKDLP.TXT in the DOCUMENT directory describe the format of the Blackjack binary data for processing to Level 1A. Typical users of GRAIL products will not need this data set. The data are provided for the advanced user who wishes to recreate the Level 1A LGRS CDR data products from scratch. Parameters : The Standard Formatted Data Unit (SFDU) products S7200, S7300, and STC00 are binary and contain (besides the appropriate headers) the unscaled, encoded instrument communication packets. For information on extracting the SFDU data contents, see the following in the DOCUMENT directory: 0161_TELECOMM_L5_8.TXT 0171_TELECOMM_NJPL_L5.TXT 090_REVC_1.TXT, and 0172_TELECOMM_CHDO_REVE_L5.TXT The remaining nine LGRS EDR product types are in ASCII format. Of those, eight originated from telemetry queries from the GRAIL Ground Data System (GDS). File type TDE00 (Time Transfer System Direct to Earth) originated from S-Band ranging data from the Time Transfer System in the LGRS that was collected on the ground. It was included in this Level 0 data set because it was an important input to the creation of the Level 1 products in the LGRS CDR data set. All types except LTB00 are spacecraft-specific. Each Level 0 product is accompanied by a minimal PDS label that points to relevant documentation. For additional information on parameters in this data set, see the DATA section below. Processing : Data in this set were extracted from telemetry (packet data). They have been corrected for telemetry errors and have been split or decommutated. They are tagged with time and location of acquisition. Level 0 files were provided by the GRAIL SDS; they are constructed so that each file contains the data for one day. Data : Time Correlation Data Record File (DRF) (DTC00) ----------------------------------------------- Clock correlation between Real Time Clock (RTC), Binary Time Code (BTC), and the 1-per-second pulse associated with LGRS time (ASCII). Spacecraft Engineering Housekeeping data (EHK00) ------------------------------------------------ Includes temperature sensor data for locations near the LGRS instrumentation (ASCII). LGRS Time Bias of the Lunar Gravity Ranging System (LTB00) ---------------------------------------------------------- Accumulated list of biases over the complete mission in BTC time (ASCII). One file combined for BOTH spacecraft. Satellite Mass Data (MAS00) --------------------------- Accumulated list of center of mass and spacecraft mass over the complete mission (ASCII). Engineering SFDU ID #72 (S7200) ------------------------------- Spacecraft unscaled, binary encoded instrument communication packets. Science SFDU ID #73 (S7300) --------------------------- Spacecraft unscaled, binary encoded instrument communication packets. Solar Array Eclipse data (SAE00) -------------------------------- Includes solar array short circuit currents and open circuit voltages, to identify eclipse events for spacecraft ephemeris models (ASCII). Star Tracker Data (SCA00) ------------------------- Includes attitudes from an on-board Kalman filter that processes Star Tracker attitude data and Inertial Measurement Unit (IMU) angular rotation data (ASCII). Time Correlation SFDU (STC00) ----------------------------- Spacecraft unscaled, binary encoded instrument communication packets. Time Transfer System Direct to Earth (TDE00) -------------------------------------------- Measured time correlation between LGRS time and UTC, using Time Transfer System (TTS) S-Band ranging collected at DSS-24. Thruster Activation Data (THR00) -------------------------------- Includes time tags, counts of cumulative work cycles for each thruster, recent thruster on time, and cumulative thruster on time (ASCII). Wheel Rotational Speed Data (WRS00) ------------------------------------------------------ WRS00 describes rotational wheel speed of each of four Reaction wheels as determined by a digital tachometer (ASCII) Coordinate System : Data from the LGRS are typically related to their location within the spacecraft frame. For more information about the spacecraft mechanical frame, see GRAILCOMPONENTS.PDF in the CALIB directory. Naming Conventions : For all LGRS data, the product identifier, in conjunction with either a date or a range of dates in a specified format, determines the filename containing the data product. The file naming convention for most Level 0/1A/1B LGRS products is: PRDID_YYYY_MM_DD_S_VV.EXT where PRDID product identification label, e.g. CLK1B YYYY year MM month DD day of month S GRAIL satellite identifier: A GRAIL-A B GRAIL-B X combined product of GRAIL-A and GRAIL-B VV data product version number (starting from 00) EXT file extension indicating binary (DAT) or ASCII (ASC) files The Product ID (PRDID) is of the form XXXLL, where: XXX is a three-character mnemonic, and LL specifies the data product Level (00, 1A, 1B). The only exception to this naming convention is TDE00. To accommodate multiple direct-to-earth measurements within the same day, the convention is: PRDID_YYYY_MM_DD_S_NNNNN_VV.EXT where PRDID product identification label, e.g. CLK1B YYYY year MM month DD day of month S GRAIL satellite identifier: A GRAIL-A B GRAIL-B X combined product of GRAIL-A and GRAIL-B NNNNN seconds past midnight start time (1 to 5 digits) VV data product version number (starting from 00) EXT file extension indicating binary (DAT) or ASCII (ASC) files The Product ID (PRDID) is of the form XXXLL, where: XXX is a three-character mnemonic, and LL specifies the data product Level (00). Files in the CALIB Directory : One file, GRAILCOMPONENTS.TXT is included in the CALIB directory. It describes the Spacecraft bus component model with dimensions and orientations, as well as the spacecraft components specular/diffuse reflectivity properties. It is likely to have wide applicability in working with the raw data. Software : Software for parsing, reducing, and analyzing data such as these has been developed at JPL and elsewhere. Because such software must usually operate at the bit-level and is written for a narrow range of platforms, it is not suitable for general distribution. No distributable software is included with this archival data set. The SOFTWARE directory contains examples of utilities or application programs to aid the user in viewing or extracting data from the Level 0 data product files. The codes are provided as illustrations of how to extract the Blackjack packets from Blackjack binary data.
DATA_SET_RELEASE_DATE 2014-04-01T00:00:00.000Z
START_TIME 2012-03-01T12:00:00.000Z
STOP_TIME 2012-12-18T12:00:00.000Z
MISSION_NAME GRAVITY RECOVERY AND INTERIOR LABORATORY
MISSION_START_DATE 2011-09-10T12:00:00.000Z
MISSION_STOP_DATE 2012-12-18T12:00:00.000Z
TARGET_NAME MOON
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID GRAIL-A
INSTRUMENT_NAME LUNAR GRAVITY RANGING SYSTEM A
INSTRUMENT_ID LGRS-A
INSTRUMENT_TYPE RADIO SCIENCE
NODE_NAME Geosciences
ARCHIVE_STATUS LOCALLY_ARCHIVED
CONFIDENCE_LEVEL_NOTE Overview : Data in this archival data set have been collected to support derivation of the gravity field of the Moon. These are similar to data collected using the GRACE spacecraft and are believed to be generally of good quality. Review : This archive underwent PDS external review from August 31, 2012 to November 30, 2012. Data Coverage and Quality : Files in this data set were constructed to cover one day each. Data coverage includes the science phase (March 1, 2012, to May 29, 2012), the extended mission phase (August 29, 2012, to December 12, 2012), and the decommissioning phase (December 12, 2012, to December 18, 2012) as described in the mission catalog. Limitations : Certain spacecraft events have an impact on the science processing. These events include propulsive maneuvers, Ka boresight calibration attitude maneuvers, telecommunication configuration changes, and Lunar Gravity Ranging System (LGRS) events. Both spacecraft performed propulsive maneuvers. The mass change history for both spacecraft can be found in the MAS1A/B Level-1 products, and the thruster on-times are available in the THR1A/B level-1 products. LGRS measurements are taken during the propulsive maneuvers, but it is recommended to break science data arcs at the propulsive maneuver event times, since the velocity changes imparted on the spacecraft are not known with sufficient accuracy for science processing. LGRS measurements are taken during the angular momentum desaturation maneuvers, but it is recommended to break science data arcs at the desaturation maneuver event times, since the velocity changes imparted on the spacecraft are not known with sufficient accuracy for science processing. For detailed thruster on time histories see level-1 product THR1A/B. The LGRS Gravity Processor Assemby (GPA) rebooted several times resulting in the loss of Ka range and the Time Transfer System (TTS) observables for about 1.5 minutes. After a GPA reboot the LGRS clock is synched with the LGRS clock on the non-rebooting spacecraft using the TTS system. GPA reboots will cause a gap in the inter-satellite range data products (KBR1B, SBR1B) of about 2 minutes. On GRAIL-B the TTS phase measurement is reset to zero due to a software bug in the LGRS software. The TTS ranging measurement is not affected, but the relative LGRS clock reconstruction analysis needs to be restarted at a phase reset. Due to orbital viewing geometry, the GRAIL spacecraft are changing between the +X and -X S-band and X-band (Radio Science Beacon) antennas approximately every 14 days. The complete history for the antenna change are listed in the VGS1B product (S-band) and VGX1B (X-band). During the primary and extended missions, the GRAIL spacecraft were in nominal science attitude called orbiter point attitude mode. For this mode the solar arrays of the spacecraft are parallel to the orbital plane and the Ka boresight vectors (2.1 degrees off the -Z axis in the YZ spacecraft frame) are pointed in the direction of line of sight toward the other spacecraft. The GRAIL spacecraft remained in orbit point attitude mode except during Ka boresight vector calibration maneuvers when the spacecraft performed two orthogonal slews of 3 degrees about the line of sight vector between the two spacecraft. LGRS measurements are taken during the maneuvers but should not be used in the science processing because the measured range change is the sum of orbit geometry, lunar gravity and range change induced by spacecraft attitude variation. Ka boresight vector data contain range corrections for the phase center to center of mass offset during the maneuvers but these corrections are not reliable and should not be used. For specific dates of the above events, see the operational considerations section in LGRS_A_INST.CAT and LGRS_B_INST.CAT.
CITATION_DESCRIPTION KAHAN, D.S., GRAIL LGRS Raw Science Data Set V1.0, GRAIL-L-LGRS-2-EDR-V1.0, NASA Planetary Data System, 2012.
ABSTRACT_TEXT This data set contains archival raw science data, acquired from the Lunar Gravity Ranging System (LGRS) on each of the two spacecraft comprising the Gravity Recovery and Interior Laboratory (GRAIL) mission. The data are at NASA Level 0 and were archived for historical purposes only. All Level 0 products were processed to NASA Level 1A in the LGRS CDR data set by the GRAIL Science Data System (SDS). The observations were used in generating high-resolution gravity field models of the Moon. The data set includes all of the LGRS raw data collected by GRAIL (March-December 2012).
PRODUCER_FULL_NAME DANIEL S. KAHAN
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