Data Set Information
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| DATA_SET_NAME |
GRAIL MOON LGRS CALIBRATED AND RESAMPLED SCIENCE V1.0
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| DATA_SET_ID |
GRAIL-L-LGRS-3-CDR-V1.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
Data Set Overview : The Gravity Recovery and Interior Laboratory (GRAIL) Lunar Gravity Ranging System (LGRS) Calibrated Data Record Archive is a time-ordered collection of processed data collected during the GRAIL mission to the Moon. The DATA_SET_ID 'GRAIL-L-LGRS-3-CDR-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., '3') Description (i.e., 'CDR' for Calibrated Data Record) Version number (i.e., 'V1.0') This data set was derived from data collected during March-December 2012. Data in this set have been created from the Level 0 files in the LGRS EDR data set. They are distinguished by two processing levels, 1A and 1B. Level 1A comprises edited data that are still in units produced by the instrument but that have been corrected so that values are expressed in or are proportional to some physical unit such as meters per second. Level 1B data have been resampled in the time or space domains in such a way that the original edited data cannot be reconstructed. Some of these data may also have been calibrated in addition to being resampled. Typical users of GRAIL products interested in original measurements will use this data set. The data of primary interest will be the KBR1C and SBR1B files. Parameters : All forty-three LGRS CDR file types are in ASCII format. Most of the file types are spacecraft-specific. Types DEL1A, PLT1A, TC61A, KBR1C, and SBR1B apply to both spacecraft together, as they convey a relationship between the two. Some of the parameters conveyed by the data include conversions between different time frames, locations of data sources within the spacecraft frame, information about spacecraft health, and ranging measurements made by the LGRS. See Data section below for more specific information about data parameters. Each Level 1A or 1B product is accompanied by a minimal PDS label that points to the relevant table in the data product SIS (DPSIS.PDF, DOCUMENT directory). Processing : The GRAIL Science Data System (SDS) is defined as the infrastructure at NASA's Jet Propulsion Laboratory (JPL) for the collection of all science and ancillary data relevant to the GRAIL mission. It includes hardware, software tools, procedures, and trained personnel. The SDS receives data and carries out calibration, editing, and processing to produce NASA Level 1A and 1B GRAIL science data The SDS creates edited data that are still in units produced by the instrument, but that have been corrected so that values are expressed in or are proportional to some physical unit such as radiance. No resampling is done, so original values can be recovered. Level 1B data have been resampled in the time or space domains in such a way that the original edited data cannot be reconstructed. They could be calibrated in addition to being resampled. Level 1A and 1B files have been processed from the Level 0 files in the LGRS EDR data set by the GRAIL SDS at JPL; they are constructed so that each file contains the data for one day. The Algorithm Theoretical Basis Document (ATDB.PDF) in the DOCUMENT directory describes the data processing flow from EDR to CDR as implemented by the GRAIL Team. GRAIL timing requires coordination of three clocks on each satellite, and two time standards: 1. LGRS: Lunar Gravity Ranging System clock. Very stable clock for on-board Ka-band ranging (KBR), X-band (RSB), and S-band Time Transfer System (TTS) instruments. Driven by an Ultra-Stable Oscillator (USO). Set to 0 when booted. Produces a pulse per second (pps) signal. LGRS time starts at 0 seconds when powered on. The SDS adds a bias to LGRS time to create an approximate UTC time tag. This time will be referred to as LGRS + bias. 2. BTC: Base Clock Time. On-board satellite clock, comparable in stability to a wristwatch. Roughly synced to UTC at launch time. 3. RTC: Real Clock Time. Flight software clock. Set to 0 when booted. Relatively unstable clock. 4. UTC: Coordinated Universal Time. 5. TDB: Barycentric Dynamical Time. Data : All forty-three LGRS CDR file types are in ASCII format. Types DEL1A, PLT1A, TC61A, KBR1C, and SBR1B apply to both spacecraft together, as they convey a relationship between the two; all of the other file types have separate files for each spacecraft. LGRS to TDB time correlation (CLK1A) ------------------------------------------------------ Time correlation between LGRS time + bias and TDB time. Clock: LGRS time + Bias Inter-satellite LGRS clock offset between spacecraft (DEL1A) ------------------------------------------------------ Inter-satellite LGRS clock offset between spacecraft by TDB time. One file combined for BOTH spacecraft. Clock: LGRS time + Bias Spacecraft temperature sensor data from Engineering Housekeeping data (EHK1A) ------------------------------------------------------ EHK1A contains temperature sensor data for locations near LGRS instruments. Clock: UTC LGRS Housekeeping Data (IHK1A) ------------------------------------------------------ Housekeeping data for the LGRS in IHK1A includes voltage, temperature, and current measurements. Clock: LGRS time + Bias LGRS Health Status data (IHS1A) ------------------------------------------------------ IHS1A includes other LGRS status data. Clock: LGRS time + Bias LGRS log messages (ILG1A) ------------------------------------------------------ ILG1A contains log messages from the LGRS. Clock: LGRS time + Bias Ka-Band Ranging Data (KBR1A) ------------------------------------------------------ KBR1A records raw carrier-phase measurements, flagged for phase breaks. Gaps of up to 2 seconds are filled in by quadratic interpolation; longer gaps are classified as missing data. Clock: LGRS time + Bias Position vector and light time between one spacecraft and DSN station (LTM1A) ------------------------------------------------------ From the best ephemeris solution, spacecraft to DSN relative position and light time are computed in the EME 2000 Lunar-Centered Solar System Barycentric Frame Clock: TDB Satellite Mass Data (MAS1A) ------------------------------------------------------ MAS1A lists spacecraft mass as a function of UTC time Clock: UTC Phase Center to Center of Mass Correction ------------------------------------------------------ PCI1A lists Ka-band antenna range corrections, range rate corrections, and range acceleration corrections. Clock: TDB Position vector and light time between two spacecraft (PLT1A) ------------------------------------------------------ From the best ephemeris solution, spacecraft to DSN relative position and light time are computed in the EME 2000 Lunar-Centered Solar System Barycentric Frame, and spacecraft to spacecraft relative position and light time are computed in the DE 421 Lunar Body-Fixed Frame. One file combined for BOTH spacecraft. Clock: TDB LGRS Pulse Per Second (PPS) Time Record (PPS1A) ------------------------------------------------------ A PPS1A product lists the LGRS time of PPS signals. Clock: LGRS time + Bias Relativistic time correction (REL1A) ------------------------------------------------------ An approximation of the relativistic time correction from TDB to on-board satellite proper time is calculated in the REL1A product, treating the Moon as a point mass. Clock: TDB Solar Array Eclipse Data (SAE1A) ------------------------------------------------------ SAE1A lists solar array short circuit currents and voltages, to identify eclipse events for spacecraft ephemeris models. Clock: UTC S-Band Ranging Data (SBR1A) ------------------------------------------------------ SBR1A tracks S-Band carrier phase and a modulating range code. Clock: LGRS time + Bias Star Tracker Data (SCA1A) ------------------------------------------------------ Because GRAIL-A and GRAIL-B antennas are offset from the spacecraft center of mass, distance between GRAIL-A and GRAIL-B Ka-band antennas depends on spacecraft attitude. An on-board Kalman filter processes Star Tracker attitude data and Inertial Measurement Unit (IMU) angular rotation data. Filtered attitudes are saved in SCA1A. Clock: BTC S-Band navigation product (SNV1A) ------------------------------------------------------ The SNV1A S-band navigation product contains ancillary information for the Time Transfer System (TTS), which primarily serves to tell the ground whether GRAIL-A and GRAIL-B are communicating correctly with each other. Clock: LGRS time + Bias LGRS to BTC time correlation (TC11A) ------------------------------------------------------ LGRS to BTC time correlation, approximated by flight software. Clock: LGRS time + Bias LGRS to BTC time correlation from BTC clock cycle counts (TC21A) ------------------------------------------------------ LGRS to BTC time correlation from BTC clock cycle counts. More accurate mapping than TC11A. Clock: LGRS time + Bias BTC to RTC time correlation (TC31A) ------------------------------------------------------ BTC to RTC time correlation. Clock: BTC LGRS to RTC time correlation (TC41A) ------------------------------------------------------ LGRS to RTC time correlation. Clock: LGRS time + Bias RTC to UTC time correlation (TC51A) ------------------------------------------------------ RTC to UTC time correlation. Clock: RTC UTC to TDB time correlation (TC61A) ------------------------------------------------------ UTC to TDB time correlation. One product applies to both spacecraft. Clock: UTC Thruster Activation Data (THR1A) ------------------------------------------------------ THR1A contains thruster activation data, including time tags, cumulative work cycles by thruster, current thruster on time, and cumulative thruster on time. Clock: UTC SCET Oscillator frequency data (USO1A) ------------------------------------------------------ Radio Science Receivers (RSR, in RSS_EDR data set), located at DSN sites, record X-band Radio Science Beacon (RSB) signals. Since the LGRS clock drives the RSB, LGRS frequency at TDB can be estimated for USO1A. Clock: TDB Center of mass displacement from spacecraft mechanical frame origin (VCM1A) ------------------------------------------------------ VCM1A describes center of mass displacement from the spacecraft mechanical frame origin. Clock: UTC SCET Wheel Rotational Speed Data (WRS1A) ------------------------------------------------------ WRS1A describes rotational wheel speed of each of four Reaction wheels as determined by a digital tachometer. Clock: UTC LGRS to TDB time correleation (CLK1B) ------------------------------------------------------ Best estimate of LGRS to TDB time correlation. Clock: LGRS time + Bias Spacecraft temperature sensor data from Engineering Housekeeping data (EHK1B) ------------------------------------------------------ EHK1B contains temperature sensor data for locations near LGRS instruments. Same as EHK1A, except in TDB time. Clock: TDB GRAIL satellite orbit solution in Moon centered Inertial frame (GNI1B) ------------------------------------------------------ Best estimate of spacecraft ephemeris in EME 2000 Lunar-Centered Solar System Barycentric Frame. Clock: TDB Satellite orbit Solution in lunar body fixed frame (GNV1B) ------------------------------------------------------ Best estimate of spacecraft ephemeris in DE 421 Lunar Body-Fixed Frame. Clock: TDB Dual-One-Way Ka-Band Ranging Data (KBR1C) ------------------------------------------------------ KBR1C contains biased dual one-way range between GRAIL-A and GRAIL-B, digitally filtered, but not corrected for time of flight or antenna offset. After the dual one-way range combination has been formed, gaps of up to 20 seconds are filled in by quadratic interpolation. KBR1C also contains corrections for time of flight and antenna offset from center of mass. In addition, KBR1C also contains the first and second derivatives of the biased dual one-way range between GRAIL-A and -B and associated time of flight and antenna offset corrections. In general, the instantaneous range, range rate, and range acceleration is used for scientific analysis. The instantaneous range, range rate, and range acceleration are computed by adding the time of flight correction and antenna offset correction to the dual one-way range, range rate, or range acceleration measurement. This (level 1B) product is designated as '1C' to distinguish it from earlier versions of KBR1B which did not contain an additional four columns of information on the temperature range corrections. The raw temperature range correction, filtered temperature range correction, filtered temperature range rate correction, and filtered temperature range acceleration correction are the final four columns of the KBR1C product. One file combined for BOTH spacecraft. Clock: TDB Spacecraft Mass Data (MAS1B) ------------------------------------------------------ MAS1B lists spacecraft mass as a function of time. Same as MAS1A except in TDB time rather than UTC SCET. Clock: TDB Solar Array Eclipse Data (SAE1B) ------------------------------------------------------ SAE1B lists solar array short circuit currents and voltages, to identify eclipse events for spacecraft ephemeris models. Same as SAE1A except time-tagged by TDB rather than UTC SCET. Clock: TDB Dual one-way S-Band Ranging data (SBR1B) ------------------------------------------------------ S-Band Carrier phase and a modulating range code are tracked in SBR1B. In SBR1B, a more accurate range is produced by carrier smoothing over each arc. One file combined for BOTH spacecraft. Clock: TDB Star Tracker Data (SCA1B) ------------------------------------------------------ Because GRAIL-A and GRAIL-B antennas are offset from the spacecraft center of mass, distance between GRAIL-A and GRAIL-B Ka-band antennas depends on spacecraft attitude. An on-board Kalman filter processes Star Tracker attitude data and Inertial Measurement Unit (IMU) angular rotation data. Filtered attitudes are saved in SCA1B. Same as SCA1A except time tagged by TDB rather than BTC time. Clock: TDB Thruster Activation Data (THR1B) ------------------------------------------------------ THR1A contains thruster activation data, including time tags, cumulative work cycles by thruster, current thruster on time, and cumulative thruster on time. Same as THR1A except time-tagged by TDB rather than UTC SCET. Clock: TDB USO Frequency Estimate (USO1B) ------------------------------------------------------ Best estimate of LGRS frequency at TDB. Clock: TDB Center of mass displacement from spacecraft mechanical frame origin (VCM1B) ------------------------------------------------------ VCM1B describes center of mass displacement from the spacecraft mechanical frame origin (See section 4.3.2 of [Kahan2012]). Same as VCM1A except lists results relative to TDB rather than UTC SCET. Clock: TDB S-Band antenna switch time (VGS1B) ------------------------------------------------------ GRAIL transmits information to the Deep Space Network using S-band. S-band communication from each GRAIL spacecraft to the DSN depends on a pair of low-gain antennas (LGAs), located on opposite sides of the spacecraft. At a given TDB, only one antenna can communicate with the DSN. The VGS1B product contains a list of the TDB times at which the antennas are switched, with the Mechanical Frame (MF) vector of the new transmitting antenna phase center. Clock: TDB X-Band antenna switch time (VGX1B) ------------------------------------------------------ Each GRAIL spacecraft transmits an unmodulated X-band carrier to the DSN through one of a pair of Radio Science Beacons (RSB). The VGX1B product contains a list of the TDB times at which beacons are switched, with the Mechanical Frame vector of the new transmitting beacon phase center. Clock: TDB Ka-Band Boresight Vector (VKB1B) ------------------------------------------------------ The VKB1B file is the Ka boresight vector, as a result of Ka-Band boresight calibration analysis. Clock: TDB Wheel Rotational Speed Data (WRS1B) ------------------------------------------------------ WRS1B describes rotational wheel speed of each of four Reaction wheels as determined by a digital tachometer. Clock: TDB 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 all Level 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). Files in the CALIB Directory : Files in the CALIB directory are those likely to have wide applicability in working with the raw data. 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. 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 software is included with this archival data set.
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| DATA_SET_RELEASE_DATE |
2014-04-01T00:00:00.000Z
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| START_TIME |
2012-03-01T12:00:00.000Z
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| STOP_TIME |
2012-12-18T12:00:00.000Z
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| MISSION_NAME |
GRAVITY RECOVERY AND INTERIOR LABORATORY
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| MISSION_START_DATE |
2011-09-10T12:00:00.000Z
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| MISSION_STOP_DATE |
2012-12-18T12:00:00.000Z
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| TARGET_NAME |
MOON
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| TARGET_TYPE |
SATELLITE
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| INSTRUMENT_HOST_ID |
GRAIL-A
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| INSTRUMENT_NAME |
LUNAR GRAVITY RANGING SYSTEM A
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| INSTRUMENT_ID |
LGRS-A
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| INSTRUMENT_TYPE |
RADIO SCIENCE
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| NODE_NAME |
Geosciences
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| ARCHIVE_STATUS |
LOCALLY_ARCHIVED
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| 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 with the GRACE spacecraft and are believed to be generally of good quality. Review : Data validation occurs in three steps: validation of the data themselves, validation of the correctness and completeness of the data set documentation, and validation of the compliance of the archive with PDS standards. The primary method by which Science Team members validated the various archive products was by using them for science. Calibrated data files (CDRs) were derived from the raw data files (EDRs) in the archive; then reduced data records (RDRs) were created from the archival CDRs. Errors in the raw and calibrated data products were caught by the Science Team in this process. In addition, 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. The GRAIL science orbits for the primary mission are based on Deep Space Network one-way Doppler and two-way Doppler tracking data. In addition, the inter-satellite range rate measurements were included in the orbit determination process. The gravity field used for the GRAIL science orbits is a GRAIL internal gravity field of degree and order 420 (420b8a), which had all primary mission inter-satellite range data included. The resulting orbit accuracy of the orbit in absolute sense is at the meter level and in relative range rate error between the spacecraft is better than 20 micrometers/sec. 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.
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| CITATION_DESCRIPTION |
KAHAN, D.S., GRAIL LGRS Calibrated and Resampled Science Data Set V1.0, GRAIL-L-LGRS-3-CDR-V1.0, NASA Planetary Data System, 2012.
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| ABSTRACT_TEXT |
This data set contains calibrated and resampled engineering (e.g., star tracker data and timing) and science data acquired from the Lunar Gravity and Ranging System (LGRS) on the two spacecraft comprising the Gravity Recovery and Interior Laboratory (GRAIL) mission. The data in the set are at NASA Level 1 and have been archived for general use. Products in this set have been derived from NASA Level 0 (the LGRS EDR data set) by the GRAIL Science Data System (SDS). The observations were used to generate high-resolution gravity field models of the Moon. The data set includes all of the Level 1 LGRS data from the GRAIL mission (March-December 2012).
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| PRODUCER_FULL_NAME |
DANIEL S. KAHAN
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| SEARCH/ACCESS DATA |
Geosciences Web Services
Geosciences Online Archives
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