Data Set Information
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| DATA_SET_NAME |
DAWN GRAND RAW (EDR) CERES COUNTS V1.0
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| DATA_SET_ID |
DAWN-A-GRAND-2-EDR-CERES-COUNTS-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 |
Acronyms and Abbreviations : BGO Bismuth Germanate EDR Experimental data records (Level 1A) EPG Spacecraft Ephemerides, Pointing, and measurement Geometry GCR Galactic Cosmic Ray HED Howardite, Eucrite, and Diogenite meteorites PDS Planetary Data System RDR Reduced data records (Level 1B) SBN Small Bodies Node of the Planetary Data System SCLK Spacecraft Clock Overview : The Dawn Mission's Gamma Ray and Neutron Detector (GRaND) is a nuclear spectrometer that will collect data needed to map the elemental composition of the surfaces of 4-Vesta and 1-Ceres [PRETTYMANETAL2003B, PRETTYMANETAL2011, PRETTYMANETAL2012]. GRaND measures the spectrum of planetary gamma rays and neutrons, which originate from cosmic ray interactions and radioactive decay within the surface, while the spacecraft (S/C) is in orbit around each body. The instrument, which is mounted on the +Z deck of the S/C, consists of 21 sensors designed to separately measure radiation originating from the surface of each asteroid and background sources, including the space energetic particle environment and cosmic ray interactions with the spacecraft. The nuclear spectroscopy data provided by GRaND will be analyzed to determine the abundance of major rock forming elements, such as O, Fe, Ti, Si, Al, Mg, Ca, Cl and radioactive elements, including K and Th, as well as light-elements such as H, C, and N, which are constituents of ices and the products of aqueous alteration of silicate minerals and ices. The GRaND Experimental Data Records (EDR) are a time-ordered collection of gamma ray and neutron counting data and histograms acquired by GRaND during different phases of the Dawn Mission, including assembly-test- and-launch- operations (ATLO), cruise, Mars Gravity Assist (MGA), and science mapping at 4-Vesta and 1-Ceres. The dataset also includes state-of-health data (instrument settings, temperature and voltage readings) needed for scientific analysis of the neutron and gamma ray data. The EDR is an intermediate data product (Level 1A) that is derived from Raw Data Records (Level 0) using reversible operations. The Level 1A are the lowest level of GRaND data archived in the PDS, from which all higher order data sets are derived. To support timely delivery of higher order products, the Level 1A data are processed using an automated pipleline, which operates on Level 0 data when it is queried by the DSC. The data set consists primarily of ASCII tables, divided into three functional categories: auxilliary information (AUX); gamma ray spectra and event data (GAMMA); and neutron spectra and event data (NEUTRON). Gamma ray and neutron event data are recorded in binary files. Some of the data in the ASCII files, which are human-readable, are repeated in the binary files to aid in the verification of user-written routines. The telemetry for GRaND consists of science and state-of-health data, accumulated over consecutive time intervals to produce a time-series data set. Each science data record includes scalers, histograms, and event data accumulated over an interval specified by the commandable parameter TELREADOUT, with units of seconds. The state of health data include average temperatures, voltages, and instrument state data acquired during time intervals specified by the commandable parameter TELSOH (also in seconds). Both intervals are adjusted, depending on the measurement conditions and objectives for each mission phase. During mapping, TELREADOUT will be set to sub-sample spatial pixels defined on the surface of Vesta or Ceres. During cruise, TELREADOUT was generally set to large values (e.g., 210s) to minimize data volume. TELSOH is generally set to subsample the science accumulation interval, providing information needed to determine, for example, whether and how many times the science scalers have rolled over. GRaND has 23 scalers, which are described in the Paramters section. Scalers are simply pulse counters. They accumulate counts over time. The value of the scaler registers are read out at the end of each science accumuluation interval and then reset to zero to begin the next interval. The same registers are read out at each state-of-health time step. Because the state-of-health data are acquired at a higher cadence than the science data, the accumulation of counts can be monitored during each TELREADOUT interval. The 16-bit scalers roll over (return to zero) when they exceed 65535 counts. Rollover can be detected and counted as a sawtooth pattern in the state-of-health telemetry if TELSOH is set to be smaller than TELREADOUT. For example, if a single reset is observed for a scaler in the state-of-health telemetry, then the counts observed in the science telemetry need to be increased by 65536. Properly accounting for rollover is particularly important for determining dead time from the scaler counting data. The data are downloaded regularly from the spacecraft by the Ground Data System. The UCLA Dawn Science Center (DSC) captures all of the payload instrument telemetry frames as binary files after the data have been cleaned up in post-pass processing to produce reconstructed Level-0 data. The files are inventoried within the Dawn Science Database (DSDb) and are retrieved by the GRaND team, which unscrambles, decompresses, decodes, and formats the raw telemetry data into scientifically useful data files. The decompressed and decoded data, along with their required PDS documentation, form the Level-1A EDR data sets. The Level- 1a EDR data are determined by performing reversible operations on the Level-1a data set, to produce counting data and spectral products useful for mapping. Parameters : The EDR data are derived from Level 0 raw data queried by the DSC over irregular time periods, roughly aligned with the mission phase boundaries. The DSC divides the Level 0 data into separate files containing state of health and science data packets. The Level 1a pipeline operates on these files to produce the Level 1a archive. The directory structure for the Level 1a data is given by GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC (top level directory) LEVEL1A_AUX (directory containing auxiliary data) LEVEL1A_GAMMA (directory containing gamma ray counting data) LEVEL1A_NEUTRON (directory containing neutron counting data) The top level directory name contains the SCET UTC dates for the first and last science data records (Y1M1D1 and Y2M2D2, respectively), and the creation date (YCMCDC) for the archive. For example, for GRD-L1A- 090217-090218_090517, the first science data record was acquired on 17- Feb-2009. The last science data record was acquired on 18-Feb- 2009. The archive was created by the pipeline on 17-May-2009. The LEVEL1A_AUX directory contains the following files derived from the Level 0 state-of-health and science data: GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-STA.TAB - Instrument state file. The instrument state file contains the instrument settings, including the mode, power supply states, high voltage settings, the data accumulation interval, and coincidence windows. The first record of the state-of-health file is recorded in the state file, stamped with SCET UTC. Thereafter, rows are added only when the instrument settings change. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-RDG.TAB - Instrument readings file. This file contains a time-ordered list of temperature and voltage readings averaged over each state-of-health accumulation interval (TELSOH), converted to physical units. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-SOH-SCL.TAB - State of health scaler data. This file contains a time-ordered list of the scaler data recorded in the state-of-health telemetry. The accumulation time for the scaler data is TELSOH. Note that the scalers are set to zero the start of each science accumulation interval (TELREADOUT). If the state-of-health accumulation interval is selected to subsample the science interval, then the state-of-health scalers can be used to detect and correct for rollover of the science scalers, such as the dead time counter. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-SCI-SCL.TAB - Science scaler data. This file contains a time-ordered list of the scaler data recorded in the science telemetry. The accumulation interval for the scalers is TELREADOUT. For each science and state of health record, values for 23 scalers are recorded in the -SCI-SCL.TAB and -SOH-SCL.TAB files, respectively. The scalers provide the following information: Index Description ------------ ----------- 0 Dead time counts 1 BGO overload events 2 CZT overload events 3 +Z phoswich overload events 4 -Y BLP overload events 5 +Y BLP overload events 6 -Z phoswich overload events 7 +Z phoswich CAT4 events 8 -Y BLP CAT4 events 9 +Y BLP CAT4 events 10 -Z phoswich CAT4 events 11 Early second interaction events 12 Multiple-crystal CZT events 13 Valid CZT events (CAT10) 14 Coincidence BGO and CZT events (CAT7) 15 Coincidence of three or more sensor elements 16 Total events processed by GRaND 17 Number of single CZT events (CAT10) in the gamma ray event buffer 18 Number of BGO-CZT coincidence events (CAT7) in the gamma ray event buffer 19 Number of events (CAT4) in the neutron event buffer 20 Total number of events allowed in the gamma ray event buffer 21 Number of single CZT events (CAT10) allowed in the gamma ray event buffer 22 Number of events allowed in the neutron event buffer Note that indices 0 through 19 are for 16-bit counters, which are reset at the end of every science accumulation interval specified by TELREADOUT. If the state-of-health accumulation interval is adjusted to subsample the science accumulation interval (for example, TELREADOUT : n * TELSOH, where n is a whole number), then the scalers will monotonically increase during each acquisition interval, unless overflow occurs. A rollover counter is not provided; however, for situations in which the counting rate is high or the accumulation intervals are large, the number of rollovers for individual scalers can be determined from the SOH scaler data if TELSOH is set to subsample the science accumulation interval. In situations where the counting rate is changing, abrupt changes in the scaler values can also indicate that rollover has occurred. Rollover is treated in production of the Level1b RDR data. Indices 20 through 21 are maximum values for the number of events that can be recorded in the event buffers. The number of gamma ray and neutron events is commandable and can be adjusted. The total number of gamma ray and neutron events must be less than 6677. The LEVEL1A_GAMMA directory contains the following science data files: GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO.TAB This file contains a time- ordered list of pulse height spectra (1024 channels with units of uncorrected counts/channel) acquired by the BGO sensor. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-EMG.DAT This file contains gamma ray event data as a time series in a binary file. Each row of this file contains data from a science data record. Each science data record contains a list of 3876 events. Each event [e.g. i:0,...3875] is specified by ID_CZT[i], the index of the CZT sensor struck, CH_CZT[i], the pulse height (0-1023) recorded for ID_CZT[i], and CH_BGO[i], the pulse height (0-511) recorded for the BGO scintillator (see GRD_L1A-GAMMA_EVENTS.FMT). If CH_BGO[i]:0, then the event was CAT7 (coincidence between the BGO and a single CZT sensor). Otherwise, the event was CAT10 (interaction with a single CZT sensor). See the instrument catalog and PRETTYMANETAL2011 for a detailed description of the event data and examples. In addition, each row of the -EMG.DAT file includes the SCLK, and 23 scalers (SCALER_SCI). These can be compared to values found in the ASCII format -SCI-SCL.TAB (e.g. for debugging programs that read the binary data). The binary file can also be examined using NASAview and IDL routines accompanying this archive in EXTRAS. The LEVEL1A_NEUTRON directory contains the following science data files: GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-PHOS_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-PHOS_PZ.TAB These files contain time ordered lists of the 256-channel CAT1 pulse height spectra for the +Z and -Z phoswiches. Note that the naming convention for the top, bottom, and side scintillators is determined by the instrument coordinate system. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_PZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_MY.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BGO2_PY.TAB These files contain time ordered lists of the 64-channel CAT2 BGO pulse height spectra for coincidences with the BGO and the four BLP sensors. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_MZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_PZ.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BLP2_MY.TAB GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-BKP2_PY.TAB These files contain time ordered lists of the 64-channel CAT2 BLP pulse height spectra for coincidences with the BGO and the four BLP sensors. GRD-L1A-Y1M1D1-Y2M2D2_YCMCDC-EMN.DAT This file contains the fast neutron double pulse event data (CAT4) as a binary time series. Each row of this file contains data from a science data record. Each science data record contains a list of 2880 events. Each event [e.g. i:0,...,2879] is specified by ID_FIRST[i], the index of the BLP scintillator that produced the first pulse (0:+Z phoswich; 1:-Y BLP; 2:+Y BLP; 3:-Z phoswich), CH_FIRST[i], the amplitude of the first pulse (0-63), ID_SECOND[i], the index of the BLP scintillator that produced second pulse (0-3), CH_SECOND[i], the amplitude of the second pulse (0-63), and the time to second pulse (0-255), with units of 100 ns per data number. See the instrument catalog and PRETTYMANETAL2011 for a detailed description of the event data and examples. In addition, each row of the -EMN.DAT file includes the SCLK, and 23 scalers (SCALER_SCI). These can be compared to values found in the ASCII format -SCI- SCL.TAB (e.g. for debugging programs that read the binary data). The binary file can also be examined using NASAview and IDL routines accompanying this archive in EXTRAS. Processing : The Level 1A data are automatically processed using a pipeline, which operates on files queried by the DSC over selected time intervals. Each DSC query separates the GRaND data into files containing state- of-health and science data records, in the order in which they were received on the ground and with corrupted packets removed. The state- of-health data are further divided into real time telemetry data and playback data. The science data are stored in a single raw data file. The pipeline merges the state-of-health data from the playback and realtime files to produce a time-ordered-list of records. Selected data are extracted to produce the Level 1A AUX files. Internal temperature readings are converted from data numbers (DN) to engineering units using a linear function determined during ground calibration: T (degrees C) : 0.4354 DN - 0.4354. The high voltage readings for the high voltage power supplies are reported in engineering units using the conversion V (Volts) : 1500 DN/255. The CZT differential bias voltage is converted using V (Volts) : 0.405 DN. The science data are decompressed, decoded, separated by functionality and written as time-ordered ASCII tables and binary time series. The raw histograms (CAT1, CAT2, and CAT9) are represented as 8 bit numbers which are decompressed and reported as 16 bit, unsigned integers. The gamma ray event buffer can store up to 3876 events for each science accumulation interval. Each event is packed into 3 bytes, which contain the ID of the CZT sensor, the CZT pulse amplitude, and the BGO pulse amplitude. The vales for each event are extracted and stored as a binary time series. When the gamma ray event buffer is not full, null events are reported as zeros, such that each row of the Level 1A time series contains 3876 events. The neutron event buffer can store up to 2800 events for each science data accumulation interval. Each event is packed into 3 bytes, which contain the BLP sensor ID and pulse amplitude for the first interaction, the BLP sensor ID and pulse amplitude for the second interaction, and the time between pulses. The time between pulses has units of 100 nanoseconds/DN. The vales for each event are extracted and stored as a binary time series. The pulse amplitudes are uncalibrated for Level 1A. When the gamma ray event buffer is not full, null events are reported as zeros, such that each row of the Level 1A time series contains 2800 events. Ancillary Data : The Level 1A data include ancillary data in the form of SCET UTC strings reported in each row of the Level 1A data tables and time series. The UTC strings are determined from the spacecraft clock ticks recorded in each state-of-health packet and for the first packet in each science data record using NAIF SPICE (leap seconds kernel). This information is used in Level 1B processing to accurately determine the mid-point of each science accumulation interval, which is needed for mapping. Coordinate System : The instrument coordinate system (Fig. 1) determines the naming convention of the sensors and orientation of the instrument relative to the spacecraft. The use of MZ indicates a sensor on the -Z (zenith- facing during mapping) side of GRaND; PZ indicates the sensor is on the +Z (spacecraft) side; MY indicates the sensor is on the -Y side (inboard) side of the instrument; and PY indicates the sensor is on the +Y side (outboard, towards the +Y solar panel) side of the instrument. The phototube assembly, marked 'P' on the diagram in Fig. 1 points along the +X axis (towards the high gain antenna). ................. . ooooooooooooo . . o o . . o o . . o +Z o . . o (PZ) o . . o o .---> +Y (PY) . ooo ooo . . P P . . P P . . PPPPPPPPP . . . ................. | v +X (PX) Figure 1. The coordinate system for GRaND is the same as that of the S/C. For the diagram above, the observer is looking in the -Z (MZ) direction and can see the outline of the phoswich assembly (o) on the +Z side of GRaND. The phototubes are on the +X side and the scintillators are on the -X side. During mapping at Vesta and Ceres, the planetary surface is in the +Z direction. Software : Proprietary software is not needed in order to use the EDR data; however, Interactive Data Language (IDL) functions are provided in the Extras directory to read selected EDR data into a structures for analysis and visualization. The IDL functions are compatible with IDL Version 7.0 or higher, distributed by Exelis Visual Information Solutions. A document illustrating the use of these functions is provided. Media/Format : The EDR label and data files are delivered by electronic transmission to the PDS. The neutron and gamma ray binary event data were written in big endian IEEE binary format (MSB order).
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| DATA_SET_RELEASE_DATE |
2016-03-01T00:00:00.000Z
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| START_TIME |
2015-03-13T03:10:00.000Z
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| STOP_TIME |
2018-10-26T06:09:05.000Z
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| MISSION_NAME |
DAWN MISSION TO VESTA AND CERES
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| MISSION_START_DATE |
2007-09-27T12:00:00.000Z
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| MISSION_STOP_DATE |
2018-10-31T12:00:00.000Z
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| TARGET_NAME |
1 CERES
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| TARGET_TYPE |
ASTEROID
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| INSTRUMENT_HOST_ID |
DAWN
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| INSTRUMENT_NAME |
GAMMA-RAY AND NEUTRON DETECTOR
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| INSTRUMENT_ID |
GRAND
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| INSTRUMENT_TYPE |
NEUTRON SPECTROMETER
GAMMA RAY SPECTROMETER
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| NODE_NAME |
Small Bodies
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| ARCHIVE_STATUS |
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| CONFIDENCE_LEVEL_NOTE |
Review : The EDR will be reviewed internally by the Dawn Science Team prior to submission to the PDS. The PDS will also conduct an external peer review of the EDR prior to releasing the data to the general public. Data Coverage/Quality : The Level 1A EDR includes all of the available data acquired during flight. The archive contains gaps in time when the instrument is off during cruise or in STANDBY or ANNEAL mode for which science data are not acquired. During ATLO, ICO, and EMC, state-of-health data were decimated by a factor of 3 for storage in the virtual recorder on board the spacecraft. Consequently, playback data contained every third state- of-health packet. Full sampling of GRaND housekeeping data was available infrequently, during the acquisition of real-time telemetry. The spacecraft flight software was modified to remove the decimation prior to GRaND power on for Mars Gravity Assist (at UTC/ SCET 2009- 020/21:19:11), and, thereafter, housekeeping data volume was controlled by the selection of TELSOH. Consequently, fully-sampled housekeeping data are available in the EDR following 20-Jan-2009. GRaND's scalers do not have accompanying roll-over counters. During solar particle events or long accumulation times, it is possible that one or more of the scalers can exceed the maximum number of counts (65535), restarting at 0. In fact, the some scalers, such as the dead time counter, can roll over multiple times. The number of times a scaler has rolled over can be determined by watching for abrupt changes in the science scaler data and by analyzing the state-of- health scaler data when the state-of-health readout interval (TELSOH) is set to subsample the science accumulation interval (TELREADOUT) (for example, see Prettyman et al., 2011). Corrections for rollover, for example to determine dead time, are made in the RDR (Level 1b) datasets. Successive EDR directories contain short overlapping time periods, such that a few science data records are repeated. Care should be taken to eliminate repeated records when processing EDR from multiple directories. Gaps in the EDR data set can occur due to missing packets (e.g. occultations) and for periods of time when the instrument was off following spacecraft safing events. For completeness, corrupted data (e.g. due to transmission errors) are not excluded from the dataset; however, instances of corrupt data are rare. Telemetry checksums are discarded in queries of instrument data by the DSC. Consequently, corrupt data can only be identified by anomalies in scaler and spectral data (e.g. incongruous patterns in counts or discontinuous pulse height spectra). Corrupt data are partially excluded from the EDR dataset by two mechanisms: 1) packet headers with incorrect SCLK values or other invalid information recognized by the query software are naturally excluded; 2) incomplete science data records (e.g. detected by gaps) in the packet sequence counter) are discarded by the EDR processing code. These result in gaps in the EDR science data. Some unknown portion of the records may be recognized as valid, yet still contain corrupted science data. These are not excluded from the archive. Some spectral data products contain artifacts, for example, abrupt increases in counts for the highest channel or a nonphysical changes in counts at high channels (e.g. for the CAT1 -Z sensor). The former is likely from events that do not exceed the overload threshold, but are not on scale. These wind up in the last channel. In addition, some distortion can occur for large pulses processed by the analog pulse processing circuit. This may account for the roll-off observed for high channels for the -Z sensor (e.g. above channel 230). GRaND was powered on and configured for science data acquisition on 13-Mar-2015 as Dawn approached Ceres (CSA). With the exception of data loss during two instances of S/C entry into safe mode, GRaND operated continuously in NORMAL mode with negligible data loss throughout the primary mission at Ceres, which ended on 19-Jun-2016, corresponding to the end of CSL Cycle 8. Data loss during safe mode occurred in CSR from 24- to 27-Apr-2015 (see GRD-L1A-150424-150501_YCMCDC-STA.TAB) and at the end of CSS from 1- to 7-Jul-2015 (see GRD-L1A-150701-150701_YCMCDC-STA.TAB). At the beginning of Ceres encounter, the BGO and +Z Phoswich sensors had noticeable gain loss, likely due to darkening of the scintillators due to radiation damage. On 28-May-2015, the BGO HV was increased from 125 DN (735 V) to 127 DN (747 V) to compensate for the observed loss in gain. The BGO HV setting briefly returned to 125 DN following recovery from safe mode on 7-Jul-2015. Soon thereafter (15-20 Jul during CTH), a HV permutation study was carried out to determine optimal settings for the BGO sensor (see GRD-L1A-150715-150722_YCMCDC-STA.TAB). Based on an analysis of the data, the optimal setting was determined to be 127 DN. On 20-Jul-2015, the HV for the phoswiches and plastic scintillators were increased to 185 DN (+Z), 173 DN (-Y), 178 DN (+Y), and 182 DN (-Z). These settings were retained for the rest of the primary mission and the extended mission, with the following exceptions. Dawn's first extended mission at Ceres began on 19-Jun-2016 while the spacecraft was in low altitude mapping orbit. On 10-Aug, during CXL, the BGO HV was decreased to 123 DN (724V) to measure high energy gamma rays up to 11 MeV, with the aim of searching for gamma rays produced by neutron capture by Ni (8.5- and 9-MeV) within Ceres' regolith. The BGO HV was restored to 127 DN on 1-Sep at the beginning of transfer to Juling orbit (CTJ). To acquire accompanying background data, the voltage was lowered again to 123 DN in Juling orbit (CXJ, from 21-Oct to 3-Nov) and in the GRaND orbit (CXG, from 14-Dec to 11-Jan). In 2017, data were lost from 14-Jan through 26-Jan when the spacecraft entered safe mode. Data were lost again from 24-Apr to 02-May as a result of another spacecraft safing and a delay in getting GRaND properly configured. A few hours of data were lost on June 3 as a result of poor DSN signal strength during solar conjunction. These data were overwritten before there was an opportunity to try and recover the data gap. Note that during recovery from safemode, multiple commands are sent to GRaND to configure the instrument for science data acquisition. During configuraton, the counting system is unstable. Changes in the instrument state can be seen by examining the state file (.STA) in the LEVEL1A_AUX subdirectory for data downlinked following safe mode recovery. For example, the state file in GRD-L1A-170126-170201 shows changes in instrument settings during recovery from safe mode on 26-Jan-2017. During CXO, while the spacecraft was at high altitude, the BGO HV was adjusted to explore the effect of gain on the gamma ray pulse height spectrum. The HV was decreased to 121 DN on 13-Jun-2017 and then decreased further to 119 DN on 20-Jun. The BGO HV was restored to 123 DN on 27-Jun. The performance of GRaND was deemed acceptable and no further adjustements to instrument settings were made through the end of the mission. In Dawn's second extended mission, the spacecraft manuevered into close proximity to Ceres. GRaND reacquired Ceres in an intermediate altitude orbit (C2I) and acquired high spatial-resolution mapping data in an elliptical orbit with low periapsis (C2E), less than 50-km from Ceres' surface. The elliptical orbit campaign commenced on 9-Jun. The spacecraft completed 123 orbits before it ran out of hydrazine on 31-Oct-2018. The loss of the spacecraft was confirmed on 1-Nov. The last GRaND data were downlinked on 26-Oct. The elliptical data were acqurired under ideal conditions, with no solar interference and negligible data loss. Nevertheless, for 10 of the 123 orbits, the spacecraft was pointed away from Ceres to downlink data through the main antenna. These orbits have limited utility for elemental analyses. Limitations : The EDR is a low-level data product, which requires significant processing prior to use in scientific analysis. The EDR directory names include the dates for the first and last science data records in the data files. The date range for the SOH data may not match that of the science data. For example, SOH data in the directory GRD_L1A-150817-150818_YCMCDC span 150817 to 150824. The date range for the SOH data can be found quickly by examining the BROWSE report that accompanies each directory.
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| CITATION_DESCRIPTION |
Prettyman, T.H., DAWN GRAND RAW (EDR) CERES COUNTS V1.0, DAWN-A-GRAND-2-EDR-CERES-COUNTS-V1.0. NASA Planetary Data System, 2016.
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| ABSTRACT_TEXT |
The GRaND EDR are a time-ordered collection of gamma rayand neutron counting data and histograms acquired by GRaND during allphases of the Dawn mission. The dataset includes state-of-health data,such as temperature and voltage readings, needed for the analysis of thecounting data. The EDR is an intermediate data product derived from theraw data records using reversible operations. All higher order dataproducts are derived from the EDR. An automated pipeline is used toprocess the EDR from the raw data records.
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| PRODUCER_FULL_NAME |
THOMAS H. PRETTYMAN
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| SEARCH/ACCESS DATA |
SBN PSI WEBSITE
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