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Availability: Archived at NSSDC, accessible from elsewhere


This description was generated automatically using input from the Planetary Data System.

Data Set Overview

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) is a stacked detector-absorber cosmic-ray telescope designed to answer key questions to enable future human exploration of the Solar System. CRaTER's primary measurement goal is to measure directly the average lineal energy transfer (LET or 'y') spectra caused by space radiation penetrating and interacting with shielding material. Such measured LET spectra are frequently unavailable. In the absence of measurements, numerical models are used to provide estimates of LET; the reliability of the models require experimental measurements to provide a ground truth. The Level 1 dataset consists of files containing data processed from the Level 0 primary science, secondary science, and housekeeping raw data records. During processing, the raw data are converted with instrumentspecific calibration and conversion factors to calibrated data records (CDR) containing science and engineering measurements and instrument operating parameters. The CDR are written to files in plain text, fixed record format; each file contains CDR for a single UTC day. All times values in Level 1 data products are in spacecraft clock units. The Level 1 data are an intermediate data product meant to be used for data processing diagnostics and troubleshooting. Although the Level 1 dataset can be used for some data analyses, it is not intended as the primary source for further data analyses or scientific research. In the Level 1 dataset all times are expressed in spacecraft clock units; spacecraft location and instrument pointing data are not included. Users seeking CRaTER data are instead encouraged to use the Level 2 derived data record (DDR) dataset. The Level 2 data contain all Level 1 data supplemented time values converted to UTC and computed spacecraft location and instrument pointing information. See the MISSION.CAT file for more information on the LRO mission. See the CRAT_INST.CAT file for more information on the CRaTER instrument. See SPENCEETAL2010 for detailed description of LRO flight version of the instrument, its operations, and data processing.

Science Objectives and Observation Strategy

CRaTER is designed to achieve characterization of the global lunar radiation environment and its biological impacts and potential mitigation as well as investigation of shielding capabilities and validation of other deep space radiation mitigation strategies involving materials. CRaTER will fill knowledge gaps regarding radiation effects, provide fundamental progress in knowledge of the Moon's radiation environment, and provide specific path-finding benefits for future planned human exploration.


LRO CRaTER flight instrument identification: --instrument model = Flight Model 1 (FM1); --instrument serial number (S/N) = 02; --FPGA revision code = 3. Data ---CRaTER's principal measurement is the energy deposited in the 3-pairs of silicon detectors by charged particles and photons passing through the instrument's 'telescope' unit. Whenever the coulombic charge signal resulting from the energy deposited in a detector exceeds a predefined and fixed threshold, the instrument's electronics performs a detailed measurement of the signals from all of the detectors. The resulting detector signal amplitudes are compared to the values of the 'lower level discriminators' (LLDs). LLDs establish minimum amplitudes for signals to qualify as valid charged-particle or photon interactions. The LLD values are generally set to insure that the desired charged-particle or photon measurements are not contaminated by system electronic noise. Seperate LLD settings are required for the thick and thin detectors due to the difference in their sensitivities; the thin and thick detector LLD values are reported in the 'DiscThin' and 'DiscThick' parameters as part of the secondary science packet. In addition to the LLD settings, measurement filtering is achieved through detector coincidence requirements--the combination of detectors registering valid signals to qualify as a charged-particle or photon measurement 'event'. To measure all charged particles arriving from the instrument's zenith or nadir directions, for example, the coincidence requirements would be valid signals in at least detectors 1, or 2, or 5, or 6. Conversely, a coincidence consisting of valid signals in all six detectors would ensure only zenith- or nadir-arriving charged particles with high energies are reported. For CRaTER's six axially-coaligned detectors there are 64 possible coincidence combinations. The desired set of coincidence combinations are stored as a coincidence mask parameter in the instrument's memory; the coincidence mask setting is reported in the 'Mask' parameter as part of the secondary science packet. To qualify as an 'event', therefore, a charged particle or photon passing through CRaTER's telescope must interact and deposit sufficient energy to generate signals with amplitudes in excess of the specified LLDs in a specified combination of detectors; only data for valid 'events' are reported in the instrument's telemetry. The measured interaction event data is written as a series of primary science packets to the instrument's output telemetry buffer for the spacecraft to read. At ~1 second intervals CRaTER receives a timing pulse from the spacecraft, at which time it flushes the primary science data from the output buffer and writes a secondary science packet for the spacecraft to read. Every 16 seconds a housekeeping packet is also created and written to the output buffer. The Level 1 data are created from the corresponding Level 0 data by converting the instrument binary output with conversion and calibration factors to science and engineering data. The Level 1 dataset is composed of the three types of time-sequential calibrated data records (CDR): (1) primary science, (2) secondary science, and 3) housekeeping. The three types of CDR are written to seperate data files in plain text, fixed record format. Each file contains CDR for a single UTC day. The Level 1 primary science data consists of a sequence of interaction event CDR--one CDR for each measured event. Each CDR consists of the energy deposited in each of the six detectors and the spacecraft time at the end of the measurement interval (receipt of spacecraft timing pulse). CDR for events recorded in the same measurement interval have the same time tags--the 'SECONDS' and 'FRACT' field values. Although numerous events may have the same time value, the events are recorded in the order in which they occurred; this relative order is captured in the CDR 'INDEX' field. The Level 1 secondary science CDR contain the majority of instrument configuration settings, status flags, and event counters. Reported configuration settings include the last command sent to CRaTER, detector LLD settings, and coincidence mask values. Status flags available in the secondary science CDR include detector bias status, selected pulse amplitude range and rate for the internal calibration pulser, and detector processing status. Counters report the number of 'singles' for each detector as well as the number of 'good', 'rejected', and total events recorded by CRaTER during the monitoring period. The Level 1 housekeeping CDR contain measured instrument operating and environmental parameters used to assess the health and performance of the instrument, such as power supply output voltages, detector bias voltages and currents, pulse amplitudes from the internal calibration pulser, and temperatures at five locations inside of the instrument's housing. The analog output signal (voltage) from radiation monitor is also included the housekeeping CDR.

These data are available on-line from the Planetary Data System (PDS) at:

Alternate Names



  • Planetary Science: Fields and Particles

Additional Information



Questions and comments about this data collection can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Harlan E. SpenceData ProviderBoston
Dr. Harlan E. SpenceGeneral ContactBoston
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