NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header



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 2 dataset consists of files containing data processed from the Level 1 primary science, secondary science, and housekeeping calibrated data records (CDR). During processing, derived data records (DDR) are formed by combining Level 1 CDR with derived parameters such as average LET, detector event flags, and instrument viewing geometry data. The DDR are written to files in plain text, fixed record format; each file contains DDR for a single UTC day. All times in Level 2 data products are reported in both spacecraft clock units and UTC. The Level 2 data products are intended as the primary CRaTER data source for further data analyses or scientific research. 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 2 data are by combining the Level 1 data with derived or supplemental parameters including average LET in each detector, detector event flags, instrument electrical power consumption, and instrument viewing geometry information. The Level 2 dataset is composed of the three types of time-sequential derived data records (DDR): (1) primary science, (2) secondary science, and 3) housekeeping. The three types of DDR are written to seperate data files in plain text, fixed record format. Each file contains DDR for a single UTC day. The Level 2 primary science data consists of a sequence of interaction event DDR--one DDR for each measured event. Each DDR consists of the energy deposited in each of the six detectors, the resulting average LET, and the spacecraft time and UTC at the end of the measurement interval (receipt of spacecraft timing pulse). Also included in the primary science DDR are two sets of flags related to the measured deposited energy in each detector: one set flags deposited energies exceeding corresponding LLD values; the second set flags deposited energies approaching the saturation value for the associated amplifier-ADC strings (signals exceeding 95% of the ADC's dynamic range). DDR for events recorded in the same measurement interval have the same time tags--the 'SECONDS','FRACT', and 'TIME' 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 DDR 'INDEX' field. The Level 2 secondary science DDR 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. The record's time tag includes both spacecraft time and UTC. Status flags available in the secondary science DDR 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. Also included in the secondary science DDR is LRO's location relative to the center of the Moon; the location is provided as three orthogonal vectors (Px, Py, Pz) in the MOON_ME (Moon Mean Earth/Rotation Axis) reference frame The Level 2 housekeeping DDR 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. The record's time tag includes both spacecraft time and UTC. Also included in the housekeeping DDR are two status flags related to the relative orientation of the instrument's boresite axis: one flag indicates when the boresite axis does not intercept the lunar surface 'OFFMOONFLAG'; the second indicates when LRO and CRaTER are in eclipse. LRO's location and CRaTER's relative boresite orientation are derived from definitive spacecraft ephemeris ('SPK') and orientation ('CK') kernels, using transformation routines from the JPL NAIF (Navigation and Ancillary Information Facility) toolkit. The daily kernel files used during the Level 2 DDR processing are stored in the EXTRAS directory.

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
[] NASA Logo -