LRO CRaTER Data Bundle
LRO Derived (Level 0) Data Collections (Housekeeping, Primary and Secondary)
Original DATA_SET_ID = LRO-L-CRAT-2-EDR-RAWDATA-V1.0
Original DATA_SET_NAME = LRO MOON CRATER EDR RAWDATA VERSION 1.0
START_TIME = 2009-06-29T00:00:00.000
STOP_TIME = 2025-09-30T23:59:59.01
Original DATA_SET_RELEASE_DATE
= 2019-12-13
PRODUCER_FULL_NAME = PROF. HARLAN SPENCE
Collections 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.
CRaTER Level 0 collections consist of files containing the raw primary
science, secondary science, and housekeeping telemetry packets and packet
headers created by the instrument. The Level 0 data are meant to be used
only for archival purposes in order to reconstruct the other CRaTER data
products in the future, should that become necessary. The Level 0 data
are not intended to be used directly in data analyses or scientific
investigations--the data are stored in binary data structures and have
not been converted to appropriate engineering or science values. Users
seeking CRaTER data are strongly encouraged to use the Level 1 or Level 2
collections.
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.
Parameters
----------
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 re-
sulting 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 re-
ported 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.
Level 0 collections is composed of the three types of time-sequential,
raw CRaTER data records: (1) primary science, (2) secondary science, and
(3) housekeeping.
The primary science raw data consists of the signal pulse heights from
each of the six detectors produced during an 'event'. The raw event data
in the primary science packets are the scalar channel numbers output by
the detector-amplifier strings' analog-to-digital converters (ADCs) fol-
lowing signal pulse height analysis.
The secondary science raw data contain the majority of instrument config-
uration settings, status flags, and event counters. Reported configura-
tion settings include the last command sent to CRaTER, detector LLD set-
tings, and coincidence mask values. Status flags available in the secon-
dary science raw data include detector bias status, selected pulse am-
plitude range and rate for the internal calibration pulser, and detector
processing status. Counters report the number of 'singles' for each de-
tector as well as the number of 'good', 'rejected', and total events re-
corded by CRaTER during the monitoring period.
The housekeeping raw data contains the output of internal monitors used
to assess the operating health of the instrument, such as power supply
voltage monitors, detector bias voltages and bias currents, pulse ampli-
tudes from the internal calibration pulser, and temperatures at five
locations inside of the instrument's housing. The analog output from
radiation monitor is also included in the housekeeping data packets.
The primary science, secondary science, and housekeeping packets are
written to seperate files in binary format. Each file begins with a
64-byte header and continues with one or more CCSDS packets. Each packet
begins with a 6-byte CCSDS header that defines the type (ApID 120,
121, or 122) and length of the packet, followed by a 6-byte secondary
header containing a time tag and instrument-specific flags. Each of the
files contains all of the data from a single UTC day. The files' binary
structures are documented in CRaTER SPDR and Archive Volume Software
Interface Specification (Document 32-01211), sections 5.2.6 and
Appendix C.
Confidence Level Overview
-------------------------
No confidence level information is provided for the Level 0 data since it
consists of only the raw instrument binary data and is not intended for
direct use in data analyses.
Confidence level information is provided with the Level 1 and Level 2
sets.
Review
------
A minimal set of automated quality control steps are used by the data
processing system to verify the integrity of the data. During the
creation of the Level 0 data files from the downlinked instrument data
files, each data packet's CCSDS header is checked for format and content.
Packets are discarded if their headers are corrupted, incorrectly
formatted, or containing invalid values. All packets are sorted into
time order and checked for temporal gaps. Duplicate packets are also
discarded. Metrics plus any detected anomalies are written to process
log files for review by scientists and engineers from the instrument
team. Anomalies noted during the processing are investigated. Anomalies
due to missing input files (e.g., instrument science and housekeeping
data files, spacecraft housekeeping data files, spacecraft ephemeris
kernels, and ancillary files such as leap second and spacecraft clock
kernels) are corrected by locating the missing input and reprocessing the
data.
Data Coverage and Quality
-------------------------
Start date for the initial version of the LRO-L-CRAT-2-EDR-RAWDATA-V2.0
archival volume is 2009-06-29T00:00:00.000. This date/time is the begin-
ning of the first full UTC day following completion of LRO lunar orbit
insertion (LOI) maneuvers and transition to the nominal nadir-pointing
observation attitude. It is also the first day for which complete re-
constructed ephemeris ('SPK') data was available from the LRO Mission
Operations Center. There is only limited re-constructed ephemeris data
currently available for the period between initial instrument power-up
(2009-06-20) and LOI completion/transition to the nominal observing
attitude. CRaTER data obtained during Cruise Phase (instrument power-up
- 2009-06-23), Lunar Orbit Acquisition (2009-06-23), and the initial
Commissioning Period (2009-06-23 - 2009-06-28) will be included when more
complete ephemeris data becomes available.
Data gaps are identified during initial data processing. Each gap's
beginning and end times are recorded in gap files stored in the DOCUMENT
directory--there are seperate gap files for primary science, secondary
science, and house-keeping data. Each gap file contains a cumulative
listing of the missing data up to and including the time span covered for
the data current volume. The minimum duration between successive data
packets to qualify as a data gap is specified during data processing.
The default gap duration specifications are:
--primary science = 2 seconds;
--secondary science = 2 seconds;
--and housekeeping =20 seconds.
These default gap duration values may be over ridden at the time of data
processing. The gap duration specifications used while processing a
specific day's data are recorded in the corresponding process log files
and stored in the data subdirectoy directory containing the data products.
Limitations
-----------
The LRO CRaTER collections include all data obtained
by the CRaTER instrument, including data from periods when the instrument
was placed into special configurations. Special configurations include
the instrument start-up tests that occur whenever the instrument is power
cycled to (e.g., initial instrument start-up, recovery following space-
craft transition to sun-safe mode) as well routine calibrations
(90-degree off-nadir GCR background measuerments, internal pulser sweeps,
LLD zero crossing measurements, and LLD sweeps).
As specified in CRaTER Standard Product Data Record and Archive Volume
Software Interface Specification, Document 32-01211, the Level 0 house-
keeping data files contain the voltage (V28BUS) and current draw (I28bus)
measured at the instrument side of the instrument-spacecraft 28 VDC bus
interface. For the LRO CRaTER instrument, the voltage (V28BUS) and cur-
rent (I28BUS) values are UNDEFINED. Immediately prior to instrument
delivery, the signal leads from these two monitors were removed to reduce
excessive EMI emmission; however, the instrument software still processes
the signals from these open leads and includes them in the housekeeping
packets stored in the instrument housekeeping files. Although no longer
defined, these values have been retained in the Level 0 housekeeping
files in order to preserve the structure defined for the instrument's
housekeeping packets (LRO telemetry ApID = 122). Although values can be
retrieved for the voltage (V28BUS) and current (I28BUS) parameters from
the Level 0 housekeeping data files, they are UNDEFINED and should be
discarded from any analyses.
Reference
=========
[Spence et al. 2010] Spence, H.E., A.W. Case, M.J. Golightly,
T. Heine, B.A. Larsen, J.B. Blake, P. Caranza, W.R. Crain, J. George,
M. Lalic, A. Lin, M.D. Looper, J.E. Mazur, D. Salvaggio, J.C. Kasper,
T.J. Stubbs, M. Doucette, P.Ford, R. Foster, R. Goeke, D. Gordon,
B. Klatt, J. O'Conner, M. Smith, T. Onsager, C. Zeitlin, L.W. Townsend,
Y. Charara (2010), CRaTER: The Cosmic Ray Telescope for the Effects of
Radiation Experiment on the Lunar Reconnaissance Orbiter Mission, Space
Sci. Rev., 150, 243-284, DOI: 10.1007/s11214-009-9584-8.
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