Cosmic Ray Telescope for the
Effects of Radiation (CRaTER)
Instrument Requirements
Justin Kasper
CRaTER Instrument Scientist
MIT & Boston University
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CRaTER Organization Chart
CRaTER
Instrument Management Team
CRaTER Project
Engineering
CRaTER Instrument Management Team
Monday, August 01, 2005 Friday, June 17, 20
Friday, June 17, 2005
CRaTER Science
Working Group
Robert Science
Goeke
CRaTER
MIT
Working
Group
Project Engineer
Harlan Spence
BU
PI
Brian Klatt
MIT
Mission
Assurance Mgr
Brian Klatt
MIT
Mission
Assurance Mgr
Robert Goeke
MIT
Project Engineer
Boston
University
Rick Foster
Program
Manager
Project Manager
Jimmy
O’Conner
MIT
Fabrication
Mgr
Kristin Sacca
BU
Coordinator
Chris Sweeney
I&T Lead
Christine
Comaceau
Aerospace
Project Manager
Aerospace Support
Harlan Spence
BU
PI
Aerospace
Corp
Bill Crain
Sr. Electrical
Engineer
Albert Lin
Jimmy
Mechanical
O’Conner
Engineer
MIT
Fabrication
Mgr
Robert Goeke
MIT
Project Engineer
MIT
Rick Foster
Program
Manager
Project Manager
Matt Smith
Mechanical
Engineer
Mike Doucette
Test Engineer Christine
Kristin Sacca
Comaceau
BU
Aerospace
Coordinator
Project Manager
Dorothy Gordan
Electrical
Engineer
Aerospace Support
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Page 1
Theory of Operation
Pairs of thin and
thick Silicon
detectors
A-150 Human tissue
equivalent plastic
(TEP)
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Moon
Theory of Operation
D6
D5
1) Energetic charged particle enters the telescope
A2
 Particle deposits energy in components through
ionizing radiation
 Nuclear interactions produce energetic secondary
particle
D4
D3
2)
Primary and secondary particles interact with one
or more detectors
 Thin detectors optimized for high LET particles
 Thick detectors optimized for low LET particles
A1
3) Detectors with sufficient energy deposition cross
trigger threshold
4) Digital logic compares coincidence with event mask
of desirable events
5) Pulse height analysis (PHA) is conducted on every
detector to measure energy deposition
D2
D1
Space
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Heritage
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CRaTER is not directly derived from an existing instrument.
The three teams (BU, MIT, Aerospace) with engineering tasks have all
produced particle instruments for spaceflight.
The company providing the silicon semiconductors (Micron Semiconductor)
has produced detectors for many successful flights. The particular detectors
we are purchasing for the engineering model (and likely for the flight model)
use dies developed for a previous mission.
Tissue equivalent plastic (TEP) has been flown in space, including
investigations on the space station.
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CRaTER Instrument Requirement Documents
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Level 1 Documents
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Level 2 Documents
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LRO Program Requirements Document, ESMD-RLEP-0010
CRaTER Instrument Requirements Document, 32-01205 01
CRaTER Data Management Plan
LRO Mission Requirements Document, 431-RQMT-000004
LRO Mission Concept of Operations, 431-OPS-000042
LRO Technical Resource Allocations, 431-RQMT-000112
LRO Pointing and Alignment Specification, 431-SPEC-000113
LRO Electrical Systems Specification, 431-SPEC-000008
LRO Mechanical Systems Specification, 431-SPEC-000012
LRO Thermal Systems Specification, 431-SPEC-000091
LRO Mission Assurance Requirements, 431-RQMT-000174
LRO Contamination Control Plan, 431-PLAN-000110
LRO Data Management Plan, 431-PLAN-000182
Level 3
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Instrument Payload Assurance Implementation Plan, 32-01204
LRO to CRaTER Mechanical Interface Document, 431-ICD-000085
LRO to CRaTER Thermal Interface Control Document, 431-ICD-000118
LRO to CRaTER Electrical Interface Control Document, 431-ICD-000094
LRO to CRaTER Data Interface Control Document, 431-ICD-000104
LRO Ground Systems ICD, 431-ICD-000049 (MOC to SOC)
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Mission Level Requirements
ESMD-RLEP-0010
LRO
Req.
Level 1: Requirements
Instrument
LRO Mission Requirement
Required Data Products
RLEP-LROM10
CRaTER
The LRO shall characterize the deep
space radiation environment in lunar
orbit, including neutron albedo.
Measure and characterize that aspect of the deep space
radiation environment, Linear Energy Transfer (LET)
spectra of galactic and solar cosmic rays (particularly
above 10 MeV), most critically important to the
engineering and modeling communities to assure safe,
long-term, human presence in space.
RLEP-LROM20
CRaTER
The LRO shall characterize the deep
space radiation environment in lunar
orbit, including biological effects caused
by exposure to the lunar orbital radiation
environment.
Investigate the effects of shielding by measuring LET
spectra behind different amounts and types of areal
density, including tissue-equivalent plastic.
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Instrument System Level Requirements
Level 1 Req.
Instrument Level 2: IRD 32-01205
Requirement
Concept/Realizability/
Comment
CRaTER Instrument Measurement Requirement
M10-CRaTER
L2-01 (4.1)
Measure the linear energy transfer (LET) spectrum dE/dx,
defined as the energy dE deposited in a silicon detector of
thickness dx.
Measure current produced by
electron-hole pair production
in silicon semiconductor
detectors
M20-CRaTER
L2-02 (4.2)
Measure change in LET through A-150 human tissue
equivalent plastic (TEP).
Place sections of TEP between
silicon detectors
M10-CRaTER,
M20-CRaTER
L2-03 (4.3)
The minimum pathlength through the total amount of TEP in
the telescope is 61 mm.
100 MeV particles just
penetrate; telescope mass is
dominated by the TEP.
M20-CRaTER
L2-04 (4.4)
The TEP is broken into two sections, 27 and 54 mm in height.
Measure LET evolution
through different areal
densities of TEP.
M20-CRaTER
L2-05 (4.5)
The minimum energy deposition measured by the Silicon
detectors is 200 keV.
Detect low energy secondary
particles without approaching
noise level of detector.
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Instrument System Level Requirements
Level 1 Req.
Instrument Level 2: IRD 32-01205
Concept/Realizability/
Comment
Requirement
CRaTER Instrument Measurement Requirement
M10-CRaTER,
M20-CRaTER
L2-06 (4.6)
At each point in the telescope where the LET spectrum is to
be observed, the minimum LET measured shall be no greater
than 0.2 keV/ micron.
Sufficient to see minimum
ionizing primary particles and
stopping secondaries
M10-CRaTER,
M20-CRaTER
L2-07 (4.7)
At each point in the telescope where the LET spectrum is to
be observed, the maximum LET measured will be no less
than 7 MeV/ micron.
This is above the maximum
expected LET due to stopping
iron nuclei
M10-CRaTER,
M20-CRaTER
L2-08 (4.8)
The pulse height analysis of the energy deposited in each
detector will have an energy resolution of at least 1/300 the
maximum energy of that detector.
To characterize the LET
spectrum accurately and
simplify the comparison
between theory and
observations
M10-CRaTER
L2-09 (4.9)
The geometrical factor created by the first and last detectors
shall be at least 0.1 cm2 sr.
Good statistics for high energy
galactic cosmic rays
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Selected Instrument Subsystem Level
Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Requirement
Concept/Realizability/
Comment
Telescope requirements
CRaTEr-L2-01,
CRaTER-L2-05,
CRaTER-L2-06,
CRaTER-L2-07,
CRaTER-L2-08
L3-01 (6.1)
The telescope stack will contain adjacent pairs of thin
(approximately 140 micron) and thick (approximately 1000
micron) Si detectors. The thick detectors will be used to
characterize energy deposition between approximately 200
keV and 100 MeV. The thin detectors will be used to
characterize energy deposits between 2 MeV and 1 GeV.
The LET range specified in the
Level 2 requirements would
require an unrealistic factor of
5000 dynamic range
CRaTER-L2-05
L3-02 (6.2)
The shielding due to the mechanical housing the CRaTER
telescope outside of the zenith and nadir fields of view shall
be no less than 0.06” of aluminum.
Cut flux of protons with
energy less than 17 MeV
coming through side
CRaTER-L2-05
L3-03 (6.3)
The zenith and nadir sides of the telescope shall have no less
than 0.06” of aluminum shielding.
Cut flux of protons with
energy less than 17 MeV
coming through telescope
CRaTER-L2-01,
CRaTER-L2-02,
CRaTER-L2-04,
CRaTER-L2-05
L3-04 (6.4)
The telescope will consist of a stack of components labeled
from the nadir side as zenith shield (S1), the first pair of thin
(D1) and thick (D2) detectors, the first TEP absorber (A1), the
second pair of thin (D3) and thick (D4) detectors, the second
TEP absorber (A2), the third pair of thin (D5) and thick (D6)
detectors, and the final nadir shield (S2).
LET measurements will be
made on either side of each
piece of TEP to understand the
evolution of the spectrum as is
passes through matter.
CRaTER-L2-01,
CRaTER-L2-02,
CRaTER-L2-03
L3-05 (6.5)
The uncertainty in the length of TEP traversed by a particle
that traverses the entire telescope axis shall be less than 10%.
sufficient accuracy for
subsequent modeling efforts to
reproduce the observed LET
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Selected Instrument Subsystem Level
Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Requirement
Concept/Realizability/
Comment
Telescope requirements
CRaTER-L2-01,
CRaTER-L2-02
L3-06 (6.6)
The zenith field of view, defined as D1D4 coincident events
incident from deep space, will be 35 degrees full width.
leads to a sufficient
geometrical factor while still
limiting the uncertainty in the
pathlength
CRaTER-L2-01
L3-07 (6.7)
The nadir field of view, defined as D3D6 coincident events
incident from the lunar surface, will be 75 degrees full width.
Trade off accuracy of LET
measurements for particles of
lunar origin to increase
geometrical factor since
should be rare
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Selected Instrument Subsystem Level
Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Requirement
Concept/Realizability/
Comment
Electronics requirements
CRaTER-L2-08
L3-08 (6.8)
The CRaTER electronics will be capable of injecting
calibration signals at 256 energies into the measurement
chain.
Verify operation without
radioactive sources, identify
detector response evolution
after testing and launch
CRaTER-L2-01
L3-09 (6.9)
A command may be sent to CRaTER to identify the set of
detector coincidences that should be analyzed and sent to the
spacecraft.
May focus on subset of
coincidences, especially
during periods of intense solar
activity
CRaTER-L2-01
L3-10 (6.10)
The maximum event rate CRaTER will transmit will be 1,250
events per second.
Keep up with rates during
intense storms, but recognize
that this rate is sufficient to
yield necessary statistics
during flares.
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CRaTER Data Product Development
Data
Level
Data Products
Inputs
ESMD Data
Product
0
Unprocessed instrument data (pulse height
at each detector, plus secondary science)
and housekeeping data.
Raw science and housekeeping data from
MOC
1
Depacketed science data at 1-s resolution.
Level 0 data, and spacecraft attitude data,
calibration files.
2
Pulse heights converted into energy
deposited in each detector. Calculation of
Si LET
Level 1 data, pulse-height to energy
conversions based on pre-launch
accelerator experiments and updated base
on in-flight calibration system
RLEP-LRO-M10
RLEP-LRO-M20
3
Data organized by particle environment
(GCR foreshock, magnetotail). SEPassociated events identified and extracted.
Level 2 data, spacecraft location, NOAA
Space Environment Center (SEC) solar
activity alerts and summary data
RLEP-LRO-M10
RLEP-LRO-M20
4
Calculation of incident energies from
modeling/calibration curves and TEP LET
spectra
Level 3 data, spectral density of major ions
from hydrogen through iron as measured by
near-Earth spacecraft including ACE,
GOES, IMP-8, output from numerical
simulations
RLEP-LRO-M20
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CRaTER Science Operations Center
Driving Level 3 Requirements
Level 2
Req.
Level 3: Driving Requirements
Paragraph
Concept/Compliance
Requirement
MRD-055
Data Product
Delivery
CRaTER
DMP, #TBD
Process up to 8.6 Gbits/day
Computing size
MRD-055
Data Product
Delivery
CRaTER
DMP, #TBD
Analyze and trend instrument performance.
Plot singles rates and
calibration output
MRD-055
Data Product
Delivery
CRaTER
DMP, #TBD
Develop CRaTER command schedule for MOC.
Same cycle every day
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CRaTER Data Flow Concept
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CRaTER Constraints on LRO
Title
Requirement
Rationale
LRO Requirement
Spacecraft shall handle a peak
data rate of 100 kbps
1250 events/second during peak solar activity
MRD-35, Low Rate
Data
Zenith
Field of
Regard
No obstruction in 40 degree
zenith field of regard
Deep space field of view for D1D4 is 35
degrees
MRD-71, Fields of
View
Nadir Field
of Regard
No obstructions in 80 degree
nadir field of regard
Lunar field of view for D3D6 is 35 degrees
MRD-71, Fields of
View
Pointing
Knowledge
Pointing knowledge to within 10
degrees
Knowledge of instrument orientation
MRD-49, Pointing
Allocations
Pointing
Accuracy
Telescope axis is aligned within
35 degree of lunar surface
during nominal operation
Insure telescope is always pointing at Lunar
surface
MRD-14, Nadir
Pointing
MRD-49, Pointing
Allocations
Data Rate
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Instrument Block Diagram
MIT
Aerospace
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Development Flow
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Instrument Verification
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The CRaTER Performance and Environmental Verification Plan (32-01206) describes
the plan to verify the CRaTER requirements in accordance with the CRaTER
Calibration Plan (32-01207), CRaTER Contamination Control Plan (32-01203), and the
CRaTER Performance Assurance Implementation Plan (32-01204)
The verification program is designed to provide the verifications listed below:
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The instrument meets its functional and design requirements.
Fabrication defects; marginal parts, and marginal components (if any exist) are detected early in
the test sequence.
The instrument can survive and perform as required in the environments predicted to be
encountered during transportation, handling, installation, launch, and operation.
The instrument has met its qualification and acceptance requirements.
The most significant verification testing beyond the standard set of environmental tests is a
series of runs in particle accelerators to verify the performance of the detectors and the
evolution of the LET spectrum after propagation through the TEP
Reporting
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If a test or analysis cannot be satisfactorily completed, then a malfunction report will be
produced by the test conductor. It will provide all the particular information detailing the
malfunction. A malfunction may result in premature test termination, depending on operation
procedures. Regardless of this, a malfunction report will be filed with the Verification Report
for the activity.
Detailed test procedures and specifications will be written, reviewed, and approved by the
CRaTER Project, prior to instrument-level verification testing. The lead individual for each
procedure depends upon the category: Environmental Requirements (Project Engineer);
Performance Requirements (Project Scientist); Contamination Requirements (Contamination
Engineer); Interface Requirements (Cognizant Design Engineer); Calibration Requirements
(Project Scientist)
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Instrument Current Status
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Major trade studies since Instrument inception which have been closed
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Major ongoing trade studies which could impact either Instrument top-level
requirements or the interface to the Spacecraft
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None
Analyses currently being performed
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We have decided to use two pieces of TEP with different lengths instead of the three TEP
sections in the original proposal
We have increased the thickness of the shielding to raise the minimum energy up to 17 MeV for
protons from the several MeV limit in the proposal
We have increased the total number of detectors from 5 to 6
The detectors now come in pairs of thin and thick detectors to span the expected range of LET
We varied the diameter of the detectors and the height of the telescope to optimize the
geometrical factor, the fields of view, and the uncertainty in pathlength
Thermal model of the instrument supplied to Goddard, spacecraft model supplied by Goddard
and integrated. Simulations are time-dependent and have been run over multiple lunar orbits
understand thermal variations
Numerical simulations of radiation transport through the current telescope design to study the
expected range of LET measurements
Mechanical model
Hardware currently in development (breadboards, prototypes)
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Designing and procuring parts for our engineering model
Eight detectors for the engineering model have been ordered
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Summary
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We have documented the flow of requirements from project to subassembly
– overall LRO Level 1 requirements down to CRaTER measurements
– CRaTER Level 2 instrument requirements
– CRaTER Level 3 subassembly requirements
• Telescope
• Electronics
Constraints on LRO have been flowed down and captured in the MRD.
We have shown that the CRaTER design can meet the data products we are
responsive to
Detectors for the engineering model have been ordered and beam tests are
being planned
Heritage technology demonstrates that CRaTER design is realizable
• The CRaTER team is ready to proceed with preliminary design
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