Cosmic RAy Telescope for the Effects of Radiation
(CRATER)
Spacecraft Requirements Review Presentation
August 2005
Justin Kasper
CRaTER Instrument Scientist
Boston University
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CRaTER Organization Chart
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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 respond to high LET particles
 Thick detectors respond to 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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Instrument Documents
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LRO Program Requirements Document; ESMD-RLEP-0010
– LRO Mission Requirements Document; 431-RQMT-00004
• LRO Technical Resource Allocations; 431-RQMT-000112
• Instrument Payload Assurance Implementation Plan
• Instrument to Spacecraft Interface Control Documents (Mechanical 431-ICD-000085, Thermal 431-ICD000118, Electrical 431-ICD-000094 & Data 431-ICD-000104)
CRaTER Project controlled documents (Configuration database: http://snebulos.mit.edu/crater/)
– 32-01200 Instrument Requirements, Plans, and Procedures
• 32-01201 A ..Configuration Management and Peer Review Process
• 32-01201.01 ....Aerospace Procedure
• 32-01201.02 ....BU Procedure
• 32-01201.03 ....MIT Procedure
• 32-01202 01 ..Risk Management Plan
• 32-01203 06 ..Contamination Control Plan
• 32-01204 A ..Performance Assurance Implementation Plan
• 32-01205 01 ..Instrument Requirements Document
• 32-01206 01 ..Performance and Environmental Verification Plan
• 32-01206.01 01 ..Environmental Verification Text Matrix
• 32-01207 ..Instrument Calibration Plan
– 32-02000 Interface Control Documents
• 32-02001 B ..Spacecraft to CRaTER Data ICD
• 32-02002 02 ..Spacecraft to CRaTER Electrical ICD GSFC 431-ICD-000094; Draft 6/23/05
• 32-02002.01 04 ....Generic LRO EICD GSFC 431-ICD-000008; Draft 6/20/05
• 32-02003 03 ..Spacecraft to CRaTER Mechanical ICD GSFC 431-ICD-000085; Draft 6/27/05
• 32-02003.01 01 ....Generic LRO MICD GSFC 431-ICD-xxxxxx; Draft 4/15/05
• 32-02003.02 A ....Mechanical Interface Drawing
• 32-02004 02 ..Spacecraft to CRaTER Thermal ICD GSFC 431-ICD-000118; Draft 1.1 4/16/05 D
• 32-02004.01 01 ....Outline Drawing
• 32-02052 01 ..Analog to Digital Subsystem Electrical ICD
• 32-02053 ..Telescope to Electronics Subsystem Mechanical ICD
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Mission Level Requirements
ESMD-RLEP-0010
LRO
Req.
Level 1: Requirements
LRO Mission Requirement
Required Data Products
RLEP-LROM10
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
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
(IRD section)
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
(IRD section)
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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Instrument Subsystem Level Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Requirement
(IRD Section)
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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Instrument Subsystem Level Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Requirement
(IRD Section)
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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Instrument Subsystem Level Requirements
Level 2 Req.
Level 3: Requirements IRD 32-01205
Concept/Realizability/Comment
Requirement
(IRD Section)
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
and detector response
evolution after testing and
launch
CRaTER-L2-01
L3-09 (6.9)
A command may be send 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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Data Product Traceability
Data Level
Description
Required Inputs
Level 0
Unprocessed instrument data (pulse height at
each detector, plus secondary science) and
housekeeping data.
Instrument data.
Level 1
Depacketed science data, at 1-s resolution.
Ancillary data pulled in (spacecraft attitude,
calibration files, etc.)
Spacecraft data.
Level 2
Pulse heights converted into energy deposited in
each detector. Calculation of Si LET (M10CRaTER, M20-CRaTER)
Pulse-height to energy conversions based on prelaunch accelerator experiments and updated
based on in-flight calibration system
Level 3
Data organized by particle environment (GCR,
foreshock, magnetotail). SEP-associated events
identified and extracted. (M10-CRaTER, M20CRaTER)
Spacecraft location; NOAA Space Environment
Center (SEC) solar activity alerts and summary
data
Level 4
Calculation of incident energies from
modeling/calibration curves and TEP LET spectra
(M20-CRaTER)
Spectral density of major ions from hydrogen
through iron as measured by near-Earth
spacecraft including ACE, GOES, IMP-8; Output
from numerical simulations
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Instrument Constraints on LRO
• Handle peak data rate of 100 kbps
– 1250 events/second during peak solar activity
• No obstructions in 40 degree zenith field of regard
– Deep space field of view for D1D4 event is 35 degrees
• No obstructions in 80 degree nadir field of regard
– Lunar field of view for D3D6 event is 35 degrees
• Pointing knowledge to within 10 degrees
• Telescope axis aligned within 35 degrees of lunar surface during
nominal operations
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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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Schedule
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Schedule
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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
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Constraints on LRO have been flowed down and captured in the MRD.
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We have shown that the CRaTER design can meet the data products we are
responsive to
CRaTER is a low-risk project with mass, power, budget, and schedule margins
Detectors for the engineering model have been ordered and beam tests are
being planned
The science and engineering teams are converting the instrument requirements
into a functional instrument description in preparation for PDR
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