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Cosmic Ray Telescope for theEffects of Radiation (CRaTER)

Instrument Requirements

Justin Kasper

CRaTER Instrument Scientist

MIT & Boston University

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CRaTER Organization Chart

Rick FosterProgram Manager

Project Manager

Jimmy O’Conner

MITFabrication

Mgr

Brian KlattMIT

Mission Assurance Mgr

Kristin SaccaBU

Coordinator

Robert GoekeMIT

Project Engineer

Friday , June 17, 2005

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CRaTER Instrument Management Team

Christine ComaceauAerospace

Project Manager

Harlan SpenceBUPI

CRaTER Science Working Group

Aerospace Support

Robert GoekeMIT

Project Engineer

Aerospace Corp

MIT Boston

University

Chris SweeneyI&T Lead

Bill CrainSr. Electrical

Engineer

Albert LinMechanical Engineer

Matt SmithMechanical Engineer

Mike DoucetteTest Engineer

Dorothy GordanElectrical Engineer

Monday, August 01, 2005

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CRaTER Project Engineering

Rick FosterProgram Manager

Project Manager

Jimmy O’Conner

MITFabrication

Mgr

Brian KlattMIT

Mission Assurance Mgr

Kristin SaccaBU

Coordinator

Robert GoekeMIT

Project Engineer

Friday , June 17, 2005

Page 1

CRaTER Instrument Management Team

Christine ComaceauAerospace

Project Manager

Harlan SpenceBUPI

CRaTER Science Working Group

Aerospace Support

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Theory of Operation

Pairs of thin andthick Silicondetectors

A-150 Human tissueequivalent plastic(TEP)

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Theory of Operation

1) Energetic charged particle enters the telescope Particle deposits energy in components through

ionizing radiation

Nuclear interactions produce energetic secondaryparticle

2) Primary and secondary particles interact with oneor more detectors Thin detectors optimized for high LET particles

Thick detectors optimized for low LET particles

3) Detectors with sufficient energy deposition crosstrigger threshold

4) Digital logic compares coincidence with event maskof desirable events

5) Pulse height analysis (PHA) is conducted on everydetector to measure energy deposition

D6

D5

A2

D4

D3

A1

D2

D1

Moon

Space

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Heritage

• CRaTER is not directly derived from an existing instrument.

• The three teams (BU, MIT, Aerospace) with engineering tasks have allproduced particle instruments for spaceflight.

• The company providing the silicon semiconductors (Micron Semiconductor)has produced detectors for many successful flights. The particular detectorswe 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, includinginvestigations on the space station.

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CRaTER Instrument Requirement Documents

• Level 1 Documents– LRO Program Requirements Document, ESMD-RLEP-0010

• Level 2 Documents– 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– 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 RequirementsESMD-RLEP-0010

The LRO shall characterize the deepspace radiation environment in lunarorbit, including biological effects causedby exposure to the lunar orbital radiationenvironment.

The LRO shall characterize the deepspace radiation environment in lunarorbit, including neutron albedo.

LRO Mission Requirement

Investigate the effects of shielding by measuring LETspectra behind different amounts and types of arealdensity, including tissue-equivalent plastic.

CRaTERRLEP-LRO-M20

Measure and characterize that aspect of the deep spaceradiation environment, Linear Energy Transfer (LET)spectra of galactic and solar cosmic rays (particularlyabove 10 MeV), most critically important to theengineering and modeling communities to assure safe,long-term, human presence in space.

CRaTERRLEP-LRO-M10

Required Data ProductsInstrument

Level 1: RequirementsLRO

Req.

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Instrument System Level Requirements

Detect low energy secondaryparticles without approachingnoise level of detector.

The minimum energy deposition measured by the Silicondetectors is 200 keV.

L2-05 (4.5)M20-CRaTER

Measure LET evolutionthrough different arealdensities of TEP.

The TEP is broken into two sections, 27 and 54 mm in height.L2-04 (4.4)M20-CRaTER

100 MeV particles justpenetrate; telescope mass isdominated by the TEP.

The minimum pathlength through the total amount of TEP inthe telescope is 61 mm.

L2-03 (4.3)M10-CRaTER,M20-CRaTER

Place sections of TEP betweensilicon detectors

Measure change in LET through A-150 human tissueequivalent plastic (TEP).

L2-02 (4.2)M20-CRaTER

Measure current produced byelectron-hole pair productionin silicon semiconductordetectors

Measure the linear energy transfer (LET) spectrum dE/dx,defined as the energy dE deposited in a silicon detector ofthickness dx.

L2-01 (4.1)M10-CRaTER

CRaTER Instrument Measurement RequirementRequirement

Concept/Realizability/

CommentInstrument Level 2: IRD 32-01205Level 1 Req.

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Instrument System Level Requirements

Good statistics for high energygalactic cosmic rays

The geometrical factor created by the first and last detectorsshall be at least 0.1 cm2 sr.

L2-09 (4.9)M10-CRaTER

To characterize the LETspectrum accurately andsimplify the comparisonbetween theory andobservations

The pulse height analysis of the energy deposited in eachdetector will have an energy resolution of at least 1/300 themaximum energy of that detector.

L2-08 (4.8)M10-CRaTER,M20-CRaTER

This is above the maximumexpected LET due to stoppingiron nuclei

At each point in the telescope where the LET spectrum is tobe observed, the maximum LET measured will be no lessthan 7 MeV/ micron.

L2-07 (4.7)M10-CRaTER,M20-CRaTER

Sufficient to see minimumionizing primary particles andstopping secondaries

At each point in the telescope where the LET spectrum is tobe observed, the minimum LET measured shall be no greaterthan 0.2 keV/ micron.

L2-06 (4.6)M10-CRaTER,M20-CRaTER

CRaTER Instrument Measurement RequirementRequirement

Concept/Realizability/

CommentInstrument Level 2: IRD 32-01205Level 1 Req.

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sufficient accuracy forsubsequent modeling efforts toreproduce the observed LET

The uncertainty in the length of TEP traversed by a particlethat traverses the entire telescope axis shall be less than 10%.

L3-05 (6.5)CRaTER-L2-01,CRaTER-L2-02,CRaTER-L2-03

LET measurements will bemade on either side of eachpiece of TEP to understand theevolution of the spectrum as ispasses through matter.

The telescope will consist of a stack of components labeledfrom the nadir side as zenith shield (S1), the first pair of thin(D1) and thick (D2) detectors, the first TEP absorber (A1), thesecond pair of thin (D3) and thick (D4) detectors, the secondTEP absorber (A2), the third pair of thin (D5) and thick (D6)detectors, and the final nadir shield (S2).

L3-04 (6.4)CRaTER-L2-01,CRaTER-L2-02,CRaTER-L2-04,CRaTER-L2-05

Cut flux of protons withenergy less than 17 MeVcoming through telescope

The zenith and nadir sides of the telescope shall have no lessthan 0.06” of aluminum shielding.

L3-03 (6.3)CRaTER-L2-05

Cut flux of protons withenergy less than 17 MeVcoming through side

The shielding due to the mechanical housing the CRaTERtelescope outside of the zenith and nadir fields of view shallbe no less than 0.06” of aluminum.

L3-02 (6.2)CRaTER-L2-05

The LET range specified in theLevel 2 requirements wouldrequire an unrealistic factor of5000 dynamic range

The telescope stack will contain adjacent pairs of thin(approximately 140 micron) and thick (approximately 1000micron) Si detectors. The thick detectors will be used tocharacterize energy deposition between approximately 200keV and 100 MeV. The thin detectors will be used tocharacterize energy deposits between 2 MeV and 1 GeV.

L3-01 (6.1)CRaTEr-L2-01,

CRaTER-L2-05,

CRaTER-L2-06,

CRaTER-L2-07,

CRaTER-L2-08

Telescope requirementsRequirement

Concept/Realizability/

CommentLevel 3: Requirements IRD 32-01205Level 2 Req.

Selected Instrument Subsystem LevelRequirements

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Trade off accuracy of LETmeasurements for particles oflunar origin to increasegeometrical factor sinceshould be rare

The nadir field of view, defined as D3D6 coincident eventsincident from the lunar surface, will be 75 degrees full width.

L3-07 (6.7)CRaTER-L2-01

leads to a sufficientgeometrical factor while stilllimiting the uncertainty in thepathlength

The zenith field of view, defined as D1D4 coincident eventsincident from deep space, will be 35 degrees full width.

L3-06 (6.6)CRaTER-L2-01,

CRaTER-L2-02

Telescope requirementsRequirement

Concept/Realizability/

CommentLevel 3: Requirements IRD 32-01205Level 2 Req.

Selected Instrument Subsystem LevelRequirements

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Keep up with rates duringintense storms, but recognizethat this rate is sufficient toyield necessary statisticsduring flares.

The maximum event rate CRaTER will transmit will be 1,250events per second.

L3-10 (6.10)CRaTER-L2-01

May focus on subset ofcoincidences, especiallyduring periods of intense solaractivity

A command may be sent to CRaTER to identify the set ofdetector coincidences that should be analyzed and sent to thespacecraft.

L3-09 (6.9)CRaTER-L2-01

Verify operation withoutradioactive sources, identifydetector response evolutionafter testing and launch

The CRaTER electronics will be capable of injectingcalibration signals at 256 energies into the measurementchain.

L3-08 (6.8)CRaTER-L2-08

Electronics requirementsRequirement

Concept/Realizability/

CommentLevel 3: Requirements IRD 32-01205Level 2 Req.

Selected Instrument Subsystem LevelRequirements

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CRaTER Data Product Development

RLEP-LRO-M10

RLEP-LRO-M20

Level 2 data, spacecraft location, NOAASpace Environment Center (SEC) solaractivity alerts and summary data

Data organized by particle environment(GCR foreshock, magnetotail). SEP-associated events identified and extracted.

3

RLEP-LRO-M10

RLEP-LRO-M20

Level 1 data, pulse-height to energyconversions based on pre-launchaccelerator experiments and updated baseon in-flight calibration system

Pulse heights converted into energydeposited in each detector. Calculation ofSi LET

2

Calculation of incident energies frommodeling/calibration curves and TEP LETspectra

Depacketed science data at 1-s resolution.

Unprocessed instrument data (pulse heightat each detector, plus secondary science)and housekeeping data.

Data Products

Level 3 data, spectral density of major ionsfrom hydrogen through iron as measured bynear-Earth spacecraft including ACE,GOES, IMP-8, output from numericalsimulations

Level 0 data, and spacecraft attitude data,calibration files.

Raw science and housekeeping data fromMOC

Inputs

RLEP-LRO-M20

ESMD DataProduct

4

1

0

DataLevel

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CRaTER Science Operations CenterDriving Level 3 Requirements

Plot singles rates andcalibration output

Analyze and trend instrument performance.CRaTERDMP, #TBD

MRD-055

Data Product

Delivery

Same cycle every dayDevelop CRaTER command schedule for MOC.CRaTERDMP, #TBD

MRD-055

Data Product

Delivery

Computing sizeProcess up to 8.6 Gbits/dayCRaTERDMP, #TBD

MRD-055

Data Product

Delivery

RequirementParagraph

Concept/ComplianceLevel 3: Driving RequirementsLevel 2

Req.

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CRaTER Data Flow Concept

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CRaTER Constraints on LRO

MRD-71, Fields ofView

Deep space field of view for D1D4 is 35degrees

No obstruction in 40 degreezenith field of regard

ZenithField ofRegard

MRD-71, Fields ofView

Lunar field of view for D3D6 is 35 degreesNo obstructions in 80 degreenadir field of regard

Nadir Fieldof Regard

MRD-14, NadirPointing

MRD-49, PointingAllocations

Insure telescope is always pointing at Lunarsurface

Telescope axis is aligned within35 degree of lunar surfaceduring nominal operation

PointingAccuracy

MRD-49, PointingAllocations

Knowledge of instrument orientationPointing knowledge to within 10degrees

PointingKnowledge

MRD-35, Low RateData

1250 events/second during peak solar activitySpacecraft shall handle a peakdata rate of 100 kbps

Data Rate

LRO RequirementRationaleRequirementTitle

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Instrument Block Diagram

Aerospace

MIT

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Development Flow

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Instrument Verification• The CRaTER Performance and Environmental Verification Plan (32-01206) describes

the plan to verify the CRaTER requirements in accordance with the CRaTERCalibration Plan (32-01207), CRaTER Contamination Control Plan (32-01203), and theCRaTER Performance Assurance Implementation Plan (32-01204)

• The verification program is designed to provide the verifications listed below:– 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 theevolution of the LET spectrum after propagation through the TEP

• Reporting– 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 themalfunction. A malfunction may result in premature test termination, depending on operationprocedures. Regardless of this, a malfunction report will be filed with the Verification Reportfor the activity.

– Detailed test procedures and specifications will be written, reviewed, and approved by theCRaTER Project, prior to instrument-level verification testing. The lead individual for eachprocedure depends upon the category: Environmental Requirements (Project Engineer);Performance Requirements (Project Scientist); Contamination Requirements (ContaminationEngineer); Interface Requirements (Cognizant Design Engineer); Calibration Requirements(Project Scientist)

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Instrument Current Status• Major trade studies since Instrument inception which have been closed

– We have decided to use two pieces of TEP with different lengths instead of the three TEPsections in the original proposal

– We have increased the thickness of the shielding to raise the minimum energy up to 17 MeV forprotons 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

• Major ongoing trade studies which could impact either Instrument top-levelrequirements or the interface to the Spacecraft

– None

• Analyses currently being performed– 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 orbitsunderstand thermal variations

– Numerical simulations of radiation transport through the current telescope design to study theexpected range of LET measurements

– Mechanical model

• Hardware currently in development (breadboards, prototypes)– Designing and procuring parts for our engineering model– Eight detectors for the engineering model have been ordered

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Summary

• 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 areresponsive to

• Detectors for the engineering model have been ordered and beam tests arebeing planned

• Heritage technology demonstrates that CRaTER design is realizable

• The CRaTER team is ready to proceed with preliminary design