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Cosmic Ray Telescope for the Effects of Radiation (CRaTER) Instrument Requirements

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Title: Cosmic Ray Telescope for the Effects of Radiation (CRaTER) Instrument Requirements


1
Cosmic Ray Telescope for the Effects of
Radiation (CRaTER) Instrument Requirements
Justin Kasper CRaTER Instrument Scientist MIT
Boston University
2
CRaTER Organization Chart
3
Theory of Operation
Pairs of thin and thick Silicon detectors
A-150 Human tissue equivalent plastic (TEP)
4
Theory of Operation
  • Energetic charged particle enters the telescope
  • Particle deposits energy in components through
    ionizing radiation
  • Nuclear interactions produce energetic secondary
    particle
  • Primary and secondary particles interact with
    one or more detectors
  • Thin detectors optimized for high LET particles
  • Thick detectors optimized for low LET particles
  • Detectors with sufficient energy deposition cross
    trigger threshold
  • Digital logic compares coincidence with event
    mask of desirable events
  • Pulse height analysis (PHA) is conducted on every
    detector to measure energy deposition

5
Heritage
  • 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.

6
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

7
Mission Level RequirementsESMD-RLEP-0010
LRO Req. Level 1 Requirements Level 1 Requirements Level 1 Requirements
Instrument LRO Mission Requirement Required Data Products
RLEP-LRO-M10 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-LRO-M20 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.
8
Instrument System Level Requirements
Level 1 Req. Instrument Level 2 IRD 32-01205 Concept/Realizability/ Comment
Requirement 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.
9
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
10
Selected Instrument Subsystem Level Requirements
Level 2 Req. Level 3 Requirements IRD 32-01205 Concept/Realizability/ Comment
Requirement 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
11
Selected Instrument Subsystem Level Requirements
Level 2 Req. Level 3 Requirements IRD 32-01205 Concept/Realizability/ Comment
Requirement 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
12
Selected Instrument Subsystem Level Requirements
Level 2 Req. Level 3 Requirements IRD 32-01205 Concept/Realizability/ Comment
Requirement 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.
13
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). SEP-associated 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
14

CRaTER Science Operations Center Driving Level 3
Requirements
Level 2 Req. Level 3 Driving Requirements Concept/Compliance
Paragraph 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
15
CRaTER Data Flow Concept
16
CRaTER Constraints on LRO
Title Requirement Rationale LRO Requirement
Data Rate 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
17
Instrument Block Diagram
MIT
Aerospace
18
Development Flow
19
Instrument Verification
  • 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
  • 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
  • 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)

20
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 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
  • Major ongoing trade studies which could impact
    either Instrument top-level requirements 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 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)
  • Designing and procuring parts for our engineering
    model
  • Eight detectors for the engineering model have
    been ordered

21
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 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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