Transcript Science Flowdown

CRaTER Science Requirements
Lunar Reconnaissance Orbiter
CRaTER Preliminary Design Review
Justin Kasper (CRaTER Proj. Sci.)
Cosmic RAy Telescope for the Effects of Radiation
Outline
 Energy deposition
 Classical ionizing radiation
 Nuclear fragmentation
 Modeling for trade studies
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Energy deposition
Fields of view
Particle fluxes and counting rates
Evolution of spectrum through instrument
 Science Requirements Flowdown
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Level 1 mission requirements in ESMD-RLEP-0010
Flowdown to CRaTER instrument and subsystem requirements
Captured in CRaTER Instrument Requirements Document (IRD)
Presented at spacecraft requirements review
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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Classical ionizing radiation
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Energy loss: Electromagnetic (electrons and nucleus) and nuclear (spallation)
Nuclear interactions occur in a fraction of events
Above plots are from a SRIM-2003 simulation of 50 MeV protons in human tissue
Cosmic RAy Telescope for the Effects of Radiation
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J. C. Kasper – CRaTER PDR - Science Requirements
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Nuclear fragmentation of 1 GeV/nuc Fe
Cosmic RAy Telescope for the Effects of Radiation
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Modeling Capabilities
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SRIM-2003
– Monte Carlo with range tables
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IDL
– Stopping from SRIM
– Instrument object
– Particle spectra
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GEANT & FLUKA
– Spectrum of secondaries produced by
propagation through telescope
Cosmic RAy Telescope for the Effects of Radiation
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J. C. Kasper – CRaTER PDR - Science Requirements
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Fields of view
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Maximum singles detector rates
Cosmic RAy Telescope for the Effects of Radiation
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January 20 2005
Energy [MeV]
Energy deposited in component [MeV]
Proton flux [p cm-2 s-1 sr-1 (MeV/nuc)-1]
Evolution of proton spectrum through stack
Energy [MeV]
Cosmic RAy Telescope for the Effects of Radiation
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J. C. Kasper – CRaTER PDR - Science Requirements
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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.
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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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.
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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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
Cosmic RAy Telescope for the Effects of Radiation
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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 more
than 0.06” of aluminum shielding.
Cut flux of protons with
energy less than 10 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
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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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-L201,
CRaTER-L2-02
L3-06 (6.6)
The zenith field of view, defined as D1D6 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
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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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.
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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Conclusions
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We have a documented 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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Simulations and analytic calculations have been conducted
– To demonstrate that the instrument design can meet the requirements
– To optimize the instrument performance with the available resources
Cosmic RAy Telescope for the Effects of Radiation
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements
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Cosmic RAy Telescope for the Effects of Radiation
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J. C. Kasper – CRaTER PDR - Science Requirements
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