1. CRaTER Science Requirements
Lunar Reconnaissance Orbiter
CRaTER Preliminary Design Review
Justin Kasper (CRaTER Proj. Sci.)

2. J. C. Kasper – CRaTER PDR - Science Requirements
Outline
Energy deposition
Classical ionizing radiation
Nuclear fragmentation
Modeling for trade studies
Fields of view
Particle fluxes and counting rates
Evolution of spectrum through instrument
Science Requirements Flowdown
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

3. Classical ionizing radiation
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

4. Nuclear fragmentation of 1 GeV/nuc Fe
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

5. Modeling Capabilities
SRIM-2003
Monte Carlo with range tables
IDL
Stopping from SRIM
Instrument object
Particle spectra
GEANT & FLUKA
Spectrum of secondaries produced by propagation through telescope
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

6. J. C. Kasper – CRaTER PDR - Science Requirements
Fields of view
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

7. Maximum singles detector rates
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

8. Evolution of proton spectrum through stack
January
Proton flux [p cm-2 s-1 sr-1 (MeV/nuc)-1]
Energy deposited in component [MeV]
Energy [MeV]
Energy [MeV]
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

9. Mission Level Requirements ESMD-RLEP-0010
LRO
Req.
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
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.
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

10. Instrument System Level Requirements
Instrument Level 2: IRD
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.
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.
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.
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

11. Instrument System Level Requirements
Instrument Level 2: IRD
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
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
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

12. Level 3: Requirements IRD 32-01205 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
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

13. Selected Instrument Subsystem Level Requirements
Level 3: Requirements IRD
Concept/Realizability/
Comment
Requirement
Telescope requirements
CRaTER-L2-01,
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

14. Selected Instrument Subsystem Level Requirements
Level 3: Requirements IRD
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
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.
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

15. J. C. Kasper – CRaTER PDR - Science Requirements
Conclusions
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
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
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements

16. J. C. Kasper – CRaTER PDR - Science Requirements
06/28/2005
J. C. Kasper – CRaTER PDR - Science Requirements