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

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

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

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

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

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

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

Evolution of proton spectrum through stack January 20 2005 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

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

Instrument System Level Requirements 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. 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

Instrument System Level Requirements 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 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

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

Selected Instrument Subsystem Level Requirements 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 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

Selected Instrument Subsystem Level Requirements 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 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

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

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