Cosmic Ray Telescope for the Effects of Radiation (CRaTER) Instrument Requirements Justin Kasper CRaTER Instrument Scientist MIT & Boston University

CRaTER Organization Chart

Theory of Operation Pairs of thin and thick Silicon detectors A-150 Human tissue equivalent plastic (TEP)

Theory of Operation 1)Energetic charged particle enters the telescope  Particle deposits energy in components through ionizing radiation  Nuclear interactions produce energetic secondary particle 2) Primary and secondary particles interact with one or more detectors  Thin detectors optimized for high LET particles  Thick detectors optimized for low LET particles 3)Detectors with sufficient energy deposition cross trigger threshold 4)Digital logic compares coincidence with event mask of desirable events 5)Pulse height analysis (PHA) is conducted on every detector to measure energy deposition D6 D5 A2 D4 D3 A1 D2 D1 Moon Space

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.

CRaTER Instrument Requirement Documents Level 1 Documents –LRO Program Requirements Document, ESMD-RLEP-0010 Level 2 Documents –CRaTER Instrument Requirements Document, –CRaTER Data Management Plan –LRO Mission Requirements Document, 431-RQMT –LRO Mission Concept of Operations, 431-OPS –LRO Technical Resource Allocations, 431-RQMT –LRO Pointing and Alignment Specification, 431-SPEC –LRO Electrical Systems Specification, 431-SPEC –LRO Mechanical Systems Specification, 431-SPEC –LRO Thermal Systems Specification, 431-SPEC –LRO Mission Assurance Requirements, 431-RQMT –LRO Contamination Control Plan, 431-PLAN –LRO Data Management Plan, 431-PLAN Level 3 –Instrument Payload Assurance Implementation Plan, –LRO to CRaTER Mechanical Interface Document, 431-ICD –LRO to CRaTER Thermal Interface Control Document, 431-ICD –LRO to CRaTER Electrical Interface Control Document, 431-ICD –LRO to CRaTER Data Interface Control Document, 431-ICD –LRO Ground Systems ICD, 431-ICD (MOC to SOC)

Mission Level Requirements ESMD-RLEP-0010 LRO Req. Level 1: Requirements InstrumentLRO Mission RequirementRequired Data Products RLEP-LRO- M10 CRaTERThe 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 CRaTERThe 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.

Instrument System Level Requirements Level 1 Req.Instrument Level 2: IRD Concept/Realizability/ Comment RequirementCRaTER Instrument Measurement Requirement M10-CRaTERL2-01 (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-CRaTERL2-02 (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-CRaTERL2-04 (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-CRaTERL2-05 (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.

Instrument System Level Requirements Level 1 Req.Instrument Level 2: IRD Concept/Realizability/ Comment RequirementCRaTER 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-CRaTERL2-09 (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

Level 2 Req.Level 3: Requirements IRD Concept/Realizability/ Comment RequirementTelescope 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-L2-05L3-02 (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-L2-05L3-03 (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 Selected Instrument Subsystem Level Requirements

Level 2 Req.Level 3: Requirements IRD Concept/Realizability/ Comment RequirementTelescope 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-L2-01L3-07 (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 Selected Instrument Subsystem Level Requirements

Level 2 Req.Level 3: Requirements IRD Concept/Realizability/ Comment RequirementElectronics requirements CRaTER-L2-08L3-08 (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-L2-01L3-09 (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-L2-01L3-10 (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. Selected Instrument Subsystem Level Requirements

CRaTER Data Product Development Data Level Data ProductsInputsESMD Data Product 0Unprocessed instrument data (pulse height at each detector, plus secondary science) and housekeeping data. Raw science and housekeeping data from MOC 1Depacketed science data at 1-s resolution.Level 0 data, and spacecraft attitude data, calibration files. 2Pulse 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 3Data 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 4Calculation 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

CRaTER Science Operations Center Driving Level 3 Requirements Level 2 Req. Level 3: Driving RequirementsConcept/Compliance ParagraphRequirement MRD-055 Data Product Delivery CRaTER DMP, #TBD Process up to 8.6 Gbits/dayComputing 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

CRaTER Data Flow Concept

CRaTER Constraints on LRO TitleRequirementRationaleLRO Requirement Data RateSpacecraft shall handle a peak data rate of 100 kbps 1250 events/second during peak solar activityMRD-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 degreesMRD-71, Fields of View Pointing Knowledge Pointing knowledge to within 10 degrees Knowledge of instrument orientationMRD-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

Instrument Block Diagram Aerospace MIT

Development Flow

Instrument Verification The CRaTER Performance and Environmental Verification Plan ( ) describes the plan to verify the CRaTER requirements in accordance with the CRaTER Calibration Plan ( ), CRaTER Contamination Control Plan ( ), and the CRaTER Performance Assurance Implementation Plan ( ) 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)

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

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