C osmic Ra y T elescope for the E ffects of R adiation ( CRaTER )

1. Cosmic Ray Telescope for the Effects of Radiation(CRaTER) Harlan E. Spence, Principal Investigator Boston University Department of Astronomy and Center for Space Physics

2. What do we know? • Pristine GCR and SEP spectra (well enough) in near-lunar (and other nearly interplanetary environments) • What don’t we know? • How GCR/SEP particles are transported through matter and how energy is desposited (e.g., LET), particularly the heavy ions and at high energy – these are needed to validate models which are currently nearly our only resource for this biologically important ionizing radiation component. What is actual LET spectrum from GCR/SEP at moon (interplanetary space)? • What do we need to do? • Instruments like CRaTER on LRO providing missing link between model/theory-data closure on effects; RAD on MSL providing data for validating SEP/GCR models • Modeling efforts like BBFRAG, HETC-HEDS, FLUKA, etc. • Better connection with radiation biology and EE communities to provide measurements of value to their needs

3. 2008 Lunar Reconnaissance Orbiter (LRO)First Step in the Robotic Lunar Exploration Program • LRO Objectives • Characterization of the lunar radiation environment, biological impacts, and potential mitigation. Key aspects of this objective include determining the global radiation environment, investigating the capabilities of potential shielding materials, and validating deep space radiation prototype hardware and software. • Develop a high resolution global, three dimensional geodetic grid of the Moon and provide the topography necessary for selecting future landing sites. • Assess in detail the resources and environments of the Moon’s polar regions. • High spatial resolution assessment of the Moon’s surface addressing elemental composition, mineralogy, and Regolith characteristics

4. LRO Mission OverviewOrbiter LRO Instruments • Lunar Orbiter Laser Altimeter (LOLA) Measurement Investigation – LOLA will determine the global topography of the lunar surface at high resolution, measure landing site slopes and search for polar ices in shadowed regions. • Lunar Reconnaissance Orbiter Camera (LROC) – LROC will acquire targeted images of the lunar surface capable of resolving small-scale features that could be landing site hazards, as well as wide-angle images at multiple wavelengths of the lunar poles to document changing illumination conditions and potential resources. • Lunar Exploration Neutron Detector (LEND) – LEND will map the flux of neutrons from the lunar surface to search for evidence of water ice and provide measurements of the space radiation environment which can be useful for future human exploration. • Diviner Lunar Radiometer Experiment – Diviner will map the temperature of the entire lunar surface at 300 meter horizontal scales to identify cold-traps and potential ice deposits. • Lyman-Alpha Mapping Project (LAMP) – LAMP will observe the entire lunar surface in the far ultraviolet. LAMP will search for surface ices and frosts in the polar regions and provide images of permanently shadowed regions illuminated only by starlight. • Cosmic Ray Telescope for the Effects of Radiation (CRaTER) – CRaTER will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation. LRO Preliminary Design

5. Competitively Selected LRO Instruments Provide Broad Benefits

6. Science/Measurement Overview CRaTER Objectives: “To characterize the global lunar radiation environment and its biological impacts.” “…to address the prime LRO objective and to answer key questions required for enabling the next phase of human exploration in our solar system. ”

8. Rationale for LET Spectra • GCR/SEP parent spectra will be measured by other spacecraft during LRO mission • Biological assessment requires not the incident CR spectrum, but the LET spectra behind tissue-equivalent material • LET spectra are a missing link, currently derived largely by models; we require experimental measurements to provide critical ground truth – CRaTER will provide information needed for this essential quantity

9. 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

10. Science Measurement Concept

11. CRaTER Traceability Matrix • Current energy spectral range: • 200 keV to 100 MeV (low LET); and • 2 MeV to 1 GeV (high LET) • This corresponds to: • a range of LET from 0.2 keV/m to 7 MeV/m (stopping 1 Gev/nuc Fe-56) • good spectral overlap in the 100 kev/m range (key range for RBEs)

12. CRaTER Telescope Configuration

13. Nuclear fragmentation of 1 GeV/nuc Fe

14. 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]

15. Maximum singles detector ratesCRaTER gets 100kbits/sec!!

16. Extra slides

17. CRaTER Science Team and Key Personnel

18. So What? Powerful Solar Variability. January 15, 2005 • Near solar minimum • Few sunspots • Few flares • Quiet corona • Giant sunspot 720 • Sudden appearance • Strong magnetic field • Very large • On west limb by January 20 Image credit: J. Koeman

19. Who Cares? Astronauts, s/c Operators dt < 30 minutes

20. Magnitude and Scope of Effects? • ISS: 1 REM (Roentgen Equivalent Man, 1 REM ~ 1 CAT Scan) • Scintillations • Hardened shelter • Spacesuit on moon 50 REM (Radiation sickness) • Vomiting • Fatigue • Low blood cell counts • 300 REM+ suddenly • Fatal for 50% within 60 days • Also • Two communication satellites lost • Airplanes diverted from polar regions • Satellite tracking problems, degradation in solar panels

21. How Big is Big? Potentially Fatal. • Apollo 16 in April 1972 • Flare on August 7, 1972 • Apollo 17 that December • Derived dosage 400 REM • Michener’s “Space” is based on this event Big Bear Solar Observatory

22. Why Characterize Radiation Sources? To understand risks to: • Astronauts • Radiation Poisoning from sudden events • Heightened long-term risk • Cancer • Cataracts • Spacecraft examples • Single event upsets • Attitude (Sun pulse & star tracker) • Radiation damage

23. Galactic Cosmic Rays: Another Source Crab Nebula (ESO)

24. When Is It Safe? Almost never. • GCR flux is low-level but continuous and has weak solar cycle dependence • Intense SEPs (>10 MeV p+) are episodic and approximately follow the solar cycle • SEP event occurrence varies with the solar cycle in anti-phase with weaker galactic cosmic ray fluxes SEP events • At solar minimum: • Min SEP occurrence • Max GCR flux Solar Minimum

25. Science Trades • As-proposed design has evolved in response to selection debrief and as a result of detailed knowledge of s/c configuration and instrument accommodation • Science trade studies ongoing to refine telescope configuration – basic design is unchanged; internal configuration modified in response to simulation studies • Other science/engineering trade studies are underway • CRaTER science requirements essentially unchanged – flowdown to be presented by J. Kasper

26. Moon D6 D5 A2 D4 D3 A1 D2 D1 Space Example Science Trade Study Modification from As-proposed Cylindrical telescope rather than conical Six-element detector stack with 2 volumes of TEP sandwiched between Five-element detector stack with 3 volumes of TEP sandwiched between