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

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

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

LRO Mission Overview Orbiter 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 Preliminary LRO Characteristics Mass 1317 kg Dry: 603 kg Fuel: 714 kg Power 745 W Measurement Data Volume 575 Gb/day

Competitively Selected LRO Instruments Provide Broad Benefits

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. ”

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

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

Science Measurement Concept

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)

CRaTER Telescope Configuration

Nuclear fragmentation of 1 GeV/nuc Fe

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]

Maximum singles detector rates CRaTER gets 100kbits/sec!!

Extra slides

CRaTER Science Team and Key Personnel Name Institution Role Harlan E. Spence BU PI Larry Kepko “ Co-I (E/PO, Cal, IODA lead) Justin Kasper MIT Co-I (Project Scientist) Bern Blake Aerospace Co-I (Detector lead) Joe Mazur Co-I (GCR/SCR lead) Larry Townsend UT Knoxville Co-I (Modeling lead) Michael Golightly AFRL Collaborator (Biological effects) Terry Onsager NOAA/SEC Collaborator (CR measurements) Rick Foster Project Manager Bob Goeke Systems Engineer Brian Klatt Q&A Chris Sweeney Instrument Test Lead

So What? Powerful Solar Variability. 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 January 15, 2005 Image credit: J. Koeman

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

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

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

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

Galactic Cosmic Rays: Another Source Crab Nebula (ESO)

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

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

Example Science Trade Study Modification from As-proposed Moon 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