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 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

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
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 rates CRaTER gets 100kbits/sec!!

16. Extra slides

17. 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

18. 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

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. 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