c osmic ra y t elescope for the e ffects of r adiation ( crater ): science overview

Cosmic RAy Telescope for the Effects of Radiation

Cosmic Ray Telescope for the Effects of Radiation

(CRaTER): Science Overview

Harlan E. Spence, Principal InvestigatorHarlan E. Spence, Principal InvestigatorBoston University

Department of Astronomy and Center for Space Physics


• PhD, Earth and Space Science, UCLA, 1989• Sr. Mem. of the Tech. Staff, The Aerospace Corp., 89-94 (“casual status” now)• Professor of Astronomy, Boston University, 1994-present

• Lead instrument scientist of Imaging Proton Spectrometer on NASA/POLAR s/c (led design, development, testing, and calibration)

• Co-I on CEPPAD and CAMMICE energetic particle instruments on POLAR• Co-investigator on energetic particle instrument suite on recently-selected

SMART consortium for NASA/MMS Mission

My BackgroundMy Background

NASA POLAR IPS instrument and analog board POLAR CEPPAD


CRaTER Science TeamCRaTER Science Team and and Key PersonnelKey Personnel

NameName InstitutionInstitution RoleRole

Harlan E. Spence BU PI

Larry Kepko “ Co-I (E/PO, Cal, IODA lead)

Justin Kasper MIT Co-I (Project Scientist)

Bernie 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 MIT Project Manager

Bob Goeke “ Systems Engineer

Brian Klatt “ Q&A

Chris Sweeney BU Instrument Test Lead


Science/Measurement OverviewScience/Measurement OverviewCRaTER 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. ”


So What? Powerful Solar Variability. 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

Image credit: J. KoemanJanuary 15, 2005


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


• 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

Magnitude and Scope of Effects?Magnitude and Scope of Effects?


How Big is Big? Potentially Fatal.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 eventBig Bear Solar Observatory


Why Characterize Radiation Sources? 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 SourceGalactic Cosmic Rays: Another Source

Crab Nebula (ESO) Advanced Composition Explorer


When Is It Safe? Almost never.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

(plot courtesy R. Mewaldt, Cal Tech)

SEP events

SolarMinimum

At solar minimum:•Min SEP occurrence•Max GCR flux


CRaTER As-Proposed Traceability MatrixCRaTER As-Proposed Traceability Matrix


Science Measurement ConceptScience Measurement Concept


• GCR/SCR 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

Rationale for LET SpectraRationale for LET Spectra


• 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

Science TradesScience Trades


Example Science Trade Study Modification Example Science Trade Study Modification from As-proposedfrom As-proposed

Five-element detector stack with 3 volumes of

TEP sandwiched between

Six-element detector stack with 2 volumes of TEP sandwiched

between

D6

D5

A2

D4

D3

A1

D2

D1

Moon

Space

Cylindrical telescope rather

than conical

c osmic ra y t elescope for the e ffects of r adiation ( crater ): science overview

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