Risk Management Strategies During Solar Particle Events on Human Missions to the Moon and Mars: The Myths, the Grail, and the Reality By Dr. Ronald Turner Presented at the workshop on Solar and Space Physics and the Vision for Space Exploration Wintergreen Resort Wintergreen, Virginia October 18, 2005 ANSER Suite South Quincy St Arlington, VA 22206

Outline Background Systems Approach to Radiation Risk Management Conclusions/Observations

The Myths, the Grail, the Reality Solar Particle Events are potent killers and mission showstoppers SPEs can be adequately mitigated with modest shielding We cannot forecast SPEs, and never will A far-side solar observatory is a necessary component to an SPE risk mitigation strategy

The Myths, the Grail, the Reality A dynamic theory and appropriate observations that enable operationally robust models to forecast SPEs at least 6-12 hours prior to onset......Contributing to an overall risk mitigation architecture that includes Adequate shelter, Effective radiation monitoring, Reliable communications, and Integrated mission planning and operations concepts to ensure the safety of astronauts throughout the various phases of missions planned for the space exploration vision

The Myths, the Grail, the Reality There is only one more solar cycle before humans return to the Moon Funding will always be limited Each component of a risk management strategy must demonstrably contribute to enhanced safety of the astronauts on exploration missions

How Bad Can an SPE Be? Selected Historical Events Lunar Surface BFO Radiation Dose (cGy) FEB 56NOV 60AUG 72AUG 89SEP 89OCT 89 CentiGray Differential Fluence Spectra (particles/MeV-cm 2 ) MeV Shielding Thickness (g/cm 2 Aluminum) 5% Chance of Vomiting 5% Chance of Death 10% Chance of Death 50% Chance of Death

What is the Worst Case SPE? Traditionally the assessment of SPE threat is done by analyzing “worst case” historical examples To provide safety factors, the analysis may: Increase flux by a factor of two or more Use composite historical SPEs: Fluence of Aug 72 with the Spectral character of Feb 56 What if the next large SPE is not a simple multiple of Aug 72?

Dose Equivalent Sensitivity to Spectral Character ( Aug 72 Example) Harder Spectra Softer Spectra Aug 72 fit EoEo Normalized Surface BFO Dose-Equivalent >60 MeV Fluence fixed BFO Dose Equivalent >30 MeV Fluence fixed >10 MeV Fluence fixed Slightly harder spectra may increase BFO dose equivalent by a factor of two or more

Dose Equivalent Sensitivity to Spectral Character ( Aug 72 Example) Harder Spectra Softer Spectra Aug 72 fit EoEo Normalized Surface Skin Dose-Equivalent Skin Dose Equivalent >60 MeV Fluence fixed >30 MeV Fluence fixed >10 MeV Fluence fixed Slightly softer spectra may increase skin dose equivalent by an order of magnitude

Potential Elements of an SPE Risk Mitigation Architecture Detection/ForecastReduction Active and passive dosimeters, dose rate monitors Solar imagers, coronagraphs In situ particle, plasma monitors Remote sensing of plasma properties Data/information communications infrastructure Forecast models, algorithms Active and Passive shielding Reconfigurable shielding Storm shelters Pharmacological measures Prescreening for radiation tolerance Particle transport, biological impact models/algorithms Alert/warning communications infrastructure Operational procedures, flight rules

Radiation Safety Information Flow Recommendations to Mission Commander Space Environment Situation Awareness Space Environment Observations Data Archive Space Environment Models Exposure Forecast Dosimetry, Radiation Transport Models Exposure Verification, Validation Impact and Risk Analysis Mission Manifest, Flight Rules, Other Safety Factors Crew Exposure History

Forecasting SPE is a Multidiscipline Challenge Predict the eruption of a CME Predict the character of the CME Predict the efficiency of the CME to accelerate particles Predict the particle escape from shock and subsequent transport through heliosphere

One Approach to Radiation Safety EVA? Consider GCR Radiation Environment Is Mission Within Limits? Is Mission Within Limits? Increase Habitat Shielding Increase Habitat Shielding Model Mission Exposure GCR Consider Worst Case SPE Model Mission Exposure Is Mission Within Limits? Is Mission Within Limits? Add/ Increase Storm Shelter SPE Shielding is the Main Defense against Radiation

Surface Operations are Rule-Driven Astronaut activities are managed against a set of “Flight Rules” These Rules define the overall Concept of Operations (CONOPS) CONOPS should reflect the best science available to the mission planners Translation of research to operations is not trivial and needs thoughtful scientist input

Converting Science to Operations Challenges Under what conditions, and with what probability, would SPEs be significant under modest shielding How can NASA ensure that astronauts are protected during EVA or surface excursions How far should astronauts be permitted to travel away from a “safe haven” Overly-restrictive rules limit the science that can be accomplished Too-lenient rules put the astronauts at risk Under what conditions must they abort an excursion; With how much urgency? Based on what observations? Based on what forecasts? Example

Mission Operations SRAG and Flight Surgeon Space Weather Forecast Center Outlook/ Warning/ Alert Impact/ Options Concept of Surface Operations Dosimeter data Instructions to astronauts Climatology Nowcast Forecast Environment Transport Code Flight Plan Flight Rules Limits Models and Analysis Input Radiation Risk Management Architecture Elements Solar Imager (s) Heliosphere Monitor(s) Particle Environment Monitor(s) Spacecraft HabitatRoverSuit Shielding Dose/Dose Rate Monitors Communications

Radiation Risk Mitigation Objective NASA will establish radiation limits Any mission must be designed to ensure that radiation exposures do not become comparable to these radiation limits Top Level Requirement Reduce the impact of the radiation environment enough to achieve the top level requirement Forecast the radiation environment with adequate timeliness to take appropriate actions System Level Requirements

Radiation Risk Management Investment Strategy Step One: Strategic Decisions Radiation Limits: Lifetime Annual 30-Day Peak Dose Rate? Radiation Risk Management Strategy: Cope and Avoid Anticipate and React Biological Effects Including Uncertainty Risk Philosophy

Radiation Risk Management Investment Strategy Step Two: Mission Design Concept Mission Architecture Elements Spacecraft Habitat Rover Suit (space and surface) Radiation Architecture Elements Shielding Dosimeters Concept of surface operations Space weather architecture

Radiation Risk Management Investment Strategy Step Three: Transit Phase Shielding Analysis Mission Limits Biological Effects Including Uncertainty Risk Philosophy Anticipated Exposure Including Uncertainty Nuclear Cross Section Database Shielding Studies SPE Worst Case SPE Climatology GCR Models Design Reference Mission In Situ Validation Transport Code Development Biological Weighting Factors Dose Estimate Spacecraft Shielding Mass Distribution Composition Transport Analysis Including Uncertainty Peak Dose Rate Estimate Final Mission Design Within Limits? Yes No Modify Shielding

Radiation Risk Management Investment Strategy Step Four: Surface Operations Concept Development Shielding Analysis for Habitat, Rover, Suits Baseline Space Weather Nowcast/Forecast Elements Integrated Surface Operations Plan Dose Estimate Peak Dose Rate Estimate Final Concept of Surface Operations ALARA? Yes No Adjust Surface Operations Plan Metrics affecting “Reasonable” Cost Probability of mission success Operational flexibility Implicit risk in other areas ALARA: As Low As Reasonably Achievable

Solar Imager (s) Heliosphere Monitor(s) Particle Environment Monitor(s) Dose and Dose Rate Monitor(s) Communications Radiation Risk Management Investment Strategy Baseline Space Weather Nowcast/Forecast Elements Climatology Physical Models ? Nowcast Forecast Baseline Space Weather Architecture Yes No Adjust Architecture Robust Timely Complete Reliable Metrics Affecting “Performance” Cost Accuracy/Precision Timeliness Reliability Availability

Radiation Risk Management Investment Strategy SW Architecture Investment Strategy Three Two One Three Two One Three Two One Three Two One Three Two One Three Two One Dosimeter particle monitor plasma monitor solar imager nowcast/ forecast Lunar Mars Express  Three Two One Three Two One Products

A Hard Lesson for Scientists to Learn Intuitively: BETTER BETTER IS THE ENEMY OF GOOD ENOUGH MORE IS BETTER However:

What is “Good Enough” What metrics are appropriate for trade-off studies? Minimizing Biological Impact (by some quantification scheme)? Maximizing Operational Flexibility? Minimizing Total System Cost? Maximizing Probability of Mission Success? How do you effectively create an interdisciplinary team? Spacecraft Designers Operators Biologists Physicists Human Factors Engineers How do you ensure communication between team members? “If I already have enough shielding for a worst case SPE, why do I need a forecast?” “If I could give you a perfect 3-hour forecast, would you do anything different?”

Only One More Solar Cycle to Learn What We Must Learn Solar Cycle 24 Solar Dynamics Sentinels Return to the Moon On to Mars Observatory Human Mission Design STEREO SOHO ACE

Observations Improve Climatology –Probability of exceeding event thresholds –Distribution of spectral hardness –Probability of multiple or correlated events Create Extreme Events Catalogue –Community consensus on contents –Characterize temporal evolution –Spectral character to high energy –Include uncertainties –Composite worst case event Develop and Validate Transport Codes –Agree to standard test cases/benchmarks –Validate in situ as well as in laboratory Develop Reliable “All Clear” Forecasts –Multiple time ranges (six hours, one day, one week)

Conclusions Important time for radiation protection, with advances underway in physics, biology, and the complexity of missions Need for quantification of benefits beyond ALARA Need for operators, biologists, physicists, and others to work together to define optimal system approach Time is right to lay the groundwork for a new paradigm –From: Cope and Avoid –To: Anticipate and React

Backup Slides

Space Weather Contributions to Support the Moon, Mars, and Beyond Vision Better understanding of Solar Dynamics  Improved Forecasting of Coronal Mass Ejections  Improved forecasting of SPEs Better understanding of Heliospheric Dynamics  Improved Forecasting of Solar Wind profiles  Improved forecasting of SPEs Better understanding of SPEs  Improved design of habitats and shelters  Higher confidence in mission planning Better forecasts of SPE evolution after on-set  Higher confidence in exposure forecast  Implementation of more flexible flight rules  Reduced period of uncertainty  Greater EVA scheduling flexibility  Less down-time of susceptible electronics Prediction of SPEs before on-set  Higher confidence in exposure forecast  Greater mission schedule assurance  Less down-time of susceptible electronics Prediction of “all clear” periods  Higher confidence in exposure forecast  Greater EVA scheduling flexibility  Greater mission schedule assurance Improved Safety and Enhanced Mission Assurance