Risk Management Strategies During Solar Particle Events on Human Missions to the Moon and Mars: The Myths, the Grail, an

1. Risk Management Strategies During Solar Particle Events on Human Missions to the Moon and Mars:The Myths, the Grail, and the Reality Presented at the workshop on Solar and Space Physics and the Vision for Space Exploration Wintergreen Resort Wintergreen, Virginia October 18, 2005 By Dr. Ronald Turner ANSER Suite 800 2900 South Quincy St Arlington, VA 22206

2. Outline • Background • Systems Approach to Radiation Risk Management • Conclusions/Observations

3. 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

4. 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

5. 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

6. 50% Chance of Death 10% Chance of Death 5% Chance of Death 5% Chance of Vomiting Differential Fluence Spectra (particles/MeV-cm2) 109 107 105 103 101 10-1 30.0 10.0 5.0 0.3 10-3 100 1000 10 MeV How Bad Can an SPE Be?Selected Historical Events Lunar Surface BFO Radiation Dose (cGy) 1000.0 100.0 CentiGray 10.0 1.0 0.1 FEB 56 NOV 60 AUG 72 AUG 89 SEP 89 OCT 89 Shielding Thickness (g/cm2 Aluminum)

7. 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?

8. 100 >10 MeV Fluence fixed Softer Spectra Harder Spectra 10 Aug 72 fit >30 MeV Fluence fixed Normalized Surface BFO Dose-Equivalent 1 >60 MeV Fluence fixed 0.1 0 50 100 150 Eo Dose Equivalent Sensitivity to Spectral Character( Aug 72 Example) BFO Dose Equivalent Slightly harder spectra may increase BFO dose equivalent by a factor of two or more

9. 100 Softer Spectra Harder Spectra 10 Aug 72 fit >10 MeV Fluence fixed Normalized Surface Skin Dose-Equivalent 1 >30 MeV Fluence fixed 0.1 0 50 100 150 >60 MeV Fluence fixed Eo Dose Equivalent Sensitivity to Spectral Character( Aug 72 Example) Skin Dose Equivalent Slightly softer spectra may increase skin dose equivalent by an order of magnitude

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

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

12. 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 Forecasting SPE is a Multidiscipline Challenge Predict the eruption of a CME

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

14. 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

15. 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? • Basedon what forecasts? Example

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

17. Radiation Risk Mitigation Objective Top Level Requirement NASA will establish radiation limits Any mission must be designed to ensure that radiation exposures do not become comparable to these radiation limits System Level Requirements 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

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

19. Radiation Risk Management Investment StrategyStep 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

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

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

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

23. Radiation Risk Management Investment StrategySW Architecture Investment Strategy solar imager plasma monitor Three Two One particle monitor Three Two One Dosimeter Three Two One Three Two One Products Lunar Mars Express F nowcast/ forecast

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

25. 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?”

26. Only One More Solar Cycleto Learn What We Must Learn SOHO Human Mission Design ACE Return to the Moon STEREO On to Mars Solar Dynamics Observatory Sentinels Solar Cycle 24 2000 2010 2020 2030

27. 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)

28. 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

29. Backup Slides

30. Space Weather Contributions toSupport 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