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

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Risk Management Strategies During Solar Particle
Events on Human Missions to the Moon and
MarsThe 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
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Outline

• Background
• Systems Approach to Radiation Risk Management
• Conclusions/Observations

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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

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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

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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

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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)
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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?

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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
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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
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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
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Radiation Safety Information Flow
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Forecasting SPE is a Multidiscipline Challenge
Predict the eruption of a CME
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One Approach to Radiation Safety
Shielding is the Main Defense against Radiation
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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

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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
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Radiation Risk Management Architecture Elements
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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
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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

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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

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Radiation Risk Management Investment
StrategyStep Three Transit Phase Shielding
Analysis
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Radiation Risk Management Investment
StrategyStep Four Surface Operations Concept
Development
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Radiation Risk Management Investment Strategy
Baseline Space Weather Nowcast/Forecast Elements
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Radiation Risk Management Investment Strategy SW
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
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A Hard Lesson for Scientists to Learn
Intuitively
MORE IS BETTER
However
BETTER IS THE ENEMY OF GOOD ENOUGH
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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?

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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
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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)

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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

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Backup Slides
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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

Improved Safety and Enhanced Mission Assurance