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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

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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


Outline l.jpg
Outline Human Missions to the Moon and Mars:

  • Background

  • Systems Approach to Radiation Risk Management

  • Conclusions/Observations


The myths the grail the reality l.jpg
The Myths Human Missions to the Moon and Mars:, 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, Human Missions to the Moon and Mars: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, Human Missions to the Moon and Mars: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 l.jpg

50% Chance of Death Human Missions to the Moon and Mars:

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)


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What is the Worst Case SPE? Human Missions to the Moon and Mars:

  • 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 l.jpg

100 Human Missions to the Moon and Mars:

>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


Dose equivalent sensitivity to spectral character aug 72 example9 l.jpg

100 Human Missions to the Moon and Mars:

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


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SPE Risk Mitigation Human Missions to the Moon and Mars:

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


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Space Environment Human Missions to the Moon and Mars:

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


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Predict the character of the CME Human Missions to the Moon and Mars:

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


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Consider GCR Radiation Human Missions to the Moon and Mars:Environment

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


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Surface Operations are Rule-Driven Human Missions to the Moon and Mars:

  • 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 Human Missions to the Moon and Mars:

  • 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


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Solar Imager (s) Human Missions to the Moon and Mars:

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


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Radiation Risk Mitigation Objective Human Missions to the Moon and Mars:

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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Biological Effects Human Missions to the Moon and Mars:

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


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Radiation Risk Management Investment Strategy Human Missions to the Moon and Mars: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


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Design Reference Mission Human Missions to the Moon and Mars:

  • 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


Radiation risk management investment strategy step four surface operations concept development l.jpg

No Human Missions to the Moon and Mars:

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


Radiation risk management investment strategy baseline space weather nowcast forecast elements l.jpg

Physical Models Human Missions to the Moon and Mars:

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


Radiation risk management investment strategy sw architecture investment strategy l.jpg
Radiation Risk Management Investment Strategy Human Missions to the Moon and Mars: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


A hard lesson for scientists to learn l.jpg
A Hard Lesson for Scientists to Learn Human Missions to the Moon and Mars:

Intuitively:

MORE IS BETTER

However:

BETTER IS THE ENEMY

OF GOOD ENOUGH


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What is “ Human Missions to the Moon and Mars: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 Cycle Human Missions to the Moon and Mars:to 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


Observations l.jpg
Observations Human Missions to the Moon and Mars:

  • 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 Human Missions to the Moon and Mars:

  • 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 Human Missions to the Moon and Mars:


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Space Weather Contributions to Human Missions to the Moon and Mars: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


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