Workshop to Support Mars Human Precursor Radiation

Measurements on the Surface of Mars

Dr. Ron Turner

October, 2005

Mars-Surface Radiation Mars-Surface Radiation Environment WorkshopEnvironment Workshop

NASA should sponsor a limited, focused workshop on the Martian surface radiation environment, providing direction for a coordinated effort to optimize instrument requirements in advance of placing a radiation instrument on a Mars Lander/Rover

Multiple high-level reviews of the current understanding of the Mars surface radiation environment have agreed there is a need for surface measurements to validate radiation transport modelsThe robotic Mars missions will provide an opportunity to make these measurements

NRC/NAS “NRC/NAS “Safe on MarsSafe on Mars” ” Radiation RecommendationRadiation Recommendation

Precursor Measurements Necessary to Support

Human Operations on the Surface of Mars

Aeronautics and Space Engineering Board/Space Studies Board

National Research Council

Published May 2002

• In order to validate the radiation transport codes, thereby ensuring the accuracy of radiation dose predictions, NASA should perform experiments to measure the absorbed dose in a tissue-equivalent material on Mars at a location representative of the expected landing site, including altitude and bulk elemental composition of the surface

– The experiment should distinguish the radiation dose contribution induced by charged particles from that induced by neutrons

– These experiments should be made a priority in the Mars exploration program

Mars Human Precursor StudyRadiation Findings

Findings of the Radiation Working Group supporting the Mars Human Precursor Requirements Development

• “MHP should address this essential issue in radiation safety: the validation of radiation transport models that predict the detailed flux of particles on the Martian surface”

• “The dose from albedo neutrons on the surface is the least understood of the various contributions to radiation exposure on a Mars mission”

• “NASA should sponsor a limited, focused workshop on the Martian surface radiation environment”

An Analysis of the Precursor Measurements of Mars

Needed to Reduce the Risk of the First Human Mission

to MarsMEPAG

June 2, 2005

“Transport model validation remains the highest priority for radiation investigation, which is the same conclusion reached by the Safe on Mars panel.”

Living With a Star Workshop (5 April 2004)

Draft Recommendations

• Radiation data collected on the surface of Mars are required for projecting crew health risks and designing protective surface habitats:

– Surface measurements of dose, dose equivalent, and LET spectral components from GCR protons, high-charge and energy (HZE) ions, and neutrons

– Determine individual contributions from protons, HZE’s, and neutrons to LET spectra including charge spectral data

• Multiple measurements are preferred to characterize temporal and spatial variations

• Solar Minimum and Solar Maximum• Atmospheric and Surface Variations

Experiment design should include input from transport modelers, experimentalists, and scientists familiar with the Mars atmosphere and surface characteristics

Solar Particle Events

Safe on Mars, MHP, and LWS workshop each recognized that SPE forecasting/characterization was an important issue

• Validation of SPE transport to surface would require an orbital instrument to determine the input spectra

• Safe on Mars did not call for explicit surface measurements during SPE

• NAS/NRC assumed that a validated GCR transport code could transport SPE protons if the incident flux were known

• MEPAG recommends a radiation instrument should be scheduled at or shortly after solar maximum (~2011), with months of operation, to increase the chance of observing an SPE, and it should be coincident with an orbiting radiation monitor

• LWS workshop suggested that in addition to individual-event monitors, it would be useful to have a neutron monitor to track SPE variability over long time periods

Surface “validation” Surface “validation” measurement presupposes measurement presupposes active modeling activityactive modeling activity

“…Researchers anticipate that with continued development of both models [Monte Carlo and analytic], transport codes will be used to simulate the Martian surface radiation environment. These codes will be integral to the design of the space vehicles, surface vehicles, surface habitats, and other shelters. The dose estimates established by these models will be used to set operational rules for surface expeditions. The rules will account for such items as the maximum amount of time an astronaut may spend on a surface EVA and the maximum distance from a shelter an astronaut may go.”

--- Safe on Mars, NRC, 2002

Mars-surface radiation environment also has relevance to Astrobiology and to long-term planning if plants grown in Martian “greenhouses” are to support human missions.

• Transport to Mars surface requires understanding of – Source Radiation (Galactic Cosmic Rays, Solar Particle Events)– Nuclear Transport (Modeling, Energetics, Cross-sections, Secondary Generation)– Mars Atmosphere (Composition, Temporal and Spatial Variation)– Mars Surface, near Sub-surface (Elevation, Composition, Variation)– Shielding Options (Habitats, Vehicles, EVA suits)

Radiation transport models Radiation transport models to Mars surface are multi-to Mars surface are multi-disciplinary activities disciplinary activities

(Simonsen et al.) (Clowdsley et al.)

Radiation Transport Model Validation

Optimal experiment design should be derived from a science-based collaboration of

Transport modelers

(Where do models agree, disagree? What are they most sensitive to?)

Experimentalists

(What can be measured? How well? At what cost?)

Experts in Mars atmosphere, surface and subsurface

(How much can the location of the measurement impact the results?)

Radiation-environment community

(What components of the environment have the largest impact on humans/systems?)

The expertise exists and is The expertise exists and is engaged, but is not focused engaged, but is not focused or coordinatedor coordinated

• However, there are no efforts dedicated to Mars’ surface, and each activity has its own set of assumptions, simplifications, and end points, rendering comparisons difficult or impossible

• Atmosphere and surface experts have not been fully engaged

– NASA Ames (Atmosphere)

– NASA JPL (Surface)

Sphere Thickness (g/cm2)

AnnualB

FO

Dose

Equiv

ale

nt(c

Sv)

0 25 50 75 1000

5

10

15

20

25

30

35

40AL2219 - 1977 min.Polyethylene - 1977 min.H Nanofibers - 1977 min.Liquid Hydrogen - 1977 min.AL2219 - 1990 max.Polyethylene - 1990 max.H Nanofibers - 1990 max.Liquid Hydrogen - 1990 max.

• Mars surface radiation models are available or under development in multiple Centers and Institutes

– NASA LaRC

– NASA JSC

– NASA MSFC

– Los Alamos National LabNASA LaRC NASA JSC

Increased communication and cooperation could significantly

enhance science contributions to Mars Human Precursor Missions

• A Workshop in 2005/6 could set the stage for optimal use of Mars lander/rover opportunities to validate radiation transport codes

• About two dozen attendees could represent the relevant communities

• Workshop findings could provide focus to modeling efforts and define validation requirements

• These findings could, in turn, support a NASA Research Announcement release for radiation instrument definition

Workshop Participants

• Natural Environment– Atmosphere, NASA Ames (1-2 participants)– Surface Composition, JPL (2)– GCR Composition and Variation, MSFC, GSFC (2)

• Transport Models– NASA LaRC (4)– NASA JSC (4)– NASA MSFC (2)– Los Alamos National Lab (2)

• Program Coordination– Mars Program Office (1-2)– Radiation Program (1-2)– Science and Exploration Directorates (2-3)

Key Questions, Major Objectives

• After accounting for differences in assumptions and end-points, are the multiple models of the Mars surface radiation environment essentially in agreement?

• What are the most critical surface measurements to validate transport models?

• What Earth-based measurements can support transport model validation?

• How can the Mars surface transport modeling activities be better supported and coordinated?

• Are there more detailed scenarios that can be formulated to best support plans for a validation mission on a near-term robotic mission?

Workshop Steering Committee

A 3-6 person Steering Committee should be established to

• Achieve consensus on key questions and objectives• Prepare list of invited contributors• Prepare and distribute a set of baseline scenarios to be

reviewed at workshop• Chair workshop sessions• Oversee production of Final Report• Disseminate Findings

The Workshop Steering Committee would likely meet 2-3 times via teleconference starting 2-3 months prior to Workshop

Notional two-day agendaFirst Day – Modeling Activities

Day One Morning• Welcome/Introduction• Workshop Objectives• Mars Surface

– Composition• Nominal and Variations

– Altitude variations– Seasonal variations

• Dust, CO2 frost, and H2O Ice

• Mars Atmosphere– Composition– Altitude variations– Temporal variations

• Diurnal, Seasonal

– Dust loading, water vapor

• Overview of Radiation Transport Techniques and Applications to Mars Surface

Day One Afternoon• Mars Surface Models –

Assumptions and Representative Results

– LaRC– JSC– MSFC – Los Alamos National Lab– Others?

• Working Session– Where are the assumptions / end

states the same or similar– Where do the assumptions / end

states differ significantly– Are the results consistent– What standard conditions should

be used across the modeling community for cross comparison

Notional two-day agendaSecond Day – Validation Support

Day Two Morning• Mars Program Overview• Mars Radiation Objectives

– MEPAG– MHP– NRC “Safe on Mars”

• MARIE – Orbital Instrument, implications for

surface measurements

• GRS– HEND Neutron measurements– Implications for surface neutron

environment

• Options for Lander/Rover Instrumentation in 2011-2015

– Prior Instrument Lessons Learned– Prior Lander instrument concept– Realistic mass, power, telemetry

constraints

Day Two Afternoon• Working Session

– How would the landing site impact instrument selection

– What are the benefits/pitfalls to putting the instrument on a rover

– What minimal but critical measurements are needed to validate models

– What detailed scenarios should be formulated to best support plans for a validation mission on a near-term robotic mission

• Wrap-up– Summarize consensus conclusions– Identify appropriate milestones– Review action items/writing

assignments

Workshop Follow-up

• Produce Workshop Proceedings– Stand-alone document, 20-30 pages– Archive presentations

• Produce Workshop Briefing– For presentation to relevant communities– For presentation to key decision makers

• Encourage publications by participants in peer-reviewed literature