Understanding and MitigatingRadiation Belt Hazards for Space Exploration

Geoffrey ReevesSpace Science and Applications, ISR-1, Los Alamos National Laboratory,

Why is radiation belt physics relevant to the Vision for Space Exploration?

• The radiation belts aren’t going to kill astronauts

• But, radiation belt doses to Apollo astronauts were ‘non-negligable’ and can be reduced with more knowledge - the goal is ALARA and this is achievable

• Radiation belt physics is critical for the space-based infrastructure that will support any significant exploration program - communications, staging, etc.

• As with other elements of LWS the radiation belt programs were designed to have direct, practical benefit to life and society - within and beyond VSE

• The goals are achievable and timely

There are three classes of problems we want to solve

• Climatology+ What are the long-term conditions and variability?+ Primarily for spacecraft and systems design/optimization

• Now-Casting+ Primarily for rapid (and cost effective) anomaly assessment+ Typically requires near real time data (which is scarce)+ Can be significantly enhanced with minor investments such as

ground stations to collect NRT data from operational assets

• Prediction+ Requires physical understanding, data, and models+ Global knowledge - e.g. plasmapause location, global field…+ Detailed physics such as the chain of causality from plasma

distributions to wave growth to electron acceleration and loss

Paulikas and Blake 1979Correlation between Vsw and Electron Flux

6-Month Averages 27-Day Averages

Standard Models like AE8/AP8 are Outdated and Wrong

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Aluminum Absorber Thickness (mils)

HEOs 1994-026 & 1997-068 (1997 D314 - 2002 D189) 4.66 Yrs

spherical geometry

AP-8min and AE-8min Total Dose(1950 km perigee) 4.66 Yrs

AE8+AP8 HEO Dose Prediction & HEO Actuals

J. B. BlakeSEEWG 2004

Extreme events, while rare, dramatically change statistics and climatological models

J. B. BlakeSEEWG 2004

New models like POLE can provide significant benefits for minimal cost

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D. G. Boscher et al. 2003,Trans IEEE Nuc. Sci.,

Under-shielding increasesrisk of component, system, or mission failure

Over-shielding increasescosts and/or reduces capability by flying oldor less capable technologies

A Fundamental Predication Challenge:Will a storm increase or decrease the belts?

100X Increase 10X Decrease No Change

• Geomagnetic storms change the radiation belts dramatically but unpredictably

• Radiation belt fluxes vary asa function of time, altitude (L),and energy

• The challenge is to reliably extrapolate in time, space, and/or energyC

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Acceleration and Losses - Low energies coupled to High through waves

The same wave fieldscan produce pitchangle scattering and loss

Unstable plasma distributionsproduce waves that coupleenergy into the relativisticpopulation

Predictive understanding requires coupling observations with the right physical models

DynamicRadiationEnvironmentAssimilationModel

Data Assimilation - Utilizing observations and models for prediction and understanding

A Pictorial Representation of the Kalman Filter

1D Radial Diffusion: Identical Twin Test• Diffusion function:

• Exact solution compared to Data Assimilation Solution

• Just 2 satellites (measuring witherrors) can determine radial diffusionrates - and precision of result

Data AssimilationModel Solution

Exact Solution

Error Matrix Error Matrix

Adaptive Extended Kalman FilterCRRES Data + Radial Diffusion + Loss Lifetimes

Shprits et al., 2005

Initiate model with t = 20/KpConverges to t = 5/Kp (independent of Kp!)

Physical equations must be solved in dynamic magnetic coordinates (µ, J, L*)

Changing the field changes phase space density and the satellites’ magnetic locations

Self-Consistent Magnetic & Ring Current Model

• Euler Potential based Equilibrium Magnetic Field model calculated from UNH-RAM ring current pressure distributions

• Feed back new B equilibrium into RAM and solve iteratively

• Self consistent results produce different current strength, drift paths, anisotropies, wave growth rates, etc…

Self-Consistent Magnetic & Ring Current Model

• Euler Potential based Equilibrium Magnetic Field model based on RAM pressure distributions

• Feed back new B equilibrium into RAM and solve iteratively

• Changes: current strength, drift path, anisotropies, wave growth rates…

LWS Radiation Belt Storm Probes (RBSP)Understanding and Application

• LWS missions were designed to achieve physical understanding that is critical to life and society

• VSE’s needs are closely coupled to the needs of our technological society and inquisitive nature

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Radiation BeltStorm Probes

RBSP fills a vital gap - 2 sat, equatorial, elliptical but does not have to do the job alone

We Have:• A vast collection of archival data spanning several solar cycles (but of

variable quality)

• A well-ordered system in which most of the basic physical equations are known (but not which processes dominate)

• Excellent physical models for parts of the system that have high fidelity when they have the right inputs

• A new satellite mission to fill critical gaps in physical understanding and in observations

• Clear, achievable goals in the 3, 5, and 10 year time scales

We Need:

• To develop new empirical, but dynamic, climatological models

• To understand which processes operate and when

• A second equatorial satellite orbit and low-altitude precipitation measurements to significantly extend the science return from RBSP (as identified by the GMDT)

• To develop global physical models that provide context for observations as well as predictive capability

• Integrate new & continuing observations with these new tools

Relevance to VSE

• The radiation belts are only one component of the VSE space environment problem but improvements in our ability to understand and predict dynamic radiation environments at Earth will directly benefit human and robotic exploration missions and the infrastructure needed to support them.

• Dramatic improvements are both achievable and timely

• Better radiation belt models can reduce risk, reduce costs, and enable new space capabilities and technologies

The Acid Test

• We will have failed if we cannot predict which events will increase radiation belt fluxes, which events will decrease radiation belt fluxes, and how large those changes will be

Thank You