Understanding and Mitigating Radiation Belt Hazards for Space Exploration

1. Understanding and Mitigating Radiation Belt Hazards for Space Exploration Geoffrey Reeves Space Science and Applications, ISR-1, Los Alamos National Laboratory,

2. 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

3. 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

5. 27-Day Averages Paulikas and Blake 1979Correlation between Vsw and Electron Flux 6-Month Averages

7. Standard Models like AE8/AP8 are Outdated and Wrong J. B. Blake SEEWG 2004

8. Extreme events, while rare, dramatically change statistics and climatological models J. B. Blake SEEWG 2004

9. New models like POLE can provide significant benefits for minimal cost Under-shielding increases risk of component, system, or mission failure Over-shielding increasescosts and/or reduces capability by flying oldor less capable technologies D. G. Boscher et al. 2003, Trans IEEE Nuc. Sci.,

10. A Fundamental Predication Challenge:Will a storm increase or decrease the belts? • 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 energy CRRES - full mission 100X Increase 10X Decrease No Change

11. The same wave fieldscan produce pitchangle scattering and loss Acceleration and Losses - Low energies coupled to High through waves Unstable plasma distributions produce waves that couple energy into the relativisticpopulation

12. Dynamic Radiation Environment Assimilation Model Predictive understanding requires coupling observations with the right physical models

13. Data Assimilation - Utilizing observations and models for prediction and understanding A Pictorial Representation of the Kalman Filter

15. Diffusion function: • Exact solution compared to Data Assimilation Solution • Just 2 satellites (measuring witherrors) can determine radial diffusionrates - and precision of result 1D Radial Diffusion: Identical Twin Test Exact Solution Error Matrix Error Matrix Data Assimilation Model Solution

16. Adaptive Extended Kalman FilterCRRES Data + Radial Diffusion + Loss Lifetimes Shprits et al., 2005

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

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

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

20. 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…

21. 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…

22. 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 Radiation BeltStorm Probes

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

24. 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

25. 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

26. 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 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

27. Thank You