Radiation and the International Space Station Recommendations to Reduce Risk (2000) / Chapter Skim
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Appendix A: Space Weather Models Applied to Radiation Risk Reduction
Appendix A: Space Weather Models Applied to Radiation Risk Reduction
Pages 57-67
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Appendixes
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~.~ it, ~, ~ ~ ~_ · _-, ~ ~-_, cost e~ecuve spacecraft for the government and commercial sectors that accommodate or mitigate the effects ofthe space environment." Towards fillfillino this anal it nrnvirle~ ~ e ~ ~ engineering GenMllOnS OI tne space environment, databases, and design guidelines and attempts to update its capabilities through directed research in response to an occasional NASA Research Announcement (NRA)
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The following discussion will focus primarily on fast CMEs, the predominant source of SPEs and geomagnetic storms. At present, we know the following: · The Sun's magnetic field is the most likely source of the substantial energy needed to launch and maintain a CME.
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The use of solar observations to establish boundary conditions in such calculations and the move to three-dimensional simulations have both become feasible only with the advent of high-performance computers. Modeling the propagation of fast CMEs and their associated shocks through the heliosphere, even with oneand two-dimensional MHD codes, has reached the point of demonstrating measurable skill in predicting shock speeds and arrival times at Earth.6 Recent improvements to these models include the incorporation of three dimensions, the ambient solar wind structure, and the heliospheric current and plasma sheets.7 Once an eruption has begun, it is a relatively straightforward matter to simulate its propagation as that of a pulse travailing through the heliosphere, as long as the plasma and magnetic-field conditions along the way are known.
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For certain radiation environment studies, direct dose measurements are preferred to flux measurements because of the uncertainty involved in transforming one to the other. CRRESRAD is a directly measured dose model constructed from CRRES data that are sorted by the same time intervals as CRRESPRo;~4 APEXRAD is a low-altitude dose model constructed from APEX satellite data and sorted by geomagnetic activity in a manner similar to that used for CRRESELE.~5 Although these empirical models take some account of various levels of geomagnetic effects, they obviously do not predict the detailed response of the radiation belts to variations in the magnetospheric configuration, as would a physics-driven model.
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Neural nets have been trained to perform diverse forecasting tasks, including the following: · Make short-term flare predictions with a success rate reported to be around 80 percent;20 · Predict the total dose of an SPE, reportedly to within 20 percent, from the fluxes observed earlier in the event;21 · Predict up to an hour ahead geomagnetic disturbance indices from L1 solar wind and interplanetary magnetic field (IMF) data,22 which can then be turned into predictions of the size of the SPE zones (see Section 2.3~; and · Predict the intensity of relativistic electrons at geostationary orbit a day ahead, based on a series of past Kp values, reportedly with an efficiency better than 90 percent.23 The evidence suggests that models based on neural nets and nonlinear dynamics can be developed that measurably reduce the radiation risk entailed in ISS construction and operations.
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can provide the missing link in magnetic topology; this would diminish considerably the lead time between a CME-based warning and the onset of geomagnetic effects and would also reduce the number of false alarms. A striking illustration of the value of this approach is given by recent studies comparing LASCO halo events with large geomagnetic storms.
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This will require examining and applying data to develop or improve statistical or empirical models. However, in parallel, as our understanding of the space environment improves, physics-based research models will be developed and modified as part of the process of improving our understanding."28 The Strategic Plan specifically calls for developing nowcast and forecast models in areas of direct importance for managing radiation risk for ISS construction and operating teams.
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Sufficient resources should therefore be devoted to developing a dynamic theoretical model of the evolution of the radiation belts in time-dependent magnetospheric electromagnetic fields calculated by a global three-dimensional MHD model of the magnetosphere driven by measurements of the solar wind.
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Vette, "AP8 trapped proton environment for solar maximum and solar minimum," NSSCE 76-06, NASA Goddard Space Flight Center, 1976.
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McPherron, "Neural networks and predictions of day-ahead relativistic electrons at geosynchronous orbit," in Proceedings of the International Workshop on Artificial Intelligence Applications in Solar-Terrestrial Physics, J.A. Joselyn, H
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