Session Y10: Invited Session: Modeling & Simulation of the Impact of Space Radiation on Electronic Systems (Avionic and Astronautic)

Mitigation of Space Radiation Effects

During low earth orbit and deep space missions, humans and spacecraft systems are exposed to high energy particles emanating from basically three sources: geomagnetically-trapped protons and electrons (Van Allen Belts), extremely high energy galactic cosmic radiation (GCR), and solar proton events (SPEs). The particles can have deleterious effects if not properly shielded. For humans, there can be a multitude of harmful effects depending on the degree of exposure. For spacecraft systems, especially electronics, the effects can range from single event upsets (SEUs) to catastrophic effects such as latchup and burnout. In addition, some materials, radio-sensitive experiments, and scientific payloads are subject to harmful effects. To date, other methods have been proposed such as electrostatic and electromagnetic shielding, but these approaches have not proven feasible due to cost, weight, and safety issues. The only method that has merit and has been effective is bulk or parasitic shielding. In this paper, we discuss in detail the sources of the space radiation environment, spacecraft, human, and onboard systems modeling methodologies, transport of these particles through shielding materials, and the calculation of the dose effects. In addition, a review of the space missions to date and a discussion of the space radiation mitigation challenges for lunar and deep space missions such as lunar outposts and human missions to Mars are presented.   

The Space Radiation Environment in Energetic Particles at the Earth

Understanding the radiation environment in energetic particles at the Earth is critical to the stability, integrity, and longevity of satellite subsystems. The radiation environment comprises particles trapped in the Earth's radiation belts and magnetosphere, those generated by solar energetic particle events (SEPs), and galactic and anomalous cosmic rays. Of these different populations, the most highly variable, and consequently difficult to anticipate, is the SEP population. This is also the population that can often cause the most damaging effects. SEP events can be either impulsive or gradual (sometimes a mixture of the two) with the gradual events being larger, much longer lasting, and often with higher particle energies. Diffusive shock acceleration at a coronal mass ejection driven shock wave is generally invoked to explain gradual SEP events. The detailed [plasma] physics of the acceleration mechanism remains to be elucidated. We are fortunate in that very detailed observations of particle acceleration at shock waves, particularly in the guise of Space Weather, are providing considerable experimental insight into the basic physics of particle acceleration at a shock wave. Detailed interplanetary observations are not easily interpreted in terms of simple steady-state models of particle acceleration at shock waves. Three fundamental aspects make the interplanetary problem much more complicated than the typical astrophysical problem: the time dependence of the acceleration and the solar wind background; the geometry of the shock; and the long mean free path for particle transport away from the shock wave. An interplanetary shock is not steady, as it decelerates and expands into an expanding, temporal solar wind. Furthermore, the shock geometry varies from quasi-parallel to quasi-perpendicular along a shock front, and multiple shocks can be present simultaneously in the solar wind. Consequently, the shock itself introduces a multiplicity of time scales, ranging from shock propagation time scales to particle acceleration time scales at parallel and perpendicular shocks, and many of these time scales feed into other time scales (such as determining maximum particle energy scalings, escape time scales, etc.). We will discuss the basic physics of particle acceleration via scalings, their relationship to particle acceleration models, observations and geometry in both an astrophysical and space physics context. This will include discussing the physics of perpendicular and parallel shocks, upstream turbulence, particle spectra, and particle injection and the seed population. After acceleration of particles at an interplanetary shock, the transport of energetic particles is non-diffusive because of their large mean free path in the quiet solar wind. We will address the coupled acceleration and transport of heavy ions, Fe/O ratios, the variability among individual events, and seed particle populations. We will discuss theoretical models and address recent modeling efforts.   

Monte Carlo Simulation of Radiation Effects in Microelectronics

Microelectronic devices are susceptible to disruption by ionizing radiation, and with the scaling of devices to ever-smaller dimensions they are increasingly vulnerable to single event effects. Single event effects are transient errors in active devices, usually although not exclusively in digital logic, that are caused by the interaction of ionizing particles with the materials from which the devices are made. This presentation describes a Monte Carlo approach for predicting the rate of single event effects from knowledge of radiation environments and device structure. The approach combines detailed physical modeling of discrete radiation events, semiconductor device simulation to estimate charge transport and collection, and circuit simulation to determine the macroscopic electrical effects of collected charge. Details of the Monte Carlo simulation will be presented, and a mathematical analysis that establishes its relationship to earlier single event rate prediction methods will be discussed. Recent experimental and computational results on the rate of single event effects in highly scaled devices will be reviewed.   

Data-driven Three-Dimensional (3D) Global Magnetohydrodynamic (MHD) Model with Radiation to Study the Solar Atmospheric Dynamics

In this presentation, we describe a self-consistent, three-dimensional, global compressible, and resistive magnetohydrodynamic (MHD) model together with time-dependent boundary conditions based on the projected method of characteristics at the source surface (photosphere) to accommodate the observations. The additional physics included in this model are differential rotation, meridional flow, effective diffusion, and cyclonic turbulence effects in which the complex magnetic field structure can be generated through the nonlinear interactions between the plasma flows and magnetic field. To illustrate the capability of this model, we selected GONG's global transverse velocity measurements of synoptic chart CR2009 near the photosphere and SOLIS full-resolution LOS magnetic field maps of synoptic chart CR2009 on the photosphere as the inputs to drive the model to simulate the equilibrium state and compute the energy transport across the photosphere. To show the advantage of using both measured magnetic field and transverse velocity data, we have investigated two cases: (1) with the inputs of the LOS magnetic field and transverse velocity measurements, and (2) with the input of only the LOS magnetic field. For these two cases, the simulation results presented here are a three-dimensional coronal magnetic field configuration, density distribution on the photosphere and 1.5 solar radii, and the solar wind in the corona. The deduced physical characteristics are the total current helicity and the synthetic emission.   

Multi-Scale Modeling of the Plasma Flow and Magnetic Fields in the Entire Heliosphere

Numerical model of the solar wind (SW) interaction with the local interstellar medium (LISM), developed in UAHuntsville and implemented in the Multi-Scale Fluid-Kinetic Simulation Suite, treats ions with MHD equations while the transport of neutral atoms is performed kinetically by solving the Boltzmann equation. Pickup ions are treated as a separate fluid or kinetically. The evolution of SW turbulence is addressed on the differential equation level. Time-dependent, based on observational data, modeling of the SW in the entire heliosphere is critical for the space weather modeling and interpretation of the spacecraft data. We choose LISM properties using remote observations and appropriate numerical modeling which allows us to constraint them by matching the ribbon of the energetic neutral atom flux detected in different energy bands by the Interstellar Boundary Explorer. We used the Ulysses data to model the SW-LISM interaction during the period of the mission and matched rather well the timing of the termination shock crossing by Voyager 1 and Voyager 2. The SW boundary conditions include those provided by the interplanetary scintillation measurements and obtained by numerical modeling of the inner heliosphere from the Sun's surface to the Earth orbit. Numerical results are extracted as time series along real spacecraft trajectories and compared with in situ measurements.