Spacecraft Environment Interactions Henry B. Garrett and Insoo Jun Jet Propulsion Laboratory 1 Introduction ............................................................................................................................... 3 1.1 Objectives .......................................................................................................................... 3 1.2 Basic Concepts ................................................................................................................... 3 2 Space Environments................................................................................................................ 10 2.1 Ambient Particulate Environments .................................................................................. 10 2.1.1 Overview ................................................................................................................... 10 2.1.2 Solar Energetic Particle Events ................................................................................. 11 2.1.2.1 Solar Proton Events.................................................................................11 2.1.2.2 Heavy Ions ..............................................................................................17 2.2 Ambient Photon Environments ........................................................................................ 18 2.2.1 General Environment ................................................................................................ 18 2.2.2 X-Ray Flares ............................................................................................................. 23 2.2.3 Interplanetary e- and H+ ........................................................................................... 24 2.2.4 Trapped Radiation ..................................................................................................... 24 2.2.4.1 Geomagnetic Field ..................................................................................26 2.2.4.2 Magnetic and Electric Field Effects ........................................................32 2.2.4.2.1 Basic Particle Motion ...................................................................33 2.2.4.2.2 Invariants of the Particle Motion ..................................................36 2.2.4.3 Electron and Proton Belts .......................................................................39 2.2.4.4 Long-Term and Short-Term Variations ..................................................43 2.2.4.5 Examples: Solar Cycle Effects, Storms, Substorms ...............................43 2.2.4.6 AE8/AP8 Comparisons With The Crres Models ....................................44 2.2.4.6.1 Coverage Limitations ....................................................................44 2.2.4.6.2 Magnetospheric Heavy Ions .........................................................46 2.2.4.7 AP-9/AE-9: New Radiation Belt Model (Version Beta) ........................46 2.2.4.8 Conclusions .............................................................................................51 2.2.5 Extraterrestrial Trapped Radiation ............................................................................ 51 2.2.5.1 Jupiter ......................................................................................................53 2.2.5.1.1 Introduction ...................................................................................54 2.2.5.1.2 Jovian Coordinate System ............................................................56 2.2.5.1.3 Magnetic Field Model ...................................................................56 2.2.5.1.4 Radiation Belt e- and H+ ..............................................................57 2.2.5.2 Saturn ......................................................................................................60 2.2.6 Galactic Cosmic Rays (GRC) ................................................................................... 61 2.2.6.1 Overview .................................................................................................61 2.2.6.2 Magnetic Shielding .................................................................................62 2.2.6.3 GCR Ion Spectra .....................................................................................65 2.2.6.4 GCR Variations .......................................................................................71 2.2.6.5 GCR Electrons ........................................................................................72 2.2.7 Neutral Particle Radiation ......................................................................................... 73 2.2.8 Nuclear Power Sources ............................................................................................. 74 2.2.8.1 Radioisotope Thermoelectric Generators (RTGs) ..................................74 2.2.8.2 Radioisotope Heater Unit (RHU)............................................................76 I-1 3 Shielding Effects and Interactions with Matter ...................................................................... 80 3.1 Radiation-Induced Anomalies: IESD .............................................................................. 81 3.2 Single Particle Interactions .............................................................................................. 85 3.2.1 Photon Interactions ................................................................................................... 85 3.2.2 Charged Particle Interactions .................................................................................... 86 3.2.3 Neutron Interactions.................................................................................................. 87 3.3 Modeling The Effects Of Shielding ................................................................................. 89 4 Radiation Environment Estimates........................................................................................... 98 4.1 Example–The Clementine Program ................................................................................. 98 4.1.1 AE8/AP8 Radiation Dosage Results ......................................................................... 99 4.1.2 Solar Proton Events................................................................................................. 102 4.1.3 Summary of Radiation Dosage Estimates............................................................... 104 4.2 Mars Mission ................................................................................................................. 106 4.3 Jovian Model Applications ............................................................................................ 109 4.4 Heinrich Flux Estimates ................................................................................................. 110 5 Conclusion ............................................................................................................................ 114 6 Acknowledgements ............................................................................................................... 114 References ................................................................................................................................... 115 I-2 1 Introduction 1.1 Objectives As electronic components have grown smaller in size and power and have increased in complexity, their enhanced sensitivity to the space radiation environment and its effects has become a major source of concern for the spacecraft engineer. As a result, the description of the sources of space radiation, the determination of how that radiation propagates through material, and, ultimately, how radiation affects specific circuit components are primary considerations in the design of modern spacecraft. The objective of this paper will be to address the first 2 aspects of the radiation problem. This will be accomplished by first reviewing the natural and man-made space radiation environments. These environments include both the particulate and, where applicable, the electromagnetic (i.e., photon) environment. As the "ambient" environment is typically only relevant to the outer surface of a space vehicle, it will be necessary to treat the propagation of the external environment through the complex surrounding structures to the point inside the spacecraft where knowledge of the internal radiation environment is required. While it will not be possible to treat in detail all aspects of the problem of the radiation environment within a spacecraft, by dividing the problem into these parts–external environment, propagation, and internal environment–a basis for understanding the practical process of protecting a spacecraft from radiation will be established. The consequences of this environment will be discussed by the other presenters at this seminar. 1.2 Basic Concepts This section will provide an overview of the basic physical concepts and definitions that will be used throughout the presentation. In particular, the concepts of energy, flux, fluence, and dosage will be briefly described. The reader is referred to the many excellent texts on space physics or astronomy for more detailed explanations [1, 2]. Consider first the concept of energy. In the case of particles that have a rest mass, the fundamental equation relating particle mass and velocity to energy is: (1) where: m = particle mass V = particle velocity E = particle kinetic energy For photons (which have no rest mass), the equivalent equation is: I-3 (2) where: h = Planck's constant ν