Guide to Mitigating Spacecraft Charging Effects

Appendix B

The Space Environment

B.1 Introduction to Space Environments

This appendix is intended to supplement the material presented in Chapter 2. It presents in more detail, for the interested reader, many of the concepts introduced in Chapter 2.

B.1.1 Quantitative Representations of the Space Environment

Earth's plasma is described properly in terms of phase space density or distribution function. Space plasmas can be described most simply in terms of the Maxwell–Boltzmann distribution. As this representation lends itself to efficient manipulation when carrying out charging calculations, it is often the preferred way of describing plasmas. The Maxwell–Boltzmann distribution F_i is given by

B.1

where

n_i = number density of species i

m_i = mass of species i

k = Boltzmann constant

T_i = characteristic temperature of species i

v = velocity

F_i = distribution function of species i

Unfortunately, the space plasma environment is seldom a Maxwell–Boltzmann distribution. However, given the actual plasma distribution function, it is possible to define (irrespective of whether the plasma is Maxwell–Boltzmann or not) moments of the particle distribution that reveal characteristics of its shape. In most cases, these moments can then be used to determine an approximate Maxwell–Boltzmann distribution. The first four of these characteristic moments are

B.2

B.3

B.4

B.5

where

< ND_i > = number ...