Measurements of electronic properties of conducting spacecraft materials with application to the modeling of spacecraft charging

Abstract

IntroductionMany spacecraft system anomalies and component failures are known to result from spacecraft charging which is due to the bombardments of spacecraft by energetic electrons, ions, and photons in natural space surrounding [Hastings and Garrett, 1996; Bedingfield et al., 1996; Leach et al., 1995]. To assist spacecraft designers in accommodating and mitigating the harmful charging effects on spacecraft, NASA has developed an extensive set of engineering tools to predict the extent of charging in various spacecraft environments (for example, NASCAP/LEO, NASCAP/GEO, and POLAR) [Mandell et al., 1993]. However, current NASCAP databases lack electronic properties of most spacecraft materials in use (only nine basic materials are presently incorporated) and many new spacecraft bulk materials and coatings need to be characterized. In an effort to improve the reliability and versatility of these models, the NASA Space Environments and Effects (NASA/SEE) Program has funded a study to measure the electronic properties of spacecraft materials related to NASCAP parameters [Dennison, 1998]. The objectives of the study are (i) to provide more accurate measurements together with sufficient materials characterization and (ii) to significantly extend the database to include a wider range of materials that are more representative of the myriad materials used in spacecraft design and incorporates newly developed materials.This paper describes the results of the first stage of this project, measurements of the electronic properties of conducting spacecraft materials. We begin with a description of the required measurements and specifics of the experimental methods used. Representative measurements for gold are described in detail. This is followed by a complete list of the conducting materials studied, justification of their selection for study, and a summary of the important results of the measurements. We end with a description of incorporation of these measurements into the NASCAP database.

Measurement Methods of Electron Emission Over a Full Range of Sample Charging

“…The individually biased elements of the hemispherical grid retarding field analyzer (HGRFA) detector also allow for extensive instrument characterization and calibration. A thorough discussion of the dc system and methods is given by Thomson [5] and others [4], [6].…”

Spacecraft Coating-Induced Charging: Materials and Modeling Study of Environmental Extremes

“…The NASCAP-2K code 8 uses parameterized expressions to represent the materials parameters involved in charge accumulation and dissipation, including (i) electron-, ion-, and photon-induced electron emission yields; (ii) mass density; (iii) dielectric constant; (iv) electrostatic breakdown potentials and field strengths; and (v) both dark current and radiation induced electron conduction. 36 Total conductivity is the sum of two temperature dependent material properties, dark current (DC) conductivity which is independent of the incident radiation and radiation induced conductivity (RIC) which by definition is conductivity enhanced by the energy imparted to a material by the incident radiation. 37 The NASCAP parameterization does not model temperature dependence of these parameters, so specific values of the materials parameters must be input into the code for the equilibrium temperatures in each environment listed in Tables 1 and 2 Table 3.…”