The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined.

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Design guidelines for assessing and controlling spacecraft charging effects

A new numerical software package to analyze spacecraft charging, named ldquomulti-utility spacecraft charging analysis toolrdquo (MUSCAT), has been developed. MUSCAT consists of an integrated graphical user interface tool called ldquoVineyardrdquo and the solver. Vineyard enables satellite engineers to compute spacecraft charging with little knowledge of the numerical calculations. Functions include 3-D satellite modeling, parameter input such as material and orbit environment, data transfer, and visualization of numerical results. Fundamental physical processes of charged-particle-surface interaction are included in the solver. These functions enable MUSCAT to analyze spacecraft charging at geostationary orbit, low Earth orbit, and polar Earth orbit (PEO). The numerical solver code is parallelized for high-speed computation, and the algorithm is optimized to achieve analysis of large-scale PEO satellite in the design phase. Variable time steps are also used to calculate the rapid change of the spacecraft body potential and the gradual change of the differential voltage in a single simulation with a practical number of iterations. In this paper, the functionality, algorithms, and simulation examples of MUSCAT are presented.

Development of Multi-Utility Spacecraft Charging Analysis Tool (MUSCAT)

A model is presented to numerically simulate the time-dependent interaction of satellites with space plasma. The approach is based on a fully kinetic description of the plasma using particle in cell modeling for all plasma species with physical charges and masses. The model also relies on a discretization of space with an unstructured tetrahedral mesh that is capable of representing complex boundaries and realistic spacecraft geometries. The code solves for the self-consistent electric fields, given calculated volume charges and charge deposition on the various satellite components. The model is purely electrostatic, but it does account for the effects of a possible constant and uniform background magnetic field.

PTetra, a Tool to Simulate Low Orbit Satellite–Plasma Interaction

Electric charging and discharging phenomena on spacecraft are reviewed. Laboratory tests of spacecraft materials, performed over the last six years by many workers, are summarized. A conceptual framework is proposed to explain the apparently diverse findings and to guide future studies: prebreakdown events (microdischarges) appear to produce small Lichtenberg trees with a plasma which conducts large current under certain conditions. An extensive set of measured pulse data in several polymers is compared to theoretical prediction of radiation induced internal electric fields which rise as high as 2×106 V/cm due to trapped irradiation spacecharge alone. Implications for spacecraft are discussed.

Electric Discharge Pulses in Irradiated Solid Dielectrics in Space

The reported investigation had the objective to illustrate the presence of important multidimensional effects in spacecraft charging. Two-dimensional codes have been under development by Parker (1976). A description is presented of a calculation which was performed using the three-dimensional NASA Charging Analyzer Program (NASCAP). NASCAP was run to calculate the electrostatic potentials on the surface of, and in the space surrounding, a sunlit Teflon-coated sphere. Currents to the sunlit surfaces were determined on the basis of an approximate photosheath model for strong differential charging.

The Decrease in Effective Photocurrents Due to Saddle Points in Electrostatic Potentials near Differentially Charged Spacecraft

A computer code, NASCAP (NASA Charging Analyzer Program), has been developed by Systems, Science and Software under contract to NASA-LeRC to simulate the charging of a complex spacecraft in geosynchronous orbit. The capabilities of the NASCAP code include a fully three-dimensional solution of Poisson's equation about an object having considerable geometrical and material complexity, particle tracking, shadowing in sunlight, calculation of secondary emission, backscatter and photoemission, and graphical output. A model calculation shows how the NASCAP code may be used to improve our understanding of the spacecraft-plasma interaction.

NASCAP, a Three-Dimensional Charging Analyzer Program for Complex Spacecraft

: The report describes additions and modifications to the CAPO system of opacity codes and presents the results of other research tasks on emission, absorption and transport of radiation in high temperature materials. The accuracy of several approximate methods of opacity treatment is assessed. The radiative properties of thin plasmas, not in local thermodynamic equilibrium (non-LTE) are considered. Several codes written to provide ionic charge distributions, excited state populations, and emission rates in non-LTE plasmas are described. Electron positron pair production rates are studied and estimates made of the times required to establish significant pair populations under various conditions. (Author)

James Harvey

Papers

NASCAP, a Three-Dimensional Charging Analyzer Program for Complex Spacecraft

A Study of Equations of State/Opacity of Ionized Gases.