Nascap-2K - A spacecraft charging analysis code for the 21st century

Abstract

Nascap-2K is being developed as a replacement for the NASCAP/GEO spacecraft charging code. Currently implemented are an Object Definition Toolkit (OTk), a Boundary Element Method (BEM) charging analysis module, and a user interface for setting up problems and displaying results. Nascap-2K is partially integrated with the DynaPAC (Dynamic Plasma Analysis Code) code, and full integration will enable the use of DynaPAC modules to study volume potentials, particle trajectories, denser plasmas, and more complex plasma processes. Examples are presented of a typical geosynchronous charging calculation, and charging of the STEREO spacecraft in the solar wind. INTRODUCTION The NASCAP/GEO code, used worldwide for surface charging analysis of geosynchronous spacecraft, was developed during the period 19761984. Since that time there have been huge advances in computer capabilities, software tools, software design, mathematical analysis techniques, and user expectations. Plus, we have advanced our knowledge of the space environment, the interactions between space plasma and spacecraft surface materials, and the algorithms to simulate spacecraft charging phenomena. Clearly, a more advanced code is needed for detailed charging analysis. Nascap-2K is being developed as a successor to NASCAP/GEO. The Air Force Research Laboratory and the NASA Space Environment Effects Program are funding the Nascap-2K effort. Currently implemented are: (1) an Object Definition Toolkit (written in Java); (2) an analysis module (written in C++ and using the Boundary Element Method (BEM)) for calculating surface charging in Geosynchronous Earth Orbit, Solar Wind or other tenuous plasma environments; and (3) a graphical interface (written in Java) for setting up problems and examining results. All information is stored in the database of the existing DynaPAC code. DynaPAC (written in Fortran and C) is a finite element code that solves potentials and tracks particles in the space external to a spacecraft model using a flexible set of plasma treatments. DynaPAC features arbitrarily nested grids to provide good spatial resolution, and strictly continuous electric fields for accurate particle tracking. In the short term, we will make Nascap2K's geometric models and BEM charging results accessible to DynaPAC's modules, so that external potentials and particle trajectories can be calculated. Over a longer time, we will use the DynaPAC synergy to extend the range of applicability of Nascap-2K to denser plasma environments such as found in low-earth or polar orbits, or resulting from thruster plumes. In this paper we describe the Object Definition Toolkit (OTk) and the BEM analysis module, and show as examples charging of a typical geosynchronous spacecraft and of a model of the STEREO spacecraft in the solar wind. Object Definition Toolkit The original NASCAP/GEO code included simple object definition routines for defining a spacecraft model (built of cubes, wedges, etc.) within the context of a cubic mesh. While quite impressive in the 1976-80 timeframe, the shortcomings of such a model (e.g., its inability to accurately represent spacecraft dimensions and angles, and the lack of variable resolution) soon became apparent. 1 9210 Skypark Court., San Diego, CA 92123 2 Marshall Space Flight Center, AL 35812 3 Hanscom Air Force Base, MA 01731 Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 1 American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.