Spacecraft Plasma Interactions (I, II, III)

Introduction

This study examined potential problems from interactions between low altitude space plasma environments and spacecraft. These effects included:

  • electrostatic charging of surfaces in polar orbits;
  • currents driven through the ambient plasma from exposed solar array interconnects;
  • electrostatic and electromagnetic noise generated by the interaction.

Following identification of the problems, several software tools were developed:

  • LEOPOLD for LEO plasma basic data;
  • EQUIPOT for simple calculations of charging in arroral and other hot plasma environments;
  • SOLARC for determining the current collection by "elevated-voltage systems" (e.g. solar arrays);
  • PICCHARGE, a "particle-in-cell" code for simulating the trajectories of charged [particles and subsequenrt charging of bodies in flowing plasmas, including the presence of hot auroral plasmas;
  • SAPPHIRE, an ion flux-tube code for computing plasma wake formation.

In addition, experimental work was performed in the AEA and NDRE plasma facilities on plasma wake formation and charging, to validate the tools.

A final part of the study, focused on electrostatic charging and hot plasma environments at high altitude:

  • Improvements were made to the NASCAP surface charging code,
  • data from the Low Energy Plasma Analyser (LEPA) on the CRRES satellite were analysed,
  • calculations of anisotropy effects using the upgraded version of NASCAP were made,
  • an analysis of internal charging using the ESA code, ESADDC, to interpret data from the CRRES Internal Discharge Monitor (IDM) as well as to perform a parametric analysis, and
  • evaluation of Russian spacecraft charging data was made.

See also the presentation from the Final Presentation Days in 1999, which were organised to report on the technology research in the space environments and effects area.


 

 

Products & Information

n the first phase, a review of previous work carried out on the subject of Spacecraft/Plasma Interactions and Electromagnetic Effects in LEO and Polar Orbits was performed and reported Vol.1 of the final report "Spacecraft Plasma Interactions". In the report:
  • A catalogue of spacecraft/environment interactions, and the interactive mechanisms and effects produced, is given. Some of the more important and relevant interactions are examined in more depth.
  • Previous attempts at simulation in the laboratory and via numerical and computational methods are then discussed, concentrating upon the range of parameters covered and the validity of, and the assumptions behind, the simulations.
  • Space based experiences relevant to the subject are also reviewed. Plasma wake studies have generally only covered model size vehicles. Spacecraft charging experiments have only recently begun. Computational studies can aid in interpretation, but assumptions inherent in several codes limit their application. There is a large literature of space-based data, but interpretation must be done with care.

The second phase results are reported in the Final Report vol.2:

  • This report describes the development of a suite of computational tools (ESPIRE), designed to aid spacecraft design, which address some specific problem areas in spacecraft/plasma interactions. The computational suite is composed of programs at three distinct levels, reflecting the increasing size and complexity of the different codes. At the top level there is a simple code for determining the characteristics of the low Earth and polar orbital environment. At the lowest level, on the other hand, there are programs that determine in detail the charging and wake characteristics of a body in a flowing plasma.
  • The report also describes the results of a comprehensive experimental programme which has been used to validate some of the computer models. The experimental program has been designed specifically to verify the models used in the lower levels of the suite. Consequently, experiments investigating the wake characteristics of a body and the charging of a surface under the influence of a high energy beam have been performed.

Followed by a "Rider No. 1" whose results are:

Additional work, carried out to address a number of areas which were felt to merit further study, improving two of the codes, and providing further experimental data for comparison. These areas are:

  • A major upgrade of the code SOLARC, modelling the interactions of solar arrays with the space plasma, and its application to the study of spacecraft grounding strategy, current collection, and sputter erosion of materials.
  • More detailed experimental work on the simulation of charging of isolated materials in a low Earth orbit (LEO) spacecraft plasma wake, to resolve inconsistencies in earlier work and provide test cases for future numerical simulation work.
  • Numerical and experimental work to study the angular and energy characteristics of the ion wake structure. This was to be carried out by further development of the PICCHARGE code, and experimental measurements using an ion probe capable of making simulations measurements of ion energy, position, and incoming angle.
  • A preliminary study of plasma fluctuations and noise in the plasma wake region.

A "Rider 2", with a somewhat different emphasis was undertaken, when it was clear that the greatest threat to future ESA missions lay in the high altitude environment:

The principal areas covered by the study were as follows:

  • Modification to the NASCAP surface charging code in order to improve known limitations of the code. These modifications included restructuring of the input/output routines, optimisation of the time stepping algorithm and improvements to the LONGTIMESTEP and ROTATE facilities. These improvements were designed to use the capabilities of modern computer systems.
  • Analysis of data from the Low Energy Plasma Analyser (LEPA) on the CRRES satellite. The data from this instrument covered the energy range from 10 eV to 30 keV and allowed many questions about the low energy plasma environment around CRRES to be answered, including those concerning surface charging.
  • Calculations of anisotropy effects using the upgraded version of NASCAP. This part of the study used data from the CRRES satellite in order to define an anisotropic environment which was subsequently used to investigate charging on both a body stabilised and a spinning satellite.
  • Analysis of internal charging phenomena. This part of the study had the objective of using the ESA internal charging code, ESADDC, to interpret data from the CRRES Internal Discharge Monitor (IDM) as well as to perform a parametric analysis. The parametric analysis was designed in order to explore the sensitivity of the calculated internal charging to changes in the characteristics of the charging model. A review of conductivity in dielectric materials was also performed.
  • Evaluation of Russian spacecraft charging data. In this part of the study a data exchange agreement between the Scientific Production Association of Applied Mechanics (NPO-PM) in Russia and ESA was used to allow data from Russian GLONAS and GORIZONT satellites to be analysed. In addition, this activity enabled an examination of the Russian charging codes COULOMB and ECO-M to be made.

 

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