Spacecraft Coating-Induced Charging: Materials and Modeling Study of Environmental Extremes
Published by the American Institute of Aeronautics and Astronautics in Journal of Spacecraft and Rockets. Publisher PDF is available through the link above. Publisher requires a subscription to access the article.
As mankind reaches to explore extreme environments in space, the application of ceramics surface coatings is increasing. The 2005 mission concept for Solar Probe used a unique design to achieve the necessary thermal control for a very close approach to the solar corona, including the use of a highly refractory, electrically insulating ceramic coating over a carbon–carbon composite heat shield. The proposed trajectory takes the spacecraft from a Jovian flyby to within 4 solar radii of the sun, spanning 5 orders of magnitude in solar radiation and solar wind plasma density as well as spacecraft temperatures from <100 K to>2000 K. Using the NASCAP-2K charging modeling program, the degree of charging expected for this spacecraft design has been calculated for this range of radiation environments. New measurements of the electron emission and estimates of related properties of the candidate materials, Al2O3, pyrolytic born nitride, and barium zirconium phosphate, are presented. Absolute and differential surface charging are found to depend strongly on temperature through increased conductivity at higher temperatures and on radiation flux through enhanced charge accumulation and radiation-induced conductivity. As the spacecraft approaches the sun, the competition between increased charge dissipation at higher temperatures and increased charge accumulation at higher fluxes leads to a maximum in differential charging between 0.2 and 2 astronomical units. Although the spacecraft charging behavior of these materials is found to be significant, it is not severe enough to endanger the mission, and a number of options exist to mitigate the degree of charging. Among the ceramics considered, the use of Al2O3 coatings is found to minimize both absolute and differential spacecraft charging.