New Frontiers in Spacecraft Charging

Abstract

Spacecraft charging, as a field, is continually being recharged by new developments in understanding, new materials and technologies, and new approaches to both new and old problems. I will discuss some of the new frontiers in understanding spacecraft charging in this paper, as well as referencing relevant papers from the 11th Spacecraft Charging Technology Conference. Spacecraft charging is highly material-property dependent. For example, the secondary electron emission, photoemission, bulk electrical resistivity, and surface resistivity are important parameters that help determine the extent of spacecraft charging (both on the surface and inside the spacecraft) in any given environment. Our understanding of these material properties is one of the new frontiers in spacecraft charging. I will discuss how these fundamental material properties have been found to depend on the following: proper measurement techniques, temperature, radiation flux, electric field, surface treatment, surface contamination from plumes and outgassing, surface modification through arcing and vacuum exposure, and synergistic effects. Modeling of spacecraft charging is a second new frontier. New developments in modeling have both improved our understanding of spacecraft charging and enabled us to model situations that are dynamic and geometrically complex. New schemes for treating both space and time variations of fields, particle fluxes, and spectra have made our modeling more precise and accurate. Now, many more spacecraft are being launched into low Earth orbit and the radiation belts. Modeling charging effects more accurately in those orbits will become more important than ever. A third new frontier in spacecraft charging is novel mitigation techniques. Surface materials and simple passive devices that emit electrons as fast as they are collected seem to make real-time charge mitigation cheaply and reliably achievable for the first time. Novel solar cell configurations and coverglass materials promise to make arcing, both of the primary electrostatic discharge (ESD) type and sustained arcing between cells or strings, a thing of the past. Superconducting cables may obviate the high voltages that lead to arcing. New cooperation between spacecraft and solar array manufacturers and spacecraft charging experts may help to prevent the spacecraft charging mistakes of the past. Furthermore, the final frontier is dealing with new materials and higher power requirements. Lightweight spacecraft materials are, in some cases, prone to exacerbate charging or arcing and may allow transmission of electromagnetic interference into sensitive electronics. New solar cell active materials may increase the effects of arcing on solar cell and solar array performance, even for primary ESD events. Higher power requirements may require longer transmission cables, which may increase the need for higher voltages, making arcing more likely. If superconducting cables become a reality, magnetics may become very important for spacecraft control and stability. What will happen to a superconducting cable if it must carry the increased current in an arcing event of very short duration?