Engineering topics
Publications and source records attributed to Coakley, P..
The progress in spacecraft charging is reviewed with particular attention given to the interactions of plasma and penetrating radiation with dielectrics. Topics discussed include the charging environments, elementary charging theory, the anomalies attributed to charging or discharging phenomena, and spacecraft engineering.
The effects of midenergy electrons on the charge and discharge characteristics of spacecraft dielectric materials and the data base from which basic discharge models can be formulated is expanded. Thin dielectric materials were exposed to low, mid combined low and mid, and spectral energy electron environments. Three important results are presented: (1) it determined electron environments that lead to dielectric discharges at potentials less negative than -5 kV; (2) two types of discharges were identified that dominate the kinds of discharges seen; and (3) it is shown that, for the thin dielectric materials tested, the worst-case discharges observed in the various environments are similar.
Charging and discharging characteristics of dielectric samples exposed to 1-25 keV and 25-100 keV electrons in a laboratory environment are reported. The materials examined comprised OSR, Mylar, Kapton, perforated Kapton, and Alphaquartz, serving as models for materials employed on spacecraft in geosynchronous orbit. The tests were performed in a vacuum chamber with electron guns whose beams were rastered over the entire surface of the planar samples. The specimens were examined in low-impedance-grounded, high-impedance-grounded, and isolated configurations. The worst-case and average peak discharge currents were observed to be independent of the incident electron energy, the time-dependent changes in the worst case discharge peak current were independent of the energy, and predischarge surface potentials are negligibly dependent on incident monoenergetic electrons.
A computer simulation is applied to the production of strong electric potential double layers (DL) in a triple plasma device. The simulation is intended to represent DL in the low magnetosphere above the auroral zones. The DL are described as standing electrostatic shocks with different energy coefficients in their strong and weak forms. The strong DL was generally found to be unstable, but stability could be imparted if a population of trapped electrons was presented. Stability increased with the length of the system. A schematic for the system is presented, and a phase-space plot of electrons (indicating system stability) is graphed.