Laboratory tests for spacecraft charging and discharging: from Hertz, Millikan and de Broglie to today's questions

Hertz (1887) generated reasonably narrow-band radio frequency oscillations in metal dipoles using air discharges between the dipole elements. Nearly 50 years later technologists working with high voltage particle accelerators and gamma-irradiators noticed arc-discharge trees entirely inside solid insulating dielectrics (glass) stimulated by irradiation alone, without applied voltage. B. Gross et al. performed an early scientific study of the phenomena and related the onset of internal discharges to the quantity, in coulombs, of irradiation charge stopped inside the dielectric and held there for long time periods. Recent international studies have related the charge-induced electric field strength in the dielectric to the propagation of the internal discharge tree. When it exits a surface of the dielectric into vacuum, gas from the tree provides a conductive path across the vacuum. Higher conductivity is produced by higher quantities of gas. Whereas Hertz air arcs were low impedance, /spl Lt/70 Ohms, generating resonant responses, the irradiated unbiased dielectric arcs appear to be high-impedance, low-Q, phenomena. Recent researches address practical questions for spacecraft subjected to space radiations: (1) How many discharge trees are initiated in the dielectric per unit time? (2) How much electric current is conducted as a function of time? (3) What is the charge decay time constant in the dielectric? (4) Over spacecraft lifetimes, how is the charge distributed in the dielectric? (5) How does the initial dielectric discharge evolve to short out a HV power system? (6) How can discharges propagate along the vacuum surface of a dielectric? (7) How does the discharge current distribute among spacecraft electronic circuits. (8) Can a discharge burn out sensitive electronic devices and how can this be prevented?.