IONOSPHERE IONIZATION EFFECTS ON SHEATH STRUCTURE AROUND A HIGH-VOLTAGE SPACECRAFT

The electric sheath structure around a cylindrical spacecraft whose su rface is biased to a high positive potential and surrounded by a water -vapor cloud in the ionosphere is studied. A small degree of ionizatio n collision inside the sheath leads to an explosive sheath expansion, because the electric sheath tries to compensate for the loss of negati ve charge by attracting more electrons. An expression for the critical neutral density above which the sheath explosion occurs is derived. F or typical conditions, the critical neutral density lies between 10(16 ) and 10(18) m(-3). Monte Carlo Particle-in-Cell simulation is done to check the validity of the expression. The simulation result shoes the expression gives a reasonable prediction of the critical neutral dens ity with the least computational time.