Micrometeoroid impact on ceramic thin components for interplanetary probe

A new advanced ceramic thruster made of monolithic silicon nitride (Si3N4) is under development for the next interplanetary probe of PLANET-C Venus exploration mission in Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). In order for secure operation of a spacecraft with a ceramic component onboard a real mission, the reliability against micrometeoroid impacts on the ceramic component has to be investigated in addition to the quasi-static mechanical and thermal analyses and verifications. First, the risk probability of the micrometeoroid impacts was evaluated by using an interplanetary flux model, and the risk evaluation in terms of impact energy was proposed by combining the velocity distribution with the flux model. The probability of impacts on the ceramic thruster during the mission was estimated with this model. Second, hypervelocity impact tests were performed with a two-stage light-gas gun. Three types of failure were observed: one was only a crater formed on the impact surface. Another type was crater formation on the front-face and spall fracture on the back-face and in the last type a perforation was formed in addition to cratering and spalling. The samples did not either shatter or breakdown for the impact energies tested in this study. The impact failure morphology observed in this study showed dependency on the plate thicknesses and the projectile kinetic energy. The energy-based risk evaluation together with the series of the hypervelocity impact tests indicated that the silicon nitride ceramic thruster onboard the interplanetary probe would have only a local damage and survive during the mission term.