An electrostatic method to model the expansion of hypervelocity impact plasma on positively biased surfaces

Abstract

Spacecraft are a major component of infrastructure and are essential to modern society. Though launch opportunities are expected to become less expensive and more frequent through commercial launch providers, spacecraft design, manufacturing, and deployment processes are far from routine. In addition, a spacecraft's operational environment is riddled with numerous hazards that may jeopardize its performance, and with a cost to orbit of $10 000 per pound, there is a desire to protect our space assets and mitigate against damage. Meteoroids and orbital debris, which are components of the space environment, are two such threats to space vehicles. While larger objects endanger spacecraft mechanically, collisions are rare; however, bodies with masses smaller than a milligram impact frequently and at speeds up to 72.8 km s−1 if in solar orbit. Shortly after contact, projectile and spacecraft materials vaporize and ionize, resulting in an expanding plasma that may interfere with onboard sensors and equipment. These hypervelocity impacts have potentially been the source of unexplained electronic anomalies through arc discharge and electromagnetic emission mechanisms. To better understand the plasma structure, hypervelocity impact experiments were conducted at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using their Van de Graaff dust accelerator and vacuum chamber, iron dust particles impacted typical spacecraft material targets with surface potentials ranging from –1000 V to +1000 V, representing charging conditions experienced in orbit. During this experiment, a suite of sensors measured impact plasma properties; among these sensors are two distinct arrays of charge collecting plates, termed Faraday plate arrays, positioned to describe the plasma's range and azimuthal distributions. The work discussed here presents a multi-species plasma expansion model and compares its results to those obtained experimentally. The particle model uses a tree structure to reduce computational complexity. The agreement between the simulated output and the sensor measurements provides confidence in the model's ability to replicate the plume accurately. Consequently, the model is used to provide initial plasma temperature and bulk expansion speed estimates, to explore the sensitivity of our measurements to shifts in sensor position, and to identify potentially hazardous regions on spacecraft.