Author: Nicolas Nik Lee

Publisher:

Published: 2012

Total Pages:

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Small meteoroids, with masses less than a microgram, are common within the solar system and routinely impact spacecraft. In Earth orbit, human-made debris also presents a risk of impact. This thesis provides the first characterization of the threat of electrical damage from these hypervelocity impacts. When an impactor encounters a spacecraft (typically at 60 km/s for meteoroids or 10 km/s for debris), its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. The behavior of hypervelocity impact plasmas was studied through ground-based experiments and a corresponding plasma expansion model to interpret the data. The experiments were conducted using a Van de Graaff dust accelerator at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Impacts of iron projectiles ranging from 0.1 fg to 10 pg at speeds of up to 70 km/s were studied using a variety of target materials. Novel plasma sensors were designed and built to characterize the plasma expansion from impacts on these targets under a range of surface charging conditions representative of space environment effects. Impact plasmas associated with bare metal targets as well as spacecraft materials were studied. The expansion behavior of the impact plasma was found to depend strongly on the surface charge of the target. From a correlation of experimental measurements with theoretical models, the dependence of plasma composition and temperature on target material, impact speed, and surface charge was analyzed. This work includes three major results. First, the initial temperature of the impact plasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impact plasmas from glass targets, unlike that of impact plasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of satellites in order to prevent impact-related electrical anomalies. Since spacecraft charging is strongly dependent on orientation and surface material, deleterious electrical effects of hypervelocity impacts can be mitigated through design and operational practices that account for the influence of spacecraft geometry and the space environment on the behavior of impact plasmas.