The Dynamic Interplay Between Spacecraft Charging, Space Environment Interactions and Evolving Materials

While the effects on spacecraft charging from varying environmental conditions and from the selection of different construction materials have been studied extensively, modification of materials properties by exposure to the space plasma environment can also have profound effects on spacecraft charging. Given the increasingly demanding nature of space missions, there is a clear need to extend our understanding of the dynamic nature of material properties that affect spacecraft charging and to expand our knowledge base of materials’ responses to specific environmental conditions so that we can more reliably predict the long term response of spacecraft to their environment. This paper focuses on the effects of environment-induced material modifications on physical properties relevant to spacecraft charging simulations. It also reviews several specific examples in which environment-induced material modifications have significant impact on predicted spacecraft charging

Effects of Temperature and Radiation Dose on Radiation Induced Conductivity

Radiation induced conductivity (RIC) is an important conduction mechanism in highly disordered insulating materials exposed to ionizing radiation. Measurements of RIC as a function of dose rate and exposure time of polymeric and glassy insulators will be presented. RIC results from excitation of carriers into conduction states by the ionizing radiation. The measurements will be discussed in terms of models for the distribution of localized disordered states. The effects of temperature and radiation damage from ionizing radiation on the density and occupation of trap states, and how this affects RIC, will also be discussed

Laboratory Simulations of Simultaneous Reduced Gravity and Ionizing Radiation Environments

A novel system has been developed to simulate the combined effects of reduced gravity and ionizing radiation present during spaceflight on biological and particulate samples. The miniature rotary cell culture system (mRCCS) was designed to synchronously rotate up to five independent vessels containing particulate samples suspended in fluid media, constructed using radiation tolerant, biocompatible, and vacuum compatible materials. Reduced gravity conditions were achieved when particles (e.g., 200 µm polystyrene microcarrier beads with or without adhered cell clusters) were suspended inside the vessels moving near terminal velocity in viscous fluid media with densities matched to the suspended particles to achieve neutral buoyancy and minimal effective gravity. Variations in centripetal acceleration from slow rotation of the vessels limited reduced gravity environments from ~2·10-2 to \u3c 1·10-5 g, comparable to similar commercially available systems. The effective gravitational acceleration experienced by the suspended particles was calibrated by tracking of particles within the mRCCS systems vessels. The entire mRCCS apparatus can be used in a standalone configuration for independent reduced gravity simulations or can be introduced into the Utah State University\u27s Space Survivability Test (SST) chamber for radiation exposure or simultaneous radiation exposure under reduced gravity. The SST chamber has a ~90 mCi 90Sr source that emits 0.2 to 2.5 MeV β radiation. The combined mRCCS and SST chamber system can provide average effective dose rates for the suspended particles, controlled over a broad range ( \u3e 900X) from ~3.7 mGy/day to 3.4 Gy/day by varying the source-to-sample distance and using varying slit width graphite shields. This system can provide stable, simultaneous space-like radiation and reduced gravity environments for experiments conducted on timescales of minutes to months

Physics-Driven Dual-Defect Model Fits of Voltage Step-Up to Breakdown Data in Spacecraft Polymers

Overly conservative estimates of breakdown strength can increase the mass and cost of spacecraft electrostatic discharge (ESD) mitigation methods. Improved estimates of ESD likelihood in the space environment require better models of ESD distributions. The purpose of this work is to evaluate our previously proposed dual-defect model of voltage step-up-to-breakdown tests with a case study across four dielectric materials. We predicted that materials best fit by mixed Weibull distributions would exhibit better fits with the dual-defect model compared to a mean field single defect theory. Additional data for biaxially oriented polypropylene (BOPP), polyimide (PI or Kapton) from three sources, and polyether ether ketone (PEEK) are compared to the previous study on low-density polyethylene (LDPE). Except in one case, the dual-defect model is a better fit to bimodal distributions of tests results