Daniel P. Engelhart

Chemical and Electrical Dynamics of Polyimide Film Damaged by Electron Radiation

The processes of electrical charge accumulation and dissipation in dielectric materials are critical to spacecraft construction and operational anomaly resolution. Electrical conductivity, and therefore surface potential, of radiation-damaged materials undergoes unpredicted changes while on orbit. The space environment causes fundamental modifications in the chemical structure of spacecraft materials by breaking intermolecular bonds and creating free radicals that act as space charge traps. Over time, free radicals react with each other and the material recovers. The rates of free radical formation and loss determine the dynamics of the conductivity of spacecraft materials. Lack of knowledge about dynamic aging is a major impediment to accurate modeling of spacecraft behavior over its mission life. This paper presents an investigation of the chemical and physical properties of polyimide (PI) films during and after irradiation with high-energy (90 keV) electrons. The constant voltage method was utilized to monitor material conductivity during the recovery process. To quantify the concentration of free radicals within the irradiated material, the electron paramagnetic resonance technique was used. Changes in the infrared (IR) absorption profile of irradiated materials during the recovery process were identified using the directional-hemispherical reflectance technique coupled with the Fourier transform IR spectroscopy. This physical/chemical collaboration allowed correlation of chemical changes in PI with the dynamic nature of spacecraft material aging.

Space environment simulation and sensor calibration facility

The Mumbo space environment simulation chamber discussed here comprises a set of tools to calibrate a variety of low flux, low energy electron and ion detectors used in satellite-mounted particle sensors. The chamber features electron and ion beam sources, a Lyman-alpha ultraviolet lamp, a gimbal table sensor mounting system, cryogenic sample mount and chamber shroud, and beam characterization hardware and software. The design of the electron and ion sources presented here offers a number of unique capabilities for space weather sensor calibration. Both sources create particle beams with narrow, well-characterized energetic and angular distributions with beam diameters that are larger than most space sensor apertures. The electron and ion sources can produce consistently low fluxes that are representative of quiescent space conditions. The particle beams are characterized by 2D beam mapping with several co-located pinhole aperture electron multipliers to capture relative variation in beam intensity and a large aperture Faraday cup to measure absolute current density.

Effect of Electron Bombardment on Polyimide Film

Interaction of high energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to cause their physical degradation. However, understanding of the chemical nature of this damage and the effect on the electrical and optical properties of PI is still limited. This lack of understanding limits predictive spacecraft models (charging, thermal, etc) as only pristine material properties are used for calculation. This is a major source of error in spacecraft construction and anomaly resolution, since PI properties change after exposure to the space environment. In the presented study, we analyze the chemical, electrical, and optical changes to polyimide after exposure to 90 keV electrons.

Effect of environment on charge transport properties of polyimide films damaged by high-energy electron radiation

Ground based measurements are critical to understanding the space environment-induced modifications of spacecraft materials and predictive spacecraft modeling. The interaction of high-energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to modify the materials chemical and consequently physical properties. Highly stable in its pristine state, radiation-damaged PI becomes chemically reactive due to the formation of species containing unpaired electrons (radicals). As a result, the reaction of residual gases, even at low partial pressures, changes the damaged PIs properties and obscures the understanding of the radiation damage mechanisms. In the presented paper, the authors demonstrated that even very limited air exposure will have a dramatic effect on the charge transport properties of radiation-damaged PI. Further, they also evaluated the effects of several major constituents of the Earths atmosphere (Ar, N2, O2, and H2O) on the charge transport properties of PI damaged by exposure to 90 keV electrons.Ground based measurements are critical to understanding the space environment-induced modifications of spacecraft materials and predictive spacecraft modeling. The interaction of high-energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to modify the materials chemical and consequently physical properties. Highly stable in its pristine state, radiation-damaged PI becomes chemically reactive due to the formation of species containing unpaired electrons (radicals). As a result, the reaction of residual gases, even at low partial pressures, changes the damaged PIs properties and obscures the understanding of the radiation damage mechanisms. In the presented paper, the authors demonstrated that even very limited air exposure will have a dramatic effect on the charge transport properties of radiation-damaged PI. Further, they also evaluated the effects of several major constituents of the Earths atmosphere (Ar, N2, O2, and H2O) on the charge transport properties of PI dama...

Effect of Atmosphere on Recovery Dynamics of Polyimide Film Damaged by Electron Radiation

Since electrons are the primary charged particles at the geosynchronous Earth orbit (GEO), understanding of their interactions with spacecraft materials, such as polyimide (PI, Kapton-H®), is important. Understanding of the chemical nature of electron damage and its effect on PIs electrical and optical properties is still limited. Thus, predictive spacecraft models (electrical charging, thermal, etc) are restricted to only pristine material properties. This is a major source of error in spacecraft construction and anomaly resolution, since material properties change after exposure to the space environment. Ground based measurements are critical to understanding the dynamics of spacecraft materials however it will be shown in this work that standard material handling practice and exposure to air are unacceptable for these studies.