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Charge Enhanced Contamination And Environmental Degradation Of Misse-6 Suspecs Materials, John R. Dennison, Amberly Evans, Danielle Fulmer, Joshua L. Hodges
Charge Enhanced Contamination And Environmental Degradation Of Misse-6 Suspecs Materials, John R. Dennison, Amberly Evans, Danielle Fulmer, Joshua L. Hodges
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The effects of prolonged exposure to the LEO space environment and charge-enhanced contamination on optical, thermal, and electron emission and transport properties of common spacecraft materials have been investigated by comparing pre- and post-flight characterization measurements. The State of Utah Space Environment and Contamination Study (SUSpECS) deployed in March 2008 on board the Materials International Space Station Experiment (MISSE-6) payload, was exposed for ~18 months on the exterior of the International Space Station (ISS), and was retrieved in September 2009. A total of 165 samples were mounted on three separate SUSpECS panels on the ram and wake sides on the …
Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, John R. Dennison
Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, John R. Dennison
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The electron emission properties of a material subject to incident radiation flux are key parameters in determining to what equilibrium charge a spacecraft will established under given environmental conditions. However, there is a complex relation between these emission properties and the charge built up in spacecraft insulators. Complex modeling codes have been developed to predict the potential a spacecraft will adopt as a consequence of its interaction with the space plasma. These require correct models of the electron yields as a function of charge to accurately predict the both the charge build up and the equilibrium potential of spacecraft components. …
The Effects Of Surface Modification On Spacecraft Charging Parameters, Amberly Evans, John R. Dennison
The Effects Of Surface Modification On Spacecraft Charging Parameters, Amberly Evans, John R. Dennison
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Charging of materials by incident radiation is affected by both environmental and physical conditions. Modifying a material’s physical surface will change its reflection, transmission and absorption of the incident radiation which are integrally related to the accumulation of charge and energy deposition in the material. An optical analysis of the effect of surface modification on spacecraft charging parameters on prototypical Kapton HN and Cu samples is presented. Samples were roughened with abrasive compounds ranging from 0.5 to 10 μm in size, comparable to the range of incident wavelengths. They were also contaminated with thin layers of DC 704 diffusion pump …
The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson
The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson
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Secondary electron emission is a critical contributor to the current balance in spacecraft charging. Spacecraft charging codes use a parameterized expression for the secondary electron yield δ(Eo) as a function of incident electron energy Eo. Simple three-step physics models of the electron penetration, transport and emission from a solid are typically expressed in terms of the incident electron penetration depth at normal incidence or range R(Eo ), and the mean free path of the secondary electron, λ(E). We recall classical models for the range R(Eo): a power law expression of the form b1Eon1 …
Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, John R. Dennison
Instrumentation For Studies Of Electron Emission And Charging From Insulators, C. D. Thomson, V. V. Zavyalov, John R. Dennison
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Making measurements of electron emission properties of insulators is difficult since insulators can charge either negatively or positively under charge particle bombardment. In addition, high incident energies or high fluences can result in modification of a material’s conductivity, bulk and surface charge profile, structural makeup through bond breaking and defect creation, and emission properties. We discuss here some of the charging difficulties associated with making insulator-yield measurements and review the methods used in previous studies of electron emission from insulators. We present work undertaken by our group to make consistent and accurate measurements of the electron/ion yield properties for numerous …
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison
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Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition—e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces can and generally do undergo significant evolution …
Solar Cycle Dependence Of Spacecraft Charging In Low Earth Orbit, T. B. Frooninckx, Jan Josef Sojka
Solar Cycle Dependence Of Spacecraft Charging In Low Earth Orbit, T. B. Frooninckx, Jan Josef Sojka
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Recent experimental evidence has shown that Defense Meteorological Satellite Program (DMSP) polar orbiting spacecraft at 840 km can develop electric potentials as severe as −1430 V while at high magnetic latitudes. To explore this charging region, an analysis of DMSP F6, F7, F8, and F9 satellite precipitating particle and ambient plasma measurements taken during periods of high, medium, and low solar flux is performed. One hundred eighty-four charging events ranging from −46 to −1430 V are identified, and an extreme solar cycle dependence is found as charging is most frequent and severe during solar minimum. Satellite measurements and time-dependent ionospheric …