Predictive Formula for Electron Range over a Large Span of Energies

An empirical model developed by the Materials Research Group that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous-Slow-Down-Approximation for energy deposition in a material to develop a composite analytical formula which estimated the range from 10 MeV with an uncertainty of v, which describes the effective number of valence electrons. NV was empirically calculated for \u3e200 materials which have tabulated range and inelastic mean free path data in the NIST ESTAR and IMFP databases. Correlations of NV with key material constants (e.g., density, atomic number, atomic weight, and band gap) were established for this large set of materials. Somewhat different correlations were found for different sub-classes of materials (e.g., solids/liquids/gases, conductors/semiconductors/insulators, elements/compounds/polymers/composites). Values of the average energy lost per inelastic collision were related to band gap and plasmon energies for solids and first excitation energies for liquids and gases. Simulations were performed to test the sensitivity of NV and the range to materials parameters; these suggest that reasonably accurate results were achievable with modest precision of the parameters. These correlations have led to methods using only basic material properties to predict Nv and the range for additional untested materials which have no supporting range data. Estimates for both simple compounds (e.g., BN and AlN), composites, and complex biological materials (e.g., brain tissue and cortical bone tissue) are presented, along with tests of the validity and accuracy of the predictive formula. These calculations are of great value for studies involving high energy electron bombardment, such as electron spectroscopy, spacecraft charging, or electron beam therapy. Efforts are underway to create a user tool available to the scientific community to estimate the range of an arbitrary material with modest accuracy over an extended width of incident electron energies. *Supported through funding from NASA Goddard Space Flight Center and a USU URCO Fellowship

Simulation Chamber for Space Environment Survivability Testing

A vacuum chamber was designed and built that simulates the space environment making possible the testing of material modification due to exposure of solar radiation. Critical environmental components required include an ultra high vacuum (10-9 Torr), a UV/VIS/NIR solar spectrum source, an electron gun and charge plasma, temperature extremes, and long exposure duration. To simulate the solar spectrum, a solar simulator was attached to the chamber with a range of 200nm to 2000nm. The exposure time can be accelerated by scaling the solar intensity up to four suns. A Krypton lamp imitates the 120 nm ultraviolet hydrogen Lymann alpha emission not produced by the solar simulator. A temperature range from 100K to 450K is achieved using an attached cryogenic reservoir and resistance heaters. An electron flood gun (mono-energetic, 20 eV to 15keV) is calibrated to replicate solar wind at desired distances from the sun. The chamber maintains 98% uniformity of the electron and electromagnetic radiation exposure relative to the center. The chamber allows for a cost-effective investigation of multiple small-scale samples. An automated data acquisition system monitors and records the reflectivity, absorptivity, and emissivity of the samples throughout the test. An integrating sphere and an IR absorptivity/emissivity probe are used to collect this data. The system allows for measurements to be taken while the samples are still under vacuum and exposed to radiation. With these accurate simulations we can closely predict the material’s behavior in near proximity to the sun. This information is vital in determining materials for satellites, probes, and any other spacecraft

Electron Penetration Range for Every Body

The penetration range of an electron into diverse materials can be estimated using an approximation fit as a function of a single parameter, N y, which describes the effective number of valence electrons. This fit is found using the Continuous-Slow Down-Approximation (CSDA), which simplifies the process of estimating an expected penetration range of a given material by applying some of the material’s key characteristics. Using the CSDA, a simple composite analytical formula is created which estimates the range or maximum penetration depth of incident electrons. This formula generates an approximation to the range using the parameter, Nv . The range of well-fit electrons encompasses energies from \u3c10 eV to \u3e10MeV with an accuracy of 20%. A list comprised of 247 materials has been compiled that greatly extends the applicability of this model. Several significant material constants were compiled for each material, including the atomic number, atomic weight, atomic density, and band gap. These materials were further separated into various subcategories including conductors, semiconductors, and insulators, and the material’s phase at room temperature. To determine Nv , the model was then fit to existing data for these materials collected from the ESTAR and IMFP databases compiled by NIST. Comparison of Nv with the material’s constants from this large database of materials will made. The resulting formula could possibly lead to the prediction of Nv for materials which have no supporting data. These calculations are of great value for studies of high electron bombardment, such as electron spectroscopy or spacecraft charging. This research may also be applied in the medical field, for instance, improving physical selectivity in radiation therapy

Small Satellite Verification and Assessment Test Facility with Space Environments Effects Ground-testing Capabilities

The Utah State University Space Dynamics Laboratory (SDL) and Materials Physics Group (MPG) have developed an extensive versatile and cost-effective pre-launch test capability for verification and assessment of small satellites, system components, and spacecraft materials. The facilities can perform environmental testing, component characterization, system level hardware in-the-loop testing, and qualification testing to ensure that each element is functional, reliable, and working per its design. Unique capabilities of SDL’s Nano-Satellite Operation Verification and Assessment (NOVA) test facility include: (i) mass and moment of inertia testing using a high resolution mass measurement table to determine the center of gravity and an inverted pendulum table; (ii) dynamic magnetic field environment capable of simulating varying magnetic fields and interorbital variations in field strength accomplished using a large Helmholtz cage; (iii) ex situ solar simulation and solar array testing using a solar simulator light source; (iv) speed, jitter, and torque measurements of attitude control systems and small satellites weighing kg; (v) attitude control sensor calibration and characterization using a combination of a zero-gauss chamber for magnetometer calibration, an Earth horizon simulator for horizon crossing sensors, and illumination sources for sun/moon recognition sensors; and (vi) communications protocol testing. Additional SDL environmental test facilities for small satellites include: (i) vacuum chambers for simulating the near-vacuum environments of space; (ii) thermal chambers for temperature bakeout and thermal swing characterization; (iii) outgassing measurement capabilities for screening new materials and (iv) a vibration table capable of a suite of sinusoidal and random vibration profiles to simulate environments seen on launch vehicles. Complimentary testing for potential environmental-induced modifications of small satellites, components, and materials are conducted at the MPG’s Space Environment Effects Materials (SEEM) test facility in their new Space Survivability Test (SST) high vacuum chamber; this provides long-duration exposure of these elements to simulated space environment conditions. The facility simulates critical environmental components including the neutral gas atmosphere/vacuum, the far UV through near IR solar spectrum, electron plasma fluxes, and temperature with exposure to within 90 β-radiation source produces a high-energy (~100 keV to \u3e2 MeV) spectrum similar to the GEO spectrum for testing of radiation damage, single event interrupts, and COTS parts. An automated data acquisition system periodically monitors and records the real-time environmental conditions—along with in situ monitoring of key satellite/component/sample performance metrics and characterization of material properties and calibration standards—during the sample exposure cycle. A wide array of results for a prototypical 1U cubesat—including performance of solar arrays, electronics, sensor and memory components, radiation damage, basic communication responses, structural integrity, etc.—acquired at the NOVA and the SST facilities are presented to demonstrate their combined test capabilities

Space Effects Survivability Testing

A versatile test facility has been designed to study the effects of space environment fluxes and radiation damage on small scale materials samples, system components, and small satellites. Cost-effective long-duration testing for potentially environmental-induced modifications is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments, make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics. The facility simulates environmental components including the neutral gas atmosphere, the solar spectrum, electron plasma fluxes, and temperature. The UV/VIS/NIR solar spectrum is simulated using a class AAA Solar Simulator with up to four Suns light intensity. Far ultraviolet radiation is provided by Kr discharge line sources also with up to four Suns intensity. A low-energy electron flood gun provides a uniform, monoenergetic (20 eV-15 keV) electron flux. A medium-energy (20-100 keV), low-flux electron source uses filament-free photoemission. A Sr90 β radiation source produces a high-energy spectrum similar to the geosynchronous spectrum. A stable, uniform temperature range from 100-450 K is achieved using a cryogenic reservoir and resistance heaters. A data acquisition system periodically records the environmental conditions, photographs, UV/VIS/NIR reflectivity, IR absorptivity/emissivity, and surface voltage of the sample surface and in situ calibration standards in the chamber