Wousik Kim

Electron Nonionizing Energy Loss for Device Applications

The electron induced nonionizing energy loss (NIEL) for representative device and detector materials are presented here. The electron NIELs are computed analytically using the Mott differential cross section. As for the partition function, which describes the portion of energy deposited into displacing lattice atoms, the expression recently developed by Akkerman was used that better fits for the low recoil energy.

Review of an Internal Charging Code, NUMIT

An internal charging code, which is called NUMerical InTegration, has been used on many occasions to study the charging and discharging characteristics of dielectrics in space. The capabilities and limitations of the code are reviewed in this paper. In particular, the basic assumptions of the model are briefly discussed, and an example for the internal charging in the Juno environment is presented.

Fault injection experiment results in space borne parallel application programs

Development of the REE Commercial-Off-The-Shelf (COTS) based space-borne supercomputer requires a detailed knowledge of system behavior in the presence of Single Event Upset (SEU) induced faults. When combined with a hardware radiation fault model and mission environment data in a medium grained system model, experimentally obtained fault behavior data can be used to: predict system reliability, availability and performance; determine optimal fault detection methods and boundaries; and define high ROI fault tolerance strategies. The REE project has developed a fault injection suite of tools and a methodology for experimentally determining system behavior statistics in the presence of application level SEU induced transient faults. Initial characterization of science data application code for an autonomous Mars Rover geology application indicates that this code is relatively insensitive to SEUs and thus can be made highly immune to application level faults with relatively low overhead strategies.

An Algorithm for Determining Energy Deposition Profiles in Elemental Slabs by Low (

Internal charging/discharging is an important concern for todays spacecraft. An important tool for tracking charge buildup in slabs of material that includes a self-consistent solution of the electric fields in the material is the NUMIT code. To date, one of limitations on use of that code has been determining the effects for particles with energy less than 100 keV. To correct this, a universal algorithm for determining dose profiles in slabs has been developed for low energy (10 keV les Ei les 100 keV) electrons. This work extends the Tabata algorithm, originally developed for Ei > 100 keV electrons, down to 10 keV. Following a brief review of the NUMIT code, the role the Tabata algorithm plays in NUMIT is discussed. As a first step in extending the algorithm, Monte Carlo simulations were performed to obtain the dose-depth profiles for various incident energies. It was found that for a given target, the dose profiles obtained for the different incident energies can be normalized to a single curve by applying the scaling factors for the depth (x-axis) and energy deposition (y-axis). These scaling factors are dependent both on the incident electron energy and on the target material. In the second step, for each target element, the normalized dose profile was fit with a simple equation and the fitting coefficients obtained. The overall fitting procedure and the parameters obtained for the fit are described in this paper.

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We present an empirical model of Jupiters electron radiation environment and its application to the design of the future NASA mission to Europa. The model is based on data from the Galileo spacecraft. Measurements of the high-energy, omni-directional electrons from the Energetic Particle Detector (EPD) and magnetic field from the Magnetometer (MAG) onboard Galileo are used for this purpose. Ten-minute averages of the EPD data are used to provide an omni-directional electron flux spectrum at 0.238, 0.416, 0.706, 1.5, 2.0, and 11.0 MeV. Additionally, data from the Geiger Tube Telescope onboard Pioneer 10 and 11 are used to calculate the flux of 31 MeV electrons. The Galileo Interim Radiation Electron model v.2 (GIRE2) combines these datasets with the original Divine model and synchrotron observations to estimate the trapped electron radiation environment. Unlike the original Divine model, which was based on flybys of the Voyager and Pioneer spacecraft, the new GIRE2 model covers about 7 years of data and more than 30 orbits around Jupiter from the Galileo spacecraft. The model represents a step forward in the study of the Jovian radiation environment and is a valuable tool to assist in the design of future missions to Jupiter. This paper gives an overview of GIRE2 and focuses on its application to the design of the future NASA mission to Europa. The spacecraft will orbit Jupiter and perform multiple flybys of the moon Europa, which is embedded in the middle of a very strong radiation environment. The radiation environment surrounding the moon as well as along the trajectory are described in the paper together with the implications of this environment on the design of a mission.

keV) Energy Electrons: An Internal Charging Application

Several space missions are being considered for Jupiter. These range from the recently launched Juno mission to possible joint NASA and ESA missions to Europa and Ganymede. Although the direct effects of radiation dose are normally considered the most pressing design issue for these missions, spacecraft charging, through surface charging, vxB, and, more importantly, internal charging, is also a key design concern. This paper reviews the current state of understanding of the jovian charging environment including the background plasma, high-energy electrons, and magnetic field. In conjunction with these environments, we will also review the range of effects to be expected in response to these environments. These effects need to be carefully considered in parallel with radiation effects in the design of the planned missions if they are to survive in the extremely challenging jovian environment.

The GIRE2 model and its application to the Europa mission

An internal electrostatic discharge monitor (IESDM) is being developed at JPL that measures the depth profile of potential in dielectrics. The JPL IESDM is described in this paper with an initial test result using electron beam.

The Jovian Charging Environment and Its Effects—A Review

The Juno mission to Jupiter will have a highly elliptical orbit taking the spacecraft through the radiation belts surrounding the planet. During these passes through the radiation belts, the spacecraft will be subject to high doses of radiation from energetic electrons and protons with energies ranging from 10 keV to 1 GeV. While shielding within the spacecraft main body will reduce the total absorbed dose to much of the spacecraft electronics, instruments and cables on the outside of the spacecraft will receive much higher levels of absorbed dose. In order to estimate the amount of degradation to two such cables, testing has been performed on two coaxial cables intended to provide high voltages to three of the instruments on Juno. Both cables were placed in a vacuum of 5x10(exp -6) torr and cooled to -50(deg)C prior to exposure to the radiation sources. Measurements of the coaxial capacitance per unit length and partial discharge noise floor indicate that increasing levels of radiation make measurable but acceptably small changes to the F EP Teflon utilized in the construction of these cables. In addition to the radiation dose testing, observations were made on the internal electrostatic charging characteristics of these cables and multiple discharges were recorded.

Internal Electrostatic Discharge Monitor (IESDM)

The baseline design of the planned Europa Mission includes large solar arrays, which may experience surface charging. The spacecraft would encounter Europa ~40 times with some passes within ~25 km. This paper will describe the plasma environment expected near Europa during these encounters. Emphasis will be on the torus near Europa and on Europa’s ionosphere. Whereas the spacecraft would encounter a cold, corotating torus plasma with a velocity of ~120 km/s near Europa, it may encounter Europa’s ionosphere at a velocity as low as 5 km/s as Europa’s orbital velocity is only ~14 km/s relative to Jupiter. The challenge is to estimate the rapid potential variations associated with these two disparate environments. This paper will present a review of models of the plasma torus and the ionosphere and their interactions with each other. Ultimately, the models will be used to estimate the effects of the varying plasmas near Europa on the planned Europa Mission’s baseline spacecraft design and on its instruments with the intent of hardening that design to surface charging and to help with the interpretation of the effects of the charging environment on its instruments.

Radiation Dose Testing on Juno High Voltage Cables

A general 3-D internal charge analysis method, 3-D NUMIT, was developed by combining a Monte Carlo radiation transport simulation tool such as MCNPX or GEANT4 and a commercial finite-element analysis software such as COMSOL. The method was validated in 1-D cases with the analytical solution and NUMIT 2.0 and in a 3-D case with previously developed CB_IESD. The internal charging behavior of a semi-rigid coax cable in space was successfully analyzed using this 3-D NUMIT method.