The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
J.s. Hofstra - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetic shielding of circular and rectangular connectors, Backshells and braid terminations
[Proceedings] 1992 Regional Symposium on Electromagnetic Compatibility, 1992Co-Authors: L.o. Hoeft, J.s. HofstraAbstract:This paper discusses electromagnetic coupling in both circular and rectangular connectors and Backshells by presenting measurements of the surface transfer impedance contributions of each of the major design features.
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Electromagnetic shielding provided by selected DB-25 subminiature connectors
IEEE 1991 International Symposium on Electromagnetic Compatibility, 1991Co-Authors: L.o. Hoeft, J.s. HofstraAbstract:The surface transfer impedance of a variety of DB-25 subminiature connectors, such as are used on personal computer peripherals, was measured over the frequency range of 1 kHz to 100 MHz. The test samples included die cast and metallized plastic Backshells, receptacles with and without gaskets, circumferential (dual cones or compression insert) and single point (strain relief devices, compression set screw or pigtail) braid terminations. All samples included several centimeters of braid beyond the point where the Backshell made contact to the braid. The measured results are presented along with a discussion of the electromagnetic significance of each of the design features. The electromagnetic performance of these samples is compared to that of circular connectors.
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Electromagnetic coupling into rectangular rack-and-panel connectors
Proceedings of International Symposium on Electromagnetic Compatibility, 1Co-Authors: L.o. Hoeft, M.t. Montoya, J.s. HofstraAbstract:Measurement of the surface transfer impedance of both standard and EMI rack-and-panel connectors from 1 kHz to 100 MHz showed that the standard rack-and-panel connector provides essentially no electromagnetic shielding because it contains no positive mechanism for maintaining electrical contact between the plug and receptacle. Supplementary grounding devices reduce the transfer impedance to desirable levels for frequencies below a few tens of kHz. Electromagnetic shielding at high frequencies is minimal. Spring fingers around the periphery of the plugs were very effective for maintaining electrical contact between the plug and receptacle and preventing electromagnetic coupling through the plug/receptacle interface. Control of the electromagnetic coupling through the plug/Backshell interface was essential for good high frequency shielding performance. Gaskets installed in the plug/Backshell interface were electromagnetically effective but cumbersome to install. At 100 MHz, the surface transfer impedance was dominated by the bonding impedance between the receptacle and the chassis. When spring fingers and a gasketted Backshell were used, the transfer impedance of the rack-and-panel connector slowly increased from a fraction of a milliohm at low frequencies to several milliohms at high frequencies. This is about equivalent to the electromagnetic shielding expected of a quality circular connector and a good Backshell.
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Effects of environmental testing on the surface transfer impedance/EMP response of cable assemblies with metal banded braid terminations
IEEE 1991 International Symposium on Electromagnetic Compatibility, 1Co-Authors: L.o. Hoeft, J.s. Hofstra, G.l. DibbleAbstract:The surface transfer impedance and electromagnetic pulse (EMP) response of two sets of samples were measured before and after a series of environmental tests. Each sample consisted of 1 m of multiconductor cable terminated to a Backshell which in turn was mounted on a MIL-C-81511 connector. The surface transfer impedance and the EMP response were measured using the procedures of MIL-C-24640 and MIL-C-85485A, modified to accommodate cable assemblies rather than samples of cables. Samples that used a metal band method of braid termination and samples that used a Metcal solder strap braid termination were evaluated and compared. The effects that mechanical and thermal environmental testing had on the integrity of the electromagnetic shielding are described. This testing was meant to simulate the adverse treatment that an interconnect system might receive during its lifetime. The results of the measurements are presented. >
Michael J. Wright - One of the best experts on this subject based on the ideXlab platform.
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Sizing and Margins Assessment of Mars Science Laboratory Aeroshell Thermal Protection System
Journal of Spacecraft and Rockets, 2014Co-Authors: Michael J. Wright, Karl T. Edquist, Robin Beck, David M. Driver, Steven Sepka, Eric Slimko, William WillcocksonAbstract:The methodology employed for the thermal design and margins assessment of the Mars Science Laboratory aeroshell thermal protection system is reviewed. A new thermal margins policy was developed in the course of this work that provides additional rigor over previous methods. Because of a late change of thermal protection materials from the heritage super lightweight ablator 561V to phenolic impregnated carbon ablator, the design of the heat shield followed a nontraditional path in which the flight thickness was selected based on a mass (rather than thermal) limit. The material switch was followed by detailed thermal analyses that demonstrated that the baselined thickness was sufficient to provide adequate thermal protection to the vehicle without violating design requirements during a 3-sigma worst-case entry condition. The Backshell material thickness was also finalized before the thermal sizing was completed, and the resulting analysis showed that there was more than sufficient material on the Backshell....
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Monte Carlo Approach to FIAT Uncertainties with Applications for Mars Science Laboratory
Journal of Thermophysics and Heat Transfer, 2011Co-Authors: Steven Sepka, Michael J. WrightAbstract:A new scriptedMonte Carlo analysis software tool has been developed for use with the fully implicit ablation and thermal response program thermal-protection-system-sizing code. This paper describes the new software tool and gives examples of its increased utility and useful insights onmany aeroshell heatshield design considerations, such as maximum bond line temperature, recession, isotherm depth, surface temperature, and char depth. Finally, results are presented that illustrate the effect of uncertainties in key parameters that were used in the Mars Science Laboratory aeroshell thermal protection system design. The parameters having the greatest influence on bond line temperature dispersion for theMars Science Laboratory Backshell are virginmaterial thermal density (34%), initial material temperature (20%), virgin material conductivity (17%), and char density (13%).
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Aerothermodynamic Design of the Mars Science Laboratory Backshell and Parachute Cone
41st AIAA Thermophysics Conference, 2009Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. Wright, Chun Y. TangAbstract:Aerothermodynamic design environments are presented for the Mars Science Laboratory entry capsule Backshell and parachute cone. The design conditions are based on Navier-Stokes flowfield simulations on shallow (maximum total heat load) and steep (maximum heat flux) design entry trajectories from a 2009 launch. Transient interference effects from reaction control system thruster plumes were included in the design environments when necessary. The limiting Backshell design heating conditions of 6.3 W/sq cm for heat flux and 377 J/sq cm for total heat load are not influenced by thruster firings. Similarly, the thrusters do not affect the parachute cover lid design environments (13 W/sq cm and 499 J/sq cm). If thruster jet firings occur near peak dynamic pressure, they will augment the design environments at the interface between the Backshell and parachute cone (7 W/sq cm and 174 J/sq cm). Localized heat fluxes are higher near the thruster fairing during jet firings, but these areas did not require additional thermal protection material. Finally, heating bump factors were developed for antenna radomes on the parachute cone
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Aerothermodynamic Environments Definition for the Mars Science Laboratory Entry Capsule
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. Wright, Chun Y. TangAbstract:An overview of the aerothermodynamic environments definition status is presented for the Mars Science Laboratory entry vehicle. The environments are based on Navier-Stokes flowfield simulations on a candidate aeroshell geometry and worst-case entry heating trajectories. Uncertainties for the flowfield predictions are based primarily on available ground data since Mars flight data are scarce. The forebody aerothermodynamics analysis focuses on boundary layer transition and turbulent heating augmentation. Turbulent transition is expected prior to peak heating, a first for Mars entry, resulting in augmented heat flux and shear stress at the same heatshield location. Afterbody computations are also shown with and without interference effects of reaction control system thruster plumes. Including uncertainties, analysis predicts that the heatshield may experience peaks of 225 W/sq cm for turbulent heat flux, 0.32 atm for stagnation pressure, and 400 Pa for turbulent shear stress. The afterbody heat flux without thruster plume interference is predicted to be 7 W/sq cm on the Backshell and 10 W/sq cm on the parachute cover. If the reaction control jets are fired near peak dynamic pressure, the heat flux at localized areas could reach as high as 76 W/sq cm on the Backshell and 38 W/sq cm on the parachute cover, including uncertainties. The final flight environments used for hardware design will be updated for any changes in the aeroshell configuration, heating design trajectories, or uncertainties.
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Aerothermodynamic Environments Definition for the Mars Science Laboratory Entry Capsule," AIAA Paper 2007-1206
2007Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. WrightAbstract:An overview of the aerothermodynamic environments definition status is presented for the Mars Science Laboratory entry vehicle. The environments are based on Navier-Stokes flowfield simulations on a candidate aeroshell geometry and worst-case entry heating trajectories. Uncertainties for the flowfield predictions are based primarily on available ground data since Mars flight data are scarce. The forebody aerothermodynamics analysis focuses on boundary layer transition and turbulent heating augmentation. Turbulent transition is expected prior to peak heating, a first for Mars entry, resulting in augmented heat flux and shear stress at the same heatshield location. Afterbody computations are also shown with and without interference effects of reaction control system thruster plumes. Including uncertainties, analysis predicts that the heatshield may experience peaks of 225 W/cm2 for turbulent heat flux, 0.32 atm for stagnation pressure, and 400 Pa for turbulent shear stress. The afterbody heat flux without thruster plume interference is predicted to be 7 W/cm2 on the Backshell and 10 W/cm2 on the parachute cover. If the reaction control jets are fired near peak dynamic pressure, the heat flux at localized areas could reach as high as 76 W/cm2 on the Backshell and 38 W/cm2 on the parachute cover, including uncertainties
L.o. Hoeft - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetic shielding of circular and rectangular connectors, Backshells and braid terminations
[Proceedings] 1992 Regional Symposium on Electromagnetic Compatibility, 1992Co-Authors: L.o. Hoeft, J.s. HofstraAbstract:This paper discusses electromagnetic coupling in both circular and rectangular connectors and Backshells by presenting measurements of the surface transfer impedance contributions of each of the major design features.
-
Electromagnetic shielding provided by selected DB-25 subminiature connectors
IEEE 1991 International Symposium on Electromagnetic Compatibility, 1991Co-Authors: L.o. Hoeft, J.s. HofstraAbstract:The surface transfer impedance of a variety of DB-25 subminiature connectors, such as are used on personal computer peripherals, was measured over the frequency range of 1 kHz to 100 MHz. The test samples included die cast and metallized plastic Backshells, receptacles with and without gaskets, circumferential (dual cones or compression insert) and single point (strain relief devices, compression set screw or pigtail) braid terminations. All samples included several centimeters of braid beyond the point where the Backshell made contact to the braid. The measured results are presented along with a discussion of the electromagnetic significance of each of the design features. The electromagnetic performance of these samples is compared to that of circular connectors.
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Electromagnetic coupling into rectangular rack-and-panel connectors
Proceedings of International Symposium on Electromagnetic Compatibility, 1Co-Authors: L.o. Hoeft, M.t. Montoya, J.s. HofstraAbstract:Measurement of the surface transfer impedance of both standard and EMI rack-and-panel connectors from 1 kHz to 100 MHz showed that the standard rack-and-panel connector provides essentially no electromagnetic shielding because it contains no positive mechanism for maintaining electrical contact between the plug and receptacle. Supplementary grounding devices reduce the transfer impedance to desirable levels for frequencies below a few tens of kHz. Electromagnetic shielding at high frequencies is minimal. Spring fingers around the periphery of the plugs were very effective for maintaining electrical contact between the plug and receptacle and preventing electromagnetic coupling through the plug/receptacle interface. Control of the electromagnetic coupling through the plug/Backshell interface was essential for good high frequency shielding performance. Gaskets installed in the plug/Backshell interface were electromagnetically effective but cumbersome to install. At 100 MHz, the surface transfer impedance was dominated by the bonding impedance between the receptacle and the chassis. When spring fingers and a gasketted Backshell were used, the transfer impedance of the rack-and-panel connector slowly increased from a fraction of a milliohm at low frequencies to several milliohms at high frequencies. This is about equivalent to the electromagnetic shielding expected of a quality circular connector and a good Backshell.
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Effects of environmental testing on the surface transfer impedance/EMP response of cable assemblies with metal banded braid terminations
IEEE 1991 International Symposium on Electromagnetic Compatibility, 1Co-Authors: L.o. Hoeft, J.s. Hofstra, G.l. DibbleAbstract:The surface transfer impedance and electromagnetic pulse (EMP) response of two sets of samples were measured before and after a series of environmental tests. Each sample consisted of 1 m of multiconductor cable terminated to a Backshell which in turn was mounted on a MIL-C-81511 connector. The surface transfer impedance and the EMP response were measured using the procedures of MIL-C-24640 and MIL-C-85485A, modified to accommodate cable assemblies rather than samples of cables. Samples that used a metal band method of braid termination and samples that used a Metcal solder strap braid termination were evaluated and compared. The effects that mechanical and thermal environmental testing had on the integrity of the electromagnetic shielding are described. This testing was meant to simulate the adverse treatment that an interconnect system might receive during its lifetime. The results of the measurements are presented. >
Karl T. Edquist - One of the best experts on this subject based on the ideXlab platform.
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Sizing and Margins Assessment of Mars Science Laboratory Aeroshell Thermal Protection System
Journal of Spacecraft and Rockets, 2014Co-Authors: Michael J. Wright, Karl T. Edquist, Robin Beck, David M. Driver, Steven Sepka, Eric Slimko, William WillcocksonAbstract:The methodology employed for the thermal design and margins assessment of the Mars Science Laboratory aeroshell thermal protection system is reviewed. A new thermal margins policy was developed in the course of this work that provides additional rigor over previous methods. Because of a late change of thermal protection materials from the heritage super lightweight ablator 561V to phenolic impregnated carbon ablator, the design of the heat shield followed a nontraditional path in which the flight thickness was selected based on a mass (rather than thermal) limit. The material switch was followed by detailed thermal analyses that demonstrated that the baselined thickness was sufficient to provide adequate thermal protection to the vehicle without violating design requirements during a 3-sigma worst-case entry condition. The Backshell material thickness was also finalized before the thermal sizing was completed, and the resulting analysis showed that there was more than sufficient material on the Backshell....
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Aerothermodynamic Design of the Mars Science Laboratory Backshell and Parachute Cone
41st AIAA Thermophysics Conference, 2009Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. Wright, Chun Y. TangAbstract:Aerothermodynamic design environments are presented for the Mars Science Laboratory entry capsule Backshell and parachute cone. The design conditions are based on Navier-Stokes flowfield simulations on shallow (maximum total heat load) and steep (maximum heat flux) design entry trajectories from a 2009 launch. Transient interference effects from reaction control system thruster plumes were included in the design environments when necessary. The limiting Backshell design heating conditions of 6.3 W/sq cm for heat flux and 377 J/sq cm for total heat load are not influenced by thruster firings. Similarly, the thrusters do not affect the parachute cover lid design environments (13 W/sq cm and 499 J/sq cm). If thruster jet firings occur near peak dynamic pressure, they will augment the design environments at the interface between the Backshell and parachute cone (7 W/sq cm and 174 J/sq cm). Localized heat fluxes are higher near the thruster fairing during jet firings, but these areas did not require additional thermal protection material. Finally, heating bump factors were developed for antenna radomes on the parachute cone
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Aerothermodynamic Environments Definition for the Mars Science Laboratory Entry Capsule
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. Wright, Chun Y. TangAbstract:An overview of the aerothermodynamic environments definition status is presented for the Mars Science Laboratory entry vehicle. The environments are based on Navier-Stokes flowfield simulations on a candidate aeroshell geometry and worst-case entry heating trajectories. Uncertainties for the flowfield predictions are based primarily on available ground data since Mars flight data are scarce. The forebody aerothermodynamics analysis focuses on boundary layer transition and turbulent heating augmentation. Turbulent transition is expected prior to peak heating, a first for Mars entry, resulting in augmented heat flux and shear stress at the same heatshield location. Afterbody computations are also shown with and without interference effects of reaction control system thruster plumes. Including uncertainties, analysis predicts that the heatshield may experience peaks of 225 W/sq cm for turbulent heat flux, 0.32 atm for stagnation pressure, and 400 Pa for turbulent shear stress. The afterbody heat flux without thruster plume interference is predicted to be 7 W/sq cm on the Backshell and 10 W/sq cm on the parachute cover. If the reaction control jets are fired near peak dynamic pressure, the heat flux at localized areas could reach as high as 76 W/sq cm on the Backshell and 38 W/sq cm on the parachute cover, including uncertainties. The final flight environments used for hardware design will be updated for any changes in the aeroshell configuration, heating design trajectories, or uncertainties.
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Aerothermodynamic Environments Definition for the Mars Science Laboratory Entry Capsule," AIAA Paper 2007-1206
2007Co-Authors: Karl T. Edquist, Artem A. Dyakonov, Michael J. WrightAbstract:An overview of the aerothermodynamic environments definition status is presented for the Mars Science Laboratory entry vehicle. The environments are based on Navier-Stokes flowfield simulations on a candidate aeroshell geometry and worst-case entry heating trajectories. Uncertainties for the flowfield predictions are based primarily on available ground data since Mars flight data are scarce. The forebody aerothermodynamics analysis focuses on boundary layer transition and turbulent heating augmentation. Turbulent transition is expected prior to peak heating, a first for Mars entry, resulting in augmented heat flux and shear stress at the same heatshield location. Afterbody computations are also shown with and without interference effects of reaction control system thruster plumes. Including uncertainties, analysis predicts that the heatshield may experience peaks of 225 W/cm2 for turbulent heat flux, 0.32 atm for stagnation pressure, and 400 Pa for turbulent shear stress. The afterbody heat flux without thruster plume interference is predicted to be 7 W/cm2 on the Backshell and 10 W/cm2 on the parachute cover. If the reaction control jets are fired near peak dynamic pressure, the heat flux at localized areas could reach as high as 76 W/cm2 on the Backshell and 38 W/cm2 on the parachute cover, including uncertainties
Thomas R Yechout - One of the best experts on this subject based on the ideXlab platform.
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investigation of the unique stability characteristics of the nasa maraia reentry vehicle
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: Joshua Hunt, Christopher Shannon, Thomas R YechoutAbstract:NASA's Maraia Capsule, currently in development, is a small, autonomous re-entry vehicle designed to return to Earth from the International Space Station (ISS). It will act as a flight test bed for various capsule systems and provide on-demand sample return for the ISS. NASA Johnson Space Center tasked the United States Air Force Academy Department of Aeronautics to define the baseline aerodynamic characteristics of the capsule in subsonic flight. This baseline characterization included lift, drag and moment data for the capsule at Mach 0.3 and Mach 0.45 between 0 and 28 degrees angle of attack. A shifting center of gravity study, which is the focus of this paper, was also performed. Although the capsule was stable in pitch for all angles of attack tested with the NASA-provided moment reference center (MRC) location, the shifting center of gravity study concluded that shifting the MRC aft had little to no effect on pitch stability up to 16 degrees angle of attack. This was quite an unexpected result. After 16 degrees angle of attack, the farthest aft MRCs became more stable for a brief range of angles of attack before becoming unstable. Beyond approximately 24 degrees, normal stability characteristics returned as farther aft MRCs demonstrated less stability. Similar results were found through computational fluid dynamics (CFD) methods using NASA's OVERFLOW code. The MRC study also provided a recommended center of gravity envelope of 0 to 9 inches aft of the heat shield for the full scale Maraia which would provide stable characteristics within the angle of attack range evaluated. The counterintuitive trends of the shifting MRC study were further investigated in terms of surface pressures. The data was obtained using a 1:4.44 scale model in the U.S. Air Force Academy's subsonic wind tunnel. This model contained 16 pressure ports at various locations along the shoulder, Backshell, and base of the Maraia model, and the model was rotated to obtain a full pressure mapping of the Maraia surface. Both Mach 0.3 and 0.45 speeds revealed very similar trends. All lower shoulder ports experienced a drop in surface pressures at 16 and 18 degrees angle of attack with various levels of increasing pressures beyond this attitude based on their relative location. Lower Backshell ports experienced a drop in surface pressures at 16 degrees angle of attack as well. Ports near the base of the capsule were shown to have a subsequent increase in pressure immediately after this drop, while ports nearer the heat shield demonstrated a delay in their pressure increase to as late as 24 degrees angle of attack. Upper Backshell port pressures and base port pressures remained essentially constant throughout the alpha sweeps. These wake characteristics were visualized with Fieldview software as well as the U.S. Air Force Academy's water tunnel. The wake region around the bottom of the capsule was shown to significantly influence the aerodynamic characteristics of Maraia in subsonic flight and was correlated to the unexpected stability trends. This analysis will be important to NASA for determination of center of gravity location envelope limits and when considering potential modifications to the Maraia capsule geometry, especially in the lower shoulder and Backshell region.
