1,721,071 research outputs found
Simulation and optimization of the ion optics for a reflectron-type cosmic dust composition analyzer
Full text linkCosmic dust particle analysis offers insight into the history and behavior of our solar system. In order to perform in situ compositional analysis of particles, a cosmic dust spectrometer requires an effective area large enough, > 500 cm2, to capture dust with low flux and a mass resolution high enough, m/∆m > 200, to detect the relative abundances of ions with similar masses. In this study, a large area time-of-flight cosmic dust reflectron-type mass spectrometer, HyperDust, is optimized using the ion optics software SIMION along with newly developed Monte Carlo routines and fine- tuning optimization algorithms. The results are a spectrometer design with a mass resolution of 385 and a reproducible method for optimizing similar instruments. The instrument is being built at the Laboratory for Atmospheric and Space Physics (LASP), and has been proposed to missions for the study of asteroids and interstellar phenomena
Simulation and optimization of the ion optics for a reflectron-type cosmic dust composition analyzer
Full text linkCosmic dust particle analysis offers insight into the history and behavior of our solar system. In order to perform in situ compositional analysis of particles, a cosmic dust spectrometer requires an effective area large enough, > 500 cm2, to capture dust with low flux and a mass resolution high enough, m/∆m > 200, to detect the relative abundances of ions with similar masses. In this study, a large area time-of-flight cosmic dust reflectron-type mass spectrometer, HyperDust, is optimized using the ion optics software SIMION along with newly developed Monte Carlo routines and fine- tuning optimization algorithms. The results are a spectrometer design with a mass resolution of 385 and a reproducible method for optimizing similar instruments. The instrument is being built at the Laboratory for Atmospheric and Space Physics (LASP), and has been proposed to missions for the study of asteroids and interstellar phenomena
Application of the Na-DEMOF Atomic Filter to 3-Frequency Na Doppler Lidar Observations of Wind and Temperature in the Lower Atmosphere
Full text linkLidar systems comprise one of several indispensable tools for derivation of wind, density, and temperature profiles in the atmosphere. 3-frequency resonance-fluorescence lidars are particularly useful for high-resolution profiles of all three quantities derived simultaneously. However, these lidars depend on atomic species restricted to the metal layers in the middle and upper atmosphere as frequency discriminators, and are not optimized for derivation of these quantities in the lower atmosphere. Rayleigh Doppler lidars typically applied to this region face other restrictions, such as dependence on high-power transmitted lasers, lack of absolute frequency references, and inabilities to derive multiple atmospheric quantities simultaneously without expensive additional transmitter and receiver channels.
A proposed solution to these difficulties is the sodium double-edge magneto-optic filter, (Na-DEMOF), which provides a frequency discriminator for the Rayleigh signal returned by the lower atmosphere and allows 3-frequency Na Doppler lidars to derive atmospheric quantity profiles within the lower atmosphere as well as within the mesospheric and lower thermospheric (MLT) metal layers.
This thesis describes the design, benefits, and restrictions of Na-DEMOFs, and uses the application methods and most recent results of the Na-DEMOFs constructed and tested by the Chu lidar group to demonstrate their successful application to simultaneous derivation of meridional and zonal winds along with temperature
Elementary processes in dusty plasmas.
No full textElementary processes in dusty plasmas were studied experimentally in 3 separate projects. The 1st project was devoted to the investigation of basic charging processes of dust particles. The samples were the time-tested spherical grains of glass and zinc dust grains that were irregular in shape. The secondary emission from zinc dust had been commonly studied previously. It was found that the yield of secondary emission from zinc grains was considerably larger than expected which could be probably the effect of the shape of the sample or its size. The ion field emission from spherical glass grains was studied. In the 2nd project a study of dust charging on surfaces was performed. The charging processes examined were induced charge due to electric field, charging by contact potential, and the effect of UV irradiation. Both conducting and insulating dust samples were used. The contacting surfaces were exclusively metals. In the 3rd project the collision cross sections of small water clusters has been measured. The water cluster production was realized in a free-jet expansion of water vapour to produce supersonic molecular beams. The beam attenuation method was used to measure the apparent collision cross-sections of water cluster molecules with 3 different gases. It was found that these collision cross sections are considerably larger than the geometrical size of the water cluster molecules. This data can be used for modelling the performance of rocket-born instruments. They also provide a starting point for estimating of the nucleation rate of ice crystals in the mesosphere.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
PRODUCTION, TRANSPORT, AND DESTRUCTION OF DUST IN THE KUIPER BELT: THE EFFECTS OF REFRACTORY AND VOLATILE GRAIN COMPOSITIONS
Full text linkThe Venetia Burney Student Dust Counter (SDC) onboard the New Horizons spacecraft measures the spatial and size distributions of dust along its trajectory. Models based on early SDC measurements predicted a peak dust number density at a heliocentric distance of ∼40 au, followed by a rapid decline. Instead, SDC observed dust fluxes 2–3 times higher than predicted between 40 and 60 au. One potential explanation for this discrepancy is that SDC may be encountering icy grains with different dynamical behavior than previously modeled silicate grains. Due to ultraviolet photo-sputtering, water-ice grains rapidly erode and migrate outward, significantly contributing to the measured dust number densities only at distances ≳40 au. We present a model of silicate and ice grain dynamics in the outer Solar System, considering gravitational and radiation forces and grain erosion. Using SDC data, we estimate that the mass production rate of ice grains between 0.1 and 10 μm in the Kuiper Belt (KB) would need to be 20–70 times higher than that of silicate grains. However, KB grains are expected to be refractory/volatile mixtures rather than pure silicate or ice. Thus, we briefly explore simple models of more realistic mixed-grain cases to further gauge the effects of grain composition on the equilibrium dust distribution. Future SDC measurements at greater distances will test the model predictions and further constrain silicate and ice grain production rates in the KB.</p
Electrostatic Tractor Analysis for GEO Debris Remediation
Full text linkThe high value of operating in the geostationary ring, coupled with increasing numbers of orbital debris, highlights the need for GEO debris remediation techniques. One recent proposed technique for GEO debris mitigation is the electrostatic tractor. Here, a tug vehicle approaches a target debris object and emits a focused electron beam onto it. This results in a negative charge on the debris, and a positive charge on the tug vehicle. Due to the near proximity of the highly charged objects (20 meters or less) an attractive electrostatic force on the order of milliNewtons results. This electrostatic force is used in conjunction with low thrusting by the tug vehicle to tow the debris object into a disposal orbit 200-300 kilometers above the GEO belt.
During the tugging period, the charged relative motion between tug and deputy is stabilized through a feedback control law. This is accomplished using a novel relative motion description that isolates separation distance from the relative orientation. The equations of motion for the relative motion description are derived from the Clohessy-Wiltshire equations, assuming the debris object is in a nearly circular orbit. Lyapunov stability theory is used to derive an asymptotically stable control law for the tug thrusters during the towing period. The control law requires an estimate of the electrostatic force magnitude, and the impacts of improperly modeled charging on control response are determined. If the electrostatic force is under-predicted too severely, a collision may result. A bound on the control gains is determined to prevent such a collision.
Expected reorbiting performance levels achievable with the electrostatic tractor are computed. An open-loop analytical performance study is performed where variational equations are used to predict how much general orbital elements may be changed using the electrostatic tractor over one orbital period for a towed object at geosynchronous altitude. In contrast to earlier work, eccentric orbits and plane changes are also considered. Requirements on relative positioning of the tug and debris for various orbit corrections are identified for the different orbit corrections. In some cases, the tug must maneuver around the debris at particular locations in the orbit, but the incurred performance losses during this repositioning are minimal. Co-planar reorbiting maneuvers with corrections of several kilometers per day are achievable, but large scale plane changes are not.
A first-order analytic current model is used to calculate the charging on tug debris during the charge transfer process. The model includes plasma currents, photoelectron current, secondary electron emission, and electron beam current. The effects of nominal changes (as a function of local time) in GEO space weather conditions on tractor performance are characterized. While the electron beam current can be modified to compensate for these changes, maintaining a fixed beam current achieves similar performance. The impacts of the relative sizes of tug and deputy are studied to determine thresholds where charge transfer is no longer possible, and the effects on tractor performance are considered. The simultaneous emission of an electron beam (onto the debris) and an ion beam (into space) is considered as a means for improving tractor performance. For smaller tug vehicles, this simultaneous emission allows for significant performance increases, enabling the tug to tow larger debris objects. The benefits are not as pronounced for larger tug vehicles. The debris object emits photoelectrons and secondary electrons that may be recaptured by the positively charged tug. NASCAP-2K is used to provide an estimate about the severity of this back flux. It is not found to hinder performance of the electrostatic tractor. Overall, the study supports the feasibility of the electrostatic tractor for GEO debris remediation, and helps to identify areas for further research
Electrostatic Tractor Analysis for GEO Debris Remediation
Full text linkThe high value of operating in the geostationary ring, coupled with increasing numbers of orbital debris, highlights the need for GEO debris remediation techniques. One recent proposed technique for GEO debris mitigation is the electrostatic tractor. Here, a tug vehicle approaches a target debris object and emits a focused electron beam onto it. This results in a negative charge on the debris, and a positive charge on the tug vehicle. Due to the near proximity of the highly charged objects (20 meters or less) an attractive electrostatic force on the order of milliNewtons results. This electrostatic force is used in conjunction with low thrusting by the tug vehicle to tow the debris object into a disposal orbit 200-300 kilometers above the GEO belt.
During the tugging period, the charged relative motion between tug and deputy is stabilized through a feedback control law. This is accomplished using a novel relative motion description that isolates separation distance from the relative orientation. The equations of motion for the relative motion description are derived from the Clohessy-Wiltshire equations, assuming the debris object is in a nearly circular orbit. Lyapunov stability theory is used to derive an asymptotically stable control law for the tug thrusters during the towing period. The control law requires an estimate of the electrostatic force magnitude, and the impacts of improperly modeled charging on control response are determined. If the electrostatic force is under-predicted too severely, a collision may result. A bound on the control gains is determined to prevent such a collision.
Expected reorbiting performance levels achievable with the electrostatic tractor are computed. An open-loop analytical performance study is performed where variational equations are used to predict how much general orbital elements may be changed using the electrostatic tractor over one orbital period for a towed object at geosynchronous altitude. In contrast to earlier work, eccentric orbits and plane changes are also considered. Requirements on relative positioning of the tug and debris for various orbit corrections are identified for the different orbit corrections. In some cases, the tug must maneuver around the debris at particular locations in the orbit, but the incurred performance losses during this repositioning are minimal. Co-planar reorbiting maneuvers with corrections of several kilometers per day are achievable, but large scale plane changes are not.
A first-order analytic current model is used to calculate the charging on tug debris during the charge transfer process. The model includes plasma currents, photoelectron current, secondary electron emission, and electron beam current. The effects of nominal changes (as a function of local time) in GEO space weather conditions on tractor performance are characterized. While the electron beam current can be modified to compensate for these changes, maintaining a fixed beam current achieves similar performance. The impacts of the relative sizes of tug and deputy are studied to determine thresholds where charge transfer is no longer possible, and the effects on tractor performance are considered. The simultaneous emission of an electron beam (onto the debris) and an ion beam (into space) is considered as a means for improving tractor performance. For smaller tug vehicles, this simultaneous emission allows for significant performance increases, enabling the tug to tow larger debris objects. The benefits are not as pronounced for larger tug vehicles. The debris object emits photoelectrons and secondary electrons that may be recaptured by the positively charged tug. NASCAP-2K is used to provide an estimate about the severity of this back flux. It is not found to hinder performance of the electrostatic tractor. Overall, the study supports the feasibility of the electrostatic tractor for GEO debris remediation, and helps to identify areas for further research
Modular and Reusable Power System Design for the BRRISON Balloon Telescope
Full text linkHigh altitude balloons are emerging as low-cost alternatives to orbital satellites in the field of telescopic observation. The near-space environment of balloons allows optics to perform near their diffraction limit. In practice, this implies that a telescope similar to the Hubble Space Telescope could be fl own for a cost of tens of millions as opposed to billions.
While highly feasible, the design of a balloon telescope to rival Hubble is limited by funding. Until a prototype is proven and more support for balloon science is gained, projects remain limited in both hardware costs and man hours. Thus, to effectively create and support balloon payloads, engineering designs must be effcient, modular, and if possible reusable. This thesis focuses specifically on a modular power system design for the BRRISON comet-observing balloon telescope. Time- and cost-saving techniques are developed that can be used for future missions.
In this thesis, a modular design process is achieved through the development of individual circuit elements that span a wide range of capabilities. Circuits for power conversion, switching and sensing are designed to be combined in any configuration. These include DC-DC regulators, MOSFET drivers for switching, isolated switches, current sensors and voltage sensing ADCs. Emphasis is also placed on commercially available hardware. Pre-fabricated DC-DC converters and an Arduino microcontroller simplify the design process and offer proven, cost-effective performance.
The design of the BRRISON power system is developed from these low-level circuits. A board for main power distribution supports the majority of flight electronics, and is extensible to additional hardware in future applications. An ATX computer power supply is developed, allowing the use of a commercial ATX motherboard as the fl ight computer. The addition of new capabilities is explored in the form of a heater control board. Finally, the power system as a whole is described, and its overall performance analyzed. The success of the BRRISON power system during testing and fl ight proves its utility, both for BRRISON and for future balloon telescopes
Application of the Na-DEMOF Atomic Filter to 3-Frequency Na Doppler Lidar Observations of Wind and Temperature in the Lower Atmosphere
Full text linkLidar systems comprise one of several indispensable tools for derivation of wind, density, and temperature profiles in the atmosphere. 3-frequency resonance-fluorescence lidars are particularly useful for high-resolution profiles of all three quantities derived simultaneously. However, these lidars depend on atomic species restricted to the metal layers in the middle and upper atmosphere as frequency discriminators, and are not optimized for derivation of these quantities in the lower atmosphere. Rayleigh Doppler lidars typically applied to this region face other restrictions, such as dependence on high-power transmitted lasers, lack of absolute frequency references, and inabilities to derive multiple atmospheric quantities simultaneously without expensive additional transmitter and receiver channels.
A proposed solution to these difficulties is the sodium double-edge magneto-optic filter, (Na-DEMOF), which provides a frequency discriminator for the Rayleigh signal returned by the lower atmosphere and allows 3-frequency Na Doppler lidars to derive atmospheric quantity profiles within the lower atmosphere as well as within the mesospheric and lower thermospheric (MLT) metal layers.
This thesis describes the design, benefits, and restrictions of Na-DEMOFs, and uses the application methods and most recent results of the Na-DEMOFs constructed and tested by the Chu lidar group to demonstrate their successful application to simultaneous derivation of meridional and zonal winds along with temperature
Relativistic Electrons in Earth’s Outer Radiation Belt: Wave-Particle Interactions and Precipitation Loss
Full text linkEarth's outer radiation belt is a highly dynamic region of the magnetosphere composed of relativistic electrons with often unpredictable variations in energy and spatial extent. Understanding this variable radiation environment is critical for protecting both spacecraft and humans in space. A number of competing acceleration and loss processes combine to produce net enhancements or depletions of the outer radiation belt. Electron precipitation into the atmosphere is a critical part of this loss, and quantified understanding of this mechanism is needed in order to understand and ultimately predict radiation belt dynamics. In the following work, we investigate the contribution of electron precipitation to radiation belt losses, looking at what times precipitation is important and at how much loss it contributes. Through a combination of long-term existing data sets as well as new CubeSat measurements we perform both statistical and detailed event studies to better understand the nature and extent of MeV electron loss to the atmosphere. We analyze measurements of precipitating electrons directly as well as electromagnetic waves that may be causing this precipitation. Our studies provide a more cohesive picture of outer radiation belt dynamics and the relationship between precipitating energetic electrons and global magnetospheric conditions
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