Bibliography
|
Notice:
|
Found 882 entries in the Bibliography.
Showing entries from 851 through 882
| 2013 |
|
Measurements from the Relativistic Electron and Proton Telescope integrated little experiment (REPTile) on board the Colorado Student Space Weather Experiment (CSSWE) CubeSat mission, which was launched into a highly inclined (65\textdegree) low Earth orbit, are analyzed along with measurements from the Relativistic Electron and Proton Telescope (REPT) and the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the Van Allen Probes, which are in a low inclination (10\textdegree) geo-transfer-like orbit. Both REPT and MagEIS measure the full distribution of energetic electrons as they traverse the heart of the outer radiation belt. However, due to the small equatorial loss cone (only a few degrees), it is difficult for REPT and MagEIS to directly determine which electrons will precipitate into the atmosphere, a major radiation belt loss process. REPTile, a miniaturized version of REPT, measures the fraction of the total electron population that has small enough equatorial pitch angles to reach the altitude of CSSWE, 480 km \texttimes 780 km, thus measuring the precipitating population as well as the trapped and quasi-trapped populations. These newly available measurements provide an unprecedented opportunity to investigate the source, loss, and energization processes that are responsible for the dynamic behavior of outer radiation belt electrons. The focus of this paper will be on the characteristics of relativistic electrons measured by REPTile during the October 2012 storms; also included are long-term measurements from the Solar Anomalous and Magnetospheric Particle Explorer to put this study into context. Li, X.; Schiller, Q.; Blum, L.; Califf, S.; Zhao, H.; Tu, W.; Turner, D.; Gerhardt, D.; Palo, S.; Kanekal, S.; Baker, D.; Fennell, J.; Blake, J.; Looper, M.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2013 YEAR: 2013 DOI: 10.1002/2013JA019342 |
|
We adopt a physics-based technique to infer chorus wave amplitudes from the low-altitude electron population (30\textendash100 keV) measured by multiple Polar Orbiting Environmental Satellites (POES), which provide extensive coverage over a broad region in L-shell and magnetic local time (MLT). This technique is validated by analyzing conjunction events between the Van Allen Probes measuring chorus wave amplitudes near the equator and POES satellites measuring the 30\textendash100 keV electron population at the conjugate low altitudes. We apply this technique to construct the chorus wave distributions during the 8\textendash9 October storm in 2012 and demonstrate that the inferred chorus wave amplitudes agree reasonably well with conjugate measurements of chorus wave amplitudes from the Van Allen Probes. The evolution of the chorus wave intensity inferred from low-altitude electron measurements can provide real-time global estimates of the chorus wave intensity, which cannot be obtained from in situ chorus wave measurements by equatorial satellites alone, but is crucial in quantifying radiation belt electron dynamics. Li, W.; Ni, B.; Thorne, R.; Bortnik, J.; Green, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 09/2013 YEAR: 2013 DOI: 10.1002/grl.v40.1710.1002/grl.50920 |
|
Lithium Ion Battery Fault Management on the Van Allen Probes The Van Allen Probes (formerly known as the Radiation Belt Storm Probes or RBSP) mission launched on 30 August 2012 as part of NASA\textquoterights Living With a Star (LWS) Program. The ultimate goal of the mission is to understand how populations of relativistic electrons and penetrating ions in the Earth\textquoterights Van Allen Radiation Belts are affected by the Sun. The mission consists of two nearly identical observatories orbiting in highly-elliptical Earth orbits. The two satellite system allows for the study of the spatial and temporal effects the Sun has on the Earth\textquoterights radiation belts. Each observatory is equipped with a suite of instruments designed to continuously study ions, electrons and the local magnetic and electric fields. A brief overview of the Van Allen Probe mission is presented with an emphasis on the power subsystem and the fault management system. A unique challenge encountered on the Van Allen Probes mission was the health monitoring and management of the Lithium Ion battery. The fault management system employed three different strategies to monitor and protect the health of the battery: a hardware implemented low voltage sense, a software implemented low voltage sense, and a low battery state of charge calculation (coulometry). The pros and cons of each of these strategies are further discussed with respect to fault management system design and the battery test data collected during the integration, test and environmental testing phases of development. Smith, Evan; Butler, Michael; Fretz, Kristin; Wilhelm, Benjamin; Published by: Published on: 09/2013 YEAR: 2013 DOI: 10.2514/6.2013-5526 |
|
Phase Space Density matching of relativistic electrons using the Van Allen Probes: REPT results 1] Phase Space Density (PSD) matching can be used to identify the presence of nonadiabatic processes, evaluate accuracy of magnetic field models, or to cross-calibrate instruments. Calculating PSD in adiabatic invariant coordinates requires a global specification of the magnetic field. For a well specified global magnetic field, nonadiabatic processes or inadequate cross calibration will give a poor PSD match. We have calculated PSD(μ, K) for both Van Allen Probes using a range of models and compare these PSDs at conjunctions in L* (for given μ, K). We quantitatively assess the relative goodness of each model for radiation belt applications. We also quantify the uncertainty in the model magnetic field magnitude and the related uncertainties in PSD, which has applications for modeling and particle data without concurrent magnetic field measurements. Using this technique, we show the error in PSD for an energy spectrum observed by the relativistic electron-proton telescope (REPT) is a factor of \~1.2 using the TS04 model. Morley, S.; Henderson, M.; Reeves, G.; Friedel, R.; Baker, D.; Published by: Geophysical Research Letters Published on: 09/2013 YEAR: 2013 DOI: 10.1002/grl.50909 |
|
Van Allen Probes Low Cost Mission Operations Concept and Lessons Learned Following a successful 60-day commissioning period, NASA\textquoterights Radiation Belt Storm Probes (RBSP) mission, was renamed Van Allen Probes in honor of the discoverer of Earth\textquoterights radiation belts \textendash James Van Allen. The Johns Hopkins University\textquoterights Applied Physics Laboratory (APL) executed the mission and is currently operating the twin spacecraft in their primary mission. Improving on the cost-savings concepts employed by prior APL projects, the Van Allen Probes mission operations was designed from the start for low-cost, highly-automated mission operations. This concept is realized with automated initial planning and contact scheduling, unattended real-time operations, and spacecraft performance assessment from the review of data products that have been automatically generated. This low-cost approach can be accomplished because of a simple spacecraft design and de-coupled spacecraft and instrument operations. This paper will present the Van Allen Probes mission operations concept focusing on the components that keep the cost of operations low and pointing out lessons learned that can be applied to future programs. Harvey, Raymond; Eichstedt, John; Published by: Published on: 09/2013 YEAR: 2013 DOI: 10.2514/MSPACE1310.2514/6.2013-5450 |
|
[1] We present NASA Van Allen Probes observations of wave-particle interactions between magnetospheric ultra-low frequency (ULF) waves and energetic electrons (20\textendash500 keV) on 31 October 2012. The ULF waves are identified as the fundamental poloidal mode oscillation and are excited following an interplanetary shock impact on the magnetosphere. Large amplitude modulations in energetic electron flux are observed at the same period (≈ 3 min) as the ULF waves and are consistent with a drift-resonant interaction. The azimuthal mode number of the interacting wave is estimated from the electron measurements to be ~40, based on an assumed symmetric drift resonance. The drift-resonant interaction is observed to be localized and occur over 5\textendash6 wave cycles, demonstrating peak electron flux modulations at energies ~60 keV. Our observation clearly shows electron drift resonance with the fundamental poloidal mode, the energy dependence of the amplitude and phase of the electron flux modulations providing strong evidence for such an interaction. Significantly, the observation highlights the importance of localized wave-particle interactions for understanding energetic particle dynamics in the inner magnetosphere, through the intermediary of ULF waves. Claudepierre, S.; Mann, I.R.; Takahashi, K; Fennell, J.; Hudson, M.; Blake, J.; Roeder, J.; Clemmons, J.; Spence, H.; Reeves, G.; Baker, D.; Funsten, H.; Friedel, R.; Henderson, M.; Kletzing, C.; Kurth, W.; Wygant, J.; Published by: Geophysical Research Letters Published on: 09/2013 YEAR: 2013 DOI: 10.1002/grl.50901 |
|
A differential Kennel-Petschek (KP) flux limit for magnetospheric energetic ions is devised taking into account multiple ion species effects on electromagnetic ion cyclotron (EMIC) waves that scatter the ions. The idea is that EMIC waves may limit the highest ion intensities during acceleration phases of storms and substorms (~ hour) while other mechanisms (e.g., charge exchange) may account for losses below those limits and over longer periods of time. This approach is applied to published Earth magnetosphere energetic ion spectra (~ keV to ~1 MeV) for radial positions (L) 3 to 6.7 RE. The flatness of the most intense spectral shapes for <100 keV indicate sculpting by just such a mechanism, but modifications of traditional KP parameters are needed to account for maximum fluxes up to 5.4 times greater than expected. Future work using the new capabilities of the Van Allen Probes mission will likely resolve outstanding uncertainties. Published by: Geophysical Research Letters Published on: 08/2013 YEAR: 2013 DOI: 10.1002/grl.50789 energetic ions; Radiation belts; ring current; Van Allen Probes |
|
Excitation of Poloidal standing Alfven waves through the drift resonance wave-particle interaction Drift-resonance wave-particle interaction is a fundamental collisionless plasma process studied extensively in theory. Using cross-spectral analysis of electric field, magnetic field, and ion flux data from the Van Allen Probe (Radiation Belt Storm Probes) spacecraft, we present direct evidence identifying the generation of a fundamental mode standing poloidal wave through drift-resonance interactions in the inner magnetosphere. Intense azimuthal electric field (Eφ) oscillations as large as 10mV/m are observed, associated with radial magnetic field (Br) oscillations in the dawn-noon sector near but south of the magnetic equator at L\~5. The observed wave period, Eφ/Br ratio and the 90\textdegree phase lag between Br and Eφ are all consistent with fundamental mode standing Poloidal waves. Phase shifts between particle fluxes and wave electric fields clearly demonstrate a drift resonance with \~90 keV ring current ions. The estimated earthward gradient of ion phase space density provides a free energy source for wave generation through the drift-resonance instability. A similar drift-resonance process should occur ubiquitously in collisionless plasma systems. One specific example is the \textquotedblleftfishbone\textquotedblright instability in fusion plasma devices. In addition, our observations have important implications for the long-standing mysterious origin of Giant Pulsations. Dai, L.; Takahashi, K; Wygant, J.; Chen, L.; Bonnell, J; Cattell, C.; Thaller, S.; Kletzing, C.; Smith, C.; MacDowall, R.; Baker, D.; Blake, J.; Fennell, J.; Claudepierre, S.; Funsten, H.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 08/2013 YEAR: 2013 DOI: 10.1002/grl.50800 |
|
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 \%. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance. Funsten, H.; Skoug, R.; Guthrie, A.; MacDonald, E.; Baldonado, J.; Harper, R.; Henderson, K.; Kihara, K.; Lake, J.; Larsen, B.; Puckett, A.; Vigil, V.; Friedel, R.; Henderson, M.; Niehof, J.; Reeves, G.; Thomsen, M.; Hanley, J.; George, D.; Jahn, J.-M.; Cortinas, S.; Santos, Los; Dunn, G.; Edlund, E.; Ferris, M.; Freeman, M.; Maple, M.; Nunez, C.; Taylor, T.; Toczynski, W.; Urdiales, C.; Spence, H.; Cravens, J.; Suther, L.; Chen, J.; Published by: Space Science Reviews Published on: 08/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9968-7 |
|
Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100\textendash2000 Hz. In the outer plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed convective linear growth rates indicate instability at the observed low frequencies. This suggests that the unusual low-frequency plasmaspheric hiss is likely to be amplified in the outer plasmasphere due to the injected energetic electrons. Li, W.; Thorne, R.; Bortnik, J.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Blake, J.; Fennell, J.; Claudepierre, S.; Wygant, J.; Thaller, S.; Published by: Geophysical Research Letters Published on: 08/2013 YEAR: 2013 DOI: 10.1002/grl.50787 |
|
Electron Acceleration in the Heart of the Van Allen Radiation Belts The Van Allen radiation belts contain ultrarelativistic electrons trapped in Earth\textquoterights magnetic field. Since their discovery in 1958, a fundamental unanswered question has been how electrons can be accelerated to such high energies. Two classes of processes have been proposed: transport and acceleration of electrons from a source population located outside the radiation belts (radial acceleration) or acceleration of lower-energy electrons to relativistic energies in situ in the heart of the radiation belts (local acceleration). We report measurements from NASA\textquoterights Van Allen Radiation Belt Storm Probes that clearly distinguish between the two types of acceleration. The observed radial profiles of phase space density are characteristic of local acceleration in the heart of the radiation belts and are inconsistent with a predominantly radial acceleration process. Reeves, G.; Spence, H.; Henderson, M.; Morley, S.; Friedel, R.; Funsten, H.; Baker, D.; Kanekal, S.; Blake, J.; Fennell, J.; Claudepierre, S.; Thorne, R.; Turner, D.; Kletzing, C.; Kurth, W.; Larsen, B.; Niehof, J.; Published by: Science Published on: 07/2013 YEAR: 2013 DOI: 10.1126/science.1237743 |
|
The Van Allen Probes Power System Launch and Early Mission Performance The Van Allen Probes are twin NASA spacecraft that were launched August 30, 2012, into lapping highly elliptical earth orbits. The twin spacecraft will operate within the Van Allen radiation belts throughout their two-year mission. The Van Allen Probes are sponsored by NASA\textquoterights Living With a Star (LWS) Program. The Johns Hopkins University, Applied Physics Laboratory designed, fabricated, and operates the twin spacecraft for NASA. The power systems of the twin spacecraft are identical. A direct energy transfer topology was selected for the power system. The loads are connected directly to the eight-cell Lithium Ion battery. The solar panels consist of triple junction cells. The design average power of each spacecraft is about 350 Watts, nominal 28.8 volt bus. A single 50 AH Lithium Ion battery is used to support the spacecraft loads during launch and eclipse periods. The battery charge control is performed using constant current/constant voltage taper charging. The two Van Allen Probes are performing as designed. This paper will describe the power system launch and early mission performance results. Published by: Published on: 07/2013 YEAR: 2013 DOI: 10.2514/MIECEC1310.2514/6.2013-3737 |
|
A quantitative analysis is performed on the decay of an unusual ring of relativistic electrons between 3 and 3.5 RE, which was observed by the Relativistic Electron Proton Telescope instrument on the Van Allen probes. The ring formed on 3 September 2012 during the main phase of a magnetic storm due to the partial depletion of the outer radiation belt for L > 3.5, and this remnant belt of relativistic electrons persisted at energies above 2 MeV, exhibiting only slow decay, until it was finally destroyed during another magnetic storm on 1 October. This long-term stability of the relativistic electron ring was associated with the rapid outward migration and maintenance of the plasmapause to distances greater than L = 4. The remnant ring was thus immune from the dynamic process, which caused rapid rebuilding of the outer radiation belt at L > 4, and was only subject to slow decay due to pitch angle scattering by plasmaspheric hiss on timescales exceeding 10\textendash20 days for electron energies above 3 MeV. At lower energies, the decay is much more rapid, consistent with the absence of a long-duration electron ring at energies below 2 MeV. Thorne, R.; Li, W.; Ni, B.; Ma, Q.; Bortnik, J.; Baker, D.; Spence, H.; Reeves, G.; Henderson, M.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Turner, D.; Angelopoulos, V.; Published by: Geophysical Research Letters Published on: 06/2013 YEAR: 2013 DOI: 10.1002/grl.50627 |
|
A novel technique for rapid L* calculation: algorithm and implementation Computing the magnetic drift invariant, L*, rapidly and accurately has always been a challenge to magnetospheric modelers, especially given the im- portance of this quantity in the radiation belt community. Min et al. (2013) proposed a new method of calculating L* using the principle of energy con- servation. Continuing with the approach outlined therein, the present pa- per focuses on the technical details of the algorithm to outline the implemen- tation, systematic analysis of accuracy, and verification of the speed of the new method. We also show new improvements which enable near real-time computation of L*. The relative error is on the order of 10-3 when \~ 0.1 RE grid resolution is used and the calculation speed is about two seconds per particle in the popular Tsyganenko and Sitnov 05 model (TS05). Based on the application examples, we suggest that this method could be an added resource for the radiation belt community. Min, Kyungguk; Bortnik, J.; Lee, Jeongwoo; Published by: Journal of Geophysical Research Published on: 05/2013 YEAR: 2013 DOI: 10.1002/jgra.50250 calculating L*; rapid L* calculation; RBSP; Van Allen Probes |
|
Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere [1] In this paper, we estimate the size of coherent activity of electromagnetic ion cyclotron (EMIC) waves using the multi-spacecraft observations made during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. We calculate the cross-correlations between EMIC wave powers measured by different THEMIS spacecraft, plot them over the separation distances between pairs of observing spacecraft, and determine the 1/e folding distance of the correlations as the characteristic dimension of the coherent wave activity. The characteristic radius in the direction transverse to the local magnetic field is found to lie in rather a wide range of 1500\textendash8600 km varying from the AM to PM sectors and also from hydrogen to helium bands. However, the characteristic dimensions normalized by either gyroradius or wavelength fall into narrower ranges almost independent of the emission band and event location. Specifically, the coherent dimension is found to be 10\textendash16 times gyroradius of 100 keV protons and 2\textendash3 times local wavelength. The former may give a useful scale for the source dimension, and the latter suggests that the EMIC wave activity maintains coherency only up to a couple of wavelengths. Lee, Jeongwoo; Min, Kyungguk; Kim, Kap-Sung; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2013 YEAR: 2013 DOI: 10.1002/jgra.50242 |
|
Since their discovery more than 50 years ago, Earth\textquoterights Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is composed predominantly of megaelectron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days, depending primarily on external forcing by the solar wind. The spatially separated inner zone is composed of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (>2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for more than 4 weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage. Baker, D.; Kanekal, S.; Hoxie, V.; Henderson, M.; Li, X.; Spence, H.; Elkington, S.; Friedel, R.; Goldstein, J.; Hudson, M.; Reeves, G.; Thorne, R.; Kletzing, C.; Claudepierre, S.; Published by: Science Published on: 04/2013 YEAR: 2013 DOI: 10.1126/science.1233518 |
|
The twin Van Allen Probe observatories developed at The Johns Hopkins University Applied Physics Laboratory for NASA\textquoterights Heliophysics Division completed final observatory integration and environmental test activities and were successfully launched into orbit around the Earth on August 30, 2012. As the science operations phase begins, the mission is providing exciting new information about the impact of radiation belt activity on the earth. The on-board boom mounted magnetometers and other instruments are the most sensitive sensors of their type that have ever flown in the Van Allen radiation belts. The observatories are producing near-Earth space weather information that can be used to provide warnings of potential power grid interruptions or satellite damaging storms. The Van Allen Probes are operating in a challenging high radiation environment, and at the same time they are designed to make an insubstantial electric and magnetic field contribution to their surroundings. This paper will describe the challenges associated with observatory integration and test activities and observatory on-orbit checkout and commissioning. The lessons learned can be applied to other observatories and payloads that will be exposed to similar environments. Published by: Published on: 03/2013 YEAR: 2013 DOI: 10.1109/AERO.2013.6496838 |
|
Mission Overview for the Radiation Belt Storm Probes Mission Provided here is an overview of Radiation Belt Storm Probes (RBSP) mission design. The driving mission and science requirements are presented, and the unique engineering challenges of operating in Earth\textquoterights radiation belts are discussed in detail. The implementation of both the space and ground segments are presented, including a discussion of the challenges inherent with operating multiple observatories concurrently and working with a distributed network of science operation centers. An overview of the launch vehicle and the overall mission design will be presented, and the plan for space weather data broadcast will be introduced. Stratton, J.; Harvey, R.; Heyler, G.; Published by: Space Science Reviews Published on: 01/2013 YEAR: 2013 DOI: 10.1007/s11214-012-9933-x |
|
A novel technique for rapid L* calculation using UBK coordinates [1] The magnetic drift invariant (L*) is an important quantity used for tracking and organizing particle dynamics in the radiation belts, but its accurate calculation has been computationally expensive in the past, thus making it difficult to employ this quantity in real-time space weather applications. In this paper, we propose a new, efficient method to calculate L* using the principle of energy conservation. This method uses Whipple\textquoterights (U, B, K) coordinates to quickly and accurately determine trajectories of particles at the magnetic mirror point from two-dimensional isoenergy contours. The method works for any magnetic field configuration and is able to accommodate constant electric potential along field lines. We compare the result of this method with those of International Radiation Belt Environment Modeling library (IRBEM-LIB) to demonstrate the performance of this new method. The method requires a preparation step, and thus may not be the optimal method for a single trajectory calculation; however, it presents a huge performance gain when adiabatically propagating a large population of particles in a given magnetic field configuration. Min, Kyungguk; Bortnik, J.; Lee, Jeongwoo; Published by: Journal of Geophysical Research Published on: 01/2013 YEAR: 2013 DOI: 10.1029/2012JA018177 |
|
Rapid acceleration of protons upstream of earthward propagating dipolarization fronts [1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz. We then use three-dimensional test-particle simulations to investigate how these acceleration processes operate in a realistic magnetotail geometry. For this purpose we construct an analytical model of the front which is superimposed onto the ambient field of the magnetotail. According to our numerical simulations, both trapping and quasi-trapping can produce rapid acceleration of protons by more than an order of magnitude. In the case of trapping, the acceleration levels depend on the amount of time particles stay in phase with the front which is controlled by the magnetic field curvature ahead of the front and the front width. Quasi-trapping does not cause particle scattering out of the equatorial plane. Energization levels in this case are limited by the number of encounters particles have with the front before they get magnetized behind it. Ukhorskiy, A; Sitnov, M.; Merkin, V.; Artemyev, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2013 YEAR: 2013 DOI: 10.1002/jgra.50452 |
|
Published by: Published on: |
| 2012 |
|
Design, Fabrication, and Testing of the Radiation Belt Storm Probes Propulsion Systems The Radiation Belt Storm Probes spacecraft , part of NASA\textquoterights Living with a Star program, are scheduled for launch into Earth orbit in August 2012. 1,2,3 The twin spacecraft possess identical blowdown monopropellant hydrazine propulsion systems to provide spinup/spindown, precession, Delt a\textendashV, and deorbit capability. Each spacecraft manifests eight Aerojet 0.2 lbf (0.9 N) MR\textendash103G thrust ers, three ARD\ E Inconel 718 propellant tanks, and other components required to control the fl ow of propellant and monitor system health and performance. The propulsion systems were fabricated and installed by Aerojet Redmond and subsequently tested at the Jo hns Hopkins University / Applied Physics Laboratory (APL) in Laurel, MD. The test se quence at APL included thermal balance; end\textendash to\textendashend phasing; leak and functional; mass properties; water load (as a propellant simulant); water\textendashloaded vibration and acoustic testing; water offload; and thermal vacuum operations. This paper will document the design of th e propulsion system, component selection challenges faced, and system\textendashl evel tests performed prior to propellant load and launch. Published by: Published on: 08/2012 YEAR: 2012 DOI: 10.2514/6.2012-4332 |
|
The RBSP Spacecraft Power System Design and Development The RBSP (Radiation Belt Storm Probes) twin spacecraft are set to launch in August 2012. The spacecraft will be inserted into the highly elliptical regions of high energy particles trapped by the magnetic field of the earth. These regions are often referred to as the Van Allen Belts. The twin spacecraft will operate entirely within the radiation belts throughout their mission. Because of the intense environment of operation and to reduce cost and risk, the approach taken in the power system electronics was to use quasi conventional design, materials, and fabrication techniques encased in a 350mil thick aluminum enclosure. The spacecraft are spin stabilized with an axial boom that creates a shadow across the solar arrays. The power system topology selected was a 28V unregulated direct energy transfer (DET) system using an eight cell Li-Ion battery with cell balance electronics. The solar arrays are electrostatically clean with each string layout for magnetic self-cancellation. The spacecraft instruments electrostatic and magnetic cleanliness requirements impacted the design of the solar array, battery, and power system electronic boxes. The paper will cover the design and development of the RBSP spacecraft Power System including the battery, solar arrays, and the power electronics. Butler, Michael; Laughery, Sean; Published by: Published on: 08/2012 YEAR: 2012 DOI: 10.2514/MIECEC1210.2514/6.2012-4059 |
|
Global distribution of EMIC waves derived from THEMIS observations [1] Electromagnetic ion cyclotron (EMIC) waves play an important role in magnetospheric dynamics and their global distribution has been of great interest. This paper presents the distribution of EMIC waves over a broader range than ever before, as enabled by observations with the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft from 2007 to 2010. Our major findings are: (1) There are two major peaks in the EMIC wave occurrence probability. One is at dusk and 8\textendash12 RE where the helium band dominates the hydrogen band waves. The other is at dawn and 10\textendash12 RE where the hydrogen band dominates the helium band waves. (2) In terms of wave spectral power the dusk events are stronger (≈10 nT2/Hz) than the dawn events (≈3 nT2/Hz). (3) The dawn waves have large normal angles (>45) in the hydrogen band and even larger normal angles Min, Kyungguk; Lee, Jeongwoo; Keika, Kunihiro; Li, W.; Published by: Journal of Geophysical Research Published on: 05/2012 YEAR: 2012 DOI: 10.1029/2012JA017515 EMIC wave occurrence; EMIC waves; plasma waves; RBSP; Van Allen Probes |
|
Radiation Belt Storm Probe Spacecraft and Impact of Environment on Spacecraft Design NASA\textquoterights Radiation Belt Storm Probe (RBSP) is an Earth-orbiting mission scheduled to launch in September 2012 and is the next science mission in NASA\textquoterights Living with a Star Program. The RBSP mission will investigate, characterize and understand the physical dynamics of the radiation belts, and the influence of the sun on the earth\textquoterights environment, by measuring particles, electric and magnetic fields and waves that comprise the geospace. The mission is composed of two identically instrumented spinning spacecraft in an elliptical orbit around earth from 600 km perigee to 30,000 km apogee at 10 degree inclination to provide full sampling of the Van Allen radiation belts. The twin spacecraft will follow slightly different orbits and will lap each other 4 times per year; this offers simultaneous measurements over a range of spacecraft separation distances. A description of the spacecraft environment is provided along with spacecraft and subsystem key characteristics and accommodations that protect sensitive spacecraft electronics and support operations in the harsh radiation belt environment. Kirby, Karen; Bushman, Stewart; Butler, Michael; Conde, Rich; Fretz, Kristen; Herrmann, Carl; Hill, Adrian; Maurer, Richard; Nichols, Richard; Ottman, Geffrey; Reid, Mark; Rogers, Gabe; Srinivasan, Dipak; Troll, John; Williams, Bruce; Published by: Published on: 03/2012 YEAR: 2012 DOI: 10.1109/AERO.2012.6187020 |
| 2011 |
|
Radiation belt storm probes: Resolving fundamental physics with practical consequences The fundamental processes that energize, transport, and cause the loss of charged particles operate throughout the universe at locations as diverse as magnetized planets, the solar wind, our Sun, and other stars. The same processes operate within our immediate environment, the Earth\textquoterights radiation belts. The Radiation Belt Storm Probes (RBSP) mission will provide coordinated two-spacecraft observations to obtain understanding of these fundamental processes controlling the dynamic variability of the near-Earth radiation environment. In this paper we discuss some of the profound mysteries of the radiation belt physics that will be addressed by RBSP and briefly describe the mission and its goals. Ukhorskiy, Aleksandr; Mauk, Barry; Fox, Nicola; Sibeck, David; Grebowsky, Joseph; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 07/2011 YEAR: 2011 DOI: 10.1016/j.jastp.2010.12.005 |
|
Understanding relativistic electron losses with BARREL The primary scientific objective of the Balloon Array for RBSP Relativistic Electron Losses (BARREL) is to understand the processes responsible for scattering relativistic electrons into Earth\textquoterights atmosphere. BARREL is the first Living with a Star Geospace Mission of Opportunity, and will consist of two Antarctic balloon campaigns conducted in the 2012 and 2013 Austral summer seasons. During each campaign, a total of 20 small View the MathML source(\~20kg) balloon payloads will be launched, providing multi-point measurements of electron precipitation in conjunction with in situ measurements from the two RBSP spacecraft, scheduled to launch in May 2012. In this paper we outline the scientific objectives of BARREL, highlighting a few key science questions that will be addressed by BARREL in concert with other ILWS missions in order to understand loss processes in the radiation belts. A summary of observations from the 2008/2009 BARREL test flight is also presented. Electron precipitation was observed during a geomagnetic storm on February 14\textendash18, 2009. This storm, though relatively weak (Dst=-36 nT), was remarkably effective in increasing the trapped electron population. Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 07/2011 YEAR: 2011 DOI: 10.1016/j.jastp.2011.01.006 inner magnetosphere; precipitation; Radiation belts; relativistic electrons; Van Allen Probes; wave-particle interactions |
| 2010 |
|
We study the relationship between the electron injection and the chorus waves during a substorm event on 23 March 2007. The chorus waves were detected at high geomagnetic latitude (\~70\textdegreeS) Antarctic observatories in the range of 0600\textendash0900 h in magnetic local time (MLT). Electrons drifting from the injection event were measured by two LANL spacecraft at 0300 and 0900 MLT. The mapping of auroral brightening areas to the magnetic equator shows that the injection occurred in an MLT range of 2200\textendash2400. This estimate is consistent with observations by the THEMIS A, B, and D spacecraft (which were located at 2100 MLT and did not observe electron injections). Our backward model tracing from the magnetic equator near the dawnside magnetopause (which magnetically connects to the Antarctic observatories) also supports the deduced injection region. Since chorus waves are believed to be generated through the electron cyclotron instability by an anisotropic temperature distribution, we examine, by performing forward model tracing, whether the electrons injected during this substorm form a pancake-like pitch angle distribution when they arrive near the dawn-side magnetopause. We find that the onset time of the modeled pitch angle anisotropy is consistent with that of the observed chorus waves. We conclude that the development of the anisotropy is due to particle drift shell splitting. Min, Kyungguk; Lee, Jeongwoo; Keika, Kunihiro; Published by: American Geophysical Union Published on: 10/2010 YEAR: 2010 DOI: 10.1029/2010JA015474 chorus and substorm; electron drift; RBSP; Substorm Injections; Van Allen Probes |
| 2009 |
|
Analysis of Spinning Spacecraft with Wire Booms Part 1: Derivation of Nonlinear Dynamics Algebraic expressions for the governing equations of motion are developed to describe a spinning spacecraft with flexible appendages. Two limiting cases are investigated: appendages that are self-restoring and appendages that require spacecraft motion to restore. Solar panels have sufficient root stiffness to self-restore perturbations. Radial wire antennae have little intrinsic root stiffness and require centripetal acceleration from spacecraft rotations to restore perturbations. External forces applied for attitude corrections can displace spacecraft appendages from their steady-state position. The Radiation Belt Storm Probe (RBSP) satellite is used as an example to explore numerical results for several maneuvers. Kemp, Brian; McGee, Timothy; Shankar, Uday; Published by: Published on: 08/2009 YEAR: 2009 DOI: 10.2514/6.2009-6202 |
|
Analysis of Spinning Spacecraft with Wire Booms Part 2: Out-of-Plane Dynamics and Maneuvers An analysis of the dynamics for a spin stabilized spacecraft consisting of a rigid central hub with four long exible wire booms is presented. The analysis focuses on the dynamics out of the spin plane of the spacecraft. Companion papers will focus on the derivations of the full nonlinear dynamics and analysis of the in plane dynamics. A linear analysis is used to estimate the mode shapes of the free response of the system, the e ects of various damping mechanisms on these modes, and the dynamic response of the system to various maneuvers. The results of an independent simulation of the full nonlinear dynamics of the system are also provided to support the linear analysis. While the dynamics and analysis approach presented can be applied to the general class of spin stabilized spacecraft having multiple exible wire booms, the numeric parameters studied represent those of the satellites from the Radiation Belt Storm Probe (RBSP) mission. The mission, part of NASA\textquoterights Living With a Star Geospace Program, will launch two Earth-orbiting spacecraft to investigate how populations of relativistic electrons and ions in the region known as the Radiation Belts are formed and change in response to variable inputs of energy from the Sun. McGee, Timothy; Shankar, Uday; Kemp, Brian; Published by: Published on: 08/2009 YEAR: 2009 DOI: 10.2514/6.2009-6203 |
|
Several science spacecraft use long wire booms as electric-field antennas and the spacecraft spins to maintain the orientation of these flexible wires. These booms account for a majority of the total spacecraft inertia while weighing only a small fraction of the total mass. The spacecraft dynamics is therefore dominated by these booms. The analysis of such spacecraft is further complicated by other flexible ap- pendages and the presence of damping in the system, both inherent in the sys- tem and from damping mechanisms deliberately added into the system. This pa- per and two companion papers analyze such spacecraft. The first of these derives the governing nonlinear equations from first principles. Under certain conditions, the dynamics neatly separate into spin-plane and out-of-plane dynamics. The sec- ond companion paper examines the out-of-plane dynamics and maneuvers. This paper examines the spin-plane dynamics of such a spin-stabilized spacecraft. It analyzes the fundamental modes and mode-shapes of the system, spin-plane ma- neuvers, and the effects of boom deployment. While this analysis is applicable to any spin-stabilized spacecraft with flexible radial booms, the analysis was driven by the needs of the Radiation Belt Storm Probes (RBSP) spacecraft currently being designed at the Johns Hopkins University Applied Physics Laboratory, as part of NASA\textquoterights \textquotedblleftLiving With a Star\textquotedblright program. This paper provides an analytical treatment of the spacecraft dynamics. These theoretical predictions are verified using fully non-linear six degree-of-freedom simulations. Shankar, Uday; McGee, Timothy; Kemp, Brian; Published by: Published on: 08/2009 YEAR: 2009 DOI: 10.2514/6.2009-6204 |
| 2007 |
|
Radiation Belt Storm Probes: The Next Generation of Space Weather Forecasting Published by: Space Weather Published on: 11/2007 YEAR: 2007 DOI: 10.1029/2007SW000341 |