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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Particle-in-cell simulations of stochastic electron acceleration

The results of a series of particle-in-cell simulations of stochastic wave-particle interaction are presented. The threshold for stochasticity was confirmed. The simulations demonstrate that in a strong magnetic field plasma waves with quiver velocities much less than the speed of light but above a certain threshold can stochastically accelerate electrons to energies far greater than 1 MeV. Moreover, self-consistency effects drive return currents and produce energetic runaway electrons that violate an invariant of motion.

Akimoto, K.↗
NASA NTRS1990

Vehicle charging effects during electron beam emission from the CHARGE-2 experiment

The CHARGE-2 sounding rocket payload has measured the transient and steady-state charging of a spacecraft in LEO during the emission of a low-power electron beam. The electron beam successfully escaped the emitting spacecraft above 240 km, rather than being degraded by the spacecraft's potentials. These potentials were limited to about half of the 1-kV beam accelerating potential at all latitudes, suggesting that the electron beam was able to escape at altitudes down to 160 km. Electrons created from beam-plasma interactions become increasingly important in the return current below 240 km, and increased with decreasing altitude.

Myers, Neil B.↗
NASA NTRS1990

The interaction of an artificial electron beam with the earth's upper atmosphere - Effects on spacecraft charging and the near-plasma evironment

The ionization created in the earth's upper atmosphere by an electron beam emitted from a low altitude spacecraft is described by two coupled nonlinear differential electron transport equations for the up-going and down-going differential energy flux. The equations are solved numerically, yielding estimates of the differential electron energy flux density at the spacecraft location. At altitudes below 200-250 km and for beam energies around 1 keV, it is shown that secondary electrons supply a significant contribution to the return current to the spacecraft and thereby reduce the spacecraft potential. The numerical results are in good agreement with observations from the Charge 2 sounding rocket experiment.

Neubert, T.↗
NASA NTRS1990

Effects of neutral gas releases on electron beam injection from electrically tethered spacecraft

The presence of high neutral densities at low altitudes and/or during thruster firings is known to modify the spacecraft potential during active electron beam injection. Two-dimensional (three velocity) particle simulations are used to investigate the ionization processes including the neutral density required, the modification of the spacecraft potential, beam profile and spatial distribution of the return current into the spacecraft. Three processes are identified: (1) beam-induced ionization, (2) vehicle-induced ionization, and (3) beam plasma discharge. Only in the first two cases does the beam propagate away with little distortion.

Winglee, R. M.↗
NASA NTRS1991

Electric fields in the solar atmosphere - A review

A review is presented of remote sensing techniques which measure the electric field component transverse to the line of sight and achieve a sensitivity range of 5-10 V/cm. Three models are shown to predict quasistatic, macroscopic values of E(parallel), the electric field component parallel to the magnetic vector, beyond the sensitivity range considered. These processes are: the discharge model of flares; the models of return currents related to flare particle beams; and the models of neutral sheets related to two-ribbon flares and postflare loops. Time dependent electric fields related to MHD and plasma waves, and to plasma disturbance, may allow the detection of both E components (parallel and perpendicular). The uncertainty relating to the emission measures, time scales, volumes, and plasma conditions of these flares and electrified plasma volumes is emphasized. It is pointed out, however, that important information can be obtained by observing electric fields at existing sensitivity levels. By measuring these E-fields, the understanding of flares and related dynamic events can be improved.

Foukal, P.↗
NASA NTRS1993

Double layer propagation in experiments with electron beam injection

Electron beam injection into a plasma is investigated using the analytical inverted Bernstein-Green-Kruskal method. Particle number and momentum conservation laws are applied to evaluate the propagation velocity and potential drop on the leading edge of the beam. Electric potential is supposed to be monotonic, thus the leading front has a double-layer-like structure. For the case of cold particles, analytical expressions for the double layer velocity and potential drop are obtained. It is pointed out that double layer velocity differs from the initial electron speed: even for weak beams a noticeable deceleration takes place. Strong beams are found incapable of penetrating into plasma - their propagation velocity is very small. Ambient electrons undergo a considerable acceleration forming a return current which neutralizes the injector. Possible instability of the distribution functions is discussed.

Bruskin, L. G.↗
NASA NTRS1922

Aerial navigation : on the problem of guiding aircraft in a fog or by night when there is no visibility

The use of magnetic fields and wire to navigate aircraft in conditions of poor visibility is presented. This field may be considered to be derived from a double lemniscate, considered in the particular case where the origin is a double point formed from the magnetic field of the slack wire, from the field produced by the return currents and from the field due to the currents induced in the conducting mass. These fields are dephased in two ways, one in the direction of the wire, the other in a direction perpendicular to it.

Loth, William↗
NASA NTRS1994

Acceleration of electrons and ions by strong lower-hybrid turbulence in solar flares

One of the outstanding problems in solar flare theory is how to explain the 10-20 keV and greater hard x-ray emissions by a thick target bremsstrahlung model. The model requires the acceleration mechanism to accelerate approximately 10(exp 35) electrons sec(exp -l) with comparable energies, without producing a large return current which persists for long time scales after the beam ceases to exist due to Lenz's law, thereby, producing a self-magnetic field of order a few mega-Gauss. In this paper, we investigate particle acceleration resulting from the relaxation of unstable ion ring distributions, producing strong wave activity at the lower hybrid frequency. It is shown that strong lower hybrid wave turbulence collapses in configuration space producing density cavities containing intense electrostatic lower hybrid wave activity. The collapse of these intense nonlinear wave packets saturate by particle acceleration producing energetic electron and ion tails. There are several mechanisms whereby unstable ion distributions could be formed in the solar atmosphere, including reflection at perpendicular shocks, tearing modes, and loss cone depletion. Numerical simulations of ion ring relaxation processes, obtained using a 2 1/2-D fully electromagnetic, relativistic particle in cell code are discussed. We apply the results to the problem of explaining energetic particle production in solar flares. The results show the simultaneous acceleration of both electrons and ions to very high energies: electrons are accelerated to energies in the range 10-500 keV, while ions are accelerated to energies of the order of MeVs, giving rise to x-ray emission and gamma-ray emission respectively. Our simulations also show wave generation at the electron cyclotron frequency. We suggest that these waves are the solar millisecond radio spikes. The strong turbulence collapse process leads to a highly filamented plasma producing many localized regions for particle acceleration and resulting in approximately 10(exp 17) electron 'beamlets' of width approximately equal to 10 lambda sub De which eliminates the production of large magnetic fields. In this paper, we demonstrate that the model produces an energetic electron spectrum with the right flux to account for the hard x-ray observations.

Spicer, D. S.↗
NASA NTRS2000

Low-Cost Approaches to Deep Space Missions

The past decade has brought about a radical transformation in NASA's planetary exploration program. At the beginning of this decade, NASA was focused on the Cassini mission to Saturn. Following on the heels of the successful Voyager and Galileo missions, Cassini represents the culmination of an evolution towards successively larger, more complex, and more expensive spacecraft. The Cassini spacecraft weighs in at over 5 metric tons, and carries an entry probe and a sophisticated suite of sensors supporting 27 different science investigations enabling a comprehensive scientific investigation of Saturn with a single spacecraft. The cost of this spacecraft exceeded $2B, including the cost of the large Titan IV launch vehicle. During Cassini development, NASA realized that it could no longer afford these "flagship" missions, and the agency moved aggressively towards a "faster, better, cheaper" design philosophy of focused science goals and simpler, rapidly-developed spacecraft, allowing much more frequent launches of smaller, lower-cost missions. The Mars Global Surveyor, launched in November 1996, is an example of this new paradigm. Developed in less than 3-years, MGS is only one-fifth the mass of Cassini, and only cost on the order of $220M. The reduced spacecraft mass allows use of the smaller, lower cost Delta launch vehicle. Currently in orbit about Mars, MGS carries a focused suite of six science instruments that are currently returning high-resolution remote sensing of the Martian surface. The future calls for continued even more aggressive mass and cost targets. Examples of these next-generation goals are embodied in the Mars Micromission spacecraft concept, targeted for launch in 2003. With a mass of only 200kg, this lightweight bus can be tailored to carry a variety of payloads to Mars or other inner-planet destinations. The design of the Micromission spacecraft enable them to be launched at extremely low cost as a secondary "piggyback" payload.

Squibb, G. F.↗
NASA NTRS2001

Galilean Satellite Surface Non-Ice Constituents: New Results from the Cassini/Huygens VIMS Jupiter Flyby in the Context of the Galileo NIMS Results

The Cassini mission Visible and Infrared Mapping Spectrometer (VIMS) is currently returning data for the Galilean satellites. Examples of the new satellite data and the initial interpretations will be presented in the context of the Galileo NIMS data and results. Additional information is contained in the original extended abstract.

McCord, T. B.↗
NASA NTRS2001

Magnetospheric Geometry in PSR B1929+10 from Radio/X-Ray Alignment

We have conducted a study of two rotation- powered pulsars that emit at both radio and x-ray wavelengths, PSR B0531+21 and PSR B1929+10. Using absolute phase information, we have phase-aligned x-ray and radio profiles from these pulsars. Observations were done using the Green Bank 140ft telescope, and ASCA. The 0531+21 X-ray profile is sharp and lines up well with the radio profile confirming that the X-ray emission from this pulsar is magnetospheric in origin. The 1929+10 profile is approximately sinusoidal with the peak of the emission arriving 67+/-23 degrees after the maximum in the radio emission. The controversy to which the PSR B1929+10 result adds fuel, is whether this "inter" -pulsar, is an "aligned" or "orthogonal" rotator -- describing the alignment of the magnetic axis to the rotation axis. Do the two peaks in the radio profile (the pulse and interpulse) come from a double crossing of a thin hollow cone nearly aligned with rotation axis, or alternatively do they come from from opposite poles of an "orthogonal" rotator where the spin axis is perpendicular to the magnetic axis? The radio to X-ray alignment we find favors the former explanation: if the X-ray hot spot is the result of return currents to the surface from the outward current that generates radio emission, then in the "double-crossing" model, the hot spot phase is expected to lie between the main pulse and interpulse as observed.

Somer, A. L.↗
NASA NTRS2009

Electrodynamic Tethers for Spacecraft Propulsion

Electrodynamic (Drag) Tether Thrust Principles: a) Uses both solar energy and consumes no propellant. b) Tether's orbital velocity v (approx. 7500 m/s) through North-pointing geomagnetic field B(sub north) (0.18 - 0.32 Gauss) induces voltage (35 - 160 V/km) in tether. c) Return current is through surrounding plasma. d) Current I produces a drag thrust force F on the tether. e) Magnetic force F from current I through insulated tether of length l: F = lI x B(sub north).

Johnson, Les↗
NASA NTRS2009

Splanchnic Compression Improves the Efficacy of Compression Stockings to Prevent Orthostatic Intolerance

Purpose: Post-spaceflight orthostatic intolerance (OI) is observed in 20-30% of astronauts. Previous data from our laboratory suggests that this is largely a result of decreased venous return. Currently, NASA astronauts wear an anti-gravity suit (AGS) which consists of inflatable air bladders over the calves, thighs and abdomen, typically pressurized from 26 to 78 mmHg. We recently determined that, thigh-high graded compression stockings (JOBST , 55 mmHg at ankle, 6 mmHg at top of thigh) were effective, though to a lesser degree than the AGS. The purpose of this study was to evaluate the addition of splanchnic compression to prevent orthostatic intolerance. Methods: Ten healthy volunteers (6M, 4F) participated in three 80 head-up tilts on separate days while (1) normovolemic (2) hypovolemic w/ breast-high compression stockings (BS)(JOBST(R), 55 mmHg at the ankle, 6 mmHg at top of thigh, 12 mmHg over abdomen) (3) hypovolemic w/o stockings. Hypovolemia was induced by IV infusion of furosemide (0.5 mg/kg) and 48 hrs of a low salt diet to simulate plasma volume loss following space flight. Hypovolemic testing occurred 24 and 48 hrs after furosemide. One-way repeated measures ANOVA, with Bonferroni corrections, was used to test for differences in blood pressure and heart rate responses to head-up tilt, stand times were compared using a Kaplan-Meyer survival analysis. Results: BS were effective in preventing OI and presyncope in hypovolemic test subjects ( p = 0.015). BS prevented the decrease in systolic blood pressure seen during tilt in normovolemia (p < 0.001) and hypovolemia w/o countermeasure (p = 0.005). BS also prevented the decrease in diastolic blood pressure seen during tilt in normovolemia (p = 0.006) and hypovolemia w/o countermeasure (p = 0.041). Hypovolemia w/o countermeasure showed a higher tilt-induced heart rate increase (p = 0.022) than seen in normovolemia; heart rate while wearing BS was not different than normovolemia (p = 0.353). Conclusion: BS may be an effective countermeasure to post-space flight OI. The addition of splanchnic compression is more effective than the previous thigh-high garments. These stockings are readily available, inexpensive, and can be worn for days following landing as astronauts re-adapt to Earth gravity.

Platts, Steven H.↗
NASA NTRS2010

Smart Power Supply for Battery-Powered Systems

A power supply for battery-powered systems has been designed with an embedded controller that is capable of monitoring and maintaining batteries, charging hardware, while maintaining output power. The power supply is primarily designed for rovers and other remote science and engineering vehicles, but it can be used in any battery alone, or battery and charging source applications. The supply can function autonomously, or can be connected to a host processor through a serial communications link. It can be programmed a priori or on the fly to return current and voltage readings to a host. It has two output power busses: a constant 24-V direct current nominal bus, and a programmable bus for output from approximately 24 up to approximately 50 V. The programmable bus voltage level, and its output power limit, can be changed on the fly as well. The power supply also offers options to reduce the programmable bus to 24 V when the set power limit is reached, limiting output power in the case of a system fault detected in the system. The smart power supply is based on an embedded 8051-type single-chip microcontroller. This choice was made in that a credible progression to flight (radiation hard, high reliability) can be assumed as many 8051 processors or gate arrays capable of accepting 8051-type core presently exist and will continue to do so for some time. To solve the problem of centralized control, this innovation moves an embedded microcontroller to the power supply and assigns it the task of overseeing the operation and charging of the power supply assets. This embedded processor is connected to the application central processor via a serial data link such that the central processor can request updates of various parameters within the supply, such as battery current, bus voltage, remaining power in battery estimations, etc. This supply has a direct connection to the battery bus for common (quiescent) power application. Because components from multiple vendors may have differing power needs, this supply also has a secondary power bus, which can be programmed a priori or on-the-fly to boost the primary battery voltage level from 24 to 50 V to accommodate various loads as they are brought on line. Through voltage and current monitoring, the device can also shield the charging source from overloads, keep it within safe operating modes, and can meter available power to the application and maintain safe operations.

Krasowski, Michael J.↗
NASA NTRS2012

Constraining Gamma-Ray Pulsar Gap Models with a Simulated Pulsar Population

With the large sample of young gamma-ray pulsars discovered by the Fermi Large Area Telescope (LAT), population synthesis has become a powerful tool for comparing their collective properties with model predictions. We synthesised a pulsar population based on a radio emission model and four gamma-ray gap models (Polar Cap, Slot Gap, Outer Gap, and One Pole Caustic). Applying gamma-ray and radio visibility criteria, we normalise the simulation to the number of detected radio pulsars by a select group of ten radio surveys. The luminosity and the wide beams from the outer gaps can easily account for the number of Fermi detections in 2 years of observations. The wide slot-gap beam requires an increase by a factor of 10 of the predicted luminosity to produce a reasonable number of gamma-ray pulsars. Such large increases in the luminosity may be accommodated by implementing offset polar caps. The narrow polar-cap beams contribute at most only a handful of LAT pulsars. Using standard distributions in birth location and pulsar spin-down power (E), we skew the initial magnetic field and period distributions in a an attempt to account for the high E Fermi pulsars. While we compromise the agreement between simulated and detected distributions of radio pulsars, the simulations fail to reproduce the LAT findings: all models under-predict the number of LAT pulsars with high E , and they cannot explain the high probability of detecting both the radio and gamma-ray beams at high E. The beaming factor remains close to 1.0 over 4 decades in E evolution for the slot gap whereas it significantly decreases with increasing age for the outer gaps. The evolution of the enhanced slot-gap luminosity with E is compatible with the large dispersion of gamma-ray luminosity seen in the LAT data. The stronger evolution predicted for the outer gap, which is linked to the polar cap heating by the return current, is apparently not supported by the LAT data. The LAT sample of gamma-ray pulsars therefore provides a fresh perspective on the early evolution of the luminosity and beam width of the gamma-ray emission from young pulsars, calling for thin and more luminous gaps.

Pierbattista, Marco↗
NASA NTRS2015

Establishing a Disruptive New Capability for NASA to Fly UAV's into Hazardous Conditions

A 2015 NASA Aeronautics Mission "Seedling" Proposal is described for a Severe-Environment UAV (SE-UAV) that can perform in-situ measurements in hazardous atmospheric conditions like lightning, volcanic ash and radiation. Specifically, this paper describes the design of a proof-of-concept vehicle and measurement system that can survive lightning attachment during flight operations into thunderstorms. Elements from three NASA centers draw together for the SE-UAV concept. 1) The NASA KSC Genesis UAV was developed in collaboration with the DARPA Nimbus program to measure electric field and X-rays present within thunderstorms. 2) A novel NASA LaRC fiber-optic sensor uses Faraday-effect polarization rotation to measure total lightning electric current on an air vehicle fuselage. 3) NASA AFRC's state-of-the-art Fiber Optics and Systems Integration Laboratory is envisioned to transition the Faraday system to a compact, light-weight, all-fiber design. The SE-UAV will provide in-flight lightning electric-current return stroke and recoil leader data, and serve as a platform for development of emerging sensors and new missions into hazardous environments. NASA's Aeronautics and Science Missions are interested in a capability to perform in-situ volcanic plume measurements and long-endurance UAV operations in various weather conditions. (Figure 1 shows an artist concept of a SE-UAV flying near a volcano.) This paper concludes with an overview of the NASA Aeronautics Strategic Vision, Programs, and how a SE-UAV is envisioned to impact them. The SE-UAV concept leverages high-value legacy research products into a new capability for NASA to fly a pathfinder UAV into hazardous conditions, and is presented in the SPIE DSS venue to explore teaming, collaboration and advocacy opportunities outside NASA.

Ely, Jay↗
NASA NTRS2008

Europa Explorer Operational Scenarios Development

In 2007, NASA conducted four advanced mission concept studies for outer planets targets: Europa, Ganymede, Titan and Enceladus. The studies were conducted in close cooperation with the planetary science community. Of the four, the Europa Explorer Concept Study focused on refining mission options, science trades and implementation details for a potential flagship mission to Europa in the 2015 timeframe. A science definition team (SDT) was appointed by NASA to guide the study. A JPL-led engineering team worked closely with the science team to address 3 major focus areas: 1) credible cost estimates, 2) rationale and logical discussion of radiation risk and mitigation approaches, and 3) better definition and exploration of science operational scenario trade space. This paper will address the methods and results of the collaborative process used to develop Europa Explorer operations scenarios. Working in concert with the SDT, and in parallel with the SDT's development of a science value matrix, key mission capabilities and constraints were challenged by the science and engineering members of the team. Science goals were advanced and options were considered for observation scenarios. Data collection and return strategies were tested via simulation, and mission performance was estimated and balanced with flight and ground system resources and science priorities. The key to this successful collaboration was a concurrent development environment in which all stakeholders could rapidly assess the feasibility of strategies for their success in the full system context. Issues of science and instrument compatibility, system constraints, and mission opportunities were treated analytically and objectively leading to complementary strategies for observation and data return. Current plans are that this approach, as part of the system engineering process, will continue as the Europa Explorer Concept Study moves toward becoming a development project.

Lock, Robert E.↗
NASA NTRS2015

A Unified Computational Model for Solar and Stellar Flares

We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

radiative transfer↗