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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Intact capture of hypervelocity particles on Shuttle

The capability for capturing micrometeoroid analogs intact through laboratory simulations in passive underdense media offers a valuable tool for cosmic dust research. However, no amount of laboratory simulations can replace actual space experiments due to the technical inability to launch high fidelity analogs of micrometeoroids in ground laboratories and then reliably simulating high hypervelocities (greater than 7 km/s). Fluffy composite micrometeoroid analogs tend to break up and have not survived laboratory launches at beyond 4 km/s, however, a new technique of launching cluster analogs was developed for the two-stage light-gas gun at NASA Ames Vertical Gun Range. Plasma drag or electrostatic accelerators may be able to achieve higher speeds than two-stage light-gas guns but only with very limited projectile compositions and may result in severe projectile deformation. Consequently, a space demonstration of intact capture was sought since 1983. Initial results from our STS-47 flight, which carried the first Shuttle Sample Return Experiment (SRE) with silica aerogel capture media, are reported.

Tsou, P.↗
NASA NTRS1994

The hypervelocity impact facilities at the University of Kent at Canterbury, UK

The University of Kent at Canterbury facilities for production of hypervelocity impacts are discussed. Meteoroids are simulated by electrostatic acceleration of small (10(exp -12) - 10(exp -17) kg) particles using a 2-MV Van de Graaff accelerator. This machine has been operational for many years; both the machine and experimental area are currently being upgraded. Larger particles (10(exp -10) - 10(exp -14) kg) are accelerated using a more recently installed light gas gun. The status of all hardware (including experimental areas) is given, along with brief details of recent, current, and future projects making use of them.

Burchell, Mark J.↗
NASA NTRS2001

1000 Hours of Testing Completed on 10-kW Hall Thruster

Between the months of April and August 2000, a 10-kW Hall effect thruster, designated T- 220, was subjected to a 1000-hr life test evaluation. Hall effect thrusters are propulsion devices that electrostatically accelerate xenon ions to produce thrust. Hall effect propulsion has been in development for many years, and low-power devices (1.35 kW) have been used in space for satellite orbit maintenance. The T-220, shown in the photo, produces sufficient thrust to enable efficient orbital transfers, saving hundreds of kilograms in propellant over conventional chemical propulsion systems. This test is the longest operation ever achieved on a high-power Hall thruster (greater than 4.5 kW) and is a key milestone leading to the use of this technology for future NASA, commercial, and military missions.

Mason, Lee S.↗
NASA NTRS2017

Experimental Hypervelocity Dust Impact in Olivine: FIB/TEM Characterization of Micron-Scale Craters with Comparison to Natural and Laser-Simulated Small-Scale Impact Effects

The space weathering of regoliths on airless bodies and the formation of their exospheres is driven to a large extent by hypervelocity impacts from the high relative flux of micron to sub-micron meteoroids that comprise approximately 90 percent of the solar system meteoroid population. Laboratory hypervelocity impact experiments are crucial for quantifying how these small impact events drive space weathering through target shock, melting and vaporization. Simulating these small scale impacts experimentally is challenging because the natural impactors are both very small and many have velocities above the approximately 8 kilometers-per-second limit attainable by conventional chemical/light gas accelerator technology. Electrostatic "dust" accelerators, such as the one recently developed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), allow the experimental velocity regime to be extended up to tens of kilometers-per-second. Even at these velocities the region of latent target damage created by each impact, in the form of microcraters or pits, is still only about 0.1 to 10 micrometers in size. Both field-emission analytical scanning electron microscopy (FE-SEM) and advanced field-emission scanning transmission electron microscopy (FE-STEM) are uniquely suited for characterizing the individual dust impact sites in these experiments. In this study, we have used both techniques, along with focused ion beam (FIB) sample preparation, to characterize the micrometer to nanometer scale effects created by accelerated dust impacts into olivine single crystals. To our knowledge this work presents the first TEM-scale characterization of dust impacts into a key solar system silicate mineral using the CCLDAS facility. Our overarching goal for this work is to establish a basis to compare with our previous results on natural dust-impacted lunar olivine and laser-irradiated olivine.

Christoffersen, R.↗
NASA NTRSDate not supplied

Hypervelocity Dust Impact in Olivine: Fib/Tem Characterization and Comparison of Experimental and Natural Microcraters

The flux of objects impacting the surfaces of solar system airless bodies is dominated by micrometeoroids less than 1 mm diameter whose impact effects play a major role in the space weathering of airless body surfaces. To obtain better understanding of how small scale impact effects vary as a function of impact speed in an important lunar and asteroidal mineral, we produced artificial microcraters in San Carlos olivine using Fe metal dust particles 0.10 to 5 µm in diameter electrostatically accelerated to speeds between 0.35 to 25 km s-1. The crater morphologies, size distrrubiton and microstruc-tures were characterized by field-emission SEM (FE-SEM) and also by FIB cross sectioning of selected craters for field-emission scanning transmission electron microscopy (FE-STEM). These same techniques were also applied to study a natural 20 µm-diameter microcrater in a olivine grain on the surface of lunar rock 12075. Measured microcrater diameters in the experimental sample range between 0.20 to 5 µm with larger craters having more irregular outlines dominated by spallation fractures. FE-SEM and FE-STEM imaging docu-ment the formation of shock melt in the size population of experimental craters below approximately 1 µm in diameter, corresponding to particle impact speeds in the 10-25 km s-1 range. The natural olivine crater exhibits similar shock melt features along the perimeter of its cavity, but the shock melt also contains nanophase Fe metal particles, something not observed in the experimental samples. FE-STEM imaging of the experimental craters reveals complex shock-generated dislocation and nanofracture microstructures in zones extend-ing 1-2 µm into the olivine from the crater cavity. The natural microcrater shows a lower density of shock-generated disloca-tions that extends a factor of 2 deeper into the the olivine than in the experimental samples.

Roy Gray Christoffersen↗
NASA NTRSDate not supplied

Characterizing Electrical Arc Behavior in Ion Engines

Gridded ion engines represent a class of electric thrusters characterized by high propulsive efficiency and high total impulse capabilities. These engines operate by applying high voltage to multi-aperture electrodes, thereby electrostatically accelerating plasma to generate thrust. Within the course of normal operations, periodic occurrences of high voltage breakdowns manifest within the thruster. These breakdowns constitute an inherent aspect of operation, with observations indicating a diminishing frequency and total count over the thruster's operational lifespan. To safeguard the propulsion system during such occurrences, the power processing unit (PPU) employs an automated arc extinction sequence, termed "recycle," which is triggered upon detection of an over-current condition. The initial phase of this sequence involves momentarily deactivating the high voltage and reducing the discharge current to a predetermined level, minimizing plasma impingement as the ion beam is defocused. The high voltage is subsequently reapplied, and the discharge current is returned to its nominal value. The entire sequence typically spans approximately 800 milliseconds. Throughout a recycle event, the propulsion system experiences various current and voltage transients as the arc current traverses the system and different power supplies are toggled on and off.

electric propulsion↗
NASA NTRS1981

Electron and ion acceleration by strong electrostatic turbulence

It is noted that, for waves observed on auroral field lines, ion trapping may be important, affecting models of transverse ion acceleration. The strength of the electrostatic ion cyclotron turbulence observed in the auroral zone may be attributed to the large convective growth rate that is associated with this mode. These waves may be destabilized by the enhancement in the field-aligned current that results from the onset of a magnetospheric substorm. The rise in the field-aligned current is associated with the passage of shear mode Alfven waves between the magnetosphere and ionosphere. When these Alfven waves have a perpendicular wavelength comparable to the ion gyroradius, they carry a parallel electric field that can accelerate the plasma in the topside auroral ionosphere, destabilizing the electrostatic ion cyclotron mode.

Lysak, R. L.↗
NASA NTRS1986

Experimental identification of electrostatic plasma waves within ion conic acceleration regions

The identification of electrostatic modes in the ionospheric and magnetospheric plasma is a difficult process. Some success has been achieved with electrostatic hydrogen cyclotron waves where Doppler broadening is insignificant and with zero-frequency turbulence where the spectrum is entirely Doppler shifted. However, it is not yet possible to identify specific modes in regions of transverse ion acceleration. If the modes are assumed to exist, some limits can be placed on their electric field amplitudes. An experimental technique to measure wavelength directly, thereby circumventing problems created by Doppler shifting, is reviewed.

Kintner, P. M.↗
NASA NTRS1972

Five-centimeter diameter ion thruster development

All system components were tested for endurance and steady state and cyclic operation. The following results were obtained: acceleration system (electrostatic type), 3100 hours continuous running; acceleration system (translation type), 2026 hours continuous running; cathode-isolator-vaporizer assembly, 5000 hours continuous operation and 190 restart cycles with 1750 hours operation; mercury expulsion system, 5000 hours continuous running; and neutralizer, 5100 hours continuous operation. The results of component optimization studies such as neutralizer position, neutralizer keeper hole, and screen grid geometry are included. Extensive mapping of the magnet field within and immediately outside the thruster are shown. A technique of electroplating the molybdenum accelerator grid with copper to study erosion patterns is described. Results of tests being conducted to more fully understand the operation of the hollow cathode are also given. This type of 5-cm thruster will be space tested on the Communication Technology Satellite in 1975.

Weigand, A. J.↗
NASA NTRS1983

Electric currents and voltage drops along auroral field lines

An assessment is presented of the current state of knowledge concerning Birkeland currents and the parallel electric field, with discussions focusing on the Birkeland primary region 1 sheets, the region 2 sheets which parallel them and appear to close in the partial ring current, the cusp currents (which may be correlated with the interplanetary B(y) component), and the Harang filament. The energy required by the parallel electric field and the associated particle acceleration processes appears to be derived from the Birkeland currents, for which evidence is adduced from particles, inverted V spectra, rising ion beams and expanded loss cones. Conics may on the other hand signify acceleration by electrostatic ion cyclotron waves associated with beams accelerated by the parallel electric field.

Stern, D. P.↗
NASA NTRS2017

Experimental Setup for the Laboratory Investigation of Micrometeoroid Ablation Using a Dust Accelerator

A facility has been developed to simulate the ablation of micrometeoroids in laboratory conditions. An electrostatic dust accelerator is used to generate iron particles with velocities of 10-70 kilometers. The particles are then introduced into a chamber pressurized with a target gas, where the pressure is adjustable between 0.01 and 0.5 Torr, and the particle partially or completely ablates over a short distance. An array of biased electrodes above and below the ablation path is used to collect the generated ions/electrons with a spatial resolution of 2.6 centimeters along the ablating particles path, thus allowing the study of the spatiotemporal evolution of the process. For completely ablated particles, the total collected charge directly yields the ionization coefficient of a given dust material-target gas combination. The first results of this facility measured the ionization coefficient of iron atoms with N2, air, CO2, and He target gases for impact velocities greater than 20 kilometers per second, and are reported by Thomas et al. The ablation chamber is also equipped with four optical ports that allow for the detection of the light emitted by the ablating particle. A multichannel photomultiplier tube system is used to observe the ablation process with a spatial and temporal resolution of 0.64 centimeters and 90 nanoseconds. The preliminary results indicate that it is possible to calculate the velocity of the ablating particle from the optical observations, and in conjunction with the spatially resolved charge measurements allow for experimental validation of ablation models in future studies.

Thomas, Evan↗
NASA NTRS1976

Characteristics of auroral electron acceleration regions observed by Atmosphere Explorer C

Satellite measurements of electron precipitation and ion drift velocities showed that electron acceleration regions (or inverted V's) in the 1200 to 1800 MLT quadrant exhibit the following systematic behavior: electron distribution functions in the accelerated region can be well described by Maxwellian primary electron beams accelerated through an electrostatic potential; the typical inverted V latitudinal structure is always observed in the accelerated regions, the electrostatic potential reaching a maximum and consequently decreasing to near zero over distances of 100 to 250 km; the Maxwellian temperature of the primary electron beam increases systematically with increasing electrostatic potential; rather weak acceleration regions, characterized by values of the electrostatic potential below 1 keV and values of the Maxwellian temperature between 100 and 350 eV, occur in the cusp and in the highest-latitude portion of the dusk side electron precipitation zone.

Burch, J. L.↗
NASA NTRS1994

Assessment of velocity/trajectory measurement technologies during a particle capture event

Since the early 1960s, the means to measure the time of flight (TOF) of dust grain within a mechanical detection array has existed, first in the laboratory and then in space experiments. Laboratory hypervelocity dust particle accelerators have used electrostatic detection of charge on accelerated particles for TOF and particle mass detections. These laboratory studies have led to the development of ultra-thin-film sensors that have been used for TOF measurements in dust particle space experiments. The prototypes for such devices were ultra-thin-film capacitors that were used in the OGO series of satellites. The main goal of the experimental work to be described is the development of the capability to determine the velocity vector or trajectory of a dust grain traversing an integrated dust detection array. The results of these studies have shown that the capability of detecting the charge liberated by hypervelocity dust grains with diameters in the micrometer range can be detected. Based on these results, detection systems have been designed to provide a precise analysis of the physical and dynamic properties of micrometer and submicrometer dust grains, namely the design verification unit (DVU). Through unique combinations of in situ detection systems, direct measurements of particle surface charge, velocity, momentum, kinetic energy, and trajectory have been achieved. From these measurements, the remaining physical parameters of mass, size, and density can be determined.

Tanner, William G.↗