SEARCH · Search NASA

Results for “POINT IMPACT”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS1992

Microwave scattering and emission properties of large impact craters on the surface of Venus

Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data.

Stacy, N. J. S.↗

NASA NTRS1992

Static and dynamic strain energy release rates in toughened thermosetting composite laminates

In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of examining rate-dependent behavior for determining the longevity of structures manufactured from composite materials.

Cairns, Douglas S.↗

NASA NTRS1977

The estimation of pointing angle and normalized surface scattering cross section from GEOS-3 radar altimeter measurements

The statistical error of the pointing angle estimation technique is determined as a function of the effective receiver signal to noise ratio. Other sources of error are addressed and evaluated with inadequate calibration being of major concern. The impact of pointing error on the computation of normalized surface scattering cross section (sigma) from radar and the waveform attitude induced altitude bias is considered and quantitative results are presented. Pointing angle and sigma processing algorithms are presented along with some initial data. The intensive mode clean vs. clutter AGC calibration problem is analytically resolved. The use clutter AGC data in the intensive mode is confirmed as the correct calibration set for the sigma computations.

Brown, G. S.↗

NASA NTRS1972

Artificial lunar impact craters: Four new identifications, part I

The Apollo 16 panoramic camera photographed the impact locations of the Ranger 7 and 9 spacecraft and the S-4B stage of the Apollo 14 Saturn launch vehicle. Identification of the Ranger craters was very simple because each photographed its target point before impact. Identification of the S-4B impact crater proved to be a simple matter because the impact location, as derived from earth-based tracking, displayed a prominent and unique system of mixed light and dark rays. By using the criterion of a dark ray pattern, a reexamination of the Apollo 14 500 mm Hasselblad sequence taken of the Apollo 13 S-4B impact area was made. This examination quickly led to the discovery of the ray system and the impact crater. The study of artificial lunar impact craters, ejecta blankets, and ray systems provides the long-needed link between the various experimental terrestrial impact and explosion craters, and the naturally occurring impact craters on the moon. This elementary study shows that lunar impact crater diameters are closely predictable from a knowledge of the energies involved, at least in the size range considered, and suggests that parameters, such as velocity, may have a profound effect on crater morphology and ejecta blanket albedo.

Whitaker, E. A.↗

NASA NTRS2011

Demonstration of a Particle Impact Monitoring System for Crewed Space Exploration Modules

When micrometeorite or debris impacts occur on a space habitat, crew members need to be quickly informed of the likely extent of damage, and be directed to the impact location for possible repairs. The goal of the Habitat Particle Impact Monitoring System (HIMS) is to develop a fully automated, end-to-end particle impact detection system for crewed space exploration modules, both in space and on the surfaces of Solar System bodies. The HIMS uses multiple thin film piezo-polymer vibration sensors to detect impacts on a surface, and computer processing of the acoustical signals to characterize the impacts. Development and demonstration of the HIMS is proceeding in concert with NASA's Habitat Demonstration Unit (HDU) Project. The HDU Project is designed to develop and test various technologies, configurations, and operational concepts for exploration habitats. This paper describes the HIMS development, initial testing, and HDU integration efforts. Initial tests of the system on the HDU were conducted at NASA?s 2010 Desert Research and Technologies Studies (Desert-RATS). Four sensor locations were assigned near the corners of a rectangular pattern. To study the influence of wall thickness, three sets of four sensors were installed at different layer depths: on the interior of the PEM wall, on the exterior of the same wall, and on the exterior of a layer of foam insulation applied to the exterior wall. Once the system was activated, particle impacts were periodically applied by firing a pneumatic pellet gun at the exterior wall section. Impact signals from the sensors were recognized by a data acquisition system when they occurred, and recorded on a computer for later analysis. Preliminary analysis of the results found that the HIMS system located the point of impact to within 8 cm, provided a measure of the impact energy / damage produced, and was insensitive to other acoustic events. Based on this success, a fully automated version of this system will be completed and demonstrated as part of a crew "Caution/Warning" system at the 2011 Desert-RATS, along with a crew response procedure.

Opiela, J. N.↗

NASA NTRS2017

Using Information from Rendezvous Missions For Best-Case Appraisals of Impact Damage to Planet Earth Caused By Natural Objects

The Asteroid Threat Assessment Project (ATAP), a part of NASAs Planetary Defense Coordination Office (PDCO) has the responsibility to appraise the range of surface damage by potential asteroid impacts on land or water. If a threat is realized, the project will provide appraisals to officials empowered to make decisions on potential mitigation actions. This paper describes a scenario for assessment of surface damage when characterization of an asteroid had been accomplished by a rendezvous mission that would be conducted by the international planetary defense community. It is shown that the combination of data from ground and in-situ measurements on an asteroid provides knowledge that can be used to pin-point its impact location and predict the level of devastation it would cause. The hypothetical asteroid 2017 PDC with a size of 160 to 290 m in diameter to be discussed at the PDC 2017 meeting is used as an example. In order of importance for appraising potential damage, information required is: (1) where will the surface impact occur? (2) What is the mass, shape and size of the asteroid and what is its entry state (speed and entry angle) at the 100 km atmospheric pierce point? And (3) is the asteroid a monolith or a rubble pile? If it is a rubble pile, what is its sub and interior structure? Item (1) is of first order importance to determine levels of devastation (loss of life and infrastructure damage) because it varies strongly on the impact location. Items (2) and (3) are used as input for ATAPs simulations to define the level of surface hazards: winds, overpressure, thermal exposure; all created by the deposition of energy during the objects atmospheric flight, and/or cratering. Topics presented in this paper include: (i) The devastation predicted by 2017 PDCs impact based on initial observations using ATAPs risk assessment capability, (ii) How information corresponding to items (1) to (3) could be obtained from a rendezvous mission, and (iii) How information from a rendezvous mission could be used, along with that from ground observations and data from the literature, could provide input for an new risk analysis capability that is emerging from ATAPs research. It is concluded that this approach would result in appraisal with the least uncertainty possible (herein called the best-case) using simulation capabilities that are currently available or will be in the future.

Arnold, James O.↗

NASA NTRS2017

Using Information from Rendezvous Missions For Best-Case Appraisals of Impact Damage to Planet Earth Caused By Natural Objects

The Asteroid Threat Assessment Project (ATAP), a part of NASAs Planetary Defense Coordination Office (PDCO) has the responsibility to appraise the range of surface damage by potential asteroid impacts on land or water. If a threat is realized, the project will provide appraisals to officials empowered to make decisions on potential mitigation actions. This paper describes a scenario for assessment of surface damage when characterization of an asteroid had been accomplished by a rendezvous mission that would be conducted by the international planetary defense community. It is shown that the combination of data from ground and in-situ measurements on an asteroid provides knowledge that can be used to pin-point its impact location and predict the level of devastation it would cause. The hypothetical asteroid 2017 PDC with a size of 160 to 290 m in diameter to be discussed at the PDC 2017 meeting is used as an example. In order of importance for appraising potential damage, information required is: (1) where will the surface impact occur? (2) What is the mass, shape and size of the asteroid and what is its entry state (speed and entry angle) at the 100 km atmospheric pierce point? And (3) is the asteroid a monolith or a rubble pile? If it is a rubble pile, what is its sub and interior structure? Item (1) is of first order importance to determine levels of devastation (loss of life and infrastructure damage) because it varies strongly on the impact location. Items (2) and (3) are used as input for ATAPs simulations to define the level of surface hazards: winds, overpressure, thermal exposure; all created by the deposition of energy during the objects atmospheric flight, andor cratering. Topics presented in this paper include: (i) The devastation predicted by 2017 PDCs impact based on initial observations using ATAPs risk assessment capability, (ii) How information corresponding to items (1) to (3) could be obtained from a rendezvous mission, and (iii) How information from a rendezvous mission could be used, along with that from ground observations and data from the literature, could provide input for an new risk analysis capability that is emerging from ATAPs research. It is concluded that this approach would result in appraisal with the least uncertainty possible (herein called the best-case) using simulation capabilities that are currently available or will be in the future.

Arnold, J. O.↗

NASA NTRS2017

Using Information from Rendezvous Missions for Best-Case Appraisals of Impact Damage to Planet Earth Caused by Natural Objects

The Asteroid Threat Assessment Project (ATAP), a part of NASAs Planetary Defense Coordination Office (PDCO) has the responsibility to appraise the range of surface damage by potential asteroid impacts on land or water. If a threat is realized, the project will provide appraisals to officials empowered to make decisions about potential mitigation actions. This paper describes a scenario for assessment of surface damage when characterization of an asteroid had been accomplished by a rendezvous mission that would be conducted by the international planetary defense community. It is shown that the combination of data from ground and in-situ measurements on an asteroid provides knowledge that can be used to pin-point its impact location and predict the level of devastation it would cause. The hypothetical asteroid 2017 PDC with a size range of 160 to 290 m in diameter to be discussed at the PDC 2017 is used as an example. In order of importance for appraising potential damage, information required is: (1) where will the surface impact occur? (2) what is the mass, shape and size of the asteroid and what is its entry state (speed and entry angle) at the 100 km atmospheric pierce point? And (3) is the asteroid a monolith or a rubble pile? If it is a rubble pile, what is its structure and heterogeneity from the surface and throughout its interior? Item (1) is of first order importance to determine levels of devastation (loss of life and infrastructure damage) because it varies strongly on the impact location. Items (2) and (3) are used as inputs for ATAPs simulations to define the level of surface hazards: winds, overpressure, thermal exposure; all created by the deposition of energy during the objects atmospheric flight, andor cratering. Topics presented in this paper include: (i) the devastation predicted by 2017 PDCs impact on land based on initial observations using ATAPs risk assessment capability, (ii) how information corresponding to items (1) to (3) could be obtained from a rendezvous mission, and (iii) how information from a rendezvous mission could be used, along with that from ground observations and data from the literature to provide input for a new risk analysis capability that is emerging from ATAPs research. It is concluded that this approach would result in the creation of an appraisal of the threat from 2017 PDC with the least uncertainty possible, herein called the best-case.

Asteroid Impact Appraisals↗

NASA NTRS2014

A Comparison of Crater-Size Scaling and Ejection-Speed Scaling During Experimental Impacts in Sand

Non‐dimensional scaling relationships are used to understand various cratering processes including final crater sizes and the excavation of material from a growing crater. The principal assumption behind these scaling relationships is that these processes depend on a combination of the projectile's characteristics, namely its diameter, density, and impact speed. This simplifies the impact event into a single point‐source. So long as the process of interest is beyond a few projectile radii from the impact point, the point‐source assumption holds. These assumptions can be tested through laboratory experiments in which the initial conditions of the impact are controlled and resulting processes measured directly. In this contribution, we continue our exploration of the congruence between crater‐size scaling and ejection‐speed scaling relationships. In particular, we examine a series of experimental suites in which the projectile diameter and average grain size of the target are varied.

Anderson, J. L. B.↗

NASA NTRSDate not supplied

Computational Fluid Dynamics Models of the NASA White Sands Test Facility Particle Impact Test Nozzles

The particle impact ignition mechanism is considered to be the most effective means for igniting metals in gaseous oxygen environments and is a concern for every oxygen system. For this reason, the National Aeronautics and Space Administration (NASA) commits a large amount of resources attempting to understand and defend against this phenomenon. The most practical means of accomplishing this is through extensive of testing. To this end, over the years NASA has developed and built a facility and various apparatuses to test material or component vulnerability to a particle impact ignition. In testing materials, NASA uses sub-sonic and supersonic nozzles to replicate the conditions that a material is expected to experience in service. However, challenges include obtaining an understanding of the gas dynamics and of the particle behavior through and up to the point of impact at the material under test. One means of addressing these challenges is the use of computational fluid dynamics (CFD). If a CFD model can be built and validated, the model can then be used to confidently interrogate changes to inlet conditions and particle geometries, as well as changes to nozzle geometries to better simulate a material’s in-situ conditions and greatly reduce or eliminate trial-and-error approaches in testing. This paper will show NASA’s approach to and results of using CFD to better understand their particle impact nozzles.

Computational Fluid Dynamics↗

NASA NTRS2004

Formation Control of the MAXIM L2 Libration Orbit Mission

The Micro-Arcsecond Imaging Mission (MAXIM), a proposed concept for the Structure and Evolution of the Universe (SEU) Black Hole Imaging mission, is designed to make a ten million-fold improvement in X-ray image clarity of celestial objects by providing better than 0.1 microarcsecond imaging. To achieve mission requirements, MAXIM will have to improve on pointing by orders of magnitude. This pointing requirement impacts the control and design of the formation. Currently the architecture is comprised of 25 spacecraft, which will form the sparse apertures of a grazing incidence X-ray interferometer covering the 0.3-10 keV bandpass. This configuration will deploy 24 spacecraft as optics modules and one as the detector. The formation must allow for long duration continuous science observations and also for reconfiguration that permits re-pointing of the formation. In this paper, we provide analysis and trades of several control efforts that are dependent upon the pointing requirements and the configuration and dimensions of the MAXIM formation. We emphasize the utilization of natural motions in the Lagrangian regions that minimize the control efforts and we address both continuous and discrete control via LQR and feedback linearization. Results provide control cost, configuration options, and capabilities as guidelines for the development of this complex mission.

Folta, David↗

NASA NTRS1986

Structural loads preliminary results

From a total of 351 instrumentation channels, 341 channels (97%) were in operation during the initial impact of the airplane. Both NASA seats, the energy absorbing seat and the standard seat, maintained their integrity during the impact. The floor accelerations at the seat locations were lower than the accelerations required for the energy absorbers to stroke; consequently, the energy absorbing seat did not stroke. The two seats remained firm in place during the crash and no seat attachment failures were observed. Due to the low accelerations experienced during the crash, both seats performed as standard seats. In the airplane structure, the accelerations were higher at both the point of impact in the left wing and at the forward end of the fuselage. The accelerations on the floor were higher toward the front than toward the rear and the floor accelerations on the left side were higher than on the right side at the front of the fuselage, but toward the rear they evened out.

Alfaro-Bou, E.↗

NASA NTRS1998

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in Space

The safety issue has been raised with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. This investigation was undertaken to evaluate if molten metal could detach and come in contact with astronauts and burn through the fabric of the astronauts' Extravehicular Mobility Unit (EMU) during electron beam welding in space. Molten metal detachments from either the weld/cut substrate or weld wire could present harm to a astronaut if the detachment was to burn through the fabric of the EMU. Theoretical models were developed to predict the possibility and size of the molten metal detachment hazards during the electron beam welding exercises at Low Earth Orbit (LEO). The primary molten metal detachment concerns were those cases of molten metal separation from the metal surface due to metal cutting, weld pool splashing, entrainment and release of molten metal due to filler wire snap-out from the weld puddle, and molten metal accumulation and release from the end of the weld wire. Some possible ways of obtaining molten metal drop detachments would include an impulse force, or bump, to the weld sample, cut surface, or filler wire. Theoretical models were developed for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. The surface tension represents the force opposing the liquid metal drop from detaching whereas the weight of the liquid metal droplet represents a force that is tending to detach the molten metal drop. Theoretical calculations have indicated that only a small amount of energy is required to detach a liquid metal drop; however, much of the energy of an impact is absorbed in the sample or weld plate before it reaches the metal drop on the cut edge or surface. The tendency for detachment is directly proportional to the weld pool radius and metal density and inversely proportional to the surface tension of the liquid metal. For a detachment the initial kinetic energy of the weld pool with respect to the plate has to exceed the energy to form the extra surface required for the detachment of the pool. The difficulty is in transferring the energy from the point of impact through the plate and sample to the cut edge. It is likely that not all of the kinetic energy is available for detaching the pool; some may be sequestered in weld pool oscillations. The coefficient of restitution for the collision will be lower than one if irreversible deformation, for example plastic flow deformation, takes place during the collision. Thus determining the amount of energy from an impact that actually reaches the molten metal droplet is critical. Various molten metal detachment scenarios were tested experimentally in an enclosed vacuum chamber using the Ukrainian Universal Hand Tool, an electron beam welder designed for space welding. The experimental testing was performed in a 4 ft. X 4 ft. vacuum chamber at Marshall Space Flight Center, evacuated to vacuum levels of at least 50 microTorr, and also some welding garment material was utilized to observe the effect of the molten metal detachments on the material. A "carillon" apparatus consisting of four pendulum hammer strikers, each weighing approximately 3.65 lbs, raised to predetermined specific heights was used to apply an impact force to the weld sample/plate during electron beam welding and cutting exercises. The strikers were released by switching on an electric motor to rotate a pin holding wires retaining the strikers at desired heights. The specimens were suspended so as to be free to respond to the blows with a sudden velocity increment. The specimens were mounted on a hinged plate for minimizing effective mass with the option to fasten it down so as to raise its effective mass closer to that anticipated for an actual space welding scenario. Measurements were made of the impact energy and the horizontal fling distances of the detached metal drops. It was not particularly easy to generate the detachments for this experiment. This document presents the details of the theoretical modeling effort and a summary of the experimental effort to measure molten metal drop detachments from terrestrial electron beam welding in the enclosed vacuum chamber. The results of the experimental effort have shown that molten metal detachments can occur from the sample/weld plate only if a sufficiently large impact force is applied to the weld plate. A "weld pool detachment parameter" was determined to indicate whether detachment would occur. Detachment can be either full or partial (dripping), Partial detachment means that the weld pool detached from one side of the liquid-solid boundary so as to leave a hole at the puddle site but remained attached over part of the liquid-solid boundary and dripped down the plate with no fully detached material detected. Full detachment, however, does not necessarily mean that the whole pool fully detached; in some cases only a smaller portion of the pool detached, the remainder dripping down the plate. The weld pool detachment parameter according to theory and according to the empirical data allows a determination of whether full detachments might occur. Theoretical calculations indicated titanium alloy would be the most difficult from which to detach molten metal droplets followed by stainless steel and then by aluminum. The experimental results were for the most part consistent with the theoretical analysis and predictions. The above theory is applicable to other situations as desired for assessing the potential for molten metal detachments.

Fragomeni, James M.↗

NASA NTRSDate not supplied

An Updated Secondary Lunar Meteoroid Ejecta Model for Engineering Design

Introduction: The surface of the Moon is constantly being bombarded by a flux of meteoroids of various sizes. Impacts due to these meteoroids produce secondary ejecta material at much lower speeds but with a total mass larger than the original impactor. Details about the secondary ejecta are important for planning missions on the lunar surface. In this work, an updated ejecta model is presented called the Meteoroid Model of Secondary Ejecta (MeMoSeE), to re-place the Apollo-era ejecta model, NASA SP-8013 [1], in the SLS-SPEC 159 Design Specification for Natural Environments (DSNE) [2]. The model pro-duces secondary ejecta flux environments for a user-specified location on the lunar surface, and sorts the incoming secondary flux by angular direction and speed. Methods: MeMoSeE is separated into three parts: the inputs, the conversion step, and the integration of fluxes. Inputs to the model include the primary meteoroid fluxes and the primary near-Earth object (NEO) fluxes. Meteoroid fluxes, both asteroidal and cometary, are calculated using the Meteoroid Engineering Model (MEM3) [3] for different locations on the Moon. For each surface location, an ephemeris is generated using the JPL HORIZONS System [4] that feeds into MEM3. The NEO fluxes are approximated by the high-density population of MEM3 (i.e., only the directionality), where the speed distribution of the NEO fluxes is renormalized to match observations [5]. The regolith properties are used as defined in the DSNE [2]. The conversion step utilizes scaling laws given by Housen & Holsapple 2011 [6] to convert the primary impactor flux to the total mass of secondary ejecta. The ejecta distribution, at the point-of-impact (POI), is separated into a zenith angle and azimuthal angle distribution. The zenith angle distribution follows a beta distribution where the peak depends on the impact altitude angle and the impact azimuth [7]. We employ an ejecta azimuth distribution that is based on Rival & Mandeville 1999 [8] which focuses ejecta in the downstream direction for more oblique impacts. Finally, during the integration step, we sum secondary ejecta number fluxes at a particular region-of-interest (ROI) that originated from many POI locations over the entire surface of the Moon. We keep track of both altitude and azimuth angle bins as well as a range of speed bins, following the igloo gridding as done in MEM3 [9]. The ejecta particle size distribution and density is assumed to be the same as the lunar regolith [10, 2]. Results: The primary fluxes are computed for one Metonic cycle (19 years) for various locations over the lunar surface with a fixed orientation. Both the angular and speed distributions of the primary fluxes are dependent on the latitude and longitude. The over-all primary fluxes show a roughly 13% increase from the eastern limb to the western limb. In general, the speed distribution of the secondary fluxes span from a user-defined minimum speed to the escape speed of the Moon (2.38 km/s), roughly following a power-law relation [6]. Different parts of the speed distribution come from different primary impact locations on the Moon. The secondary ejecta is dominated by the slowest speeds, where these particles originate nearby the ROI. For speeds around 71% of the escape speed, the secondary ejecta originates from locations near the antipodal point. On the other hand, for secondary ejecta speeds that exceed roughly 90% the escape speed, the ejecta particles come from all over the lunar surface to the ROI. Comparing the secondary ejecta fluxes from MeMoSeE with NASA SP-8013 [1], there is a reduction by about 2-3 orders of magnitude for secondary ejecta particles greater than 1 µg. These estimates agree with recent findings from Bjorkman & Christiansen 2019 [11]. The secondary ejecta fluxes are also compared with the primary fluxes, where the ejecta fluxes are roughly an order of magnitude greater than the primary fluxes. References: [1] Cour-Palais, B. G., (1969) NASA SP-8013. [2] NASA SLS-SPEC-159 Rev. H (2020). [3] Moorhead, A. V., et al. (2019) JS&R, 1-17. [4] Giorgini, J. D., (2015) IAUGA, 29, 2256293. [5] Moorhead, A. V., (2020) Memo OSMA/MEO/Lunar-001. [6] Housen, K. R., and Holsapple, K. A., (2011) Icarus, 211(1), 856-875. [7] Gault, D. E., and Wedekind, J. A., (1978) L&PSCP, 9, 3843-3875. [8] Rival, M., and Mandeville, J., (1999) Space Debris, 1(1), 45-57. [9] Moorhead, A. V., (2019) MEM3 User Guide. [10] Carrier, W. D., (1973) The Moon, 6(3-4), 250-263. [11] Bjorkman, M. D. & Christiansen, E. L., (2019) ODC

impacts↗

NASA NTRS1976

Resistive anode image converter

The invention of an apparatus for imaging soft X-ray and ultraviolet electromagnetic radiation and charged particles was described. The apparatus includes a pair of microchannel electron multiplier plates connected in a cascaded chevron configuration which intercepts an incident beam of radiation or charged particles. Incident photons or charged particles strike the front surface of the chevron configuration causing emission of electrons. The electrons are accelerated by a voltage gradient and strike the inner side walls of the individual channels, causing emission of secondary electrons. Accelerated and multiplied secondary electrons impinge upon a resistive anode after they transverse the chevron configuration. A pulse position circuit converts the magnitude or transit time of the currents flowing from the point of impact of the electrons on the resistive anode to four contact electrodes mounted on their periphery of the resistive anode into the spatial coordinates of electron impact.

Lampton, M. L.↗

NASA NTRS1979

Analytical prediction with multidimensional computer programs and experimental verification of the performance, at a variety of operating conditions, of two traveling wave tubes with depressed collectors

Experimental and analytical results are compared for two high performance, octave bandwidth TWT's that use depressed collectors (MDC's) to improve the efficiency. The computations were carried out with advanced, multidimensional computer programs that are described here in detail. These programs model the electron beam as a series of either disks or rings of charge and follow their multidimensional trajectories from the RF input of the ideal TWT, through the slow wave structure, through the magnetic refocusing system, to their points of impact in the depressed collector. Traveling wave tube performance, collector efficiency, and collector current distribution were computed and the results compared with measurements for a number of TWT-MDC systems. Power conservation and correct accounting of TWT and collector losses were observed. For the TWT's operating at saturation, very good agreement was obtained between the computed and measured collector efficiencies. For a TWT operating 3 and 6 dB below saturation, excellent agreement between computed and measured collector efficiencies was obtained in some cases but only fair agreement in others. However, deviations can largely be explained by small differences in the computed and actual spent beam energy distributions. The analytical tools used here appear to be sufficiently refined to design efficient collectors for this class of TWT. However, for maximum efficiency, some experimental optimization (e.g., collector voltages and aperture sizes) will most likely be required.

Dayton, J. A., Jr.↗

NASA NTRS1981

Analytical prediction and experimental verification of performance at various operating conditions of a dual-mode traveling wave tube with multistage depressed collectors

A comparison of analytical and experimental results is presented for a high performance dual-mode traveling wave tube (TWT) operated over a wide range conditions. The computations are carried out with advanced multidimensional computer programs. These programs model the electron beam as a series of disks or rings of charge and follow their trajectories from the rf input of the TWT through the slow-wave structure refocusing system to their points of impacts in the depressed collector. TWT performance, collector efficiency, and collector current distribution are computed and compared with measurements. Very good agreement was obtained between computed and measured TWT performance and collector efficiencies, and the computer design of a highly efficient collector was demonstrated.

Dayton, J. A., Jr.↗

NASA NTRS1981

Experimental verification of a computational procedure for the design of TWT-refocuser-MDC systems

A comparison of analytical and experimental results is presented for a high performance dual-mode helix TWT, equipped with multistage depressed collectors (MDC), and operated over conditions ranging from saturation to the linear regime. The computations are carried out with advanced multidimensional computer programs which model the electron beam as a series of disks or rings of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure, through the refocusing system, to their points of impact in the depressed collector. TWT performance, collector efficiency, and collector current distribution are computed and compared with measurements. Very good agreement is obtained between computed and measured TWT performance and collector efficiencies. The analytical techniques were subsequently applied to the design of a smaller MDC of nearly equal efficiency.

Dayton, J. A., Jr.↗