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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The effect of the near earth micrometeoroid environment on a highly reflective mirror surface

A resurgence of interest in placing large solar concentrator solar dynamic systems in space for power generation has brought up again a concern for maintaining the integrity of the optical properties of highly specular reflecting surfaces in the near earth space environment. One of the environmental hazards needing evaluation is the micrometeoroid environment. It has been shown that highly reflective polished metals and thin film coatings degrade when exposed to simulated micrometeoroids in the lab. At NASA-Lewis, a shock tube was used to simulate the phenomenon of micrometeoroid impact by accelerating micron sized particles to hypervelocities. Any changes in the optical properties of surfaces exposed to this impact were then evaluated. The degradation of optical properties of polished metals and thin metallic films after exposure to simulated micrometeoroids was determined as a function of impacting kinetic energy area of the particles. A calibrated sensor was developed to not only detect the micrometeoroid environment, but also to evaluate the degradation of the optical properties of thin aluminum films in space. Results of the simulation are presented and discussed.

Mirtich, Michael J.↗
NASA NTRS1988

The effect of the near earth micrometeoroid environment on a highly reflective mirror surface

A resurgence of interest in placing large solar concentrator solar dynamic systems in space for power generation has brought up again a concern for maintaining the integrity of the optical properties of highly specular reflecting surfaces in the near earth space environment. One of the environmental hazards needing evaluation is the micrometeoroid environment. It has been shown that highly reflective polished metals and thin film coatings degrade when exposed to simulated micrometeoroids in the lab. At NASA-Lewis, a shock tube was used to simulate the phenomenon of micrometeoroid impact by accelerating micron sized particles to hypervelocities. Any changes in the optical properties of surfaces exposed to this impact were then evaluated. The degradation of optical properties of polished metals and thin metallic films after exposure to simulated micrometeoroids was determined as a function of impacting kinetic energy area of the particles. A calibrated sensor was developed to not only detect the micrometeoroid environment, but also to evaluate the degradation of the optical properties of thin aluminum films in space. Results of the simulation are presented and discussed.

Mirtich, Michael J.↗
NASA NTRS1990

The effect of the near earth micrometeoroid environment on a mirror surface after 20 years in space

The effect of micrometeoroid impact on the optical properties of polished metals and thin film coatings has been simulated by accelerating micron-sized particles to hypervelocities in a shock tube. The degradation of these properties after exposure to simulated meteoroids was determined as a function of impacting kinetic energy/area of the particles. A calibrated sensor, 2000-A Al/stainless steel, was developed to detect the micrometeoroid environment and to evaluate the degradation of the optical properties of thin aluminum films in space. No changes in the optical properties of the highly reflective surface sensor on SERT II, launched in 1970, were measured during 19 years in space. These results are found to be in agreement with the 1969 Micrometeoroid Flux Model. It is concluded that a highly reflective surface should lose less than 1 percent of its specular reflectance in near-earth orbit during 19 years.

Mirtich, Michael J.↗
NASA NTRS1992

Space debris characterization in support of a satellite breakup model

The Space Kinetic Impact and Debris Branch began an ambitious program to construct a fully analytical model of the breakup of a satellite under hypervelocity impact. In order to provide empirical data with which to substantiate the model, debris from hypervelocity experiments conducted in a controlled laboratory environment were characterized to provide information of its mass, velocity, and ballistic coefficient distributions. Data on the debris were collected in one master data file, and a simple FORTRAN program allows users to describe the debris from any subset of these experiments that may be of interest to them. A statistical analysis was performed, allowing users to determine the precision of the velocity measurements for the data. Attempts are being made to include and correlate other laboratory data, as well as those data obtained from the explosion or collision of spacecraft in low earth orbit.

Fortson, Bryan H.↗
NASA NTRS1992

Relationship between mechanical-property and energy-absorption trends for composite tubes

U.S. Army helicopters are designed to dissipate prescribed levels of crash impact kinetic energy without compromising the integrity of the fuselage. Because of the complexity of the energy-absorption process it is imperative for designers of energy-absorbing structures to develop an in-depth understanding of how and why composite structures absorb energy. A description of the crushing modes and mechanisms of energy absorption for composite tubes and beams is presented. Three primary crushing modes of composite structures including transverse shearing, lamina bending, and local buckling are described. The experimental data presented show that fiber and matrix mechanical properties and laminate stiffness and strength mechanical properties cannot reliably predict the energy-absorption response of composite tubes.

Farley, Gary L.↗
NASA NTRS1999

Scale Effects in Strength-Dominated Collisions of Rocky Asteroids

The application of laboratory collision experimental results to the larger scales of asteroid impacts is complicated by the fact that the dynamic strength of rock typically decreases as the loading duration increases. Because loading times increase with the size scale of a collision, large bodies are effectively weaker than small ones. While this effect has been postulated for over a decade, it has never been verified in actual collision experiments. This paper summarizes collision tests performed under the conditions required to examine scale effects, i.e., increasing the size scale of the experiment while holding the impact velocity and impact kinetic energy per target mass constant. Granite targets are used, with a diameter variation of a factor of 18. The larger targets experienced significantly more collisional damage than small ones, confirming a decrease in dynamic strength with increasing size scale. The results are compared to a scaling model based on the concept that fragmentation is accomplished through the growth and coalescence of preexisting flaws. Measurements of the actual flaw-size distribution are used to validate the model. Field observations of flaw and fault sizes at scales to 10 km are used to construct a scaling model that is believed to apply to the shattering of a wide range of rock types. The results show that kilometer-sized rocky bodies may be significantly weaker than indicated by previous estimates.

Housen, Kevin R.↗
NASA NTRS1999

Compaction as the Origin of the Unusual Craters on the Asteroid Mathilde

Asteroid Mathilde has been pummeled by at least five giant impacts (Figure 1). Previous experience with cratering suggests Mathilde's giant craters should each be surrounded by kilometer-deep blankets of ejecta, i.e. material excavated during the impact events. Curiously, there appears to be very little ejecta around Mathilde's craters; they show no evidence of filling by ejecta from adjacent large craters. A previous explanation for the missing ejecta, based on computer simulations, is that Mathilde's unusually high porosity (50 +/- 20%) confines the deposited impact kinetic energy to a localized volume, and produces excavation velocities so high (greater than approximately 20m/s) that nearly all ejecta escape Mathilde's gravitational field. Here we report on laboratory experiments in a highly porous material that give a different explanation. The crater is formed primarily by compaction, not excavation. The small amount of material that is lofted has velocities and ranges so small that nearly all of it is re-deposited within the crater bowl, thereby sparing neighboring craters from ejecta in-filling. This peculiar style of cratering implies that highly porous asteroids are minor contributors of meteorites, because essentially no ejecta escape these asteroids.

Housen, Kevin R.↗
NASA NTRS2009

Micro-Satellite Impact Tests to Investigate Multi-Layer Insulation Fragments

This paper summarizes two satellite impact experiments completed in 2008. The objective of the experiments is to investigate the physical properties of satellite fragments, including those originated from Multi-Layer Insulation (MLI) and solar panels. The ultimate goal is to use the results to improve the NASA Standard Breakup Model. The targets were two cubic micro-satellites, 20 cm by 20 cm by 20 cm in size, and approximately 1,500 g in mass. The main structure of each micro-satellite was composed of five layers; the top and bottom layers and three internal layers parallel to the top and bottom layers, plus four side panels. The top layer was equipped with solar cells that was mounted to an aluminum honeycomb sandwich panel with CFRP face sheets. The four side panels and the bottom layer are all covered with MLI. The two satellite impact experiments were conducted using the two-stage light gas gun at the Kyushu Institute of Technology in Kitakyusyu, Japan. For the first experiment (labeled Shot F), the satellite was oriented in such a way that the solar panel was facing the incoming projectile, a 39.3 g aluminum alloy solid sphere. For the second experiment (labeled Shot R), the satellite was oriented so that the solar panel was on the opposite side of the impact surface. The projectile used in the second shot was a 39.2 g aluminum alloy solid sphere. The impact speeds of Shot F and Shot R were 1.74 km/s and 1.78 km/s, respectively. The ratio of the impact kinetic energy to satellite mass for the two experiments was about 40 J/g. Both target satellites were completely fragmented, although there were noticeable differences in the characteristics of the fragments. Approximately 1,800 fragments were collected from Shot F but only 1,000 fragments were collected from Shot R. This difference primarily comes from the number of needle-like CFRP and MLI fragments. The difference in CFRP pieces depends on how the CFRP panels were fragmented. Regarding the MLI pieces, a significant difference in size and number can be observed. The largest MLI pieces in Shot F are almost of the same size as the side panels, whereas those in Shot R are larger by about a factor of two. The collected fragments and MLI pieces will be measured and analyzed using the same method as described in the NASA Standard Breakup Model. This paper will present: (1) the area-to-mass ratio, size, and mass distributions of the fragments, and (2) the differences in fragment properties between Shot F and Shot R.

Liou, J.C.↗
NASA NTRS2011

Lunar Meteoroid Impact Observations and the Flux of Kilogram-sized Meteoroids

Lunar impact monitoring provides useful information about the flux of meteoroids in the hundreds of grams to kilograms size range. The large collecting area of the night side of the lunar disk, approximately 3.8 10(exp 6)sq km in our camera field-of-view, provides statistically significant counts of the meteoroids striking the lunar surface. Over 200 lunar impacts have been observed by our program in roughly 4 years. Photometric calibration of the flashes observed in the first 3 years along with the luminous efficiency determined using meteor showers and hypervelocity impact tests (Bellot Rubio et al. 2000; Ortiz et al. 2006; Moser et al. 2010; Swift et al. 2010) provide their impact kinetic energies. The asymmetry in the flux on the evening and morning hemispheres of the Moon is compared with sporadic and shower sources to determine their most likely origin. These measurements are consistent with other observations of large meteoroid fluxes.

Suggs, R. M.↗
NASA NTRS2011

Magnetic Shielding of the Channel Walls in a Hall Plasma Accelerator

In a qualification life test of a Hall thruster it was found that the erosion of the acceleration channel practically stopped after approx 5,600 h. Numerical simulations using a two-dimensional axisymmetric plasma solver with a magnetic field-aligned mesh reveal that when the channel receded from its early-in-life to its steady-state configuration the following changes occurred near the wall: (1) reduction of the electric field parallel to the wall that prohibited ions from acquiring significant impact kinetic energy before entering the sheath, (2) reduction of the potential fall in the sheath that further diminished the total energy ions gained before striking the material, and (3) reduction of the ion number density that decreased the flux of ions to the wall. All these changes, found to have been induced by the magnetic field, constituted collectively an effective shielding of the walls from any significant ion bombardment. Thus, we term this process in Hall thrusters "magnetic shielding."

ion density↗
NASA NTRS2017

Multi-Organization Multi-Discipline Effort Developing a Mitigation Concept for Planetary Defense

There have been significant recent efforts in addressing mitigation approaches to neutralize Potentially Hazardous Asteroids (PHA). One such research effort was performed in 2015 by an integrated, inter-disciplinary team of asteroid scientists, energy deposition modeling scientists, payload engineers, orbital dynamist engineers, spacecraft discipline engineers, and systems architecture engineer from NASAs Goddard Space Flight Center (GSFC) and the Department of Energy (DoE) National Nuclear Security Administration (NNSA) laboratories (Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratories (LLNL) and Sandia National Laboratories). The study team collaborated with GSFCs Integrated Design Centers Mission Design Lab (MDL) which engaged a team of GSFC flight hardware discipline engineers to work with GSFC, LANL, and LLNL NEA-related subject matter experts during a one-week intensive concept formulation study in an integrated concurrent engineering environment. This team has analyzed the first of several distinct study cases for a multi-year NASA research grant. This Case 1 study references the Near-Earth Asteroid (NEA) named Bennu as the notional target due to the availability of a very detailed Design Reference Asteroid (DRA) model for its orbit and physical characteristics (courtesy of the Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission team). The research involved the formulation and optimization of spacecraft trajectories to intercept Bennu, overall mission and architecture concepts, and high-fidelity modeling of both kinetic impact (spacecraft collision to change a NEAs momentum and orbit) and nuclear detonation effects on Bennu, for purposes of deflecting Bennu.

Planetary Defense↗
NASA NTRS2019

Ion Propulsion for Solar System Exploration

NASA's Evolutionary Xenon Thruster (NEXT) is ready for transition-to-flight. The thruster has completed all qualification-level environmental testing, and has demonstrated a xenon propellant throughput, total impulse, and total operating hours greatly in excess of anticipated planetary science mission requirements, and exceeding that achieved by any other thruster technology in the history of electric propulsion. NEXT is the next generation system, a natural progression in technology from that implemented successfully on the Deep-Space one and Dawn missions, developed at NASA's Glenn Research Center in Cleveland, Ohio. The first implementation of NEXT will be on NASA 's Double Asteroid Redirection Test (DART). DART will be the first demonstration of the kinetic impact technique to change the motion of an asteroid in space. The DART mission is in Phase C, led by Johns Hopkins University Applied Physics Laboratory. The DART spacecraft will utilize the NASA Evolutionary Xenon Thruster solar electric propulsion system as its primary in-space propulsion system. By utilizing NEXT, DART is able to gain significant flexibility to the mission timeline and launch window, as well as decrease in launch vehicle cost. This presentation will review NASA's investment strategy in electric propulsion _ in particular gridded ion thruster technology _ as it applies to solar system exploration. Results obtained from implementing this technology on Deep-Space one and Dawn will be reviewed. Mission studies which highlight the impacts of the NEXT technology will be discussed, and near-term proposed and scheduled missions including DART and CAESAR (Comet Astrobiology Exploration Sample Return) will be reviewed.

Electric Propulsion↗
NASA NTRS2016

Trajectories for Europa Flyby Sample Return

Ballistic trajectories are computed which would enable a sample return mission to Europa without capturing, descending, or landing. The low-cost mission concept utilizes a free return trajectory that also involves a close flyby of Europa. Near Europa, a small impactor would kinetically impact the icy moon and generate a plume, subsequently sampled by the spacecraft. A broad search algorithm is developed to construct feasible itineraries, which considers Venus and Earth gravity assist sequences. High-quality solutions are then differentially corrected to be continuous using high-fidelity dynamics. The complete methodology is applicable to other outer-planet moons, notably Enceladus. The outbound VEEGA option is found to signifcantly reduce launch C3 compared to alternate options. The characteristics and quality of the solutions exhibit substantial variation over the 12-year period of Jupiter. Nevertheless, a variety of optimized results are computed with C3 as low as 16.0 sq.km/sq.sec, re-entry speed well below that of the Stardust capsule, and flight times of 9 to 15 years.

Jones, Drew Ryan↗
NASA NTRS2019

High Velocity Impact Performance of a Dual Layer Thermal Protection System for the Mars Sample Return Earth Entry Vehicle

The Mars Sample Return (MSR) Earth Entry Vehicle (EEV) is currently planned on being released from its Micro-Meteorite/Orbital Debri (MM/OD) shielding housing about two days before the Earth entry phase. This leaves the EEV exposed to incoming MM/OD impacts, potentially damaging the heat shield and compromising its Entry, Decent, and Landing (EDL) integrity. Currently, two materials are proposed to comprise the MSR-EEV heat shield, a dual layer material Heat-shield for Extreme Entry Environment Technology (HEEET) and Phenolic Impregnated Carbon Ablator (PICA). PICA has been well characterized for OD class impacts, ~7km/s high mass impacts, from previous testing done in the Orion program, but hasn't under-gone extensive MM impact testing. HEEET is a rela-tively new material with minimal prior testing in re-gards to High Velocity Impacts (HVI). In order to in-form selectability of a material, it is crucial to under-stand the material performance when faced with an HVI, directly affecting mission success probability.The current measure of a Thermal Protection Sys-tem's (TPS) performance against an HVI is evaluating a thermally sized material against its derived Balistic Limit Equation (BLE). A BLE is generated empirically from multiple shots of HVI testing, and is used as a first order method in evaluating TPS's performance against the expected MM/OD environment. This method has proved useful for previous uniform densi-ty TPS materials, but has never been validated against a dual layer recession material such as HEEET. Testing in the MSR program for FY19 has a re-quirement to assess the effects of a dual layer TPS by testing various thicknesses of HEEET's Recession Layer, seen in Figure 1. From this data, BLE's will be derived for the individual thickness ratio samples, as well as the material as a whole to evaluate if a heritage form of the BLE can capture the complex physics associated with a dual layer system. Crater morpholo-gy will also be assessed with post-test Non-Destructive Evaluation (NDE) methods such as CT scanning to visualize if a BLE can well predict the associated pene-tration depths, since a BLE assumes full disinigration of the impacting particle and is generally only used to size a spherical crater ? disregarding any shrapenel effects from a high density impactor.To inform this analysis, expected MM environ-ments from the Meteoroid Engineering Model (MEM) and analytical equations for mass flux of incoming MM were evaluated against the notional MSR-EEV trajectory [1]. Using those dispersions, a monte-carlo was run to determine the most probable particle pa-rameters, as well as the riskiest in terms of full bondline penetration. From these probabilities, a test matrix was designed to test against bounding cases for the various parameters of the BLE: projectile density, projectile mass, projectile velocity, and the impact angle.This presentation will discuss the performance of the dual layer TPS material HEEET against a wide range of impact kinetic energies and densitites, as well as the comparison of HEEET to PICA in terms of MM/OD performance and selectability criteria.

Libben, B. J.↗
DOE OSTI2025

Quantifying how the cis/trans ratio of N,N -dimethyl-3,5-dimethylpiperidinium hydroxide impacts the growth kinetics, composition and local structure of SSZ-39

This work integrates experiments and computational methods to quantify how the cis/trans ratio of the OSDA used in SSZ-39 synthesis impacts the crystallization kinetics, material properties, and final product composition. The crystallization kinetics increase by 30% when increasing the trans isomer content from 14% to 80%. Per prior work, in all cases based on the synthesis gel composition and product yield aluminum is the limiting reagent, and the absence of any amorphous material detected in the time resolved PXRD studies leads us to conclude that FAU dissolution is the rate limiting step in the formation of SSZ-39 in this synthesis protocol. The TGA and NMR results suggest that the trans isomer of OSDA is selectively incorporated into the product. The NMR binding studies, and corresponding DFT-based results show that the trans isomer binds to FAU more strongly than the cis isomer, providing one possible explanation for this enhancement in kinetics and preferential uptake of the trans isomer. The EDS analysis indicates that the Si/Al ratios are between 7.7 and 8.6 at low and high trans OSDA content, indicating zeolite composition is mildly sensitive to the trans isomer content. EDS results show this decrease in aluminum content leads to a corresponding decrease in sodium uptake. DFT-based calculations confirm OSDA–sodium interactions cannot explain any decrease in sodium uptake, reinforcing lower aluminum content as the cause of lower sodium uptake. Preliminary cobalt titration experiments show a surprisingly low cobalt uptake but also show a clear dependence of the cobalt uptake on the solution pH.

Cui, Zheng [Tulane University, New Orleans, LA (Un↗
NASA NTRS1978

Field ionization kinetic and electron impact studies of gas phase transition states - The cyclic bromonium ion

Cis- and trans-isomers of 4-t-butylcyclohexyl bromide were studied to determine the mechanism of cyclic bromonium ion formation. The field ionization kinetic and electron impact data indicate that the formation of the cyclic structure occurs simultaneously with loss of the neutral fragment. The data also show that little or no gas-phase cis-trans isomerization occurs.

Green, M. M.↗
NASA NTRS1985

The kinetic energy spectrum of protons produced by the dissociative ionization of H2 by electron impact

The kinetic energy spectra of protons resulting from the dissociative ionization of H2 by electron impact have been measured for electron impact energies from threshold (approximately 17 eV) to 160 eV at 90 deg and 30 deg detection angles, using a crossed-beam experimental arrangement. To check reliability, two separate proton energy analysis methods have been employed, i.e., a time-of-flight proton energy analysis and an electrostatic hemispherical energy analyzer. The present results are compared with previous measurements.

Khakoo, M. A.↗