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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Tutorial on Solar Energetic-Particle Events

Particles from the Sun at energies above approx. 1 MeV/nucleon have been studied in space for over 35 years. There have been major advances in instrumentation for studying elemental and isotopic composition, kinetic energy, charge states, time intensity histories, and anisotropies of energetic particles. There have also been extensive improvements in the observations of solar phenomena, including radio bursts, Coronal Mass Ejections (CMEs), and solar photons from soft X-ray to gamma-ray energies. Despite these advances, there is a lack of agreement as to the acceleration processes responsible for the particles seen in space shortly after the solar event. In particular, the relative importance of solar flares and CME-driven shocks is disputed for events of moderate to larger size. The reasons for this will be reviewed, and the prospects for resolving this issue will be evaluated.

vonRosenvinge, Tycho T.↗
NASA NTRS2013

Spectral State Evolution of 4U 1820-30: the Stability of the Spectral Index of Comptonization Tail

We analyze the X-ray spectra and their timing properties of the compact Xray binary 4U 1820-30. We establish spectral transitions in this source seen with BeppoSAX and the Rossi X-ray Timing Explorer (RXTE). During the RXTE observations (1996 - 2009), the source were approximately approximately 75% of its time in the soft state making the lower banana and upper banana transitions combined with long-term low-high state transitions. We reveal that all of the X-ray spectra of 4U 1820-30 are fit by a composition of a thermal (blackbody) component, a Comptonization component (COMPTB) and a Gaussian-line component. Thus using this spectral analysis we find that the photon power-law index Gamma of the Comptonization component is almost unchangeable (Gamma approximately 2) while the electron temperature kTe changes from 2.9 to 21 keV during these spectral events. We also establish that for these spectral events the normalization of COMPTB component (which is proportional to mass accretion rate ˙M) increases by factor 8 when kTe decreases from 21 keV to 2.9 keV. Before this index stability effect was also found analyzing X-ray data for Z-source GX 340+0 and for atolls, 4U 1728-34, GX 3+1. Thus, we can suggest that this spectral stability property is a spectral signature of an accreting neutron star source. On the other hand in a black hole binary Γ monotonically increases with ˙Mand ultimately its value saturates at large ˙M.

evolution↗
NASA NTRS1988

X-rays from supernova 1987A

Detailed calculations of the development of the X-ray spectrum of 1987A are presented using more realistic models for the supernova composition and density structure provided by Woosley. It is shown how the emergence of the X-ray spectrum depends on the parameters of the model and the nature of its central energy source. It is shown that the soft X-ray spectrum should be dominated by a 6.4 keV Fe K(alpha) emission line that could be observed by a sensitive X-ray telescope.

Xu, Yueming↗
NASA NTRS2009

Thermal Performance Testing of Order Dependancy of Aerogels Multilayered Insulation

Robust multilayer insulation systems have long been a goal of many research projects. Such insulation systems must provide some degree of structural support and also mechanical integrity during loss of vacuum scenarios while continuing to provide insulative value to the vessel. Aerogel composite blankets can be the best insulation materials in ambient pressure environments; in high vacuum, the thermal performance of aerogel improves by about one order of magnitude. Standard multilayer insulation (MU) is typically 50% worse at ambient pressure and at soft vacuum, but as much as two or three orders of magnitude better at high vacuum. Different combinations of aerogel and multilayer insulation systems have been tested at Cryogenics Test Laboratory of NASA Kennedy Space Center. Analysis performed at Oak Ridge National Laboratory showed an importance to the relative location of the MU and aerogel blankets. Apparent thermal conductivity testing under cryogenic-vacuum conditions was performed to verify the analytical conclusion. Tests results are shown to be in agreement with the analysis which indicated that the best performance is obtained with aerogel layers located in the middle of the blanket insulation system.

Johnson, Wesley L.↗
NASA NTRS2015

Flexible Electrostatic Technologies for Capture and Handling, Phase 1

Fundamental to many of NASA's in-space transportation missions is the capture and handling of various objects and vehicles in various orbits for servicing, debris disposal, sample retrieval, and assembly without the benefit of sufficient grapple fixtures and docking ports. To perform similar material handling tasks on Earth, pincher grippers, suction grippers, or magnetic chucks are used, but are unable to reliably grip aluminum and composite spacecraft, insulation, radiators, solar arrays, or extra-terrestrial objects in the vacuum of outer space without dedicated handles in the right places. The electronic Flexible Electrostatic Technologies for space Capture and Handling (FETCH) will enable reliable and compliant gripping (soft dock) of practically any object in various orbits or surfaces without dedicated mechanical features, very low impact capture, and built-in proximity sensing without any conventional actuators. Originally developed to handle semiconductor and glass wafers during vacuum chamber processing without contamination, the normal rigid wafer handling chucks are replaced with thin metal foil segments laminated in flexible insulation driven by commercial off-the-shelf solid state, high-voltage power supplies. Preliminary testing in NASA Marshall Space Flight Center's (MSFC's) Flat Floor Robotics Lab demonstrated compliant alignment and gripping with a full-sized, 150-lb microsat mockup and translation before a clean release with a flip of a switch. The flexible electrostatic gripper pads can be adapted to various space applications with different sizes, shapes, and foil electrode layouts even with openings through the gripper pads for addition of guidance sensors or injection of permanent adhesives. With gripping forces estimated between 0.5 and 2.5 lb/in2 or 70-300 lb/ft2 of surface contact, the FETCH can turn on and off rapidly and repeatedly to enable sample handling, soft docking, in-space assembly, precision relocation, and surface translation for accurate anchoring.

Bryan, Thomas↗
NASA NTRS2020

A NICER View of Spectral and Profile Evolution for Three X-ray-Emitting Millisecond Pulsars

We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821−24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at >3σ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821−24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821−24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission.

Dominick M Rowan↗
NASA NTRS1990

The experimental evaluation and application of high-temperature solid lubricants

A research program is described which developes an understanding of high-temperature solid lubrication and experimental techniques through the development of a composite lubricant coating system. The knowledge gained through this research was then applied to a specific engineering challenge, the tribology of a sliding seal for hypersonic flight vehicles. The solid lubricant coating is a chromium carbide based composite combined with silver, which acts as a low temperature lubricant, and barium fluoride/calcium fluoride eutectic, which acts as a high-temperature lubricant. This composite coating provides good wear resistance and low friction for sliding contacts from room temperature to over 900 C in reducing or oxidative environments. The specific research on this coating included a composition screening using a foil gas bearing test rig and the use of thin silver films to reduce initial wear using a pin-on-disk test rig. The chemical stability of the materials used was also addressed. This research indicated that soft metallic films and materials which become soft at elevated temperatures are potentially good lubricants. The general results from the experiments with the model solid lubricant coating were then applied to a sliding seal design concept. This seal design requires that a braided ceramic fabric slide against a variety of metal counterface materials at temperatures from 25 to 850 C in an oxidative environment. A pin-on-disk tribometer was used to evaluate the tribological properties of these materials and to develop lubrication techniques. The results indicate that these seal materials must be lubricated to prevent wear and reduce friction. Thin films of silver, gold and calcium fluoride provided lubrication to the sliding materials.

Dellacorte, Christopher↗
NASA NTRS2014

Exploration of the Saturn System by the Cassini Mission: Observations with the Cassini Infrared Spectrometer

The Cassini mission is a joint NASA-ESA international mission, launched on October 17, 1997 with 12 instruments on board, for exploration of the Saturn system. A composite Infrared Spectrometers is one of the major instruments. Successful insertion of the spacecraft in Saturn's orbit for an extended orbital tour occurred on July 1, 2004. The French Huygens-Probe on board, with six instruments was programmed for a soft landing on Titan's surface occurred in January 2005. The broad range scientific objectives of the mission are: Exploration of the Saturn system for investigations of the origin, formation, & evolution of the solar system, with an extensive range of measurements and the analysis of the data for scientific interpretations. The focus of research dealing with the Cassini mission at NASA/MSFC in collaboration with the NASA/Goddard Space Flight Center, JPL, as well as the research teams at Oxford/UK and Meudon Observatory/France, involves the Infrared observations of Saturn and its satellites, for measurements of the thermal structure and global distributions of the atmospheric constituents. A brief description of the Cassini spacecraft, the instruments, the objectives, in particular with the infrared observations of the Saturn system will be given. The analytical techniques for infrared radiative transfer and spectral inversion programs, with some selected results for gas constituent distributions will be presented.

Abbas, Mian M.↗
NASA NTRS1981

Transversely accelerated ions in auroral arcs

Ionospheric ions apparently accelerated transversely to the geomagnetic field in the topside ionosphere are regularly detected by the soft particle spectrometers on the ISIS satellites. Such gyro-accelerated ions are observed in association with precipitating auroral electrons. A detailed study of their relationship with such electrons and with field-aligned currents, together with simultaneous measurements of the local plasma composition and density, reveals the specific conditions present in the topside ionosphere during the generation of such transversely accelerated ions (TAI). A proposed mechanism for generation of TAI involving acceleration by electrostatic ion cyclotron waves is consistent with the present observations.

Klumpar, D. M.↗
NASA NTRS1989

Effects of silicate-graphite dust in H II regions

Interstellar dust that is present in H II regions will most likely absorb H-ionizing photons more efficiently than He-ionizing photons. Assuming a silicate-graphite dust composition, the effects of such selective absorption on the ionization structure of H, He, O, and N are investigated with emphasis on a blister geometry. Scattering by the dust grains is included in the generalized on-the-spot approximation. For a relatively soft radiation field of effective temperature about 35,000 K, the radiation hardening may cause the He(+) zone to be nearly coextensive with the H(+) zone, and the O(++) volume is strongly increased relative to the N(++) volume. The smaller grains (radii about 0.005 micron) contribute most to the selective absorption. We show that because of a cancellation of effects a simple analytical formula for the fraction of ionizing photons absorbed by the dust given by Petrosian, Silk, and Field is quite accurate in the case of silicate-graphite dust, even for blister regions.

Aannestad, Per A.↗
NASA NTRS2003

Water Impact Test and Simulation of a Composite Energy Absorbing Fuselage Section

In March 2002, a 25-ft/s vertical drop test of a composite fuselage section was conducted onto water. The purpose of the test was to obtain experimental data characterizing the structural response of the fuselage section during water impact for comparison with two previous drop tests that were performed onto a rigid surface and soft soil. For the drop test, the fuselage section was configured with ten 100-lb. lead masses, five per side, that were attached to seat rails mounted to the floor. The fuselage section was raised to a height of 10-ft. and dropped vertically into a 15-ft. diameter pool filled to a depth of 3.5-ft. with water. Approximately 70 channels of data were collected during the drop test at a 10-kHz sampling rate. The test data were used to validate crash simulations of the water impact that were developed using the nonlinear, explicit transient dynamic codes, MSC.Dytran and LS-DYNA. The fuselage structure was modeled using shell and solid elements with a Lagrangian mesh, and the water was modeled with both Eulerian and Lagrangian techniques. The fluid-structure interactions were executed using the fast general coupling in MSC.Dytran and the Arbitrary Lagrange-Euler (ALE) coupling in LS-DYNA. Additionally, the smooth particle hydrodynamics (SPH) meshless Lagrangian technique was used in LS-DYNA to represent the fluid. The simulation results were correlated with the test data to validate the modeling approach. Additional simulation studies were performed to determine how changes in mesh density, mesh uniformity, fluid viscosity, and failure strain influence the test-analysis correlation.

Fasanella, Edwin L.↗
NASA NTRS2013

Compact Termination for Structural Soft-goods

Glass fiber is unique in its ability to withstand atomic oxygen and ultraviolet radiation in-space environments. However, glass fiber is also difficult to terminate by traditional methods without decreasing its strength significantly. Glass fiber products are especially sensitive to bend radius, and do not work very well with traditional 'sewn loop on pin' type connections. As with most composites, getting applied loads from a metallic structure into the webbing without stress concentrations is the key to a successful design. A potted end termination has been shown in some preliminary work to out-perform traditional termination methods. It was proposed to conduct a series of tensile tests on structural webbing or cord to determine the optimum potting geometry, and to then be able to estimate a weight and volume savings over traditional sewn-overa- pin connections. During the course of the investigation into potted end terminations for glass fiber webbing, a new and innovative connection was developed that has lower weight, reduced fabrication time, and superior thermal tolerance over the metallic end terminations that were to be optimized in the original proposal. This end termination essentially transitions the flexible glass fiber webbing into a rigid fiberglass termination, which can be bolted/fastened with traditional methods

Wilkes, Robert, Jr.↗
NASA NTRS1997

MS212--A Homogeneous Sputtered Solid Lubricant Coating for Use to 800 C

Composite coatings containing chromium carbide, stable fluorides and silver were prepared by magnetron sputtering. The microstructure of the coatings is very homogeneous compared to that of plasma sprayed and sintered versions of the same chemical composition. Friction and wear of MS212-coated and baseline uncoated aluminum and Inconel X-750 are compared. At room temperature, the friction and wear of coated aluminum is dramatically better compared to the baseline. The acceptable load is limited by deformation of the soft aluminum substrate. In the case of the nickel alloy, lower friction is observed for the coated alloy at all temperatures up to the maximum test temperature of 800 C. Pin wear factors for sliding against the coated alloy are lower than the baseline at room temperature and 350 C, and comparable to baseline wear at higher test temperatures. Low baseline wear at high temperatures is due to the lubricious nature of the natural oxides formed on nickel-chromium alloys in a hot, oxidizing atmosphere. No load limit was found for coated Inconel X-750 at loads up to five times the load limit for coated aluminum.

Sliney, Harold E.↗
NASA NTRS2002

Design and Test of an Improved Crashworthiness Small Composite Airframe

The purpose of this small business innovative research (SBIR) program was to evaluate the feasibility of developing small composite airplanes with improved crashworthiness. A combination of analysis and half scale component tests were used to develop an energy absorbing airframe. Four full scale crash tests were conducted at the NASA Impact Dynamics Research Facility, two on a hard surface and two onto soft soil, replicating earlier NASA tests of production general aviation airplanes. Several seat designs and restraint systems including both an air bag and load limiting shoulder harnesses were tested. Tests showed that occupant loads were within survivable limits with the improved structural design and the proper combination of seats and restraint systems. There was no loss of cabin volume during the events. The analysis method developed provided design guidance but time did not allow extending the analysis to soft soil impact. This project demonstrated that survivability improvements are possible with modest weight penalties. The design methods can be readily applied by airplane designers using the examples in this report.

Terry, James E.↗
NASA NTRS1999

Aeroelastic Stability for Straight and Swept-Tip Rotor Blades in Hover and Forward Flight

Two isolated, hingeless rotors with identical fiber-reinforced composite root flexures were tested in hover and forward flight at realistic tip speeds. The rotors differed in blade planform and structure. The first blade set was of rectangular planform. The second set had blades of stiffer construction with swept-tips. The purpose of these tests was to measure the isolated rotor aeroelastic stability of bending/torsion coupled rotor blades over a range of flight conditions. The two soft inplane rotor systems were designed with low first torsion frequency to emphasize the effects of torsion. Regressing lag mode damping is shown in hover with precone and collective pitch variations and in forward flight with airspeed, shaft angle, precone and collective pitch variations. Correlation with comprehensive analysis for a number of test conditions is shown. Agreement in hover is excellent and forward flight correlation is reasonably good.

REGRESSING LAG MODE DAMPING↗
NASA NTRS1985

Atomic nitrogen densities near the polar cusp

The neutral atmospheric composition spectrometer on board the Dynamics Explorer 2 spacecraft sampled several major and minor thermospheric gases including atomic nitrogen. A selection of passes over the polar cusp that provide a quantitative measure of N densities in this region and provide evidence of localized density increases due to soft particle precipitation is presented. Increases in N densities are frequently observed but are smaller than accompanying increases in N2 densities. The observations support earlier studies suggesting that (1) N densities increase more rapidly than O densities during periods of high solar EUV flux and (2) N densities are larger in the summer hemisphere than in the winter hemisphere. A series of passes in February 1983, late in the lifetime of DE 2, indicated N densities at 200 km altitude were a factor of 2 larger near the southern cusp than near the northern cusp.

Engebretson, M. J.↗
NASA NTRS1986

Atomic nitrogen densities near the polar cusp

The neutral atmospheric composition spectrometer on board the Dynamics Explorer 2 spacecraft sampled several major and minor thermospheric gases including atomic nitrogen. A selection of passes over the polar cusp that provide a quantitative measure of N densities in this region and provide evidence of localized density increases due to soft particle precipitation is presented. Increases in N densities are frequently observed but are smaller than accompanying increases in N2 densities. The observations support earlier studies suggesting that N densities increase more rapidly than O densities during periods of high solar EUV flux and N densities are larger in the summer hemisphere than in the winter hemisphere. A series of passes in February 1983, late in the lifetime of DE 2, indicated N densities at 200 km altitude were a factor of 2 larger near the southern cusp than near the northern cusp.

Engebretson, M. J.↗
NASA NTRS1986

X-ray-selected M dwarfs and the diffuse X-ray background

A systematic optical identification program was carried out for serendipitous X-ray sources discovered by the Einstein Observatory. A total of 104 were detected above the threshold flux of 3 x 10 to the -13th ergs/sq cm per sec in the 114 sq deg survey region; 11 of these 104 sources are dM stars. Including X-ray-selected M dwarfs from the LMC survey, the Medium Sensitivity Survey, and the Einstein Deep Survey, a dwarf M star composite X-ray spectrum was constructed; the best-fit thermal model yields kT = 1.3 + or - 0.3 keV, consistent with typical active star spectra. An M dwarf X-ray luminosity function was also constructed and it is concluded that the integrated contribution to the diffuse soft (0.28-1.0 keV) X-ray background from such stars is less than 10 percent, a factor of more than about 2 lower than previous estimates. This result is consistent with a limit on the dwarf M star contribution derived from a spectral decomposition of the observed X-ray background spectrum.

Caillault, J.-P.↗