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Results for “attainable yield”

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 109 records · Page 6

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NASA NTRS1995

Physics of magnetospheric emission in soft gamma-ray repeaters

Soft gamma-ray repeaters appear to be relatively young, strongly magnetized neutron stars embedded within plerions. The observationally inferred presence of teragauss fields and energetic outflows in these sources provides some support for a model in which the bursts results from crustal disturbances that load and energize the magnetosphere with the ensuing generation of sheared Alfven waves. We here determine accurately the structure of the particle efflux and calculate the spectrum of the resultant radiation, incorporating the key effects due to mildly relativistic magnetic bremsstrahlung, a frequency-dependent photospheric radius and angle-dependent boosting of the intensity for emitting elements at different inclinations. We find that the average photospheric radius during the transient event is approximately 4 stellar radii and that the particles attain a Lorentz factor approximately 13.2 by the time the gas becomes optically thin. The calculated spectrum is a weighted integral over the boosted intensity determined from the physical conditions (i.e., magnetic field, particle density, and temperature) at the photospheric radius corresponding to the relevant frequency. When applied to SGR 1806-20, this procedure yields a distance D approximately equals 10 kpc to this source, which appears to be consistent with the range (approximately 8-17 kpc) inferred from its apparent coincidence with the supernova remnant G10.0-0.3.

Melia, Fulvio↗

NASA NTRS1997

Interchange for Joint Research Entitled: Measurement of Stable Nitrogen and Sulfur Isotopes

Viking measurements of the Martian atmosphere indicate a value of N-15/N-14 which is markedly greater than that found in Earth's atmosphere. These isotopic measurements provide a powerful diagnostic tool which may be used to derive valuable information regarding the past history of Mars and they have been used to place important constraints on the evolution of Mars' atmosphere. Initial partial pressures of nitrogen, outgassing rates, and integrated deposition of nitrogen into minerals have been calculated from this important atmospheric data (McElroy et al., 1976 and 1977; Fox and Dalgarno, 1983). The greater precision obtained in laser spectrometer isotopic measurements compared to the Viking data will greatly improve these calculated values. It has also been proposed that the N-15/N-14 value in Mars' atmosphere has increased monotonically over time (McElroy et al., 1977; Fox and Dalgarno, 1983; Wallis, 1989) owing to preferential escape of atmospheric 14N to space. Nitrogen isotopic ratios might be used to identify relatively ancient crustal rocks (R. Mancinelli, personal communication), and perhaps determine relative aces of surface samples. As a first step in successfully measuring nitrogen isotopes optically we have demonstrated the measurement of 15NI14N to a precision of 0.1% (See Figures 1-4) using a tunable diode laser and an available gas (N-,O) with spectral lines in the 2188 cm-1 region. The sample and reference gas cells contained gases of identical isotopic composition so that the 15NI14N absorption ratio determined from the sample cell, when divided by the 15NI14N absorption ratio determined from the reference cell, should yield an ideal value of unity. The average measured value of this "ratio of ratios" was 0.9983 with a standard deviation (20 values) of 0.0010. This corresponds to a precision of 0.1% (1 per mil) for nitrogen isotopes, a value sufficiently precise to provide important isotopic data of interest to exobiologists. The precision presently attainable in gases is sufficient to permit the instrument to be used in the measurement of isotopic ratios of interest to exobiologists as well as geologists and planetary scientists.

Becker, Joseph F.↗

NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li3AlF6) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li3AlF6 as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

optical coatings↗

NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

optical coatings↗

NASA NTRS1977

Impurity concentrations and surface charge densities on the heavily doped face of a silicon solar cell

Increased solar cell efficiencies are attained by reduction of surface recombination and variation of impurity concentration profiles at the n(+) surface of silicon solar cells. Diagnostic techniques are employed to evaluate the effects of specific materials preparation methodologies on surface and near surface concentrations. It is demonstrated that the MOS C-V method, when combined with a bulk measurement technique, yields more complete concentration data than are obtainable by either method alone. Specifically, new solar cell MOS C-V measurements are combined with bulk concentrations obtained by a successive layer removal technique utilizing measurements of sheet resistivity and Hall coefficient.

Weinberg, I.↗

NASA NTRS1989

Solar probe mission status

The penetration of coronal regions by a solar probe employing planetary gravity-assist trajectories to attain perihelia of only a few solar radii will allow unique in situ experiments to be conducted. The trajectory design options will fundamentally impact solar probe spacecraft design criteria. The aerogravity-assist method, which requires the bending of a trajectory in the vicinity of a planet by passing through a portion of its atmosphere will yield large changes in direction and velocity. This option would in the case of a solar probe mission involve the use of either the earth or Venus as a target for a specially aerodynamically configured 'waverider' spacecraft with L/D of the order of 10.

Randolph, J. E.↗

NASA NTRS2004

Far-Infrared Space Interferometers: Future Windows on Star and Planet Formation

Far-IR space interferometers will provide observational access to a spectral region containing many important cooling and diagnostic spectral lines and the bulk of the thermal emission from dust at angular scales critical to advancing our understanding of the star and planet formation process. We will describe concepts for the Space Infrared Interferometric Telescope (SPIRIT) and the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). Both of these candidate NASA missions are imaging and spectral Michelson interferometers operating in the wavelength range -40 - 800 microns. SPIRIT, which could be launched in a decade as a NASA Origins Probe, is built on a deployable boom and has a maximum baseline length of -30 - 50 m, yielding sub-arcsecond resolution in the far-IR. SPIRIT will thus provide far-IR/sub-mm measurements complementary to the near- and mid-IR measurements obtainable with the James Webb Space Telescope (JWST), and well matched to JWST observations in angular resolution. Ultimately SPECS, a NASA Vision Mission, will use formation flying to attain baseline lengths up to 1 km, and thus angular resolution comparable to that of the Hubble Space Telescope and the Atacama Large Millimeter Array. We will report preliminary results of the NASA-sponsored SPIRIT and SPECS mission studies, which are now underway.

Leisawitz, David↗

NASA NTRS2017

Cassini Spacecraft Strategy for Recovering from a Complete Loss-Of-Signal Condition

Unlike other faults where the space craft’s automated Fault Protection (FP) routines can be relied upon to provide a carrier signal and telemetered data to the ground-based Spacecraft Operations Flight Support (SOFS) team to facilitate vehicle acquisition, diagnosis, and fault recovery, a complete Loss-of-Spacecraft-Signal (LOS) condition will yield no information at all to help re-acquire the vehicle and resolve the fault. For any FP response activation, the spacecraft’s downlink signal must be acquired via the Deep Space Network (DSN) on the expected (post-fault) Radio Frequency Subsystem (RFS) device configuration commanded by the FP; data that will not be attainable in the case of a complete LOS condition since there is no signal available for the ground station to lock onto. In the case of the Cassini Mission-to-Saturn spacecraft, numerous fault possibilities exist that can cause a LOS condition. Activations of the onboard RFS-related FP can reconfigure the post-fault RFS states, impeding the ground team’s ability to acquire the spacecraft’s downlink signal

Morgan, Paula S.↗

NASA NTRS1988

Topographical Mapping With Synthetic-Aperture Radar

Interferometric side-looking synthetic-aperture radar shows promise for high-resolution topographical mapping of terrain. Airplane carries two radar antennas. Radar signal transmitted by right antenna, reflected from ground received by both antennas. Amplitudes and phases of received signals recorded and processed separately to yield two 10-m-resolution amplitude-and-phase images of illuminated terrain. Two images mathematically combined point by point to obtain signal image containing interference fringes: phase at each location of image is difference between phases in two signals and amplitude at each location is project of amplitudes of two signals. Theoretically, technique has potential to attain a root-mean-square (rms) altitude error as small as 2 m.

Zebker, Howard A.↗

NASA NTRS2005

Variability of the ocean-induced magnetic field predicted at sea surface and at satellite altitudes

Spatial and temporal variability of the magnetic field component induced by ocean circulation is investigated on the basis of a standard thin-shell approximation of electro- and magneto-static equations. Well-known difficulties of numerical solution of the governing equations are resolved by reducing the problem to an equation for the electric field potential,(ef) as opposed to a more conventional approach focused on the vertical jump, (psi), of the magnetic field potential across a combined ocean/ marine-sediment-layer spherical shell. The present formulation permits using more realistic input data on ocean currents and ultimately yields much greater (by at least an order of magnitude) values of the magnetic field at sea surface than predicted in earlier studies. Such large values are comparable to, and in some cases exceed, magnetic field variations caused by lithospheric and ionospheric sources on monthly to interannual timescales. At the 400-km altitude (of CHAMP satellite), the field attains 6 nT. The model predictions show favorable comparisons with some in situ measurements as well as with Challenging Minisatellite Payload (CHAMP) satellite magnetometer data.

ocean induced magnetic field↗

NASA NTRS1985

Calculation of compressible flow about three-dimensional inlets with auxiliary inlets, slats and vanes by means of a panel method

An efficient and user oriented method was constructed for calculating flow in and about complex inlet configurations. Efficiency is attained by: (1) the use of a panel method; (2) a technique of superposition for obtaining solutions at any inlet operating condition; and (3) employment of an advanced matrix iteration technique for solving large full systems of equations, including the nonlinear equations for the Kutta condition. User concerns are addressed by the provision of several novel graphical output options that yield a more complete comprehension of the flowfield than was possible previously.

Hess, J. L.↗

NASA NTRS1985

Calculation of compressible flow about three-dimensional inlets with auxiliary inlets, slats and vanes by means of a panel method

An efficient and user-oriented method has been constructed for calculating flow in and about complex inlet configurations. Efficiency is attained by: the use of a panel method, a technique of superposition for obtaining solutions at any inlet operating condition, and employment of an advanced matrix-iteration technique for solving large full systems of equations, including the nonlinear equations for the Kutta condition. User concerns are addressed by the provision of several novel graphical output options that, taken together, yield a more complete comprehension of the flowfield than had been possible previously. Examples of these features are presented for some complicated configurations, and where possible, comparisons are made between calculation and experiment.

Hess, J. L.↗

NASA NTRS2019

An X-Ray Detection of Star Formation in A Highly Magnified Giant Arc

In the past decade, our understanding of how stars and galaxies formed during the first 5 billion years after the Big Bang has been revolutionized by observations that leverage gravitational lensing by intervening masses, which act as natural cosmic telescopes to magnify background sources. Previous studies have harnessed this effect to probe the distant Universe at ultraviolet, optical, infrared and millimetre wavelengths1,2,3,4,5,6. However, strong-lensing studies of young, star-forming galaxies have never extended into X-ray wavelengths, which uniquely trace high-energy phenomena. Here, we report an X-ray detection of star formation in a highly magnified, strongly lensed galaxy. This lensed galaxy, seen during the first third of the history of the Universe, is a low-mass, low-metallicity starburst with elevated X-ray emission, and is a likely analogue to the first generation of galaxies. Our measurements yield insight into the role that X-ray emission from stellar populations in the first generation of galaxies may play in reionizing the Universe. This observation paves the way for future strong-lensing-assisted X-ray studies of distant galaxies reaching orders of magnitude below the detection limits of current deep fields, and previews the depths that will be attainable with future X-ray observatories.

M B Bayliss↗

NASA NTRS2006

Intertwining Risk Insights and Design Decisions

The state of systems engineering is such that a form of early and continued use of risk assessments is conducted (as evidenced by NASA's adoption and use of the 'Continuous Risk Management' paradigm developed by SEI). ... However, these practices fall short of theideal: (1) Integration between risk assessment techniques and other systems engineering tools is weak. (2) Risk assessment techniques and the insights they yield are only informally coupled to design decisions. (3) Individual riskassessment techniques lack the mix of breadth, fidelity and agility required to span the gamut of the design space. In this paper we present an approach that addresses these shortcomings. The hallmark of our approach is a simple representation comprising objectives (what the system is to do), risks (whose occurrence would detract from attainment of objectives) and activities (a.k.a. 'mitigations') that, if performed, will decrease those risks. These are linked to indicate by how much a risk would detract from attainment of an objective, and by how much an activity would reduce a risk. The simplicity of our representational framework gives it the breadth to encompass the gamut of the design space concerns, the agility to be utilized in even the earliest phases of designs, and the capability to connect to system engineering models and higher-fidelity risk tools. It is through this integration that we address the shortcomings listed above, and so achieve the intertwining between risk insights and design decisions needed to guide systems engineering towards superior final designs while avoiding costly rework to achieve them. The paper will use an example, constructed to be representative of space mission design, to illustrate our approach.

systems engineering↗

NASA NTRS1982

Low NO subx heavy fuel combustor concept program. Phase 1A: Coal gas addendum

The performance and emissions from a rich-lean combustor fired on simulated coal gas fuels were investigated using a 12.7-cm diameter axially-staged burner originally designed for operation with high heating value liquid fuels. A simple, tubular fuel injector was substituted for the liquid fuel nozzle; no other combustor modifications were made. Four test fuels were studied including three chemically bound nitrogen-free gas mixtures with higher heating values of 88, 227, and 308 kj/mol (103, 258 and 349 Btu/scf), and a 227 kj/mol (258 Btu/scf) heating value doped with ammonia to produce a fuel nitrogen content of 0.5% (wt). Stable, ultra-low nitrogen oxide, smoke-free combustion was attained for the nitrogen-free fuels. Results with the doped fuel indicated that less than 5% conversion of NH3 to nitrogen oxide levels below Environmental Protection Agency limits could be achieved. In some instances, excessive CO levels were encountered. It is shown that use of a burner design employing a less fuel-rich primary zone than that found optimum for liquid fuels would yield more acceptable CO emissions.

Rosfjord, T.↗

NASA NTRS1988

Mechanical design engineering. NASA/university advanced design program: Lunar Bulk Material Transport Vehicle

The design of a Lunar Bulk Material Transport Vehicle (LBMTV) is discussed. Goals set in the project include a payload of 50 cubic feet of lunar soil with a lunar of approximately 800 moon-pounds, a speed of 15 mph, and the ability to handle a grade of 20 percent. Thermal control, an articulated steering mechanism, a dump mechanism, a self-righting mechanism, viable power sources, and a probable control panel are analyzed. The thermal control system involves the use of small strip heaters to heat the housing of electronic equipment in the absence of sufficient solar radiation and multi-layer insulation during periods of intense solar radiation. The entire system uses only 10 W and weighs about 60 pounds, or 10 moon-pounds. The steering mechanism is an articulated steering joint at the center of the vehicle. It utilizes two actuators and yields a turning radius of 10.3 feet. The dump mechanism rotates the bulk material container through an angle of 100 degree using one actuator. The self-righting mechanism consists of two four bar linkages, each of which is powered by the same size actuator as the other linkages. The LBMTV is powered by rechargeable batteries. A running time of at least two hours is attained under a worst case analysis. The weight of the batteries is 100 pounds. A control panel consisting of feedback and control instruments is described. The panel includes all critical information necessary to control the vehicle remotely. The LBMTV is capable of handling many types of cargo. It is able to interface with many types of removable bulk material containers. These containers are made to interface with the three-legged walker, SKITTER. The overall vehicle is about 15 feet in length and has a weight of about 1000 pounds, or 170 lunar pounds.

Daugherty, Paul↗

NASA NTRS2013

The Effectiveness of Magnetic Shielding in High-Isp Hall Thrusters

A series of numerical simulations and experiments have been performed to assess the effectiveness of magnetic shielding in a Hall thruster operating in the discharge voltage range of 300-700 V (Isp 2000-2700 s) at 6 kW, and 800 V (Isp 3000) at 9 kW. In this paper we report on the simulation results and their validation with experimental measurements. At 6 kW the magnetic field topology with which we recently demonstrated highly effective magnetic shielding at 300 V was retained for all other discharge voltages; only the magnitude of the field was changed to achieve optimum thruster performance. It is found that magnetic shielding remains highly effective for all discharge voltages studied. Maximum erosion rates that remain fairly constant across the range of 300-700 V are computed, with values not exceeding 10-2 mm/kh. Such rates are ~3 orders of magnitude less than those observed in the unshielded version of the same thruster at 300 V. At 9 kW and 800 V, saturation of the magnetic circuit did not permit us to attain precisely the same magnetic shielding topology as that employed during the 6-kW operation since this thruster was not designed to operate at this condition. Consequently, the maximum erosion rate at the inner wall is found to be ~1 order of magnitude higher (~10-1 mm/kh) than that at the 6-kW level. At the outer wall the ion energy is below the sputtering yield threshold so no measurable erosion is expected. The reasons behind the effectiveness of magnetic shielding at higher discharge voltages are discussed.

magnetic-field-aligned-mesh (MFAM) code↗

NASA NTRS1986

Laser and sunlight-induced fluorescence from chlorophyll pigments

Fluorescence properties of chlorophyll pigment bearing plant foliage utilizing a 337 nm nitrogen laser and integrating sphere were studied. Measured yields, in terms of number of photons emitted per 100 photons absorbed, range from 1.5 to 0.1 for the 685 nm peak, and from 4.2 to 0.2 for the 730 nm peak. Decreasing order of magnitude puts herbaceous leaves ahead of all others followed by broad leaves of hardwoods and coniferous needles. Meaningful quantization for the fluorescence peaks at 430 and 530 nm could not be attained. Passive monitoring of these fluorescence peaks is successful only for the 685 nm from the ocean surface. Field data show the reflectance changes at 685 nm due to the algae presence amounts to 1% at most.

Kim, H. H.↗