11,724 research outputs found
Nuclear Electric Propulsion Technology Panel findings and recommendations
Summarized are the findings and recommendations of a triagency (NASA/DOE/DOD) panel on Nuclear Electric Propulsion (NEP) Technology. NEP has been identified as a candidate nuclear propulsion technology for exploration of the Moon and Mars as part of the Space Exploration Initiative (SEI). The findings are stated in areas of system and subsystem considerations, technology readiness, and ground test facilities. Recommendations made by the panel are summarized concerning: (1) existing space nuclear power and propulsion programs, and (2) the proposed multiagency NEP technology development program
Blazing the trailway: Nuclear electric propulsion and its technology program plans
An overview is given of the plans for a program in nuclear electric propulsion (NEP) technology for space applications being considered by NASA, DOE, and DOD. Possible missions using NEP are examined, and NEP technology plans are addressed regarding concept development, systems engineering, nuclear fuels, power conversion, thermal management, power management and distribution, electric thrusters, facilities, and issues related to safety and environment. The programmatic characteristics are considered
Evidence for self-interaction of charge distribution in charge-coupled devices
Charge-coupled devices (CCDs) are widely used in astronomy to carry out a
variety of measurements, such as for flux or shape of astrophysical objects.
The data reduction procedures almost always assume that ther esponse of a given
pixel to illumination is independent of the content of the neighboring pixels.
We show evidence that this simple picture is not exact for several CCD sensors.
Namely, we provide evidence that localized distributions of charges (resulting
from star illumination or laboratory luminous spots) tend to broaden linearly
with increasing brightness by up to a few percent over the whole dynamic range.
We propose a physical explanation for this "brighter-fatter" effect, which
implies that flatfields do not exactly follow Poisson statistics: the variance
of flatfields grows less rapidly than their average, and neighboring pixels
show covariances, which increase similarly to the square of the flatfield
average. These covariances decay rapidly with pixel separation. We observe the
expected departure from Poisson statistics of flatfields on CCD devices and
show that the observed effects are compatible with Coulomb forces induced by
stored charges that deflect forthcoming charges. We extract the strength of the
deflections from the correlations of flatfield images and derive the evolution
of star shapes with increasing flux. We show for three types of sensors that
within statistical uncertainties,our proposed method properly bridges
statistical properties of flatfields and the brighter-fatter effect
Finite element analysis of thermal distortion effects on optical performance of solar dynamic concentrator for Space Station Freedom
An analysis was performed to predict the thermal distortion of the solar dynamic concentrator for Space Station Freedom in low earth orbit and to evaluate the effects of that thermal distortion on concentrator on-orbit performance. The analysis required substructural finite element modeling of critical concentrator structural subsystems, structural finite element modeling of the concentrator, mapping of thermal loading onto the structural finite element model, and the creation of specialized postprocessors to assist in interpreting results. Concentrator temperature distributions and thermally induced displacements and slope errors and the resulting receiver flux distribution profiles are discussed. Results determined for a typical orbit indicate that concentrator facet rotations are less than 0.2 mrad and that the change in facet radius due to thermal flattening is less than 5 percent. The predicted power loss due to thermal distortion effects is less than 0.3 percent. As a consequence the thermal distortions of the solar dynamic concentrator in low earth orbit will have a negligible effect on the flux distribution profiles within the receiver
Summary and recommendations on nuclear electric propulsion technology for the space exploration initiative
A project in Nuclear Electric Propulsion (NEP) technology is being established to develop the NEP technologies needed for advanced propulsion systems. A paced approach has been suggested which calls for progressive development of NEP component and subsystem level technologies. This approach will lead to major facility testing to achieve TRL-5 for megawatt NEP for SEI mission applications. This approach is designed to validate NEP power and propulsion technologies from kilowatt class to megawatt class ratings. Such a paced approach would have the benefit of achieving the development, testing, and flight of NEP systems in an evolutionary manner. This approach may also have the additional benefit of synergistic application with SEI extraterrestrial surface nuclear power applications
Enhanced drag in pipe turbulent flow by an aqueous electrolyte: an electroviscous effect
Drag enhancement is reported for turbulent pipe flow of aqueous electrolyte solutions. No electroviscous effect was obtained with laminar flow. Nor was any unusual pressure drop observed for laminar or turbulent flow of non-electrolyte aqueous solutions such as sugar. An electroviscous theory was advanced that predicted the drag enhancement for a 1/1 electrolyte solution. The theory depended on consideration of Debye length
Applying matrix product operators to model systems with long-range interactions
An algorithm is presented which computes a translationally invariant matrix
product state approximation of the ground state of an infinite 1D system; it
does this by embedding sites into an approximation of the infinite
``environment'' of the chain, allowing the sites to relax, and then merging
them with the environment in order to refine the approximation. By making use
of matrix product operators, our approach is able to directly model any
long-range interaction that can be systematically approximated by a series of
decaying exponentials. We apply our techniques to compute the ground state of
the Haldane-Shastry model and present results.Comment: 7 pages, 3 figures; manuscript has been expanded and restructured in
order to improve presentation of the algorith
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