Special Pyrheliometer Shroud Development

To insure that the insolation values accurately represent the input power to a power conversion unit the field of view (FOV) of the concentrator aperture and the insolation radiometer must be the same. The calculations, implementation, and results of this approach are covered. Three instruments were used to measure the insolation: an Eppley Normal Incidence Radiometer (NIP) and two versions of the kendall cavity radiometer. The shrouds used to limit the FOV of the radiometers were designed to simulate the FOV of the PDC-1 concentrater with the cold water cavity calorimeter. This technique of matching the FOV of an insolation radiometer to the FOV of a specific concentrater and receiver aperture appears to be both practical and effective. The efficiency of a power conversion unit will be too low if the insolation is measured with a radiometer which has a FOV which is larger than the FOV of the concentrator

Memory systems for signal generating photoelectric image detectors

Digital systems are discussed which have the capacity to handle the large amounts of information contained in a typical image. It was used with a high gain pulse counting television camera tube, with a silicon target image detector and an analog to digital converter between the detector and the memory

Parabolic Dish Concentrator (PDC-1)

The design, construction, and installation of the Parabolic Dish Concentrator, Type 1 (PDC-1) has been one of the most significant JPL concentrator projects because of the knowledge gained about this type of concentrator and the development of design, testing, and analysis procedures which are applicable to all solar concentrator projects. The need for these procedures was more clearly understood during the testing period which started with the prototype panel evaluation and ended with the performance characterization of the completed concentrator. For each phase of the test program, practical test procedures were required and these procedures defined the mathematical analysis which was essential for successful concentrator development. The concentrator performance appears to be limited only by the distortions resulting from thermal gradients through the reflecting panels. Simple optical testing can be extremely effective, but comprehensive mechanical and optical analysis is essential for cost effective solar concentrator development

View-limiting shrouds for insolation radiometers

Insolation radiometers (normal incidence pyrheliometers) are used to measure the solar radiation incident on solar concentrators for calibrating thermal power generation measurements. The measured insolation value is dependent on the atmospheric transparency, solar elevation angle, circumsolar radiation, and radiometer field of view. The radiant energy entering the thermal receiver is dependent on the same factors. The insolation value and the receiver input will be proportional if the concentrator and the radiometer have similar fields of view. This report describes one practical method for matching the field of view of a radiometer to that of a solar concentrator. The concentrator field of view can be calculated by optical ray tracing methods and the field of view of a radiometer with a simple shroud can be calculated by using geometric equations. The parameters for the shroud can be adjusted to provide an acceptable match between the respective fields of view. Concentrator fields of view have been calculated for a family of paraboloidal concentrators and receiver apertures. The corresponding shroud parameters have also been determined

The Potential Constants of Ethane

The infrared and Raman data of light and heavy ethane (C2H6 and C2D6) have been reexamined for the purpose of determining as accurately as possible the potential constants of the ethane molecule. In order to fill in some of the gaps in the spectroscopic data, additional high resolution measurements have been made on the infrared spectrum of heavy ethane which have given more precise values for the active fundamental frequencies and zeta‐values. Resolution of the fine structure associated with the parallel band ν5* has given the value of the large moment of inertia of C2D6, thus completing the information required for the spectroscopic determination of the dimensions of ethane. The data yield, C☒C distance=1.543A, C☒H distance=1.102A, H☒C☒C angle=109°37′, and H☒C☒H angle=109°19′. The twenty‐two distinct potential constants compatible with the D3d symmetry of ethane have been determined through their relationships to the normal frequencies and zeta‐values of C2H6 and C2D6. The normal frequencies have been obtained by addition of anharmonic corrections to the spectroscopically observed fundamental frequencies. These corrections were estimated by means of the known anharmonic corrections for methane and the conditions imposed by the Teller product rule. The fundamental frequencies and zeta‐values have been taken directly from the observed band centers and rotational spacings wherever possible. In the cases of resonance, the influence of the couplings were either calculated or estimated and the corresponding unperturbed values for the frequencies and zeta‐values selected. The potential function is determined first in terms of a set of simple symmetry coordinates, and then reexpressed in terms of valence coordinates to permit comparison of the valence force constants of ethane and methane.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70194/2/JCPSA6-20-2-313-1.pd

Evolution of secondary electron emission characteristics of spacecraft surfaces: Importance to spacecraft charging

Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition—e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces can and generally do undergo significant evolution during their operational lifetimes is a fact well established by NASA\u27s Long Duration Exposure Facility (LDEF) [Crutcher, et al., 1991a]. Deposition and removal of contaminants can occur as a result of preferential adsorption of gases on cooler surfaces, the collection of ionized gases on negatively charged surfaces, atomic-oxygen-induced oxidation, photodissociation under vacuum uv bombardment, and ion-induced desorption. Since SEE is material-dependent phenomenon, it is reasonable to assume that as a spacecraft\u27s surfaces evolve, so too do it\u27s SEE characteristics. In order to determine whether or not charging models need incorporate the effects of changing surface conditions aboard operating spacecraft, data assessing the impact of these changes on the SEE characteristics of various surfaces are required. Measurements have therefore been made investigating the dynamic evolution of secondary electron (SE) yields resulting from energetic electron bombardment of typical spacecraft materials in a rarefied atmosphere representative of the microenvironment surrounding space vehicles. A detailed report of the experiment and results has been given elsewhere [Davies, 1996; Davies and Dennison, 1997]; what follows here is a brief summary

JPL tests of a LaJet concentrator facet

A LaJet Energy Company (LEC) concentrator facet, 60 in. in diameter, was tested for imaging quality. The following two methods were used: (1) autofocus tests with a point source of light at the facet's radius of curvature; and (2) tests with the Sun close to the horizon as a distant source. The tests of the LaJet facet indicate that all of the solar image reflected by an LEC 460 solar concentrator made of like facets should fall within a 9-in. aperture if the outer facets are carefully adjusted. Such a concentrator would have acceptable performance, but complete evaluation must be made with an assembled concentrator

Extended BEG Model of Monhalogenated Methanes Physisorbed on Ionic Crystals

The 2D dielectric phases and phase transitions of adsorbed dipolar molecules are modeled using a dilute spin-one Ising model. This model is studied in the Blume–Emery–Griffiths formalism, using a mean-field approximation, where the interaction parameters are uniquely determined from the system interaction energies using an averaging procedure. The model is applied to four monhalogenated methane species physisorbed on MgO(1 0 0) and NaCl(1 0 0) surfaces using previous experimental and theoretical studies to estimate the interaction energy parameters. We find that temperature- and coverage-dependent antiferroelectric to ferroelectric, coverage-dependent ferroelectric up to ferroelectric down, reentrant ferroelectric to ferrielectric, and order-disorder dipole phase transitions can occur. Phase diagrams based on this model are presented