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Small modular alkali metal thermoelectric generator with no moving parts directly converts heat to electrical energy with efficiency of 20 to 40 percent. Unit uses closed regenerative electrochemical concentration cell based on sodium-ion conductor beta alumina.
A detailed observational treatment of bidirectional electrons (about 50 to 500 eV) in the distant magnetotail (r not below 100 earth radii) is presented. It is found that electrons in this energy range commonly exhibit strong, field-aligned anisotropies in the tail lobes. Because of large tail motions, the ISEE 3 data provide extensive sampling of both the north and south lobes in rapid succession. These data directly demonstrate the strong asymmetries that exist between the north and south lobes at any one time. The bidirectional fluxes are found to occur predominantly in the lobe directly connected to the sunward interplanetary magnetic field in the open magnetosphere model (north lobe for away sectors and south lobe for toward sectors). Electron anisotropy and magnetic field data are presented which show the transition from unidirectional (sheath) electron populations to bidirectional (lobe) populations. The open nature of the distant magnetopause is demonstrated and it is shown that the source of the higher-energy, bidirectional lobe electrons is the tailward directed electron heat flux population in the distant magnetosheath. Taken together, the present evidence suggests that the bidirectional electrons that were observed in the distant tail are closely related to the polar rain electrons observed previously at lower altitudes. Furthermore, these data provide strong evidence that the distant tail is composed largely of open magnetic field lines in contradistinction to some recently advanced models.
Simulations of the electron acoustic instability for a finite-size electron beam system are performed with a particle-in-cell code to investigate the heating phenomena associated with the instability and the width of the heating region. The results show that the beam radiates electrostatic electron acoustic waves whose decay time outside the beam agrees with the spatial decay length derived from the linear dispersion equation. The ambient cold electrons in a diffusion region surrounding the beam are heated to a higher temperature by absorbing the radiated electron acoustic waves, with the heating occurring mainly in the parallel direction. In the heat diffusion region, the temperature of the cold electrons decreases with distance from the beam with a temperature gradient length smaller than the decay length of the wave energy. The results are discussed with respect to the DE 1 plasma and wave observations in the polar cusp region.
A few hours prior to the crossing of the Comet Halley bow shock, the Giotto spacecraft intermittently encountered an electron foreshock region. The electron foreshock is characterized by magnetic connection to the cometary bow shock and increased field aligned electron heat flux directed away from the bow shock. A similar region was intermittently encountered by the ICE spacecraft prior to its crossing of the Giacobini-Zinner bow wave. During periods of magnetic connection with the Halley bow shock, enhanced magnetic field fluctuations were observed. These enhancements are interpreted as indirect evidence of an ion foreshock in the electron foreshock. No clearly identifiable backstreaming protons are observed during these periods of magnetic connection, however, because it may be difficult to separate a backstreaming population from the cometary pick-up proton population already present in the upstream region.
A simplified system model is under development for evaluating the thermal characteristics and thermal performance of a solar dynamic spacecraft energy system's heat receiver. Results based on baseline orbit, power system configuration, and operational conditions, are generated for three basic receiver concepts and three concentrator surface slope errors. Receiver thermal characteristics and thermal behavior in LEO conditions are presented. The configuration in which heat is directly transferred to the working fluid is noted to generate the best system and thermal characteristics. as well as the lowest performance degradation with increasing slope error.
An aerothermal study was performed in the Langley 8-Foot High Temperature Tunnel at Mach number 6.6 to define the pressures and heating rates on the surfaces between split elevons similar to those used on the Space Shuttle. Tests were performed with both laminar and turbulent boundary layers on the wing surface upstream of the elevons. The flow in the chordwise gap between the elevons was characterized by flow separation at the gap entrance and flow reattachment at a depth into the gap inversely proportional to the gap width. The gap pressure and heating rate increased significantly with decrease of elevon gap width, and the maximum gap heating rate was proportional to the maximum gap pressure. Correlation of the present results indicate that the gap heating was directly proportional to the elevon windward surface pressure and was not dependent upon whether the boundary layer on the windward elevon surface was laminar or turbulent.
A continuous process for producing prepreg from carbon fiber and thermoplastic matrix is described. After the tow has been spread using a pneumatic device, the process utilizes a fluidized bed to apply thermoplastic powder to the bundle. Finally, direct electrical heating of the coated fiber tow melts the polymer on the individual fibers, creating a uniform and extremely flexible prepreg. The efficiency of the process was evaluated during initial trials in which a thermoplastic polyimide, LaRC-TPI, was applied to T-300, 3K (3000 filament) carbon fiber tow. The physical properties of unidirectional composite specimens fabricated from this prepreg were measured, and the matrix uniformity and void content of the samples was determined. The results of these evaluations are detailed and discussed.
One of the objectives of CaPE is to better understand the convective process in central and south Florida during the warm season. The energy and moisture exchanges between the surface and the atmosphere are closely related to this process. Some recent studies have shown that the surface energy balance plays an important role in the climatic fields (Shukla and Mintz, 1982; Sud and Smith, 1985; Sato et. al, 1989). Surface energy fluxes and related surface processes such as evapotranspiration and sensible heat transfer directly effect the temperature, humidity, cloud formation and precipitation. For example, mesoscale circulation around a discontinuity in vegetation type were shown to be stronger with wet soil than with dry soil using an evapotranspiration model (Pinty et. al, 1989). In order to better describe the processes in the atmosphere at various scales and improve our ability of modeling and predicting weather related events, it is crucial to understand the mechanism of surface energy transfer in relation to atmospheric events. Surface energy flux measurements are required to fully understand the interactions between the atmosphere and the surface.
An innovative pumped loop concept for 600 K space power system radiators is under development utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup. The melting/freezing process of Li in a NaK flow was studied experimentally to demonstrate the Li/NaK radiator feasibility during startup (thawing) and shutdown (cold-trapping). Results of the vapor grown carbon fiber/composite thermal conductivity measurements are also presented.
This paper describes the design and test of a heat exchanger that transfers heat from one two-phase thermal loop to another with very small drops in temperature and pressure. The heat exchanger condenses the vapor in one loop while evaporating the liquid in the other without mixing of the condensing and evaporating fluids. The heat exchanger is bidirectional in that it can transfer heat in reverse, condensing on the normally evaporating side and vice versa. It is fully compatible with capillary pumped loops and mechanically pumped loops. Test results verified that performance of the heat exchanger met the design requirements. It demonstrated a heat transfer rate of 6800 watts in the normal mode of operation and 1000 watts in the reverse mode with temperature drops of less than 5 C between two thermal loops.
The possibility that condensed volatiles might be stable in the permanently shadowed polar regions of the Moon and Mercury has been anticipated in a number of theoretical studies. In 1992, VLA-Goldstone and Arecibo observations revealed the presence of bright, depolarized radar features near the poles of Mercury that have been widely interpreted as evidence for the presence of polar ice deposits. Recently acquired high-resolution Arecibo radar images show that the anomalous radar features are concentrated in crater-sized regions whose locations can be made to coincide exactly with the locations of known impact craters in the Mariner-10 images. These new Arecibo images provide an unusual opportunity to learn more about the distribution and history of Mercury's polar ice deposits. We have constructed a thermal model that can predict surface and subsurface temperatures within impact craters on Mercury and the Moon. Included in the calculations are the effects of 1-dimensional subsurface heat conduction, direct sunlight, multiply reflected sunlight within the crater, and re-radiated infrared radiation within the crater. We also use realistic crater topographic profiles for larger flat-floored craters as well as smaller spherical bowl-shaped craters.
The outflow of coronal plasma into interplanetary space is a consequence of the coronal heating process. Therefore the formation of the corona and the acceleration of the solar wind should be treated as a single problem. Traditionally the mass or particle flux emanating from the extended corona has been thought of as being determined by the coronal temperature or scale height and the coronal (base) density. This argument follows from considerations of the momentum balance of the corona-wind system from which one obtains models of a close to hydrostatic corona out to the critical point where the flow becomes supersonic. With this approach to the acceleration of the wind is has been difficult to reconcile the relatively small variation observed in the proton flux at 1 AU with the predicted exponential dependence of the proton flux on the coronal temperature. In this talk we would like to emphasize another approach in which coronal energetics play the primary role. The deposition of energy into the corona through some 'mechanical' energy flux is balanced by the various energy sinks available to the corona and the sum of these processes determine the coronal structure, i.e. its temperature and density. The corona loses energy through heat conduction into the transition region, through radiative losses, and through the gravitational potential energy and kinetic energy put into the solar wind itself. We will show from a series of models of the chromosphere transition region-corona-solar wind system that most of the energy deposited in a magnetically open region will go into the solar wind, with roughly half going into kinetic energy and half into lifting the plasma out of the solar gravity field. The coronal base density will adjust itself in such a way that the heat conductive flux flowing into the transition region is radiated away in the upper chromosphere. The coronal temperature is set by the requirements that most of the deposited energy goes into accelerating the solar wind; the coronal scale height will adjust itself so that the solar wind energy losses conform to the amplitude of the input energy. These processes are modified by the 'mode' of energy deposition, and we will show the effects on coronal structure of changing the parameters describing coronal heating as well as the effects of including a helium fluid in the models. However, the location, scale height and/or form of the energy deposition (i.e. heating or direct acceleration) are not too important for the solar wind, the coronal density and temperature structure will vary with the 'mode' of energy deposition, but the solar wind mass flux depends mainly on the amplitude of the energy flux.
Sunlike stars are born with disks. Based on our recently developed model to understand how a magnetized new star interacts with its surrounding accretion disk, we advanced an astrophysical theory for the early solar system. The aerodynamic drag of a magnetocentrifugally driven wind out of the inner edge of a shaded disk could expose solid bodies lifted into the heat of direct sunlight, when material is still accreting onto the protosun. Chondrules, calcium-aluminum-rich inclusions (CAI's), and rims could form along the flight for typical self-consistent parameters of the outflow in different stages of star formation. The process gives a natural sorting mechanism that explains the size distribution of CAI's and chondrules, as well as their associated rims. Chondritic bodies then subsequently form by compaction of the processed solids with the ambient nebular dust comprising the matrices after their reentry at great distances from the original launch radius.
We investigate the optical properties of new "selective emitter" materials for possible use in high-efficiency thermophotovoltaic power systems. These are systems which directly convert heat to radiation at a wavelength closely matched to the bandgap energy of the solar cell. Candidate materials which have strong absorption lines fairly close to the bandgap of good solar-cell materials were chosen for study. Their emittance was measured as a function of wavelength to evaluate their promise as selective TPV emitters. Useful and informative results were obtained. Some of these results were presented at a January 1996 solar energy conference of the American Institute of Aeronautics and Astronautics.
The scientific goal of UVCS is to obtain detailed empirical descriptions of the extended solar corona as it evolves from a period of minimum activity to maximum and to use these descriptions to identify and understand the physical processes responsible for coronal heating, solar wind acceleration, coronal mass ejections (CME's), and the phenomena that establish the plasma properties of the solar wind as measured by the CELIAS/SOHO experiment. We must observe a wide range of conditions (e.g., heating rate, impulsive mass ejections, magnetic field opening) in order to choose among competing theoretical explanations of the observed coronal structures and dynamics. During the first year of scientific observations (1 April 1996 through 31 March 1997), the LTVCS made the first extensive ultraviolet spectroscopic observations above the base of the solar corona. Those observations revealed extremely high most probable speeds along the line of sight for O(5+) in polar coronal holes above 2 solar radii from sun center and smaller such speeds for H(0) and protons. Doppler dimming and pumping diagnostics indicated that O(5+) and H(0) I reached supersonic outflow velocities within 2 solar radii. The observations appeared to be consistent with O95+) heating and direct momentum transfer by high frequency MHD waves through ion cyclotron resonance. Equatorial streamers were found to appear much different when observed in O VI, Fe XII and Mg X than when observed in H I Lyman-alpha or visible light. This led G. Noci to suggest that the elemental abundance of O, Fe, and Mg are lower in the dark center region of the O VI streamer image than it is in the brighter outer legs of the streamer. The O VI line ratio indicated a much smaller outflow speed in streamers than in the surrounding coronal holes. Spectroscopic observations of CME's in June and December 1996 showed large Doppler shifts indicating macroscopic flows of up to 200 km/s transverse to the apparent motion of the CME. The December event displayed factor of 500 intensity increases in H I Lyman lines and bright emissions in cool ion lines like C III 977 A indicating that the origin of some of the gas was a prominence. UVCS also observed two comets, several stars and interplanetary hydrogen. In the current reporting period, the initial results were published and detailed analyses including self consistent empirical models were developed. The research results were reported, published or submitted/accepted for publication. New observations were made to uncover additional information about the surprising results of the first year and other new observations revealed more surprises. A UVCS Tutorial was developed to familiarize potential users of UVCS data with the data products, analysis techniques and coronal models needed to analyze the data.
The development of energy efficient, lightweight sorption systems for removal of environmental contaminants in space flight applications is an area of continuing interest to NASA. The current CO2 removal system on the International Space Station employs two pellet bed canisters of 5A molecular sieve that alternate between regeneration and sorption. A separate disposable charcoal bed removes trace contaminants. An alternative technology has been demonstrated using a sorption bed consisting of metal meshes coated with a sorbent, trademarked and patented as Microlith by Precision Combustion, Inc. (PCI); thesemeshes have the potential for direct electrical heating for this application. This allows the bed to be regenerable via resistive heating and offers the potential for shorter regeneration times, reduced power requirement, and net energy savings vs. conventional systems. The capability of removing both CO2 and trace contaminants within the same bed has also been demonstrated. Thus, the need for a separate trace contaminant unit is eliminated resulting in an opportunity for significant weight savings. Unlike the charcoal bed, zeolites for trace contaminant removal are amenable to periodic regeneration. This paper describes the design and performance of a prototype sorber device for simultaneous CO2 and trace contarninant removal and its attendant weight and energy savings.
The heating units shown in the accompanying photos are Panelbloc infrared heaters, energy savers which burn little fuel in relation to their effective heat output. Produced by Bettcher Manufacturing Corporation, Cleveland, Ohio, Panelblocs are applicable to industrial or other facilities which have ceilings more than 12 feet high, such as those pictured: at left the Bare Hills Tennis Club, Baltimore, Maryland and at right, CVA Lincoln- Mercury, Gaithersburg, Maryland. The heaters are mounted high above the floor and they radiate infrared energy downward. Panelblocs do not waste energy by warming the surrounding air. Instead, they beam invisible heat rays directly to objects which absorb the radiation- people, floors, machinery and other plant equipment. All these objects in turn re-radiate the energy to the air. A key element in the Panelbloc design is a coating applied to the aluminized steel outer surface of the heater. This coating must be corrosion resistant at high temperatures and it must have high "emissivity"-the ability of a surface to emit radiant energy. The Bettcher company formerly used a porcelain coating, but it caused a production problem. Bettcher did not have the capability to apply the material in its own plant, so the heaters had to be shipped out of state for porcelainizing, which entailed extra cost. Bettcher sought a coating which could meet the specifications yet be applied in its own facilities. The company asked The Knowledge Availability Systems Center, Pittsburgh, Pennsylvania, a NASA Industrial Applications Center (IAC), for a search of NASA's files
Due to its high specific impulse and favorable thermal properties for storage, liquid methane (LCH4) is being considered as a candidate propellant for exploration architectures. In order to gain an -understanding of any unique considerations involving micro-gravity pressure control with LCH4, testing was conducted at the Marshall Space Flight Center using the Multipurpose Hydrogen Test Bed (MHTB) to evaluate the performance of a spray-bar thermodynamic vent system (TVS) with subcooled LCH4 and gaseous helium (GHe) pressurant. Thirteen days of testing were performed in November 2006, with total tank heat leak conditions of about 715 W and 420 W at a fill level of approximately 90%. The TVS system was used to subcool the LCH4 to a liquid saturation pressure of approximately 55.2 kPa before the tank was pressurized with GHe to a total pressure of 165.5 kPa. A total of 23 TVS cycles were completed. The TVS successfully controlled the ullage pressure within a prescribed control band but did not maintain a stable liquid saturation pressure. This was likely. due to a TVS design not optimized for this particular propellant and test conditions, and possibly due to a large artificially induced heat input directly into the liquid. The capability to reduce liquid saturation pressure as well as maintain it within a prescribed control band, demonstrated that the TVS could be used to seek and maintain a desired liquid inlet temperature for an engine (at a cost of propellant lost through the TVS vent). One special test was conducted at the conclusion of the planned test activities. Reduction of the tank ullage pressure by opening the Joule-Thomson valve (JT) without operating the pump was attempted. The JT remained open for over 9300 seconds, resulting in an ullage pressure reduction of 30 kPa. The special test demonstrated the feasibility of using the JT valve for limited ullage pressure reduction in the event of a pump failure.