ALBERT

Description: We have investigated the interaction of Io, Jupiter's innermost Galilean satellite, with the Io plasma torus. The interaction of Io with the plasma surrounding it has been a subject of interest for almost 30 years, dating from the discovery by Bigg (1964) that radio emissions from the Jovian magnetosphere are controlled by Io's position. Since that time, both ground-based and spacecraft observations have shown that Io is a unique satellite that influences the Jovian magnetosphere in important ways. In particular, material from Io is a major source of plasma for the magnetosphere, and the energy that this plasma harnesses from Jupiter's co-rotating magnetic field is an important power source for the magnetosphere. It is apparent that the local interaction of the torus plasma with Io plays a key role in the formation, composition, and energetics of the Io torus; the interaction is also highly nonlinear. We have modeled this interaction using time-dependent three-dimensional magnetohydrodynamic (MHD) simulations. During this past year, we have used NASA support to develop a new MHD code to study the interaction. As part of the Galileo spacecraft's recent successful insertion into orbit around Jupiter, the spacecraft passed within 900 km of Io's surface. Our calculations have focused on using Galileo particles and fields data to examine a question that was not resolved by the Voyager observations: Does Io have an intrinsic magnetic field? In this progress summary, we describe our efforts on this problem to date.

Description: Estimates of the mass of dust suspended in the Martian atmosphere are derived from global and regional 9-micrometer opacity maps produced from Viking Infrared Thermal Mapper data. During the peak of the 1977b storm, a total dust mass of approximately 4.3 x 10(exp 14) g was suspended, equivalent to 4.3 x 10(exp -4) g/sq cm, or a layer 1.4 micrometers thick. During a local dust storm near Solis Planum at L(sub s) 227 deg, approximately 1.3 x 10(exp 13) g of dust were lofted, equal to about a 6-micrometer layer in that vicinity.

Description: We model an infrared outburst on Io as being due to a large, erupting lava flow which increased its area at a rate of 1.5 x 10(exp 5)/sq m and cooled from 1225 to 555 K over the 2.583-hr period of observation. The inferred effusion rate of 3 x 10(exp 5) cu m/sec for this eruption is very high, but is not unprece- dented on the Earth and is similar to the high eruption rates suggested for early lunar volcanism. Eruptions occur approxi- mately 6% of the time on Io. These eruptions provide ample resurfacing to explain Io's lack of impact craters. We suggest that the large total radiometric heat flow, 10(exp 14) W, and the size and temperature distribution of the thermal anomalies (McEwen et al. 1992; Veeder et al. 1994) can be accounted for by a series of silicate lava flows in various stages of cooling. We propose that the whole suite of Io's currently observed thermal anomalies was produced by multiple, high-eruptive-rate silicate flows within the past century.

Description: We investigate the orbital dynamics of small dust particles generated via the continuous micrometeoroid bombardment of the Martian moons. In addition to Mar's oblateness, we also consider the radiation pressure perturbation that is complicated by the planet's eccentric orbit and tilted rotational axis. Considering the production rates and the lifetimes of dust grains, we show that particles from Deimos with radii of about 15 micrometers are expected to dominate the population of a permanently present and tilted dust torus. This torus has an estimated peak number density of approximately equals 5 x 10(exp -12)/cu cm and an optical depth of approximately equals 4 x 10(exp -8).

Description: The valley network channels on the heavily cratered ancient surface of Mars suggest the presence of liquid water approximately 3.8 Gyr ago. However, the implied warm climate is difficult to explain in the context of the standard solar model, even allowing for the maximum CO2 greenhouse heating. In this paper we investigate the astronomical and planetary implications of a nonstandard solar model in which the zero-age, main-sequence Sun had a mass of 1.05 +/- 0.02 Solar Mass. The excess mass was subsequently lost in a solar wind during the first 1.2(-0.2, +0.4) Gyr of the Sun's main sequence phase. The implied mass-loss rate of 4(+3, -2) x 10(exp -11) M/yr, or about 10(exp 3) x that of the current Sun, may be detectable in several nearby young solar type stars.

Description: Hellas basin on Mars has been the site of volcanism, tectonism, and modification by fluvial, mass-wasting, and eolian processes over its more than 4-b.y. existence. Our detailed geologic mapping and related studies have resulted in the following new interpretations. The asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low-angle bolide having a trajectory heading S60E. During the Late Noachian, the basin was infilled, perhaps by lava flows, that were sufficiently thick (greater than 1 km) to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin. At about the same time, deposits buried northern Malea Planum, which are interpreted to be pyroclastic flows from Amphitrites and Peneus Paterae on the basis of their degraded morphology, topology, and the application of a previous model for pyroclastic volcanism on Mars. Peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma, whereas Amphitrites is a less distinct circular feature surrounded by a broad, low, dissected shield that suggests generally smaller volume eruptions. During the Early Hesperian, an approximately 1-to 2km-thick sequence of primarily fined-grained, eolian material was deposited on the floor of Hellas basin. Subsequently, the deposit was deeply eroded, except where armored by crater ejecta, and it retreated as much as 200-300 km along its western margin, leaving behind pedestal craters and knobby outliers of the deposit. Local debris flows within the deposit attest to concentrations of groundwater, perhaps in part brought in by outflow floods along the east rim of the basin. These floods may have deposited approximately 100-200m of sediment, subduing wrinkle ridges in the eastern part of the basin floor. During the Late Hesperian and Amazonian, eolian mantles were emplaced on the basin rim and floor and surrounding highlands. Their subsequent erosion resulted in pitted and etched plains and crater fill, irregular mesas, and pedestal craters. Local evidence occurs for the possible former presence of ground ice or ice sheets approximately 100 km across; however, we disagree with a hypothesis that suggest that the entire south rim and much of the floor of Hellas have been glaciated. Orientations of dune fields and yardangs in lower parts of Hellas basin follow directions of the strongest winds predicted by a recently published general circulation model (GCM). Transient frost and dust splotches in the region are, by contrast, related to the GCM prediction for the season in which the images they appear in were taken.

Description: Visible and near-IR refectivity, Moessbauer, and X ray diffraction data were obtained on powders of impact melt rock from the Manicouagan Impact Crater located in Quebec, Canada. The iron mineralogy is dominated by pyroxene for the least oxidized samples and by hematite for the most oxidized samples. Phyllosilicate (smectite) contents up to approximately 15 wt % were found in some heavily oxidized samples. Nanophase hematite and/or paramagnetic ferric iron is observed in all samples. No hydrous ferric oxides (e.g., goethite, lepidocrocite, and ferrihydrite) were detected, which implies the alteration occurred above 250 C. Oxidative alteration is thought to have occurred predominantly during late-stage crystallization and subsolidus cooling of the impact melt by invasion of oxidizing vapors and/or solutions while the impact melt rocks were still hot. The near-IR band minimum correlated with the extent of aleration Fe(3+)/Fe(sub tot) and ranged from approximately 1000 nm (high-Ca pyroxene) to approximately 850 nm (bulk, well-crystalline hematite) for least and most oxidized samples, respectively. Intermediate band positions (900-920 nm) are attributed to low-Ca pyroxene and/or a composite band from hematite-pyroxene assemblages. Manicouagan data are consistent with previous assignments of hematite and pyroxene to the approximately 850 and approximately 1000nm bands observed in Martian reflectivity spectra. Manicouagan data also show that possible assignments for intermediate band positions (900-920 nm) in Martian spectra are pyroxene and/or hematite-pyroxene assemblages. By analogy with impact melt sheets and in agreement with observables for Mars, oxidative alteration of Martian impact melt sheets above 250 C and subsequent erosion could produce rocks and soils with variable proportions of hematite (both bulk and nanophase), pyroxene, and phyllosilicates as iron-bearing mineralogies. If this process is dominant, these phases on Mars were formed rapidly at relativly high temperatures on a sporadic basis throughout the history of the planet. The Manicouagan samples also show that this mineralogical diversity can be accomplished at constant chemical composition, which is also indicated for Mars from the analyses of soil at the two Viking landing sites.

Description: The orbiting shadowing analysis computer program was developed by NASA in order to assess the shadowing effects on various power systems. The algorithms, the inputs and outputs are discussed. Examples of typical shadowing analysis, performed for the International Space Station Freedom, the International Space Station Alpha and the joint United States/International Mir Solar Dynamic Flight Experimental Project are presented.

Description: A contactless method for the determination of the free-carrier density and the composition distribution across the thickness of 3-5 multi-layer solar cell structures, using the Raman scattering method, is developed. The method includes a step analysis of Raman spectra from optical phonons and phonon-plasmon modes of different layers. The method provides simultaneous measurements of the element composition and the thickness of the structure's layers together with the free-carrier density. The results of measurements of the free-carrier density composition distributions of the liquid phase epitaxy grown AlGaAs/GaAs and GaSb solar cell structures are presented and discussed.

Description: The photovoltaic array space power (PASP)-Plus solar cell flight experiment is described, and the observed performances of different solar cell types during the first six months of their operation, are summarized. The solar cell types include single crystal and amorphous silicon, GaAs, several multijunction cell types, indium phosphide and GaAs/GaSb concentrator cells. The radiation degradation experienced by some of the solar cell types agrees with theoretical predictions. Other samples, including silicon, are degraded less than predicted. Effects, including the increase in temperature of all the experiments and the effect of sun glint on cell measurement, are discussed.

Description: The conceptual design and experimental results for two types of space application concentrator photovoltaic modules, employing reflective optical elements, are presented. The first type is based on the use of compound parabolic concentrators, the second type is based on the use of line-focus parabolic troughs. Lightweight concentrators are formed with nickel foil coated silver with a diamond-like carbon layer protection. Secondary optical elements, including lenses and cones, are introduced for a better matching of concentrators and solar cells. Both types of modules are characterized by concentration ratios in the range 20x to 30x, depending on the chosen range of misorientation angles. The estimated specific parameters of these modules operating with single junction AlGaAs/GaAs solar cells are 240 W/sq m and 3 kg/sq m.

Description: Two contact systems for use on shallow junction InP solar cells are described. The feature shared by these two contact systems is the absence of the metallurgical intermixing that normally takes place between the semiconductor and the contact metallization during the sintering process. The n(+)pp(+) cell contact system, consisting of a combination of Au and Ge, not only exhibits very low resistance in the as-fabricated state, but also yields post-sinter resistivity values of 1(exp -7) ohms-sq cm, with effectively no metal-InP interdiffusion. The n(+)pp(+)cell contact system, consisting of a combination of Ag and Zn, permits low resistance ohmic contact to be made directly to a shallow junction p/n InP device without harming the device itself during the contacting process.

Description: The effects of irradiation of In(0.53)Ga(0.47)As/InP (InGaAs/InP) solar cells illuminated through a transparent InP substrate with 1 MeV electrons were measured. These solar cells were developed for bottom cells in tandem solar photovoltaic cell structures. Some InGaAs/InP heterostructures with four layers were grown by liquid phase epitaxy. The structure of the solar cells allowed lightly doped materials in n and p photoactive layers to be used. The base dopant levels ranged from 1.10(exp 17) to 5.10(exp 17) cm(exp -3). The open circuit voltage and the short circuit current were moderately degraded after irradiation with 10(exp 16) cm(exp-2) 1 MeV electrons. This behavior is explained in terms of the device structure and the n and p layer thicknesses.

Description: Based on the conservation of chemical elements in chemical reactions, a rule is proved that the number of boundary conditions given by densities and/or nonzero velocities should not be less than the number of chemical elements in the system, and the boundary conditions for species given by densities and velocities should include all elements in the system. Applications of this rule to Mars are considered. It is shown that the problem of the CO2-H2O chemistry in the lower and middle atmosphere of Mars, say, in the range of 0-80 km does not have a unique solution, if only CO2 and H2O densities are given at the lower boundary, and the remaining boundary conditions are fluxes. Two examples of models of this type are discussed. Two models of the photochemistry of the Martian atmosphere, with and without nitrogen chemistry, are considered. The oxygen nonthermal escape ratio of 1.2 x 10(exp 8)/cu cm/s is given at 240 km and is balanced with the total hydrogen escape rate within an uncertainty of 1% for both models. Both models fit the measured O2 and CO mixing ratios, the O3 abundance, and the O2 1.27-micrometer dayglow almost within the uncertainties of the measured values, though the model without nitrogen chemistry fits better. The importance of nitrogen chemistry in the lower and middle atmosphere of Mars depends on a fine balance between production of NO and N in the upper atmosphere which is not known within the required accuracy.

Description: Goethite-bearing samples with values of Mn(s) (Mn/(Mn+Fe) mole fraction) up to 0.206 were synthesized by precipitation from alkaline solution. Samples with Mn(s) less than or equal 0.061 were single-phase Mn-goethites: samples with higher Mn(s) values contained another Mn-bearing phase (probably jacobsite). Mn-hematites were prepared by dehydroxylation of corresponding Mn-goethites at 500 C. Orthorhombic a and b unit cell dimensions of Mn-goethites changed in a linear manner with Mn(s), but not at rates predicted by the Vegrad law. Hexagonal unit cell dimensions of Mn-hematites did not vary with Mn(s). Moessbauer parameters isomer shift (IS), quadrupole splitting (QS), and hyperfine field (B(sub hf)) were measured at 293 and 15 K. For all single-phase Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061), magnetic splitting was observed at both temperatures. At 293 K, small but systematic decreases in B(sub hf) were observed with increasing Mn substitution; IS and QS were not dependent on Mn(s). Mn substitution strongly lowered the Morin transition temperature of hematite. At 15 K, the Morin transition was not present for Mn(s) greater than 0.020(4). The saturation magnetization of Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061) was the expected zero (within error) for antiferromagnetic goethite and for hematites obtained from dehydroxylation of goethites. Mn-geothites with Mn(s) greater than 0.061 were magnetic because of the presence of strongly magnetic jacobsite. For reflectivity spectra, bands resulting from MN(3+) were centered near 454 and 596 nm for Mn-goethites and near 545 and 700 nm for Mn-hematites. There is evidence for a approximately 700 nm band in spectral data for Martian bright regions, but association of it with Mn(3+) is not a unique interpretation. Comparison of laboratory and Martian spectral data implies that Mn(s) less than 0.032 for the Mn(3+) content of Martian hematites.

Description: Ferric-iron-bearing materials play an important role in the interpretation of visible to near-IR Mars spectra, and they may play a similarly important role in the analysis of new mid-IR spacecraft spectral observations to be obtained over the next decade. We review exisiting data on mid-IR transmission spectra of ferric oxides/oxyhydroxides and present new transmission spectra for ferric-bearing materials spanning a wide range of mineralogy and crystallinity. These materials include 11 samples of well-crystallized ferric oxides (hematite, maghemite, and magnetite) and ferric oxyhydroxides (goethite, lepidocrocite). We also report the first transmission spectra for purely nanophase ferric oxide samples that have been shown to exhibit spectral similarities to Mars in the visible to near-IR and we compare these data to previous and new transmission spectra of terrestial palagonites. Most of these samples show numerous, diagnostic absorption features in the mid-IR due to Fe(3+) - 0(2-) vibrational transitions, structural and/or bound OH, and/or silicates. These data indicate that high spatial resolution, moderate spectral resolution mid-IR ground-based and spacecraft observations of Mars may be able to detect and uniquely discriminate among different ferric-iron-bearing phases on the Martian surface or in the airborne dust.

Description: The main objective of this study is to develop a new test method that is suitable for the assessment of the resistance of aerospace cables to arc tracking for different specific environmental and network conditions of spacecrafts. This paper reports the purpose, test conditions, test specimen, test procedure, and test acceptance criteria of seven different (200-250 mm long) cables.

Description: This report contains viewgraphs on arc tracking tests in various aerospace environments. It has the following six sections: LeRC arc tracking tests parameters, apparatus, sample description, procedure, arc tracking test results, and discussion.

Description: The results of the testing of wire insulation materials for space applications is presented in this report. The wire insulations tested were partially fluorinated polyimide, extruded ETFE, extruded PTFE, PTFE tape, and PTFE/Kapton. The tests performed were flammability tests, odor tests, compatibility tests with aerospace fluids, offgassing tests, and thermal vacuum stability tests.

Description: The objectives of the NASA Wiring for Space Applications program were to investigate the effects of atomic oxygen (AO), ultraviolet (UV) radiation, and AO with UV synergistic effects on wire insulation materials. The AO exposure was on the order of 10(exp 21) atoms/sq cm and the vacuum UV radiation was on the order of 10,000 ESH. The results of these tests are presented in this document

Description: The electrical power wiring tests results from the NASA Wiring for Space Applications program are presented. The goal of the program was to develop a base for the building of a lightweight, arc track-resistant electrical wiring system for aerospace applications. This new wiring system would be applied to such structures as pressurized modules, trans-atmospheric vehicles, LEO/GEO environments, and lunar and Martian environments. Technological developments from this program include the fabrication of new insulating materials, the production of new wiring constructions, an improved system design, and an advanced circuit protection design.

Description: The Voyager 1 spacecraft flew by Jupiter on March 5, 1979. Spacecraft navigation was performed with radio tracking data from NASA's Deep Space Network. In the years since then, there has been a great deal of progress in the definition of celestial reference frames and in determining the orbit and orientation of the Earth. Using these improvements, the radio metric range and Doppler data acquired from the Voyager 1 spacecraft near its encounter with Jupiter have been reanalyzed to determine the plane-of-sky position of Jupiter with much greater accuracy than was possible at the time of the encounter. The position of Jupiter at the time of encounter has been determined with an accuracy of 40 nrad in right ascension and 140 nrad in declination with respect to the celestial reference frame defined by the International Earth Rotation Service. This position estimate has been done to improve the ephemeris of Jupiter prior to the upcoming encounter of the Galileo spacecraft with Jupiter.

Description: Oxidizer propellant systems for liquid-fueled rocket engines must meet stringent cleanliness requirements for particulate and nonvolatile residue. These requirements were established to limit residual contaminants which could block small orifices or ignite in the oxidizer system during engine operation. Limiting organic residues in high pressure oxygen systems is particularly important. The current method of cleanliness verification used by Rocketdyne requires an organic solvent flush of the critical hardware surfaces. The solvent is filtered and analyzed for particulate matter, followed by gravimetric determination of the nonvolatile residue (NVR) content of the filtered solvent. The organic solvents currently specified for use (1,1,1-trichloroethane and CFC-113) are ozone-depleting chemicals slated for elimination by December 1995. A test program is in progress to evaluate alternative methods for cleanliness verification that do not require the use of ozone-depleting chemicals and that minimize or eliminate the use of solvents regulated as hazardous air pollutants or smog precursors. Initial results from the laboratory test program to evaluate aqueous-based methods and organic solvent flush methods for NVR verification are provided and compared with results obtained using the current method. Evaluation of the alternative methods was conducted using a range of contaminants encountered in the manufacture of rocket engine hardware.

Description: The Solid Rocket Motors (SRM) used by NASA to propel the Space Shuttle employ gimballing nozzles as a means for vehicular guidance during launch and ascent. Gimballing a nozzle renders the pressure field of the exhaust gases nonaxisymmetric. This has two effects: (1) it exerts a torque and side load on the nozzle; and (2) the exhaust gases flow circumferentially in the aft-dome region, thermally loading the flexible boot, case-to-nozzle joint, and casing insulation. The use of CFD models to simulate such flows is imperative in order to assess SRM design. The grids for these problems were constructed by obtaining information from drawings and tabulated coordinates. The 2D axisymmetric grids were designed and generated using the EZ-Surf and GEN2D surface and grid generation codes. These 2D grids were solved using codes such as FDNS, GASP, and MINT. These axisymmetric grids were rotated around the center-line to form 3D nongimballed grids. These were then gimballed around the pivot point and the gaps or overlaps resurfaced to obtain the final domains, which contained approximately 366,000 grid points. The 2D solutions were then rotated and manipulated as appropriate for geometry and used as initial guesses in the final solution. The analyses were used in answering questions about flight criteria.

Description: This paper is a survey of the waste minimization efforts of industries outside of aerospace for possible applications in the manufacture of solid rocket motors (SRM) for NASA. The Redesigned Solid Rocket Motor (RSRM) manufacturing plan was used as the model for processes involved in the production of an SRM. A literature search was conducted to determine the recycling, waste minimization, and waste treatment methods used in the commercial sector that might find application in SRM production. Manufacturers, trade organizations, and professional associations were also contacted. Waste minimization efforts for current processes and replacement technologies, which might reduce the amount or severity of the wastes generated in SRM production, were investigated. An overview of the results of this effort are presented in this paper.

Description: The numerical model for a rocket thermal analysis code (RTE) is discussed. RTE is a comprehensive thermal analysis code for thermal analysis of regeneratively cooled rocket engines. The input to the code consists of the composition of fuel/oxidant mixture and flow rates, chamber pressure, coolant temperature and pressure. dimensions of the engine, materials and the number of nodes in different parts of the engine. The code allows for temperature variation in axial, radial and circumferential directions. By implementing an iterative scheme, it provides nodal temperature distribution, rates of heat transfer, hot gas and coolant thermal and transport properties. The fuel/oxidant mixture ratio can be varied along the thrust chamber. This feature allows the user to incorporate a non-equilibrium model or an energy release model for the hot-gas-side. The user has the option of bypassing the hot-gas-side calculations and directly inputting the gas-side fluxes. This feature is used to link RTE to a boundary layer module for the hot-gas-side heat flux calculations.

Description: On July 4,1997, the Mars Pathfinder spacecraft lands on Mars and starts conducting technological and scientific experiments. One experiment, the Alpha-Proton-X-ray Spectrometer, uses a sensor head placed against rocks and soil to determine their composition. To guarantee proper placement, a deployment mechanism mounted on the Mars Rover aligns the sensor head to within 20 deg of the rock and soil surfaces. In carrying out its task, the mechanism mimics the action of a human hand and arm. Consisting of a flexible wrist, a parallel link arm, a brush dc motor actuator, and a revolutionary non-pyrotechnic fail-safe release device, the mechanism correctly positions the sensor head on rocks as high as 0.29 m and on targets whose surfaces are tilted as much as 45 deg from the nominal orientation of the sensor head face. The mechanism weighs less than 0.5 kg, can withstand 100 g's, and requires less than 2.8 N x m of actuation torque. The fail-safe coupler utilizes Cerrobend, a metal alloy that melts at 60 C, to fuse the actuator and the rest of the mechanism together. A film heater wrapped around the coupler melts the metal, and Negator springs drive the mechanism into its stowed position. The fail-safe actuates using 6.75 Watts for 5 minutes in the event of an actuator failure.

Description: The specific energy density and the performance of nickel electrodes are generally limited by the electrode microstructure and the nature of the active material within the electrode matrix. Progress is being made in our laboratory in a collaborative effort with NASA-LEWIS Research Center to develop lighter weight, mechanically stable and highly efficient nickel electrodes for aerospace applications. Our approach is based on an electrode microstructure fabricated from a mixture of nickel fibers as small as 2 micro m diameter and cellulose fibers. Results will be presented to show the optimum conditions for impregnating this electrode microstructure with nickel hydroxide active material. Performance data in half-cell tests and cycle life data will also be presented. The flexibility of this electrode microstructure and the significant advantages it offers in terms of weight and performance will be demonstrated, in particular its ability to accept charge at high rates and to discharge at high rates.

Description: Two symposia related to the exploration of the Venus and Mars atmospheres produced papers which described the results of spacecraft-based and ground-based observations of these two planets. The topics addressed included solar wind interactions, molecular ions, planetary magnetospheres, planetary ionospheres, planetary thermospheres, gravity waves, the homopause, radiative transfer, radiative balance, atmospheric water, planetary lightning, very low frequency bursts, cosmic-ray ionization, planetary loss, and future missions to study Mars aeronomy, energetic particles near Mars, radar exploration of Mars, and the Mars Environmental Survey (MESUR) mission.

Description: The deep space and planetary exploration project have been acquiring more and more importance and some of them are now well established both in ESA and NASA programs. This paper presents the possibility to utilize both silicon and gallium arsenide solar cells as spacecraft primary power source for missions far from the Sun, in order to overcome the drawbacks related to the utilisation of radioisotope thermoelectric generators - such as cost, safety and social acceptance. The development of solar cells for low illumination intensity and low temperature (LILT) applications is carried out in Europe by ASE (Germany) and CISE (Italy) in the frame of an ESA programme, aimed to provide the photovoltaic generators for ROSETTA: the cometary material investigation mission scheduled for launch in 2003. The LILT cells development and testing objectives are therefore focused on the following requirements: insolation intensity as low as 0.03 Solar Constant, low temperature down to -150 C and solar flare proton environment. At this stage of development, after the completion of the technology verification tests, it has been demonstrated that suitable technologies are available for the qualification of both silicon and gallium arsenide cells and both candidates have shown conversion efficiencies over 25% at an illumination of 0.03 SC and a temperature of -150 C. In particular, when measured at those LILT conditions, the newly developed 'Hl-ETA/NR-LILT' silicon solar cells have reached a conversion efficiency of 26.3%, that is the highest value ever measured on a single junction solar cell. A large quantity of both 'Hl-ETA/NR-LILT' silicon and 'GaAs/Ge-LILT' solar cells are presently under fabrication and they will be submitted to a qualification test plan, including radiation exposure, in order to verify their applicability with respect to the mission requirements. The availability of two valid options will minimize the risk for the very ambitious scientific project. The paper describes how the technical achievements have been possible with Si and GaAs LILT solar cells (including a comparison between measured and modelled l-V characteristics) and it presents the technology verification tests results.

Description: A newly discovered source of energetic particle streams directed at Venus' nightside may cause several exosphere phenomena. The streams evolve from dispersed cosmoids, a surreptitious population of meteoroids in nearly hyperbolic orbits, measured with three dust experiments on Pioneer 10/11. Loose fragile comet-like ensembles of frozen volatile material, they are orders of magnitude more populous than short-period meteoroids. Dispersion is forced near a planet masking the meteor signature at Earth, but recently terrestrial exosphere interactions have been detected principally from VLF radar returns and as suddenly formed layers of neutral sodium and iron probed by lidar. Venus influx is estimated greater than 10(exp -14)(g)/((sq cm)(s)) with nightside directed kinetic power of greater than 0.3 (erg)/((sq cm)s)). Compared to Earth, Venus, lacking a dipole field with almost no rotation, has a readily recognized set of nightside interaction signatures of these downward energetic particle streams: i.e., density depressions of the neutral thermosphere, hydrogen and helium bulges, a non-disappearing ionosphere, electron holes, nightglows, VLF bursty signals, and local magnetic fields. From Pioneer Venus Orbiter (PVO) measurements, the cosmoid population, its temporal and solar azimuthal variation may be determined.

Description: High-resolution, near-infrared (1.09 to 2.5 micrometers) spectra of the night side of Venus have been obtained in 1990 and 1991 using the Fourier Transform Spectrometer at the 3.6-m Canada-France-Hawaii telescope. Absorptions due to H2O were detected in spectral windows near 2.3, 1.74, and 1.18 micrometers. Our analysis of these absorptions constrains the abundance of water vapor in three different altitude ranges located between the clouds and the surface: 30-40 km, 15-25 km and 0-15 km. A constant water vapor mixing ratio of 30 +/- 15 ppm below the clouds can fit the observations. These values are consistent with recent near-infrared studies of the night side of Venus at lower spectral resolution. The atmosphere of Venus appears to be dryer than originally suggested by the in-situ measurements made by the Pioneer Venus and Venera mass-spectrometers and gas-chromatographs.

Description: Using Pioneer Venus data, hydrogen and deuterium ions are shown to escape from the hydrogen bulge region in the nightside ionosphere. The polarization electric field propels these light ions upward through the ionosphere and into the ion-exosphere, where H(+) and D(+) continue to be accelerated away from Venus and move into the ionotail and beyond. The vertical flow speeds of H(+) and D(+) are found to be about the same; therefore, selective escape between H(+) and D(+) is negligible for this mechanism. Present day planetary loss rates of about 8.6 x 10(exp 25)/s and 3.2 X 10(exp 23)/s were obtained for H(+) and D(+), respectively. Such rates, persisting over a few billion years, should have significantly affected the planetary water budget.

Description: A method and apparatus of manufacturing a grid member for use in an ion discharge apparatus provides a woven carbon fiber in a matrix of carbon. The carbon fibers are orientated to provide a negatibe coefficient of thermal expansion for at least a portion of the grid member's operative range of use.

Description: Substantial evidence suggests that a UV spectrally Absorbing Material (UV-SAM) exists on Triton's surface. This evidence is found in the positive slope in Triton's spectrum from the UV to the near-IR, and the increasing contrast in Triton's light curve in the blue and UV. Although it is now widely-thought that UV-SAMs exist on Triton, little is known about their distribution and spectral properties. The goal of this NDAP Project is to determine the spatial distribution and geological context of the UV-SaM material. We hope to determine if UV-SAMs on Triton are correlated with geologic wind streaks, craters, calderas, geomorphic/topographic units, regions containing (or lacking) volatile frosts, or some other process (e.g., magnetospheric interactions). Once the location and distribution of UV-SAMs has been determined, further constraints on their composition cable made by analyzing the spectrographic data set. To accomplish these goals, various data sets will be used, including Voyager 2 UV and visible images of Triton's surface, IUE and HST spectra of Triton, and a geologic map of the surface based on voyager 2 and spectrophotometric data. The results of this research will be published in the planetary science literature.

Description: Work on completing our analysis of the Voyager UVS solar occultation data acquired during Neptune encounter is essentially complete, as testified by the attached poster materials. The photochemical modeling addresses the recent revision in branching ratios for radical production in the photolysis of methane at H Lyman alpha implied by the lab measurements of Mordaunt et al. (1993). The software generated in this effort has been useful for checking the degree to which photochemical models addressing other datasets (mainly infrared) are consistent with the UVS data. This work complements the UVS modeling results in that the IR data refer to deeper pressure levels; as regards the modeling of UVS data, the most significant result is the convincing support for the presence of a stagnant lower stratosphere. Evidence for strong dynamical (mixing) transport of minor constituents at shallower pressures is provided by the UVS data analysis.

Description: Spectral observations providing evidence for the presence of volatile-bearing minerals on the surface of Mars were obtained in 1988 and 1990 from the KAO. The 1988 data suggest the presence of 1-3 weight percent (wt%) of carbonate/bicarbonate and 10-15 wt% sulfate/bisulfate associated with martian atmospheric dust. Estimates of the optical depths are approximately 0.60 and approximately 0.35 in 1988 and 1990, respectively.

Description: This report presents the results obtained from an experimental analysis of the flow field in the slots of the star grain section in the head-end of the advanced solid rocket motor during the ignition transient. This work represents an extension of the previous tests and analysis to include the effects of using a center port in conjunction with multiple canted igniter ports. The flow field measurements include oil smear data on the star slot walls, pressure and heat transfer coefficient measurements on the star slot walls and velocity measurements in the star slot.

Description: Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, reveal the presence of an auroral emission near 80 deg N with a peak brightness of about 150 kR of total H2 emission. The maximum optical depth of the polar haze layer is found to be located approximately 5 deg equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the observed haze optical depth requires an efficiency of aerosol formation of about 6 percent, indicating that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze.

Description: The main objective of this test was to obtain detailed radial and circumferential flow surveys at the inlet and exit of the SSME High Pressure Fuel Turbine model using three-hole cobra probes, hot-film probes, and a laser velocimeter. The test was designed to meet several objectives. First, the techniques for making laser velocimeter, hot-film probe, and cobra probe measurements in turbine flows were developed and demonstrated. The ability to use the cobra probes to obtain static pressure and, therefore, velocity had to be verified; insertion techniques had to be established for the fragile hot-film probes; and a seeding method had to be established for the laser velocimetry. Once the measurement techniques were established, turbine inlet and exit velocity profiles, temperature profiles, pressure profiles, turbulence intensities, and boundary layer thicknesses were measured at the turbine design point. The blockage effect due to the model inlet and exit total pressure and total temperature rakes on the turbine performance was also studied. A small range of off-design points were run to obtain the profiles and to verify the rake blockage effects off-design. Finally, a range of different Reynolds numbers were run to study the effect of Reynolds number on the various measurements.

Description: A solar thermal upper stage (STUS) is envisioned as a propulsive concept for the future. The STUS will be used for low Earth orbit (LEO) to geostationary-Earth orbit (GEO) transfer and for planetary exploration missions. The STUS offers significant performance gains over conventional chemical propulsion systems. These performance gains translate into a more economical, more efficient method of placing useful payloads in space and maximizing the benefits derived from space activity. This paper will discuss the economical advantages of an STUS compared to conventional chemical propulsion systems, the potential market for an STUS, and the recent activity in the development of an STUS. The results of this assessment combined with the performance gains, will provide a strong justification for the development of an STUS.

Description: The Optical Plume Anomaly Detection (OPAD) system is under development to provide early-warning failure detection in support of ground-level testing of the Space Shuttle Main Engine (SSME). Failure detection is to be achieved through the acquisition of spectrally resolved plume emissions and subsequent identification of abnormal levels indicative of engine corrosion or component failure. Two computer codes (one linear and the other non-linear) are used by the OPAD system to iteratively determine specific element concentrations in the SSME plume, given emission intensity and wavelength information. Since this analysis is extremely labor intensive, a study was initiated to develop neural networks that would model the 'inverse' of these computer codes. Optimally connected feed-forward networks with imperceptible prediction error have been developed for each element modeled by the linear code, SPECTRA4. Radial basis function networks were developed for the non-linear code, SPECTRA5, and predict combustion temperature in addition to element concentrations.

Description: An assessment of engine and component health is routinely made after each test firing or flight firing of a Space Shuttle Main Engine (SSME). Currently, this health assessment is done by teams of engineers who manually review sensor data, performance data, and engine and component operating histories. Based on review of information from these various sources, an evaluation is made as to the health of each component of the SSME and the preparedness of the engine for another test or flight. The objective of this project - the SSME Post Test Diagnostic System (PTDS) - is to develop a computer program which automates the analysis of test data from the SSME in order to detect and diagnose anomalies. This report primarily covers work on the Systems Section of the PTDS, which automates the analyses performed by the systems/performance group at the Propulsion Branch of NASA Marshall Space Flight Center (MSFC). This group is responsible for assessing the overall health and performance of the engine, and detecting and diagnosing anomalies which involve multiple components (other groups are responsible for analyzing the behavior of specific components). The PTDS utilizes several advanced software technologies to perform its analyses. Raw test data is analyzed using signal processing routines which detect features in the data, such as spikes, shifts, peaks, and drifts. Component analyses are performed by expert systems, which use 'rules-of-thumb' obtained from interviews with the MSFC data analysts to detect and diagnose anomalies. The systems analysis is performed using case-based reasoning. Results of all analyses are stored in a relational database and displayed via an X-window-based graphical user interface which provides ranked lists of anomalies and observations by engine component, along with supporting data plots for each.

Description: Among the hazards that must be negotiated by lunar-landing spacecraft are blocks on the surface of the Moon. Unfortunately, few data exist that can be used to evaluate the threat posed by such blocks to landing spacecraft. Perhaps the best information is that obtained from Surveyor photographs, but those data do not extend to the dimensions of the large blocks that would pose the greatest hazards. Block distributions in the vicinities of the Surveyor 1, 3, 6, and 7 sites have been determined from Lunar Orbiter photography and are presented here. Only large (i.e., greater than or equal to 2.5 m) blocks are measurable in these pictures, resulting in a size gap between the Surveyor and Lunar Orbiter distributions. Nevertheless, the orbital data are self-consistent, a claim supported by the similarity in behavior between the subsets of data from the Surveyor 1, 3, and 6 sites and by the good agreement in position (if not slopes) between the data obtained from the Surveyor 3 photography and those derived from the Lunar Orbiter photographs. Confidence in the results is also justified by the well-behaved distribution of large blocks at the surveyor site. Comparisons between the Surveyor distributions and those derived from the orbital photography permit these observations: (1) in all cases but that for Surveyor 3, the density of large blocks is overestimated by extrapolation of the Surveyor-derived trends; (2) the slopes of the Surveyor-derived distributions are consistently lower than those determined for the large blocks; and (3) these apparent disagreements could be mitigated if the overall shapes of the cumulative lunar block populations were nonlinear, allowing for different slopes over different size intervals. The relatively large gaps between the Surveyor-derived and Orbiter-derived data sets, however, do not permit a determination of those shapes.

Description: The Space Studies Board of the National Research Council charged its Committee on Planetary and Lunar Exploration (COMPLEX) to (1) examine the degree to which small missions, such as those fitting within the constraints of the Discovery program, can achieve priority objectives in the lunar and planetary sciences; (2) determine those characteristics, such as level of risk, flight rate, target mix, university involvement, technology development, management structure and procedures, and so on, that could allow a successful program; (3) assess issues, such as instrument selection, mission operations, data analysis, and data archiving, to ensure the greatest scientific return from a particular mission, given a rapid deployment schedule and a tightly constrained budget; and (4) review past programmatic attempts to establish small planetary science mission lines, including the Planetary Observers and Planetary Explorers, and consider the impact management practices have had on such programs. A series of small missions presents the planetary science community with the opportunity to expand the scope of its activities and to develop the potential and inventiveness of its members in ways not possible within the confines of large, traditional programs. COMPLEX also realized that a program of small planetary missions was, in and of itself, incapable of meeting all of the prime objectives contained in its report 'An Integrated Strategy for the Planetary Sciences: 1995-2010.' Recommendations are provided for the small planetary missions to fulfill their promise.

Description: Several methods for coupling the SP-100 space nuclear reactor to the NASA Lewis Research Center's Free Piston Stirling Power Convertor (FPSPC) are presented. A 25 kWe, dual opposed Stirling convertor configuration is used in these designs. The concepts use radiative coupling between the SP-100 lithium loop and the sodium heat pipe of the Stirling convertor to transfer the heat from the reactor to the convertor. Four separate configurations are presented. Masses for the four designs vary from 41 to 176 kgs. Each design's structure, heat transfer characteristics, and heat pipe performance are analytically modeled.

Description: The Optical Plume Anomaly Detection (OPAD) system is under development to predict engine anomalies and engine parameters of the Space Shuttle's Main Engine (SSME). The anomaly detection is based on abnormal metal concentrations in the optical spectrum of the rocket plume. Such abnormalities could be indicative of engine corrosion or other malfunctions. Here, we focus on the second task of the OPAD system, namely the prediction of engine parameters such as rated power level (RPL) and mixture ratio (MR). Because of the high dimensionality of the spectrum, we developed a linear algorithm to resolve the optical spectrum of the exhaust plume into a number of separate components, each with a different physical interpretation. These components are used to predict the metal concentrations and engine parameters for online support of ground-level testing of the SSME. Currently, these predictions are labor intensive and cannot be done online. We predict RPL using neural networks and give preliminary results.

Description: The objectives are to look at time scales of overpressure compared to cratering and to determine: what are the transient pressure and density due to atmospheric entry; do shock waves evacuate ambient gas; do transient atmospheric disturbances 'settle down' during cratering; can the pressure/density field be approximated as quasi-static; how does disturbance scale with impactor size; and what is the role of atmospheric thickness. The general approach is to perform inexpensive exploratory calculations, perform experiments to validate code and observe crater growth, and to follow up with more realistic coupling calculations. This viewgraph presentation presents progress made with the objective to obtain useful scaling relationships for crater formation when atmospheric effects are important.

Description: The experimental study on the fundamental processes involved in fuel decomposition and boundary-layer combustion in hybrid rocket motors is continuously being conducted at the High Pressure Combustion Laboratory of The Pennsylvania State University. This research will provide a useful engineering technology base in the development of hybrid rocket motors as well as a fundamental understanding of the complex processes involved in hybrid propulsion. A high-pressure, 2-D slab motor has been designed, manufactured, and utilized for conducting seven test firings using HTPB fuel processed at PSU. A total of 20 fuel slabs have been received from the Mcdonnell Douglas Aerospace Corporation. Ten of these fuel slabs contain an array of fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. Diagnostic instrumentation used in the test include high-frequency pressure transducers for measuring static and dynamic motor pressures and fine-wire thermocouples for measuring solid fuel surface and subsurface temperatures. The ultrasonic pulse-echo technique as well as a real-time x-ray radiography system have been used to obtain independent measurements of instantaneous solid fuel regression rates.

Description: Polyimide has been used extensively as the primary wiring insulation in commercial planes, military aircraft, and space vehicles due to its low weight, high service temperature, and good dielectric strength. New failure modes, however, have been associated with the use of polyimide because of the susceptibility of the insulation to pyrolization and arc tracking. A new wiring construction utilizing partially fluorinated polyimide insulation has been tested and compared with the standard military polyimide wire. Electrical properties which were investigated include AC corona inception and extinction voltages (sea level and 60,000 feet), time/current to smoke, and wire fusing time. The two constructions were also characterized in terms of their mechanical properties including abrasion resistance, dynamic cut through, and notch propagation. These test efforts and the results obtained are presented and discussed.

Description: A method for the mathematical analysis of linear alternator and linear motor devices and designs is described, and an example of its use is included. The technique seeks to surpass other methods of analysis by including more rigorous treatment of phenomena normally omitted or coarsely approximated such as eddy braking, non-linear material properties, and power losses generated within structures surrounding the device. The technique is broadly applicable to linear alternators and linear motors involving iron yoke structures and moving permanent magnets. The technique involves the application of Amperian current equivalents to the modeling of the moving permanent magnet components within a finite element formulation. The resulting steady state and transient mode field solutions can simultaneously account for the moving and static field sources within and around the device.

Description: The past few decades have witnessed significant advances in our understanding of how stars form, and there has been an associated increase in our knowledge of conditions and phenomena in the early solar system. These have led to the formulation of a paradigm for the origin of the solar system that is sufficiently complete that its basic elements can be tested directly through observations. A simple, but profound, consequence of the paradigm is that most if not all stars should be accompanied by planetary systems. The accuracy of instruments that can be used in such searches has improved to the point that Jupiter-like companions to a number of nearby stars could be detected. However, the results to date are that no other planetary systems have been detected, and the absence of detection is becoming statistically significant, particularly as it relates to the existence of brown dwarf companions to main-sequence stars.

Description: This workshop addressed key technology issues in the field of electrical power wiring for space applications, and transferred information and technology related to space wiring for use in government and commercial applications. Speakers from space agencies, U.S. Federal labs, industry, and academia presented program overviews and discussed topics on arc tracking phenomena, advancements in insulation materials and constructions, and new wiring system topologies.

Description: Four tasks were completed in this period and results were published in AIAA papers. First, a Boltzmann-2D code, was developed and applied to compute MSFC-A2 nozzle/plume flow field. It solved the two-dimensional Boltzmann-BGK equation using the Finite Difference Discrete Ordinate (FDDO) numerical technique. The code was validated by experimental data for one-dimensional shock structure predictions, paper 95-2056. Successful results for nozzle/plume flow simulation using the developed Boltzmann-2D code were presented at the 1995 AIAA Aerospace Science Conference, paper 95-0627. Second, a computer code solving two-dimensional Burnett equations was developed and applied to low-density nozzle flow field calculation. Results were also published at the 1994 AIAA Thermophysics Conference, paper 94-2055. Third, the developed two-dimensional Burnett code was extended to compute axisymmetric flow field inside MSFC-A2 nozzle, paper 95-2008. The computed nozzle exit conditions are used as input data for Direct Simulation Monte Carlo (DSMC) plume calculation. Fourth, a DSMC code was modified to compute the exhausted plume near the nozzle exit and in the backflow region.

Description: Electrical power, as an area of study, is relatively young as compared to language, chemistry, physics, mathematics, philosophy, metallurgy, textiles, transportation, or farming. Practically all of the technology that has enabled the huge, continent-spanning power grids that have become ubiquitous in developed countries was developed in the last 150 years. In fact, Tesla's advocacy of alternating current for transmission just won out in the beginning of this century. Despite the novelty of the field as a whole, space power applications are, of course, much newer. This paper looks at the history of space power, and compares it to its older sibling on earth, forming a basis for determining appropriate transitions of technology from the terrestrial realm to space applications.

Description: This document contains results obtained in the process of performing a power system definition study of the TROPIX power management and distribution system (PMAD). Requirements derived from the PMADs interaction with other spacecraft systems are discussed first. Since the design is dependent on the performance of the photovoltaics, there is a comprehensive discussion of the appropriate models for cells and arrays. A trade study of the array operating voltage and its effect on array bus mass is also presented. A system architecture is developed which makes use of a combination of high efficiency switching power convertors and analog regulators. Mass and volume estimates are presented for all subsystems.

Description: Humans can perform many complicated tasks without explicit rules. This inherent and advantageous capability becomes a hurdle when a task is to be automated. Modern computers and numerical calculations require explicit rules and discrete numerical values. In order to bridge the gap between human knowledge and automating tools, a knowledge model is proposed. Knowledge modeling techniques are discussed and utilized to automate a labor and time intensive task of detecting anomalous bearing wear patterns in the Space Shuttle Main Engine (SSME) High Pressure Oxygen Turbopump (HPOTP).

Description: Future spacecraft power systems must be capable of supplying power to various loads. This delivery of power may necessitate the use of high-voltage, high-power dc distribution systems to transmit power from the source to the loads. Using state-of-the-art power conditioning electronics such as dc-dc converters, complex series and parallel configurations may be required at the interface between the source and the distribution system and between the loads and the distribution system. This research will use state-variables to model and simulate a dc spacecraft power system. Each component of the dc power system will be treated as a multiport network, and a state model will be written with the port voltages as the inputs. The state model of a component will be solved independently from the other components using its state transition matrix. A state-space averaging method is developed first in general for any dc-dc switching converter, and then demonstrated in detail for the particular case of the boost power stage. General equations for both steady-state (dc) and dynamic effects (ac) are obtained, from which important transfer functions are derived and applied to a special case of the boost power stage.

Description: The potential for a revolutionary step in the durability of reusable rocket engines is made possible by the combination of several emerging technologies. The recent creation and analytical demonstration of life extending (or damage mitigating) control technology enables rapid rocket engine transients with minimum fatigue and creep damage. This technology has been further enhanced by the formulation of very simple but conservative continuum damage models. These new ideas when combined with recent advances in multidisciplinary optimization provide the potential for a large (revolutionary) step in reusable rocket engine durability. This concept has been named the robust rocket engine concept (RREC) and is the basic contribution of this paper. The concept also includes consideration of design innovations to minimize critical point damage.

Description: This is the second part of a two-part report that describes the AJ10-221, a high performance iridium-coated rhenium (Ir-Re) 110 lbf (490N) welded rocket chamber with 286:1 area ratio nozzle. This engine was designed, built, and hot fired for over 6 hours on this program. It demonstrated an I(s) of 321.8 sec, which is 10 sec higher than conventional 110 lbf silicide coated Cb chambers now in use. The approach used in this portion of the program was to demonstrate the performance improvement that can be made by the elimination of fuel film cooling and the use of a high temperature (4000 F) (2200 C) iridium-coated rhenium (Ir-Re) rocket chamber. Detailed thermal, performance, mechanical, and dynamic design analyses of the full engine were conducted by Aerojet. Two Ir-Re chambers were built to the Aerojet design by Ultramet, using the chemical vapor deposition (CVD) process. Incorporation of a secondary mixing device or Boundary Layer Trip (BLT) within the combustion chamber (Aerojet Patents 4882904 and 4936091) results in improvement in flow uniformity, and a significant life and performance increase. The 110 lbf engine design was verified in bolt-up hardware tests at sea level and altitude. The effects of injector design on performance were studied. Two duplicate injectors were fabricated matching the preferred design and were demonstrated to be interchangeable in operation. One of these units were welded into a flight type thruster which was tested for an accumulated duration of 22,590 sec in 93 firings, one of which was a continuous burn of two hours. A design deficiency in the C-103 nozzle near the Re-Cb transition joint was discovered, studied and corrected design has been prepared. Workhardening studies have been conducted to investigate methods for increasing the low yield strength of the Re in the annealed conditions. An advanced 490N high performance engine has been demonstrated which, when proven to be capable of withstanding launch vibration, is ready for flight qualification.

Description: This report describes the AJ10-221, a high performance Iridium-coated Rhenium (Ir-Re) 110 lbf (490N) welded rocket chamber with 286:1 area ratio nozzle. This engine was designed, built, and hot fired for over 6 hours on this program. It demonstrated an I(s) of 321.8 sec, which is 10 sec higher than conventional 110 lbf silicide coated Cb chambers now in use. The approach used in this portion of the program was to demonstrate the performance improvement that can be made by the elimination of fuel film cooling and the use of a high temperature (4000F) (2200C) iridium-coated rhenium (Ir-Re) rocket chamber. Detailed thermal, performance, mechanical, and dynamic design analyses of the full engine were conducted by Aerojet. Two Ir-Re chambers were built to the Aerojet design by Ultramet, using the chemical vapor deposition (CVD) process. Incorporation of a secondary mixing device or Boundary Layer Trip (BLT) within the combustion chamber (Aerojet Patents 4882904 and 4936091) results in improvement in flow uniformity, and a significant life and performance increase. The 110 lbf engine design was verified in bolt-up hardware tests at sea level and altitude. The effects of injector design on performance were studied. Two duplicate injectors were fabricated matching the preferred design and were demonstrated to be interchangeable in operation. One of these units was fabricated matching the preferred design and was demonstrated to be interchangeable in operation. One of these units was welded into a flight type thruster which was tested for an accumulated duration of 22,590 sec in 93 firings, one of which was a continuous burn of two hours. A design deficiency in the C-103 nozzle near the Re-Cb transition joint was discovered, studied and corrected design has been prepared. Workhardening studies have been conducted to investigate methods for increasing the low yield strength of the Re in the annealed conditions. An advanced 490N high performance engine has been demonstrated which, when proven to be capable of withstanding launch vibration, is ready for flight qualification.

Description: This report summarizes the current JPL efforts of generating a Mars gravity field from Viking 1 and 2 and Mariner 9 Doppler tracking data. The Mars 50c solution is a complete gravity field to degree and order 50 with solutions as well for the gravitational mass of Mars, Phobos, and Deimos. The constants and models used to obtain the solution are given and the method for determining the gravity field is presented. The gravity field is compared to the best current gravity GMM1 of Goddard Space Flight Center.

Description: The Solar Dynamic (SD) Ground Test Demonstration (GTD) program demonstrates the availability of SD technologies in a simulated space environment at the NASA Lewis Research Center (LERC) vacuum facility. Data from the SD GTD program will be provided to the joint U.S. and Russian team which is currently designing a 2 kW SD flight demonstration power system. This SD technology has the potential as a future power source for the International Space Station. This paper reviews the goals and status of the SD GTD program. A description of the SD GTD system includes key design features of the system, subsystems and components.

Description: The HIPES Program was conducted for NASA-LeRC by TRW. The Basic Program consisted of system studies, design of testbed engine, fabrication and testing of engine. Studies of both pressure-fed and pump-fed systems were investigated for N2O4 and both MMH and N2H4 fuels with the result that N2H4 provides the maximum payload for all satellites over MMH. The higher pressure engine offers improved performance with smaller envelope and associated weight savings. Pump-fed systems offer maximum payload for large and medium weight satellites while pressure-fed systems offer maximum payload for small light weight satellites. The major benefits of HIPES are high performance within a confined length maximizing payload for lightsats which are length (volume) constrained. Three types of thrust chambers were evaluated -- Copper heatsink at 400, 500 and 600 psia chamber pressures for performance/thermal; water cooled to determine heat absorbed to predict rhenium engine operation; and rhenium to validate the concept. The HIPES engine demonstrated very high performance at 50 lbf thrust (epsilon = 150) and Pc = 500 psia with both fuels: Isp = 337 sec using N2O4-N2H4 and ISP = 327.5 sec using N2O4-MMH indicating combustion efficiencies greater than 98%. A powder metallurgy rhenium engine demonstrated operation with high performance at Pc = 500 psia which indicated the viability of the concept.

Description: Substantial evidence suggests that a UV (ultraviolet) Spectrally Absorbing Material (UV-SAM) exists on Triton's surface. This evidence is found in the positive slope in Triton's spectrum from the UV to the near-IR, and the increasing contrast in Triton's light curve in the blue and UV. Although it is now widely-thought that UV-SAM's exist on Triton, little is known about their distribution and spectral properties. The goal of this NDAP Project is to determine the spatial distribution and geological context of the UV-SAM material. We hope to determine if UV-SAM's on Triton are correlated with geologic wind streaks, craters, calderas, geomorphic/topographic units, regions containing (or lacking) volatile frosts, or some other process (e.g., magnetospheric interactions). Once the location and distribution of UV-SAM's has been determined, further constraints on their composition can be made by analyzing the spectrographic data set. To accomplish these goals, various data sets will be used, including Voyager 2 UV and visible images of Triton's surface, IUE and HST spectra of Triton, and a geologic map of the surface based on Voyager 2 and spectrophotometric data. The results of this research will be published in the planetary science literature.

Description: High resolution numerical simulations of thermal convection in a rapidly rotating channel with gravity perpendicular to the rotation vector are described. The convecting columns are subject to a beta-effect resulting from cross-channel topographic vortex stretching. The symmetries of the problem allow many invariant wavenumber sets, and this property is associated with the existence of stable multiple-equilibria at modest supercriticality. The transition to chaotic behavior involves the production of intermittent unstable orbits off a two-torus in energy space. At very high Rayleigh number (of order 10(exp 6) to 10(exp 7)) the motion can be turbulent, depending on the size of beta. However, the turbulence is usually characterized by an almost-periodic formation of patches of small scale convection that cause regular pulsations in the accompanying strong zonal jets. The processes maintaining these flows may be related to those responsible for the zonal currents on Jupiter and for cyclic variability on the Sun.

Description: The computation of flows within interconnected, multiple-disk cavities shows strong interaction between the cavities and the power stream. For this reason, simulations of single cavities in such cases are not realistic; the complete, linked configuration must be considered. Unsteady flow fields affect engine stability and can engender power-stream-driven secondary flows that produce local hot spotting or general cavity heating. Further, a concentric whirling rotor produces a circumferential pressure wave, but a statically eccentric whirling rotor produces a radial wave; both waves affect cavity ingestion and the stability of the entire engine. It is strongly suggested that seals be used to enhance turbojet engine stability. Simple devices, such as swirl brakes, honeycomb inserts, and new seal configurations, should be considered. The cost effectiveness of the NASA Lewis Research Center seals program can be expressed in terms of program goals (e.g., the Integrated High-pressure/Temperature Engine Technology (IHPTET) cannot be achieved without such a program), cost (savings to $250 million/1-percent decrease in specific fuel consumption), and indirect benefits (reduction of atmospheric NO(x) and CO2 and reduction of powerplant downtime).

Description: Several failures in the electrical wiring systems of many aircraft and space vehicles have been attributed to arc tracking and damaged insulation. In some instances, these failures proved to be very costly as they have led to the loss of many aircraft and imperilment of space missions. Efforts are currently underway to develop lightweight, reliable, and arc track resistant wiring for aerospace applications. In this work, six wiring constructions were evaluated in terms of their breakdown behavior as a function of temperature. These hybrid constructions employed insulation consisting of Kapton, Teflon, and cross-linked Tefzel. The properties investigated included the 400 Hz AC dielectric strength at ambient and 200 C, and the lifetime at high temperature with an applied bias of 40, 60, and 80% of breakdown voltage level. The results obtained are discussed, and conclusions are made concerning the suitability of the wiring constructions investigated for aerospace applications.

Description: This report describes the results from the geologic mapping of the central and southern Argyre basin of Mars. At the Mars Geologic Mapper's Meeting in Flagstaff during July, 1993, Dave Scott (United States Geological Survey, Mars Geologic Mapping Steering Committee Chair) recommended that all four quadrangles be combined into a single 1:1,000,000 scale map for publication. It was agreed that this would be cost-effective and that the decrease in scale would not compromise the original science goals of the mapping. Tim Parker completed mapping on the 1:500,000 scale base maps, for which all the necessary materials had already been produced, and included the work as a chapter in his dissertation, which was completed in the fall of 1994. Geologic mapping of the two southernmost quadrangles (MTM -55036 and MTM -55043; MTM=Mars Transverse Mercator) was completed as planned during the first year of work. These maps and a detailed draft of the map text were given a preliminary review by Dave Scott during summer, 1993. Geologic mapping of the remaining two quadrangles (MTM -50036 and MTM -50043) was completed by summer, 1994. Results were described at the Mars Geologic Mappers Meeting, held in Pocatello, Idaho, during July, 1994. Funds for the third and final year of the project have been transferred to the Jet Propulsion Laboratory, where Tim Parker will revise and finalize all maps and map text for publication by the United States Geological Survey at the 1:1,000,000 map scale.

Description: The Space Shuttle main engine (SSME) alternate high-pressure liquid oxygen pump experienced synchronous vibration and ball bearing life problems that were program threatening. The success of the program hinged on the ability to solve these development problems. The design and solutions to these problems are engirded in the lessons learned and experiences from prior programs, technology programs, and the ability to properly conduct failure or anomaly investigations. The failure investigation determines the problem cause and is the basis for recommending design solutions. For a complex problem, a comprehensive solution requires that formal investigation procedures be used, including fault trees, resolution logic, and action items worked through a concurrent engineering-multidiscipline team. The normal tendency to use an intuitive, cut-and-try approach will usually prove to be costly, both in money and time and will reach a less than optimum, poorly understood answer. The SSME alternate high-pressure oxidizer turbopump development has had two complex problems critical to program success: (1) high synchronous vibrations and (2) excessive ball bearing wear. This paper will use these two problems as examples of this formal failure investigation approach. The results of the team's investigation provides insight into the complexity of the turbomachinery technical discipline interacting/sensitivities and the fine balance of competing investigations required to solve problems and guarantee program success. It is very important to the solution process that maximum use be made of the resources that both the contractor and Government can bring to the problem in a supporting and noncompeting way. There is no place for the not-invented-here attitude. The resources include, but are not limited to: (1) specially skilled professionals; (2) supporting technologies; (3) computational codes and capabilities; and (4) test and manufacturing facilities.

Description: An assessment of engine and component health is routinely made after each test or flight firing of a space shuttle main engine (SSME). Currently, this health assessment is done by teams of engineers who manually review sensor data, performance data, and engine and component operating histories. Based on review of information from these various sources, an evaluation is made as to the health of each component of the SSME and the preparedness of the engine for another test or flight. The objective of this project is to further develop a computer program which automates the analysis of test data from the SSME high-pressure oxidizer turbopump (HPOTP) in order to detect and diagnose anomalies. This program fits into a larger system, the SSME Post-Test Diagnostic System (PTDS), which will eventually be extended to assess the health and status of most SSME components on the basis of test data analysis. The HPOTP module is an expert system, which uses 'rules-of-thumb' obtained from interviews with experts from NASA Marshall Space Flight Center (MSFC) to detect and diagnose anomalies. Analyses of the raw test data are first performed using pattern recognition techniques which result in features such as spikes, shifts, peaks, and drifts being detected and written to a database. The HPOTP module then looks for combination of these features which are indicative of known anomalies, using the rules gathered from the turbomachinery experts. Results of this analysis are then displayed via a graphical user interface which provides ranked lists of anomalies and observations by engine component, along with supporting data plots for each.

Description: A Navier-Stokes code, finite difference Navier-Stokes (FDNS), is used to analyze the complicated internal flowfield of the SRM (solid rocket motor) to explore the impacts due to the effects of chemical reaction, particle dynamics, and slag accumulation on the solid rocket motor (SRM). The particulate multi-phase flowfield with chemical reaction, particle evaporation, combustion, breakup, and agglomeration models are included in present study to obtain a better understanding of the SRM design. Finite rate chemistry model is applied to simulate the chemical reaction effects. Hermsen correlation model is used for the combustion simulation. The evaporation model introduced by Spalding is utilized to include the heat transfer from the particulate phase to the gase phase due to the evaporation of the particles. A correlation of the minimum particle size for breakup expressed in terms of the Al/Al2O3 surface tension and shear force was employed to simulate the breakup of particles. It is assumed that the breakup occurs when the Weber number exceeds 6. A simple L agglomeration model is used to investigate the particle agglomeration. However, due to the large computer memory requirements for the agglomeration model, only 2D cases are tested with the agglomeration model. The VOF (Volume of Fluid) method is employed to simulate the slag buildup in the aft-end cavity of the redesigned solid rocket motor (RSRM). Monte Carlo method is employed to calculate the turbulent dispersion effect of the particles. The flowfield analysis obtained using the FDNS code in the present research with finite rate chemical reaction, particle evaporation, combustion, breakup, agglomeration, and VOG models will provide a design guide for the potential improvement of the SRM including the use of materials and the shape of nozzle geometry such that a better performance of the SRM can be achieved. The simulation of the slag buildup in the aft-end cavity can assist the designer to improve the design of the RSRM geometry.

Description: The Magellan radar-mapping mission collected a large amount of science and engineering data. Now available to the general scientific community, this data set can be overwhelming to someone who is unfamiliar with the mission. This user guide outlines the mission operations and data set so that someone working with the data can understand the mapping and data-processing techniques used in the mission. Radar-mapping parameters as well as data acquisition issues are discussed. In addition, this user guide provides information on how the data set is organized and where specific elements of the set can be located.

Description: The Martian regolith is the most substantial volatile reservoir on the planet; estimates of its adsorbed inventory have been based on simple measurements of the adsorption of either water or CO2 in isolation. Under some conditions, H2O can poison adsorbate surfaces, such that CO2 uptake is greatly reduced. We have made the first measurements of the simultaneous adsorption of CO2 and H2O under conditions appropriate to the Martian regolith and have found that at H2O monolayer coverage above about 0.5, CO2 begins to be displaced into the gas phase. We have developed an empirical expression that describes our co-adsorption data and have applied it to standard models of the Martian regolith. We find that currently, H2O does not substantially displace CO2, implying that the adsorbate inventories previously derived may be accurate, not more than 3-4 kPa (30-40 mbar). No substantial increase in atmospheric pressure is predicted at higher obliquities because high-latitude ground ice buffers the partial pressure of H2O in the pores, preventing high monolayer coverages of H2O from displacing CO2. The peak atmospheric pressure at high obliquity does increase as the total inventory of exchangeable CO2 increases.

Description: We present plasma, magnetic field, and electric field data of the Pioneer Venus Orbiter (PVO) showing that the shocked solar wind in the Venus inner ionosheath exhibits flow conditions substantially different from those in the outer ionosheath. In particular, the plasma density is seen to drop significantly to low values within a layer adjacent to, and downstream from, the planet's ionopause. This change is not seen to develop gradually as the PVO moves into that region of space but occurs abruptly across a well-defined transition which extends downstream along the flanks of the Venus ionosheath. We explore the implications that these observations have in regard to the character of the interaction process between the shocked solar wind and the ionospheric plasma. It is argued that the existence of a sharply bounded region in the inner ionosheath within which the plasma density is severely depressed is consistent with the existence of friction at and near the ionopause. Plasma perturbations generated at this latter boundary, and distributed downstream through the ionosheath flow, may be responsible for the change of properties exhibited by the solar wind plasma in the inner ionosheath.

Description: Statistical studies of the VLF bursts detected in the nightside ionosphere of Venus show that the bursts fall into two classes. The first consists of signals detected when vertical propagation within the whistler-mode resonance cone is allowed. The second consists of signals whose burst rate decreases rapidly as a function of increasing altitude, with a scale height of about 20 km. These non-whistler-mode signals also display a strong dependence on local time, with the burst rates being largest in the post-dusk local time sector. Since these signals are not propagating we assume that they correspond to a 'near-field' or prompt response to a lightning stroke. As such we can use these signals to estimate the planetary lightning rate, and we find that the rate at Venus is comparable to or greater than the terrestrial planetary rate of 100 flashes/sec.

Description: Solar electric propulsion (SEP) technology is currently being used for geostationary satellite station keeping to increase payload mass. Analyses show that advanced electric propulsion technologies can be used to obtain additional increases in payload mass by using these same technologies to perform part of the orbit transfer. In this work three electric propulsion technologies are examined at two power levels for an Atlas 2AS class spacecraft. The on-board chemical propulsion apogee engine fuel is reduced to allow the use of electric propulsion. A numerical optimizer is used to determine the chemical burns which will minimize the electric propulsion transfer time. Results show that for a 1550 kg Atlas 2AS class payload, increases in net mass (geostationary satellite mass less wet propulsion system mass) of 150 to 800 kg are possible using electric propulsion for station keeping, advanced chemical engines for part of the transfer, and electric propulsion for the remainder of the transfer. Trip times are between one and four months.

Description: In this study, we sought to characterize variations in the abundance and distribution of subcloud H2SO4(g) in the Venus atmosphere by using a number of 13cm radio occultation measurements conducted with the Pioneer Venus Orbiter near the inferior conjunction of 1991. A total of ten data sets were examined and analyzed, producing vertical profiles of temperature and pressure in the neutral atmosphere, and sulfuric acid vapor abundance below the main cloud layer. Two of the vertical profiles of the abundance of H2SO4(g) were correlated with NIR images of the night side of Venus made during the same period of time by Boris Ragent (under a separate PVO Guest Investigator Grant). Initially, we had hoped that the combination of these two different types of data would make it possible to constrain or identify the composition of the large particles causing the features observed in the NIR images. However, the sparseness of the radio occultation data set, combined with the sparseness of the NIR data set (one image per day over an 8 day period) made it impossible to draw strong conclusions. Considered on their own, however, the parameters retrieved from the radio occultation experiments are valuable science products.

Description: The results of an experimental investigation on the combined effects of cooling channel aspect ratio and curvature for rocket engines are presented. Symmetrically heated tubes with average heat fluxes up to 1.7 MW/m(exp 2) were used. The coolant was gaseous nitrogen at an inlet temperature of 280 K (500 R) and inlet pressures up to 1.0 x 10(exp 7) N/m(exp 2) (1500 psia). Two different tube geometries were tested: a straight, circular cross-section tube, and an aspect-ratio 10 cross-section tube with a 45 deg bend. The circular tube results are compared to classical models from the literature as validation of the system. The curvature effect data from the curved aspect-ratio 10 tube compare favorably to the empirical equations available in the literature for low aspect ratio tubes. This latter results suggest that thermal stratification of the coolant due to diminished curvature effect mixing may not be an issue for high aspect-ratio cooling channels.

Description: The Supplemental Multilayer Insulation Research Facility (SMIRF) provides a small scale test bed for conducting cryogenic experiments in a vacuum environment. The facility vacuum system is capable of simulating a Space Shuttle launch pressure profile as well as providing a steady space vacuum environment of 1.3 x 10(exp -4) Newton/sq meter (1 x 10(exp -6) torr). Warm side boundary temperatures can be maintained constant between 111 K (200 R) and 361 K (650 R) using a temperature controlled shroud. The shroud can also simulate a typical lunar day-night temperature profile. The test hardware consists of a cryogenic calorimeter supported by the lid of the vacuum chamber. A 0.45 cu meter (120 gallon) vacuum jacketed storage/supply tank is available for conditioning the cryogen prior to use in the calorimeter. The facility was initially designed to evaluate the thermal performance of insulation systems for long-term storage in space. The facility has recently been used to evaluate the performance of various new insulation systems for LH2 and LN2 ground storage dewars.

Description: A workshop was convened at Ames Research Center on September 28 and 29, 1993, to address the unexplained electrical anomalies experienced in December 1978 by the four Pioneer Venus probes below a Venus altitude of 12.5 km. These anomalies caused the loss of valuable data in the deep atmosphere, and, if their cause were to remain unexplained, could reoccur on future Venus missions. The workshop participants reviewed the evidence and studied all identified mechanisms that could consistently account for all observed anomalies. Both hardware problems and atmospheric interactions were considered. Based on a workshop recommendation, subsequent testing identified the cause as being an insulation failure of the external harness. All anomalous events are now explained.

Description: This paper describes the Orbiting Spacecraft Shadowing Analysis (OSSA) computer program that was developed at NASA Lewis Research Center in order to assess the shadowing effects on various power systems. The algorithms, inputs and outputs are discussed. Examples of typical shadowing analyses that have been performed for the International Space Station Freedom, International Space Station Alpha and the joint United States/Russian Mir Solar Dynamic Flight Experiment Project are covered. Effects of shadowing on power systems are demonstrated.

Description: Experimental data from several test series are compared to an existing correlation that predicts the amount of pressurant gas mass required to expel liquid hydrogen from axisymmetric tanks. It was necessary to use an alternate definition of the tank equivalent diameter to accommodate thermal mass in the tank wall that is initially warm and to accommodate liquid residuals in the tank after expulsion is stopped. With this modification, the existing correlation predicted mass requirements to within 14 percent of experimental results. Revision of the correlation constants using a nonlinear least-squares fit of the current experimental data has a minor effect, thus supporting the validity of the original correlation's form, its fitted constants, and the alternate definition of the tank equivalent diameter.

Description: A fully-instrumented firing of a propulsion system typically generates a very large quantity of data. In the case of the Space Shuttle Main Engine (SSME), data analysis from ground tests and flights is currently a labor-intensive process. Human experts spend a great deal of time examining the large volume of sensor data generated by each engine firing. These experts look for any anomalies in the data which might indicate engine conditions warranting further investigation. The contract effort was to develop a 'first-cut' screening system for application to SSME engine firings that would identify the relatively small volume of data which is unusual or anomalous in some way. With such a system, limited and expensive human resources could focus on this small volume of unusual data for thorough analysis. The overall project objective was to develop a fully operational Automated Propulsion Data Screening (APDS) system with the capability of detecting significant trends and anomalies in transient and steady-state data. However, the effort limited screening of transient data to ground test data for throttle-down cases typical of the 3-g acceleration, and for engine throttling required to reach the maximum dynamic pressure limits imposed on the Space Shuttle. This APDS is based on neural networks designed to detect anomalies in propulsion system data that are not part of the data used for neural network training. The delivered system allows engineers to build their own screening sets for application to completed or planned firings of the SSME. ERC developers also built some generic screening sets that NASA engineers could apply immediately to their data analysis efforts.

Description: RL10A-3-3A rocket engines have served as the main propulsion system for Centaur upper stage vehicles since the early 1980's. This hydrogen/oxygen expander cycle engine continues to play a major role in the American launch industry. The Space Propulsion Technology Division at the NASA Lewis Research Center has created a computer model of the RL10 engine, based on detailed component analyses and available test data. This RL10 engine model can predict the performance of the engine over a wide range of operating conditions. The model may also be used to predict the effects of any proposed design changes and anticipated failure scenarios. In this paper, the results of the component analyses are discussed. Simulation results from the new system model are compared with engine test and flight data, including the start and shut-down transient characteristics.

Description: The NASA Lewis Research Center is currently working with RSC-Energia, the Russian Space Agency, and Allied Signal in developing a flight demonstration solar dynamic power system. This type of power system is dependent upon solar flux that is reflected and concentrated into a thermal storage system to provide the thermal energy input to a closed-cycle Brayton heat engine. The solar dynamic unit will be flown on the Russian Mir space station in anticipation of use on the International Space Station Alpha. By the time the power system is launched, the Mir will be a spatially complex configuration which will have, in addition to the three-gimbaled solar dynamic unit, eleven solar array wings that are either fixed or track the Sun along one axis and a variety or repositionable habitation and experiment modules. The proximity of arrays to modules creates a situation which makes it highly probable that there will be varying solar flux due to shadowing on the solar dynamic unit and some of the arrays throughout the orbit. Shadowing causes fluctuations in the power output from the arrays and the solar dynamic power system, thus reducing the energy capabilities of the spacecraft. An assessment of the capabilities of the power system under these conditions is an important part in influencing the design and operations of the spacecraft and predicting its energy performance. This paper describes the results obtained from using the Orbiting Spacecraft Shadowing Analysis Station program that was integrated into the Station Power Analysis for Capability Evaluation (SPACE) electrical power system computer program. OSSA allows one to consider the numerous complex factors for analyzing the shadowing effects on the electrical power system including the variety of spacecraft hardware geometric configurations, yearly and daily orbital variations in the vehicle attitude and orbital maneuvers (for communications coverage, payload pointing requirements and rendezvous/docking with other vehicles). The geometric models of the MIR with a solar dynamic power unit that were used in performing shadowing analyses are described. Also presented in this paper are results for individual orbits for several flight attitude cases which include assessments of the shadowing impacts upon the solar dynamic unit and the solar arrays. These cases depict typical MIR flight attitudes likely to have shadowing impact. Because of the time varying nature of the Mir orientation with respect to the Sun and the lack of knowledge of the precise timing of the attitude changes, strategies must be devised to assess and depict the shadowing impacts on power generation throughout the year. To address this, the best, nominal and worst impacts of shadowing considering a wide possible range of parameter changes for typical mission operation period are shown.

Description: The United States and Russia have agreed to jointly develop a solar dynamic (SD) system for flight demonstration on the Russian MIR space station starting in late 1997. Two important components of this SD system are the solar concentrator and heat receiver provided by Russia and the U.S., respectively. This paper describes optical analysis of the concentrator and solar flux predictions on target receiver surfaces. The optical analysis is performed using the code CIRCE2. These analyses account for finite sun size with limb darkening, concentrator surface slope and position errors, concentrator petal thermal deformation, gaps between petals, and the shading effect of the receiver support struts. The receiver spatial flux distributions are then combined with concentrator shadowing predictions. Geometric shadowing patterns are traced from the concentrator to the target receiver surfaces. These patterns vary with time depending on the chosen MIR flight attitude and orbital mechanics of the MIR spacecraft. The resulting predictions provide spatial and temporal receiver flux distributions for any specified mission profile. The impact these flux distributions have on receiver design and control of the Brayton engine are discussed.

Description: Ignition testing of hollow cathode assemblies being developed for the Space Station plasma contactor system has been initiated to validate reliable multiple restart capability. An ignition approach was implemented that was derived from an earlier arcjet program that successfully demonstrated over 11,600 ignitions. For this, a test profile was developed to allow accelerated cyclic testing at expected operating conditions. To date, one hollow cathode assembly has been used to demonstrate multiple ignitions. A prototype hollow cathode assembly has achieved 3,615 successful ignitions at a nominal anode voltage of 18.0 V. During the ignition testing several parameters were investigated, of which the heater power and pre-heat time were the only parameters found to significantly impact ignition rate.

Description: Power processing units (PPU's) in an electric propulsion system provide many challenging integration issues. The PPU must provide power to the electric thruster while maintaining compatibility with all of the spacecraft power and data systems. Inefficiencies in the power processor produce heat, which must be radiated to the environment in order to ensure reliable operation. Although PPU efficiencies are generally greater than 0.9, heat loads are often substantial. This heat must be rejected by thermal control systems which generally have specific masses of 15-30 kg/kW. PPU's also represent a large fraction of the electric propulsion system dry mass. Simplification or elimination of power processing in a propulsion system would reduce the electric propulsion system specific mass and improve the overall reliability and performance. A direct drive system would eliminate all or some of the power supplies required to operate a thruster by directly connecting the various thruster loads to the solar array. The development of concentrator solar arrays has enabled power bus voltages in excess of 300 V which is high enough for direct drive applications for Hall thrusters such as the Stationary Plasma Thruster (SPT). The option of solar array direct drive for SPT's is explored to provide a comparison between conventional and direct drive system mass.

Description: Solar electric propulsion (SEP) technology is already being used for geostationary satellite stationkeeping to increase payload mass. By using this same technology to perform part of the orbit transfer additional increases in payload mass can be achieved. Advanced chemical and N2H4 arcjet systems are used to increase the payload mass by performing stationkeeping and part of the orbit transfer. Four mission options are analyzed which show the impact of either sharing the orbit transfer between chemical and SEP systems or having either complete the transfer alone. Results show that for an Atlas 2AS payload increases in net mass (geostationary satellite mass less wet propulsion system mass) of up to 100 kg can be achieved using advanced chemical for the transfer and advanced N2H4 arcjets for stationkeeping. An additional 100 kg can be added using advanced N2H4 arcjets for part of a 40 day orbit transfer.

Description: The general objective for this work was to develop a theoretically and experimentally consistent explanation for the diffuse component of radar backscatter from Mars. The strength, variability, and wavelength independence of Mars' diffuse backscatter are unique among our Moon and the terrestrial planets. This diffuse backscatter is generally attributed to wavelength-scale surface roughness and to rock clasts within the Martian regolith. Through the combination of theory and experiment, the authors attempted to bound the range of surface characteristics that could produce the observed diffuse backscatter. Through these bounds they gained a limited capability for data inversion. Within this umbrella, specific objectives were: (1) To better define the statistical roughness parameters of Mars' surface so that they are consistent with observed radar backscatter data, and with the physical and chemical characteristics of Mars' surface as inferred from Mariner 9, the Viking probes, and Earth-based spectroscopy; (2) To better understand the partitioning between surface and volume scattering in the Mars regolith; (3) To develop computational models of Mars' radio emission that incorporate frequency dependent, surface and volume scattering.

Description: In this period of performance a conference (The 1994 Conference on Advanced Earth-to-Orbit Propulsion Technology) was organized and implemented by the University of Alabama in Huntsville and held May 15-17 to assemble and disseminate the current information on Advanced Earth-to-Orbit Propulsion Technology. The results were assembled for publication as NASA-CP-3282, Volume 1 and 2 and NASA-CP-3287.

Description: This paper on nickel hydrogen batteries is an overview of the various nickel hydrogen battery design options, technical accomplishments, validation test results and trends. There is more than one nickel hydrogen battery design, each having its advantage for specific applications. The major battery designs are individual pressure vessel (IPV), common pressure vessel (CPV), bipolar and low pressure metal hydride. State-of-the-art (SOA) nickel hydrogen batteries are replacing nickel cadmium batteries in almost all geosynchronous orbit (GEO) applications requiring power above 1 kW. However, for the more severe low earth orbit (LEO) applications (greater than 30,000 cycles), the current cycle life of 4000 to 10,000 cycles at 60 percent DOD should be improved. A NASA Lewis Research Center innovative advanced design IPV nickel hydrogen cell led to a breakthrough in cycle life enabling LEO applications at deep depths of discharge (DOD). A trend for some future satellites is to increase the power level to greater than 6 kW. Another trend is to decrease the power to less than 1 kW for small low cost satellites. Hence, the challenge is to reduce battery mass, volume and cost. A key is to develop a light weight nickel electrode and alternate battery designs. A common pressure vessel (CPV) nickel hydrogen battery is emerging as a viable alternative to the IPV design. It has the advantage of reduced mass, volume and manufacturing costs. A 10 Ah CPV battery has successfully provided power on the relatively short lived Clementine Spacecraft. A bipolar nickel hydrogen battery design has been demonstrated (15,000 LEO cycles, 40 percent DOD). The advantage is also a significant reduction in volume, a modest reduction in mass, and like most bipolar designs, features a high pulse power capability. A low pressure aerospace nickel metal hydride battery cell has been developed and is on the market. It is a prismatic design which has the advantage of a significant reduction in volume and a reduction in manufacturing cost.

Description: Three primary issues will drive the design and control used in next generation reuseable rocket engines. In addition to steady-state and dynamic performance, the requirements for increased durability, reliability and operability (with faults) will dictate which new controls and design technologies and features will be brought to bear. An array of concepts which have been brought forward will be tested against the measures of cost and benefit as reflected in the above 'ilities'. This paper examines some of the new concepts and looks for metrics to judge their value.

Description: In separate series of YT-700 engine tests, direct comparisons were made between the forward-facing labyrinth and dual brush compressor discharge seals. Compressor speeds to 43 000 rpm, surface speeds to 160 m/s (530 ft/s), pressures to 1 MPa (145 psi), and temperatures to 680 K (765 F) characterized these tests. The wear estimate for 46 hr of engine operations was less than 0.025 mm (0.001 in.) of the Haynes 25 alloy bristles running against a chromium-carbide-coated rub runner. The pressure drops were higher for the dual-brush seal than for the forward-facing labyrinth seal and leakage was lower-with the labyrinth seal leakage being 2-1/2 times greater-implying better seal characteristics, better secondary airflow distribution, and better engine performance (3 percent at high pressure to 5 percent at lower pressure) for the brush seal. (However, as brush seals wear down (after 500 to 1000 hr of engine operation), their leakage rates will increase.) Modification of the secondary flow path requires that changes in cooling air and engine dynamics be accounted for.

Description: The objectives of the research are to measure low temperature laboratory rate coefficients for key reactions relevant to the atmospheres of Titan and Saturn. These reactions are, for example, C2H + H2, CH4, C2H2, and other hydrocarbons which need to be measured at low temperatures, down to approximately 150 K. The results of this work are provided to NASA specialists who study modeling of the hydrocarbon chemistry of the outer planets. The apparatus for this work consists of a pulsed laser photolysis system and a tunable F-center probe laser to monitor the disappearance of C2H. A low temperature cell with a cryogenic circulating fluid in the outer jacket provides the gas handling system for this work. These elements have been described in detail in previous reports. Several new results are completed and the publications are just being prepared. The reaction of C2H with C2H2 has been measured with an improved apparatus down to 154 K. An Arrhenius plot indicates a clear increase in the rate coefficient at the lowest temperatures, most likely because of the long-lived (C4H3) intermediate. The capability to achieve the lowest temperatures in this work was made possible by construction of a new cell and addition of a multipass arrangement for the probe laser, as well as improvements to the laser system.

Description: Laser and optical emission-based measurements have been developed and implemented for use on low-power hydrogen arcjet thrusters and xenon-propelled electric thrusters. In the case of low power hydrogen arcjets, these laser induce fluorescence measurements constitute the first complete set of data that characterize the velocity and temperature field of such a device. The research performed under the auspices of this NASA grant includes laser-based measurements of atomic hydrogen velocity and translational temperature, ultraviolet absorption measurements of ground state atomic hydrogen, Raman scattering measurements of the electronic ground state of molecular hydrogen, and optical emission based measurements of electronically excited atomic hydrogen, electron number density, and electron temperature. In addition, we have developed a collisional-radiative model of atomic hydrogen for use in conjunction with magnetohydrodynamic models to predict the plasma radiative spectrum, and near-electrode plasma models to better understand current transfer from the electrodes to the plasma. In the final year of the grant, a new program aimed at developing diagnostics for xenon plasma thrusters was initiated, and results on the use of diode lasers for interrogating Hall accelerator plasmas has been presented at recent conferences.

Description: We report on further studies of radio wave bursts detected by the Orbiting Electric Field Detector (OEFD) on the Pioneer Venus Orbiter (PVO) in the nightside ionosphere of Venus. We have tested a total of 25 cases of wave burst activity for evidence of whistler-mode propagation to the spacecraft from impulsive subionospheric sources. As in a previous study of 11 of these cases (Sonwalkar et al., 1991) we find at least two distinct classes of events, one, mostly involving bursts at 100 Hz only, that passes certain tests for whistler-mode propagation, and another, mostly involving bursts in two or more of the four PVO narrowband channels (at 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz), that fails to pass the tests. The subionospheric lightning hypothesis continues to be tenable as a candidate explanation for many of the 100 Hz-only events, but its number of 100 Hz-only cases that do no pass all the applicable whistler-mode tests, as well as the existence at a wide range of altitudes of multichannel cases that are clearly not propagating whistler-mode waves. The wideband bursts are often observed at altitudes above 1000 km and frequently occur in regions of locally reduced electron density. Those observed at high altitude (and possibly low altitude as well) are believed to be generated near the spacecraft, possibly by an as yet unknown mechanism responsible for similar burst observations made near Earth and other planets.

Description: Plasma wave data from the Pioneer Venus Orbiter provide the largest body of data cited as evidence for lightning on Venus. These data are also the most controversial, mainly because of the ambiguity in mode identification due to limited spectral information. We review some of the more recent studies of the plasma wave data at Venus, and we demonstrate that the characteristics of the 100 Hz waves are consistent with whistler-mode waves propagating vertically from below the ionosphere. We further show that in situ instabilities are too weak to generate whistler-mode waves, mainly because the thermal pressure is comparable with the magnetic field pressure in the ionosphere of Venus. The lower hybrid drift instability has also been suggested as an alternative source for the 100 Hz waves. However, the wave properties are more consistent with whistler-mode propagation; the lower hybrid dirft instability requires very short gradient scale lengths to overcome damping due to collisions. We also note that an apparent association between Langmuir probe anomalies and 100 Hz waves is much lower than previously reported, once we apply a consistent intensity threshold for identifying wave bursts. The lightning hyposthesis remains the most probable explanation of the plasma waves detected at low altitudes in the nightside ionosphere of Venus.

Description: Very low frequency (VLF) signals detected in the nightside ionosphere of Venus have generally been attributed to atmospheric lightning. However it has recently been suggested that these bursts could be generated by either whistler-mode or lower hybrid drift instabilities. It has previously been shown that the growth rate for whistler-mode instabilities in the nightside ionosphere is too small for appreciable growth at altitudes less than 200 km, where the VLF burst rate is highest. We show that the bursts are usually observed in regions of low electron beta, where whistler-mode attenuation is small. We further show that many of the bursts are detected in regions of high collision frequency, which stabilizes the lower hybrid drift instability. Lastly, the waves are also detected in regions where the wavelength required for Doppler-shift of lower hybrid waves to 100 Hz is shorter than the electron Larmor radius, which also argues against a lower hybrid drift instability. Planetary lightning is consequently a more likely source for the VLF bursts.