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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1949

Investigation of Stability and Control Characteristics of a 1/10-scale Model of a Canadian Tailless Glider in the Langley Free-flight Tunnel

An investigation of the stability and control characteristics of a 1/10-scale model of a Canadian tailless glider has been conducted in the 10 Langley free-flight tunnel. The glider designated the N.R.L. tailless glider has a straight center section and outboard panels sweptback 43 deg. along the leading edge of the wing. The aspect ratio is 5.83 and the taper ratio is 0.323. From the results of the investigation and on the basis of comparison with higher-scale static tests of the National Research Council of Canada, it is expected that the longitudinal stability of the airplane will be satisfactory with flap up but unsatisfactory near the stall with flap down. The airplane is expected to have unsatisfactory lateral stability and control characteristics in the design configuration with either flap up or flap down. The model flights showed very low damping of the lateral oscillation. Increasing the vertical-tail area improved the lateral stability, and it appeared that a value of the directional-stability parameter C(sub n beta) of at least 0.002 per degree would probably be necessary for satisfactory lateral flying characteristics. A comparison of the calculated dynamic lateral stability characteristics of the N.R.L. tailless glider with those of a conventional-type sweptback airplane having a similar wing plan form and about the same inclination of the principal longitudinal axis of inertia showed that the tailless glider had poorer lateral stability because of the relatively larger radius of gyration in roll and the smaller damping-in-yaw factor C(sub nr).

Johnson, Joseph L.↗
NASA NTRS1982

Calculation of a mirror asymmetric effect in electron scattering from chiral targets

A dynamical calculation is presented of the helicity induced in an initially unpolarized electron beam after elastic scattering from an optically active medium, a process analogous to the circular polarization induced in unpolarized light following Rayleigh scattering from chiral targets. The calculation is based on the bound helical electron model of a chiral molecule, according to which the major contribution to the helicity is provided by the perturbation of the electron bound state by the spin-orbit interaction of the bound electrons moving in the electric field of the molecular core. The net helicity acquired is found to depend directly on a molecular asymmetry factor and the square of the atomic number of the heaviest atom in an asymmetric environment. For the case of carbon, the induced helicity is on the order of 0.00001, which would account for its lack of observation in a recent experiment. Results may have implications for the origin of optical activity in biological molecules by the differential ionization of D and L isomers by beta-decay electrons.

Rich, A.↗
NASA NTRS1998

The Sun and the Solar Wind Close to the Sun

The structure of the solar corona is directly reflected in the structure of the solar wind. But, the importance of this simple observation to coronal modeling has become much greater with the arrival of results from Ulysses and SOHO. High speed wind is relatively smooth and uniform (Ulysses) but the coronal holes from which it comes contain highly filamented flows that expand in area by factors of two to sevenfold between the solar surface and 10 solar radii (SOHO). Different models of the relationship between solar and interplanetary magnetic fields produce similar predictions and are still being reconciled. Slow wind seems to come from the boundaries of streamers (Ulysses) by a process which is even less well understood. Again, there are different ideas for the leakage of slow wind from streamers but these models are quickly becoming highly constrained by new data on composition in the core and boundaries of streamers (SOHO). Perhaps the most significant conclusion is that there is a changing paradigm for the processes governing solar wind acceleration and energy flow, one that requires the presence of filamented, energetic, transient flows in a low-beta plasma close to the Sun that become mixed to produce the evolving turbulent MHD plasma that Is observed in the interplanetary medium.

Suess, S. T.↗
NASA NTRS1984

Ultraviolet and visible flare observations of EQ Pegasi B

EQ Peg AB (dM43+dM5.5e) was monitored in the visible at the Whipple Observatory and ultraviolet with IUE on September 2, 1981. In the visible spectrophotometry of EQ Peg B the H-beta emission strengthened by a factor of 2 relative to the nearby stellar continuum within a few minutes and decayed over an hour. This flare in EQ Peg B was coincident with the enhancement of ultraviolet emission lines of C IV 1550 A, He II 1640 A, and C II 1335 A in the combined light of EQ Peg AB. The ultraviolet fluxes during the flare can be interpreted as similar to those either in the thermal phases of large two-ribbon solor flares where radiative cooling balances thermal conduction or in gas cooling quickly from X-ray emitting temperatures. The appearance of the ultraviolet continuum at 1700-1900 A and ratio of H-alpha to H-beta fluxes during the flare are consistent with models producing these emissions in the chromosphere.

Baliunas, S. L.↗
NASA NTRS2002

Insulin secretion and sensitivity in space flight: diabetogenic effects

Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

Review↗
NASA NTRS2017

Vascular Patterning Analysis by VESGEN 2D/3D with Bioinformatics: Updates for Rodent Tissues

Fractally branching vascular systems are a complex physiological requirement shared by humans with all higher terrestrial life forms, including other vertebrates, insects, and higher land plants. Vascular trees, networks, and tree-network composites are therefore mapped and quantified by the VESsel GENeration Analysis (VESGEN) software according to weighted physiological vascular rules that include vessel connectivity, tapering and bifurcational branching. According to fluid dynamics, successful vascular transport depends upon a complex distributed system of highly regulated laminar flow. VESGEN has elucidated changes in vascular patterning resulting from inflammatory, developmental and other signaling pathways within numerous tissues of major model organisms important for Space Biology, especially for rodents. Important early stage regenerative opportunities have been identified by VESGEN vascular analysis for visual impairments in the human retina, and is currently being used for research into astronaut visual and ocular disorders associated with long duration missions. The VESGEN 2D software is a mature, automated, widely published capability for which beta testing and public release by NASA is planned for the upcoming year. Early-stage capabilities for VESGEN 3D analysis are under development for the rodent retina and intestine as prototype tissues. A prototype VESGEN 2D Bioinformatics software capability has also been developed to associate phenotypic changes in molecular expression with vascular structure and function. By new VESGEN bioinformatic innovations, expression patterns of the genetic, transcriptional, protein and other markers for regulatory molecules such as vascular endothelial growth factor (VEGF) and their receptors, often indicators of tissue oxygenation status, are co-localized with alterations in vascular pattern. Biomarkers are therefore mapped and quantified as information dimensions directly correlated with the spatial dimensions of a vascular pattern. Further important technology innovations by NASA include substantial image segmentation advances for more automated binary extraction of the grayscale vascular patterns, together with informative associated image quality assessments. Vascular mapping and quantification capabilities for the rodent retina and intestine are illustrated for VESGEN 2D, along with technology status reports on VESGEN 3D and Bioinformatic capabilities. Research partially supported by Ames Center Innovation Awards.

Parsons-Wingerter, P.↗
NASA NTRS2001

Physical and biological studies with protons and HZE particles in a NASA supported research center in radiation health

NASA has established and supports a specialized center for research and training (NSCORT) to specifically address the potential deleterious effects of HZE particles on human health. The NSCORT in radiation health is a joint effort between Lawrence Berkeley National Laboratory (LBNL) and Colorado State University (CSU). The overall scope of research encompasses a broad range of subjects from microdosimetric studies to cellular and tissue responses to initial damage produced by highly energetic protons and heavy charged particles of the type found in galactic cosmic rays (GCR) spectrum. The objectives of the microdosimetry studies are to determine the response of Tissue Equivalent Proportional Counter (TEPC) to cosmic rays using ground based accelerators. This includes evaluation of energy loss due to the escape of high-energy delta rays and increased energy deposition due to the enhanced delta ray production in the wall of the detector. In this report major results are presented for 56Fe at 1000, 740, 600 and 400 MeV/nucleon. An assessment of DNA repair and early development of related chromosomal changes is extremely important to our overall understanding of enhanced biological effectiveness of high LET particle radiation. Results are presented with respect to the fidelity of the rejoining of double strand breaks and the implications of misrejoining. The relationship between molecular and cytogenetic measurements is presented by studying damage processing in highly heterochromatic supernumerary (correction of sypernumerary) X chromosomes and the active X-chromosome. One of the important consequences of cell's inability to handle DNA damage can be evaluated through mutation studies. Part of our goal is the assessment of potential radioprotectors to reduce the mutation yield following HZE exposures, and some promising results are presented on one compound. A second goal is the integration of DNA repair and mutation studies. Results are presented on a direct comparison of initial double strand breaks induction, the time course and fidelity of double strand break rejoining, cell killing and mutation induction in the same human model system. In order to understand the carcinogenic potential of protons and HZE particles, the role of damaged microenvironment in this process must be understood. In this project it has been postulated that radiation affects the microenvironment, which then modifies cell interactions in a manner conducive to neoplastic progression. Both TGF-beta and FGF-2 are important components of microenvironment. A recent result on the assessment of the role of FGF-2 and its cross-talk with TGF-beta as a function of radiation quality is presented. Theoretical modeling has so far played a central role in analyzing and integrating experimental data on repair and mutation studies and predicting new phenomena. The integrated NSCORT program also provides a broad training experience for students and postdoctoral fellows in space radiation health.

NASA Discipline Radiation Health↗
NASA NTRS1994

Hot proton anisotropies and cool proton temperatures in the outer magnetosphere

The hot protons of the outer magnetosphere typically exhibit a temperature anistropy such that T(sub perp)/T(sub parallel) greater than 1, where perpendicular and parallel symbols denote directions relative to the background magnetic field. If this anisotrpy is sufficiently large, the electomagneitc proton cyclotron anistropy instability may be excited. This instability is studied using linear Vlasov theory and one-dimensional hybrid simulations for a homogeneous plasma model representative of conditions in the outer magnetosphere with a hot anisotropic proton component (denoted by subscript h) and a cool, initially isotropic proton component (subscript c). Linear theory yields an instability threshold condition on the hot proton temperature anistropy where as the simulations imply an upper bound on T(sub perp h)/T(sub parallel h); both the threshold and the upper bound have similar scaling with the maximum growth rate gamma (sub m), the parallel beta of the hot component, beta(sub parallel h), and the relative density of the hot component n(sub h)/n(sub e). An anlysis of plasma observations from the Los Alamos magnetospheric plasma analyzer (MPA) in geosynchronous orbits finds that the maximum value of the hot proton temperature anisotropy approximately satisfies the predicted scaling with beta(sub parallel h) and nu(sub h)/n(sub e) and yields the proportionality factor that quantifies this upper bound. The simulations are also used to examine the heating of the cool proton cyclotron instability. The simulations yield a scaling for the dimensionless late-time cool proton average temperature T(sub c)/T(sub parallel h) as (n(sub h)/n(sub e))/beta(sub parallel h exp 0.5). Analysis of MPA data shows that the observed values of T(sub c)/T(sub parallel h) have similar scaling and again yield the proportionality factor which quantifies this relationship.

Gary, S. Peter↗
NASA NTRS2015

Constraints on the Gas Content of the Fomalhaut Debris Belt: Can Gas-Dust Interactions Explain the Belt's Morphology?

Context. The 440 Myr old main-sequence A-star Fomalhaut is surrounded by an eccentric debris belt with sharp edges. This sort of a morphology is usually attributed to planetary perturbations, but the orbit of the only planetary candidate detected so far, Fomalhaut b, is too eccentric to efficiently shape the belt. Alternative models that could account for the morphology without invoking a planet are stellar encounters and gas-dust interactions. Aims. We aim to test the possibility of gas-dust interactions as the origin of the observed morphology by putting upper limits on the total gas content of the Fomalhaut belt. Methods. We derive upper limits on the CII158 microns and OI 63 microns emission by using non-detections from the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory. Line fluxes are converted into total gas mass using the non-local thermodynamic equilibrium (non-LTE) code radex. We consider two different cases for the elemental abundances of the gas: solar abundances and abundances similar to those observed for the gas in the Beta Pictoris debris disc. Results. The gas mass is shown to be below the millimetre dust mass by a factor of at least approx. 3 (for solar abundances) respectively approx. 300 (for Beta Pic-like abundances). Conclusions. The lack of gas co-spatial with the dust implies that gas-dust interactions cannot efficiently shape the Fomalhaut debris belt. The morphology is therefore more likely due to a yet unseen planet (Fomalhaut c) or stellar encounters.

Fomalhaut b↗
NASA NTRS2015

Common Cause Failure Modeling in Space Launch Vehicles

Common Cause Failures (CCFs) are a known and documented phenomenon that defeats system redundancy. CCFs are a set of dependent type of failures that can be caused for example by system environments, manufacturing, transportation, storage, maintenance, and assembly. Since there are many factors that contribute to CCFs, they can be reduced, but are difficult to eliminate entirely. Furthermore, failure databases sometimes fail to differentiate between independent and dependent CCF. Because common cause failure data is limited in the aerospace industry, the Probabilistic Risk Assessment (PRA) Team at Bastion Technology Inc. is estimating CCF risk using generic data collected by the Nuclear Regulatory Commission (NRC). Consequently, common cause risk estimates based on this database, when applied to other industry applications, are highly uncertain. Therefore, it is important to account for a range of values for independent and CCF risk and to communicate the uncertainty to decision makers. There is an existing methodology for reducing CCF risk during design, which includes a checklist of 40+ factors grouped into eight categories. Using this checklist, an approach to produce a beta factor estimate is being investigated that quantitatively relates these factors. In this example, the checklist will be tailored to space launch vehicles, a quantitative approach will be described, and an example of the method will be presented.

Hark, Frank↗
NASA NTRS2016

First NuSTAR Observations of the BL Lac-Type Blazar PKS 2155-304: Constraints on the Jet Content and Distribution of Radiating Particles

We report the first hard X-ray observations with NuSTAR of the BL Lac-type blazar PKS2155-304, augmented with soft X-ray data from XMM-Newton and gamma-ray data from the Fermi Large Area Telescope, obtained in 2013April when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5-60 keV, is best described by a model consisting of a log-parabola component with curvature Beta = -0.3(+0.2 -0.1) and a (local) photon index 3.04 +/- 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 +/- 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous gamma-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p 2.2. Assuming that the power-law electron distribution extends down to gamma (sub min) = 1 and that there is one proton per electron, an unrealistically high total jet power of Lp approximately 10 (exp 47) erg s(sub -1) is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron-positron pairs with lepton-to-proton ratio n(sub e+e-/n(sub p) approx. 30, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor gamma br1 approx. 100. In either case, the jet composition is expected to be strongly matter-dominated

gamma ray↗
NASA NTRS2009

Simulation of TGF-Beta Activation by Low-Dose HZE Radiation in a Cell Culture

High charge (Z) and energy (E) (HZE) nuclei comprised in the galactic cosmic rays are main contributors to space radiation risk. They induce many lesions in living matter such as non-specific oxidative damage and the double-strand breaks (DSBs), which are considered key precursors of early and late effects of radiation. There is increasing evidence that cells respond collectively rather than individually to radiation, suggesting the importance of cell signaling1. The transforming growth factor (TGF ) is a signaling peptide that is expressed in nearly all cell type and regulates a large array of cellular processes2. TGF have been shown to mediate cellular response to DNA damage3 and to induce apoptosis in non-irradiated cells cocultured with irradiated cells4. TFG molecules are secreted by cells in an inactive complex known as the latency-associated peptide (LAP). TGF is released from the LAP by a conformational change triggered by proteases, thrombospondin-1, integrins, acidic conditions and .OH radical5. TGF then binds to cells receptors and activates a cascade of events mediated by Smad proteins6, which might interfere with the repair of DNA. Meanwhile, increasingly sophisticated Brownian Dynamics (BD) algorithms have appeared recently in the literature7 and can be applied to study the interaction of molecules with receptors. These BD computer models have contributed to the elucidation of signal transduction, ligand accumulation and autocrine loops in the epidermal growth factor (EGF) and its receptor (EFGR) system8. To investigate the possible roles of TGF in an irradiated cell culture, our Monte-Carlo simulation codes of the radiation track structure9 will be used to calculate the activation of TFG triggered by .OH produced by low doses of HZE ions. The TGF molecules will then be followed by a BD algorithm in a medium representative of a cell culture to estimate the number of activated receptors.

Plante, Ianik↗
NASA NTRS2015

Common Cause Failure Modeling

Common Cause Failures (CCFs) are a known and documented phenomenon that defeats system redundancy. CCFS are a set of dependent type of failures that can be caused by: system environments; manufacturing; transportation; storage; maintenance; and assembly, as examples. Since there are many factors that contribute to CCFs, the effects can be reduced, but they are difficult to eliminate entirely. Furthermore, failure databases sometimes fail to differentiate between independent and CCF (dependent) failure and data is limited, especially for launch vehicles. The Probabilistic Risk Assessment (PRA) of NASA's Safety and Mission Assurance Directorate at Marshall Space Flight Center (MFSC) is using generic data from the Nuclear Regulatory Commission's database of common cause failures at nuclear power plants to estimate CCF due to the lack of a more appropriate data source. There remains uncertainty in the actual magnitude of the common cause risk estimates for different systems at this stage of the design. Given the limited data about launch vehicle CCF and that launch vehicles are a highly redundant system by design, it is important to make design decisions to account for a range of values for independent and CCFs. When investigating the design of the one-out-of-two component redundant system for launch vehicles, a response surface was constructed to represent the impact of the independent failure rate versus a common cause beta factor effect on a system's failure probability. This presentation will define a CCF and review estimation calculations. It gives a summary of reduction methodologies and a review of examples of historical CCFs. Finally, it presents the response surface and discusses the results of the different CCFs on the reliability of a one-out-of-two system.

Hark, Frank↗
NASA NTRS2016

Common Cause Failure Modeling

Common Cause Failures (CCFs) are a known and documented phenomenon that defeats system redundancy. CCFS are a set of dependent type of failures that can be caused by: system environments; manufacturing; transportation; storage; maintenance; and assembly, as examples. Since there are many factors that contribute to CCFs, the effects can be reduced, but they are difficult to eliminate entirely. Furthermore, failure databases sometimes fail to differentiate between independent and CCF (dependent) failure and data is limited, especially for launch vehicles. The Probabilistic Risk Assessment (PRA) of NASA's Safety and Mission Assurance Directorate at Marshal Space Flight Center (MFSC) is using generic data from the Nuclear Regulatory Commission's database of common cause failures at nuclear power plants to estimate CCF due to the lack of a more appropriate data source. There remains uncertainty in the actual magnitude of the common cause risk estimates for different systems at this stage of the design. Given the limited data about launch vehicle CCF and that launch vehicles are a highly redundant system by design, it is important to make design decisions to account for a range of values for independent and CCFs. When investigating the design of the one-out-of-two component redundant system for launch vehicles, a response surface was constructed to represent the impact of the independent failure rate versus a common cause beta factor effect on a system's failure probability. This presentation will define a CCF and review estimation calculations. It gives a summary of reduction methodologies and a review of examples of historical CCFs. Finally, it presents the response surface and discusses the results of the different CCFs on the reliability of a one-out-of-two system.

Hark, Frank↗
NASA NTRS1985

The gaseous component of the disk around Beta Pictoris

Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.

Hobbs, L. M.↗
NASA NTRS2002

Microgravity modifies protein kinase C isoform translocation in the human monocytic cell line U937 and human peripheral blood T-cells

Individual protein kinase C (PKC) isoforms fulfill distinct roles in the regulation of the commitment to differentiation, cell cycle arrest, and apoptosis in both monocytes and T-cells. The human monocyte like cell line U937 and T-cells were exposed to microgravity, during spaceflight and the translocation (a critical step in PKC signaling) of individual isoforms to cell particulate fraction examined. PKC activating phorbol esters induced a rapid translocation of several PKC isoforms to the particulate fraction of U937 monocytes under terrestrial gravity (1 g) conditions in the laboratory. In microgravity, the translocation of PKC beta II, delta, and epsilon in response to phorbol esters was reduced in microgravity compared to 1 g, but was enhanced in weak hypergravity (1.4 g). All isoforms showed a net increase in particulate PKC following phorbol ester stimulation, except PKC delta which showed a net decrease in microgravity. In T-cells, phorbol ester induced translocation of PKC delta was reduced in microgravity, compared to 1 g, while PKC beta II translocation was not significantly different at the two g-levels. These data show that microgravity differentially alters the translocation of individual PKC isoforms in monocytes and T-cells, thus providing a partial explanation for the modifications previously observed in the activation of these cell types under microgravity.

STS-81 Shuttle Project↗
NASA NTRS1992

Radar-anomalous, high-altitude features on Venus

Over nearly all of the surface of Venus the reflectivity and emissivity at centimeter wavelengths are about 0.15 and 0.85 respectively. These values are consistent with moderately dense soils and rock populations, but the mean reflectivity is about a factor of 2 greater than that for the Moon and other terrestrial planets. Pettingill and Ford, using Pioneer Venus reflectivities and emissivities, found a number of anomalous features on Venus that showed much higher reflectivities and much lower emissivities with both values approaching 0.5. These include Maxwell Montes, a number of high regions in Aphrodite Terra and Beta Regio, and several isolated mountain peaks. Most of the features are at altitudes above the mean radius by 2 to 3 km or more. However, such features have been found in the Magellan data at low altitudes and the anomalies do not exist on all high structures, Maat Mons being the most outstanding example. A number of papers have been written that attempt to explain the phenomena in terms of the geochemistry balance of weathering effects on likely surface minerals. The geochemists have shown that the fundamentally basaltic surface would be stable at the temperatures and pressures of the mean radius in the form of magnetite, but would evolve to pyrite and/or pyrrhotite in the presence of sulfur-bearing compounds such as SO2. Pyrite will be stable at altitudes above 4 or 5 km on Venus. Although the geochemical arguments are rather compelling, it is vitally important to rationally look at other explanations for radar and radio emission measurements such as that presented by Tryka and Muhleman. The radar reflectivity values are retrieved from the raw Magellan backscatter measurements by fitting the Hagfors' radar scattering model in which a surface roughness parameters and a normal incidence electrical reflectivity are estimated. The assumptions of the theory behind the model must be considered carefully before the results can be believed. These include that the surface roughness exists only at horizontal scales large compared to the wavelength, the vertical deviations are gaussianly distributed, there is no shadowing, and that the reflection occurs at the interface of two homogeneous dielectric half-spaces. Probably all these conditions are violated at the anomalous features under discussion. The most important of these is the homogeneity of the near surface of Venus, particularly in highlands. Under the assumptions of the theory, all of the radio energy is reflected by the impedance jump at the very boundary. However, in heterogeneous soil some fraction of the illuminating energy is propagated into the soil and then scattered back out by impedance discontinuities such as rock, voids, and cracks. In light soils, the latter effect can overwhelm the scattering effects of the true surface and greatly enhance the backscatter power, suggesting a much higher value of an effective dielectric constant that would be estimated from Hagfors' model.

Muhleman, Duane O.↗
NASA NTRS1995

Implementation of a Single-Stage-To-Orbit (SSTO) model for stability and control analysis

Three NASA centers: Marshall Space Flight Center (MSFC), Langley Research Center (LaRC), and Johnson Space Center (JSC) are currently involved in studying a family of single-stage- and two-stage-to-orbit (SSTO/TSTO) vehicles to serve as the next generation space transportation system (STS). A rocketed winged-body is the current focus. The configuration (WB001) is a vertically-launched, horizontally-landing system with circular cross-section. Preliminary aerodynamic data was generated by LaRC and is a combination of wind-tunnel data, empirical methods, and Aerodynamic Preliminary Analysis System-(APAS) generated values. JSC's efforts involve descent trajectory design, stability analysis, and flight control system synthesis. Analysis of WB001's static stability indicates instability in 'tuck' (C(sub mu) less than 0: Mach = 0.30, alpha greater than 3.25 deg; Mach = 0.60, alpha greater than 8.04), an unstable dihedral effects (C(sub l(beta)) greater than 0: Mach = 30,alpha less than 12 deg.; Mach = 0.60, alpha less than 10.00 deg.), and, most significantly, an unstable weathercock stability derivative, C(sub n(beta)), at all angles of attack and subsonic Mach numbers. Longitudinal trim solutions for Mach = 0.30 and 0.60 indicate flight path angle possibilities ranging from around 12 (M = 0.30) to slightly over 20 degrees at Mach = 0.60. Trim angles of attack increase from 6.24 at Mach 0.60 and 10,000 feet to 17.7 deg. at Mach 0.30, sea-level. Lateral trim was attempted for a design cross-wind of 25.0 knots. The current vehicle aerodynamic and geometric characteristics will only yield a lateral trim solution at impractical tip-fin deflections (approximately equal to 43 deg.) and bank angles (21 deg.). A study of the lateral control surfaces, tip-fin controllers for WB001, indicate increased surface area would help address these instabilities, particularly the deficiency in C(sub n(beta)), but obviously at the expense of increased vehicle weight. Growth factors of approximately 7 were determined using a design C(sub n(beta)) of 0.100/radian (approximate subsonic values for the orbiter).

Ingalls, Stephen A.↗