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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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Thermal Protection System Design of Aerocapture Systems for Uranus Orbiters

The National Academies Planetary Science and Astrobiology Decadal Survey recently identified Uranus and Neptune - called Ice Giants - as the priority destinations for science[1]. The survey assessed both a mission to Uranus through the Uranus Orbiter and Probe (UOP) concept, and Neptune through the Neptune-Triton Odyssey concept and determined that Uranus is the highest priority for a Flagship class mission. The UOP mission will deliver an in situ probe and conduct a multi-year orbital tour of the system to meet the science objectives. While the Uranus mission is currently viable with launch windows starting in 2031 using existing launch vehicles, the mission has a long cruise time to destination (between 12 and 15 years) and would require more than half of its weight in fuel propellant to achieve the change in velocity necessary for orbital insertion. Aerocapture is a method of orbital control that uses aerodynamic forces generated on a vehicle by the planet’s atmosphere to modulate a spacecraft’s trajectory, allowing mission designers to target the final orbital state. For the Uranus mission, using aerocapture for orbital insertion can decrease not only the cruise time to the destination by 2 - 3 years, but the propellant required to achieve orbital insertion (by more than 40%) which would, in turn, increase the available science payload and reduce the timeline for retrieving data vital to the mission’s science objectives[2]. Achieving orbital insertion via aerocapture requires novel algorithms for Guidance, Navigation and Control[3], and mass-efficient Thermal Protection Systems (TPS) performing in a new atmosphere. This paper will focus on the selection and tailoring of the Thermal Protection Systems for the forebody and aftbody heatshields of an aerocapture mission to Uranus. While preliminary results indicate that multiple systems in NASA’s repertoire are capable of performing in the predicted aerothermal environment there are unique aspects like the inert environment that affect ablation efficiency, and the heatload for aerocapture trajectories to the outer planets are among the highest of any mission to-date[4]. These two factors may impose operational requirements to heatshield separation in order to minimize thermal soak to the payload, and may demand TPS thickness and configurations that have not yet been demonstrated. This paper will discuss the updated maturity, manufacturing, and performance capabilities of candidate thermal protection systems, with specific areas of need highlighted to make thermal protection systems viable for use in the recommended Uranus Orbiter and Probe mission.

Uranus↗
NASA NTRS1984

Integral boundary-layer models for turbulent separated flows

Two-dimensional, integral boundary-layer methods of the entrainment and dissipation type, with closure relationships which account for turbulent separated flows through the velocity and turbulence models, are developed. Kinematic shape factor relations used in the two methods are evaluated by comparison with recently obtained experimental data for separated flows. Prescribed-displacement-thickness computations are made with both methods and compared to experiment for a series of separated flows, including low speed and transonic shock-induced separation. Effects of upstream history on the turbulent shear stress development are shown to be important for the accurate prediction of the separated flows considered and the experimental trends are reasonably modeled by a rate equation derived from the turbulent kinetic energy equation.

Thomas, J. L.↗
NASA NTRS1976

Stage separation study of Nike-Black Brant V Sounding Rocket System

A new Sounding Rocket System has been developed. It consists of a Nike Booster and a Black Brant V Sustainer with slanted fins which extend beyond its nozzle exit plane. A cursory look was taken at different factors which must be considered when studying a passive separation system. That is, one separation system without mechanical constraints in the axial direction and which will allow separation due to drag differential accelerations between the Booster and the Sustainer. The equations of motion were derived for rigid body motions and exact solutions were obtained. The analysis developed could be applied to any other staging problem of a Sounding Rocket System.

Ferragut, N. J.↗
NASA NTRS1975

Binary galaxy orbit statistics. I - Fixed mass and major axis

Averages for the projected separation, squared radial velocity difference, and the product of these, are presented for a binary galaxy system of fixed mass and major axis, but any orbital eccentricity. The average of the product varies by a factor about 3 for eccentricities from 0 to 1.0. For circular orbits, the results agree with those of Page (1952, 1960, 1961), but for linear orbits his mass estimate is too small by a factor 6. The mutual regressions of the velocity and separation on each other are calculated, and are presented in such a way as to exhibit the relative likelihood of occupation of the different parts of the regression curves. 'Isopleths' for the probability distribution are presented for a few values of the eccentricity to illustrate the underlying cause of pileup at certain parts of the regression curves. It is concluded that previous analyses were inadequate for failing to take into account that the regression curves represent in many cases a distribution that is almost wholly depopulated through most of the range. It is evident that the data are insufficient to draw a firm conclusion about the distribution of eccentricities.

Noerdlinger, P. D.↗
NASA NTRS1994

Computation of Separated and Unsteady Flows with One- and Two-Equation Turbulence Models

The ability of one- and two-equation turbulence models to predict unsteady separated flows over airfoils is evaluated. An implicit, factorized, upwind-biased numerical scheme is used for the integration of the compressible, Reynolds averaged Navier-Stokes equations. The turbulent eddy viscosity is obtained from the computed mean flowfield by integration of the turbulent field equations. The two-equation turbulence models are discretized in space with an upwind-biased, second order accurate total variation diminishing scheme. One and two-equation turbulence models are first tested for a separated airfoil flow at fixed angle of incidence. The same models are then applied to compute the unsteady flowfields about airfoils undergoing oscillatory motion at low subsonic Mach numbers. Experimental cases where the flow has been tripped at the leading edge and where natural transition was allowed to occur naturally are considered. The more recently developed field-equation turbulence models capture the physics of unsteady separated flow significantly better than the standard kappa-epsilon and kappa-omega models. However, certain differences in the hysteresis effects are obtained. For an untripped high-Reynolds-number flow, it was found necessary to take into account the leading edge transitional flow region in order to capture the correct physical mechanism that leads to dynamic stall.

Ekaterinaris, John A.↗
NASA NTRS1988

Gravitational lensing in a cold dark matter universe

Gravitational lensing due to mass condensations in a biased cold dark matter (CDM) universe is investigated using the Press-Schechter (1974) theory with density fluctuation amplitudes taken from previous N-body work. Under the critical assumption that CDM haloes have small core radii, a distribution of image angular separations for high-z lensed quasars with a peak at about 1 arcsec and a half-width of a factor of about 10. Allowing for selection effects at small angular separations, this is in good agreement with the observed separations. The estimated frequency of lensing is somewhat lower than that observed, but the discrepancy can be removed by invoking amplification bias and by making a small upward adjustment to the density fluctuation amplitudes assumed in the CDM model.

Narayan, Ramesh↗
NASA NTRS1993

The frequency of T Tauri companion stars

We present the results of a magnitude-limited multiplicity survey of T Tauri stars in two nearby star-forming regions, Taurus-Auriga and Ophiuchus-Scorpius. Each of the 69 stars in the sample was observed at K with an infrared array camera on the Hale 5-m Telescope at Palomar Observatory and imaged using 2D speckle imaging techniques. Thirty-three companion stars were found of which 15 were new detections. One of the main results of this survey indicates that the binary star frequency in the projected linear separation range 14 to 225 AU for T Tauri stars is a factor of 3.5 greater than that of the solar-type main-sequence stars. Given the limited angular separation range of this survey, the rate at which binaries are detected suggests that most T Tauri stars have companions. We propose that the observed overabundance of companions to T Tauri stars relative to their older counterparts on the main sequence is an evolutionary effect; in this scheme, triple and higher order T Tauri star systems, which are observed at higher frequencies than for the solar-type main-sequence stars, are disrupted by close encounters with another star or system of stars.

Ghez, A. M.↗
NASA NTRS1985

Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.

Obara, C. J.↗
NASA NTRS1988

Effect of bulges on the stability of boundary layers

The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear-layer instabilities. Separation is found to increase significantly the amplification factor.

Nayfeh, Ali H.↗
NASA NTRS1991

A non-linear mathematical model for dynamic analysis of spur gears including shaft and bearing dynamics

A six-degree-of-freedom nonlinear semi-definite model with time varying mesh stiffness has been developed for the dynamic analysis of spur gears. The model includes a spur gear pair, two shafts, two inertias representing load and prime mover, and bearings. As the shaft and bearing dynamics have also been considered in the model, the effect of lateral-torsional vibration coupling on the dynamics of gears can be studied. In the nonlinear model developed several factors such as time varying mesh stiffness and damping, separation of teeth, backlash, single- and double-sided impacts, various gear errors and profile modifications have been considered. The dynamic response to internal excitation has been calculated by using the 'static transmission error method' developed. The software prepared (DYTEM) employs the digital simulation technique for the solution, and is capable of calculating dynamic tooth and mesh forces, dynamic factors for pinion and gear, dynamic transmission error, dynamic bearing forces and torsions of shafts. Numerical examples are given in order to demonstrate the effect of shaft and bearing dynamics on gear dynamics.

Ozguven, H. Nevzat↗
NASA NTRS2009

Gaussian and Lognormal Models of Hurricane Gust Factors

A document describes a tool that predicts the likelihood of land-falling tropical storms and hurricanes exceeding specified peak speeds, given the mean wind speed at various heights of up to 500 feet (150 meters) above ground level. Empirical models to calculate mean and standard deviation of the gust factor as a function of height and mean wind speed were developed in Excel based on data from previous hurricanes. Separate models were developed for Gaussian and offset lognormal distributions for the gust factor. Rather than forecasting a single, specific peak wind speed, this tool provides a probability of exceeding a specified value. This probability is provided as a function of height, allowing it to be applied at a height appropriate for tall structures. The user inputs the mean wind speed, height, and operational threshold. The tool produces the probability from each model that the given threshold will be exceeded. This application does have its limits. They were tested only in tropical storm conditions associated with the periphery of hurricanes. Winds of similar speed produced by non-tropical system may have different turbulence dynamics and stability, which may change those winds statistical characteristics. These models were developed along the Central Florida seacoast, and their results may not accurately extrapolate to inland areas, or even to coastal sites that are different from those used to build the models. Although this tool cannot be generalized for use in different environments, its methodology could be applied to those locations to develop a similar tool tuned to local conditions.

Merceret, Frank↗
NASA NTRS1976

Coefficients of associated Legendre functions

The exact coefficients for the explicit forms of the associated Legendre functions Pm for integer values of m,n=0,1,2,...25 are presented in tabular form together with two cross-referenced listings of the zeroes for these functions rounded to five decimal places. The unfactored coefficients and the interger coefficients are presented in adjacent columns for each function. The greatest common factor and divisor have been removed and listed separately for the integer coefficients.

Peasley, Q. D.↗
NASA NTRS1976

Optical pulsations in HZ Herculis. 5. Pulse-resolved spectrophotometry

Digital spectra of HZ Herculis were obtained with 10 A resolution in the 3,600 - 6,000 A region, synchronously dividing the 1.24-s optical pulsation period into eight 155-ms phase bins. The optical pulses are detected in the data, but their fractional amplitude is only 0.08 percent, a factor of 4 less than typically observed. The separate spectra of each one-eighth of the pulse are identical to within the statistics of the observation. If the X-ray to optical pulse reprocessing mechanism concentrates the optical pulsations into discrete spectral line features, data require the pulses to be distributed among more than four such lines.

Margon, B.↗
NASA NTRS1981

Distance-independent evidence for relativistic motion in the quasar NRAO 140

VLBI radio and X-ray observations were made of the bright X-ray quasar NRAO 140. The radio structure consists of two very compact components plus a more diffuse jet. Based on the standard synchrotron theory, the Compton X-ray emission from one of these compact components was found to exceed the observed value by three orders of magnitude. Since this result is independent of distance and there is no evidence for coherent emission, it is concluded that the component is moving toward us at a relativistic speed with a Lorentz factor exceeding 4. Future observations should reveal superluminal separation of the components, as well as help in determining which components are undergoing relativistic motion.

Marscher, A. P.↗
NASA NTRS1984

Selected tether applications in space: An analysis of five selected concepts

Ground rules and assumptions; operations; orbit considerations/dynamics; tether system design and dynamics; functional requirements; hardware concepts; and safety factors are examined for five scenarios: tethered effected separation of an Earth bound shuttle from the space station; tether effected orbit boost of a spacecraft (AXAF) into its operational orbit from the shuttle; an operational science/technology platform tether deployed from space station; a tether mediated rendezvous involving an OMV tether deployed from space station to rendezvous with an aerobraked OTV returning to geosynchronous orbit from a payload delivery mission; and an electrodynamic tether used in a dual motor/generator mode to serve as the primary energy storage facility for space station.

Source record↗
NASA NTRS1985

Composition of cosmic-ray nuclei from boron to nickel for 1200 to 2400 MeV per nucleon

Balloon-borne measurements of cosmic-ray nuclear abundances for Z = 5-28 and energies 1.2-1.4 GeV/nucleon, obtained using the scintillation/Cerenkov-counter telescope and multiwire proportional counter described by Dwyer et al. (1984) on four flights from Texas and Oklahoma during 1973-1975, are reported. The data are presented in tables and graphs and compared with published observations. Charge separation (sigma = 0.2 units for Fe) and exposure factor (38 sq m sr h) are attained, and the findings are found to be in good agreement with the predictions of a simple leaky-box model of the Galaxy and a pure exponential path-length distribution, although a nested-leaky-box model with some truncation is possible. The delay between e-process nucleosynthesis and cosmic-ray acceleration is estimated on the basis of the Co abundance at greater than 100 d and probably greater than 100,000 yr.

Dwyer, R.↗
NASA NTRS1995

Fragmentation cross sections of O-16 between 0.9 and 200 GeV/nucleon

Inclusive cross sections for high energy interactions at 0.9, 2.3, 3.6, and 13.5 GeV/nucleon of O-16 with C, CR-39 (C12H18O7), CH2, Al, Cu, Ag, and Pb targets were measured. The total charge-changing cross sections and partial charge-changing cross sections for the production of fragments with charge Z = 6 and Z = 7 are compared to previous experiments at 60 and 200 GeV/nucleon. The contributions of Coulomb dissociation to the total cross sections are calculated. Using factorization rules the partial electromagnetic cross sections are separated from the nuclear components. Energy dependence of both components are investigated and discussed.

Hirzebruch, S. E.↗
NASA NTRS2004

Multi-Epoch XMM Observations of NGC4258

The goal of this project was detection of variability in the X-ray absorption column of the AGN in NGC4258 through monitoring with the XMM satellite. We have accomplished this goal and submitted the results to ApJ for publication in a paper entitled, "X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser Galaxy NGC4258 from Weeks to Years," by Fruscione, A., Greenhill, L.J., Filippedco, A.V., Moran, J.M., Hermstein, J.R., and Galle, E. We have received a favorable referee report and expect the article will appear in 2005. To complete the project, we reduced our four epochs of XMM data for NGC4258, one archival XMM observation, and all existing Chandra datasets for NGC4258 (with the latest calibration tables and a grid of corrections for pileup). Self-consistent reduction of all these data permitted detailed comparison that could not have been accomplished simply by taking published model fits that appear in the literature. To accumulate a broader monitoring record, we combined the Chandra and XMM results with those published for SAX and ASCA. We modeled the Chandra and XMM data self-consistently with partially absorbed, hard power-law, soft thermal plasmas, and soft power-law components. Over nine years, the photo-electric absorbing column exhibited a 40% drop between two ASCA epochs separated by 3 years and a 60% rise between two XMM epochs separated by just 5 months. In contract, uncorrelated factor of of 2-3 changes were seen in absorbed flux on te timescale of years, which suggests intrinsic variability of the central engine. The warped disk that is a known source of H2O maser emission in 4258 is believed to cross the line of sight to the central engine. We have proposed that the variations in absorbing column arise from inhomogeneities in the rotating disk, as they sweep across the line of sight. We estimate from the XMM data that the inhomogeneities are about 1E+15 cm in size at radii greater than 0.27 pc. This is consistent with the estimated radius of the disk crossing estimated entirely independently, and it solidifies evidence that the warped accretion disk is the absorber in this (and possible other) AGN.

Greenhill, Lincoln J.↗