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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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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Solar modulation of protons and alpha particles at rigidities of 4-10 GV/c

The high statistics and high resolution rigidity spectra from geomagnetic cutoff to 160 GV/c were provided by a superconducting-magnet spectrometer flown on a balloon. The spectra above 8.3 GV/c fit a power law in rigidity for protons and alphas; below 8.3 GV/c, no clear evidence of solar modification is available. The analysis of data from 5.5 to 8.3 GV/c by the Gleeson-Axford model for solar modulation indicated that the modulation parameter was 0.3 + or - 0.05 Gev/nucleon; the spectra below 5.5 GV/c are being analyzed using a portion of the flight data recorded while the balloon was essentially stationary

Badhwar, G. D.↗
NASA NTRS1980

Drag reduction characteristics of small amplitude rigid surface waves

The possibility of reducing drag by using rigid, wavy surfaces is investigated both analytically and experimentally. Although pressure drag for rigid sine-wave surfaces can be predicted empirically, viscous drag for even shallow waves was poorly predicted by state-of-the-art turbulent boundary layer calculation procedures. Calculations for the effects of geometric and fluid variables on total wave drag are presented under the philosophy that trends will be nearly correct even though levels are probably incorrect. Experiments by the present authors indicate that a total drag reduction with wavy walls is possible.

Cary, A. M., Jr.↗
NASA NTRS1982

A two-degree-of-freedom flutter mount system with low damping for testing rigid wings at different angles of attack

A wind tunnel model mount system for conducting flutter research using a rigid wing was developed. The wing is attached to a splitter plate so that the two move as one rigid body. The splitter plate is supported away from the tunnel wall by a system of rods with fixed fixed and conditions. The rods flex in such a way that only pitch and plunge oscillations are permitted. At the tunnel wall the rods are attached to a remotely controlled turntable so that angle of attack can be varied. Wind tunnel data obtained by using the mount system are presented for a supercritical and a conventional airfoil. Both classical flutter and stall flutter data are presented.

Farmer, M. G.↗
NASA NTRS1981

The rigidity dependence of cosmic ray solar modulation

Continuous particle flux measurements above rigidity thresholds of 1.2, 2.2, 5.5 and 11 GV were made by using the thresholds of two Cerenkov detectors aboard the ISEE-3 spacecraft. The ISEE-3 was launched in August 1978, near the beginning of the current solar cycle's heavy modulation phase, and the data presented represent the first direct measurement made at these energies with such a long time base. The measured long term modulation rigidity spectrum is compared with other data and with the spectrum of Forbush decreases, and it is found that the agreement between electron and positively charged particle results must be considered a constraint on cosmic ray modulation models involving the mechanism of gradient and curvature drift in the interplanetary magnetic field.

Evenson, P.↗
NASA NTRS1982

Tidal rigidity of Phobos

A novel scenario is proposed in which the orbital eccentricity of Phobos results from several gravitational resonance excitations within the past one billion years, assuming that tidal friction in Phobos has had only a small effect on its orbit. Both the primordial eccentricity and inclination may have been much smaller than presently observed. Constraints imposed on tidal friction in Phobos by the apparent age of its surface, which is greater than one billion years, in addition to those of the gravitational resonance excitation scenario, can be satisfied only if the product of the rigidity and the Q factor is greater than 10 to the 12th dynes/sq cm. In view of the fact that the Q factor is only about 100, so that the rigidity must be greater than 10 to the 10th dynes/sq cm, Phobos should have substantial internal strength.

Yoder, C. F.↗
NASA NTRS1983

Rigid closed-cell polyimide foams for aircraft applications and foam-in-place technology

Significant accomplishments generated are summarized. Testing of closed cell foams, which has resulted in the characterization of compositions which produce rigid foams for use in galley structure applications is reported. It is shown that the density, compressive strength and shear strength of the foams are directly related to the concentrations of the microballoons. The same properties are also directly related to the resin loading. Prototype samples of rigid closed cell foams meeting the requirements of the program were submitted. Investigation of the apparatus to produce polyimide foams using foam in place techniques, resulted in the selection of a spray gun apparatus, capable to deliver a mixture of microballoons and resin binder on substrates which cures to yield a closed cell foam. It is found that the adhesion of the foam on aluminum, titanium and steel substrates is satisfactory. It is concluded that the material meets the mechanical and thermal requirements of the program.

Gagliani, J.↗
NASA NTRS1983

Planar dynamics of a uniform beam with rigid bodies affixed to the ends

The planar dynamics of a uniform elastic beam subject to a variety of geometric and natural boundary conditions and external excitations were analyzed. The beams are inextensible and capable of small transverse bending deformations only. Classical beam vibration eigenvalue problems for a cantilever with tip mass, a cantilever with tip body and an unconstrained beam with rigid bodies at each are examined. The characteristic equations, eigenfunctions and orthogonality relations for each are derived. The forced vibration of a cantilever with tip body subject to base acceleration is analyzed. The exact solution of the governing nonhomogeneous partial differential equation with time dependent boundary conditions is presented and compared with a Rayleigh-Ritz approximate solution. The arbitrary planar motion of an elastic beam with rigid bodies at the ends is addressed. Equations of motion are derived for two modal expansions of the beam deflection. The motion equations are cast in a first order form suitable for numerical integration. Selected FORTRAN programs are provided.

Storch, J.↗
NASA NTRS1985

Absolute rigidity spectrum of protons and helium nuclei above 10 GV/c

Proton and helium nuclei differential spectra were gathered with a balloon borne magnet spectrometer. The data were fitted to the assumption that the differential flux can be represented by a power law in rigidity. In the rigidity range 10 to 25 GV/c the spectral indices were found to be -(2.74 plus or minus 0.04) for protons and -(2.71 plus or minus 0.05) for helium nuclei. A brief discussion is given by systematic errors.

Golden, R. L.↗
NASA NTRS1985

Solar tri-diurnal variation of cosmic rays in a wide range of rigidity

Solar tri-diurnal variations of cosmic rays have been analyzed in a wide range of rigidity, using data from neutron monitors, and the surface and underground muon telescopes for the period 1978-1983. The rigidity spectrum of the anisotropy in space is assumed to be of power-exponential type as (P/gamma P sub o) to the gamma exp (gamma-P/P sub o). By means of the best-fit method between the observed and the expected variations, it is obtained that the spectrum has a peak at P (=gamma P sub o) approx = 90 GV, where gamma=approx 3.0 and P sub o approx. 30 GV. The phase in space of the tri-diurnal variation is also obtained as 7.0 hr (15 hr and 23 hr LT), which is quite different from that of approx. 1 hr. arising from the axisymmetric distribution of cosmic rays with respect to the IMF.

Mori, S.↗
NASA NTRS1985

Rigidity spectrum of Forbush decrease

Using data from neutron monitors and muon telescopes at surface and underground stations, the average rigidity spectrum of Forbush decreases (Fds) during the period of 1978-1982 were obtained. Thirty eight Ed-events are classified into two groups Hard Fd and Soft Fd according to size of Fd at Sakashita station. It is found that a spectral form of fractional-power type (P to the-gamma sub 1 (P+P sub c) to the -gamma sub2) is more suitable for the present purpose than that of power-exponential type or of power type with an upper limiting rigidity. The best fitted spectrum of fractional-power type is expressed by gamma sub1 = 0.37, gamma sub2 = 0.89 and P subc = 10 GV for Hard Fd and gamma sub1 = 0.77, gamma sub2 = 1.02 and P sub c - 14GV for Soft Fd.

Sakakibara, S.↗
NASA NTRS1985

The influence of quiet asymmetric magnetosphere on the cutoff rigidities of the main cone

Some earlier studies show that cutoff rigidities of cosmic-ray particles in the model magnetospheric fields of internal and external sources have daily variations caused by asymmetry of the magnetic field due to the currents induced at the magnetopause and tail currents. Cutoff rigidities of the charged particles coming down at the middle latitudes are examined in this paper. The mathematical model of the magnetospheric field is based on the merged IMP-HEOS experimental data set and includes all known at the present time current systems of the magnetosphere: magnetopause, ring, and magnetotail currents.

Tyasto, M. I.↗
NASA NTRS1985

The use of the McIlwain L-parameter to estimate cosmic ray vertical cutoff rigidities for different epochs of the geomagnetic field

Secular changes in the geomagnetic field between 1955 and 1980 have been large enough to produce significant differences in both the verical cutoff rigidities and in the L-value for a specified position. A useful relationship employing the McIlwain L-parameter to estimate vertical cutoff rigidities has been derived for the twenty-five year period.

Shea, M. A.↗
NASA NTRS1984

On the attitude motion of a self-excited rigid body

Leimanis (1965) has published a monograph, which contains Boedewadt's solution of Euler's equations of motion for a symmetric rigid body subject to a time-independent, self-excitement in a body-fixed direction. In addition, the monograph provided also Boedewadt's solution for the corresponding angles of rotation. It is pointed out that the solution of Euler's equations of motion provides a poor approximation to the problem of nearly symmetric rigid bodies in cases in which a high degree of accuracy (less than 1 percent error) is required. A much more accurate approximate solution has been provided by Longuski (1980). The result given by Leimanis in the case of the Eulerian angles is incorrect for arbitrary constant torques. The approximate solution given by Longuski, however, is extremely accurate and suitable for computer design work and error analysis of spacecraft performance. The present investigation is concerned with a review of the solutions and the specific regions of validity of the solution for the Eulerian angles.

Longuski, J. M.↗
NASA NTRS1983

The isotopic composition of helium at high rigidities

The isotopic abundance distribution of the cosmic radiation at energies beyond 1 GeV/AMU can at the present time be determined only with the geomagnetic method. A balloon-borne instrument was flown for 12 hours near the geomagnetic equator to measure the relative abundance of the helium isotopes He-3 and He-4 around 12 GV rigidity. The sharp rigidity cut-off at equatorial latitudes permitted separation of the two isotopes using a high-resolution-gas Cerenkov counter. The experiment thus confirms the predicted sharp cut-off at those latitudes and demonstrates the potential for isotopic separation of other elements, once flights of longer duration can be made.

Jordan, S. P.↗
NASA NTRS1984

Error analysis of analytic solutions for self-excited near-symmetric rigid bodies - A numerical study

Analytic error bounds are presented for the solutions of approximate models for self-excited near-symmetric rigid bodies. The error bounds are developed for analytic solutions to Euler's equations of motion. The results are applied to obtain a simplified analytic solution for Eulerian rates and angles. The results of a sample application of the range and error bound expressions for the case of the Galileo spacecraft experiencing transverse torques demonstrate the use of the bounds in analyses of rigid body spin change maneuvers.

Kia, T.↗
NASA NTRS1987

Boundary value problem for the solution of magnetic cutoff rigidities and some special applications

Since a planet's magnetic field can sometimes provide a spacecraft with some protection against cosmic ray and solar flare particles, it is important to be able to quantify this protection. This is done by calculating cutoff rigidities. An alternate to the conventional method (particle trajectory tracing) is introduced, which is to treat the problem as a boundary value problem. In this approach trajectory tracing is only needed to supply boundary conditions. In some special cases, trajectory tracing is not needed at all because the problem can be solved analytically. A differential equation governing cutoff rigidities is derived for static magnetic fields. The presense of solid objects, which can block a trajectory and other force fields are not included. A few qualititative comments, on existence and uniqueness of solutions, are made which may be useful when deciding how the boundary conditions should be set up. Also included are topics on axially symmetric fields.

Edmonds, Larry↗
NASA NTRS1988

Minimum time attitude slewing maneuvers of a rigid spacecraft

The minimum time attitude slewing motion of a rigid spacecraft with its controls provided by torques and forces, which have their upper and lower limits prescribed, is considered. The two-point boundary-value problem is derived by applying the Pontriagin's Maximum Principle to the system and solved by using a quasi-linearization algorithm. The nominal solutions to the problem as well as the starting values of the total slewing time and the unknown initial costates for this algorithm are generated by using Euler's eigenaxis rotation theorem. It is pointed out that one of the four initial costates associated with the quaternions can be arbitrarily selected without affecting the optimal controls and, thus, simplifying the computation. The minimum slewing time is determined by shortening the total slewing time until at least one of the controls becomes a bang-bang type. Several numerical tests for the rigidized SCOLE model are presented to show the applications of the methods.

Li, Feiyue↗