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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Experimental study of transient liquid motion in orbiting spacecraft

The results are presented of a twofold study of transient liquid motion such as that which will be experienced during orbital maneuvers by space tug. A test program was conducted in a low-g test facility involving twenty-two drops. Biaxial, low-g accelerations were applied to an instrumented, model propellant tank during free-fall testing, and forces exerted during liquid reorientation were measured and recorded. Photographic records of the liquid reorientation were also made. The test data were used to verify a mechanical analog which portrays the liquid as a point mass moving on an ellipsoidal constraint surface. The mechanical analog was coded into a FORTRAN IV digital computer program: LAMPS, Large AMPlitude Slosh. Test/analytical correlation indicates that the mechanical analog is capable of predicting the overall force trends measured during testing.

Berry, R. L.↗
NASA NTRS1972

Current to a moving cylindrical electrostatic probe

The current collection characteristics of a moving cylindrical Langmuir probe are evaluated for a range of probe speeds and potentials which are applicable to earth and planetary measurements. The current expressions derived include the cases of the general accelerated current, sheath area limited current, orbital motion limited current, and retarded current. For the orbital motion limited current, a simple algebraic expression is obtained which includes and generalizes the Mott-Smith and Langmuir expressions for both a stationary probe and a rapidly moving probe. For a rapidly moving probe a single formula adequately represents both the accelerated and the retarded current.

Hoegy, W. R.↗
NASA NTRS1973

Current to a moving cylindrical electrostatic probe

The current collection characteristics of a moving cylindrical Langmuir probe are evaluated for a range of probe speeds and potentials which are applicable to earth and planetary measurements. The current expressions derived include the cases of the general accelerated current, sheath area limited current, orbital motion limited current, and retarded current. For the orbital motion limited current, a simple algebric expression is obtained which includes and generalizes the Mott-Smith and Langmuir expressions for both a stationary probe and a rapidly moving probe. For a rapidly moving probe, a single formula adequately represents both the accelerated and the retarded current.

Hoegy, W. R.↗
NASA NTRS2009

Miniature Scroll Pumps Fabricated by LIGA

Miniature scroll pumps have been proposed as roughing pumps (low - vacuum pumps) for miniature scientific instruments (e.g., portable mass spectrometers and gas analyzers) that depend on vacuum. The larger scroll pumps used as roughing pumps in some older vacuum systems are fabricated by conventional machining. Typically, such an older scroll pump includes (1) an electric motor with an eccentric shaft to generate orbital motion of a scroll and (2) conventional bearings to restrict the orbital motion to a circle. The proposed miniature scroll pumps would differ from the prior, larger ones in both design and fabrication. A miniature scroll pump would include two scrolls: one mounted on a stationary baseplate and one on a flexure stage (see figure). An electromagnetic actuator in the form of two pairs of voice coils in a push-pull configuration would make the flexure stage move in the desired circular orbit. The capacitance between the scrolls would be monitored to provide position (gap) feedback to a control system that would adjust the drive signals applied to the voice coils to maintain the circular orbit as needed for precise sealing of the scrolls. To minimize power consumption and maximize precision of control, the flexure stage would be driven at the frequency of its mechanical resonance. The miniaturization of these pumps would entail both operational and manufacturing tolerances of <1 m. Such tight tolerances cannot be achieved easily by conventional machining of high-aspect-ratio structures like those of scroll-pump components. In addition, the vibrations of conventional motors and ball bearings exceed these tight tolerances by an order of magnitude. Therefore, the proposed pumps would be fabricated by the microfabrication method known by the German acronym LIGA ( lithographie, galvanoformung, abformung, which means lithography, electroforming, molding) because LIGA has been shown to be capable of providing the required tolerances at large aspect ratios.

Wiberg, Dean↗
NASA NTRS1979

Geophysical observations pertaining to solid-state convection in the terrestrial planets

Observational evidence for solid-state convection in the interiors of the terrestrial planets is reviewed. For the earth, the motion of the lithospheric plates constitutes clear evidence of large-scale convection in the mantle. Although Mars has been found to lack evidence of plate tectonics, the morphology of the Tharsis uplift and the elevation dichotomy between the northern and southern hemispheres may be evidence of mantle convection at one time. Measurements of lunar heat flow and seismic Q imply a convective mechanism limited to the lower mantle. Evidence for internal convection on Mercury consists of its dipole magnetic field and the 3/2 resonance between its rotational motion and its orbital motion, both of which can also be explained by other processes. The limited radar imagery of Venus has not yet provided conclusive evidence of either the presence or absence of convection features. It is concluded that although interior convection in terrestrial planets is implied by rheological, energy and momentum considerations, only on earth is the lithosphere thin enough to provide conclusive evidence of convection.

Phillips, R. J.↗
NASA NTRS1983

Discovery of 9.3 s X-ray pulsations from 2S 1553-542 and a determination of the orbit

X-ray pulsations with a period of 9.3 s from the transient galactic X-ray source 2S 1553-542 were detected. The data were obtained with SAS 3 during the only known outburst of the source in 1975 June. Pulse-timing analyses of the data, which span an interval of 20 days, show that there were large changes in the pulse period that are readily attributable to binary orbital motion. The inferred orbital period is 30.6 + or - 2.2 days and the X-ray mass function is 5.0 + or - 2.1 solar masses. These orbital parameters, the transient nature of the source, and the probable lack of an early-type giant companion star, lead to the tentative conclusion that 2S 1553-542 is a Be/X-ray binary system.

Kelley, R. L.↗
NASA NTRS2015

Electrostatic Model Applied to ISS Charged Water Droplet Experiment

The electrostatic force can be used to create novel relative motion between charged bodies if it can be isolated from the stronger gravitational and dissipative forces. Recently, Coulomb orbital motion was demonstrated on the International Space Station by releasing charged water droplets in the vicinity of a charged knitting needle. In this investigation, the Multi-Sphere Method, an electrostatic model developed to study active spacecraft position control by Coulomb charging, is used to simulate the complex orbital motion of the droplets. When atmospheric drag is introduced, the simulated motion closely mimics that seen in the video footage of the experiment. The electrostatic force's inverse dependency on separation distance near the center of the needle lends itself to analytic predictions of the radial motion.

Stevenson, Daan↗
NASA NTRS1993

On the location of the oscillations in AE Aquarii

There is much recent interest on the nature of the oscillations in the cataclysmic variable AE Aquarii. Detected in the optical, UV, X-ray, and possibly gamma-ray bands, the origin of these 33-sec oscillations remains poorly understood; the oscillation time-delay curve is phase shifted by about 60 deg with respect to the emission-line radial velocity curve, although both should track the orbital motion of the white dwarf. We present simultaneous absorption and emission-line radial velocities, and from the absorption lines we derive an improved ephemeris. Our emission-line velocities are phase shifted by about 75 deg, and hence are unreliable tracers of the orbital motion of the white dwarf. However, the oscillation orbit is shifted by only 5 deg +/- 3 deg percent confirming that the oscillations arise from a region concentric with the white dwarf. Thus the arrival times of the oscillations yield a measure of the white dwarfs apparent orbital velocity, independent of emission-line radial velocity measurements.

Welsh, William F.↗
NASA NTRS1981

The long-term motion of comet Halley

The orbital motion of comet Halley is numerically integrated back to 1404 BC. Starting with an orbit based on the 1759, 1682, and 1607 observations of the comet, the integration was run back in time with full planetary perturbations and nongravitational forces taken into account at each 0.5 day time-step. Small empirical corrections were made to the computed perihelion passage time in 837 and to the osculating orbital eccentricity in 800. In nine cases, the perihelion passage times calculated by Kiang (1971) from Chinese observations have been redetermined, and osculating orbital elements are given at each apparition from 1910 back to 1404 BC.

Yeomans, D. K.↗
NASA NTRS1973

Transformation between orbital parameters in different coordinate systems of the general relativistic Schwarzschild problem.

The relationships between the osculating orbital elements for a family of solutions of the general relativistic Schwarzschild problems are developed. These relationships provide a method for evaluating orbital elements in different Schwarzschild coordinate systems without the necessity of fitting to real data every time the system of coordinates is changed. The objectivity of different coordinate systems is discussed. Considerations of orbital motions favor the standard Schwarzschild metric, but the propagation of light signals is more objective in the metric of Painleve. Because the orbital motions usually dominate the representation of data, the standard Schwarzschild coordinates are the best objective choice for most applications.

Georgevic, R. M.↗
NASA NTRS1972

Nonthermal radio observations of the major planets

Seventeen years of observations have shown that Jupiter is a complex and intriguing source of emission over the entire radio spectrum accessible from the ground. The observations indicate the presence of intense radiation belts and a strong magnetic field inclined to the axis of rotation. At decametric wavelengths, several remarkably powerful sources are correlated with the rotation of the planet and the orbital motion of the satellite Io. Longer-term variations of these sources may be associated with the sunspot cycle, with Jupiter's orbital motion, or with changes in the internal structure of the planet. There is at most marginal evidence of nonthermal emission from Saturn, and as yet no evidence for such radiation from Uranus or Neptune.

Smith, A. G.↗
NASA NTRS1989

OTVE turbopump condition monitoring, task E.5

Recent work has been carried out on development of isotope wear analysis and optical and eddy current technologies to provide bearing wear measurements and real time monitoring of shaft speed, shaft axial displacement and shaft orbit of the Orbit Transfer Vehicle hydrostatic bearing tester. Results show shaft axial displacement can be optically measured (at the same time as shaft orbital motion and speed) to within 0.3 mils by two fiberoptic deflectometers. Evaluation of eddy current probes showed that, in addition to measuring shaft orbital motion, they can be used to measure shaft speed without having to machine grooves on the shaft surface as is the usual practice for turbomachinery. The interim results of this condition monitoring effort are presented.

Coleman, Paul T.↗
NASA NTRS1992

A magnitude-limited survey of Cepheid companions in the ultraviolet

Results of a magnitude-limited survey of classic Cepheids brighter than 8th mag carried out to search for hot main-sequence companions are presented. Spectra of 76 stars obtained with the IUE satellite in the 2000-3200-A region were compared with the spectra of nonvariable supergiants and also the single Cepheid Delta Cep to search for excess flux at 2500 A from possible companions. Photometric companions were found for 21 percent of the sample. When the Cepheids known to be binary from either orbital motion or spectra in the 1200-2000-A region are included, the percentage of companions rises to 29 percent. If a statistical correction from stars with orbital motion is included, 34 percent have companions. This percentage is compared with that found by Abt et al. (1990) for B2-B5 main-sequence stars. If only systems with periods longer than a year and separations not more than 30 arcsec are considered, only 18 percent of the B stars will become Cepheids with companions.

Evans, Nancy R.↗
NASA NTRS1995

Astrometric studies in the region of Algol

The distance and masses of the components of the triple star Algol (Beta Persei) are derived from photographic and electronic data collected with the two 0.76 m objectives of the Thaw Refractor at the University of Pittsburgh's Allegheny Observatory and with the 0.61 m visual refractor at Swarthmore College's Sproul Observatory. These datasets constitute the major narrow-field astrometric collections of this star. The newly derived weighted mean trigonometric parallax of Algol is now +0.0343 +/- 0.00085 corresponding to a distance modulus of 2.32 +/- 0.054 mag. The total mass of the Algol system is estimated at 6.05 +/- 0.45 solar mass. The photocentric semimajor axis of the AB/C orbit is determined in the blue, yellow, and red bandpasses of the three independent astrometric systems. The total mass for the A and B component stars is found to be 4.63 +/- 0.35 solar mass and the mass of the C component is determined to be 1.42 +/- 0.13 solar mass. Residuals to this solution showed no meaningful correlation to the orbital motion of A/B. Thus it is probable that the photocenter is located near the center of mass of the A/B subsystem. There is no evidence of a previously suggested 32 yr orbital motion and no significant acceleration is evident in the 60 yr photographic series. It is therefore unlikely that the system has a fourth stellar mass component. It is noted that the visual band interferometric studies of the Algol system have the AB and C components interchanged.

Gatewood, George↗
NASA NTRS2004

Coronal Structures in Cool Stars

Many papers have been published that further elucidate the structure of coronas in cool stars as determined from EUVE, HST, FUSE, Chandra, and XMM-Newton observations. In addition we are exploring the effects of coronas on the He I 1083081 transition that is observed in the infrared. Highlights of these are summarized below including publications during this reporting period and presentations. Ground-based magnetic Doppler imaging of cool stars suggests that active stars have active regions located at high latitudes on their surface. We have performed similar imaging in X-ray to locate the sites of enhanced activity using Chandra spectra. Chandra HETG observations of the bright eclipsing contact binary 44i Boo and Chandra LETG observations for the eclipsing binary VW Cep show X-ray line profiles that are Doppler-shifted by orbital motion. After careful analysis of the spectrum of each binary, a composite line-profile is constructed by adding the individual spectral lines. This high signal-to-noise ratio composite line-profile yields orbital velocities for these binaries that are accurate to 30 km/sec and allows their orbital motion to be studied at higher time resolutions. In conjunction with X-ray lightcurves, the phase-binned composite line-profiles constrain coronal structures to be small and located at high latitudes. These observations and techniques show the power of the Doppler Imaging Technique applied to X-ray line emission.

Oliversen, Ronald↗
NASA NTRS1990

Synthetic-aperture-radar imaging of the ocean surface using the slightly-rough facet model and a full surface-wave spectrum

A new model of synthetic-aperture-radar (SAR) imaging of ocean waves is described. The model is based on mapping individual, slightly-rough surface facets through the SAR processor into the image and responses of the facets in the image domain are added together coherently to give the composite image. A windowing technique allows both the orbital motion and the phase velocity of the long waves to be included. It is determined that the azimuthal cut-off is due to a smearing of the response of the facets in the image induced by the random orbital motion of the intermediate large-scale waves and that the focus adjustment that gives the greatest image contrast is half the phase velocity of the dominant long wave. The optimal processing technique, however, may consist of spatially offsetting the multiple looks on the image domain to compensate the propagation of long waves during the integration time of the SAR.

West, James C.↗
NASA NTRS1974

Relative motion of orbiting particles under the influence of perturbing forces. Volume 2: Analytical results

The mathematical developments carried out for this investigation are reported. In addition to describing and discussing the solutions which were acquired, there are compendia of data presented herein which summarize the equations and describe them as representative trace geometries. In this analysis the relative motion problems have been referred to two particular frames of reference; one which is inertially aligned, and one which is (local) horizon oriented. In addition to obtaining the classical initial values solutions, there are results which describe cases having applied specific forces serving as forcing functions. Also, in order to provide a complete state representation the speed components, as well as the displacements, have been described. These coordinates are traced on representative planes analogous to the displacement geometries. By this procedure a complete description of a relative motion is developed; and, as a consequence range rate as well as range information is obtained.

Eades, J. B., Jr.↗