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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Do Close-in Giant Planets Orbiting Evolved Stars Prefer Eccentric Orbits?

The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity (RV) measurements of three of these systems, revealing significantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moderately eccentric phase where they shrink faster than they circularize due to tides raised on evolved host stars. Additional RV measurements of currently known systems, along with new systems discovered by the recently launched NASA Transiting Exoplanet Survey Satellite (TESS) mission, may constrain the timescale and mass dependence of this process.

Thomas Barclay↗
NASA NTRS2022

Alma Images the Eccentric HD 53143 Debris Disk

We present ALMA 1.3 mm observations of the HD 53143 debris disk—the first infrared or millimeter image produced of this ∼1 Gyr old solar analog. Previous HST STIS coronagraphic imaging did not detect flux along the minor axis of the disk, which could suggest a face-on geometry with two clumps of dust. These ALMA observations reveal a disk with a strikingly different structure. In order to fit models to the millimeter visibilities and constrain the uncertainties on the disk parameters, we adopt a Markov Chain Monte Carlo approach. This is the most eccentric debris disk observed to date with a forced eccentricity of 0.21 ± 0.02, nearly twice that of the Fomalhaut debris disk, and also displays an apocenter glow. Although this eccentric model fits the outer debris disk well, significant interior residuals remain, which may suggest a possible edge-on inner disk, which remains unresolved in these observations. Combined with the observed structure difference between HST and ALMA, these results suggest a potential previous scattering event or dynamical instability in this system. We also note that the stellar flux changes considerably over the course of our observations, suggesting flaring at millimeter wavelengths. Using simultaneous TESS observations, we determine the stellar rotation period to be 9.6 ± 0.1 days.

Radio astronomy↗
NASA NTRS2023

First VLTI/GRAVITY Observations of HIP 65426 b: Evidence for a Low or Moderate Orbital Eccentricity

Giant exoplanets have been directly imaged over orders of magnitude of orbital separations, prompting theoretical and observational investigations of their formation pathways. In this paper, we present new VLTI/GRAVITY astrometric data of HIP 65426 b, a cold, giant exoplanet which is a particular challenge for most formation theories at a projected separation of 92 au from its primary. Leveraging GRAVITY's astrometric precision, we present an updated eccentricity posterior that disfavors large eccentricities. The eccentricity posterior is still prior dependent, and we extensively interpret and discuss the limits of the posterior constraints presented here. We also perform updated spectral comparisons with self-consistent forward-modeled spectra, finding a best-fit ExoREM model with solar metallicity and C/O = 0.6. An important caveat is that it is difficult to estimate robust errors on these values, which are subject to interpolation errors as well as potentially missing model physics. Taken together, the orbital and atmospheric constraints paint a preliminary picture of formation inconsistent with scattering after disk dispersal. Further work is needed to validate this interpretation. Analysis code used to perform this work is available on GitHub: https://github.com/sblunt/hip65426.

Sarah Blunt↗
NASA NTRS1972

Ephemeris of a highly eccentric orbit - Explorer 28.

An ephemeris has been obtained for Explorer 28 (IMP 3) which agrees well with 2 years of radio observations and with SAO observations a year later. This ephemeris is generated over the 3 year lifetime by a numerical integration method utilizing a set of initial conditions at launch and without requiring further differential correction. Because highly eccentric orbits are difficult to compute with acceptable accuracy and because a long continuous arc has been obtained which compares with actual data to a known precision, this ephemeris may be used as a standard for computing highly eccentric orbits in the earth-moon system. Orbit improvement was used to obtain the initial conditions which generated the ephemeris. This improvement was based on correcting the energy by adjusting the semimajor axis to match computed times of perigee passage with the observed. This procedure may generate errors in semimajor axis to compensate for model errors in the energy; however, this compensation error is also implicit in orbit determination itself.

Lowrey, B. E.↗
NASA NTRS1975

Solutions of the motion of synchronous satellites with arbitrary eccentricity and inclination

A first order, semianalytical theory for the long term motion of resonant satellites is presented. The theory is valid for all eccentricities and inclinations and for all commensurability ratios. The method allows the inclusion of all the zonal and tesseral harmonics as well as luni solar perturbations and radiation pressure. The method is applied to a synchronous satellite including only the J sub 2 and J sub 22 harmonics. Global, long term solutions for this problem, eccentricity, argument of perigee, and inclination are obtained.

Nacozy, P. E.↗
NASA NTRS1976

Buckling of eccentrically stringer-stiffened cylindrical panels under axial compression

The paper presents numerical results, based on Donnell shell theory, for the axial compressive buckling loads for eccentrically stringer-stiffened circular cylindrical panels, in a study of the effect of boundary conditions and panel width on the buckling load. The two cases of inside and outside stiffeners were considered. The complete cylinder buckling load was reached only for panels under classical simply supported boundary conditions. The prevention of circumferential displacement is found to be the most important in-plane boundary condition from the point of view of increasing the buckling load. Clamping is found more effective in increasing the buckling loads of panels with free circumferential edge displacement than of panels with zero edge displacement. When panel width is equal to or greater than 180 deg, the panel buckling loads are within 10% of the complete cylinder load for all cases except one simply supported panel with outside stringers. Buckling loads were higher for outside stringers, except for very narrow panels that are restrained against circumferential edge displacement. Eccentricity effects are generally similar for clamped and simply supported panels with the same in-plane boundary conditions.

Sobel, L. H.↗
NASA NTRS1979

Gravitational spectra from the tracking of planetary spacecraft in eccentric orbits

Two dimensional gravitational spectra are derived from simple harmonic analysis of range rate tracking data on planetary orbiters. The eccentricity of the orbit is arbitrary and results are shown to vary substantially with the aspect angle of the tracking line of sight with the orbit plane. The development for arbitrary start with stop times (with respect to periapsis) uses modified eccentricity functions evaluated by quadrature. Simulations with a point-masses model of Venus using tracking data on the Pioneer Venus Orbiter show excellent predictions of the average orbiter spectrum over one Venus day. The Venus gravitational signal should be above the tracking noise level for arc lengths longer than 40 deg (in true anomaly) about periapsis and for terms as high as 55th degree. analysis has been made of tracking residuals from a short arc fit to Mariner Mars 9 data over the Hellas Basin (using a complete 6th degree field). Results are most consistent with higher residual gravitational power than predicted from Kaula's rule for Mars.

Wagner, C. A.↗
NASA NTRS1978

Dynamics of short eccentric plain seals with high axial Reynolds number

Plain seals with high axial flow rates produce large stiffness and damping coefficients that can help stabilize high-speed rotating machinery. When the shaft is eccentric in the seal, a Bernoulli effect low-pressure region occurs on the large-clearance side of the shaft. A fluid-restoring force tends to center the shaft and reduce vibrations. This work extends the previous theory for short plain centered seals to large eccentricities using a perturbation analysis. Surface roughness effects are also included. An analysis of seals used in the Space Shuttle main engine hydrogen fuel turbopump indicates the desirability of plain seals over the labyrinth type. Experimental results confirm this.

Allaire, P. E.↗
NASA NTRS1979

Choice reaction time to movement of eccentric visual targets during concurrent rotary acceleration

This study investigates the influence of concurrent rotary acceleration on choice reaction time (RT) to a small, accelerating visual cursor on a cathode-ray tube. Subjects sat in an enclosed rotating device at the center of rotation and observed a 3-mm dot accelerating at different rates across a cathode-ray tube. The dot was viewed at various eccentricities under conditions of visual stimulation alone and with concurrent rotary acceleration. Subjects responded to both vertical and horizontal dot movements. There was a significant inverse relationship between choice RT and level of dot acceleration (p less than .001), and a significant direct relationship between choice RT and eccentricity (p less than .001). There was no significant difference between choice RT to vertical or horizontal dot motion (p greater than .25), and choice RT was not significantly affected by concurrent rotary acceleration (p greater than .10). The results are discussed in terms of the effects of vestibular stimulation on choice RT to visual motion.

Hamerman, J. A.↗
NASA NTRS1980

Binary model of Circinus X-1. I - Eccentricity from combined X-ray and radio observations

A binary star model is used to account for the 16.59-d flaring behavior of the X-ray emission from Circinus X-1. The orbital eccentricity of 0.8 + or - 0.1 is derived from the X-ray light curve by assuming that the sharp X-ray cut-off every 16.59-d is a result of bound-free absorption in the primary star's stellar wind. The shape of the light curve has changed over the last eight years, and this is interpreted as due to orbital precession of the binary system. Simultaneous radio and X-ray observations of the flare from Circinus X-1 on February 1-5, 1978 are reported. These are accounted for within the framework of the model. The radio observations at 5 GHz are used independently to derive a high value of the orbital eccentricity (e = 0.7).

Murdin, P.↗
NASA NTRS1981

Effect of load eccentricity and substructure deformation on ultimate strength of shuttle orbiter thermal protection system

The effect of load eccentricity and substructure deformation on the ultimate strength and stress displacement properties of the shuttle orbiter thermal protection system (TPS) was determined. The LI-900 Reusable Surface Insulation (RSI) tiles mounted on the .41 cm thick Strain Isolator Pad (SIP) were investigated. Substructure deformations reduce the ultimate strength of the SIP/tile TPS and increase the scatter in the ultimate strength data. Substructure deformations that occur unsymmetric to the tile can cause the tile to rotate when subjected to a uniform applied load. Load eccentricity reduces SIP/tile TPS ultimate strength and causes tile rotation.

Sawyer, J. W.↗
NASA NTRS1982

Long-term motion of resonant satellites with arbitrary eccentricity and inclination

A first-order, semi-analytical method for the long-term motion of resonant satellites is introduced. The method provides long-term solutions, valid for nearly all eccentricities and inclinations, and for all commensurability ratios. The method allows the inclusion of all zonal and tesseral harmonics of a nonspherical planet. We present here an application of the method to a synchronous satellite including J2 and J22 harmonics. Global, long-term solutions for this problem are given for arbitrary values of eccentricity, argument of perigee and inclination.

Nacozy, P. E.↗
NASA NTRS1984

Theory for Eccentric and Misalined Annular Seals

Theory describes behavior of eccentric and angularly-misalined incompressible-fluid shaft seals. Direct and cross-coupled stiffness and damping coefficients expressed in terms of degree of eccentricity and coefficients of concentric system.

Jackson, E.↗
NASA NTRS1983

The variations in eccentricity and apse precession rate of a narrow ring perturbed by a close satellite

The first-order perturbations of orbital eccentricity and apse precession rate for the case of a narrow ring, due to a close satellite whose orbit is also eccentric, are described by means of a Hamiltonian. The present treatment covers cases in which the satellite crosses the ring, and the level curves of the Hamiltonian are displayed for several parameter values. The results obtained are applied to the interaction of Saturn's F ring with its inner shepherd satellite.

Borderies, N.↗
NASA NTRS1984

The eccentric Saturnian ringlets at 1.29 R(s) and 1.45 R(s)

The shapes and kinematics of the Titan and Maxwell ringlets of Saturn's C ring are studied. The ringlets are narrow and eccentric, with mean widths of about 25 km for Titan and abut 64 km for Maxwell, and with eccentricities of order 10 to the -4th. They have sharp edges on a scale of about 1 km, normal optical depths of roughly 0.5-2.0, normal optical depth of the surrounding region, and positive linear width-radius relations. The Titan ringlet is the only feature whose dynamics appears to be completely determined by an external satellite; the kinematics of the Maxwell ringlet are determined solely by Saturn's nonspherical gravity field. The comparatively large measured optical depths and large inferred mass extinction coefficients for the ringlets suggest an environment and particle size distribution different from the remainder of the C ring and presumably caused by the mechanism responsible for ring confinement.

Porco, C.↗
NASA NTRS1988

A new constraint on Saturn's zonal gravity harmonics from Voyager observations of an eccentric ringlet

The results obtained by Porco et al. (1984) from an analysis of the kinematics of an eccentric ringlet in Saturn's inner ring are used to add an additional constraint to the gravity solution of Null et al. (1981) and thus to derive the first experimental estimate of the Saturn's J6 gravitational field. On the assumption that the eccentricity of this ringlet is forced by the satellite Titan, the location of the Titan apsidal resonance is determined to an accuracy of + or - 13 km, which in turn provides a strong constraint on Saturn's zonal gravity harmonics. Combining this constraint with the results of Null et all. and adopting a priori values for J8, J10, and J12 based on interior models, new estimates are obtained for the first three zonal gravity coefficients J2, J4, and J6.

Nicholson, Philip D.↗