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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

An abrupt change in ridge axis gravity with spreading rate

A total of 44 Geosat profiles over ridges with spreading rates ranging from 14 to 155 mm/yr were analyzed. In agreement with previous studies, it is found that slow spreading ridges usually have high amplitude gravity troughs, while fast spreading ridges are characterized by low-amplitude ridge axis highs. Unexpectedly, it is found that the transition from axial trough to axial high occurs abruptly at a spreading rate of 60-70 mm/yr. Ridge axis gravity signatures are highly variable for rates less than 65 mm/yr and very uniform at higher rates. The transition of the gravity signature appears to get more abrupt than the transition of the topographic signature, suggesting an abrupt change in the style of isostatic compensation with spreading rate. Published models of ridge axis dynamics do not explain this sharp transition.

Small, Christopher↗
NASA NTRS1990

Effects of off-axis radiation on reflective concentrating systems for space power

Off-axis incident radiation, resulting from misalignment of a concentrator relative to incident solar flux, can potentially result in high flux concentrations at positions other than the design focal point. It is suggested that the impact of these concentrations should be considered when choosing materials and thermal control strategies for structures adjacent to the concentrator. A numerical (ray tracing) analysis of the effects of off-axis radiation on the proposed solar concentrator for the Space Station Freedom is performed. The magnitude and position of the reflected flux peaks are identified for a matrix of off-axis angles and target distances. The principles of geometric optics are presented to illustrate that the results of the numerical study are justified, and these results are explained in terms of these basic optical principles. A method that allows prediction of the reflected flux field for a generalized parabolic reflective concentrating system is presented.

Campbell, J. S.↗
NASA NTRS1992

Multi-axis transient vibration testing of space objects: Test philosophy, test facility, and control strategy

IABG has been using various servohydraulic test facilities for many years for the reproduction of service loads and environmental loads on all kinds of test objects. For more than 15 years, a multi-axis vibration test facility has been under service, originally designed for earthquake simulation but being upgraded to the demands of space testing. First tests with the DFS/STM showed good reproduction accuracy and demonstrated the feasibility of transient vibration testing of space objects on a multi-axis hydraulic shaker. An approach to structural qualification is possible by using this test philosophy. It will be outlined and its obvious advantages over the state-of-the-art single-axis test will be demonstrated by example results. The new test technique has some special requirements to the test facility exceeding those of earthquake testing. Most important is the high reproduction accuracy demanded for a sophisticated control system. The state-of-the-art approach of analog closed-loop control circuits for each actuator combined with a static decoupling network and an off-line iterative waveform control is not able to meet all the demands. Therefore, the future over-all control system is implemented as hierarchical full digital closed-loop system on a highly parallel transputer network. The innermost layer is the digital actuator controller, the second one is the MDOF-control of the table movement. The outermost layer would be the off-line iterative waveform control, which is dedicated only to deal with the interaction of test table and test object or non-linear effects. The outline of the system will be presented.

Lachenmayr, Georg↗
NASA NTRS1993

High-resolution Y-axis readout for delay-line microchannel anodes

We have devised a method to obtain a high-resolution Y-axis event position determination from microchannel plate delay-line detectors. The method is based on the double-delay-line wedge-wedge charge partition principle of Lampton et al. (1990), where the X axis is read out by a pair of side-by-side delay lines and the Y-axis coordinate is determined by comparing the charges on the two parallel delay lines. However, our new method abandons the common field return path of the two delay lines, and splits them into two adjacent but independent transformer coupled timing circuits having no common ground connection except via the charge-measurement amplifiers. Thus we eliminate the large electrostatic capacitance of the delay lines from the input of the charge-measuring system. Over its limited working field, the spatial resolution in the Y coordinate can easily equal the resolution provided in the X coordinate by the delay line. Applications to extreme and FUV photon-counting spectroscopy are envisioned.

Raffanti, R.↗
NASA NTRS1995

The axis ratio distribution of faint galaxies: Evidence for a populatin of dwarfgalaxies at I approximately 20.5

The axis ratio distribution of faint galaxies observed by the Hubble Space Telescope (HST) as part of the Medium Deep Survey (MDS) key project suggests that a very large fraction of the total population at magnitudes I greater than or equal to 20 mag consists of a class of galaxies with luminosity profile, axis ratio distribution, angular size, and color that resemble local dwarfs. We find that galaxies with exponential light profiles and small angular sizes (half-light radius less than 0.6 sec) have an axis ratio distribution that is incompatible with their being intrinsically flattened objects and is instead consistent with local elliptical galaxies. We call these objects 'Small Exponential Ellipticals.' They are most likely dwarf galaxies, and they are numerous enough that, together with irregular galaxies, they can account for most if not all of the excess in the number counts at I approximately 20-21 mag with respect to the standard no-evolution models. This may suggest that the excess number counts are best explained by dwarf-rich models with strong luminosity evolution of the dwarf galaxies. Our data also supports a very mild luminosity evolution of the giant galaxy populations, which contributes little to the excess number counts.

Im, Myungshin↗
NASA NTRS1996

Flight Test of a Propulsion-Based Emergency Control System on the MD-11 Airplane with Emphasis on the Lateral Axis

A large, civilian, multi-engine transport MD-11 airplane control system was recently modified to perform as an emergency backup controller using engine thrust only. The emergency backup system, referred to as the propulsion-controlled aircraft (PCA) system, would be used if a major primary flight control system fails. To allow for longitudinal and lateral-directional control, the PCA system requires at least two engines and is implemented through software modifications. A flight-test program was conducted to evaluate the PCA system high-altitude flying characteristics and to demonstrate its capacity to perform safe landings. The cruise flight conditions, several low approaches and one landing without any aerodynamic flight control surface movement, were demonstrated. This paper presents results that show satisfactory performance of the PCA system in the longitudinal axis. Test results indicate that the lateral-directional axis of the system performed well at high attitude but was sluggish and prone to thermal upsets during landing approaches. Flight-test experiences and test techniques are also discussed with emphasis on the lateral-directional axis because of the difficulties encountered in flight test.

Burken, John J.↗
NASA NTRS1997

Polar Spin Axis Anomaly

The Global Geospace Science (GGS) Polar Plasma Laboratory (POLAR) spacecraft was launched on February 24, 1996, by a Delta 2. The spacecraft, a major axis spinner, appeared to function nominally throughout the early mission phase, which included several deployments, and orbit and attitude maneuvers. Of particular interest is the fact that the spacecraft was launched with a deliberate dynamic imbalance. During a segment of early orbit operations, a pair of Lanyard Deployed Booms (LDB) were extended. These booms were not identical; the intent was that the spacecraft would be nearly dynamically balanced after they were deployed. The spacecraft contained two dynamic balance mechanisms intended to fine tune the balance on orbit. However, subsequent images taken by the science instruments on the Despun Platform during the dynamic balancing segment indicated an offset of the principal spin axis from the geometric axis. This offset produced a sinusoidal blurring of the science images sufficiently large to degrade science data below mission requirement specifications. In the end, the imbalance encountered in flight was significantly outside the correction capability of the balances. The purpose of this paper is to examine the flight data during the various deployment and maneuver stages of the early orbit operations coupled with analytical simulations to discuss some of the potential causes of the resultant imbalance.

Crouse, Patrick L.↗
NASA NTRS1994

Off-Axis Drag of Dendrite Fragments at Low Reynolds Number

The aim of the present investigation is to characterize the motion of dendrite fragments falling under the influence of gravity in a uniform liquid medium at low Reynolds number. In an earlier study, Zakhem, Weidman and de Groh (1992) reported on the settling speed of model equiaxed dendrite grains released along their axis of symmetry. In this follow-up study uniaxial model dendrite grains were released off-axis to observe and document their motion at different orientations. It was hypothesized that the dendrite models might rotate when released off-axis in which case an attempt would be made to document the ensuing unsteady motion. This latter event turned out to be in fact true: at the small but finite Reynolds numbers that existed, each uniaxial dendrite slowly rotated towards its equilibrium orientation while failing under the influence of gravity. In addition to completing the original goal, we have made use of a beads-on-a shell Stokes flow code to numerically determine the drag coefficient for capsules, i.e.. uniaxial dendrites without arms. The drag on horizontally and vertically falling capsules are reported and compared with measurements.

Weidman, P. D.↗
NASA NTRS2001

Spacecraft Formation Flying Maneuvers Using Linear Quadratic Regulation With No Radial Axis Inputs

Regarding multiple spacecraft formation flying, the observation has been made that control thrust need only be applied coplanar to the local horizon to achieve complete controllability of a two-satellite (leader-follower) formation. A formulation of orbital dynamics using the state of one satellite relative to another is used. Without the need for thrust along the radial (zenith-nadir) axis of the relative reference frame, propulsion system simplifications and weight reduction may be accomplished. This work focuses on the validation of this control system on its own merits, and in comparison to a related system which does provide thrust along the radial axis of the relative frame. Maneuver simulations are performed using commercial ODE solvers to propagate the Keplerian dynamics of a controlled satellite relative to an uncontrolled leader. These short maneuver simulations demonstrate the capacity of the controller to perform changes from one formation geometry to another. Control algorithm performance is evaluated based on measures such as the fuel required to complete a maneuver and the maximum acceleration required by the controller. Based on this evaluation, the exclusion of the radial axis of control still allows enough control authority to use Linear Quadratic Regulator (LQR) techniques to design a gain matrix of adequate performance over finite maneuvers. Additional simulations are conducted including perturbations and using no radial control inputs. A major conclusion presented is that control inputs along the three axes have significantly different relationships to the governing orbital dynamics that may be exploited using LQR.

Starin, Scott R.↗
NASA NTRS1993

Deep cytoplasmic rearrangements in axis-respecified Xenopus embryos

In fertilized eggs of the frog Xenopus, the vegetal yolk mass rotates away from the future dorsal side (J. P. Vincent and J. Gerhart, 1987, Dev. Biol. 123, 526-539), and a major rearrangement of the deep animal hemisphere cytoplasm produces a characteristic swirl in the prospective dorsal side (M. V. Danilchik and J. M. Denegre, 1991, Development 111, 845-856). The relationship between this swirl and determination of the dorsal-ventral axis was further investigated by attempting to experimentally separate the positions of the swirl and the dorsal-ventral axis. Eggs were obliquely oriented in the gravity field to respecify the direction of yolk mass rotation and the position of the dorsal-ventral axis. When yolk mass rotation occurred in the absence of a sperm, as in activated eggs, a swirl pattern formed on the side away from which the yolk mass had rotated. In fertilized eggs tipped with the sperm entry point (SEP) down or to the side, swirl patterns were always found to form on the side away from which the yolk mass was displaced. However, in eggs tipped SEP up, in which the yolk mass was forced to rotate away from the SEP, more complicated rearrangements were observed in addition to the rotation-oriented swirl. Because the direction of yolk mass rotation was found to be influenced by both gravity and the actual position of the SEP in obliquely oriented eggs (SEP to the side), such complicated rearrangement patterns may result from opposing forces generated by both yolk mass rotation and the expanding sperm aster. Thus, except in cases in which the influences of SEP position and unit gravity opposed each other, it was not possible to experimentally separate the position of the deep cytoplasmic swirl from the direction of yolk mass rotation, and therefore the position of the prospective dorsal side.

Non-NASA Center↗
NASA NTRS1992

Off-vertical axis rotation: a test of the otolith-ocular reflex

The vestibulo-ocular reflex was studied via off-vertical axis rotation (OVAR) in the dark. The axis of the turntable could be tilted from vertical by up to 30 degrees. Eye movements were measured with electro-oculography. Results from healthy asymptomatic subjects indicated that 1) a reliable otolith-induced response could be obtained during constant velocity OVAR using a velocity of 60 degrees/s with a tilt of 30 degrees; 2) constant velocity OVAR rotation was nausea-producing and, especially if subjects were rotated in the dark about an earth-vertical axis prior to being tilted, disorienting; and 3) sinusoidal OVAR produced minimal nausea; the eye movement response appeared to be the result of a combination of semicircular canal and otolith components. We conclude that OVAR has the potential of becoming a useful method for clinically assessing both the otolith-ocular reflex and semicircular canal-otolith interaction.

NASA Discipline Neuroscience↗
NASA NTRS2005

Ocular Reflex Phase During Off-Vertical Axis Rotation In Humans Is Modified By Head-On-Trunk Position

Constant velocity Off-Vertical Axis Rotation (OVAR) imposes a continuously varying orientation of the head and body relative to gravity. The ensuing ocular reflexes include modulation of both horizontal and torsional eye velocity as a function of the varying linear acceleration along the lateral plane. The purpose of this study was to examine whether the modulation of these ocular reflexes would be modified by different head-on-trunk positions. Ten human subjects were rotated in darkness about their longitudinal axis 20 deg off-vertical at constant rates of 45 and 180 deg/s, corresponding to 0.125 and 0.5 Hz. Binocular responses were obtained with video-oculography with the head and trunk aligned, and then with the head turned relative to the trunk 40 deg to the right or left of center. Sinusoidal curve fits were used to derive amplitude, phase and bias velocity of the eye movements across multiple cycles for each head-on-trunk position. Consistent with previous studies, the modulation of torsional eye movements was greater at 0.125 Hz while the modulation of horizontal eye movements was greater at 0.5 Hz. Neither amplitude nor bias velocities were significantly altered by head-on-trunk position. The phases of both torsional and horizontal ocular reflexes, on the other hand, shifted towards alignment with the head. These results are consistent with the modulation of torsional and horizontal ocular reflexes during OVAR being primarily mediated by the otoliths in response to the sinusoidally varying linear acceleration along the interaural head axis.

Wood, Scott↗
NASA NTRS2005

An Off-Axis Four-Quadrant Phase Mask (FQPM) Coronagraph for Palomar: High-Contrast Near Bright Stars Imager

Direct detection of planets around nearby stars requires the development of high-contrast imaging techniques because of the high difference between their respective fluxes. This led us to test a new coronagraphic approach based on the use of phase mask instead of dark occulting ones. Combined with high-level wavefront correction on an unobscured off-axis section of a large telescope, this method allows imaging very close to the star. Calculations indicate that for a given ground-based on-axis telescope, use of such an off-axis coronagraph provides a near-neighbor detection capability superior to that of a traditional coronagraph utilizing the full telescope aperture. Setting up a laboratory experiment working in near infrared allowed us to demonstrate the principle of the method, and a rejection of 2000:1 has already been achieved.

coronagraphy↗
NASA NTRS2008

Three Axis Control of the Hubble Space Telescope Using Two Reaction Wheels and Magnetic Torquer Bars for Science Observations

The Hubble Space Telescope (HST) is renowned for its superb pointing accuracy of less than 10 milli-arcseconds absolute pointing error. To accomplish this, the HST relies on its complement of four reaction wheel assemblies (RWAs) for attitude control and four magnetic torquer bars (MTBs) for momentum management. As with most satellites with reaction wheel control, the fourth RWA provides for fault tolerance to maintain three-axis pointing capability should a failure occur and a wheel is lost from operations. If an additional failure is encountered, the ability to maintain three-axis pointing is jeopardized. In order to prepare for this potential situation, HST Pointing Control Subsystem (PCS) Team developed a Two Reaction Wheel Science (TRS) control mode. This mode utilizes two RWAs and four magnetic torquer bars to achieve three-axis stabilization and pointing accuracy necessary for a continued science observing program. This paper presents the design of the TRS mode and operational considerations necessary to protect the spacecraft while allowing for a substantial science program.

Hur-Diaz, Sun↗
NASA NTRS1935

The Effect of Lateral Inclination of the Thrust Axis and of Sweepback of the Leading Edge of the Wing on Propulsive and Net Efficiencies of a Wing-Nacelle-Propeller Combination

This report describes and gives the results of tests made to determine the effect of lateral inclination of the propeller thrust axis to the direction of flight. A wing-nacelle-propeller combination with the nacelle axis located successively parallel to and at 15 degrees to the perpendicular to the leading edge of a wing was tested with the combination at several angles of yaw. Tests of the wing alone at the same angles of yaw were also made. The data are presented in the usual graphic form. An increase in propulsive efficiency with increase in angle of the thrust axis was found. The change in net efficiency, found by charging the whole nacelle drag to the power unit, was negligible, however, within the range of the tests.

Wood, Donald H.↗
NASA NTRS2010

A Two-Axis Direct Fluid Shear Stress Sensor

This innovation is a miniature or micro sized semiconductor sensor design that provides two axis direct non-intrusive measurement of skin friction or wall shear stress in fluid flow. The sensor is fabricated by micro-electro-mechanical system (MEMS) technology, enabling small size and low cost reproductions. The sensors have been fabricated by utilizing MEMS fabrication processes to bond a sensing element wafer to a fluid coupling wafer. This layering technique provides for an out of plane dimension that is on the same order of length as the inplane dimensions. The sensor design has the following characteristics: a shear force collecting plate with dimensions that can be tailored to various application specific requirements such as spatial resolution, temporal resolution and shear force range and resolution. This plate is located coplanar to both the sensor body and flow boundary, and is connected to a dual axis gimbal structure by a connecting column or lever arm. The dual axis gimbal structure has torsional hinges with embedded piezoresistive torsional strain gauges which provide a voltage output that is correlated to the applied shear stress (and excitation current) on force collection plate that is located on the flow boundary surface (hence the transduction method). This combination of design elements create a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from the small shear stress on the flow boundary wall. This design as well as the use of back side electrical contacts establishes a non-intrusive method to quantitatively measure the shear force vector on aerodynamic bodies.

Adcock, Edward E.↗
NASA NTRS2010

Antenna Axis Offset Estimation from VLBI

The antenna axis offsets were estimated from global solutions and single sessions. We have built a set of global solutions from R1 and R4 sessions and from the sets of sessions between SVETLOE repairs. We compared our estimates with local survey data for the stations of the QUASAR network. Svetloe station axis offset values have changed after repairs. For non-global networks, the axis offset value of a single station can significantly affect the EOP estimations.

Kurdubov, Sergey↗
NASA NTRS2020

Mock Catalogs for the Extragalactic X-ray Sky: Simulating AGN Surveys with ATHENA and with the AXIS Probe

We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10-20 erg cm-2 s-1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ~225 000 AGNs and ~50 000 nonactive galaxies, reaching a flux limit of f0:5-2 ~ 5 x 10-19 erg cm-2 s-1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ~20 000 z > 3 AGNs and ~250 sources at redshift z > 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.

X-ray galaxies↗