Results for “conditional shift” — Page 25

NASA NTRS2002

Design and Stress Analysis of Low-Noise Adjusted Bearing Contact Spiral Bevel Gears

An integrated computerized approach for design and stress analysis of low-noise spiral bevel gear drives with adjusted bearing contact has been developed. The computation procedure is an iterative process, requiring four separate steps that provide: (a) a parabolic function of transmission errors that is able to reduce the effect of errors of alignment, and (b) reduction of the shift of bearing contact caused by misalignment. Application of finite element analysis permits the contact and bending stresses to be determined and investigate the formation of the bearing contact. The design of finite element models and boundary conditions is automated and does not require an intermediate CAD computer program. A commercially available finite element analysis computer program with contact capability was used to conduct the stress analysis. The theory developed is illustrated with numerical examples.

Litvin, Faydor L.↗

NASA NTRS2002

Design and Stress Analysis of Low-Noise Adjusted Bearing Contact Spiral Bevel Gears

An integrated computerized approach for design and stress analysis of low-noise spiral bevel gear drives with adjusted bearing contact is proposed. The procedure of computations is an iterative process that requires four separate procedures and provide: (a) a parabolic function of transmission errors that is able to reduce the effect of errors of alignment on noise and vibration, and (b) reduction of the shift of bearing contact caused by misalignment. Application of finite element analysis enables us to determine the contact and bending stresses and investigate the formation of the bearing contact. The design of finite element models and boundary conditions is automated and does not require intermediate CAD computer programs for application of general purpose computer program for finite element analysis.

Fuentes, A.↗

NASA NTRS2021

Long-Duration Wear Testing of the ASTRAEUS Hall Thruster, Phases II & III: 72 kg Xe Throughput & 1.2 MN-s Total Impulse

The thruster component of the Ascendant Sub-kW Transcelestial Electric Propulsion System successfully completed a propellant throughput demonstration of 72 kg Xe in a long-duration wear test planned to eventually exceed 100 kg. The thruster has been operated for a total of 5450 h over three operating conditions: 3287 h at 300 V – 1000 W, 1745 h at 500 V – 1000 W, and 417 h at 400 V – 600 W. A total of 1.2 MN-s of impulse has been demonstrated to date. Thrust, telemetry, and temperature measurements periodically recorded at four operating conditions spanning 200 – 500 V and 200 – 1000 W revealed constant performance across the full test duration. The erosion of the downstream faces of the thruster was observed to be higher than anticipated after the first 5032 h of thruster operation. This issue was traced to the application of sub-nominal magnetic field strengths throughout the LDWT, caused by an electrical-related ground-support equipment issue, which resulted in a downstream shift of the discharge plasma and enhanced erosion of the thruster’s pole covers. Nevertheless, the thruster performance and operational behaviour remained unaffected. High-fidelity plasma simulations of the erosion of the thruster’s downstream faces, supported by prior short-duration wear testing, suggest a theoretical lifetime capability of >30 kh, corresponding to propellant throughput of >450 kg Xe and a total impulse of >7 MNs, at the 300 V – 1000 W operating condition. The test was voluntarily paused after 68 kg Xe and 72 kg Xe throughput, respectively, to take these erosion measurements at the 500 V and 400 V operating conditions before the test was resumed at a different operating condition.

Goebel, Dan↗

NASA NTRS1995

Acute exposure to 2G phase shifts the rat circadian timing system

The circadian timing system (CTS) provides internal and external temporal coordination of an animal's physiology and behavior. In mammals, the generation and coordination of these circadian rhythms is controlled by a neural pacemaker, the suprachiasmatic nucleus (SCN), located within the hypothalamus. The pacemaker is synchronized to the 24 hour day by time cures (zeitgebers) such as the light/dark cycle. When an animal is exposed to an environment without time cues, the circadian rhythms maintain internal temporal coordination, but exhibit a 'free-running' condition in which the period length is determined by the internal pacemaker. Maintenance of internal and external temporal coordination are critical for normal physiological and psychological function in human and non-human primates. Exposure to altered gravitational environments has been shown to affect the amplitude, mean, and timing of circadian rhythms in species ranging from unicellular organisms to man. However, it has not been determined whether altered gravitational fields have a direct effect on the neural pacemaker, or affect peripheral parameters. In previous studies, the ability of a stimulus to phase shift circadian rhythms was used to determine whether a stimulus has a direct effect on the neural pacemaker. The present experiment was performed in order to determine whether acute exposure to a hyperdynamic field could phase shift circadian rhythms.

Hoban-Higgins, T. M.↗

NASA NTRS1972

Broadening of the D lines and the relaxation of the resonance levels of sodium due to collisions with helium.

Calculated potentials for the NaHe molecule are used to obtain collision-induced widths and shifts for the sodium D lines together with cross sections for fine-structure transitions and the relaxation of the multipole polarizations of the resonance levels. The atomic collision is treated in an adiabatic approximation in which the colliding atoms form a molecular system which rotates during the collision. We find the resonance lines to be broadened equally and to be approximately 70% wider, and with associated shifts of an order of magnitude smaller, than expected on the basis of van der Waals forces. The dependence of the cross sections for relaxation of the multipole polarizations of the resonance levels on the molecular-coupling conditions and the rotation of the system during collision is discussed and indicates a limitation of the sum rule for these cross sections.

Lewis, E. L.↗

NASA NTRS1981

Effect of physical aging on stress relaxation of poly/methyl methacrylate/

A study was made on the stress relaxation behavior at 25 C of poly(methyl methacrylate) in uniaxial tension as a function of physical aging at both room temperature and 60 C. Test specimens were compression molded at 165 C, then quenched to room temperature and allowed to age for up to 30 days prior to testing. Stress relaxation curves measured after different aging times could be superposed to a single master curve for each aging temperature. Superposition was achieved by applying vertical and horizontal shifts. Hence, the shape of the response curves was not changed by aging. This is in accordance with observations made by Struik for tensile creep curves. Volume changes as a function of physical aging were also determined. Simple exponential relationships were observed between volume and both horizontal and vertical shifts. The horizontal shift implies a shift in the effective time scale caused by a change in free volume. The vertical shifts could be correlated with changes in Young's modulus caused by a change in density. For the range of aging studied, the response time scale varied over nearly two decades of log-time. For the same conditions modulus varied by 30 percent.

Cizmecioglu, M.↗

NASA NTRS1992

Velocity structure in optical CH(+) lines toward HD 190603 and implications for the formation of CH(+)

Observations of CH(+) and other species accessible in optical wavelengths in the line of sight to HD 190603, a B 1.5 Iae supergiant are reported. In this line of sight a shift in radial velocity between the CH(+) line and other interstellar absorption lines such as CH and Ca I is observed. The most likely explanation for this effect is the shock formation of CH(+). Likely preshock and postshock conditions which are consistent with the observations are also estimated.

Allen, M. M.↗

NASA NTRS1999

The timing of galvanic vestibular stimulation affects responses to platform translation

We compared the effects of galvanic vestibular stimulation applied at 0, 0.5, 1.5 and 2.5 s prior to a backward platform translation on postural responses. The effect of the galvanic stimulation was largest on the final equilibrium position of the center of pressure (CoP). The largest effects occurred for the 0.5 and 0-s pre-period, when the dynamic CoP pressure changes in response to both the galvanic stimulus and the platform translation coincided. The shift in the final equilibrium position was also larger than the sum of the shifts for the galvanic stimulus and the platform translation alone for the 0.5 and 0-s pre-periods. The initial rate of change of the CoP response to the platform translation was not significantly affected in any condition. Changes in the peak CoP position could be accounted for by local interaction of CoP velocity changes induced by the galvanic and translation responses alone, but the changes in final equilibrium position could only be accounted for by a change in global body orientation. These findings suggest that the contribution of vestibulospinal information is greatest during the dynamic phase of the postural response, and that the vestibular system contributes most to the later components of the postural response, particularly to the final equilibrium position. These findings suggest that a nonlinear interaction between the vestibular signal induced by the galvanic current and the sensory stimuli produced by the platform translation occurs when the two stimuli are presented within 1 s, during the dynamic phase of the postural response to the galvanic stimulus. When presented at greater separations in time, the stimuli appear to be treated as independent events, such that no interaction occurs. Copyright 1999 Elsevier Science B.V.

Non-NASA Center↗

NASA NTRS2011

30 WS North Base Wind Study

The 30 Weather Squadron (30 WS) is concerned about strong winds observed at their northern towers without advance warning. They state that terrain influences along the extreme northern fringes of Vandenberg Air Force Base (VAFB) make it difficult for forecasters to issue timely and accurate high wind warnings for northeasterly wind events. These events tend to occur during the winter or early spring when they are under the influence of the Great Basin high pressure weather regime. The Launch Weather Officers (LWOs) have seen these rapid wind increases in the current northern Towers 60, 70 and 71 in excess of their 35 kt operational warning threshold. For this task, the 30 WS requested the Applied Meteorology Unit (AMU) analyze data from days when these towers reported winds in excess of 35 kt and determine if there were any precursors in the observations that would allow the LWOs to better forecast and warn their operational customers for these wind events. The 30 WS provided wind tower data for the cool season (October - March) from the period January 2004-March 20 IO. The AMU decoded and evaluated the wind tower data for 66 days identified by the 30 WS as having high-wind events. Out of the 66 event days, only 30 had wind speed observations of > or =35 kt from at least one of the three northern towers. The AMU analyzed surface and upper air charts to determine the synoptic conditions for each event day along with tower peak wind speed and direction time series and wind rose charts for all 30 event days. The analysis revealed a trend on all event days in which the tower winds shifted to the northeast for a period of time before the first recorded > or =35 kt wind speed. The time periods for the 30 event days ranged from 20 minutes to several hours, with a median value of 110 minutes. This trend, if monitored, could give the 30 WS forecasters a precursor to assist in issuing an operational warning before a high wind event occurs. The AMU recommends developing a high-wind alert capability for VAFB using a local mesoscale model to forecast these wind events. The model should incorporate all of the VAFB local data sets and have a forecast capability of between 2 to 24 hours. Such a model would allow the meteorologists at VAFB to alert the operational customers of high wind events in a timely manner so protective action could be taken.

Wheeler, Mark↗

NASA NTRS2019

Evidence for Oscillating Two-Stream Instability and Spatial Collapse of Langmuir Waves in a Solar Type II Radio Burst

We present the high time resolution in situ observations of Langmuir waves, likely excited by an electron beam accelerated by a coronal-mass ejection-driven super-critical quasi-perpendicular interplanetary shock into its upstream solar wind, which happens to be the source region of a solar type II radio burst. We show that (1) these waves occur as coherent localized magnetic-field-aligned, one-dimensional wave packets with durations of a few milliseconds and with peak intensities well in excess of the threshold for strong turbulence processes, (2) they provide what is believed to be the first evidence for: (a) the oscillating two-stream instability (OTSI) L(sub 1) + L(sub 2) S/⟶ U + D, where L(sub 1) and L(sub 2), U and D, and S are the pump Langmuir waves, up- and down-shifted side bands, and ion sound waves, respectively, (b) a three-wave interaction U + D ⟶ T(sub 2f(sub pe)), where T(sub 2f(sub pe)) is the second harmonic electromagnetic wave, (3) they satisfy the threshold condition for formation of collapsing solitons, and (4) they are accompanied by their ponderomotive force induced density cavities with δn(sub p)/n(sub e) > δn(sub b)/n(sub e), where δn(sub p)/n(sub e) is the level of ponderomotive force induced density fluctuations and δn(sub b)/n(sub e) is that of the ambient fluctuations. These findings strongly suggest that the observed wave packets provide evidence for the collapsing solitons formed as a result of OTSI. The implication is that the strong turbulence processes probably play very important roles in excitation of type II radio emissions as well as in stabilization of shock-accelerated electron beams.

Sun radio radiation↗

NASA NTRS1996

Stratospheric Meteorological Conditions for the 3-12 Nov. 1994 ATMOS/ATLAS-3 Measurements

During the ATLAS-3 mission (3-12 Nov 1994), United Kingdom Meteorological Office fields show that the SH vortex was still strong below about 700 K (approximately 16 hPa), with coherent vortex fragments apparent up to about 1300 K (approximately 3 hPa). The SH vortex was shifted off the pole toward 270 deg E throughout ATLAS-3, although its shape varied from day to day. SH temperatures were increasing during ATLAS-3; temperatures below 188 K were last seen 35-45 days before the mission, but were below 195 K as late as 2 Nov 1994. The NH polar vortex had developed at levels above about 550 K (approximately 35 hPa). Simulated high-resolution potential vorticity (PV) fields clearly show low latitude air being drawn up around the polar vortices in both hemispheres. These fields indicate that meteorological analyses underestimate the amount of atmospheric variability, including the strength of local PV gradients, and small-scale structure. Structure such as that in the simulated fields can result in apparent discrepancies between tracer measurements and PV fields.

Manney, G. L.↗

NASA NTRSDate not supplied

Preliminary Medical Risk Estimates and Clinical Capability Needs for Artemis IV

BACKGROUND Human exploration spaceflight missions to the Moon and Mars present unprecedented challenges for in- mission medical care. Compared with the ISS, the greater distance from Earth will mean increased mission durations, communication delays, limited to no resupply opportunities, and significant limitations on the evacuation of ill or injured crew. Spacecraft mass, volume, and power will be curtailed while higher demands will be placed on the crew’s knowledge, skills, and abilities. In this higher risk environment, it is important to: a) quantitatively estimate human system risk attributable to medical conditions, a process known as Probabilistic Risk Analysis, and b) use these estimates to inform medical system design. IMPACT (Informing Mission Planning via Analysis of Complex Tradespaces) is a PRA and medical trade space analysis tool developed by NASA to advance exploration mission medical system design. IMPACT v1.0 improves upon and will soon replace NASA’s existing tool, the Integrated Medical Model, with: a novel evidence base baselined to exploration environments; an expanded list of 119 medical conditions; a significant increase in the number of medical resources that can be utilized and in the flexibility of their use; and the modelling of time lost performing mission-specific tasks due to medical conditions. METHODOLOGY: This abstract will present IMPACT estimates of medical system risk and clinical capability needs for the Artemis IV mission. Artemis IV is currently scheduled for 2026 and will visit the Gateway space station in lunar orbit prior to the second lunar landing of the Artemis program. The baseline Artemis IV mission that was modeled was 28 days in duration with phases including Orion outbound, 4 days on the Gateway space station in lunar orbit, 2 crew on the surface of the Moon for approximately one week, an additional 5 days on Gateway, and then return to Earth. This baseline was compared to two alternative 34-day design reference missions (DRMs) that shifted the lunar sortie earlier or later in the mission profile. Assumptions included 2 female and 2 male crew and a notional medical system mass of 25 kg. Medical system risk estimates include loss of crew life (LOCL), consideration of medical evacuation (known as return to definitive care – RTDC), and an estimate of crew time lost due to medical conditions (Task Time Lost – TTL). The presentation will also describe the medical conditions that are the greatest drivers of risk as well as the clinical capabilities and resources that have the largest effect on risk. RESULTS: All three DRMs had very low probability of LOCL from medical conditions, primarily due to short duration. RTDC was also similar across the DRMs. In contrast, TTL was higher in the early lunar sortie DRM due to earlier occurrence of EVA-related medical conditions. Taken as a whole, there was no clinically significant difference in medical risk across the three missions. Results for clinical capabilities and an example medical equipment list will be discussed but were similar across DRMs.

D Hilmers↗

NASA NTRS2024

Preliminary Medical Risk Estimates and Clinical Capability Needs for Late Artemis Missions

BACKGROUND Human exploration spaceflight missions to the Moon and Mars present unprecedented challenges for in- mission medical care. Compared with the ISS, the greater distance from Earth will mean increased mission durations, communication delays, limited to no resupply opportunities, and significant limitations on the evacuation of ill or injured crew. Spacecraft mass, volume, and power will be curtailed while higher demands will be placed on the crew’s knowledge, skills, and abilities. In this higher risk environment, it is important to: a) quantitatively estimate human system risk attributable to medical conditions, a process known as Probabilistic Risk Analysis, and b) use these estimates to inform medical system design. IMPACT (Informing Mission Planning via Analysis of Complex Tradespaces) is a PRA and medical trade space analysis tool developed by NASA to advance exploration mission medical system design. IMPACT v1.0 improves upon and will soon replace NASA’s existing tool, the Integrated Medical Model, with: a novel evidence base baselined to exploration environments; an expanded list of 119 medical conditions; a significant increase in the number of medical resources that can be utilized and in the flexibility of their use; and the modelling of time lost performing mission-specific tasks due to medical conditions. METHODOLOGY: This abstract will present IMPACT estimates of medical system risk and clinical capability needs for the Artemis IV mission. Artemis IV is currently scheduled for 2026 and will visit the Gateway space station in lunar orbit prior to the second lunar landing of the Artemis program. The baseline Artemis IV mission that was modeled was 28 days in duration with phases including Orion outbound, 4 days on the Gateway space station in lunar orbit, 2 crew on the surface of the Moon for approximately one week, an additional 5 days on Gateway, and then return to Earth. This baseline was compared to two alternative 34-day design reference missions (DRMs) that shifted the lunar sortie earlier or later in the mission profile. Assumptions included 2 female and 2 male crew and a notional medical system mass of 25 kg. Medical system risk estimates include loss of crew life (LOCL), consideration of medical evacuation (known as return to definitive care – RTDC), and an estimate of crew time lost due to medical conditions (Task Time Lost – TTL). The presentation will also describe the medical conditions that are the greatest drivers of risk as well as the clinical capabilities and resources that have the largest effect on risk. RESULTS: All three DRMs had very low probability of LOCL from medical conditions, primarily due to short duration. RTDC was also similar across the DRMs. In contrast, TTL was higher in the early lunar sortie DRM due to earlier occurrence of EVA-related medical conditions. Taken as a whole, there was no clinically significant difference in medical risk across the three missions. Results for clinical capabilities and an example medical equipment list will be discussed but were similar across DRMs.

D. Hilmers↗

NASA NTRS1977

On propagation direction of ring current proton ULF waves observed by ATS 6 at 6.6 R sub E

From June 11 to September 16, 1974, the NOAA low-energy proton detector on board the ATS 6 satellite observed 71 cases of ultralow-frequency oscillations of proton flux intensities. The oscillation periods varied from 40 s to 6 min, and the events were observed most frequently during moderate geomagnetic conditions. The flux oscillations occurred at various local times, yet almost two thirds of the events were detected in the near-dusk region of the magnetosphere. For a majority of the events in this set a substantial phase shift in flux oscillation was detected between different energy channels and/or between two oppositely oriented detector telescopes. The phase shift is mainly due to the finite gyroradius effect of the protons gyrating in the geomagnetic field. By examining this finite gyroradius effect on the perturbed particle distribution function associated with the wave in a nonuniform magnetic field, the propagation direction of the wave from particle observations made by a single spacecraft is determined

Su, S.-Y.↗

NASA NTRS1992

Measurement of Attachment-Line Location in a Wind-Tunnel and in Supersonic Flight

As a part of the supersonic laminar flow control research program, experiments are being conducted to measure the attachment-line flow characteristics and its location on a highly swept aircraft wing. Initially, subsonic wind tunnel tests were performed on two-dimensional models to develop sensors and techniques for the flight application. The wind tunnel test results suggest that, under certain conditions at the leading edge there are low frequency streamwise velocity fluctuations present in the laminar boundary layer which undergo a phase change at the stagnation point Therefore, if present in flight, this distinct change in phase, i.e., time shift of signals from either side of the stagnation point, can be used to determine the stagnation-line or attachment-line location. The phase-reversal phenomenon was examined to determine the attachment-line location on a highly swept wing. Test results indicate that the phase-reversal phenomenon may not be applicable in flight. Additional data analyses is continuing to account for phase differences introduced by the recording system. A final determination on the existence of phase-reversal in flight will require the results of further analysis and possibly additional flight testing. Some representative attachment-line data are presented and discussed as well as the results from the wind tunnel investigation.

Flight Testing↗

NASA NTRS2007

Performance of a Herriott Cell, Designed for Variable Temperatures between 296 and 20 K

We designed, fabricated and tested a multipath Herriott cell (or off-axis spherical mirror interferometer) to achieve low temperature absorption measurements. The cell is fabricated entirely from copper and the 15 cm radius of curvature copper mirrors have gold coated reflective surfaces. The cell was tested at temperatures between 296 and 30 K with a folded absorption path length of 5.37 m utilizing a lead salt tunable diode laser. Short term temperature stability (1 h) of the Herriott cell is better than 0.005 K under normal operating conditions with a temperature uniformity better than 0.01 K (not measurable). The cell was tested by performing collisional cooling experiments on 13C16O2 in helium at temperatures between 70 and 20 K and by performing more traditional pressure broadening and shift measurements on molecular infrared absorption lines at temperatures between 300 and about 80 K on 13C16O2 methane.

Mondelain, Didier↗

NASA NTRS1989

Soil moisture and the persistence of North American drought

Numerical sensitivity experiments on the effects of soil moisture on North American summertime climate are performed using a 12-layer global atmospheric general circulation model. Consideration is given to the hypothesis that reduced soil moisture may induce and amplify warm, dry summers of midlatitude continental interiors. The simulations resemble the conditions of the summer of 1988, including an extensive drought over much of North America. It is found that a reduction in soil moisture leads to an increase in surface temperature, lower surface pressure, increased ridging aloft, and a northward shift of the jet stream. It is shown that low-level moisture advection from the Gulf of Mexico is important in the maintenance of persistent soil moisture deficits.

Oglesby, Robert J.↗

NASA NTRS1998

Calculations of multiple scattering-induced errors in the GLAS mission

The Geoscience Lidar Altimeter System (GLAS) is a laser altimeter designed to measure temporal changes in the topography and mass balance of the Earth's ice sheets. GLAS is scheduled to be launched as part of the Earth Observing System (EOS) in 2001. Due to the large pulse width of GLAS and the slope (and roughness) of the ice sheets, the mean elevation of the laser's surface spot will be estimated from the centroid of the return pulse. While the accuracy of individual altimetry measurements is expected to be 15 cm, a cross-over technique that averages the elevation differences at selected points on the ice sheets will allow GLAS to detect mean ice elevation changes as small as 2 cm per year. One factor that may degrade the proposed accuracy of the altimeter measurements is the effect of multiple scattering by thin clouds and aerosols over the ice sheets. In the return pulse, some photons from the lidar are slightly deflected by cloud particles but still return to the instrument detector. Since these photons travel a longer path than photons that pass directly to and from the surface, the mean travel time of the pulse is lengthened and the centroid of the return pulse is shifted toward a later time . This study intends to determine the importance of this source of altimetry error in the GLAS measurements. Two methods will be used to estimate path delays in the GLAS lidar for a range of cloud conditions. An analytic expression of a doubly scattered return signal (Eloranta, 1972) will be compared to Monte Carlo simulations that estimate path delays by cloud, aerosol and molecular scattering. The results from both methods will be discussed in relationship to current knowledge of Arctic cloud climatology, and the impact of multiple scattering on GLAS altimeter measurements will be evaluated.

Duda, David P.↗