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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Oscillatory Dynamics of Single Bubbles and Agglomeration in a Sound Field in Microgravity

A dual-frequency acoustic levitator containing water was developed for studying bubble and drop dynamics in low gravity. It was flown on USML-1 where it was used in the Glovebox facility. High frequency (21 or 63 kHz) ultrasonic waves were modulated by low frequencies to excite shape oscillations on bubbles and oil drops ultrasonically trapped in the water. Bubble diameters were typically close to 1 cm or larger. When such large bubbles are acoustically trapped on the Earth, the acoustic radiation pressure needed to overcome buoyancy tends to shift the natural frequency for quadrupole (n = 2) oscillations above the prediction of Lamb's equation. In low gravity, a much weaker trapping force was used and measurements of n = 2 and 3 mode frequencies were closer to the ideal case. Other video observations in low gravity include: (i) the transient reappearance of a bulge where a small bubble has coalesced with a large one, (ii) observations of the dynamics of bubbles coated by oil indicating that shape oscillations can shift a coated bubble away from the oil-water interface of the coating giving a centering of the core, and (iii) the agglomeration of bubbles induced by the sound field.

Marston, Philip L.↗
NASA NTRS1993

Low cloud investigations for project FIRE: Island studies of cloud properties, surface radiation, and boundary layer dynamics. A simulation of the reflectivity over a stratocumulus cloud deck by the Monte Carlo method

The radiation field over a broken stratocumulus cloud deck is simulated by the Monte Carlo method. We conducted four experiments to investigate the main factor for the observed shortwave reflectively over the FIRE flight 2 leg 5, in which reflectivity decreases almost linearly from the cloud center to cloud edge while the cloud top height and the brightness temperature remain almost constant through out the clouds. From our results, the geometry effect, however, did not contribute significantly to what has been observed. We found that the variation of the volume extinction coefficient as a function of its relative position in the cloud affects the reflectivity efficiently. Additional check of the brightness temperature of each experiment also confirms this conclusion. The cloud microphysical data showed some interesting features. We found that the cloud droplet spectrum is nearly log-normal distributed when the clouds were solid. However, whether the shift of cloud droplet spectrum toward the larger end is not certain. The decrease of number density from cloud center to cloud edges seems to have more significant effects on the optical properties.

Ackerman, Thomas P.↗
NASA NTRSDate not supplied

Mitigating Headward Fluid Shifts With Veno-Constrictive Thigh Cuffs During Spaceflight

Astronauts experience a chronic headward fluid shift in weightlessness as evidenced by increased cardiac output, decreased leg volume, a redistribution of venous fluid, and venous congestion in the upper body. Alterations in cerebrospinal fluid hydrodynamics and changes in cerebral venous pressure secondary to the headward fluid shift may contribute to ocular changes associated with spaceflight-associated neuro-ocular syndrome (SANS). Veno-constrictive thigh cuffs (VTC; Braslets) provided to Soyuz crewmembers alleviate symptoms of the headward fluid shift during the first week of spaceflight and have been documented to reduce internal jugular vein (IJV) distension during weightlessness. Application of VTCs designed collaboratively by NASA Johnson Space Center Cardiovascular and Vision Laboratory (CVL) and Clemson Textile Laboratory at Clemson University to improve fit and comfort was documented to mitigate changes in choroid thickness, intraocular pressure, and IJV area during posture-induced headward fluid shifts. VTC are demonstrated to reduce headward fluid shifts in both ground-based and spaceflight studies, and thus, may be a countermeasure against development of SANS. In addition, VTC are a simple mechanical countermeasure currently at a high technical readiness level (TRL) and are compact and lightweight, making them compatible with the spaceflight operations environment

Connor R. Ferguson↗
NASA NTRS1986

Dual-pilot tone calibration technique

Pilot-based calibration techniques are used to reduce the effects of multipath fading in mobile satellite receivers. One of the more recent of these techniques, namely the tone calibration technique (TCT), suggests transmitting double sideband modulation with the pilot tone located at the center of its spectrum where the amplitude and phase characteristics of the channel are most stable. To 'make room' for the pilot in the presence of the Doppler shift, the equivalent low-pass data sidebands must be shaped so as to have zero response in the neighborhood of dc. Other techniques such as transparent tone-in-band (TTIB) similarly 'notch out' a hole in the center of the data spectrum for location of the pilot. An alternate possibility which is at the same time much more bandwidth efficient than TCT is a dual-pilot tone calibration technique (DPTCT) that symmetrically locates a pair of pilots outside the data spectrum near the band edges of the channel. The operation and performance of DPTCT are analyzed, and its effectiveness is compared to that of the single tone TCT technique.

Simon, Marvin K.↗
NASA NTRS1998

Resetting of circadian melatonin and cortisol rhythms in humans by ordinary room light

The present study was designed to investigate whether a weak photic stimulus can reset the endogenous circadian rhythms of plasma melatonin and plasma cortisol in human subjects. A stimulus consisting of three cycles of 5 h exposures to ordinary room light (approximately 180 lux), centered 1.5 h after the endogenous temperature nadir, significantly phase-advanced the plasma melatonin rhythm in eight healthy young men compared with the phase delays observed in eight control subjects who underwent the same protocol but were exposed to darkness (p < or = 0.003). After light-induced phase advances, the circadian rhythms of plasma melatonin and plasma cortisol maintained stable temporal relationships with the endogenous core body temperature cycle, consistent with the conclusion that exposure to ordinary indoor room light had shifted a master circadian pacemaker.

Non-NASA Center↗
NASA NTRS2012

Frequency Shift During Mass Properties Testing Using Compound Pendulum Method

During mass properties testing on the X-48B Blended Wing Body aircraft (The Boeing Company, Chicago, Illinois) at the National Aeronautics and Space Administration Dryden Flight Research Center, Edwards, California, large inertia measurement errors were observed in results from compound pendulum swings when compared to analytical models. By comparing periods of oscillations as measured from an average over the test period versus the period of each oscillation, it was noticed that the frequency of oscillation was shifting significantly throughout the test. This phenomenon was only noticed during compound pendulum swings, and not during bifilar pendulum swings. The frequency shift was only visible upon extensive data analysis of the frequency for each oscillation, and did not appear in averaged frequency data over the test period. Multiple test articles, test techniques, and hardware setups were used in attempts to eliminate or identify the cause of the frequency shift. Plotting the frequency of oscillation revealed a region of minimal shift that corresponded to a larger amplitude range. This region of minimal shift provided the most accurate results compared to a known test article; however, the amplitudes that produce accurate inertia measurements are amplitudes larger than those generally accepted in mass properties testing. This paper examines two case studies of the frequency shift, using mass properties testing performed on a dummy test article, and on the X-48B Blended Wing Body aircraft.

Wolfe, David↗
NASA NTRS1977

CW ultrasonic bolt tensioning monitor

A CW ultrasonic device is described for measuring frequency shifts of the peak of a mechanical resonance in a body. One application of the device is measuring the strain in a bolt, and other applications such as measuring the thickness of a body, measuring the depth of a flaw in a body, measuring the elongation of a body, and measuring changes in velocity of sound in a body. The body is connected, by means of a CW transducer, to electrical circuit means including a narrow band RF amplifier to form a closed loop feedback marginal oscillator that frequency locks the device to the peak of a mechanical resonance in the body. When the frequency of this peak changes, because of a physical change in the body, the frequency of the oscillator changes. The device includes an automatic frequency resonant peak tracker that produces a voltage that is related to a change in frequency of the oscillator. This voltage is applied to the RF amplifier to change the center of its frequency band to include the frequency of the peak and is a measure of the frequency shift.

Heyman, J. S.↗
NASA NTRS1978

Remote sensing of crop type and maturity

A red-shift in the chlorophyll absorption edge of heading wheat and grain sorghum is clearly visible in high-spectral-resolution measurements made from a low-flying aircraft over Imperial Valley, California. The position of the absorption edge shifts progressively toward the longer wavelengths during the crop growth cycle. The red-shift of 7 to 10 nm can be measured by using 10 nm-wide spectral bands, centered at 745 nm and 785 nm. These two bands, plus a band in the pigment absorption region at 670 nm, contain enough information to identify wheat and grain sorghum in the heading stage, to indicate the degree of heading, and to indicate canopy density during the heading stage

Collins, W.↗
NASA NTRS1988

The longitudinal and radial distribution of magnetic reconfigurations in the near-earth magnetotail as observed by AMPTE/CCE

The longitudinal and radial distribution of 103 substorm dipolarization events in the equatorial nightside magnetosphere from low altitude to about 9 R(E) observed by AMPTE/CCE is examined. The center of the distribution was located near midnight. For Kp of 3- or less, the distribution peak shifted toward the premidnight region, whereas for Kp of 4+ and higher, the distribution peak was inside the postmidnight region. The substorm frequency for the high-Kp case was about four times larger than the low-to-moderate-Kp case. The occurrence frequency of events increased with increasing radial distance, and no events were observed inside of 6.4 R(E). This radial distribution suggests that, on average, the substorm initiation region is greater than about 8 R(E). In addition, the average radial position of the signatures decreased with increasing Kp.

Lopez, R. E.↗
NASA NTRS1993

Tidal disruptions by supermassive black holes - Hydrodynamic evolution of stars on a Schwarzschild background

We present a three-dimensional numerical study of tidal disruption of a main-sequence star by a supermassive black hole. The simulations include general relativistic effects which are important in this regime. We analyze stars in a marginally bound orbit around the black hole with pericentric separation of a few Schwarzschild radii. We show that during a close passage, as a result of relativistic effects analogous to the perihelion shift, the trajectories of the debris of the star fan out into a crescent-like shape centered on the black hole. We also discuss the increase of the central density of the star as it approaches pericentric distance, the fraction of the debris accreted by the hole, its accretion rate, the distribution of debris orbits bound to the hole, and the velocity of unbound ejected material. We compare these results with the disruption of the star by a Newtonian point mass.

Laguna, Pablo↗
NASA NTRS1954

Wind-tunnel Tests of a Model of a Wingless Fin-controlled Missile to Obtain Static Stability and Control Characteristics Through a Range of Mach Numbers from 0.5 to 0.88

An investigation at medium to high subsonic speeds has been conducted in the Langley low-turbulence pressure tunnel to determine the static stability and control characteristics and to measure the fin normal forces and moments for a model of a wingless fin-controlled missile. The data were obtained at Reynolds number of 2.1 x 10(6) based on the missile maximum diameter or 17.7 x 10(6) based on missile length; this Reynolds number was found to be large enough to avoid any large scale effects between the test and the expected flight Reynolds number. With the horizontal-fin deflection limited to a maximum of 6 degrees, longitudinally stable and trimmed flight could not be maintained beyond an angle of attack of 17 degrees for a Mach number of 0.88 and beyond 20 degrees for a Mach number of 0.50 for any center-of-gravity location without the use of some auxiliary stability or control device such as jet vanes. Mach number had no appreciable effect on the center-of-pressure positions and only a slight effect on neutral-point position. There was a shift in neutral-point position of about 1 caliber as the angle of attack was varied through the range for which the neutral point could be determined. Yawing the model to angles of sideslip up to 7 degrees had little effect on the longitudinal stability at angles of attack up to 15 degrees; however, above 15 degrees, the effect of sideslip was destabilizing. With the vertical fins at a plus-or-minus 6 degree roll deflection, the rolling moment caused by yawing the model at high angles of attack could be trimmed out up to angles of sideslip of 6.5 degrees and an angle of attack of 26 degrees for a Mach number of 0.50; this range of sideslip angles was reduced to 3 degrees at a Mach number of 0.88. The data indicated that, at lower angles of attack, the trim range extended to higher angles of sideslip. The total normal-force and hinge-moment coefficients for both horizontal fins were slightly nonlinear with both angle-of-attack and fin deflection. The effect of Mach number was to reduce the slopes of the hinge-moment coefficient with angle of attack and deflection angle. In general, the effort of increasing the sideslip angle was to reduce the values of the fin normal-force and hinge-moment coefficients.

Burrows, Dale L↗
NASA NTRS1996

Advanced Air Traffic Management Research (Human Factors and Automation): NASA Research Initiatives in Human-Centered Automation Design in Airspace Management

NASA has initiated a significant thrust of research and development focused on providing the flight crew and air traffic managers automation aids to increase capacity in en route and terminal area operations through the use of flexible, more fuel-efficient routing, while improving the level of safety in commercial carrier operations. In that system development, definition of cognitive requirements for integrated multi-operator dynamic aiding systems is fundamental. The core processes of control and the distribution of decision making in that control are undergoing extensive analysis. From our perspective, the human operators and the procedures by which they interact are the fundamental determinants of the safe, efficient, and flexible operation of the system. In that perspective, we have begun to explore what our experience has taught will be the most challenging aspects of designing and integrating human-centered automation in the advanced system. We have performed a full mission simulation looking at the role shift to self-separation on board the aircraft with the rules of the air guiding behavior and the provision of a cockpit display of traffic information and an on-board traffic alert system that seamlessly integrates into the TCAS operations. We have performed and initial investigation of the operational impact of "Dynamic Density" metrics on controller relinquishing and reestablishing full separation authority. (We follow the assumption that responsibility at all times resides with the controller.) This presentation will describe those efforts as well as describe the process by which we will guide the development of error tolerant systems that are sensitive to shifts in operator work load levels and dynamic shifts in the operating point of air traffic management.

Corker, Kevin M.↗
NASA NTRS2010

The Right Stuff: A Look Back at Three Decades of Flight Controller Training for Space Shuttle Mission Operations

This paper will summarize the thirty-year history of Space Shuttle operations from the perspective of training in NASA Johnson Space Center's Mission Control Center. It will focus on training and development of flight controllers and instructors, and how training practices have evolved over the years as flight experience was gained, new technologies developed, and programmatic needs changed. Operations of human spaceflight systems is extremely complex, therefore the training and certification of operations personnel is a critical piece of ensuring mission success. Mission Control Center (MCC-H), at the Lyndon B. Johnson Space Center, in Houston, Texas manages mission operations for the Space Shuttle Program, including the training and certification of the astronauts and flight control teams. This paper will give an overview of a flight control team s makeup and responsibilities during a flight, and details on how those teams are trained and certified. The training methodology for developing flight controllers has evolved significantly over the last thirty years, while the core goals and competencies have remained the same. In addition, the facilities and tools used in the control center have evolved. These changes have been driven by many factors including lessons learned, technology, shuttle accidents, shifts in risk posture, and generational differences. Flight controllers will share their experiences in training and operating the Space Shuttle throughout the Program s history. A primary method used for training Space Shuttle flight control teams is by running mission simulations of the orbit, ascent, and entry phases, to truly "train like you fly." The audience will learn what it is like to perform a simulation as a shuttle flight controller. Finally, we will reflect on the lessons learned in training for the shuttle program, and how those could be applied to future human spaceflight endeavors.

Dittemore, Gary D.↗
NASA NTRS2011

The Right Stuff: A Look Back at Three Decades of Flight Controller Training for Space Shuttle Mission Operations

Operations of human spaceflight systems is extremely complex, therefore the training and certification of operations personnel is a critical piece of ensuring mission success. Mission Control Center (MCC-H), at the Lyndon B. Johnson Space Center, in Houston, Texas manages mission operations for the Space Shuttle Program, including the training and certification of the astronauts and flight control teams. This paper will give an overview of a flight control team s makeup and responsibilities during a flight, and details on how those teams are trained and certified. The training methodology for developing flight controllers has evolved significantly over the last thirty years, while the core goals and competencies have remained the same. In addition, the facilities and tools used in the control center have evolved. These changes have been driven by many factors including lessons learned, technology, shuttle accidents, shifts in risk posture, and generational differences. Flight controllers will share their experiences in training and operating the Space Shuttle throughout the Program s history. A primary method used for training Space Shuttle flight control teams is by running mission simulations of the orbit, ascent, and entry phases, to truly "train like you fly." The reader will learn what it is like to perform a simulation as a shuttle flight controller. Finally, the paper will reflect on the lessons learned in training for the shuttle program, and how those could be applied to future human spaceflight endeavors. These endeavors could range from going to the moon or to Mars. The lessons learned from operating the space shuttle for over thirty years will help the space industry build the next human transport space vehicle and inspire the next generation of space explorers.

Dittemore, Gary D.↗
NASA NTRS2011

The Final Count Down: A Review of Three Decades of Flight Controller Training Methods for Space Shuttle Mission Operations

Operations of human spaceflight systems is extremely complex, therefore the training and certification of operations personnel is a critical piece of ensuring mission success. Mission Control Center (MCC-H), at the Lyndon B. Johnson Space Center, in Houston, Texas manages mission operations for the Space Shuttle Program, including the training and certification of the astronauts and flight control teams. As the space shuttle program ends in 2011, a review of how training for STS-1 was conducted compared to STS-134 will show multiple changes in training of shuttle flight controller over a thirty year period. This paper will additionally give an overview of a flight control team s makeup and responsibilities during a flight, and details on how those teams have been trained certified over the life span of the space shuttle. The training methods for developing flight controllers have evolved significantly over the last thirty years, while the core goals and competencies have remained the same. In addition, the facilities and tools used in the control center have evolved. These changes have been driven by many factors including lessons learned, technology, shuttle accidents, shifts in risk posture, and generational differences. A primary method used for training Space Shuttle flight control teams is by running mission simulations of the orbit, ascent, and entry phases, to truly "train like you fly." The reader will learn what it is like to perform a simulation as a shuttle flight controller. Finally, the paper will reflect on the lessons learned in training for the shuttle program, and how those could be applied to future human spaceflight endeavors.

Dittemore, Gary D.↗
NASA NTRS2011

Launch Control Systems: Moving Towards a Scalable, Universal Platform for Future Space Endeavors

The redirection of NASA away from the Constellation program calls for heavy reliance on commercial launch vehicles for the near future in order to reduce costs and shift focus to research and long term space exploration. To support them, NASA will renovate Kennedy Space Center's launch facilities and make them available for commercial use. However, NASA's current launch software is deeply connected with the now-retired Space Shuttle and is otherwise not massively compatible. Therefore, a new Launch Control System must be designed that is adaptable to a variety of different launch protocols and vehicles. This paper exposits some of the features and advantages of the new system both from the perspective of the software developers and the launch engineers.

Sun, Jonathan↗
NASA NTRS2023

A Technique to Measure Coronal Electron Density, Temperature, and Velocity Above 2.5 R from Sun Center Using Polarized Brightness Spectrum

The current model for the polarized brightness (pB) spectrum has a decades-long history of progressively incorporating its dependence on electron density N(e), temperature T(e), and flow velocity in the radial direction V(e). The pBNe spectrum follows the exact shape of the photosphere spectrum, which is not smooth, which is expected from the thermal Doppler broadening of the photosphere spectrum due to the high coronal T(e). The pBN(e) spectrum is smooth, but the free coronal electrons remain static and unaffected by solar wind, and the pBN(e)T(e)V(e) spectrum is red-shifted by electrons seeing a red-shifted photosphere spectrum as they flow away from the Sun as solar wind, which takes a radial direction above 2.5 R from Sun center. In this article, we review the progress of the above three model pB spectra in describing the observations and highlight the differences, first by comparing the three model pB spectra against wavelength using a model for Ne and constant values for T(e) and V (e), and second by generating three model 2D pB maps by integrating over a selected wavelength region in the three model pB spectra along lines of sight passing through the 14 July 2000 (“Bastille Day”) coronal mass ejection (CME) model, which contains 3D information on N(e), T(e), and V e. In this regard, the COronal Diagnostic EXperiment (CODEX) on the International Space Station (ISS) in 2024 will measure N(e), T(e), and V(e) by matching the measured pB with modeled pBN(e)T(e)V(e) in selected wavelength regions using multiple filters.

Electron density↗