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At least 199 records · Page 11

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NASA NTRS1992

A physical model of Titan's aerosols

A modeling effort is presented for the nature of the stratospheric haze on Titan, under several simplifying assumptions; chief among these is that the aerosols in question are of a single composition, and involatile. It is further assumed that a one-dimensional model is capable of simulating the general characteristics of the aerosol. It is suggested in this light that the detached haze on Titan may be a manifestation of organized, Hadley-type motions above 300 km altitude, with vertical velocities of 1 cm/sec. The hemispherical asymmetry of the visible albedo may be due to organized vertical motions within the upper 150-200 km of the haze.

Toon, O. B.↗

NASA NTRS1994

Molecular Dynamics of a Water-Lipid Bilayer Interface

We present results of molecular dynamics simulations of a glycerol 1-monooleate bilayer in water. The total length of analyzed trajectories is 5ns. The calculated width of the bilayer agrees well with the experimentally measured value. The interior of the membrane is in a highly disordered fluid state. Atomic density profile, orientational and conformational distribution functions, and order parameters indicate that disorder increases toward the center of the bilayer. Analysis of out-of-plane thermal fluctuations of the bilayer surfaces occurring at the time scale of the present calculations reveals that the distribution of modes agrees with predictions of the capillary wave model. Fluctuations of both bilayer surfaces are uncorrelated, yielding Gaussian distribution of instantaneous widths of the membrane. Fluctuations of the width produce transient thinning defects in the bilayer which occasionally span almost half of the membrane. The leading mechanism of these fluctuations is the orientational and conformational motion of head groups rather than vertical motion of the whole molecules. Water considerably penetrates the head group region of the bilayer but not its hydrocarbon core. The total net excess dipole moment of the interfacial water points toward the aqueous phase, but the water polarization profile is non-monotonic. Both water and head groups significantly contribute to the surface potential across the interface. The calculated sign of the surface potential is in agreement with that from experimental measurements, but the value is markedly overestimated. The structural and electrical properties of the water-bilayer system are discussed in relation to membrane functions, in particular transport of ions and nonelectrolytes across membranes.

Wilson, Michael A.↗

NASA NTRS2000

A Composite View of Ozone Evolution in the 1995-1996 Northern Winter Polar Vortex Developed from Airborne Lidar and Satellite Observations

The processes which contribute to the ozone evolution in the high latitude northern lower stratosphere are evaluated using a three dimensional model simulation and ozone observations. The model uses winds and temperatures from the Goddard Earth Observing System Data Assimilation System. The simulation results are compared with ozone observations from three platforms: the differential absorption lidar (DIAL) which was flown on the NASA DC-8 as part of the Vortex Ozone Transport Experiment; the Microwave Limb Sounder (MLS); the Polar Ozone and Aerosol Measurement (POAM II) solar occultation instrument. Time series for the different data sets are consistent with each other, and diverge from model time series during December and January. The model ozone in December and January is shown to be much less sensitive to the model photochemistry than to the model vertical transport, which depends on the model vertical motion as well as the model vertical gradient. We evaluate the dependence of model ozone evolution on the model ozone gradient by comparing simulations with different initial conditions for ozone. The modeled ozone throughout December and January most closely resembles observed ozone when the vertical profiles between 12 and 20 km within the polar vortex closely match December DIAL observations. We make a quantitative estimate of the uncertainty in the vertical advection using diabatic trajectory calculations. The net transport uncertainty is significant, and should be accounted for when comparing observations with model ozone. The observed and modeled ozone time series during December and January are consistent when these transport uncertainties are taken into account.

Douglass, A. R.↗

DOE OSTI2026

First EarthCARE CPR Observations of Dynamics–Microphysics Coupling in Marine Cold‐Air Outbreak Clouds

Marine cold-air outbreak (MCAO) clouds begin as shallow cloud streets near the ice edge and evolve into broken open-cell convection downstream. Their rapid transitions in cloud structure and microphysics are closely linked to vertical motions, but this interplay has not previously been observed from space. The EarthCARE satellite, carrying the first spaceborne Doppler radar (Cloud Profiling Radar, CPR), now measures hydrometeor sedimentation velocity and vertical air motion. Using CPR observations over the Norwegian and Barents Seas (December 2024–May 2025), we analyze MCAO and non-MCAO clouds. We find that strong updrafts in MCAO clouds coincide with larger supercooled liquid water (SLW) path (LWP). These conditions are accompanied by increases in sedimentation velocity and its vertical gradient, reflecting rapid riming-driven ice growth. In contrast, non-MCAO clouds show lower riming efficiency at similar LWP due to relatively weaker dynamical support. This emphasizes the importance of dynamics in shaping polar cloud structure and microphysics.

Kim, Jiseob [McGill Univ., Montreal, QC (Canada)] ↗

NASA NTRS1996

Yaw Motion Cues in Helicopter Simulation

A piloted simulation that examined the effects of yaw motion cues on pilot-vehicle performance, pilot workload, and pilot motion perception was conducted on the NASA Ames Vertical Motion Simulator. The vehicle model that was used represented an AH-64 helicopter. Three tasks were performed in which only combinations of vehicle yaw and vertical displacement were allowed. The commands issued to the motion platform were modified to present the following four motion configurations for a pilot located forward of the center of rotation: (1) only the linear translations, (2) only the angular rotation, (3) both the linear translations and the angular rotation, and (4) no motion. The objective data indicated that pilot-vehicle performance was reduced and the necessary control activity increased when linear motion was removed; however, the lack of angular rotation did not result in a measured degradation for almost all cases. Also, pilots provided subjective assessments of their compensation required, the motion fidelity, and their judgment of whether or not linear or rotational cockpit motion was present. Ratings of compensation and fidelity were affected only by linear acceleration, and the rotational motion had no significant impact. Also, when only linear motion was present, pilots typically reported the presence of rotation. Thus, linear acceleration cues, not yaw rotational cues, appear necessary to simulate hovering flight.

Schroeder, Jeffrey A.↗

NASA NTRS1988

Oblique-wing research airplane motion simulation with decoupling control laws

A large piloted vertical motion simulator was used to assess the performance of a preliminary decoupling control law for an early version of the F-8 oblique wing research demonstrator airplane. Evaluations were performed for five discrete flight conditions, ranging from low-altitude subsonic Mach numbers to moderate-altitude supersonic Mach numbers. Asymmetric sideforce as a function of angle of attack was found to be the primary cause of both the lateral acceleration noted in pitch and the tendency to roll into left turns and out of right turns. The flight control system was shown to be effective in generally decoupling the airplane and reducing the lateral acceleration in pitch maneuvers.

Kempel, Robert W.↗

NASA NTRS1973

Automatic control of a helicopter with a hanging load

An autopilot logic is designed here for controlling a helicopter with a hanging load. A 16th order model for the system is decoupled into four subsystems: (1) a second order system for yawing motion, (2) a second order system for vertical motion, (3) a sixth order system for longitudinal motion, and (4) a sixth order system for lateral motion. A measuring scheme, which could be used in remote areas, is developed and filters are designed to estimate the state variables from these measurements. The autopilot can be used to move the load over short distances without retracting the cables. This is done by automatically shifting the autopilot modes from position-hold (hover) to acceleration-hold to velocity-hold (cruise) to deceleration-hold to velocity-hold (near hover) to position-hold (hover). Use of such an autopilot might save considerable turnaround time. The Sikorsky S-61 helicopter is chosen as an example vehicle. The performance of the controlled system is studied in the presence of longitudinal and lateral winds.

Gupta, N. K.↗

NASA NTRS1983

Active stabilization of a flexible antenna feed tower

Active stabilization logic is synthesized to hold a feed at the focus of a spacecraft antenna dish. The feed support structure is modeled as a tetrahedron made up of flexible bars and connected to the dish by six short legs containing force actuators. Using the symmetry of the structure, the model can be decomposed into four uncoupled subsystems: pitch/forward motions with four degrees of freedom (DOF) and two controls; roll/lateral motions with four DOF and two controls; vertical motions with three DOF and one control; and yaw motion with one DOF and one control. This greatly simplifies the synthesis of control logic.

Bryson, A. E., Jr.↗

NASA NTRS1989

The use of vestibular models for design and evaluation of flight simulator motion

Quantitative models for the dynamics of the human vestibular system are applied to the design and evaluation of flight simulator platform motion. An optimal simulator motion control algorithm is generated to minimize the vector difference between perceived spatial orientation estimated in flight and in simulation. The motion controller has been implemented on the Vertical Motion Simulator at NASA Ames Research Center and evaluated experimentally through measurement of pilot performance and subjective rating during VTOL aircraft simulation. In general, pilot performance in a longitudinal tracking task (formation flight) did not appear to be sensitive to variations in platform motion condition as long as motion was present. However, pilot assessment of motion fidelity by means of a rating scale designed for this purpose, were sensitive to motion controller design. Platform motion generated with the optimal motion controller was found to be generally equivalent to that generated by conventional linear crossfeed washout. The vestibular models are used to evaluate the motion fidelity of transport category aircraft (Boeing 727) simulation in a pilot performance and simulator acceptability study at the Man-Vehicle Systems Research Facility at NASA Ames Research Center. Eighteen airline pilots, currently flying B-727, were given a series of flight scenarios in the simulator under various conditions of simulator motion. The scenarios were chosen to reflect the flight maneuvers that these pilots might expect to be given during a routine pilot proficiency check. Pilot performance and subjective rating of simulator fidelity was relatively insensitive to the motion condition, despite large differences in the amplitude of motion provided. This lack of sensitivity may be explained by means of the vestibular models, which predict little difference in the modeled motion sensations of the pilots when different motion conditions are imposed.

Bussolari, Steven R.↗

NASA NTRS1992

Does a motion base prevent simulator sickness?

The use of high-fidelity motion cues to reduce the discrepancy between visually implied motion and actual motion is tested experimentally using the NASA Vertical Motion Simulator (VMS). Ten pilot subjects use the VMS to fly simulated S-turns and sawtooths which generate a high incidence of motion sickness. The subjects fly the maneuvers on separate days both with and without use of a motion base provided by the VMS, and data are collected regarding symptoms, dark focus, and postural equilibrium. The motion-base condition is shown to be practically irrelevant with respect to the incidence and severity of motion sickness. It is suggested that the data-collection procedure cannot detect differences in sickness levels, and the false cues of the motion condition are theorized to have an adverse impact approximately equivalent to the absence of cues in a fixed-base condition.

Sharkey, Thomas J.↗

NASA NTRS1992

Algorithmic improvements for simulator motion drive

Contemporary simulator motion drive algorithms typically are designed in an analog (continuous) environment, but are implemented in a digital (discrete) environment. The intended continuous system, specified as frequency domain (Laplace transform) transfer functions, may not be represented properly by the algorithms used for digital implementation. The motion drive software in use with the Vertical Motion Simulator at Ames Research Center was investigated recently; the original algorithms (Euler) were changed to a state transition method. Comparison of the frequency responses of the original and new implementations showed that the state transition method more closely approximates the desired analog responses. In addition, test pilots who evaluated both implementations preferred the motions generated with the state transition method over those generated with the Euler integration method.

Laforce, Soren↗

NASA NTRS1995

Moving base simulation of an integrated flight and propulsion control system for an ejector-augmentor STOVL aircraft in hover

A piloted motion simulator evaluation, using the NASA Ames Vertical Motion Simulator, was conducted in support of a NASA Lewis Contractual study of the integration of flight and propulsion systems of a STOVL aircraft. Objectives of the study were to validate the Design Methods for Integrated Control Systems (DMICS) concept, to evaluate the handling qualities, and to assess control power usage. The E-7D ejector-augmentor STOVL fighter design served as the basis for the simulation. Handling-qualities ratings were obtained during precision hover and shipboard landing tasks. Handling-qualities ratings for these tasks ranged from satisfactory to adequate. Further improvement of the design process to fully validate the DMICS concept appears to be warranted.

Mcneill, Walter, E.↗

NASA NTRS2002

Characterizing the Severe Turbulence Environments Associated With Commercial Aviation Accidents: 44 Case Study Synoptic Observational Analyses - Part 1

A 44 case study analysis of the large-scale atmospheric structure associated with development of accident-producing aircraft turbulence is described. Categorization is a function of the accident location, altitude, time of year, time of day, and the turbulence category, which classifies disturbances. National Centers for Environmental Prediction Reanalyses data sets and satellite imagery are employed to diagnose synoptic scale predictor fields associated with the large-scale environment preceding severe turbulence. These analyses indicate a predominance of severe accident-producing turbulence within the entrance region of a jet stream at the synoptic scale. Typically, a flow curvature region is just upstream within the jet entrance region, convection is within 100 km of the accident, vertical motion is upward, absolute vorticity is low, vertical wind shear is increasing, and horizontal cold advection is substantial. The most consistent predictor is upstream flow curvature and nearby convection is the second most frequent predictor.

Kaplan, Michael L.↗

NASA NTRS1986

Continuous measurement of nontidal variations of gravity

Records from seven superconducting gravimeters operated at five different locations in California and one in Boulder, CO, are examined after removal of tides and the gravitational attraction of the atmosphere. Fluctuations over periods between a few days and several months were observed at all sites with peak amplitudes of order 10 microgal. By contrast, a 640-day record obtained with one of the instruments in Germany showed peak fluctuations of only 2 microgal. In most of the records the causes of these aperiodic variations were not determined so that they serve to set limits on the vertical motion or displacement of mass at the respective locations. However, at The Geysers geothermal field, much of the gravity variation is correlated with seismic activity, reinjection rate, and rainfall. Measurements of this type were not possible prior to the development of the superconducting device. Consequently, these results provide the first evidence for the existence of gravity variations on the time scale and of the magnitude described here. Vertical crustal motion, motion related to seismic events, and hydrological phenomena can lead to variations on this scale. Unambiguous identification of causal relationships will require either special circumstances such as found at The Geysers or operation of the instruments in pairs.

Goodkind, John M.↗

NASA NTRS2022

Atmospheric Lunar Tide in the Low Latitude Thermosphere-Ionosphere

We present simultaneous, independent measurements of the atmospheric semidiurnal lunar tide in neutral winds and plasma velocities from NASA's Ionospheric Connection Explorer, and in atomic oxygen 135.6 nm airglow measured by the Global-scale Observations of the Limb and Disk. Westward tidal winds near 115 km at the magnetic equator occur during part of the upward phase of the in-situ plasma drift. Vertical motions associated with the field-aligned plasma velocity occur away from the magnetic equator. The morphology of the lunar tide, and the phasing between the airglow and plasma velocities are consistent with E × B drift as a mechanism for linking neutral wind and plasma perturbations. This work provides the first observational quantification of global-scale E- and F-region coupling through E × B and field-aligned vertical drifts. Plain Language Summary: Tidal winds propagating upward from the neutral atmosphere influence ionospheric dynamo electric fields and vertical plasma drifts. However, these mechanisms have never been fully identified in comprehensive and simultaneous measurements spanning the ionosphere-thermosphere-mesosphere (ITM) system. The atmospheric lunar tide is an effective marker of ITM coupling because it originates at Earth's surface, propagates vertically, and is fully sampled in daytime-only and post-sunset satellite measurements. We utilize measurements from two new NASA missions to track the lunar tide in neutral and plasma velocities, and in an electron density proxy. Our work provides observational confirmation, and quantitative estimates of F-region vertical plasma motions driven by neutral winds and electrodynamical forces

Ruth S. Lieberman↗

NASA NTRS1986

A densely spaced array of sea level monitors for the detection of vertical crustal deformation in the Shumagin seismic gap, Alaska

A network of sea level gauges has been installed with about 40 km spacing in the Shumagin Islands in order to detect relative vertical motion, in particular, possible crustal motion precursory to an expected major earthquake. This required the development and deployment of a pressure sensor sea level gauge suitable for installation on remote and harsh coastlines. Data are collected in near-real-time via satellite, both in order to exploit fully any precursors that may be observed and to provide continuous information on the status of the instruments. Using Wiener filtering techniques, it has been determined conservatively that no relative vertical crustal motion greater than 0.1 m between stations has occurred during 1981-1985. This is consistent with independent geodetic leveling and trilateration data, though evidence exists for more rapid deformation during 1978-1980. The sea level data collected so far have an rms noise level of about 0.04 m after processing; this is limited in part by the pressure sensor and associated electronics. Improved prressure gauges with better long-term stability have recently been installed. A short-baseline tiltmeter operating in a tunnel has demonstrated that suitably designed and located land-based tiltmeters have a lower noise level, and hence better precursor detection characteristics than the sea level gauges, at monthly and shorter periods.

Beavan, John↗

NASA NTRSDate not supplied

High Fidelity Aerospace Simulations at NASA Ames SimLabs

An overview of the simulation facilities at SimLabs at NASA Ames. Main focus is on the Vertical Motion Simulator or VMS, also brief descriptions of other simulators. Discussion of the history and general specifications of the VMS. Also, provide an overview of past research and training conducted on the simulators, and some future developments with a focus on AR/VR technologies.

flight simulators↗

NASA NTRSDate not supplied

Analysis of Handling Qualities and Power Consumption for Urban Air Mobility (UAM) eVTOL Quadrotors with Degraded Heave Disturbance Rejection and Control Response

A piloted handling qualities study of urban air mobility (UAM) electric vertical take-off and landing (eVTOL) quadrotors was performed utilizing the Vertical Motion Simulator (VMS) facility at NASA Ames Research Center. Rotor speed and variable pitch-controlled variants of a six-passenger conceptual design vehicle were assessed with different levels of degradation to control response and disturbance rejection bandwidth (DRB) in the heave axis. In previous work, preliminary trends across several handling quality rating categories reflected the effects of these degradations. Additionally, the impact of using different test standards and turbulence on the ratings were discussed. This paper elaborates on those results, but also provides insight into unexpected trends observed during the study including: a disharmony in attitude response, subpar ratings for the baseline Level 1 performance vehicle, and excessive drift and yaw couplings observed in a lateral reposition maneuver. Moreover, shortcomings of the handling quality scales and comparisons of power consumption among the vehicles in the various test conditions are presented.

Handling Qualities↗