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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Relationship of peroxyacetyl nitrate to active and total odd nitrogen at northern high latitudes: influence of reservoir species on NOx and O3

Measurements of peroxyacetyl nitrate (PAN), NO, NO2, HNO3, NOy (total odd nitrogen), and O3 were made in the high-latitude troposphere over North America and Greenland (35 degrees to 82 degrees N) during the Arctic Boundary Layer Expedition (ABLE 3A) (July-August 1988) throughout 0-to 6-km altitudes. These data are analyzed to quantitatively describe the relationships between various odd nitrogen species and assess their significance to global tropospheric chemistry. In the free troposphere, PAN was as much as 25 times more abundant than NOx. PAN to NOx ratio increased with increasing altitude and latitude. PAN was found to be the single most abundant reactive nitrogen species in the free troposphere and constituted a major fraction of NOy, PAN to NOy ratios were about 0.1 in the boundary layer and increased to 0.4 in the free troposphere. A 2-D global photochemical model with C1-C3 hydrocarbon chemistry is used to compare model predictions with measured results. A sizable portion (approximately 50%) of the gaseous reactive nitrogen budget is unaccounted for, and unknown organic nitrates and pernitrates are expected to be present. Model calculations (August 1, 70 degrees N) show that a major fraction of the observed NOx (50 to 70% of median) may find its source in the available PAN reservoir. PAN and the unknown reservoir species may have the potential to control virtually the entire NOx availability of the high latitude troposphere. It is predicted that the summer NOx and O3 mixing ratios in the Arctic/sub-Arctic troposphere would be considerably lower in the absence of the ubiquitous PAN reservoir. Conversely, this PAN reservoir may be responsible for the observed temporal increase in tropospheric O3 at high latitudes.

NASA Center ARC↗
NASA NTRS2018

Developing a Foundation for Space-Based Two-Phase Thermal Control Systems: Future of 2-Phase Thermal Control

Two-phase thermal control systems in microgravity, with significant density differences between phases, pose challenges for many current and proposed spacecraft systems. Because of the lack of understanding of these effects and the inability to scale multiphase systems in low gravity, NASA generally opts to avoid using two-phase systems for spacecraft despite the significant performance increases and lower mass. The goal of this panel discussion will be to identify key technology gaps and challenges that thermal engineers face today when considering a two-phase thermal management system. The panel discussion will begin with a brief overview of recent and on-going NASA projects designed to elicit a fundamental understanding of gas-liquid two phase behavior as it applies to thermal control systems in the Space environment. The projects/experiments discussed will range from boiling/condensation fundamentals, heat pipes, and cryogenic storage systems. We will identify what fundamental question or questions are being addressed in each case. An overview will be also be presented to address future mission needs and the specific advantages multi-phase systems offer, in particular for low cost planetary science missions and enabling missions in extreme environments. The need for efficient heat transfer with concurrent spatial and temporal temperature stability to reduce thermally-induced noise drives a serious look at multi-phase systems as a solution. Furthermore, missions to environments such as the Venus surface or penetration of ice layers in ocean worlds will likely require them. Time will be allocated at the end of this session to allow comments and questions from attendees. The intent is to use this session as a starting point to advocate for a coordinated technology development effort in this area.

Thermal Control Systems↗
NASA NTRS1990

A task control architecture for autonomous robots

An architecture is presented for controlling robots that have multiple tasks, operate in dynamic domains, and require a fair degree of autonomy. The architecture is built on several layers of functionality, including a distributed communication layer, a behavior layer for querying sensors, expanding goals, and executing commands, and a task level for managing the temporal aspects of planning and achieving goals, coordinating tasks, allocating resources, monitoring, and recovering from errors. Application to a legged planetary rover and an indoor mobile manipulator is described.

Simmons, Reid↗
NASA NTRS2004

Chemistry and Transport in a Multi-Dimensional Model

Our work has two primary scientific goals, the interannual variability (IAV) of stratospheric ozone and the hydrological cycle of the upper troposphere and lower stratosphere. Our efforts are aimed at integrating new information obtained by spacecraft and aircraft measurements to achieve a better understanding of the chemical and dynamical processes that are needed for realistic evaluations of human impact on the global environment. A primary motivation for studying the ozone layer is to separate the anthropogenic perturbations of the ozone layer from natural variability. Using the recently available merged ozone data (MOD), we have carried out an empirical orthogonal function EOF) study of the temporal and spatial patterns of the IAV of total column ozone in the tropics. The outstanding problem about water in the stratosphere is its secular increase in the last few decades. The Caltech/PL multi-dimensional chemical transport model (CTM) photochemical model is used to simulate the processes that control the water vapor and its isotopic composition in the stratosphere. Datasets we will use for comparison with model results include those obtained by the Total Ozone Mapping Spectrometer (TOMS), the Solar Backscatter Ultraviolet (SBUV and SBUV/2), Stratosphere Aerosol and Gas Experiment (SAGE I and II), the Halogen Occultation Experiment (HALOE), the Atmospheric Trace Molecular Spectroscopy (ATMOS) and those soon to be obtained by the Cirrus Regional Study of Tropical Anvils and Cirrus Layers Florida Area Cirrus Experiment (CRYSTAL-FACE) mission. The focus of the investigations is the exchange between the stratosphere and the troposphere, and between the troposphere and the biosphere.

Yung, Yuk L.↗
NASA NTRS2003

Functional Coordination of a Full-Body Gaze Control Mechanisms Elicited During Locomotion

Control of locomotion requires precise interaction between several sensorimotor subsystems. Exposure to the microgravity environment of spaceflight leads to postflight adaptive alterations in these multiple subsystems leading to postural and gait disturbances. Countermeasures designed to mitigate these postflight gait alterations will need to be assessed with a new generation of functional tests that evaluate the interaction of various elements central to locomotor control. The goal of this study is to determine how the multiple, interdependent, full- body sensorimotor subsystems aiding gaze stabilization during locomotion are functionally coordinated. To explore this question two experiments were performed. In the first study (Study 1) we investigated how alteration in gaze tasking changes full-body locomotor control strategies. Subjects (n=9) performed two discreet gaze stabilization tasks while walking at 6.4 km/hr on a motorized treadmill: 1) focusing on a central point target; 2) reading numeral characters; both presented at 2m in front at eye level. The second study (Study 2) investigated the potential of adaptive remodeling of the full-body gaze control systems following exposure to visual-vestibular conflict. Subjects (n=14) walked (6.4 km/h) on the treadmill before and after they were exposed to 0.5X minifying lenses worn for 30 minutes during self-generated sinusoidal vertical head rotations performed while seated. In both studies we measured: temporal parameters of gait, full body sagittal plane segmental kinematics of the head, trunk, thigh, shank and foot, accelerations along the vertical axis at the head and the shank, and the vertical forces acting on the support surface. Results from Study 1 showed that while reading numeral characters as compared to the central point target: 1) compensatory head pitch movements were on average 22% greater 2) the peak acceleration measured at the head was significantly reduced by an average of 13% in four of the six subjects 3) the knee joint total movement was on average 11% greater during the period from the heel strike event to the peak knee flexion event in stance phase of the gait cycle. Results from Study 2 indicate that following exposure to visual-vestibular conflict changes in full-body strategies were observed consistent with the requirement to aid gaze stabilization during locomotion.

Bloomberg, Jacob J.↗
NASA NTRS2015

Precision Closed-Loop Orbital Maneuvering System Design and Performance for the Magnetospheric Multiscale Formation

NASAs Magnetospheric Multiscale (MMS) mission successfully launched on March 13,2015 (UTC) consists of four identically instrumented spin-stabilized observatories that function as a constellation to study magnetic reconnection in space. The need to maintain sufficiently accurate spatial and temporal formation resolution of the observatories must be balanced against the logistical constraints of executing overly-frequent maneuvers on a small fleet of spacecraft. These two considerations make for an extremely challenging maneuver design problem. This paper focuses on the design elements of a 6-DOF spacecraft attitude control and maneuvering system capable of delivering the high-precision adjustments required by the constellation designers specifically, the design, implementation, and on-orbit performance of the closed-loop formation-class maneuvers that include initialization, maintenance, and re-sizing. The maneuvering control system flown on MMS utilizes a micro-gravity resolution accelerometer sampled at a high rate in order to achieve closed-loop velocity tracking of an inertial target with arc-minute directional and millimeter-per second magnitude accuracy. This paper summarizes the techniques used for correcting bias drift, sensor-head offsets, and centripetal aliasing in the acceleration measurements. It also discusses the on-board pre-maneuver calibration and compensation algorithms as well as the implementation of the post-maneuver attitude adjustments.

Maneuver and Attitude Dynamics↗
NASA NTRS2015

Precision Closed-Loop Orbital Maneuvering System Design and Performance for the Magnetospheric Multi-Scale Mission (MMS) Formation

NASA's Magnetospheric Multi-Scale (MMS) mission successfully launched on March 13, 2015 (UTC) consists of four identically instrumented spin-stabilized observatories that function as a constellation to study magnetic reconnection in space. The need to maintain sufficiently accurate spatial and temporal formation resolution of the observatories must be balanced against the logistical constraints of executing overly-frequent maneuvers on a small fleet of spacecraft. These two considerations make for an extremely challenging maneuver design problem. This paper focuses on the design elements of a 6-DOF spacecraft attitude control and maneuvering system capable of delivering the high-precision adjustments required by the constellation designers---specifically, the design, implementation, and on-orbit performance of the closed-loop formation-class maneuvers that include initialization, maintenance, and re-sizing. The maneuvering control system flown on MMS utilizes a micro-gravity resolution accelerometer sampled at a high rate in order to achieve closed-loop velocity tracking of an inertial target with arc-minute directional and millimeter-per-second magnitude accuracy. This paper summarizes the techniques used for correcting bias drift, sensor-head offsets, and centripetal aliasing in the acceleration measurements. It also discusses the on-board pre-maneuver calibration and compensation algorithms as well as the implementation of the post-maneuver attitude adjustments.

Determination and Control↗
NASA NTRS2000

Effects of Gravity on Insect Circadian Rhythmicity

Circadian rhythms - endogenous daily rhythmic fluctuations in virtually all characteristics of life - are generated and coordinated by the circadian timing system (CTS). The CTS is synchronized to the external 24-hour day by time cues such as the light/dark cycle. In an environment without time cues, the length of an animal's day is determined by the period of its internal pacemaker (tau) and the animal is said to be free-running. All life on earth evolved under the solar day; the CTS exists as an adaptation that allows organisms to anticipate and to prepare for rhythmic environmental fluctuations. All life on earth also evolved under the force of earth's gravitational environment. While it is therefore not surprising that changes in the lighting environment affect the CTS, it is surprising that changes in the gravitational environment would do so. However, recent data from one of our laboratories using the brn-3.1 knockout mouse revealed that this model, which lacks the sensory receptor hair cells within the neurovestibular system, does not respond to exposure to a hyperdynamic environment in the same fashion as normal mice. The brn-3.1 mice did not show the expected suppression of circadian rhythmicity shown by control mice exposed to 2G. Exposure to altered ambient force environments affects the amplitude, mean and timing of circadian rhythms in species from unicellular organisms to man. In addition, there is a circadian influence on the homeostatic response to acute 2G acceleration and pulses of 2G can act as a time cue, synchronizing the CTS. This is of significance because maintenance of internal and external temporal coordination is critical for normal physiological and psychological function. Typically, during adaptation to an increased gravitational environment (+G), an initial acute reaction is followed by adaptation and, eventually, a new steady state (14-16), which can take weeks to months to establish. Until the development of space stations, exposure to microgravity was, of necessity, relatively short in duration. In early spaceflight experiments an organism's internal rhythms often expressed periods that were different from each other, even in the presence of a 24.0 hour light-dark cycle, suggesting that the organism was experiencing internal desynchronization (17, 18). In (micro)G, the body temperature rhythm was delayed with respect to other body rhythms and to the light-dark cycle in rhesus macaques (19) and man (20, 21). In the absence of a light-dark cycle, the circadian rhythm of spore formation persisted in Neurospora crassa, however, both the variability and average period of the rhythm increased (22). The beetle Trigonoscelis gigas, exhibited changes in period during and following 11-13 days in (micro)G (23, 24). Resynchronization of the urinary calcium rhythm following a 1800 phase shift of the LID cycle was retarded in rats exposed to (micro)G compared to 1G controls (25). With the development of the Russian Mir Space Station, long-term controlled microgravity exposure became possible. We recorded activity rhythms from black-bodied Tenebrionid beetles, Trigonoscelis gigas, in (micro)G (spaceflight). Each insect was housed individually within an activity monitor (26) and data (activity counts) were collected and stored in five-minute bins. Thirty-two individual activity monitors were housed within each of 2 experimental kits. The beetles within each kit were divided into two groups and the lighting was controlled separately for each group.

Hoban-Higgins, Tana M.↗
NASA NTRS1972

Patterns of sleep behaviour.

Discussion of the electroencephalogram as the critical measurement procedure for sleep research, and survey of major findings that have emerged in the last decade on the presence of sleep within the twenty-four-hour cycle. Specifically, intrasleep processes, frequency of stage changes, sequence of stage events, sleep stage amounts, temporal patterns of sleep, and stability of intrasleep pattern in both man and lower animals are reviewed, along with some circadian aspects of sleep, temporal factors, and number of sleep episodes. It is felt that it is particularly critical to take the presence of sleep into account whenever performance is considered. When it is recognized that responsive performance is extremely limited during sleep, it is easy to visualize the extent to which performance is controlled by sleep itself.

Webb, W. B.↗
NASA NTRS1977

Tolerance of females to +Gz centrifugation before and after bedrest

Because women may be included as passengers in the proposed Space Shuttle System, experiments were conducted on 12 female subjects aged 24-35 yr to investigate the +Gz tolerance of women and the possible degradation of this tolerance after a period of weightlessness as simulated by bedrest. Over a 1-week period, each subject was exposed to +Gz levels starting at +2 Gz and increasing by 0.5 Gz increments to a gray-out point. This point was determined by peripheral vision loss with a standard lightbar and by reverse blood flow in the temporal artery. Ultimately, each woman was subjected to three runs at the +3 Gz level for about 55 min long each, separated by 5-min rest periods. Eight subjects with the best tolerance times were selected for 14 days of bedrest in a horizontal position; the other four being ambulatory controls. Tests before bedrest, immediately following, and 5 d later showed that average +Gz tolerance decreased by 67% after bedrest.

Newsom, B. D.↗
NASA NTRS1979

The charge injection device /CID/ as a stellar tracking sensor

A 128 x 128 element CID imager was operated in a simulated stellar trackling environment and evaluated for temporal and pattern noise and spectral response over a temperature range of -40 C to +25 C. The test devices were fabricated on long-lifetime bulk silicon material and utilized very thin upper-level polysilicon electrodes for enhanced spectral response. A standard microcomputer was used to generate all control signals and to collect and process performance data. The results of this program were used to predict the performance of a 400 x 400 CID array designed specifically for stellar-tracking.

Burke, H. K.↗
NASA NTRS1986

A study of the upper atmosphere of Uranus using the IUE

IUE data on the 1600-2000 A spectral features for Uranus during 1980 are discussed in comparison with equivalent data for Saturn and Jupiter. Attention was focused on detecting possible temporal changes in the C2H2 abundance at 1700 A. The C2H2 abundance in 1980 is estimated to have been a column density of 3.4-10.2 x 10 to the 16th/sq cm. The presence of C2H2 was attributed to photochemical reactions in a layer below 100 km altitude, and was not controlled by saturation, which took place at lower altitudes. A K value of 100,000-1 million/sq cm per sec for Uranus was comparable to Jupiter's and 10-100 times lower than Saturn's.

Encrenaz, T.↗
NASA NTRS1989

Gravity waves and turbulence in the middle atmosphere program (GRATMAP): An overview of gravity wave studies during MAP/MAC

Considerable progress was made in understanding gravity waves and their effects in the middle atmosphere during the MAP and MAC periods. During this time, gravity waves were recognized to play a central role in controlling the large scale circulation and the thermal and constituent structure of this region through wave transports of energy and momentum, a significant induced meridional circulation, and through the action of wave induced turbulence. Both theoretical and observational studies also have contributed to the understanding of the gravity wave spectrum, its temporal and spatial variability, and the processes responsible for wave saturation. As a result, the propagation, interactions, and detailed effects of such motions in the middle atmosphere are beginning to be understood. An overview is provided.

Fritts, D. C.↗
NASA NTRS1994

Regional rainfall climatologies derived from Special Sensor Microwave Imager (SSM/I) data

Climatologies of convective precipitation were derived from passive microwave observations from the Special Sensor Microwave Imager using a scattering-based algorithm of Adler et al. Data were aggregated over periods of 3-5 months using data from 4 to 5 years. Data were also stratified by satellite overpass times (primarily 06 00 and 18 00 local time). Four regions (Mexico, Amazonia, western Africa, and the western equatorial Pacific Ocean (TOGA COARE area) were chosen for their meteorological interest and relative paucity of conventional observations. The strong diurnal variation over Mexico and the southern United States was the most striking aspect of the climatologies. Pronounced morning maxima occured offshore, often in concativities in the coastline, the result of the increased convergence caused by the coastline shape. The major feature of the evening rain field was a linear-shaped maximum along the western slope of the Sierra Madre Occidental. Topography exerted a strong control on the rainfall in other areas, particularly near the Nicaragua/Honduras border and in Guatemala, where maxima in excess of 700 mm/month were located adjacent to local maxima in terrain. The correlation between the estimates and monthly gage data over the southern United States was low (0.45), due mainly to poor temporal sampling in any month and an inadequate sampling of the diurnal cycle. Over the Amazon Basin the differences in morning versus evening rainfall were complex, with an alternating series of morning/evening maxima aligned southwest to northeast from the Andes to the northeast Brazilian coast. A real extent of rainfall in Amazonia was slightly higher in the evening, but a maximum in morning precipitation was found on the Amazon River just east of Manaus. Precipitation over the water in the intertropical convergence zone (ITCZ) north of Brazil was more pronounced in the morning, and a pronounced land-/sea-breeze circulation was found along the northeast coast of Brazil. Inter-comparison of four years revealed 1992 to be the driest over Amazonia, with about a 23% decrease in mean rate compared to the 4-year mean estimated rain rate.

Negri, Andrew J.↗
NASA NTRS2005

Sensor Webs: Autonomous Rapid Response to Monitor Transient Science Events

To better understand how physical phenomena, such as volcanic eruptions, evolve over time, multiple sensor observations over the duration of the event are required. Using sensor web approaches that integrate original detections by in-situ sensors and global-coverage, lower-resolution, on-orbit assets with automated rapid response observations from high resolution sensors, more observations of significant events can be made with increased temporal, spatial, and spectral resolution. This paper describes experiments using Earth Observing 1 (EO-1) along with other space and ground assets to implement progressive mission autonomy to identify, locate and image with high resolution instruments phenomena such as wildfires, volcanoes, floods and ice breakup. The software that plans, schedules and controls the various satellite assets are used to form ad hoc constellations which enable collaborative autonomous image collections triggered by transient phenomena. This software is both flight and ground based and works in concert to run all of the required assets cohesively and includes software that is model-based, artificial intelligence software.

Mandl, Dan↗
NASA NTRS2019

Fully-polarimetric millimeter-wave spectrometers for measurement of Earth's magnetic field

Earth’s ionosphere responds dynamically over a wide range of temporal and spatial scales to changes in the magnetosphere and solar wind from above, and to neutral atmospheric dynamics from below. Determining the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere by vector magnetic field measurements at all altitudes is essential, as the field plays a major role in controlling the distribution of ionospheric plasma. It is difficult to measure the magnetic B-field, either locally or globally, at the altitudes of the upper mesosphere and lower thermosphere (UMLT) where the transfer of energy and momentum between the plasma and neutral components of the system occur. The 118-GHz imaging magnetometer will measure all four Stokes parameters as a function of frequency about the Zeeman-split center of the 118-GHz molecular oxygen line. We are developing an array of fully-polarimetric millimeterwave radiometer/spectrometers operating near 118 GHz. These low cost, low power, low mass polarimetric 118 GHz millimeter-wave array receivers do not require cooling to meet the sensitivity requirements. With digital spectrometers we will be able to integrate the complete end-to-end system. This work will enable a second generation small satellite mission with an off-nadir viewing instrument comprised of 120 such receivers (arranged so that each spot on the Earth is observed simultaneously by four receivers each) that will globally map the magnetic field in the mesosphere at 42-76 km altitude at a horizontal resolution ~100 km with 1-sigma error of 40-120 nT, in typical mesospheric temperature conditions.

Mannucci, Anthony↗
NASA NTRS1991

Characteristics of a dynamic holographic sensor for shape control of a large reflector

Design of a distributed holographic interferometric sensor for measuring the surface displacement of a large segmented reflector is proposed. The reflector's surface is illuminated by laser light of two wavelengths and volume holographic gratings are formed in photorefractive crystals of the wavefront returned from the surface. The sensor is based on holographic contouring with a multiple frequency source. It is shown that the most stringent requirement of temporal stability affects both the temporal resolution and the dynamic range. Principal factor which limit the sensor performance include the response time of photorefractive crystal, laser power required to write a hologram, and the size of photorefractive crystal.

Welch, Sharon S.↗
NASA NTRS1983

Computer program for analysis of split-Stirling-cycle cryogenic coolers

A computer program for predicting the detailed thermodynamic performance of split-Stirling-cycle refrigerators has been developed. The mathematical model includes the refrigerator cold head, free-displacer/regenerator, gas transfer line, and provision for modeling a mechanical or thermal compressor. To allow for dynamic processes (such as aerodynamic friction and heat transfer) temperature, pressure, and mass flow rate are varied by sub-dividing the refrigerator into an appropriate number of fluid and structural control volumes. Of special importance to modeling of cryogenic coolers is the inclusion of real gas properties, and allowance for variation of thermo-physical properties such as thermal conductivities, specific heats and viscosities, with temperature and/or pressure. The resulting model, therefore, comprehensively simulates the split-cycle cooler both spatially and temporally by reflecting the effects of dynamic processes and real material properties.

Brown, M. T.↗