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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25

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NASA NTRS1988

Guidance for an aeroassisted orbital transfer vehicle

The use of atmospheric drag for slowing satellite in high energy, high apogee orbits to a lower energy, lower apogee orbit about the Earth is investigated. The high energy orbit is assumed to intercept the Earth's atmosphere. Guidance for the atmospheric phase of the trajectory may be done using the aerodynamic forces generated by the passage through the atmosphere. This research was concerned with the investigation of several methods of guidance during the atmospheric phase to cause a significant reduction in the final velocity as the vehicle leaves the atmosphere. In addition, the velocity direction was controlled to exit to a desired target orbit. Lastly excess aerodynamic lift was used to effect a plane change between the entry orbit plane and the exit orbit plane to achieve a desired orbit plane. The guidance methods were applied to a 3 degree-of-freedom simulation which included an oblate Earth gravity model and a rotating atmosphere. Simulation results were compared on the basis of speed of computation of the guidance parameters and amount of added velocity necessary to achieve the desired orbit.

Hall, Kenneth R.↗

NASA NTRS1991

The role of global cloud climatologies in validating numerical models

Reliable estimates of the components of the surface radiation budget are important in studies of ocean-atmosphere interaction, land-atmosphere interaction, ocean circulation and in the validation of radiation schemes used in climate models. The methods currently under consideration must necessarily make certain assumptions regarding both the presence of clouds and their vertical extent. Because of the uncertainties in assumed cloudiness, all these methods involve perhaps unacceptable uncertainties. Here, a theoretical framework that avoids the explicit computation of cloud fraction and the location of cloud base in estimating the surface longwave radiation is presented. Estimates of the global surface downward fluxes and the oceanic surface net upward fluxes were made for four months (April, July, October and January) in 1985 to 1986. These estimates are based on a relationship between cloud radiative forcing at the top of the atmosphere and the surface obtained from a general circulation model. The radiation code is the version used in the UCLA/GLA general circulation model (GCM). The longwave cloud radiative forcing at the top of the atmosphere as obtained from Earth Radiation Budget Experiment (ERBE) measurements is used to compute the forcing at the surface by means of the GCM-derived relationship. This, along with clear-sky fluxes from the computations, yield maps of the downward longwave fluxes and net upward longwave fluxes at the surface. The calculated results are discussed and analyzed. The results are consistent with current meteorological knowledge and explainable on the basis of previous theoretical and observational works; therefore, it can be concluded that this method is applicable as one of the ways to obtain the surface longwave radiation fields from currently available satellite data.

HARSHVARDHAN↗

NASA NTRS1992

Longwave radiation budget parameters computed from ISCCP and HIRS2/MSU products

The International Satellite Cloud Climatology Project (ISCCP) retrieved cloud fields and the high-resolution radiation sounder 2 (HIRS2) retrieved cloud fields yield similar outgoing longwave radiation (OLR) due to the cancelation effect of cloud-top altitudes and cloud amount on OLR. For the large regional discrepancies of the order of 30 W/sq m found over northern Africa are largely due to surface temperature differences, and extensive discrepancies over the ocean are due to humidity differences. Harmonic analysis is applied to OLR, clear-sky OLR, and cloud-radiative forcing at the top of the atmosphere using the ISCCP products. The diurnal variations of these parameters from 60 deg S to 60 deg N are larger over land than over the ocean. The clear-sky OLR peaks around 1500 LST, usually over land areas, and is associated with the surface/air temperature maximum. The OLR over cloudy regions shows a similar diurnal phase as the cloud top pressure. The cloud radiative forcing at the top of the atmosphere has maximum value near 2100 LST mountain areas and near 0000 and 0300 LST over equatorial regions. The ISCCP-computed longwave cloud radiative forcing has smaller diurnal variations over the ocean than the HIRS2-computed longwave cloud radiative forcing. The global mean bias of OLR is around 0.74 W/sq m, and locally, the bias can be as large as 5 to 10 W/sq m. This appears to indicate that the twice-a-day measurements of the HIRS2/MSU (around 0315 and 1515 LST, which are the equatorial cross times at nadir track) can be used to derive monthly mean OLR without significant bias.

Wu, Man L. C.↗

NASA NTRS1984

On the dynamics of equatorial forcing of climate teleconnections

A number of observational, theoretical, and modeling studies have been conducted on the remote influence of the tropics on the midlatitudes. Teleconnection in the geopotential height field between the tropics and the extratropics associated with the Southern Oscillation in the so-called Pacific-North America (PNA) pattern, has often been cited as an example of such remote influence. Simmons et al. (1983) have shown that teleconnections such as PNA may arise both from barotropic instability of the extratropical zonal flow and from tropical forcing. The present investigation is only concerned with the dynamics of the part of the atmospheric teleconnection which arises from tropical forcing. Some fundamentals of Rossby wave theory in unsheared flow are discussed along with the linear response to equatorial forcing for horizontally, sheared zonal mean flow. A global shallow-water spectral model is employed in conjunction with a theoretical analysis to show the teleconnection patterns which develop under different large-scale mean circulation conditions.

Lau, K.-M.↗

NASA NTRS1990

The 27-28 October 1986 FIRE cirrus case study - Meteorology and clouds

A detailed case study is conducted of cirrus clouds that were observed intensely over a 36-h period from 1200 UTC October 27 to 0000 UTC October 29, 1986. The clouds varied in density and structure as synoptic and mesoscale features passed through the region. The study seeks to provide a meteorological overview including a synoptic and regional perspective; to document the rawinsonde-resolved atmospheric structure and large-scale forcing associated with the observed cloud systems; and to provide understanding of the relationship between atmospheric structure and the character of the corresponding cloud fields. Regional analyses of the static stability structure and vertical motion are presented and interpreted with respect to the characteristics of the corresponding cloud fields as deduced from satellite and lidar observations. It is suggested that mesoscale organization must be taken into account in parametric treatments of cirrus for large-scale atmospheric models. It is shown that cloud generation typically occurred at multiple levels.

Starr, David O'C.↗

NASA NTRS1994

Scientific analysis of satellite ranging data

A network of satellite laser ranging (SLR) tracking systems with continuously improving accuracies is challenging the modelling capabilities of analysts worldwide. Various data analysis techniques have yielded many advances in the development of orbit, instrument and Earth models. The direct measurement of the distance to the satellite provided by the laser ranges has given us a simple metric which links the results obtained by diverse approaches. Different groups have used SLR data, often in combination with observations from other space geodetic techniques, to improve models of the static geopotential, the solid Earth, ocean tides, and atmospheric drag models for low Earth satellites. Radiation pressure models and other non-conservative forces for satellite orbits above the atmosphere have been developed to exploit the full accuracy of the latest SLR instruments. SLR is the baseline tracking system for the altimeter missions TOPEX/Poseidon, and ERS-1 and will play an important role in providing the reference frame for locating the geocentric position of the ocean surface, in providing an unchanging range standard for altimeter calibration, and for improving the geoid models to separate gravitational from ocean circulation signals seen in the sea surface. However, even with the many improvements in the models used to support the orbital analysis of laser observations, there remain systematic effects which limit the full exploitation of SLR accuracy today.

Smith, David E.↗

NASA NTRS1996

Comparison of Arc Tracking Tests in Various Aerospace Environments

Momentary short-circuit arcs between a polyimide insulated wire with defective insulation and another conductor may cause pyrolization of the insulation resulting in a conductive path capable of sustaining the arc. These sustained arcs may propagate along the wires or to neighboring wires leading to complete failure of the wire bundle. Wire insulation susceptibility to arc tracking may be dependent on its environment. Because all wire insulation types tested to date arc track, a test procedure has been developed to compare different insulation types with respect to their arc tracking susceptibility. This test procedure is presented along with a comparison of arc tracking in the following three environments: (1) Air at atmospheric pressure and 1 gravitational(g) force; (2) Vacuum (2.67 x 10(exp -3) Pa) and 1g, and (3) Air at atmospheric pressure and microgravity (less than 0.04g).

Stueber, Thomas J.↗

NASA NTRS2013

Sensitivity of the Atmospheric Response to Warm Pool El Nino Events to Modeled SSTs and Future Climate Forcings

Warm pool El Nino (WPEN) events are characterized by positive sea surface temperature (SST) anomalies in the central equatorial Pacific. Under present-day climate conditions, WPEN events generate poleward propagating wavetrains and enhance midlatitude planetary wave activity, weakening the stratospheric polar vortices. The late 21st century extratropical atmospheric response to WPEN events is investigated using the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM), version 2. GEOSCCM simulations are forced by projected late 21st century concentrations of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) and by SSTs and sea ice concentrations from an existing ocean-atmosphere simulation. Despite known ocean-atmosphere model biases, the prescribed SST fields represent a best estimate of the structure of late 21st century WPEN events. The future Arctic vortex response is qualitatively similar to that observed in recent decades but is weaker in late winter. This response reflects the weaker SST forcing in the Nino 3.4 region and subsequently weaker Northern Hemisphere tropospheric teleconnections. The Antarctic stratosphere does not respond to WPEN events in a future climate, reflecting a change in tropospheric teleconnections: The meridional wavetrain weakens while a more zonal wavetrain originates near Australia. Sensitivity simulations show that a strong poleward wavetrain response to WPEN requires a strengthening and southeastward extension of the South Pacific Convergence Zone; this feature is not captured by the late 21st century modeled SSTs. Expected future increases in GHGs and decreases in ODSs do not affect the polar stratospheric responses to WPEN.

stratosphere↗

NASA NTRSDate not supplied

Orion Artemis-1 Post-Flight Characterization

This abstract discusses the post-flight characterization of the heatshield used in the Orion Artemis-1 mission, which is a significant milestone in human space exploration. The Artemis-1 heatshield is a crucial component designed to protect the spacecraft during re-entry into Earth's atmosphere. It experiences extreme temperatures and forces as it encounters the intense heat generated by the friction between the spacecraft and the atmospheric gases. The post-flight characterization of the Artemis-1 heatshield involves analyzing its surface morphology and elemental composition. This analysis provides valuable insights into the performance and durability of the heatshield during the mission. By utilizing techniques such as Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX), a detailed examination of the heatshield’s surface features, and elemental composition can be conducted. The SEM analysis offers high-resolution imaging capabilities, enabling detailed observations of the heatshield’s surface morphology. EDX analysis provides elemental analysis, allowing for an assessment of any compositional changes induced by the thermal and environmental conditions experienced during the mission. This information is crucial for understanding the material's response to the extreme conditions and identifying any potential issues or degradation. Furthermore, density profiling analysis is performed to measure density variations across the depth of the heatshield material. This analysis offers insights into the effects of the mission on the heatshield, such as potential ablation, or changes in material porosity. Understanding these density variations helps to evaluate the heatshield's structural integrity and its ability to withstand future missions. This knowledge contributes to the ongoing development of advanced heatshield designs, enhancing their thermal protection capabilities and ensuring the safety of future manned missions to the Moon and beyond.

Tane Boghozian↗

NASA NTRS1994

Radiative-convective model with an explicit hydrologic cycle. 2: Sensitivity to large changes in solar forcing

The one-dimensional radiative-convective equilibrium model with an explicit hydrologic cycle introduced in part 1 is used to study the sensitivity of the model's atmosphere to large changes in the solar forcing, when various cumulus convection parameterizations are used. When the concentration of the absorbing as in the atmosphere is temperature dependent, equilibrium is impossible for values of the solar forcing larger than a critical value. This result is referred to as a runaway greenhouse. The cumulus convection parameterization schemes currently in use in global climate models (GCMs) employ different assumptions about moistening. This causes the critical solar forcing above which a runaway greenhouse occurs to be very sensitive to the cumulus convection scheme employed. Furthermore, we show that the sensitivity of the equilibrium temperature to changes in the solar forcing depends crucially on the microphysics of cumulus convection. For fixed cloud conditions, the critical forcing for a runaway greenhouse to occur is between approximately 1.22 and 1.49 times the global mean value for the Earth, and for clear sky conditions, it is a few percent lower. The runaway greenhouse in the experiments with the mass flux schemes generally occurs more rapidly than in the experiments with the adjustment schemes. In addition, the inability of the hard convective adjustment scheme to produce an efficient vertical transport of moisture, together with the saturation requirement for convection to occur, leads to the breakdown of the radiative-convective equilibria when other processes are not available to provide the necessary vertical transport of water vapor.

Renno, Nilton O.↗

NASA NTRS2010

Demonstration of an Aerocapture GN and C System Through Hardware-in-the-Loop Simulations

Aerocapture is an orbit insertion maneuver in which a spacecraft flies through a planetary atmosphere one time using drag force to decelerate and effect a hyperbolic to elliptical orbit change. Aerocapture employs a feedback Guidance, Navigation, and Control (GN&C) system to deliver the spacecraft into a precise postatmospheric orbit despite the uncertainties inherent in planetary atmosphere knowledge, entry targeting and aerodynamic predictions. Only small amounts of propellant are required for attitude control and orbit adjustments, thereby providing mass savings of hundreds to thousands of kilograms over conventional all-propulsive techniques. The Analytic Predictor Corrector (APC) guidance algorithm has been developed to steer the vehicle through the aerocapture maneuver using bank angle control. Through funding provided by NASA's In-Space Propulsion Technology Program, the operation of an aerocapture GN&C system has been demonstrated in high-fidelity simulations that include real-time hardware in the loop, thus increasing the Technology Readiness Level (TRL) of aerocapture GN&C. First, a non-real-time (NRT), 6-DOF trajectory simulation was developed for the aerocapture trajectory. The simulation included vehicle dynamics, gravity model, atmosphere model, aerodynamics model, inertial measurement unit (IMU) model, attitude control thruster torque models, and GN&C algorithms (including the APC aerocapture guidance). The simulation used the vehicle and mission parameters from the ST-9 mission. A 2000 case Monte Carlo simulation was performed and results show an aerocapture success rate of greater than 99.7%, greater than 95% of total delta-V required for orbit insertion is provided by aerodynamic drag, and post-aerocapture orbit plane wedge angle error is less than 0.5 deg (3-sigma). Then a real-time (RT), 6-DOF simulation for the aerocapture trajectory was developed which demonstrated the guidance software executing on a flight-like computer, interfacing with a simulated IMU and simulated thrusters, with vehicle dynamics provided by an external simulator. Five cases from the NRT simulations were run in the RT simulation environment. The results compare well to those of the NRT simulation thus verifying the RT simulation configuration. The results of the above described simulations show the aerocapture maneuver using the APC algorithm can be accomplished reliably and the algorithm is now at TRL-6. Flight validation is the next step for aerocapture technology development.

Masciarelli, James↗

NASA NTRS1990

Stratospheric dynamics

A global circulation model is being used to study the dynamical behavior of stratospheric planetary waves (waves having horizontal wavelengths of tens of thousands of kilometers) forced by growing cyclonic disturbances of intermediate scale, typically with wavelengths of a few thousand kilometers, which occur in the troposphere. Planetary scale waves are the dominant waves in the stratosphere, and are important for understanding the distribution of atmospheric trace constituents. Planetary wave forcing by intermediate scale tropospheric cyclonic disturbances is important for producing eastward travelling planetary waves of the sort which are prominent in the Southern Hemisphere during winter. The same global circulation model is also being used to simulate and understand the rate of dispersion and possible stratospheric climatic feedbacks of the El Chichon volcanic aerosol cloud. By comparing the results of the model calculation with an established data set now in existence for the volcanic cloud spatial and temporal distribution, stratospheric transport processes will be better understood, and the extent to which the cloud modified stratospheric wind and temperature fields can be assessed.

Young, Richard E.↗

NASA NTRS1974

Atmospheric diffusion predictions for the exhaust effluents from the launch of a Titan 3C, December 13, 1973

Results for the predictions with the NASA/MSFC Multilayer Diffusion Model for the dispersive transport of the Titan 3C rocket exhaust effluents for the 1857 EST launch on December 13, 1973, from the Eastern Test Range at Cape Canaveral Air Force Station are presented. An atmospheric assessment is made in support of the joint Marshall Space Flight Center, Langley Research Center, and Kennedy Space Center rocket exhaust prediction and measurement program. The predictions are primarily intended to define a monitoring grid and for a postflight assessment of the field measurements in order to improve diffusion prediction techniques.

Stephens, J. B.↗

NASA NTRS1986

General circulation model simulations of superrotation in slowly rotating atmospheres - Implications for Venus

The results of three-dimensional general circulation model experiments simulating the earth atmosphere with planetary rotation rates between 1 and 1/64th times the earth's and diurnally averaged thermal forcing are used to evaluate Venus atmospheric superrotation theories invoking the upward transport of angular momentum from the solid planet by the zonal mean circulation. While the theories predict that superrotation is a common feature of slowly rotating planetary atmospheres, suggesting that superrotation should appear in the present, slowly rotating cases, the steady state circulations are noted to include only weak globally averaged superrotation, consistent with previously reported results from lower resolution models. The thermally driven equator-to-pole circulation rapidly generates zonal mean winds during spinup, near the planetary surface, precluding vertical angular momentum transport and suppressing further superrotation development.

Covey, C.↗

NASA NTRS1998

Global tropospheric ozone investigations

Ozone (O3) is one of the most important trace gases in the troposphere, and it is responsible for influencing many critical chemical and radiative processes. Ozone contributes to the formation of the hydroxyl radical (OH), which is central to most chemical reactions in the lower atmosphere, and it absorbs UV, visible, and infrared radiation which affects the energy budget and atmospheric temperatures. In addition, O3 can be used as a tracer of atmospheric pollution and stratosphere troposphere exchange. At elevated concentrations, O3 can also produce detrimental biological and human health effects. The US National Research Council (NRC) Board on Sustainable Development reviewed the US Global Change Research Program (USGCRP) [NRC, 1995], and it identified tropospheric chemistry as one of the high priority areas for the USGCRP in the next decade. The NRC identified the following specific challenges in tropospheric chemistry. Although we understand the reason for the high levels of 03 over several regions of the world, we need to better establish the distribution of O3 in the troposphere in order to document and understand the changes in the abundance of global tropospheric O3. This information is needed to quantify the contribution of O3 to the Earth' s radiative balance and to understand potential impacts on the health of the biosphere. Having recognized the importance of particles in the chemistry of the stratosphere, we must determine how aerosols and clouds affect the chemical processes in the troposphere. This understanding is essential to predict the chemical composition of the atmosphere and to assess the resulting forcing effects in the climate system. We must determine if the self-cleansing chemistry of the atmosphere is changing as a result of human activities. This information is required to predict the rate at which pollutants are removed from the atmosphere. Over nearly two decades, airborne Differential Absorption Lidar (DIAL) systems have been used in over fifteen major field experiments conducted all over the world to address important atmospheric processes affecting the amount and distribution of 03 and aerosols across the troposphere. This paper discusses some of these wide-ranging field experiments and their results and presents a direction for future global studies of O3 and aerosols from space.

Browell, Edward V.↗

NASA NTRS2006

Vacuum-Assisted, Constant-Force Exercise Device

The vacuum-assisted, constant-force exercise device (VAC-FED) has been proposed to fill a need for a safe, reliable exercise machine that would provide constant loads that could range from 20 to 250 lb (0.09 to 1.12 kN) with strokes that could range from 6 to 36 in. (0.15 to 0.91 m). The VAC-FED was originally intended to enable astronauts in microgravity to simulate the lifting of free weights, but it could just as well be used on Earth for simulated weight lifting and other constant-force exercises. Because the VAC-FED would utilize atmospheric/vacuum differential pressure instead of weights to generate force, it could weigh considerably less than either a set of free weights or a typical conventional exercise machine based on weights. Also, the use of atmospheric/ vacuum differential pressure to generate force would render the VAC-FED inherently safer, relative to free weights and to conventional exercise machines that utilize springs to generate forces. The overall function of the VAC-FED would be to generate a constant tensile force in an output cable, which would be attached to a bar, handle, or other exercise interface. The primary force generator in the VAC-FED would be a piston in a cylinder. The piston would separate a volume vented to atmosphere at one end of the cylinder from an evacuated volume at the other end of the cylinder (see figure). Hence, neglecting friction at the piston seals, the force generated would be nearly constant equal to the area of the piston multiplied by the atmospheric/vacuum differential pressure. In the vented volume in the cylinder, a direct-force cable would be looped around a pulley on the piston, doubling the stroke and halving the tension. One end of the direct-force cable would be anchored to a cylinder cap; the other end of the direct-force cable would be wrapped around a variable-ratio pulley that would couple tension to the output cable. As its name suggests, the variable-ratio pulley would contain a mechanism that could be used to vary the ratio between the tension in the direct-force cable and the tension in the output cable. This mechanism could contain gears, pulleys, and/or levers, for example.

Hansen, Christopher P.↗

NASA NTRS1980

Climatic effects of atmospheric aerosols

It is shown quantitatively how radiative climatic forcing by aerosols depends on the physical properties of the aerosols. The special case of atmospheric aerosols produced by volcanic explosions is considered, and evidence is presented which indicates that even the simple climate models available today may be able to capture some of the basic effects of aerosols on global climate. Possible effects of anthropogenic aerosols are briefly examined. It is noted that additional evidence for the significant influence of aerosols on climate may be found in data obtained from recent spacecraft missions to Venus and Mars.

Hansen, J. E.↗

NASA NTRS2011

Responding to the Consequences of Climate Change

The talk addresses the scientific consensus concerning climate change, and outlines the many paths that are open to mitigate climate change and its effects on human activities. Diverse aspects of the changing water cycle on Earth are used to illustrate the reality climate change. These include melting snowpack, glaciers, and sea ice; changes in runoff; rising sea level; moving ecosystems, an more. Human forcing of climate change is then explained, including: greenhouse gasses, atmospheric aerosols, and changes in land use. Natural forcing effects are briefly discussed, including volcanoes and changes in the solar cycle. Returning to Earth's water cycle, the effects of climate-induced changes in water resources is presented. Examples include wildfires, floods and droughts, changes in the production and availability of food, and human social reactions to these effects. The ~lk then passes to a discussion of common human reactions to these forecasts of climate change effects, with a summary of recent research on the subject, plus several recent historical examples of large-scale changes in human behavior that affect the climate and ecosystems. Finally, in the face for needed action on climate, the many options for mitigation of climate change and adaptation to its effects are presented, with examples of the ability to take affordable, and profitable action at most all levels, from the local, through national.

Hildebrand, Peter H.↗