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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

LACE flight dynamics experiment

The Low Power Atmospheric Compensation Experiment (LACE) is scheduled for launch in late 1989 into a 556 km altitude circular orbit of 43 deg inclination. The LACE flight dynamics experiment is an experiment secondary to the primary LACE mission. The purpose of the experiment is to provide on-orbit systems identification of the LACE spacecraft. The structure of the LACE spacecraft is of special interest to the CSI community. It incorporates 3 deployable/retractable booms of maximum length 45.72 m (150 ft) mounted on a rectangular parallelepiped bus of mass 1,200 kg. The zenith directed gravity gradient boom is mounted on the top of the bus; the retroreflector boom is mounted forward and deployed along the velocity vector, the balance boom is mounted and pointed aft. Attitude stabilization is accomplished by means of gravity gradient torques and by a momentum wheel. The LACE flight dynamics experiment is designed to measure modal frequencies, damping ratios, and oscillation amplitudes of the LACE spacecraft, as well as the vibration intensity generated by boom deployments and retractions. It is anticipated that this experiment will provide an opportunity for improvements in the accuracy of computer simulations of flexible structures and multibody dynamics.

Fisher, Shalom↗
NASA NTRS1990

Water-tunnel study results of a TF/A-18 and F/A-18 canopy flow visualization

A water tunnel study examining the influence of canopy shape on canopy and leading edge extension flow patterns was initiated. The F/A-18 single-place canopy model and the TF/A-18 two place canopy model were the study subjects. Plan view and side view photographs showing the flow patterns created by injected colored dye are presented for 0 deg and 5 deg sideslip angles. Photographs taken at angle of attack and sideslip conditions correspond to test departure points found in flight test. Flight experience has shown that the TF/A-18 airplane departs in regions where the F/A-18 airplane is departure-resistant. The study results provide insight into the differences in flow patterns which may influence the resulting aerodynamics of the TF/A-18 and F/A-18 aircraft. It was found that at 0 deg sideslip, the TF/A-18 model has more downward flow on the sides of the canopy than the F/A-18 model. This could be indicative of flow from the leading edge extension (LEX) vortexes impinging on the sides of the wider TF/A-18 canopy. In addition, the TF/A-18 model has larger areas of asymmetric separated and unsteady flow on the LEXs and fuselage, possibly indicating a lateral and directional destabilizing effect at the conditions studied.

Johnson, Steven A.↗
NASA NTRS1988

Lunar material transport vehicle

The proposed vehicle, the Lunar Material Transport Vehicle (LMTV), has a mission objective of efficient lunar soil material transport. The LMTV was designed to meet a required set of performance specifications while operating under a given set of constraints. The LMTV is essentially an articulated steering, double-ended dump truck. The vehicle moves on four wheels and has two identical chassis halves. Each half consists of a chassis frame, a material bucket, two wheels with integral curvilinear synchronous motors, a fuel cell and battery arrangement, an electromechanically actuated dumping mechanism, and a powerful microprocessor. The vehicle, as designed, is capable of transporting up to 200 cu ft of material over a one mile round trip per hour. The LMTV is capable of being operated from a variety of sources. The vehicle has been designed as simply as possible with attention also given to secondary usage of components.

Fisher, Charles D.↗
NASA NTRS1990

In-flight flow visualization with pressure measurements at low speeds on the NASA F-18 high alpha research vehicle

In-flight results from surface and off-surface flow visualizations and from extensive pressure distributions document the vortical flow on the leading edge extensions (LEX) and forebody of the NASA F-18 high alpha research vehicle for low speeds and angles of attack up to 50 degs. Surface flow visualization data, obtained using the emitted fluid technique, were used to define separation lines and laminar separation bubbles. Off-surface flow visualization data, obtained by smoke injection, were used to document both the path of the vortex cores and the location of vortex core breakdown. The location of vortex core breakdown correlated well with the loss of suction pressure on the LEX and with the flow visualization results from ground facilities. Surface flow separation lines on the LEX and forebody corresponded well with the end of pressure recovery under the vortical flows. Correlation of the pressures with wind tunnel results show fair to good correlation.

Delfrate, John H.↗
NASA NTRS1988

Heavy hydrocarbon main injector technology

One of the key components of the Advanced Launch System (ALS) is a large liquid rocket, booster engine. To keep the overall vehicle size and cost down, this engine will probably use liquid oxygen (LOX) and a heavy hydrocarbon, such as RP-1, as propellants and operate at relatively high chamber pressures to increase overall performance. A technology program (Heavy Hydrocarbon Main Injector Technology) is being studied. The main objective of this effort is to develop a logic plan and supporting experimental data base to reduce the risk of developing a large scale (approximately 750,000 lb thrust), high performance main injector system. The overall approach and program plan, from initial analyses to large scale, two dimensional combustor design and test, and the current status of the program are discussed. Progress includes performance and stability analyses, cold flow tests of injector model, design and fabrication of subscale injectors and calorimeter combustors for performance, heat transfer, and dynamic stability tests, and preparation of hot fire test plans. Related, current, high pressure, LOX/RP-1 injector technology efforts are also briefly discussed.

Fisher, S. C.↗
NASA NTRS1989

The Atlas/Centaur lightning strike incident

Consideration is given to an incident on March 26, 1987, in which an Atlas/Centaur 67 vehicle carrying a naval communication satellite was struck by a triggered, cloud-to-ground lightning flash about 48 s into the flight. The lightning current coupled a transient signal into the wiring of the Centaur digital computer unit, ultimately causing the breakup of the vehicle. The meteorological conditions at the time of the launch and the lightning flash triggered by the Atlas/Centaur 67 vehicle are analyzed on the basis of studies of the incident by the NASA Investigation Board.

Christian, H. J.↗
NASA NTRS1989

Dynamics of flare-driven chromospheric condensations

A general model of chromospheric condensation dynamics is developed under the assumption of sudden impulsive-phase flare energy release. The basic equation of motion for the downward-moving condensation is derived from the momentum equation and from general features seen in numerical simulations. This equation is solved for a number of different cases. The 'lifetime' of condensation and the time for the velocity to drop to half its peak value are computed. The peak downflow speed is examined as a function of the flare energy flux, and comparisons are made between downflow speeds predicted by both thick-target 'explosive evaporation' and evaporation driven conductively.

Fisher, George H.↗
NASA NTRS1990

Voyager photopolarimeter observations of Uranian ring occultations

Occultation profiles have been derived from Voyager 2 photopolarimeter observations of the nine pre-Voyager Uranian rings as well as of 1986U1R. The epsilon ring, which is the broadest and most massive, is noted to possess a wealth of structure which appears to persist coherently around the ring. The photopolarimeter data do not show any features globally ascribable to all the rings observed. Results are presented from a statistical analysis of photopolarimeter data for previously undetected or partial ring arcs.

Colwell, Joshua E.↗
NASA NTRS1990

The solar coronal density irregularity n squared bar/(n bar) squared derived from simultaneous measurements of the EUV and K-coronal brightness

Results are reported from a study of the low corona based on cospatial and cotemporal measurements of the K-coronal polarized brightness pB, and the intensity of the strong resonance line Mg x 625A as a function of height between 1.05 and 1.24 solar radius. Taken together, these measurements yield an estimate of the solar coronal density irregularity. This quantity, is found to be much greater than 1. On the basis of a simple two-component model, it is found that the well-studied resolved structures of the inner corona as presently understood are not capable of explaining the observed irregularity. It is conjectured that subresolution density fluctations associated with coronal dissipation and heating may be the source of the excess irregularity.

Orrall, F. Q.↗
NASA NTRS1989

Geometric transformations for video compression and human teleoperator display

A method for bandwidth-efficient processing of video imagery to be viewed by the teleoperator of a remotely-operated vehicle on which the camera is mounted is described. The method comprises image coding, transmission, and reconstruction. It is assumed that the transmission bandpass is the limiting factor rather than encoding/decoding schemata; that image coding and reconstruction will be done within the general abilities of the NASA/TI Programmable Remapper; and that the ratio of retained local detail to the operator's visual resolution is held constant throughout the large-field image that is seen. Novel features include that the compression and reconstruction address certain characteristics of the human visual system, that two-way communication controls a moving 'fovea' in the transformation, and that resolution varies over the image. Conventional motivations accommodated include the Cartesian raster-scan nature of available imagers and display devices and a need for low bandwidth in the image transmission. Unique image processing hardware, NASA's Programmable Remapper, allows demonstration of the method. Once refined, the technology could be adapted to special purpose imagers and display devices, or otherwise to dedicated image processing hardware.

Juday, Richard D.↗
NASA NTRS1990

Model calculations of the relative effects of CFCs and their replacements on stratospheric ozone

Because chlorine has been linked to the destruction of stratospheric ozone, the use of many fully halogenated compounds, such as the chlorofluorocarbons CFC-11 and -12, is restricted by international agreement. Hydrohalocarbons are under intensive development as replacements for CFCs. Because they contain hydrogen, these gases are susceptible to tropospheric destruction which significantly shortens their atmospheric lifetimes,. Model calculations show that chlorine-containing hydrohalocarbons have less effect on ozone, by an order of magnitude, than their regulated counterparts.

Fisher, Donald A.↗
NASA NTRS1990

Multistroke cloud-to-ground strike to the NASA F-106B airplane

An analysis of electromagnetic waveform records and video images of a multistroke cloud-to-ground (CG) strike to the NASA F-106B instrumented airplane is presented. The CG flash started as a lightning strike triggered by the airplane and later produced multiple return strokes to the ground (the ground strike network registered six return strokes). Although there are some uncertainties in data interpretation resulting from lack of independent measurements with other than the airborne instruments, recoil streamers and eight sequences of dart leaders followed by return strokes (two more than were indicated by the ground network) were identified in the airborne data. At least three of the subsequent return strokes were attached to the airplane. The analysis provides evidence that formation of recoil streamers and dart leaders is accompanied by a surge in continuous current. This feature is similar to that observed in the bidirectional leader development during lightning initiation on the airplane.

Mazur, Vladislav↗
NASA NTRS1989

An improved architecture for video rate image transformations

Geometric image transformations are of interest to pattern recognition algorithms for their use in simplifying some aspects of the pattern recognition process. Examples include reducing sensitivity to rotation, scale, and perspective of the object being recognized. The NASA Programmable Remapper can perform a wide variety of geometric transforms at full video rate. An architecture is proposed that extends its abilities and alleviates many of the first version's shortcomings. The need for the improvements are discussed in the context of the initial Programmable Remapper and the benefits and limitations it has delivered. The implementation and capabilities of the proposed architecture are discussed.

Fisher, Timothy E.↗
NASA NTRS1989

Three-dimensional visualization and display technologies; Proceedings of the Meeting, Los Angeles, CA, Jan. 18-20, 1989

Special attention was given to problems of stereoscopic display devices, such as CAD for enhancement of the design process in visual arts, stereo-TV improvement of remote manipulator performance, a voice-controlled stereographic video camera system, and head-mounted displays and their low-cost design alternatives. Also discussed was a novel approach to chromostereoscopic microscopy, computer-generated barrier-strip autostereography and lenticular stereograms, and parallax barrier three-dimensional TV. Additional topics include processing and user interface isssues and visualization applications, including automated analysis and fliud flow topology, optical tomographic measusrements of mixing fluids, visualization of complex data, visualization environments, and visualization management systems.

Robbins, Woodrow E.↗
NASA NTRS1990

An equation for the evolution of solar and stellar flare loops

An ordinary differential equation describing the evolution of a coronal loop subjected to a spatially uniform but time-varying heating rate is discussed. It is assumed that the duration of heating is long compared to the sound transit time through the loop, which is assumed to have uniform cross section area. The form of the equation changes as the loop evolves through three states: 'strong evaporation', 'scaling law behavior', and 'strong condensation'. Solutions to the equation may be used to compute the time dependence of the average coronal temperature and emission measure for an assumed temporal variation of the flare heating rate. The results computed from the model agree reasonably well with recent published numerical simulations and may be obtained with far less computational effort. The model is then used to study the May 21, 1980, solar flare observed by SMM and the giant April 12, 1985, flare observed on the star AD Leo.

Fisher, George H.↗
NASA NTRS1989

In-flight flow visualization characteristics of the NASA F-18 high alpha research vehicle at high angles of attack

Surface and off-surface flow visualization techniques have been used to visualize the three-dimensional separated flows on the NASA F-18 high alpha research vehicle at high angles of attack. Results near alpha = 25 deg to 26 deg and alpha = 45 deg to 49 deg are presented. Both the forebody and leading-edge extension (LEX) vortex cores and breakdown locations were visualized using smoke. Forebody and LEX vortex separation lines on the surface were defined using an emitted-fluid technique. A laminar separation bubble was also detected on the nose cone using the emitted fluid technique and was similar to that observed in the wind-tunnel test, but not as extensive. Regions of attached, separated, and vortical flow were noted on the wing and the leading-edge flap using tufts and flow cones, and compared well with limited wind-tunnel results.

Fisher, David F.↗