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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Multi-axis transient vibration testing of space objects: Test philosophy, test facility, and control strategy

IABG has been using various servohydraulic test facilities for many years for the reproduction of service loads and environmental loads on all kinds of test objects. For more than 15 years, a multi-axis vibration test facility has been under service, originally designed for earthquake simulation but being upgraded to the demands of space testing. First tests with the DFS/STM showed good reproduction accuracy and demonstrated the feasibility of transient vibration testing of space objects on a multi-axis hydraulic shaker. An approach to structural qualification is possible by using this test philosophy. It will be outlined and its obvious advantages over the state-of-the-art single-axis test will be demonstrated by example results. The new test technique has some special requirements to the test facility exceeding those of earthquake testing. Most important is the high reproduction accuracy demanded for a sophisticated control system. The state-of-the-art approach of analog closed-loop control circuits for each actuator combined with a static decoupling network and an off-line iterative waveform control is not able to meet all the demands. Therefore, the future over-all control system is implemented as hierarchical full digital closed-loop system on a highly parallel transputer network. The innermost layer is the digital actuator controller, the second one is the MDOF-control of the table movement. The outermost layer would be the off-line iterative waveform control, which is dedicated only to deal with the interaction of test table and test object or non-linear effects. The outline of the system will be presented.

Lachenmayr, Georg↗
NASA NTRS1993

Gas turbine system simulation: An object-oriented approach

A prototype gas turbine engine simulation has been developed that offers a generalized framework for the simulation of engines subject to steady-state and transient operating conditions. The prototype is in preliminary form, but it successfully demonstrates the viability of an object-oriented approach for generalized simulation applications. Although object oriented programming languages are-relative to FORTRAN-somewhat austere, it is proposed that gas turbine simulations of an interdisciplinary nature will benefit significantly in terms of code reliability, maintainability, and manageability. This report elucidates specific gas turbine simulation obstacles that an object-oriented framework can overcome and describes the opportunity for interdisciplinary simulation that the approach offers.

Drummond, Colin K.↗
NASA NTRS1993

A model-based approach for detection of objects in low resolution passive millimeter wave images

A model-based vision system to assist the pilots in landing maneuvers under restricted visibility conditions is described. The system was designed to analyze image sequences obtained from a Passive Millimeter Wave (PMMW) imaging system mounted on the aircraft to delineate runways/taxiways, buildings, and other objects on or near runways. PMMW sensors have good response in a foggy atmosphere, but their spatial resolution is very low. However, additional data such as airport model and approximate position and orientation of aircraft are available. These data are exploited to guide our model-based system to locate objects in the low resolution image and generate warning signals to alert the pilots. Also analytical expressions were derived from the accuracy of the camera position estimate obtained by detecting the position of known objects in the image.

Kasturi, Rangachar↗
NASA NTRS1992

Herbig-Haro objects in the receding lobe of the L 1551 outflow

A spectrum has been obtained of two Herbig-Haro objects which are seen against the receding lobe of the bipolar outflow within the dark cloud Lynds 1551. Positive heliocentric velocities up to 90 km/s have been measured from the H-alpha line which point to an association of these emission knots with the embedded infrared source L 1551-IRS 5 rather than with other young stellar objects in this part of the sky. There is a velocity range of 50-100 km/s within each object. (S II) lambda 6716 is also detected at a strength of about 50 pct of H-alpha. Along the entire length of the slit there is broad H-alpha emission with strength about four times that normally seen in emission from the night sky. This feature partially resolves into two components, one of which we suggest is from the general Galactic field, and the other from extended bow-shock emission.

Graham, J. A.↗
NASA NTRS1993

Ultraviolet polarimetry and spectroscopy of the BL Lacertae object PKS 2155-304

HST and Faint Object Spectrograph spectropolarimetry is presented for the BL Lac object PKS 2155-304; attention is given to the wavelength dependence of the UV linear polarization in a BL Lac object. The UV polarimetry yields evidence that the UV polarized flux is generated by the synchrotron mechanism responsible for optical polarization. Both the UV and optical emission are produced in the same region of the source.

Allen, Richard G.↗
NASA NTRS1993

Ultraviolet spectra of QSOs, BL Lacertae objects, and Seyfert galaxies

Motivated by the possibility of detecting strong absorption features toward extragalactic background objects, we present optimally extracted and co-added IUE spectra of QSOs, BL Lac objects, and Seyfert galaxies. These spectra together with those presented (in a similar work) by Kinney et al. form an essentially complete sample of the SWP, LWP, and LWR observations of QSOs, BL Lac objects, and Seyfert galaxies with redshifts z greater than 0.05 available in the IUE merged observation log as of 1991 December.

Lanzetta, Kenneth M.↗
NASA NTRS1992

Time-dependent inhomogeneous jet models for BL Lac objects

Relativistic beaming can explain many of the observed properties of BL Lac objects (e.g., rapid variability, high polarization, etc.). In particular, the broadband radio through X-ray spectra are well modeled by synchrotron-self Compton emission from an inhomogeneous relativistic jet. We have done a uniform analysis on several BL Lac objects using a simple but plausible inhomogeneous jet model. For all objects, we found that the assumed power-law distribution of the magnetic field and the electron density can be adjusted to match the observed BL Lac spectrum. While such models are typically unconstrained, consideration of spectral variability strongly restricts the allowed parameters, although to date the sampling has generally been too sparse to constrain the current models effectively. We investigate the time evolution of the inhomogeneous jet model for a simple perturbation propagating along the jet. The implications of this time evolution model and its relevance to observed data are discussed.

Marlowe, A. T.↗
NASA NTRS1993

Mission objectives and comparison of strategies for Mars exploration

Over the past several years, a number of candidate scenarios for the human exploration of Mars have been advanced. These have had a range of mission objectives, scope, scale, complexity and probable cost. The Exploration Programs Office (ExPO) has developed a reference Mars exploration program and a means of comparing it to other proposed Mars programs. The reference program was initiated in a workshop of Mars exploration advocates which defined two objectives of equal importance for early Mars exploration - understanding Mars and understanding the potential of Mars to support humans. These goals were used to define a set of transportation and surface elements that could carry out a robust exploration program. The approach to comparing alternate architectures has three principal parts: (1) Bringing the architectures into rough commonality in terms of surface mission objectives and hardware capabilities; (2) Providing a common level of human support for flights to and from Mars; and (3) Comparing the complexity of the elements needed to carry out the program and using partial redundancy to approximate the same statistical probability of mission success. This top-level approach has been applied to the ExPO reference program, the 'Mars Directs strategy (Zubrin, 1991) and the Stanford International Mars Mission (Lusignan, 1992).

Duke, Michael B.↗
NASA NTRS1993

BL Lacertae objects, Fanaroff-Riley type I radio sources, and cluster cooling flows

The correctness of the view that the Fanaroff-Riley type I (F-R I) radio galaxies and the BL Lac objects are intrinsically the same and that the strong emission seen in BL Lac may be the result of beaming of radiation from the galactic nucleus is examined. Expressions are derived for the surface brightness of scattered beams of polarized or unpolarized radiation, and the expected scattered light surface is calculated assuming the beams have spectra and fluxes consistent with those observed for BL Lac objects. The models are compared to recent observations of lobes of excess, polarized blue light in Cy-A, and observations of lobes of UV light in the central regions of the cD galaxies in A1795 and A2597. It was found that the models predict scattered surface brightnesses in reasonable agreement with those observed. If these lobes are indeed scattered light, this would indicate that F-R I radio galaxies do possess beams of radiation with apparent luminosities similar to BL Lac objects and that the radiation is actively beamed and not merely obscured by a torus of dust around the nucleus.

Sarazin, Craig L.↗
NASA NTRS1993

The generation and use of numerical shape models for irregular Solar System objects

We describe a procedure that allows the efficient generation of numerical shape models for irregular Solar System objects, where a numerical model is simply a table of evenly spaced body-centered latitudes and longitudes and their associated radii. This modeling technique uses a combination of data from limbs, terminators, and control points, and produces shape models that have some important advantages over analytical shape models. Accurate numerical shape models make it feasible to study irregular objects with a wide range of standard scientific analysis techniques. These applications include the determination of moments of inertia and surface gravity, the mapping of surface locations and structural orientations, photometric measurement and analysis, the reprojection and mosaicking of digital images, and the generation of albedo maps. The capabilities of our modeling procedure are illustrated through the development of an accurate numerical shape model for Phobos and the production of a global, high-resolution, high-pass-filtered digital image mosaic of this Martian moon. Other irregular objects that have been modeled, or are being modeled, include the asteroid Gaspra and the satellites Deimos, Amalthea, Epimetheus, Janus, Hyperion, and Proteus.

Simonelli, Damon P.↗
NASA NTRS1993

Explosions of small Spacewatch objects in the Earth's atmosphere

It is shown here that explosions due to Spacewatch objects with diameters less than 50 m typically occur too high in the atmosphere to cause substantial surface damage. Exclusive of relatively rare iron objects, no comet or asteroid with an energy below about 2 megatons threatens the Earth's surface. The high flux of small Earth-crossing objects identified by Spacewatch therefore does not imply a greater terrestrial hazard.

Chyba, Christopher F.↗
NASA NTRS1993

Lick slit spectra of thirty-eight objective prism quasar candidates and low metallicity halo stars

Lick Observatory slit spectra of 38 objects which were claimed to have pronounced UV excess and emission lines are presented. Eleven QSOs, four galaxies at z of about 0.1, 22 stars, and one unidentified object with a low S/N spectrum were found. Of 11 objects which Zhan and Chen (1987, 1989) suggested were QSO with z(prism) not greater than 2.8; eight are QSOs. Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C IV absorption system, and Q0008+008 with a damped Ly-alpha system with an H I column density of 10 exp 21/sq cm. The equivalent widths of the Ca II K line, the G band, and the Balmer lines in 10 stars with the best spectra are measured, and metallicities are derived. Seven of them are in the range -2.5 to -1.7, while the others are less metal-poor.

Tytler, David↗
NASA NTRS1993

Infrared spectra of transition objects and the composition and evolution of carbon dust

We obtained IR (5-23 microns) spectra of five carbon-rich objects in transition from the asymptotic giant branch (AGB) to the planetary nebula stage of evolution. These spectra show a variety of IR emission features due to circumstellar materials. In particular, all sources show the 6.2 and '7.7' micron bands, commonly observed in PNs and ascribed to polycyclic aromatic hydrocarbon molecules (PAHs). Some transition nebulae also show a strong 6-9 micron plateau characteristic for larger PAH clusters (about 400 C-atoms). A new broad feature at about 8.8 microns is present in some sources. This feature is distinctly different from the 8.6-micron PAH feature. This 8.8-micron feature may be present in the spectra of C-rich giants as well, but is not evident in PN spectra. We suggest that large amorphous carbon grains are responsible for the 8.8-micron feature. The transition objects show large spectral variations from source to source. This contrasts with C-rich PNs, which all show very similar IR spectra dominated by PAHs. These spectral variations between transition objects of similar effective temperatures cannot be due to excitation variations but imply compositional variations of the dust. Moreover, this result suggests that circumstellar dust evolves during the transition phase from red giant to PN, perhaps as a result of grain-grain collisions and shattering in the fast winds.

Buss, R. H., Jr.↗
NASA NTRS1957

Identification of Foreign Objects Damaging Compressor Blades in Turbojet Engines

Damage to the compressor blades of turbojet engines due to ingestion of foreign objects is a growing problem, the solution of which has been made more difficult by the large percentage of damaging materials that have remained unknown. A rapid emission spectroscopic method was devised to identify the chemical composition of these foreign objects. Results on laboratory-prepared specimens and blades from damaged engines show that the method can be utilized to determine the nature of the ingested foreign objects.

Spakowski, A E↗
NASA NTRS1993

A model-based approach for detection of objects in low resolution passive-millimeter wave images

We describe a model-based vision system to assist pilots in landing maneuvers under restricted visibility conditions. The system was designed to analyze image sequences obtained from a Passive Millimeter Wave (PMMW) imaging system mounted on the aircraft to delineate runways/taxiways, buildings, and other objects on or near runways. PMMW sensors have good response in a foggy atmosphere; but, their spatial resolution is very low. However, additional data such as airport model and approximate position and orientation of aircraft are available. We exploit these data to guide our model-based system to locate objects in the low resolution image and generate warning signals to alert the pilots. We also derive analytical expressions for the accuracy of the camera position estimate obtained by detecting the position of known objects in the image.

Tang, Yuan-Liang↗
NASA NTRS1994

Object-based task-level control: A hierarchical control architecture for remote operation of space robots

Expanding man's presence in space requires capable, dexterous robots capable of being controlled from the Earth. Traditional 'hand-in-glove' control paradigms require the human operator to directly control virtually every aspect of the robot's operation. While the human provides excellent judgment and perception, human interaction is limited by low bandwidth, delayed communications. These delays make 'hand-in-glove' operation from Earth impractical. In order to alleviate many of the problems inherent to remote operation, Stanford University's Aerospace Robotics Laboratory (ARL) has developed the Object-Based Task-Level Control architecture. Object-Based Task-Level Control (OBTLC) removes the burden of teleoperation from the human operator and enables execution of tasks not possible with current techniques. OBTLC is a hierarchical approach to control where the human operator is able to specify high-level, object-related tasks through an intuitive graphical user interface. Infrequent task-level command replace constant joystick operations, eliminating communications bandwidth and time delay problems. The details of robot control and task execution are handled entirely by the robot and computer control system. The ARL has implemented the OBTLC architecture on a set of Free-Flying Space Robots. The capability of the OBTLC architecture has been demonstrated by controlling the ARL Free-Flying Space Robots from NASA Ames Research Center.

Stevens, H. D.↗
NASA NTRS1994

Accurate estimation of object location in an image sequence using helicopter flight data

In autonomous navigation, it is essential to obtain a three-dimensional (3D) description of the static environment in which the vehicle is traveling. For a rotorcraft conducting low-latitude flight, this description is particularly useful for obstacle detection and avoidance. In this paper, we address the problem of 3D position estimation for static objects from a monocular sequence of images captured from a low-latitude flying helicopter. Since the environment is static, it is well known that the optical flow in the image will produce a radiating pattern from the focus of expansion. We propose a motion analysis system which utilizes the epipolar constraint to accurately estimate 3D positions of scene objects in a real world image sequence taken from a low-altitude flying helicopter. Results show that this approach gives good estimates of object positions near the rotorcraft's intended flight-path.

Tang, Yuan-Liang↗
NASA NTRS1994

A model-based approach for detection of runways and other objects in image sequences acquired using an on-board camera

This research was initiated as a part of the Advanced Sensor and Imaging System Technology (ASSIST) program at NASA Langley Research Center. The primary goal of this research is the development of image analysis algorithms for the detection of runways and other objects using an on-board camera. Initial effort was concentrated on images acquired using a passive millimeter wave (PMMW) sensor. The images obtained using PMMW sensors under poor visibility conditions due to atmospheric fog are characterized by very low spatial resolution but good image contrast compared to those images obtained using sensors operating in the visible spectrum. Algorithms developed for analyzing these images using a model of the runway and other objects are described in Part 1 of this report. Experimental verification of these algorithms was limited to a sequence of images simulated from a single frame of PMMW image. Subsequent development and evaluation of algorithms was done using video image sequences. These images have better spatial and temporal resolution compared to PMMW images. Algorithms for reliable recognition of runways and accurate estimation of spatial position of stationary objects on the ground have been developed and evaluated using several image sequences. These algorithms are described in Part 2 of this report. A list of all publications resulting from this work is also included.

Kasturi, Rangachar↗