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At least 217 records · Page 12

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NASA NTRS1991

STS-38 Space Shuttle mission report

The STS-38 Space Shuttle Program Mission Report contains a summary of the vehicle subsystem activities on this thirty-seventh flight of the Space Shuttle and the seventh flight of the Orbiter vehicle Atlantis (OV-104). In addition to the Atlantis vehicle, the flight vehicle consisted of an External Tank (ET) (designated as ET-40/LWT-33), three Space Shuttle main engines (SSME's) (serial numbers 2019, 2022, 2027), and two Solid Rocket Boosters (SRB's), designated as BI-039. The STS-38 mission was a classified Department of Defense mission, and as much, the classified portions of the mission are not presented in this report. The sequence of events for this mission is shown. The significant problems that occurred in the Space Shuttle Orbiter subsystem during the mission are summarized and the official problem tracking list is presented. In addition, each Space Shuttle Orbiter problem is cited in the subsystem discussion.

Camp, David W.↗

NASA NTRS1992

Inelastic Deformation of Metal Matrix Composites: Plasticity and Damage Mechanisms - Part 1

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper.

Majumdar, B. S.↗

NASA NTRS1992

RF FEL for power beaming

The laser device components associated with operating a radio frequency-free electron laser (RF-FEL) for beaming power from Earth were designed and tested. Analysis of the power beaming system requirements reveals that the FEL, identified by NASA as the laser of choice, is the major subsystem requiring demonstration before proceeding further in proving the efficacy of laser power beaming. Rocketdyne has identified a series of low cost, low risk demonstrations which proceed sequentially, as follows: (1) a 1 kW proof-of-principle demonstration; (2) a 150 kW demonstration of beaming power to a satellite; and (3) a MW class demonstration of Earth to lunar surface power transmission. This sequence of events can be completed in 5.5 years at a cost of $188M, with key milestones each year.

Burke, Robert↗

NASA NTRS1991

Structure and evolution of compound streams at not greater than 1 AU

Two cases of compound stream formation and evolution at heliocentric distances of not greater than 1 AU have been studied using simultaneous data from both multipoint in situ and global sources. The sequences of events analyzed occurred around December 16, 1978, and February 19, 1979, respectively. The sources of the multipoint observations were Helios A, Helios B, IMP 8, and ISEE 3. The global observations were obtained by interplanetary scintillation analysis of radio sources. It was found that the radio and in situ data complemented each other and that both were needed for a unique interpretation of complex, time-dependent flows. The cases studied show that a single corotating stream can interact with different transient flows at different times, and a single transient flow can interact with different corotating streams at different times. In each instance, a compound stream is formed. This work further shows that the cosmic ray intensity at a point depends on the global compound stream configuration in the vicinity of the point.

Burlaga, L. F.↗

NASA NTRS1992

Shock breakout in SN 1987A

Detailed models for the UV burst from SN 1987A are calculated using a two-temperature radiation hydrodynamics code. The sequence of events which occur during shock breakout is described, including the formation of a radiative precursor, the disappearance of the shock, and the growth of a thin, dense shell above the photosphere which gives rise to a new viscous, isothermal shock. Continuum spectra are calculated under the assumption that the emergent radiation is a dilute blackbody with a color temperature equal to the radiation temperature at the thermalization depth. This color temperature is 2-3 times higher than the effective temperature. Light-travel-time corrections have been included in the light curves and the spectra. Quantities most relevant to accurate modeling of the fluorescing ring around SN 1987A are highlighted.

Ensman, Lisa↗

NASA NTRS1992

The morphology and evolution of coronae on Venus

The morphology and morphometry of a number of coronae and related features on Venus are discussed with reference to new data from the Magellan spacecraft. The specific features discussed are concentrated in the portion of Venus imaged during about the first three months of Magellan mapping. Sequences of events and basic geophysical processes involved in the formation of these features are inferred.

Squyres, Steven W.↗

NASA NTRS1993

Evolution of luminous IRAS galaxies: Radio imaging

In a recent study of IRAS galaxies' optical morphologies, we found that luminous IR sources lie in the IR color-luminosity plane in groups which separate out by optical spectroscopic type and also by degree of tidal disturbance. We found that the most luminous steep-IR-spectrum sources are generally galaxies in the initial stages of a major tidal interaction. Galaxies with active nuclei were generally found to have flatter IR spectra, to cover a range of IR luminosity, and to be in the later stages of a tidal interaction. We proposed a sequence of events by which luminous IR sources evolve: they start as interacting or merging galaxies, some develop active nuclei, and most undergo extensive star-formation in their central regions. Another way to study these objects and their individual evolution is to study their radio morphologies. Radio emission may arise at a detectable level from supernovae in star-forming regions and/or the appearance of an active nucleus can be accompanied by a nuclear radio source (which may develop extended structure). Therefore, the compact radio structure may trace the evolution of the inner regions of IRAS-luminous sources. If the radio sources are triggered by the interactions, we would expect to find the radio morphology related to the optical 'interactivity' of the systems. Here, we explore using the radio emission of IRAS galaxies as a possible tracer of galaxy evolution. We present and discuss observations of the compact radio morphology of 111 luminous IRAS-selected active galaxies covering a wide range of IR and optical properties.

Neff, S. G.↗

NASA NTRS1992

Volatile history of Mangala Valles, Mars

The Mangala Valles channel system differs from other Mars outflow channels as they emanate from a point source determined by the local interplay of tectonism, volcanism, and volatiles that led directly to the release of groundwater. Water discharge rates through the southern reaches of Mangala Valles may have been substantially lower than estimates determined fron the canyon system as a whole, suggesting that the accumulation and release of water may have lasted longer than previously envisioned. The sequence of events determined from mapping of units along the southern reaches of Mangala Valles is closely related to the area structures.

Zimbelman, James R.↗

NASA NTRS1992

Geologic evolution of the east rim of the Hellas basin, Mars

The east rim of the Hellas basin, one of the largest obvious impact features on Mars, is studied. The distribution of geologic materials in the region is documented, and their modes of origin are constrained based on their geomorphologic characteristics. Superposition relationship and crater size-frequency distributions allow the relative ages of the geologic units to be determined and provide information regarding the timing and extent of the geologic processes emplacing and modifying the surface materials. Systematic analysis of the degradation of the Hellas basin is used to illustrate the sequence of events and interplay of geologic processes which control the evolution of many regions on Mars.

Crown, David A.↗

NASA NTRS1992

The canyon system on Mars

Individual Martian equatorial troughs are described, and their stratigraphy, geomorphology and structure are discussed. Possible origins and the overall sequence of events are addressed. Wall rock, interior layered deposits, irregular floor deposits, fractured floor material, and surficial deposits are examined. Chasma walls, wall stability, pits and pit chains, tributary canyons, and the transition from troughs to channels are also discussed.

Lucchitta, B. K.↗

NASA NTRS1992

Disconnection of open coronal magnetic structures

We have examined the Solar Maximum Mission coronagraph/polarimeter observations for evidence of magnetic disconnection of previously open magnetic structures and a number of likely examples have been found. Probable coronal disconnections typically appear as pinching off of helmet streamers followed by the release and outward acceleration of a large U or V-shaped structure. The observed sequence of events is consistent with reconnection across the heliospheric current sheet between previously open magnetic field regions, and the creation of a detached magnetic structure which is open to interplanetary space at both ends. Sunward of the reconnection point, coronal disconnection events would return previously open magnetic flux to the Sun as closed field arches. Here we (1) describe one clear disconnection event (1 June 1989); (2) examine the results of a limited survey of disconnection events; and (3) discuss the potential importance of coronal disconnections for maintaining flux in interplanetary space.

Mccomas, D. J.↗

NASA NTRS1993

Delamination, durability, and damage tolerance of laminated composite materials

Durability and damage tolerance may have different connotations to people from different industries and with different backgrounds. Damage tolerance always refers to a safety of flight issue where the structure must be able to sustain design limit loads in the presence of damage and return to base safely. Durability, on the other hand, is an economic issue where the structure must be able to survive a certain life under load before the initiation of observable damage. Delamination is typically the observable damage mechanism that is of concern for durability, and the growth and accumulation of delaminations through the laminate thickness is often the sequence of events that leads to failure and the loss of structural integrity.

Obrien, T. Kevin↗

NASA NTRS1992

On the relative importance of magnetospheric and ionospheric processes during substorm onset and expansion: A case study

The question of whether substorm onset is triggered in the magnetotail or the ionosphere is presented. The possible influence of the ionosphere in the subsequent development of a substorm is discussed. Theoretical considerations involved are reviewed and a case study to address this question is examined. The evidence indicates that magnetotail processes initiate the sequence of events called a substorm, while the ionosphere appears to play a critical role in the subsequent evolution of the substorm expansion phase. However, the necessary observations, in particular high time resolution coordinated observations in the ionosphere and magnetotail are relatively rare. Continued examination of existing ground and space based data sets, in particular underutilized observations such as the Scatha data, may provide a more solid foundation for clarifying this issue and determining the relative importance of magnetospheric and ionospheric processes during substorms.

Lopez, Ramon E.↗

NASA NTRS1994

Flight parameters monitoring system for tracking structural integrity of rotary-wing aircraft

Recent developments in advanced monitoring systems used in conjunction with tracking structural integrity of rotary-wing aircraft are explained. The paper describes: (1) an overview of rotary-wing aircraft flight parameters that are critical to the aircraft loading conditions and each parameter's specific requirements in terms of data collection and processing; (2) description of the monitoring system and its functions used in a survey of rotary-wing aircraft; and (3) description of the method of analysis used for the data. The paper presents a newly-developed method in compiling flight data. The method utilizes the maneuver sequence of events in several pre-identified flight conditions to describe various flight parameters at three specific weight ranges.

Mohammadi, Jamshid↗

NASA NTRS1994

Software fault tolerance in computer operating systems

This chapter provides data and analysis of the dependability and fault tolerance for three operating systems: the Tandem/GUARDIAN fault-tolerant system, the VAX/VMS distributed system, and the IBM/MVS system. Based on measurements from these systems, basic software error characteristics are investigated. Fault tolerance in operating systems resulting from the use of process pairs and recovery routines is evaluated. Two levels of models are developed to analyze error and recovery processes inside an operating system and interactions among multiple instances of an operating system running in a distributed environment. The measurements show that the use of process pairs in Tandem systems, which was originally intended for tolerating hardware faults, allows the system to tolerate about 70% of defects in system software that result in processor failures. The loose coupling between processors which results in the backup execution (the processor state and the sequence of events occurring) being different from the original execution is a major reason for the measured software fault tolerance. The IBM/MVS system fault tolerance almost doubles when recovery routines are provided, in comparison to the case in which no recovery routines are available. However, even when recovery routines are provided, there is almost a 50% chance of system failure when critical system jobs are involved.

Iyer, Ravishankar K.↗

NASA NTRS1992

Technology integration box beam failure study

The objective of this paper is to describe current results from an on-going study of the mechanisms that led to the failure of the TIBB. Experimental and analytical results are presented. Experimental results include load, strain, and deflection data for the TIBB (Technology Integration Box Beam). An analytical investigation was conducted to compliment the experimental investigation and to gain additional insight into the TIBB structural response. Analytical results include strain and deflection results from a global analysis of the TIBB. A local analysis of the failure region is being completed. These analytical results are validated through comparisons with the experimental results from the TIBB tests. The experimental and analytical results from the TIBB tests are used to determine a sequence of events that may have resulted in failure of the TIBB. A potential cause of failure is high stresses in a stiffener runout region. Typical analytical results are presented for a stiffener runout specimen that is being defined to simulate the TIBB failure mechanisms. The results of this study are anticipated to provide better understanding of potential failure mechanisms in composite aircraft structures, to lead to future design improvements, and to identify needed analytical tools for design and analysis.

Shuart, Mark J.↗

NASA NTRS1993

Technology integration box beam failure study

Composite structures have the potential to be cost-effective, structurally efficient primary aircraft structures. The Advanced Composites Technology (ACT) Program has the goal to develop the technology to exploit this potential for heavily loaded aircraft structures. As part of the ACT Program, Lockheed Aeronautical Systems Company completed the design and fabrication of the Technology Integration Box Beam (TIBB). The TIBB is an advanced composite prototype structure for the center wing section of the C-130 aircraft. Lockheed subjected the TIBB to downbending, upbending, torsion and combined upbending and torsion load conditions to verify the design. The TIBB failed at 83 percent of design ultimate load for the combined upbending and torsion load condition. The objective of this paper is to describe the mechanisms that led to the failure of the TIBB. The results of a comprehensive analytical and experimental study are presented. Analytical results include strain and deflection results from both a global analysis of the TIBB and a local analysis of the failure region. These analytical results are validated by experimental results from the TIBB tests. The analytical and experimental results from the TIBB tests are used to determine a sequence of events that resulted in failure of the TIBB. A potential cause of failure is high stresses in a stiffener runout region. Analytical and experimental results are also presented for a stiffener runout specimen that was used to simulate the TIBB failure mechanisms.

Shuart, M. J.↗

NASA NTRS1994

The evolution of convective storms from their footprints on the sea as viewed by synthetic aperture radar from space

SEASAT synthetic aperture radar (SAR) echoes from the sea have previously been shown to be the result of rain and winds produced by convective stroms; rain damps the surface waves and causes ech-free holes, while the diverging winds associated with downdraft generate waves and associated echoes surrounding the holes. Gust fronts are also evident. Such a snapshot from 8 July 1978 has been examined in conjunction with ground-based radar. This leads to the conclusion that the SAR storm footprints resulted from storm processes that occurred up to an hour or more prior to the snapshot. A sequence of events is discerned from the SAR imagery in which new cell growth is triggered in between the converging outflows of two preexisting cells. In turn, the new cell generates a mini-squall line along its expanding gust front. While such phenomena are well known over land, the spaceborne SAR now allows important inferences to be made about the nature and frequency of convective storms over the oceans. The storm effects on the sea have significant implications for spaceborne wind scatterometry and rainfall measurements. Some of the findings herein remain speculative because of the great distance to the Miami weather radar-the only source of corroborative data.

Atlas, David↗