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NASA NTRS1978

Surface waves generated by shallow underwater explosions

Surface water waves generated by surface and near surface point explosions are calculated. Taking the impulse distribution imparted at the water surface by the explosion as the overriding mechanism for transferring energy of the explosive to surface wave motion, the linearized theory of Kranzer and Keller is used to obtain the wave displacement in the far field. The impulse distribution is obtained by integrating the pressure wave over an appropriate time interval on a horizontal surface just beneath the undisturbed water surface. For surface explosions, a modified form of the similarity method first used by Collins and Holt is used to obtain the flow field. In the case of submerged explosions, the flow field is estimated by making necessary modifications to Sedov's similarity solution to account for the venting that accompanies the interaction of the leading (blast) wave with the ocean surface. Surface waves generated by a charge at six depths of placement (0.15 m, 0.30 m, 0.61 m, 0.91 m, 1.37 m, 3.05 m) are considered in addition to surface explosions. The results seem to support the existence of an upper critical depth phenomenon (of the type already established for chemical explosions) for point (nuclear) explosions.

Falade, A.↗

NASA NTRS1979

Space Shuttle communications RF switch matrix

The Shuttle Orbiter communications equipment includes phase modulation (PM) and frequency modulation (FM) channels. The PM section has the capability of routing high levels of energy (175 W) from any one of four transmitters to any one of four antennas, mutually exclusive. The FM channel uses a maximum of 15-W power routed from either of two transmitters to one of two antennas, mutually exclusive. The paper describes the design and the theory of a logic-controlled RF switch matrix devised for the purposes cited. Both PM and FM channels are computer-controlled with manual overrides. The logic interface is realized with CMOS logic for low power consumption and high noise immunity. The interior of the switch matrix is maintained at a pressure of 15 psi (90% nitrogen, 10% helium) by an electron beam-welded encapsulation. The computational results confirm the viability of the RF switch matrix concept.

Winch, R.↗

NASA NTRS1979

A tidal theory for the origin of the solar nebula

A model for the origin of the solar nebula is developed with attention to the significance of angular momentum considerations. Evidence that stars are born in groups rather than singly is examined. It is shown that protostars which are members of typical galactic clusters have some probability of undergoing a gravitational encounter with another star while they are collapsing. According to the model, these encounters impart disproportionate amounts of angular momentum to the later material to fall in toward already centrally condensed fragments. The amount of central condensation of a fragment is the overriding factor in determining its stability against destruction by tidal forces. The encounter also imparts angular momentum to matter that is still accreting onto the protosun.

Kobrick, M.↗

NASA NTRS1979

Radiator heat rejection options for Shuttle payloads

The paper describes four separate advanced space radiator concepts that have been pursued in an integrated effort to develop multipayload use, low-cost heat rejection systems which can overcome the limitations of current radar systems. These four concepts are the following: (1) a wide heat load range, modularized space radiation system; (2) a heat rejection subsystem designed as a compact self-contained heat rejection module which provides a refrigeration cycle to accomodate a wide variation in payload heat loads and cooling temperature requirements; (3) a lightweight flexible fin radiator system with heat rejection capability; and (4) a radiator which does not require a circulating coolant on the radiator panel with heat pipes and thus particularly applies to very-long-duration free-flying payloads where long life reliability is an overriding design parameter. The Orbiter active thermal control system is briefly described.

Ellis, W. E.↗

NASA NTRS1981

Integrated control system for a gas turbine engine

A control system for a turbofan engine receives signals from a number of engine sensors and from the engine operator, and generates control signals. One control signal regulates the fan exhaust nozzle area in order to control inlet throat Mach number to maintain a low level of engine noise. Additional control signals regulate fuel flow to control engine thrust and fan pitch to control fan speed. A number of schedules are utilized to maintain a predetermined relationship between the controlled parameters and a number of fixed and calculated limits can override the control signals to prevent unsatisfactory engine performance.

Cornett, J. E.↗

NASA NTRS1980

Application of fiber optics in spacecraft

The unique requirements placed on an optical fiber data system in space are briefly reviewed in this paper. These include temperature extremes, particle radiation, and, in some cases, a stringent electrical power budget. An overriding need is for the best possible reliability. Results related to the power consumption of a fiber terminal pair are reported, with the conclusion that a 32-port transmission star bus configuration could be operated error-free at 10 Mbits/s on 1/8 watt per transmitting terminal. The design of a transmitter terminal optimized for low idling power consumption is discussed. Although the electronic elements on a spacecraft are protected, the fiber cable may be subjected to large temperature extremes. Measured effects of temperature on fibers and cables are discussed and related to bus design. Radiation effects are briefly reviewed, with special reference to the long-duration low dose rate environment of a spacecraft.

Johnston, A. R.↗

NASA NTRS1982

Flight support system mechanisms

The Flight Support System (FSS) which contains twelve mechanisms (six different types) which are used for retention and positioning of a Multimission Modular Spacecraft (MMS) within the Space Shuttle's cargo bay during launch, retrieval, and servicing missions is described. Retention latches were designed to provide the capability for structural support of the MMS during launch and retrieval, and during servicing operations the mechanisms on the Positioning Platform provide the capability for positioning the MMS in virtually any orientation necessary for the work to be performed. In addition, there are mechanisms for matching and demating umbilical connectors and a mechanism for locking the Positioning Platform during maneuvers. Each Mechanism is driven by a Common Drive Unit. Manual overrides were provided for those mechanisms that would present a safety hazard for the crew, if they should fail.

Source record↗

NASA NTRS1980

Impact cratering in viscous targets - Laboratory experiments

To determine the effects of target yield strength and viscosity on the formation and morphology of Martian multilobed, slosh and rampart-type impact craters, 75 experiments in which target properties and impact energies were varied were carried out for high-speed motion picture observation in keeping with the following sequence: (1) projectile initial impact; (2) crater excavation and rise of ejecta plume; (3) formation of a transient central mound which generates a surge of material upon collapse that can partly override the plume deposit; and (4) oscillation of the central mound with progressively smaller surges of material leaving the crater. A dimensional analysis of the experimental results indicates that the dimensions of the central mound are proportional to (1) the energy of the impacting projectile and (2) to the inverse of both the yield strength and viscosity of the target material, and it is determined that extrapolation of these results to large Martian craters requires an effective surface layer viscosity of less than 10 to the 10th poise. These results may also be applicable to impacts on outer planet satellites composed of ice-silicate mixtures.

Greeley, R.↗

NASA NTRS1981

Digital image processing on a small computer system

A minicomputer-based image processing facility provides a relatively low-cost entry point for education about image analysis applications in remote sensing. While a minicomputer has sufficient processing power to produce results quite rapidly for low volumes of small images, it does not have sufficient power to perform CPU- or 1/0-bound tasks on large images. A system equipped with a display terminal is ideally suited for interactive tasks. Software procurement is a limiting factor for most end users, and software availability may well be the overriding consideration in selecting a particular hardware configuration. The hardware chosen should be selected to be compatible with the software and with concern for future expansion.

Danielson, R.↗

NASA NTRS1983

Seventh Foray - Whitlockite-rich lithologies, a diopside-bearing troctolitic anorthosite, ferroan anorthosites, and KREEP

Seventeen nonmare samples, most of them pristine, are characterized, and implications of the new data are discussed. Five pristine samples are from Apollo 14, near the center of the KREEP-rich zone in the moon's western hemisphere. Three of them are alkali anorthosites rich in Ca-phosphate (whitlockite), which apparently crystallized from magmas with REE contents roughly 6 x those of high-K KREEP. The alkali anorthosites probably formed from Mg-rich magmas that assimilated large amounts of urKREEP, but some might have formed by metasomatism of ferroan anorthosite by urKREEP. The gabbronorite/norite classification scheme is not well suited to western hemisphere lithologies, probably due mainly to the overriding effects of longitude-petrochemistry correlations. A diopside-bearing Mg-rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic (high-Ca pyroxene-rich) Mg-rich magmas, and suggests that some source regions of Mg-rich magmas were relatively Ca-rich. Several pristine KREEP fragments from Apollo 15 station 2 are texturally and compositionally much like other pristine KREEP, and thus reinforce the evidence that KREEP is highly uniform. The pristine anorthosites, on the other hand, demonstrate further that lunar anorthosites are diverse.

Warren, P. H.↗

NASA NTRS1984

Tectonic implications of the microearthquake seismicity and fault plane solutions in southern Peru

Because the contortion in the seismic zone in southern Peru is aligned approximately parallel to the direction of relative plate motion, rather than perpendicular to the coast of Peru, the position of the contortion need not migrate with respect to the overriding South American plate as the Nazca plate subducts beneath it, and the flow in the surrounding asthenosphere could be in a steady state. In addition, the position of the contortion defines the northern boundary of the volcanic arc in southern Peru. The inference that a wedge of asthenospheric material must overlie the downgoing slab for subduction-related volcanism to occur is thereby strengthened.

Grange, F.↗

NASA NTRS1984

Focal depths and fault plane solutions of earthquakes and active tectonics of the Himalaya

Synthetic seismograms were compared with long-period body waves for nine earthquakes with epicenters in the Himalayan arc to determine depths of foci and to improve fault plane solutions. Focal depths are shallow (10-20 km). Inferred slip vectors are locally perpendicular to the mountain range; they plunge very gently (about 10 deg) in the eastern sections of the range and more steeply (about 25 deg) in western sections. Assuming India to be a rigid plate, the radially oriented slip vectors imply that southern Tibet extends at about half the rate of underthrusting in the Himalaya and therefore probably at about 5-10 mm/yr. The shallow depths and gentle dips of the fault planes, at least for the events in the eastern half of the range, are consistent with coherent underthrusting of the Indian plate beneath, at least, the Lesser Himalaya. The steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the Greater Himalaya.

Baranowski, J.↗

NASA NTRS1986

Autopilot Servoactuator With Pressurized Detented Centering

Centering valve allows use of mechanical override in autopilot mode. Alternate system designed incorporates centering valves into four FBW servos, providing detents for reacting mechanical system forces following FBW shutdown. Required linkage hard point incorporated directly into autopilot servoactuator by centering valve assembly shown. All components in this functional hydraulic schematic usually present in contemporary aircraft flight-control-system autopilot servoactuators, with exception of centering valve. Centering valve, which serves as hard-point linkage for mechanical system forces, incorporated directly into flight control system.

Aring, J. A.↗

NASA NTRS1985

Basaltic Pressure Ridges: Formation and Relationship to Flow Emplacement

Pressure ridges and pressure plateau are common but not ubiquitous surface features on terrestrial basaltic lava flows and may reflect a specific flow emplacement mechanism. Many of the ridges are large enough to be detected on high-resolution orbital images; therefore, understanding these features could provide a means for interpreting volcanic flows on the mechanism of pressure ridge formation and how their formation relates to flow emplacement. Results from detailed field studies indicate that pressure ridges and plateaus: (1) are emplaced as individual flow lobes, (2) can be composed of primary or secondary material, (3) are dependent on duration and volume of activity within the flow unit, (4) are penecontemporaneous in formation, and (5) are indicative of slowly advancing flows with numerous flow lobes continuously forming and overriding each other.

Theilig, E.↗

NASA NTRS1985

Size and DNA distributions of electrophoretically separated cultured human kidney cells

Electrophoretic purification of purifying cultured cells according to function presumes that the size of cycle phase of a cell is not an overriding determinant of its electrophoretic velocity in an electrophoretic separator. The size distributions and DNA distributions of fractions of cells purified by density gradient electrophoresis were determined. No systematic dependence of electrophoretic migration upward in a density gradient column upon either size or DNA content were found. It was found that human leukemia cell populations, which are more uniform function and found in all phases of the cell cycle during exponential growth, separated on a vertical sensity gradient electrophoresis column according to their size, which is shown to be strictly cell cycle dependent.

Kunze, M. E.↗

NASA NTRS1985

To catch a childs's imagination: Educational overview of CAN DO G-324

When a public school district is involved in the flight of a GAS package, they have a The desire to produce an serious responsibility, along with an unprecedented opportunity. experiment with real scientific validity must be tempered by the schools' primary mission to make the adventure educationally meaningful to the greatest possible number of students. Such a project can easily become the personal plaything of the select few that are highly scientifically motivated, and technologically gifted. A public school system must, in addition, insure that the resources invested in such a project also reach out to the average student, and those whose interests lie in other directions. Such a broad reach is only possible if the GAS canister is but one part of a comprehensive and ongoing educational effort that involves as many disciplines and levels of student interest as possible. The total program should include: 1) A background of previous programs which have trained teachers and prepared students to fully utilize special activities as part of the educational process. 2) Direct student involvement in the design of experimental packages to be flown, and in the evaluation of data derived. 3) Supplementary related activities that use a Get Away Special as a motivational catalyst to generate efforts in other disciplines, other schools and other student groups. 4) Future plans to fully exploit and maintain the momentum developed by this one dramatic event. The one overriding goal of all these activities as articulated by one of our leading classroom teachers: "TO CHOOSE AND DEVELOP HIGHLY MOTIVATION& ACTIVITIES WHICH WILL CAPTURE THE IMAGINATION AND INTEREST OF STUDENTS, AND TO TAKE ADVANTAGE OF THE "TEACHABLE MOMENT" WHICH IS SO ELUSIVE."

James H. Nicholson↗

NASA NTRS1985

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile

Between 10,000 and 500 yr ago the Socompa volcano in northern Chile experienced a catastrophic collapse of a 70 deg sector of the original cone, causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano. The deposits cover some 490 sq km and have a minimum volume of 15 cu km. Parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high. The primary avalanche traveled northwestward over sloping ground before coming to rest transiently, forming a prominent marginal ridge, and then slid away northeastward to form a secondary flow, overriding much of the primary avalanche deposit. Abundant, prismatic, jointed dacite blocks within the debris avalanche deposit and a thin, fine-grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast. Collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes.

Francis, P. W.↗

NASA NTRS1987

An astrometric facility for planetary detection on the space station

An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential space station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distance within the Milky Way Galaxy. The results of a recently completed ATF preliminary systems definition study are summarized. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objective without the development of any new technologies. A simple straightforward operations approach was developed for the ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for the facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the space station crew with the ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance.

Nishioka, Kenji↗