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At least 1,423 records · Page 79

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NASA NTRS1990

New parameter-free polarization potentials in low-energy positron collisions

The polarization potential plays a decisive role in shaping up the cross sections in low energy positron collisions with atoms and molecules. However, its inclusion without involving any adjustable parameter, is still a challenge. Various other techniques employed so far for positron collisions are summarized, and a new, nonadjustable and very simple form of the polarization potential for positron-atom (molecule) collisions below the threshold of positronium formation is discussed. This new recently proposed potential is based on the correlation energy of a single positron in a homogeneous electron gas. The correlation energy was calculated by solving the Schrodinger equation of the positron-electron system and fitted to an analytical form in various ranges of the density parameter. In the outside region, the correlation energy is joined smoothly with the correct asymptotic form. This new positron correlation polarization (PCOP) potential was tested on several atomic and molecular targets such as the Ar, CO, and CH4. The results on the total and differential cross sections on these targets are shown along with the experimental data where available.

Jain, Ashok↗

NASA NTRS1989

Double swivel toggle release

A pyrotechnic actuated structural release device is disclosed which is mechanically two fault tolerant for release. The device comprises a fastener plate and fastener body each attachable to one of a pair of structures to be joined. The fastener plate and the fastener body are fastened by a dual swivel toggle member. The toggle member is supported at one end on the fastener plate and mounted for universal pivotal movement thereon. Its other end is received in a central opening in the fastener body, and has a universally mounted retainer ring member. The toggle member is restrained by three retractable latching pins symmetrically disposed in equiangular spacing about the axis of the toggle member and positionable in latching engagement with the retainer ring member on the toggle member. Each pin is retractable by a pyrotechnic charge, the expanding gases of which are applied to a pressure receiving face on the latch pins to effect retraction from the ring member. While retraction of all three pins releases the ring member, the fastener is mechanically two fault tolerant since the failure of any single one or pair of the latch pins to retract results in an asymmetrical loading on the ring member and its dual pivotal movement ensures a release.

King, Guy L.↗

NASA NTRS1990

Programmatic status of NASA's CSTI high capacity power Stirling space power converter program

An overview is presented of the NASA Lewis Research Center Free-Piston Stirling Space Power Converter Technology Development Program. This work is being conducted under NASA's Civil Space Technology Initiative (CSTI). The goal of the CSTI High Capacity Power element is to develop the technology base needed to meet the long duration, high capacity power requirements for future NASA space initiatives. Efforts are focused upon increasing system thermal and electric energy conversion efficiency at least fivefold over current SP-100 technology, and on achieving systems that are compatible with space nuclear reactors. The status of test activities with the Space Power Research Engine (SPRE) is discussed. Design deficiencies are gradually being corrected and the power converter is now outputting 11.5 kWe at a temperature ratio of 2 (design output is 12.5 kWe). Detail designs were completed for the 1050 K Component Test Power Converter (CTPC). The success of these and future designs is dependent upon supporting research and technology efforts including heat pipes, gas bearings, superalloy joining technologies and high efficiency alternators. An update of progress in these technologies is provided.

Dudenhoefer, James E.↗

NASA NTRS1990

NASA/USRA high altitude reconnaissance aircraft

At the equator, the ozone layer ranges from approximately 80,000 to 130,000+ feet which is beyond the capabilities of the ER-2, NASA's current high altitude reconnaissance aircraft. This project is geared to designing an aircraft that can study the ozone layer at the equator. This aircraft must be able to cruise at 130,000 lbs. of payload. In addition, the aircraft must have a minimum of a 6,000 mile range. The low Mach number, payload, and long cruising time are all constraints imposed by the air sampling equipment. A pilot must be able to take control in the event of unforseen difficulties. Three aircraft configurations were determined to be the most suitable for meeting the above requirements, a joined-wing, a bi-plane, and a twin-boom conventional airplane. The techniques used have been deemed reasonable within the limits of 1990 technology. The performance of each configuration is analyzed to investigate the feasibility of the project requirements. In the event that a requirement can not be obtained within the given constraints, recommendations for proposal modifications are given.

Richardson, Michael↗

NASA NTRS1990

A direct-interface, fusible heat sink for astronaut cooling

Astronaut cooling during extravehicular activity is a critical design issue in developing a portable life support system that meets the requirements of a space station mission. Some of the requirements are that the cooling device can be easily regenerable and nonventing during operation. In response to this, a direct-interface, fusible heat sink prototype with freezable quick-disconnects was developed. A proof-of-concept prototype was constructed and tested that consists of an elastic container filled with normal tap water and having two quick-disconnects embedded in a wall. These quick-disconnects are designed so that they may be frozen with the ice and yet still be joined to the cooling system, allowing an immediate flow path. The inherent difficulties in a direct-interface heat sink have been overcome, i.e., (1) establishing an initial flow path; (2) avoiding low-flow freeze-up; and (3) achieving adequate heat-transfer rates at the end of the melting process. The requirements, design, fabrication, and testing are discussed.

Lomax, Curtis↗

NASA NTRS1990

MTP: An atomic multicast transport protocol

Multicast transport protocol (MTP); a reliable transport protocol that utilizes the multicast strategy of applicable lower layer network architectures is described. In addition to transporting data reliably and efficiently, MTP provides the client synchronization necessary for agreement on the receipt of data and the joining of the group of communicants.

Freier, Alan O.↗

NASA NTRS1990

Superconducting film on metallic wire

For technological applications of high T(sub c) superconductors, it will be necessary to overcome the inherent problem of brittleness, to develop materials with high current carrying capacity, and to devise ways of joining superconductors with other materials. These issues will be addressed in the context of superconducting films on metallic wires. These composite systems are expected to produce flexible wires with desirable properties.

Akbar, Sheikh A.↗

NASA NTRS1990

Ultrasonic verification of five wave fronts in unidirectional graphite epoxy composite

The existence of five different waves fronts in a unidirectional graphite fiber reinforced epoxy composite with energy flux propagation at the angle of 60 deg with respect to the fiber direction is verified by measuring their corresponding group and phase velocities of longitudinal and shear waves using the through transmission technique. The experimental and theoretical values of phase velocities show excellent agreement for all three modes of wave propagation. It is also verified that the maximum output voltage amplitude is obtained when the line joining the centers of the transmitting and receiving transducers is parallel to the energy propagation direction defined by the deviation angle.

Seng, Han-Song↗

NASA NTRS1989

Optimal payload rate limit algorithm for zero-G manipulators

An algorithm for continuously computing safe maximum relative velocities for two bodies joined by a manipulator is discussed. The maximum velocities are such that if the brakes are applied at that instant, the ensuing travel between the bodies will be less than or equal to a predetermined amount. An improvement in the way this limit is computed for space manipulators is shown. The new method is explained, test cases are posed, and the results of these tests are displayed and discussed.

Ross, M. L.↗

NASA NTRS1989

The discovery of a new infrared emission feature at 1905 wavenumbers (5.25 microns) in the spectrum of BD + 30 deg 3639 and its relation to the polycyclic aromatic hydrocarbon model

A new IR emission feature at 1905/cm (5.25 microns) has been discovered in the spectrum of BD + 30 deg 3639. This feature joins the family of well-known IR emission features at 3040, 2940, 1750, 1610, '1310', 1160, and 890/cm. The origin of this new feature is discussed and it is assigned to an overtone or combination band involving C-H bending modes of polycyclic aromatic hydrocarbons (PAHs). Laboratory work suggests that spectral studies of the 2000-1650/cm region may be very useful in elucidating the molecular structure of interstellar PAHs. The new feature, in conjunction with other recently discovered spectral structures, suggests that the narrow IR emission features originate in PAH molecules rather than large carbon grains.

Allamandola, L. J.↗

NASA NTRS1989

Eclipsing binary stars as tests of gravity theories - The apsidal motion of AS Camelopardalis

AS Camelopardalis is an 8th-magnitude eclipsing binary that consists of two main-sequence (B8 V and a B9.5 V) components in an eccentric orbit (e = 0.17) with an orbital period of 3.43 days. Like the eccentric eclipsing system DI Herculis, and a few other systems, AS Cam is an important test case for studying relativistic apsidal motion. In these systems, the theoretical general relativistic apsidal motion is comparable to that expected from classical effects arising from tidal and rotational deformation of the stellar components. Accurate determinations of the orbital and stellar properties of AS Cam have been made by Hilditch (1972) and Khalliulin and Kozyreva (1983) that permit the theoretical relativistic and classical contributions to the apsidal motion to be determined reasonably well. All the published timings of primary and secondary minima have been gathered and supplemented with eclipse timings from 1899 to 1920 obtained from the Harvard plate collection. Least-squares solutions of the eclipse timings extending over an 80 yr interval yield a smaller than expected apsidal motion, in agreement with that found by Khalliulin and Kozyreva from a smaller set of data. The observed apsidal motion for AS Cam is about one-third that expected from the combined relativistic and classical effects. Thus, AS Cam joins DI Her in having an observed apsidal motion significantly less than that predicted from theory.

Maloney, Frank P.↗

NASA NTRS1990

Three-dimensional kinematic reconnection in the presence of field nulls and closed field lines

The present investigation of three-dimensional reconnection of magnetic fields with nulls and of fields with closed lines gives attention to the geometry of the former, with a view to their gamma-line and Sigma-surface structures. The geometric structures of configurations with a pair of type A and B nulls permit reconnection across the null-null lines; these are the field lines which join the two nulls. Also noted is the case of magnetostatic reconnection, in which the magnetic field is time-independent and the electrostatic potential is constant along field lines.

Lau, Yun-Tung↗

NASA NTRS1990

Formed platelet liner concept for regeneratively cooled chambers

A process for the fabrication of a formed platelet regeneratively cooled combustion chamber liner is described, and the benefits offered by the combustor liner are discussed. The advantages of using formed platelet combustor liners include a substantially increased cycle life and decreased coolant pressure drop in conjunction with low manufacturing costs. In the initial experiments, zirconium copper combustor liner sections with a hot gas wall thickness as small as 0.008 inch and channel aspect ratios of 15 have been achieved. It is also shown that HIP provides an excellent bonding technique for joining chamber liner panels.

Burkhardt, W. M.↗

NASA NTRS1989

Fabrication and evaluation of enhanced diffusion bonded titanium honeycomb core sandwich panels with titanium aluminide face sheets

A joining process was developed for fabricating lightweight, high temperature sandwich panels for aerospace applications using Ti-14Al-21Nb face sheets and Ti-3Al-2.5V honeycomb core. The process, termed Enhanced Diffusion Bonding (EDB), relies on the formation of a eutectic liquid through solid-state diffusion at elevated temperatures and isothermal solidification to produce joints in thin-gage titanium and titanium aluminide structural components. A technique employing a maskant on the honeycomb core was developed which permitted electroplating a controlled amount of EDB material only on the edges of the honeycomb core in order to minimize the structural weight and metallurgical interaction effects. Metallurgical analyses were conducted to determine the interaction effects between the EDB materials and the constituents of the sandwich structure following EDB processing. The initial mechanical evaluation was conducted with butt joint specimens tested at temperatures from 1400 - 1700 F. Further mechanical evaluation was conducted with EDB sandwich specimens using flatwise tension tests at temperatures from 70 - 1100 F and edgewise compression tests at ambient temperature.

Hoffmann, E. K.↗

NASA NTRS1990

A direct-interface fusible heat sink for astronaut cooling

Astronaut cooling during extravehicular activity is a critical design issue in developing a portable life support system that meets the requirements of a space station mission. Some the requirements are that the cooling device can be easily regenerable and nonventing during operation. In response to this, a direct-interface, fusible heat sink prototpye with freezable quick-disconnects was developed. A proof-of-concept prototype was constructed and tested that consists of an elastic container filled with normal tap water and having two quick-disconnects embedded in a wall. These quick-disconnects are designed so that they may be frozen with the ice and yet still be joined to the cooling system, allowing an immediate flow path. The inherent difficulties in a direct-interface heat sink have been overcome, i.e., (1) establishing an initial flow path; (2) avoiding low-flow freeze-up; and (3) achieving adequate heat-transfer rates at the end of the melting process. The requirements, design, fabrication, and testing are discussed.

Lomax, Curtis↗

NASA NTRS1991

Bonding Aramid Rope To Metal Fitting

Method for joining Kevlar (or equivalent) aramid rope to tubular corrosion-resistant steel end fitting increases strength of joint under tension to approximately three-fourths that of rope itself. End fitting contains internal thread, which provides good bonding surface. Small radial hole enables injection of adhesive into bore.

To, Dung T.↗

NASA NTRS1991

Two-Phase Bidirectional Heat Exchanger

Heat exchanger transfers heat from one two-phase thermal loop to another. Condenses vapor in one loop while evaporating liquid in other. Transfers heat with very small drops in temperature and pressure, and efficiently joins heat pipes thermally without mixing of their working fluids. Several such heat exchangers used to build long, complex multiloop heat-control systems. Exchanger bidirectional: transfers heat in reverse, condensing on normally evaporating side, and vice versa. Can warm equipment it normally cools, without using auxiliary heater. In reverse transfer, wicks on evaporating side supply liquid continuously by capillary action; reverse-flow pump not needed. Design modified for other working fluids and larger heat-transfer rates.

Kroliczek, Edward↗

NASA NTRS1991

Laser Welding Of Contoured Thin-Wall Housings

Superalloy parts joined with less distortion. Carbon dioxide laser beam directed by optics in numerically controlled robot arm welds shell-type turbopump housings having complicated shapes. 5-kW laser, following single programmed three-dimensional pass, produces high-quality, full-penetration weld pass in age-hardenable nickel superalloy. Operator easily programs robot by using teaching pendant to track weld joint and keeps laser focused on workpiece while following contour of shell. Shells welded in rapid succession, with minimal change in setup for each.

Spiegel, Lyle B.↗