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At least 757 records · Page 42

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NASA NTRS1988

Power transmission studies for tethered SP-100

The tether and/or transmission line connecting the SP-100 to Space Station presents some unorthodox challenges in high voltage engineering, power transmission, and distribution. The line, which doubles as a structural element of this unusual spacecraft, will convey HVDC from SP-100 to the platform in low Earth orbit, and environment where the local plasma is sufficient to cause breakdown of exposed conductors at potentials of only a few hundred volts. Its anticipated several years operation, and continuously accumulating exposure to meteoroids and debris, raises an increasing likelihood that mechanical damage, including perforation, will be sustained in service. The present concept employs an array of gas insulated solid wall aluminum coaxial tubes; a conceptual design which showed basic feasibility of the SP-100 powered Space Station. Practical considerations of launch, deployment and assembly have led to investigation of reel deployable, dielectric insulated coaxial cables. To be competitive, the dielectric would have to operate reliably in a radiation environment under electrical stresses exceeding 50 kV/cm. The SP-100 transmission line high voltage interfaces are also considered.

Bents, David J.↗

NASA NTRS1988

Improved synthesis of ceramic superconductors with alkaline earth peroxides - Synthesis and processing of Ba2YCu3O(7-x)

Synthesis processes for the preparation of ceramic conductors Ba2YCu3O(7-x) from BaO2 or BaCO3 in flowing O2 or N2 are described, and the characteristics of the materials produced in these processes are compared. Results of EDAX, XRD, SEM, and dc resistivity analyses demonstrated that superconducting materials made from BaO2 were more homogeneous, denser, and more metallic than materials produced from BaCO3, because of the higher reactivity of BaO2. Potential applications of this processes are discussed.

Hepp, A. F.↗

NASA NTRS1989

Large structure current collection in plasma environments

The floating potential, relative to the space plasma, of large satellites proposed for future missions is an important factor in the current balance between the plasma particle collection of biased surfaces and exposed conductors. To solve this balance, a knowledge of the plasma current collection processes is required. One of the unknowns in these relationships is the current collection of large areas of conducting surfaces. Only limited experimental data is available on this collection process. Data from one of the few available tests is used herein to verify the applicability of a plasma collection model for large surfaces. The model is then applied to determine the floating potential of the NASA Space Station.

Stevens, N. John↗

NASA NTRS1989

Mosaic wedge-and-strip arrays for large format microchannel plate detectors

The authors present a novel method for joining wedge-and-strip patterns on single anodes in a mosaic array. With only a modest increase in complexity over three-conductor anodes currently in use, the ultimate detector position resolution can be significantly improved, and large-format microchannel plate detectors with pore-size-limited resolution are made possible. The problem of the transition from one anode to the next has been solved with a novel linear encoding scheme, which exhibits essentially distortionless behavior at boundaries parallel to the conducting elements and only slight distortion at the orthogonal boundaries. The ultimate resolution for two anode designs, one designed for large-format imaging and the other for high-resolution spectroscopy, is also predicted.

Martin, Christopher↗

NASA NTRS1989

A comparison of current-voltage relationships of collectors in the earth's ionosphere with and without electron beam emission

Currents measurements obtained by the two sections of the Cooperative High Altitude Rocket Gun Experiment-2 sounding rocket, a mother vehicle carrying a 1-keV electron gun and a daughter vehicle tethered to the mother, are compared with the results of previous models of current collection by a charged conductor in a plasma. The current collection of the daughter vehicle, a conducting body in the ionosphere, is found to agree with the Parker-Murphy (1967) limit. The additional current collection found for the mother vehicle is attributed to beam-plasma interactions.

Myers, Neil B.↗

NASA NTRS1988

Acceptance and qualification test results of the 20 km electromechanical tether for TSS-1

Acceptance and qualification tests have been performed on the TSS-1 flight tether and its associated qualification tether. Acceptance testing during production included periodic measurement of conductor resistance, off-line breakstrength tests on strength member samples, continuous measurement of the insulation layer voltage withstand capability, and a continuous mechanical proof-loading procedure during the tether jacketing operation. The qualification test sequence consisted of thermal vacuum, voltage withstand and breakstrength tests on samples taken from the production runs for both the qualification and flight tethers. This paper will analyze the acceptance and qualification test data, respectively. Results indicate that the completed flight tether exceeds the design requirements for the TSS-1 mission.

Marshall, L. S.↗

NASA NTRS1989

Low-frequency electrostatic instabilities excited by injections of an electron beam in space

One-dimensional particle simulations have been carried out to study the low-frequency broadband electrostatic noise that propagates almost perpendicularly from the magnetic field line when a nonrelativistic electron beam is injected into space from a spacecraft. For T(e) = T(i) the electrostatic ion cyclotron waves appear as well as the waves near the lower hybrid frequency. When the magnetic field is reduced so that Omega(e) is much less than omega(pe) in a nonisothermal plasma, T(e) greater than T(i) oblique ion acoustic instabilities appear to propagate almost perpendicular to the magnetic field. In addition, a very low frequency mode at omega much less than Omega(i) is found to be generated by the electrons flowing into the conductor. Both the injected beam electrons as well as the ambient electrons flowing into the spacecraft are responsible for generating those instabilities, which accelerate ions perpendicular to the magnetic field.

Hwang, Y. S.↗

NASA NTRS1990

Tester Detects Steady-Short Or Intermittent-Open Circuits

Momentary open circuits or steady short circuits trigger buzzer. Simple, portable, lightweight testing circuit sounds long-duration alarm when it detects steady short circuit or momentary open circuit in coaxial cable or other two-conductor transmission line. Tester sensitive to discontinuities lasting 10 microseconds or longer. Used extensively for detecting intermittent open shorts in accelerometer and extensometer cables. Also used as ordinary buzzer-type continuity checker to detect steady short or open circuits.

Anderson, Bobby L.↗

NASA NTRS1990

Electrostatic Linear Actuator

Electrically charged helices attract or repel each other. Proposed electrostatic linear actuator made with intertwined dual helices, which holds charge-bearing surfaces. Dual-helix configuration provides relatively large unbroken facing charged surfaces (relatively large electrostatic force) within small volume. Inner helix slides axially in outer helix in response to voltages applied to conductors. Spiral form also makes components more rigid. Actuator conceived to have few moving parts and to be operable after long intervals of inactivity.

Collins, Earl R., Jr.↗

NASA NTRS1989

Microwave microstrip resonator measurements of Y1Ba2Cu3O(7-x) and Bi2Sr2Ca1Cu2O(8-y) thin films

Radio frequency (RF) surface resistance measurement experiments on high T(sub c) thin films were performed. The method uses a microstrip resonator comprising a top gold conductor strip, an alumina dielectric layer, and a separate superconductivity ground plane. The surface resistance of the superconducting ground plane can be determined, with reference to a gold calibration standard, from the measured quality factor of the half-wave resonator. Initial results near 7 GHz over the temperature range from 25 to 300 K are presented for YBa2Cu3O(7-x) and Bi2Sr2CaCu2O(8-y) thin film samples deposited by an electron beam flash evaporation process. The RF surface resistance at 25 K for both materials in these samples was found to be near 25 milliohms.

Lichtenberg, Christopher L.↗

NASA NTRS1990

A fiber-optic current sensor for aerospace applications

A robust, accurate, broad-band, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low and high voltage 60 Hz terrestrial power systems and in 400 Hz aircraft systems. It is intrinsically electromagnetic interference (EMI) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a novel fiber-optic temperature sensor embedded in the sensing head. The technology contained in the sensor is examined and the results of precision tests conducted at various temperatures within the wide operating range are given. The results of early EMI tests are also given.

Patterson, Richard L.↗

NASA NTRS1990

Kinetics and thermodynamics of ceramic/metal interface reactions related to high T(sub c) superconducting applications

Superconducting ceramic materials, no matter what their form, size or shape, must eventually make contact with non-superconducting materials in order to accomplish current transfer to other parts of a real operating system, or for testing and measurement of properties. Thus, whether the configuration is a clad wire, a bulk superconducting disc, tape, or a thick or thin superconducting film on a substrate, the physical and mechanical behavior of interface (interconnections, joints, etc.) between superconductors and normal conductor materials of all kinds is of extreme importance to the technological development of these systems. Fabrication heat treatments associated with the particular joining process allow possible reactions between the superconducting ceramic and the contact to occur, and consequently influence properties at the interface region. The nature of these reactions is therefore of great broad interest, as these may be a primary determinant for the real capability of these materials. Research related both to fabrication of composite sheathed wire products, and the joining contacts for physical property measurements, as well as, a review of other related literature in the field are described. Comparison are made between 1-2-3, Bi-, and Tl-based ceramic superconductors joined to a variety of metals including Cu, Ni, Fe, Cr, Ag, Ag-Pd, Au, In, and Ga. The morphology of reaction products and the nature of interface degradation as a function of time will be highlighted.

Notis, Michael R.↗

NASA NTRS1989

Fiber optics for advanced aircraft

The increased use of composites makes the digital control more susceptible to electromagnetic effects. In order to provide the protection to the digital control additional shielding will be required as well as protective circuitry for the electronics. This results in increased weight and reduced reliability. The advantages that fiber optic technology provides for advanced aircraft applications is recognized. The use of optical signals to carry information between the aircraft and the control module provides immunity from contamination by electromagnetic sources as well as other important benefits such as reduced weight and volume resulting from the elimination of the shielding and the replacement of metal conductors with low weight glass fibers. In 1975 NASA began work to develop passive optical sensors for use with fiber optics in aircraft control systems. The problem now is to choose the best optical sensor concepts and evaluate them for use. In 1985 NASA and DOD entered into a joint program, Fiber Optic Control System Integration (FOCSI), to look at optical technology specifically for use in advanced aircraft systems. The results of this program are discussed. The conclusion of the study indicated that the use of fiber optic technology in advanced aircraft systems is feasible and desirable. The study pointed to a lack of available sensors from vendors capable of operating in the adverse environments of advanced aircraft.

Baumbick, Robert J.↗

NASA NTRS1988

Water-module interaction studies

Mechanisms by which moisture enters photovoltaic modules and techniques for reducing such interactions are reported. Results from a study of the effectiveness of various module sealants are given. Techniques for measuring the rate and quantity of moisture ingress are discussed. It is shown that scribe lines and porous frit bridging conductors provide preferential paths for moisture ingress and that moisture diffusion by surface/interfacial paths is considerably more rapid than diffusion by bulk paths, which implies that thin-film substrate and supersubstrate modules are much more vulnerable to moist environments than are bulk-encapsulated crystalline-silicon modules. Design approaches that reduce moisture entry are discussed.

Mon, G.↗

NASA NTRS1990

Recent observations of high voltage spacecraft-environment interaction at LEO altitudes using sounding rockets

The paper addresses the subject of the interaction of positively and negatively charged bodies with the terrestrial ionosphere at low earth orbit altitudes. Data from two recent sounding rocket flights are used to establish that the current collected by exposed conductors biassed positively at up to 45kV relative to the ionospheric plasma generally follow predictions which account for strong control of electron flow by the geomagnetic field. If the biased structure is in the vicinity of disturbing influences such as an emitted charged particle beam, or locally enhanced gas pressure, then large deviations from the space-charge-limited return currents occur.

Raitt, W. J.↗

NASA NTRS1990

Propagation of a nonrelativistic electron beam in three dimensions

The propagation of a nonrelativistic electron beam injected into space plasma from a conductor was studied by means of an electrostatic three-dimensional simulation model. Only the injection of an electron beam along a magnetic field was considered. Contrary to one- and two-dimensional simulations, an overdense electron beam whose density is much larger than the ambient plasma density can escape a spacecraft without causing significant charging. It was found that the radial electric field arising from the space charge of the beam electrons can give rise to a rotation of both the beams and ambient electrons with respect to ambient ions. The rotation speed can easily exceed the electron thermal speed even when the beam density is smaller than the ambient density. Instabilities arising from such a rotating electron beam are discussed.

Okuda, Hideo↗

NASA NTRS1990

Ion drag for a negatively biased solar array in low earth orbit

Highly biased solar arrays in the space environment are found to have a number of significant interactions with the space environment. The enhanced drag suffered by highly biased solar arrays is studied with the particle-in-cell code. The results are compared to recent numerical work. The drag calculations contain the effect of having the conductor surrounded by dielectrics as well as the charging of the dielectric by electrons. The results are used to calculate the attitude change expected on the high-voltage solar array of the Japanese Space Flyer Unit.

Hastings, Daniel E.↗

NASA NTRS1990

Coax-to-channelised coplanar waveguide in-phase N-way, radial power divider

A novel nonplanar, wideband power divider which makes use of a coax-to-CCPW transition is demonstrated. The transition utilizes a coaxial transformer whose outer conductor is slotted along the length for RF power division and also for exciting the CCPWs in equal amplitude and phase at the radial junction. The measured (8-16 GHz) excess insertion loss at the output ports is 0.5 dB for a four-way divider. The amplitude and phase balance are within 0.5 dB and 5 deg, respectively. The power divider should find applications in the feed network of phased arrays.

Simons, R. N.↗