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At least 415 records · Page 23

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NASA NTRS1973

Martian surface coordinates.

This paper presents methods and results for primary and secondary triangulation of the Martian surface. The primary network is based on multiphotograph stereophotogrammetry in which the pictures are rotated around fixed centers; these centers are provided as spacecraft stations from the tracking data. The computations use the latest Mars spin axis determined by Mariner 9 experiments and the new first meridian passing through a small crater, Airy-0, seen on Mariner 9 imagery. The secondary triangulation is performed in the map plane using rectified pictures as map fragments, assumed to be of correct shape. In this paper, 1205 primary positions are given.

Davies, M. E.↗

NASA NTRS1973

Bone mineral measurement, experiment M078

Measurement tests revealed few deviations from baseline bone mineral measurements after 56 days in a Skylab-type environment. No mineral change was observed in the right radius. One individual, however, showed a possible mineral loss in the left os calcis and another gained mineral in the right ulna. The cause of the gain is unclear but may be attributable to the heavy exercise routines engaged in by the crewmember in question. Equipment problems were identified during the experiment and rectified.

Rambaut, P. C.↗

NASA NTRS1974

Photomultiplier circuit including means for rapidly reducing the sensitivity thereof

A simple, reliable and inexpensive control circuit is described for rapidly reducing the bias voltage across one or more of the dynode stages of a photomultiplier, to substantially decrease its sensitivity to incoming light at those times where excess light intensity might damage the tube. The control circuit comprises a switching device, such as a silicon controlled rectifier (SCR), coupled between a pair of the electrodes in the tube, preferably the cathode and first dynode, or the first and second dynodes, the switching device operating in response to a trigger pulse applied to its gate to short circuit the two electrodes. To insure the desired reduction in sensitivity, two switching stages, the devices be employed between two of the electrode stages, the devices being operated simultaneously to short circuit both stages.

Mcclenahan, J. O.↗

NASA NTRS1973

Experimental investigation of aeronautical and maritime communications and surveillance using satellites

The experimental program described included an evaluation of every significant factor affecting the accuracy of position fixing by range measurements from geostationary satellites. The tone-code ranging technique was found to provide a precision of roughly 0.1 n mi at mid-lattitudes with one range measurement at L-band and one at VHF. The factors which introduce bias errors were studied analytically and experimentally, and means of rectifying the bias errors were developed. An operational system at L-band may be expected to provide position fix accuracy of 0.1 n mi over large regions of the earth. The ranging technique developed within this program is digital, and uses a single signalling waveform and a single modem for communications and ranging.

Anderson, R. E.↗

NASA NTRS1973

20 kA PFN capacitor bank with solid-state switching

A compact high-current pulse-forming network capacitor bank using paralleled silicon controlled rectifiers as switches is described. The maximum charging voltage of the bank is 1kV and maximum load current is 20 kA. The necessary switch equalization criteria and performance with dummy load and an arc plasma generator are described.

Posta, S. J.↗

NASA NTRS1973

Evaluation of digitally corrected ERTS imagery

Utilizing all digital processing techniques, precision rectified ERTS multispectral imagery have been produced. Precision geometric correction is accomplished by: (1) utilizing a low order piecewise approximation to the image distortions; (2) incorporating spacecraft attitude refinement derived from ground control points utilized in a Kalman filter; (3) utilizing interpolation techniques which preserve value and slope continuity in the image data. Imagery produced is represented in a UTM projection, and has been evaluated for precision by statistical and analytical methods. Extrapolations to modest size computers indicate good throughput with no sacrifice in precision.

Rifman, S. S.↗

NASA NTRS1975

Voltage monitoring system

A description is given of a system for monitoring the voltage at a remote location and determining when the voltage exceeds upper and lower levels. The system includes transmission lines for transmitting the voltage back to a central station and applying such to an amplifier having a pair of outputs. One of the outputs of the amplifier is applied to an oscillograph. The other output is fed through an isolation transformer, a full wave rectifier, to a pair of unijunctional transistor circuits for producing pulses when the voltage exceeds or drops below a predetermined level. These pulses, in turn, energize a relay which turns on the oscillograph for recording the voltages being monitored.

Canicatti, C. L.↗

NASA NTRS1974

Power processor for a 30cm ion thruster

A thermal vacuum power processor for the NASA Lewis 30cm Mercury Ion Engine was designed, fabricated and tested to determine compliance with electrical specifications. The power processor breadboard used the silicon controlled rectifier (SCR) series resonant inverter as the basic power stage to process all the power to an ion engine. The power processor includes a digital interface unit to process all input commands and internal telemetry signals so that operation is compatible with a central computer system. The breadboard was tested in a thermal vacuum environment. Integration tests were performed with the ion engine and demonstrate operational compatibility and reliable operation without any component failures. Electromagnetic interference data were also recorded on the design to provide information on the interaction with total spacecraft.

Biess, J. J.↗

NASA NTRS1975

Dynamic testing of the Kearfott 2401 accelerometer

A Kearfott pendulous accelerometer was integrated with a United Aircraft pulse torque servo assembly (PTSA) forced binary loop. The test objective was to measure dynamic errors due to anisoinertia and OA coupling effects. The instrument and its torque loop are described, and the technique for isolating the anisoinertia error from centripetal acceleration effects is discussed in detail. The measured anisoinertia error coefficient was 3.0 cm, and the testing confirmed that no rectified OA coupling error was present.

Katz, B.↗

NASA NTRS1974

High voltage power Schottky diodes

Calculations of the low frequency rectification efficiency of power Schottky diodes show that silicon Schottky rectifiers have lower losses than silicon p-n junctions for all voltage applications up to approximately 150 volts. These calculations are presented. Large area Schottky diodes have been fabricated which exhibit near ideal reverse leakage at 100 C out to approximately 100 volts and which have current capability of 100 A. Fabrication details and performance data are presented.

Cordes, L. F.↗

NASA NTRS1975

Report on studies of space to earth microwave power transmission systems

The studies reported include a preliminary analysis, conceptual design, technical and economic evaluation, and planning for a technology development, a ground demonstration, and an orbital test program. The concept investigated involves a transmitting antenna in geosynchronous orbit which beams microwave power to a ground antenna where it is rectified to DC power. The amplitron and the klystron are considered as devices for converting DC power to RF power at microwave frequencies.

Edwards, A., Jr.↗

NASA NTRS1976

Free-space microwave-power transmission

Laboratory-scale wireless transmission of microwave power approaches fifty-four percent efficiency. DC is converted to a 2.45-GHz signal and is transmitted through horn antenna array; microwave signal is received at rectenna and is simultaneously collected and rectified back to dc at receiving sites; dc is then processed for wired distribution.

Brown, W. C.↗

NASA NTRS1977

A nonsaturating dc-to-dc parallel power converter

Device is conventional circuit modified with pair of diode rectifiers coupled to switching transistors via feedback winding. Transient-causing collector-current overlap between transistors is eliminated. Technique may be used with nonsaturating parallel-transistor converters operating from voltage source which remains fixed or varies over small range.

Lavigna, T.↗

NASA NTRS1977

Power supply with optical-isolator control

Power supply consists of several stages, interconnected and programmed for required output. In capacitor charging mode, transistor switches are closed. Last stage is in series with rectifier that prevents current from flowing backward into circuit. In capacitor discharge mode, transistor switches are closed, and voltage delivered to load is sum of voltages across capacitors.

Baker, R. H.↗

NASA NTRS1975

Exploratory study on microanalysis of thin films by backscattering techniques

Solid phase epitaxial growth of Si layers was studied by backscattering spectrometry for controllable electrical characteristics. Samples were fabricated by vacuum deposition on a thin layer of Sb before deposition of the amorphous Si layer. Analysis of the resulting SPEG layer showed that Sb was present in the SPEG layer of Si. The characteristic of the SPEG layer against the Si substrate was rectifying. A scanning microprobe picture of a cleaved sample established the presence of a depletion region more than 1 micron below the surface. Hall effect data indicated that the SPEG layer was n-type, with average free carrier concentration of about 10 to the 19th power cm/3 and average electron mobility of about 40 sq cm/Vs. SPEG with Pd silicide or Ni silicide transport layers showed fast initial transient growth regimes with slower growth in the steady state regimes.

Mayer, J. W.↗

NASA NTRS1975

Microwave Power Transmission System Studies. Volume 1: Executive Summary

A study of microwave power generation, transmission, reception and control was conducted as a part of a program to demonstrate the feasibility of power transmission from geosynchronous orbit. A summary is presented of results concerning design approaches, estimated costs (ROM), critical technology, associated ground and orbital test programs with emphasis on dc to rf conversion, transmitting antenna, phase control, mechanical systems, flight operations, ground power receiving-rectifying antenna with systems analysis, and evaluation. Recommendations for early further in-depth studies complementing the technology program are included.

Maynard, O. E.↗

NASA NTRS1975

Microwave power transmission system studies. Volume 4: Sections 9 through 14 with appendices

The microwave rectifier technology, approaches to the receiving antenna, topology of rectenna circuits, assembly and construction, ROM cost estimates are discussed. Analyses and cost estimates for the equipment required to transmit the ground power to an external user. Noise and harmonic considerations are presented for both the amplitron and klystron and interference limits are identified and evaluated. The risk assessment discussion is discussed wherein technology risks are rated and ranked with regard to their importance in impacting the microwave power transmission system. The system analyses and evaluation are included of parametric studies of system relationships pertaining to geometry, materials, specific cost, specific weight, efficiency, converter packing, frequency selection, power distribution, power density, power output magnitude, power source, transportation and assembly. Capital costs per kW and energy costs as a function of rate of return, power source and transportation costs as well as build cycle time are presented. The critical technology and ground test program are discussed along with ROM costs and schedule. The orbital test program with associated critical technology and ground based program based on full implementation of the defined objectives is discussed.

Maynard, O. E.↗

NASA NTRS1975

Discriminating coastal rangeland production and improvements with computer aided techniques

The feasibility and utility of using satellite data and computer-aided remote sensing analysis techniques to conduct range inventories were tested. This pilot study was focused over a 250,000 acre site in Galveston and Brazoria Counties along the Texas Gulf Coast. Rectified enlarged aircraft color infrared photographs of this site were used as the ground truth base. The different land categories were identified, delineated, and measured. Multispectral scanner (MSS) bulk data from LANDSAT-1 was received and analyzed with the Image 100 pattern recognition system. Features of interest were delineated on the image console giving the number of picture elements classified; the picture elements were converted to acreages and the accuracy of the technique was evaluated by comparison with data base results for three test sites. The accuracies for computer aided classification of coastal marshes ranged from 89% to 96%.

Reeves, C. A.↗