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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Adjacent channel interference degradation with minimum shift keyed modulation

Computer simulation results for degradation in signal-to-noise ratio for various values of bit error probability are given for minimum shift-keyed-type signaling in the presence of adjacent channel interference. A serial modulator structure which utilizes spectral shaping is characterized in terms of envelope deviation and bandwidth efficiency. This serial generation technique is convenient for implementation at high data rates and results in signal spectra with lower sidelobe levels than conventional minimum shift-keyed modulation at the expense of moderate envelope deviation. Because of the lower sidelobe levels, the resulting spectra allow denser channel packing than does ideal MSK.

Ziemer, R. E.↗
NASA NTRS1981

Tri-state delta modulation system for Space Shuttle digital TV downlink

Future requirements for Shuttle Orbiter downlink communication may include transmission of digital video which, in addition to black and white, may also be either field-sequential or NTSC color format. The use of digitized video could provide for picture privacy at the expense of additional onboard hardware, together with an increased bandwidth due to the digitization process. A general objective for the Space Shuttle application is to develop a digitization technique that is compatible with data rates in the 20-30 Mbps range but still provides good quality pictures. This paper describes a tri-state delta modulation/demodulation (TSDM) technique which is a good compromise between implementation complexity and performance. The unique feature of TSDM is that it provides for efficient run-length encoding of constant-intensity segments of a TV picture. Axiomatix has developed a hardware implementation of a high-speed TSDM transmitter and receiver for black-and-white TV and field-sequential color. The hardware complexity of this TSDM implementation is summarized in the paper.

Udalov, S.↗
NASA NTRS1981

Advances in Serial MSK modems

Lumped element as well as distributed element networks are used in the Serial MSK (SMSK) modems, for 20-1000 Mbps data rate range applications, whose design and performance characteristics are described. It is noted that the use of baseband conversion filters for the modulator yields good performance in many applications, with typical matched filter designs (structurally simple to implement) causing less than 0.5 dB bit error rate performance degradation. The SMSK modem technique begins with the use of a biphased shift-keyed modulator, and then employs passive filters to obtain the MSK signal.

Ryan, C. R.↗
NASA NTRS1983

Data systems - Optical bus will connect distributed system

The fiber optics buses currently under consideration for the NASA space station program will have data rates of at least 20 Mb/sec. The network interconnection scheme that will eventually be used is, however, uncertain. A NASA-Langley effort on graph networks includes adaptive, fault-tolerant and self-correcting operations. A breadboard program at NASA-Johnson includes evaluations of standard devices, called 'bus interface units', in an adaptive and fault-correcting chordal or concentric ring type of network. Fiber optics would allow an evolution to wavelength modulation techniques in such systems.

Swingle, W. L.↗
NASA NTRS1982

Wide Field and Planetary Camera for Space Telescope

The Space Telescope's Wide Field and Planetary Camera instrument, presently under construction, will be used to map the observable universe and to study the outer planets. It will be able to see 1000 times farther than any previously employed instrument. The Wide Field system will be located in a radial bay, receiving its signals via a pick-off mirror centered on the optical axis of the telescope assembly. The external thermal radiator employed by the instrument for cooling will be part of the exterior surface of the Space Telescope. In addition to having a larger (1200-12,000 A) wavelength range than any of the other Space Telescope instruments, its data rate, at 1 Mb/sec, exceeds that of the other instruments. Attention is given to the operating modes and projected performance levels of the Wide Field Camera and Planetary Camera.

Lockhart, R. F.↗
NASA NTRS1983

Experimental aerodynamic heating to simulated Shuttle tiles

The heat transfer to simulated Shuttle thermal protection system tiles was investigated experimentally using a highly instrumented metallic thin wall tile arranged with other metal tiles in a staggered tile array. Cold-wall heating rate data for laminar and turbulent flow were obtained in the Langley 8-Foot High-Temperature Tunnel at a nominal Mach number of 7, a nominal total temperature of 3300 deg R, free-stream unit Reynolds number from 340,000 to 2,200,000 per foot, and free-stream dynamic pressure of 1.8 to 9.1 psia. Experimental data are presented to illustrate the effects of flow angularity and gap width on both local peak heating and overall heating loads.

Avery, D. E.↗
NASA NTRS1983

Space Shuttle base heating

First-stage and second-stage heating environments of the base region of the Space Shuttle are characterized in detail in terms of Orbiter-main-engine-plume and booster-plume radiation, freestream-air convective cooling, and reversed-plume-flow convective heating as they affect each base-region design point. Design predictions are compared with selected heating-rate data from flights STS-1 through STS-5; the flight data are found to show excellent interflight repeatability independent of small changes in trajectory, and to verify the validity of the prediction methodology. The impact of individual flight events on base heating is indicated.

Greenwood, T. F.↗
NASA NTRS1982

The effects of rain on system performance for the NASA 30/20 GHz Experimental Satellite

A 30/20 GHz Experimental Communications Satellite System is presently under study by NASA to evaluate system technology and high data rate multi-beam communications techniques. In this paper the expected system performance for the 30/20 GHz Satellite is presented, for both trunking and customer premise service (CPS) modes, with particular emphasis on the effects of severe rain events on link reliability. A rain attenuation prediction model technique is described and path and two-way link availabilities are developed for the various modes of operation. The results indicate that acceptable link availabilities can be expected on the 30/20 GHz system for both the trunking and CPS modes, and the experimental satellite system can form the basis for verification of system performance for operational 30/20 GHz systems.

Ippolito, L. J.↗
NASA NTRS1983

Effect of swaging on the 1000 C compressive slow plastic flow characteristics of the directionally solidified eutectic alloy gamma/gamma prime-alpha

Swaging between 750 and 1050 C has been investigated as a means to introduce work into the directionally solidified eutectic alloy gamma/gamma prime-alpha (Ni-32.3 wt percent Mo-6.3 wt percent Al) and increase the elevated temperature creep strength. The 1000 C slow plastic compressive flow stress-strain rate properties in air of as-grown, annealed, and worked nominally 10 and 25 percent materials have been determined. Swaging did not improve the slow plastic behavior. In fact large reductions tended to degrade the strength and produced a change in the deformation mechanism from uniform flow to one involving intense slip band formation. Comparison of 1000 C tensile and compressive strength-strain rate data reveals that deformation is independent of the stress state.

Whittenberger, J. D.↗
NASA NTRS1983

V-band integrated quadriphase modulator

A V-band integrated circuit quadriphase shift keyed modulator/exciter for space communications systems was developed. Intersatellite communications systems require direct modulation at 60 GHz to enhance signal processing capability. For most systems, particularly space applications, small and lightweight components are essential to alleviate severe system design constraints. Thus to achieve wideband, high data rate systems, direct modulation techniques at millimeter waves using solid state integrated circuit technology are an integral part of the overall technology developments.

Grote, A.↗
NASA NTRS1984

Effect of RF Filtering on the Performance of Uncoded PCM/PM Telemetry Channels

A method for calculating the increase in received telemetry signal power required to compensate for the use of a radio frequency interference (RFI) filter in front of the DSN receiving system low-noise amplifier is described. The telemetry system for which the degradation is calculated is an uncoded PCM/PM system in which the NRZ data directly modulates the carrier at a modulation level which leaves a discrete carrier. A phase-locked loop in the RF receiver tracks the discrete carrier and coherently demodulates the PCM data. The RFI filter may be a series of Butterworth, Tchebychev, or Bessel low-pass, high-pass, band-pass, or band-reject filters, each with arbitrary bandwidth, number of poles, and, for band-pass or band-reject filters, resonant frequency. The only restriction is that the RFI filter must have only simple poles. Numerical results are presented for the RFI filters the DSN plans to place in front of the S-band FET, S-band maser, and X-band maser low noise amplifiers. The main conclusion is that the filters will produce negligible degradation at data rates below 4 Mbps.

Koerner, M. A.↗
NASA NTRS1983

Low-frequency radio navigation system

A method of continuous wave navigation using four transmitters operating at sufficiently low frequencies to assure essentially pure groundwave operation is described. The transmitters are keyed to transmit constant bursts (1/4 sec) in a time-multiplexed pattern with phase modulation of at least one transmitter for identification of the transmitters and with the ability to identify the absolute phase of the modulated transmitter and the ability to modulate low rate data for transmission. The transmitters are optimally positioned to provide groundwave coverage over a service region of about 50 by 50 km for the frequencies selected in the range of 200 to 500 kHz, but their locations are not critical because of the beneficial effect of overdetermination of position of a receiver made possible by the fourth transmitter. Four frequencies are used, at least two of which are selected to provide optimal resolution. All transmitters are synchronized to an average phase as received by a monitor receiver.

Wallis, D. E.↗
NASA NTRS1984

The LANDSAT-4 Program: an Overview

LANDSAT 4 was launched on July 22, 1982. This is the first satellite to carry the high resolution, high data rate Thematic Mapper (TM). An overview of the LANDSAT 4 Program is presented in terms of the program plan, accomplishments and future events, the transition of operational responsibility to National Oceanic and Atmospheric Administration (NOAA) management and the challenges remaining to both NASA personnel and LANDSAT 4 Investigations Program participants.

Webb, W.↗
NASA NTRS1984

Electronic Switching Spherical Array (ESSA) antenna systems

ESSA (Electronic Switching Spherical Array) is an antenna system conceived, developed and qualified for linking satellite data transmissions with NASA's tracking and data relay satellites (TDRSS) and tracking and data acquisition satellites (TDAS). ESSA functions in the S band frequency region, cover 2 pi or more steradians with directional gain and operates in multiple selectable modes. ESSA operates in concert with the NASA's TDRS standard transponder in the retrodirective mode or independently in directional beam, program track and special modes. Organizations and projects to the ESSA applications for NASA's space use are introduced. Coverage gain, weight power and implementation and other performance information for satisfying a wide range of data rate requirements are included.

Hockensmith, R. P.↗
NASA NTRS1983

A versatile ground data display system for Spacelab experiments

A microprocessor-based data capture and display system suited to the needs of many Spacelab experimenters is described. Although developed specifically for the needs of the FAUST UV astronomy telescope, several features of the system may make it attractive to other groups who need to interact with their Spacelab data in real or near-real time. The display system captures data from the serial data stream originating in the Spacelab experiment computer input/output (ECIO) data channel, and can reformat and display several hundred variables per second in real time. The system offers a combination of CRT display and analog paper strip-chart output. A facility is also provided for simultaneously creating floppy-disk records of short segments of data according to prearranged criteria, to allow detailed examination of critical events in the operation of the experiment. The simplicity, economy, reliability, and flexibility of the display system suggest its use for monitoring a variety of low- and medium-data-rate Spacelab experiments.

Werthimer, D.↗
NASA NTRS1983

The NASA SETI Program - Objectives of the R&D activity

The current activity in NASA's SETI Program is a research and development program jointly carried out by the NASA Ames Research Center and the Jet Propulsion Laboratory. The purpose of this R&D phase is to develop all prerequisites for a well defined microwave observing program. The specific objectives include the development of a prototype search system which will ultimately be capable of processing data rates up to 10 gigabytes/second. Specialized signal detection algorithms and automated search procedures will be developed and tested with the prototype hardware. A series of field tests will be carried out with the NASA Deep Space Network facilities at Goldstone, CA and with the 305-m radio telescope at the Arecibo Ionospheric Observatory in Puerto Rico.

Klein, M. J.↗
NASA NTRS1982

Power efficient optical communications for space applications

Optical communications technology promises substantial size, weight and power consumption savings for space to space high data rate communications over presently used microwave technology. These benefits are further increased by making the most efficient use of the available optical signal energy. This presentation will describe the progress to date on a project to design, build and demonstrate in the laboratory an optical communication system capable of conveying 2.5 bits of information per effective received photon. Such high power efficiencies will reduce the need for photon collection at the receiver and will greatly reduce the requirements for optical pointing accuracy, both at the transmitter as well as the receiver. A longer range program to demonstrate even higher photon efficiencies will also be described.

Lesh, J. R.↗
NASA NTRS1982

Digital TV tri-state delta modulation system for Space Shuttle ku-band downlink

A tri-state delta modulation/demodulation (TSDM) technique which provides for efficient run-length coding of constant-intensity segments of a TV picture is described. Aspects of the hardware implementation of a high-speed TSDM transmitter and receiver for black-and-white TV or field-sequential color or NTSC format color are reviewed. Run-length encoding of the TSDM output can consistently reduce the required channel data rate well below one bit per sample. As compared with a bistate delta modulation system, the present technique eliminates granularity in the reconstructed video without degrading rise or fall times. About 40 chips are used by TSDM when used to handle the luminance information in a color link. A possible overall space and ground functional configuration to accommodate Shuttle digital TV with scrambling for privacy is presented.

Udalov, S.↗