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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

On board processing for future satellite communications systems: Comparison of FDM, TDM and hybrid accessing schemes

Several satellite uplink and downlink accessing schemes for customer premises service are compared. Four conceptual system designs are presented: satellite-routed frequency division multiple access (FDMA), satellite-switched time division multiple access (TDMA), processor-routed TDMA, and frequency-routed TDMA, operating in the 30/20 GHz band. The designs are compared on the basis of estimated satellite weight, system capacity, power consumption, and cost. The systems are analyzed for fixed multibeam coverage of the continental United States. Analysis shows that the system capacity is limited by the available satellite resources and by the terminal size and cost.

Berk, G.↗
NASA NTRS1982

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗
NASA NTRS1982

Application of MMIC modules in future multiple beam satellite antenna systems

Multiple beam antenna systems for advanced communication satellites operating in the 30/20 GHz frequency bands (30 GHz uplink, 20 GHz downlink) were developed. Up to twenty 0.3 deg HPBW fixed spot beams and six 0.3 deg HPBW scanning spot beams will be required. Array-fed dual reflector antenna systems in which monolithic microwave integrated circuit (MMIC) phase shift and amplifier modules are used with each radiating element of the feed array for beam pointing and power gain were developed. The feasibility of distributed power amplification and beam pointing with MMIC modules in the elements of an array and to develop a data base for future development were demonstrated. The technical discussion centers around the potential advantages of ""monolithic'' antennas for specific applications as compared to systems using high powered TWT's. These include: reduced losses in the beam forming network; advantage of space combining and graceful degradation; dynamic control of beam pointing and illumination contour; and possibilities for cost and weight reduction.

Smetana, J.↗
NASA NTRS1983

Pacific area data collection stations

The installation of environmental data collection systems at several remotely located sites in islands in the Pacific Ocean is summarized. The effort was designed to enhance the ability to collect hydrological information. The data collection station consists of a data acquisition system for handling data, a transmitter for uplinking information to the GOES-W geostationary satellite, and a variety of environmental sensors for data accumulation. Each system was assembled, tested, and deployed on designated islands. The concept of using microprocessors for handling data at remote sites and relaying it via a satellite link is a cost effective approach. Such systems require high reliability and proven performance in the field.

Rector, R. C.↗
NASA NTRS1983

The Deep Space Network: A Radio Communications Instrument for Deep Space Exploration

The primary purpose of the Deep Space Network (DSN) is to serve as a communications instrument for deep space exploration, providing communications between the spacecraft and the ground facilities. The uplink communications channel provides instructions or commands to the spacecraft. The downlink communications channel provides command verification and spacecraft engineering and science instrument payload data.

Renzetti, N. A.↗
NASA NTRS1982

Comparative study of FDMA, TDMA and hybrid 30/20 GHz satellite communications systems for small users

This study compares several satellite uplink and downlink accessing schemes for a Customer Premises Service. Four conceptual system designs are presented: Satellite-Routed FDMA, Frequency-Routed TDMA, Satellite-Switched TDMA, and Processor-Routed TDMA, operating in the 30/20 GHz band. The designs are compared on the basis of estimated satellite weight, power consumption, and cost. The system capacities are analyzed for a fixed multibeam coverage of CONUS. Analysis shows that the system capacity is limited by the available satellite resources and by the terminal size and cost.

Berk, G.↗
NASA NTRS1982

Onboard processing for a 30/20 GHz communications satellite

A systems configuration for the baseband processor for a TDMA communications satellite utilizing the 30 GHz uplink and 20 GHz downlink bands will be discussed. The baseband processor functions include QPSK burst demodulation, convolutional decoding, data routing, encoding, QPSK modulation, and antenna steering. The performance of the burst demodulator will be examined. Power and weight estimates for the baseband processor will be presented.

Reisenfeld, S.↗
NASA NTRS1984

ISEE-3 Microwave Filter Requirements

The 64 m subnet is committed to support the International Sun Earth Explorer (ISEE-3) spacecraft. The uplink and one of the downlink frequencies will be respectively, 2090 and 2217 MHz. As these two frequencies fall outside the normal DSN transmit and receive bands, the 64-m antennas present new filter requirements, which are analyzed.

Galvez, J. L.↗
NASA NTRS1984

Test results for 27.5- to 30-GHz communications satellite receivers

Five proof of concept receivers are tested. The receivers operate in the 27.5 to 30 GHz uplink band for communications satellites and produce an output at C band. Receiver requirements and test results are given. Test methods are discussed and results are compared with the contractor's test results.

Conroy, M. J.↗
NASA NTRS1984

Attitude Control System for the Extreme Ultraviolet Explorer Satellite

The requirements, design, and expected performance of the Attitude Control Subsystem for the spin-stabilized Extreme Ultraviolet Explorer Satellite are presented. In the sky-mapping phase, closed-loop magnetic control keeps the spin axis pointed toward the sun. In the spectroscopy phase, the attitude control loop is closed via the ground. The satellite's attitude and spin rate are determined using periodically downlinked star data. An attitude control algorithm generates commands to be uplinked to the satellite for spin axis precession and spin rate control. Computer simulations of the satellite dynamic response, pointing error, and stability during spin axis precession are presented, and parameters that affect the pointing performance are evaluated.

Wong, E. C.↗
NASA NTRS1984

Application of speech recognition and synthesis in the general aviation cockpit

Interactive speech recognition/synthesis technology is assessed as a method for the aleviation of single-pilot IFR flight workloads. Attention was given during this series of evaluations to the conditions typical of general aviation twin-engine aircrft cockpits, covering several commonly encountered IFR flight condition scenarios. The most beneficial speech command tasks are noted to be in the data retrieval domain, which would allow the pilot access to uplinked data, checklists, and performance charts. Data entry tasks also appear to benefit from this technology.

North, R. A.↗
NASA NTRS1984

An approach to autonomous, onboard orbit determination

An orbit determination subsystem that will operate as an integral part of an autonomous, onboard navigation system is presented and analyzed. The navigation system is required to interface solely with the downlink telemetry stream and uplink command stream of an existing class of geostationary satellites. In particular, the orbit will be determined from a set of onboard sensors, which previously were used only for attitude determination. The design of the orbit determination subsystem is described in detail. The rationale behind the choice of each component of the design is given. Finally, the performance of the orbit determination subsystem, under a variety of assumptions, is determined by a combination of numerical simulation and analytical methods.

Mease, K. D.↗
NASA NTRS1984

Comet rendezvous

A Mariner Mark II spacecraft rendezvous mission with comet Kopff has been recommended by NASA's Solar System Exploration Committee, and is scheduled for a Shuttle launch in 1990. The spacecraft, which is scheduled to encounter the comet in 1994, will conduct a series of experiments including the study of the cometary nucleus, coma, and tail during perihelion passage; the determination of the nucleus and coma chemical/isotropic composition; the description of the nucleus's size, mass, rotation period, and pole occultation; distinctions of gas and dust hydrodynamics; and distinctions of solar wind interactions with the coma. The three-axis-stabilized spacecraft will be modular in design, and will incorporate a 490-Newton Insat engine, Viking Orbiter propulsion tanks, an Integrated Platform Pointing and Attitude Control Subsystem, and several scientific instruments. The spacecraft's Radio Frequency Subsystem will only use X-band telemetry with a downlink frequency of 8415 MHz, and an uplink frequency of 7161 MHz. The power sources in the present design include one radioisotope thermoelectric generator, three 3 Ah batteries, and a solar panel of approximately 7 sq m.

Draper, R. F.↗
NASA NTRS1983

The NASA data systems standardization program - Radio frequency and modulation

The modifications being considered by the NASA-ESA Working Group (NEWG) for space-data-systems standardization to maximize the commonality of the NASA and ESA RF and modulation systems linking spaceborne scientific experiments with ground stations are summarized. The first phase of the NEWG project shows that the NASA MK-IVA Deep Space Network and Shuttle Interrogator (SI) systems in place or planned for 1985 are generally compatible with the ESA Network, but that communications involving the Tracking and Data Relay Satellite (TDRS) are incompatible due to its use of spread-spectrum modulation, pseudonoise ranging, multiple-access channels, and Mbit/s data rates. Topics under study for the post-1985 period include low-bit-rate capability for the ESA Network, an optional 8-kHz command subcarrier for the SI, fixing the spacecraft-transponder frequency-multiplication ratios for possible X-band uplinks or X-band nondeep-space downlinks, review of incompatible TDRS features, and development of the 32-GHz band.

Martin, W. L.↗
NASA NTRS1983

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗
NASA NTRS1985

High-Speed Computer-Controlled Switch-Matrix System

High-speed computer-controlled switch-matrix system developed for communication satellites. Satellite system controlled by onboard computer and all message-routing functions between uplink and downlink beams handled by newly developed switch-matrix system. Message requires only 2-microsecond interconnect period, repeated every millisecond.

Spisz, E.↗
NASA NTRS1984

SARSAT 406 MHz system technical evaluation

The location accuracy, access to spacecraft, uplink margin, and interference problems of the COSPAS-SARSAT system are reviewed. Over 90% of positions are accurate to within 5 km, in local mode, slightly worse in global mode. The random access parameters of SARSAT provide for the location of up to 90 beacons with a uniform distribution in the satellite visibility circle (2600 km radius). The ratio of messages correctly processed on board to messages transmitted to the satellite is 0.8, increasing as number of beacons decreases. Interference, particularly over western Europe and the United States degrades performance, but sources can be located.

Goudy, P.↗