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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Low Power Ground-Based Laser Illumination for Electric Propulsion Applications

A preliminary evaluation of low power, ground-based laser powered electric propulsion systems is presented. A review of available and near-term laser, photovoltaic, and adaptive optic systems indicates that approximately 5-kW of ground-based laser power can be delivered at an equivalent one-sun intensity to an orbit of approximately 2000 km. Laser illumination at the proper wavelength can double photovoltaic array conversion efficiencies compared to efficiencies obtained with solar illumination at the same intensity, allowing a reduction in array mass. The reduced array mass allows extra propellant to be carried with no penalty in total spacecraft mass. The extra propellant mass can extend the satellite life in orbit, allowing additional revenue to be generated. A trade study using realistic cost estimates and conservative ground station viewing capability was performed to estimate the number of communication satellites which must be illuminated to make a proliferated system of laser ground stations economically attractive. The required number of satellites is typically below that of proposed communication satellite constellations, indicating that low power ground-based laser beaming may be commercially viable. However, near-term advances in low specific mass solar arrays and high energy density batteries for LEO applications would render the ground-based laser system impracticable.

Lapointe, Michael R.↗
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 NTRS1984

Trade-off between land vehicle antenna cost and gain for satellite mobile communications

Trade-offs between antenna cost and gain made for nine antennas as a feasibility study for the experimental land mobile satellite system, M-SAT(X) reported. This system is under development by JPL-NASA for a mobile telephone system to be used throughout the continental USA and Alaska. The mobile antenna is a key element in the development of this system.

Source record↗
NASA NTRS2008

Mitigating Aviation Communication and Satellite Orbit Operations Surprises from Adverse Space Weather

Adverse space weather affects operational activities in aviation and satellite systems. For example, large solar flares create highly variable enhanced neutral atmosphere and ionosphere electron density regions. These regions impact aviation communication frequencies as well as precision orbit determination. The natural space environment, with its dynamic space weather variability, is additionally changed by human activity. The increase in orbital debris in low Earth orbit (LEO), combined with lower atmosphere CO2 that rises into the lower thermosphere and causes increased cooling that results in increased debris lifetime, adds to the environmental hazards of navigating in near-Earth space. This is at a time when commercial space endeavors are posed to begin more missions to LEO during the rise of the solar activity cycle toward the next maximum (2012). For satellite and aviation operators, adverse space weather results in greater expenses for orbit management, more communication outages or aviation and ground-based high frequency radio used, and an inability to effectively plan missions or service customers with space-based communication, imagery, and data transferal during time-critical activities. Examples of some revenue-impacting conditions and solutions for mitigating adverse space weather are offered.

Tobiska, W. Kent↗
NASA NTRS2012

Characterizing Orbital Debris and Spacecrafts Through a Multi-Analytical Approach

Defining the risks present to both crewed and robotic spacecrafts is part of NASA s mission, and is critical to keep these resources out of harms way. Characterizing orbital debris is an essential part of this mission. We present a proof-of-concept study that employs multiple techniques to demonstrate the efficacy of each approach. The targets of this study are IDCSPs (Initial Defense Communications Satellite Program). 35 of these satellites were launched by the US in the mid-1960s and were the first US communications satellites in the GEO regime. They were emplaced in slightly sub-synchronous orbits. These targets were chosen for this proof-of-concept study for the simplicity of their observable exterior surfaces. The satellites are 26-sided polygons (86cm in diameter), initially spin-stabilized and covered on all sides in solar panels. Data presented here include: (a) visible broadband photometry (Johnson B and Cousins R bands) taken with the University of Michigan s 0.6-m aperture Curtis-Schmidt telescope MODEST (for Michigan Orbital DEbris Survey Telescope) in Chile in November, 2011, (b) laboratory broadband photometry (Johnson BV Cousins RI) of solar cells, obtained using the Optical Measurements Center (OMC) at NASA/JSC (see Cowardin et al., this meeting for more details), (c) visible-band spectra taken using the Magellan 6.5m Baade Telescope at Las Campanas Observatory in Chile in March, 2012 (see also Seitzer et al., this meeting), and (d) visible-band laboratory spectra of solar cells using a Field Spectrometer. Color-color plots using broadband photometry (e.g. B-R vs. R-I) demonstrate that different material types fall into distinct areas on the plots (Cowardin, AMOS 2010). Spectra will be binned in wavelength to compare with photometry results and plotted on the same graph for comparison. This allows us to compare lab data with telescopic data, and photometric results with spectroscopic results. In addition, the spectral response of solar cells in the visible wavelength regime varies from relatively flat (modern black solar cells with uniform albedo as a function of wavelength) to older solar cells whose reflectivity is sharply peaked in the blue (similar to the IDCSP solar cells). With a target like IDCSPs, the material type is known a priori. Therefore, this study will also be used to determine whether laboratory spectra of pre-launch (pristine) solar cells differ from the telescopic spectra of IDCSPs that have been exposed to the harsh environment of space for ~45 years to investigate whether space weathering effects are evident.

Lederer, S. M.↗
NASA NTRS1992

A prototype automatic phase compensation module

The growing demands for high gain and accurate satellite communication systems will necessitate the utilization of large reflector systems. One area of concern of reflector based satellite communication is large scale surface deformations due to thermal effects. These distortions, when present, can degrade the performance of the reflector system appreciable. This performance degradation is manifested by a decrease in peak gain, and increase in sidelobe level, and pointing errors. It is essential to compensate for these distortion effects and to maintain the required system performance in the operating space environment. For this reason the development of a technique to offset the degradation effects is highly desirable. Currently, most research is direct at developing better material for the reflector. These materials have a lower coefficient of linear expansion thereby reducing the surface errors. Alternatively, one can minimize the distortion effects of these large scale errors by adaptive phased array compensation. Adaptive phased array techniques have been studied extensively at NASA and elsewhere. Presented in this paper is a prototype automatic phase compensation module designed and built at NASA Lewis Research Center which is the first stage of development for an adaptive array compensation module.

Terry, John D.↗
NASA NTRS2012

Preliminary Characterization of IDCSP Spacecrafts Through a Multi-Analytical Approach

Defining the risks present to both crewed and robotic spacecrafts is part of NASA s mission, and is critical to keep these resources out of harm s way. Characterizing orbital debris is an essential part of this mission. We present a proof-of-concept study that employs multiple techniques to demonstrate the efficacy of each approach. The targets of this study are IDCSPs (Initial Defense Communications Satellite Program). 35 of these satellites were launched by the US in the mid-1960s and were the first US military communications satellites in the GEO regime. They were emplaced in slightly sub-synchronous orbits. These targets were chosen for this proof-of-concept study for the simplicity of their observable exterior surfaces. The satellites are 26-sided polygons (86cm in diameter), initially spin-stabilized, and covered on all sides in solar panels. Data presented here include: (a) visible broadband photometry (Johnson/Kron-Cousins BVRI) taken with the 0.9m SMARTs telescope (Small and Medium Aperture Telescopes) at the Cerro Tololo Inter-American Observatory (CTIO) in Chile in April, 2012, (b) laboratory broadband photometry (Johnson/ Bessell BVRI) of solar cells, obtained using the Optical Measurements Center (OMC) at NASA/JSC [1], (c) visible-band spectra taken using the Magellan 6.5m Baade Telescope at Las Campanas Observatory in Chile in May, 2012 [2], and (d) visible-band laboratory spectra of solar cells using an ASD Field Spectrometer. Color-color plots using broadband photometry (e.g. B-R vs. B-V) demonstrate that different material types fall into distinct areas on the plots [1]. Spectra of the same material types as those plotted in the color-color plots each display their own signature as well. Here, we compare lab data with telescopic data, and photometric results with spectroscopic results. The spectral response of solar cells in the visible wavelength regime varies from relatively flat to somewhat older solar cells whose reflectivity can be gently or sharply peaked in the blue. With a target like IDCSPs, the material type is known a priori, aiding in understanding how material type affects one s observations.

Lederer, S. M.↗
NASA NTRS1993

Land mobile satellite propagation measurements in Japan using ETS-V satellite

Propagation characteristics of land mobile satellite communications channels have been investigated actively in recent years. Information of propagation characteristics associated with multipath fading and shadowing is required to design commercial land mobile satellite communications systems, including protocol and error correction method. CRL (Communications Research Laboratory) has carried out propagation measurements using the Engineering Test Satellite-V (ETS-V) at L band (1.5 GHz) through main roads in Japan by a medium gain antenna with an autotracking capability. This paper presents the propagation statistics obtained in this campaign.

Obara, Noriaki↗
NASA NTRS1986

Application of intersatellite links to domestic satellite systems

The results of a study on intersatellite link (ISL) applications for domestic satellite communications are presented. It was determined if any technical, economic, or performance benefits could be gained by introducing intersatellite links into a domestic satellite communication network. Several key systems issues of domestic ISL's are addressed. These include the effect of a skewed traffic distribution on the selection of ISL satellite orbit locations, tolerable satellite spacing, and crosslink traffic-handling requirements. An ISL technology assessment is made by performing a parametric link analysis for several microwave and optical implementations. The impact of the crosslink on the end-to-end link performance is investigated for both regenerative and nonregenerative ISL architectures. A comparison is made between single satellite systems operating at C-, and Ku-bands and the corresponding ISL systems in terms of ground segment cost, space segment cost, and net link performance. Results indicate that ISL's can effectively expand the CONUS orbital arc, with a 60 GHz ISL implementation being the most attractive.

Ponchak, D. S.↗
NASA NTRS1986

Application of intersatellite links to domestic satellite systems

The results of a study on intersatellite link (ISL) applications for domestic satellite communications are presented. It was determined if any technical, economic, or performance benefits could be gained by introducing intersatellite links into a domestic satellite communication network. Several key systems issues of domestic ISL's are addressed. These include the effect of a skewed traffic distribution on the selection of ISL satellite orbit locations, tolerable satellite spacing, and crosslink traffic-handling requirements. An ISL technology assessment is made by performing a parametric link analysis for several microwave and optical implementations. The impact of the crosslink on the end-to-end link performance is investigated for both regenerative and nonregenerative ISL architectures. A comparison is made between single satellite systems operating at C-, and Ku-bands and the corresponding ISL systems in terms of ground segment cost, space segment cost, and net link performance. Results indicate that ISL's can effectively expand the CONUS orbital arc, with a 60 GHz ISL implementation being the most attractive.

Ponchak, D. S.↗
NASA NTRS1993

NASA Lewis Meshed VSAT Workshop meeting summary

NASA Lewis Research Center's Space Electronics Division (SED) hosted a workshop to address specific topics related to future meshed very small-aperture terminal (VSAT) satellite communications networks. The ideas generated by this workshop will help to identify potential markets and focus technology development within the commercial satellite communications industry and NASA. The workshop resulted in recommendations concerning these principal points of interest: the window of opportunity for a meshed VSAT system; system availability; ground terminal antenna sizes; recommended multifrequency for time division multiple access (TDMA) uplink; a packet switch design concept for narrowband; and fault tolerance design concepts. This report presents a summary of group presentations and discussion associated with the technological, economic, and operational issues of meshed VSAT architectures that utilize processing satellites.

Ivancic, William↗
NASA NTRS1980

Satellite personal communications system

Voice channel communication between low power mobile stations dispersed over a large area is provided by a system which includes a geostationary satellite utilizing a large UHF antenna that can receive a transmission from a caller and retransmit it over any one beam of a matrix of narrow beams, so the chosen beam covers an area in which a designated called party is located. A single up-link control channel occupying a narrow frequency band, can be utilized to receive dial up signals from a caller, and another single down link control channel can be utilized to ring up the called party located anywhere within the continental United States. The satellite antenna includes a matrix of feed horns that not only direct the beams in a controlled matrix onto the area of the continental United States, but also permit detection of the region from which the caller's signal is transmitted and the region from which the called party's answer is received, to enable the interconnection of signals received from these two regions. The system is particularly useful for rural areas.

Reilly, N. B.↗
NASA NTRS2001

Power and Efficiency Optimized in Traveling-Wave Tubes Over a Broad Frequency Bandwidth

A traveling-wave tube (TWT) is an electron beam device that is used to amplify electromagnetic communication waves at radio and microwave frequencies. TWT's are critical components in deep space probes, communication satellites, and high-power radar systems. Power conversion efficiency is of paramount importance for TWT's employed in deep space probes and communication satellites. A previous effort was very successful in increasing efficiency and power at a single frequency (ref. 1). Such an algorithm is sufficient for narrow bandwidth designs, but for optimal designs in applications that require high radiofrequency power over a wide bandwidth, such as high-density communications or high-resolution radar, the variation of the circuit response with respect to frequency must be considered. This work at the NASA Glenn Research Center is the first to develop techniques for optimizing TWT efficiency and output power over a broad frequency bandwidth (ref. 2). The techniques are based on simulated annealing, which has the advantage over conventional optimization techniques in that it enables the best possible solution to be obtained (ref. 3). Two new broadband simulated annealing algorithms were developed that optimize (1) minimum saturated power efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum power efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA coupled-cavity TWT computer model (ref. 4) and used to design optimal phase velocity tapers using the 59- to 64-GHz Hughes 961HA coupled-cavity TWT as a baseline model. In comparison to the baseline design, the computational results of the first broad-band design algorithm show an improvement of 73.9 percent in minimum saturated efficiency (see the top graph). The second broadband design algorithm (see the bottom graph) improves minimum radiofrequency efficiency with constant input power drive by a factor of 2.7 at the high band edge (64 GHz) and increases simultaneous bandwidth by 500 MHz.

Wilson, Jeffrey D.↗
NASA NTRS1986

Simulated performance of the NASA 30/20 GHz test transponder using multi-H phase coded modulation

The performance of a proposed NASA 30/20 GHz satellite communications system is studied for multi-h phase coded modulation (MHPM) schemes. The techniques used to model and simulate a satellite communications channel including transmitter, receiver, filters, nonlinearities, and interferers are presented. The performance of various MHPM schemes is compared for several different channel configurations. As a measure of performance, the probability of bit error vs Eb/NO is computed using a Monte Carlo simulation technique. It is found that, regardless of the channel configuration, MHPM schemes can provide power efficiency over serial minimum shift keying modulation.

Meader, C. B.↗
NASA NTRS1995

A new RF package suitable for aeronautical commercial and DSCS satellite applications

Higher levels of integration through the use of GaAs and silicon MMIC devices, a die-cast housing, and the reduction of the number of subassemblies has enabled a large reduction of the size and weight of the electronics package for commercial and military satellite communications. This paper presents an electronics architecture and hardware that utilizes many new integrated circuits and design techniques, and allows flexibility for future satellite frequency changes and expansion. Key features of the radio are extended C-band, InSat, Defense Satellite Communications System (DSCS), and Ku-band coverage options; 70 (or 140) MHz transponder bandwidth or L-band block bandwidth IFs; integrated RS-232 control through local handheld terminal or remote computer; remote control of crystal reference oscillator for aging and temperature compensation; integrated 2 or 5 watt solid-state power amplifiers (SSPA); optional integrated solid-state booster amplifiers to 40 watts; optional external amplifiers to 100 watts; integral beacon tracking with second integrated downcoverter for antenna positioning; radio, including low-noise block converter (LNB) and SSPA, weighs 8.5 kg and measures 32 x 23 x 16.5 cm; environmentally ruggedized for -40 to +60 C; O-ring sealed for waterproofing; passive (convection) cooling; and simple cabling and installation, with a single cable between radio and LNB, and two cables between radio and IF interface. The small size and light weight of the radio make it ideal for mounting on stabilized antenna platforms (gyroscopic or servo). Several input power options (110 or 220 VAC; +48, +12, or -24 VDC) facilitate operation on multiple platforms.

Hamilton, Robert J., Jr.↗