Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “communication satellites”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Satellite communication performance evaluation: Computational techniques based on moments

Computational techniques that efficiently compute bit error probabilities when only moments of the various interference random variables are available are presented. The approach taken is a generalization of the well known Gauss-Quadrature rules used for numerically evaluating single or multiple integrals. In what follows, basic algorithms are developed. Some of its properties and generalizations are shown and its many potential applications are described. Some typical interference scenarios for which the results are particularly applicable include: intentional jamming, adjacent and cochannel interferences; radar pulses (RFI); multipath; and intersymbol interference. While the examples presented stress evaluation of bit error probilities in uncoded digital communication systems, the moment techniques can also be applied to the evaluation of other parameters, such as computational cutoff rate under both normal and mismatched receiver cases in coded systems. Another important application is the determination of the probability distributions of the output of a discrete time dynamical system. This type of model occurs widely in control systems, queueing systems, and synchronization systems (e.g., discrete phase locked loops).

Omura, J. K.↗
NASA NTRS1980

Crossbar switching requirements for future multibeam TDMA communications satellites

Requirements for microwave switching in space, based on a frequency translating satellite are discussed. A 100 x 100 switch with a bandwidth of 2.5 GHz is considered for the more than 70 U.S. metropolitan areas with populations over half of a million. Switch architectures are outlined and switching devices, logic requirements, and reliability are described.

Hoffman, M.↗
NASA NTRS1980

Applications Technology Satellite and Communications Technology Satellite user experiments for 1967-1980 reference book. Volume 4: Abstracts

The important user experiments conducted during the fourteen year period from 1966 to 1980 are summarized. A description of each of the satellites and a brief summary of each user experiment is presented. A cross index of user experiments sorted by various parameters and a listing of keywords versus experiment number is included. The experiments are grouped by type of service offered; for example, education, health services, and data transmission. A bibliography of reports by accession number and by author is also presented. User viewpoints of the systems are presented.

Engler, N. A.↗
NASA NTRS1981

NASA to launch second business communications satellite

The two stage Delta 3910 launch vehicle was chosen to place the second small business satellite (SBS-B) into a transfer orbit with an apogee of 36,619 kilometers and a perigee of 167 km, at an inclination of 27.7 degrees to Earth's equator. The firing and separation sequence and the inertial guidance system are described as well as the payload assist module. Facilities and services for tracking and control by NASA, COMSAT, Intelsat, and SBS are outlined and prelaunch operations are summarized.

Source record↗
NASA NTRS1981

Modulation/demodulation techniques for satellite communications. Part 4: Appendices

The use of the Viterbi algorithm in a general context is examined. The generalized transfer function bounds are given which permit the following applications to be carried out: maximum likelihood demodulation of such bandwidth modulations as minimum-shift-keying and continuous phase frequency-shift-keying, demodulation of intersymbol interference and partial response signals, estimation and smoothing, and simultaneous phase synchronization, and data detection. Sufficient conditions are reviewed for tightening Chernoff and Rhattacharyya bounds.

Omura, J. K.↗
NASA NTRS1981

Scan performance of dual offset reflector antennas for satellite communications

The basic numerical steps of a method to analyze dual offset reflector antennas are reviewed. The technique employs an alternative approach to calculating the secondary pattern of an arbitrarily shaped offset dual reflector antenna, and is based on the application of the geometrical theory of diffraction from the subreflector and physical optics (PO) scattering from the main reflector. The PO integral is evaluated using the Jacobi-Bessel series expansions, and numerical results are presented for the off-axis scan performance of an offset clear aperture Cassegrain antenna. Results indicate that the equivalent paraboloid concept can be used to determine the location of displaced feed and define the local optimal focal plane, and the scan performance of the Cassegrain reflector can be improved if the feed is located on the true opimal surface.

Rahmat-Samii, Y.↗
NASA NTRS1982

30/20 GHz communications satellite multibeam antenna

A 20 GHz downlink satellite antenna design is described. The aperture simultaneously radiates 18 fixed, 0.3 deg width pencil beams directed at 18 cities distributed over CONUS for Trunking Service. All beams use the same trunk frequency allocation for 18 reuses of the band. The same aperture also radiates six additional 0.3 deg spot beams for Customer Premises Service (CPS) for TDMA beam hopping operation to small terminals anywhere in CONUS. Each CPS beam scans one sector of CONUS and all six beams are frequency reused in a CPS band. Offset dual reflector optics are used with a feed array and multiport beam forming network (BFN). For so many frequency reuses, sidelobes per beam must be 30 to 40 dB down over CONUS. Novel dual reflector optics were devised with shaped surfaces providing low aberrations for all beam positions over CONUS (+ or - 12 BW by + or - 5 BW). Scan loss under 1 dB is calculated with nearly constant sidelobes. For each beam position, a 7-element cluster of feeds is activated in the feed array with coefficients adjusted by the BFN to maintain low sidelobes and thus high beam isolation for frequency reuse.

Scott, W. G.↗
NASA NTRS1982

Centaur capabilities for communications satellite launches

The configurations, payload capabilities, and payload envelopes for Centaur in various applications are presented. The Centaur launch record is summarized and the Atlas/Centaur launch schedule is shown. Improvements in capability are reported on, and current and proposed vehicles are depicted. Dual Delta class spacecraft will be flown using a tandem adapter or large direct broadcast satellites in a single launch model. Shuttle/Centaur will permit spacecraft weights of up to 14,000 lb to be put into orbit, including payload lengths up to 40 ft. A new capability to transfer large deployed space systems from the Shuttle to high-altitude orbits at low thrusts will be available. Spacecraft lengths requiring the full, 60-foot cargo bay and weighing 20,000 lb could be placed in geosynchronous orbit with on-orbit rendezvous and assembly of the Centaur and spacecraft in low earth orbit.

Rector, W. F., III↗
NASA NTRS1982

Next generation communications satellites: multiple access and network studies

Efficient resource allocation and network design for satellite systems serving heterogeneous user populations with large numbers of small direct-to-user Earth stations are discussed. Focus is on TDMA systems involving a high degree of frequency reuse by means of satellite-switched multiple beams (SSMB) with varying degrees of onboard processing. Algorithms for the efficient utilization of the satellite resources were developed. The effect of skewed traffic, overlapping beams and batched arrivals in packet-switched SSMB systems, integration of stream and bursty traffic, and optimal circuit scheduling in SSMB systems: performance bounds and computational complexity are discussed.

Meadows, H. E.↗
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

Millimeter wave satellite communication studies. Results of the 1981 propagation modeling effort

Theoretical modeling associated with rain effects on millimeter wave propagation is detailed. Three areas of work are discussed. A simple model for prediction of rain attenuation is developed and evaluated. A method for computing scattering from single rain drops is presented. A complete multiple scattering model is described which permits accurate calculation of the effects on dual polarized signals passing through rain.

Stutzman, W. L.↗