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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Mission support plan STS-2

The plan defines the anticipated GSTDN/DOD station support and configuration requirements for a nominal flight with an orbital inclination of 38.4 degrees and a circular orbit of 120 nautical miles for the first 5 orbits and 137 nautical miles thereafter. A complete set of preliminary site configuration messages (SCM) define nominal station AOS/LOS times and configurations for S-Band and UHF support. This document is intended for use as a planning tool, providing the necessary guidelines and data base for SCM generation in support of STS-2.

Ibanez, F.↗
NASA NTRS1982

Land Mobile Satellite Service (LMSS): A conceptual system design and identification of the critical technologies. Part 1: Executive summary

A system design for a satellite aided land mobile service is described. The advanced system is based on a geostationary satellite which employs a large UHF reflector to communicate with small user antennas on mobile vehicles. It is shown that the system through multiple beam antennas and frequency reuse provides for radiotelephone and dispatch channels. It is concluded that the system is technologically feasible to provide service to rural and remote regions.

Naderi, F.↗
NASA NTRS1982

Land Mobile Satellite Service (LMSS): A conceptual system design and identification of the critical technologies: Part 2: Technical report

A conceptual system design for a satellite-aided land mobile service is described. A geostationary satellite which employs a large (55-m) UHF reflector to communicate with small inexpensive user antennas on mobile vehicles is discussed. It is shown that such a satellite system through multiple beam antennas and frequency reuse can provide thousands of radiotelephone and dispatch channels serving hundreds of thousands of users throughout the U.S.

Naderi, F.↗
NASA NTRS1982

LMSS communication network design

The architecture of the telecommunication network as the first step in the design of the LMSS system is described. A set of functional requirements including the total number of users to be served by the LMSS are hypothesized. The design parameters are then defined at length and are systematically selected such that the resultant system is capable of serving the hypothesized number of users. The design of the backhaul link is presented. The number of multiple backhaul beams required for communication to the base stations is determined. A conceptual procedure for call-routing and locating a mobile subscriber within the LMSS network is presented. The various steps in placing a call are explained, and the relationship between the two sets of UHF and S-band multiple beams is developed. A summary of the design parameters is presented.

Source record↗
NASA NTRS1982

Cassegrain dual reflector antenna design

A folded optics reflector system could mitigate problems associated with the pointability and controllability of the large UHF antenna for MSAT. Such a system is comprised of a parabolic main reflector and a hyperboloidal subreflector (Cassegrain arrangement) or an ellipsoidal subreflector (Gregorian arrangement), either of which brings the feed closer to the main reflector. By shaping the subreflector and the main reflector, an improved scan capability might be achieved and the size of the required feed aperture-per-beam could be reduced. In such a shaped dual reflector system, the need for overlapping cluster feed arrangement and its concomitant beam forming network could be removed. In this system, a relatively low gain feed element together with the shaped subreflector would be sufficient to produce the required high illumination taper that at the main reflector.

Source record↗
NASA NTRS1981

Shuttle STS-2 mission communication systems RF coverage and performance predictions. Volume 1: Ascent

The RF communications capabilities and nominally expected performance for the ascent phase of the second orbital flight of the shuttle are provided. Predicted performance is given mainly in the form of plots of signal strength versus elapsed mission time for the STDN (downlink) and shuttle orbiter (uplink) receivers for the S-band PM and FM, and UHF systems. Performance of the NAV and landing RF systems is treated for RTLS abort, since in this case the spacecraft will loop around and return to the launch site. NAV and landing RF systems include TACAN, MSBLS, and C-band altimeter. Signal strength plots were produced by a computer program which combines the spacecraft trajectory, antenna patterns, transmit and receive performance characteristics, and system mathematical models. When available, measured spacecraft parameters were used in the predictions; otherwise, specified values were used. Specified ground station parameter values were also used. Thresholds and other criteria on the graphs are explained.

Porter, J. A.↗
NASA NTRS1983

STS-3/OSS-1 Plasma Diagnostics Package (PDP) measurements of the temperature pressure and plasma

Designed to withstand the thermal extremes of the STS-3 mission through the use of heaters and thermal blankets, the plasma diagnostics package sat on the release/engagement mechanism on the OSS-1 payload pallet without a coldplate and was attached to the RMS for two extended periods. Plots show temperature versus mission elapsed time for two temperature sensors. Pressure in the range of 10 to the -3 power torr and 10 to the -7 power torr, measured 3 inches from the skin of the package is plotted against GMT during the mission. The most distinctive feature of the pressure profile is the modulation at the obit period. It was found that pressure peaks when the atmospheric gas is rammed into the cargo bay. Electric and magnetic noise spectra and time variability due to orbiter systems, UHF and S-band transmitter field strengths, and measurements of the ion spectra obtained both in the cargo bay and during experiments are plotted.

Shawhan, S. D.↗
NASA NTRS1983

STS-3/OSS-1 Plasma Diagnostics Package (PDP) measurements of Orbiter transmitter and subsystem electromagnetic interference

The plasma diagnostics package receiver system is described to identify the various antennas and to characterize the complement of receivers which cover the frequency range of 30 Hz to 800 Hz and S-band at 2200 + or - 300 MHz. Sample results are presented to show the variability of electromagnetic effects associated with the orbiter and the time variability of these effects. The electric field and magnetic field maximum and minimum field strength spectra observed during the mission at the pallet location are plotted. Values are also derived for the maximum UHF transmitter and S-band transmitter field strengths. Calibration data to convert from the survey plots to actual narrowband and broadband field strengths are listed.

Shawhan, S. D.↗
NASA NTRS1982

Lightning strike experience in the NASA F-106B storm hazards program

A heavily instrumented F-106B aircraft was flown in thunderstorms to gather data for characterizing lightning at aircraft operating altitudes. Conventional weather finding techniques are supplemented with UHF lightning mapping radar to select the most active storm cells and the most likely altitude for obtaining direct lightning strikes to the airplane. One hundred seventy-six strikes were obtained in a 3 year period, mostly at an altitude of above 25,000 feet.

Norman L Crabill↗
NASA NTRS1984

The influence of ground conductivity on the structure of RF radiation from return strokes

The combination of the finite conductivity of the Earth plus the propagation of the return stroke current up the channel which results in an apparent time delay between the fast field changes and RF radiation for distant observers is shown. The time delay predicted from model return strokes is on the order of 20 micro and the received signal has the characteristics of the data observed in Virginia and Florida. A piecewise linear model for the return stroke channel and a transmission line model for current propagation on each segment was used. Radiation from each segment is calculated over a flat Earth with finite conductivity using asymptotics approximations for the Sommerfeld integrals. The radiation at the observer is processed by a model AM radio receiver. The output voltage was calculated for several frequencies between HF-UHF assuming a system bandwidth (300 kHz) characteristic of the system used to collect data in Florida and Virginia. Comparison with the theoretical fast field changes indicates a time delay of 20 microns.

Levine, D. M.↗
NASA NTRS1983

Interpretation of radar returns from clear air: Discrimination against clutter

Different kinds of inteference may cause problems to the proper detection and analysis of the atmospheric signals, when using VHF and UHF radars. These are separated into passive and active contributions. Passive contributions are existent in the receiving system without the radar transmitter switched on. Active contributions are due to scatter and reflection of the own transmitted radar signal from unwanted targets, which are called clutter. Of major importance to radar systems are active interference contributions. Different methods can be applied for elimination or at least suppressing unwanted effects. These are; (1) Directional filtering, i.e., applying optimum suppression of antenna sidelobes, (2) Range filtering, i.e., suppressing unwanted signals only in affected range gates, (3) selection by amplitude distributions, (4) Temporal filtering, i.e., recognizing typical temporal variations of the clutter signals, through spectral characteristics, and applying matched filters.

Rottger, J.↗
NASA NTRS1983

Capabilities and limitations of EISCAT as an MST radar

The European Incoherent Scatter Radar Facility also has facilities which can be used for coherent scatter research of the middle atmosphere. The observatory consists of two independent systems which allow observations of the upper, middle, and lower atmosphere: a tristatic UHF radar capable of vector drift measurements, and a monostatic VHF system. The characteristics of the components are are described including inter-site communication, on-line displays, and the real-time operating system. Analysis of about 60 hours of middle atmosphere observations in 1982 indicate that EISCAT's capabilities to measure mesospheric parameters should improve during moderately or strongly disturbed conditions, enabling measurement of profiles of wind velocity, electron density, and temperature/collision frequency, and in some instances, ion masses. Because of not yet optimized transmit-receive switching, some limitations exist in the monostatic mode when observing coherent scattering in the stratosphere at short ranges.

Rottger, J.↗
NASA NTRS1984

Conditions for lightning strikes to an airplane in a thunderstorm

Conditions conducive to lightning strikes on aircraft were determined through the 1982 Storm Hazards Program. UHF-radar and SPANDAR were used to guide a NASA F-106B research aircraft through the upper regions of active thunderstorms to facilitate direct lightning strikes to the aircraft. Analysis of radar echoes from lightning at the moments of the strikes suggests that the aircraft itself triggers the lightning, in both stormy and nonstormy clouds, and that the induced flashes are not much different from naturally occurring intra-cloud flashes. The highest risk for a direct strike in the upper portions of a thunderstorm occurred where the ambient temperature was -40 C or colder, where turbulence and precipitation were negligible to light, and where the lightning flash rate was no greater than 5 flashes per minute.

Mazur, V.↗
NASA NTRS1984

F layer ionization patches in the polar cap

Ground-based optical and digital ionosonde measurements were conducted at Thule, Greenland to measure ionospheric structure and dynamics in the nighttime polar cap F layer. These observations showed the existence of large-scale (800-1000 km) plasma patches drifting in the antisunward direction during a moderately disturbed (Kp greater than or equal to 4) period. Simultaneous Dynamics Explorer (DE-B) low-altitude plasma instrument (LAPI) measurements show that these patches with peak densities of about 10 to the 6th el per cu cm are not locally produced by structured particle precipitation. The LAPI measurements show a uniform precipitation of polar rain electrons over the polar cap. The combined measurements provide a comprehensive description of patch structure and dynamics. They are produced near or equatorward of the dayside auroral zone and convect across the polar cap in the antisunward direction. Gradients within the large scale, drifting patches are subject to structuring by convective instabilities. UHF scintillation and spaced receiver measurements are used to map the resulting irregularity distribution within the patches.

Weber, E. J.↗
NASA NTRS1984

Thermal considerations in the use of solid state power amplifiers on the GOES spacecraft

The use of solid state power amplifiers (SSPA) in satellites has been quite prevalent in several frequency bands. This trend is evidenced by the use of SSPAs at Hughes in the UHF band (Leasat/Syncom IV), S band (GOES), C band (Telstar), and SHF band. The junction temperature of the transistor is the driving requirement which determines the lifetime of the transistor, SSPA, and the payload. This temperature is determined by the transistor characteristics, use of the device, and mounting temperature of the SSPA. The temperature of the spacecraft in the area of the SSPA can be controlled by active or passive means. The various factors and interrelationships used to calculate and control the temperatures of SSPAs are described. The thermal design and calculation of junction temperatures are exemplified with the Geostationary Operational Environmental Satellite spacecraft.

Mallette, L.↗
NASA NTRS1984

Characteristics of lightning strikes experienced by the NASA F-1068 airplane

Thunderstorm penetrations were made during the 1980-1983 thunderstorm seasons by a NASA F-106B instrumented research aircraft in order to record lightning strike data and associated flight conditions. In 1980 and 1981, 10 direct lightning hits were received each year, with most penetrations occurring near the freezing level. In 1982 and 1983, a ground-based UHF-band radar was used to guide this aircraft through the upper, electrically active regions of thunderstorms (at altitudes above 6 km, corresponding to temperatures of less than -20 C), and 370 direct hits were recorded. The results of analyses of the radar, photographic, and surface inspection data are presented. The highest risk of lightning strike in the upper portions of a thundercloud occurred in regions where the ambient temperature was -40 to -50 C. Lightning strikes appear to be triggered by the aircraft.

Fisher, B. D.↗
NASA NTRS1984

Measurements of electromagnetic interference on OV102 Columbia using the plasma diagnostics package

The third Space Shuttle mission's OSS-1 payload included 30 Hz-800 MHz and S-band receivers which assessed the intentional (transmitter) and unintentional (subsystem) EMI levels. It was noted that, at the pallet location, the UHF voice downlink transmitter field strengths did not exceed 0.1 V/m. At the remote manipulator system, the figure was 0.5 V/m. Below 300 kHz, the magnetic field noise was 30 dB pT + or - 20 dB, while the electric field noise was broadband and variable over at least 60 dB, depending on thruster firings and Orbiter attitude. This noise may have been generated by the Orbiter's interaction with the ambient plasma.

Shawhan, S. D.↗
NASA NTRS1984

A proof-of-principle getaway special free-flying satellite demonstration

An air traffic control radar calibration satellite is described that will be used by the U.S. Federal Aviation Administration, U.S. military agencies and cooperating governments around the world to measure antenna patterns associated with the existing international air traffic control network. The satellite will employ three L-band receivers, a UHF command receiver, a VHF telemetry transmitter, associated antennas, a microprocessor, fixed solar arrays, and a power supply to acquire, store and forward signal strength data from some of the tracking radars. A second satellite is planned for launch in 1986 into a high altitude polar orbit with a lifetime of several years in order to provide a long-lived calibration service to the entire international air traffic control system. The initial satellite and associated ground station are being designed and built by a volunteer consortium of three educational institutions and more than a dozen aerospace companies. Following this initial demonstration of a free-flying Getaway Special satellite, a substantial number of organizations are contemplating commercial uses of the concept. Discussions are being held with NASA concerning the establishing of an appropriate fee for this new class of service.

Moore, R. G.↗