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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

A Transmittance-optimized, Point-focus Fresnel Lens Solar Concentrator

The development of a point-focus Fresnel lens solar concentrator for high-temperature solar thermal energy system applications is discussed. The concentrator utilizes a transmittance-optimized, short-focal-length, dome-shaped refractive Fresnel lens as the optical element. This concentrator combines both good optical performance and a large tolerance for manufacturing, deflection, and tracking errors. The conceptual design of an 11-meter diameter concentrator which should provide an overall collector efficiency of about 70% at an 815 C (1500 F) receiver operating temperature and a 1500X geometric concentration ratio (lens aperture area/receiver aperture area) was completed. Results of optical and thermal analyses of the collector, a discussion of manufacturing methods for making the large lens, and an update on the current status and future plans of the development program are included.

Oneill, M. J.↗
NASA NTRS1984

Spectroscopy and transmittances for the LIMS experiment

The Limb Infrared Monitor of the Stratosphere (LIMS) instrument on the Nimbus 7 spacecraft sensed limb emission profiles for 7 months, starting in October 1979. Vertical temperature profiles are inferred from measurements in two CO2 channels, and constituent profiles are obtained form the O3, HNO3, NO2, and water vapor channels. The line parameters used to calculate transmittances in the retrieval algorithm are presented. Their adequacy for LIMS and for other applications are assessed, and recommendations for future investigations are outlined.

Drayson, S. R.↗
NASA NTRS1984

Increase of antenna area instead of transmitter power, part 6.3A

An extension of the antenna area may be preferred to an increase of transmitter power, when it is considered that reflection often dominates the scatter contribution at near zenith angles. It is noticed that an increase of the antenna area A, linearly increases the contribution of reflection. This most likely occur at vertical incidence, since the mean generalized refractive index gradient (M) is largest in the vertical direction. The altitude ranges at which the echo power gets weak and we have to consider improvements of sensitivity are mostly larger than 5 to 8 km. It follows that the considerations are valid up to antenna diameters close to 200 m for wavelengths of 6 m. On the other hand the reflected component has to be larger than the scattered component which only holds for near zenith angles.

Rottger, J.↗
NASA NTRS1985

Spectral broadening of VLF transmitter signals observed on DE 1 - A quasi-electrostatic phenomenon?

Spectrally broadened VLF transmitter signals are observed on the DE 1 satellite using alternatively both electric and magnetic field sensors. It is found that at times when the electric field component undergoes significant bandwidth expansion (up to about 110 Hz) the magnetic field component has a bandwidth of less than 10 Hz. The results support the theory that the off-carrier components are quasi-electrostatic in nature. Measurement of the absolute E and B field magnitudes of the broadened signals are used to determine the wave Poynting vector. It is found that the observed power levels can be understood without invoking any strong amplification process that operates in conjunction with the spectral broadening. The implications of this finding in distinguishing among the various possible mechanisms for spectral broadening are discussed.

Inan, U. S.↗
NASA NTRS1986

Mark 4A DSN receiver-exciter and transmitter subsystems

The present configuration of the Mark 4A DSN Receiver-Exciter and Transmitter Subsystems is described. Functional requirements and key characteristics are given to show the differences in the capabilities required by the Networks Consolidation task for combined High Earth Orbiter and Deep Space Network tracking support.

Wick, M. R.↗
NASA NTRS1986

Measurements of Siple transmitter signals on the DE 1 satellite - Wave normal direction and antenna effective length

A new experimental technique is developed to simultaneously measure the wave propagation direction and the effective length of a small (L value much smaller than wavelength) electric dipole antenna on a spin-stabilized satellite in the magnetosphere. The technique relies on the near simultaneous measurement of single components of the electric and magnetic fields of a coherent VLF signal injected into the medium from a ground-based source. The spin fading characteristics of the signal received by the electric dipole and the magnetic loop antenna permit the measurement of the wave normal direction assuming whistler-mode propagation. In-situ and remote measurements of the local cold plasma density are used to determine the refractive index. The wave electric field is then inferred from the wave magnetic field as measured on the loop antenna, the refractive index and the direction of propagation. Comparing this electric field with the measured voltage across the dipole antenna leads to the determination of the effective length of the receiving electric dipole. The technique is applied to data from the Dynamics Explorer 1 satellite observations of whistler mode signals injected into the magnetosphere from the Siple, Antarctica, VLF transmitter. In one case, with the measured background cold plasma density being 15 el/cu cm, the effective length of the 200 m-long electric dipole antenna is found to be 222 + or - 56 m, i.e., about twice the conventional value.

Sonwalker, V. S.↗
NASA NTRS1985

A new type of VLF emission triggered at low altitude in the subauroral region by Siple Station VLF transmitter signals

The present paper has the objective to report the existence of a new phenomenon in which coherent VLF signals from the Siple Station VLF transmitter (Antarctica, 76 deg S, 84 deg W) are observed to trigger a new type of VLF emission, taking into account the propagation of these signals upward through the ionosphere and low-altitude magnetosphere to the ISIS 2 satellite at 1400 km altitude. The existence of the impulsive emission (IE) effect lends credence to the idea that coherent VLF signals can act as catalysts to trigger natural plasma instabilities in the subauroral ionosphere and lower magnetosphere. Controlled studies of these instabilities may, therefore, be possible.

Bell, T. F.↗
NASA NTRS1986

Long-term amplitude and phase stability of the 400-kW 2.115-GHz transmitter

Results of recent measurements of the long-term phase, amplitude and group delay stability of the 400-kW S-band (2.115-GHz) transmitter are reported. Various control parameters which are responsible for many of the observed instabilities are identified. Further tests to identify the parameters responsible for the remaining instabilities are suggested.

Hoppe, D. J.↗
NASA NTRS1987

Phase noise measurements of the 400-kW, 2.115-GHz (S-band) transmitter

The measurement theory is described and a test method to perform phase noise verification using off-the-shelf components and instruments is presented. The measurement technique described consists of a double-balanced mixer used as phase detector, followed by a low noise amplifier. An FFT spectrum analyzer is then used to view the modulation components. A simple calibration procedure is outlined that ensures accurate measurements. A block diagram of the configuration is presented as well as actual phase noise data from the 400 kW, 2.115 GHz (S-band) klystron transmitter.

Boss, P.↗
NASA NTRS1987

An overview of DREV's activities on pulsed CO2 laser transmitters: Frequency stability and lifetime aspects

After introducing the desired features in a transmitter for laser radar applications, the output characteristics of several configurations of frequency-stable TEA-CO2 lasers are reviewed. Based on work carried out at the Defence Research Establishment Valcartier (DREV), output pulses are examined from short cavity lasers, CW-TEA hybrid lasers, and amplifiers for low power pulses. It is concluded that the technique of injecting a low-power laser beam into a TEA laser resonator with Gaussian reflectivity mirrors should be investigated because it appears well adapted to producing high energy, single mode, low chirp pulses. Finally, a brief report on tests carried out on catalysts composed of stannic oxide and noble metals demonstrates the potential of these catalysts, operating at close to room temperature, to provide complete closed-cycle laser operation.

Cruickshank, James↗
NASA NTRS1987

Reduction of ground noise in the transmitter crowbar instrumentation system by the use of baluns and other noise rejection methods

Electrical noise interference in the transmitter crowbar monitoring instrumentation system creates false sensing of crowbar faults during a crowbar firing. One predominant source of noise interference is the conduction of currents in the instrumentation cable shields. Since these circulating ground noise currents produce noise that is similar to the crowbar fault sensing signals, such noise interference reduces the ability to determine true crowbar faults.

Daeges, J.↗
NASA NTRS1986

Lidar telescope overlap function and effects of misalignment for unstable resonator transmitter and coherent receiver

Effects of lidar telescope overlap function modeling on the accuracy of aerosol backscatter measurements are discussed. The treatment pertains primarily to a lidar arrangement which combines high sensitivity and a large degree of geometrical signal compression but places stringent requirements on the accuracy of the overlap function modeling - coherent IR lidar with noncoaxial (side-by-side) transmit and receive telescopes. A model is presented which includes an unstable resonator transmitter and accommodates both coaxial and noncoaxial arrangements, and comparison is made to experimental results including effects of misalignment.

Ancellet, G. M.↗
NASA NTRS1988

Standards For Bidirectional Reflectance And Transmittance

Sample-to-sample variations reduced. Improved reference or standard samples for measurement of bidirectional reflectance or transmittance distribution functions made by depositing single layers of spheres of same size on flat surfaces. New reference samples replicated easily and consistently, durable with moderate care. Used to reconcile different measurement facilities.

Witherow, William K.↗
NASA NTRS1988

Calculating Optical-Transmitter Radiation Pattern s

New formula gives more-accurate gains and pointing losses. Set of approximate formulas predicts angular dependence of far radiation field coherent optical transmitter, telescope having central obscuring disk. Formulas derived without recourse to simplifying assumption of uniform plane-wave illumination used to derive less-accurate traditional formulas.

Marshall, William K.↗
NASA NTRS1988

Legislated emergency locating transmitters and emergency position indicating radio beacons

An emergency locating transmitting (ELT) system comprising a legislated ELT modified with an interface unit and connected by a multiwire cable to a remote control monitor (RCM), typically located at the pilot position. The RCM can remotely (1) test the ELT by disabling the legislated swept tone and allowing transmission of a single tone, (2) turn the ELT "on" for the legislated ELT transmission, and (3) reset the ELT to an "armed" condition. The RCM also provides visual and audio indications for transmitter operating condition as well as ELT battery condition. Removing the RCM or shorting or opening the interface input connections will not affect traditional ELT operation.

William R Wade↗
NASA NTRS1988

Transmitter data collection using Ada

A data collection system installed on the 400 kilowatt X-band transmitter of the Goldstone Solar System Radar is described. The data collection system is built around the off-the-shelf IEEE 488 instrumentation, linked with fiber optics, controlled by an inexpensive computer, and uses software written in the Ada language. The speed and accuracy of the system is discussed, along with programming techniques used for both data collection and reduction.

Conroy, B. L.↗
NASA NTRS1989

Thermal measurements of microwave transmitter feedhorn window

Thermal measurements of microwave transmitter feedhorn windows were performed using an imaging infrared radiometer. The measurement technique is described and results are presented for windows made of 0.001-in. Kapton (trademark of Dupont Chemical Co.) and 0.1-in. HTP-6 (Space Shuttle tile material). Measured and calculated temperatures agree well.

Perez, R. M.↗