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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Spatial frequency response of an optical heterodyne receiver

The principles of transfer function analysis are applied to a passive optical heterodyne receiver to obtain the modulation transfer function (MTF). MTF calculations are performed based on an optical platform which is imaging vertically varying profiles at worst case shuttle orbit altitudes. An analysis of the derogatory effects of sampling (aliasing) and central obscurations on both resolution and heterodyne efficiency is given. It is found that the cascading property of MTF analysis must be carefully applied since the coherent transfer function of the optical receiver and that due to the local oscillator-detector combination are not separable but are related by the convolution of their products. Application of these results to the specific case of a space-lab type optical heterodyne receiver shows that resolutions of the order of 1.5-2.0 Km are possible for worst-case type orbital scenarios. Further, comparison of obscured-type receivers (e.g., Cassegrains) with unobscured receivers shows that both resolution and efficiency are severely degraded in an obscured-type receiver and consequently should not be used for a passive heterodyne detection scheme.

Fales, C. L.↗
NASA NTRS1980

Thermal buffering of receivers for parabolic dish solar thermal power plants

A parabolic dish solar thermal power plant comprises a field of parabolic dish power modules where each module is composed of a two-axis tracking parabolic dish concentrator which reflects sunlight (insolation) into the aperture of a cavity receiver at the focal point of the dish. The heat generated by the solar flux entering the receiver is removed by a heat transfer fluid. In the dish power module, this heat is used to drive a small heat engine/generator assembly which is directly connected to the cavity receiver at the focal point. A computer analysis is performed to assess the thermal buffering characteristics of receivers containing sensible and latent heat thermal energy storage. Parametric variations of the thermal inertia of the integrated receiver-buffer storage systems coupled with different fluid flow rate control strategies are carried out to delineate the effect of buffer storage, the transient response of the receiver-storage systems and corresponding fluid outlet temperature. It is concluded that addition of phase change buffer storage will substantially improve system operational characteristics during periods of rapidly fluctuating insolation due to cloud passage.

Manvi, R.↗
NASA NTRS1980

Spatial frequency response of an optical heterodyne receiver

The analysis of a passive heterodyne receiver with respect to its imaging performance (transfer function) and its heterodyne efficiency shows departures from the results which are obtained in strictly coherent or incoherent imaging systems. The cascading property of modulation transfer function analysis must be carefully applied, since the coherent transfer function of the optical receiver and that due to the local oscillator-detector combination are not separable but are related by the convolution of their products. Application of these results to a spacelab-type optical heterodyne receiver shows that resolutions of the order of 1.5 to 2.0 km are possible for worst-case type orbital scenarios. In addition to an analysis of the derogatory effects of sampling (aliasing) a comparison of obscured-type receivers (e.g., Cassegrains) with unobscured receivers shows that both resolution and efficiency are severly degraded in an obscured-type receiver and, consequently, should not be used for passive heterodyne detection schemes.

Robinson, D. M.↗
NASA NTRS1982

Sideband-aided receiver arraying

Efforts to increase the amount of data that can be received from outer planet missions by coherently combining signals from ground antennas in such a way as to increase the total effective aperture of the receiving system are discussed. As these signals become weaker, the baseband arraying technique in current use degrades somewhat due to carrier jitter. One solution to this problem is Sideband-Aided Receiver Arraying (SARA). In SARA, sidebands demodulated to baseband in a master receiver at the largest antenna are used to allow slave receivers in the other antennas to track the sideband power in the signal rather than the carrier power. The already existing receivers can be used in the slaves to track and demodulate the signals in either a residual carrier or a suppressed carrier environment. The resultant baseband signals from all the antennas can then be combined using existing baseband combining equiment. Computer simulations of SARA show increases in throughput (measured in data bits per second) over baseband-only combining 17 percent at Voyager 2 Uranum encounter and 31 percent at Neptune for a four-element antenna array and (7, 1/2) convolutional coding.

Butman, S. A.↗
NASA NTRS1980

Performance of a near-optimum receiver for optical antipodal signals

The well known photon-counting, heterodyning and homodyning optical receivers (operating over a free-space channel) do not achieve the performance of the optimum quantum receiver, which attains significantly lower error-probabilities than the above receiver structures. A demonstration and analysis are given of a binary antipodal optical receiver that exponentially approaches the performance of the optimum quantum receiver. A general mathematical model is developed, and subsequently used to evaluate the effects of external interference and internal error-sources on receiver performance.

Vilnrotter, V. A.↗
NASA NTRS1985

Receiver For Solar Air Turbine

Solar receiver heats air to temperature high enough to drive gas turbine. Receiver has thermal output of about 70 kilowatts. Pointing downward at focal position of solar reflector, proposed receiver accepts intense concentrated sunlight. Although temperatures in receiver may rise to 1,500 degrees F (816 degrees C) or more, calculations show receiver loses less than 10 percent of insolation by convection through aperture. Receiver designed for 30-year life without scheduled maintenance or replacement.

Kofal, A.↗
NASA NTRS1985

Method of measuring sea surface water temperature with a satellite including wideband passive synthetic-aperture multichannel receiver

A wideband passive synthetic-aperture multichannel receiver with an antenna is mounted on a satellite which travels in an orbit above the Earth passing over large bodies of water, e.g., the Atlantic Ocean. The antenna is scanned to receive signals over a wide frequency band from each incremental surface area (pixel) of the water which are related to the pixel's sea temperature. The received signals are fed to several channels which are tuned to separate selected frequencies. Their outputs are fed to a processor with a memory for storage. As the antenna points to pixels within a calibration area around a buoy of known coordinates, signals are likewise received and stored. Exactly measured sea temperature is received from the buoy. After passing over several calibration areas, a forward stepwise regression analysis is performed to produce an expression which selects the significant from the insignificant channels and assigns weights (coefficients) to them. The expression is used to determine the sea temperature at each pixel based on the signals received therefrom. Wind temperature, pressure, and wind speed at each pixel can also be calculated.

Stacey, J. M.↗
NASA NTRS1986

A superconducting tunnel junction receiver for millimeter-wave astronomy

The development and construction of an ultralow noise heterodyne receiver for millimeter wave astronomy is described along with its use for 115.3 GHz Co line observations. The receiver uses a Superconductor-Insulator-Superconductor (SIS) quasiparticle tunnel junction mixer to convert the millimeter wave signal to a microwave intermediate frequency. Experiments aimed at quantitative verification of J. R. Tucker's quantum mixer theory are studied, to see whether it could be used as the basis for the design of a practical receiver. The experimental results were in excellent agreement with the theory, assuming the three frequency approximation. Infinite available gain and negative output resistance were observed for the first time, nonclassical effects which are not seen in conventional diode mixers. Using Tucker's theory, an SIS receiver was then designed and constructed. At 115 GHz, the single sideband receiver noise temperature is 83K, the lowest ever reported in this frequency range. A CO survey toward Cygnus-X region, using this SIS receiver on the Columbia-GISS 4 ft. telescope, is also described.

Pan, S. K.↗
NASA NTRS1988

Advanced sensible heat solar receiver for space power

NASA Lewis, through in-house efforts, has begun a study to generate a conceptual design of a sensible heat solar receiver and to determine the feasibility of such a system for space power applications. The sensible heat solar receiver generated in this study uses pure lithium as the thermal storage medium and was designed for a 7 kWe Brayton (PCS) operating at 1100 K. The receiver consists of two stages interconnected via temperature sensing variable conductance sodium heat pipes. The lithium is contained within a niobium vessel and the outer shell of the receiver is constructed of third generation rigid, fibrous ceramic insulation material. Reradiation losses are controlled with niobium and aluminum shields. By nature of design, the sensible heat receiver generated in this study is comparable in both size and mass to a latent heat system of similar thermal capacitance. The heat receiver design and thermal analysis was conducted through the combined use of PATRAN, SINDA, TRASYS, and NASTRAN software packages.

Bennett, Timothy J.↗
NASA NTRS1988

Telemetry SNR improvement using the DSN Advanced Receiver with results for Pioneer 10

A series of tracking tests was conducted in the spring of 1987 to demonstrate the reduced tracking threshold and the improved telemetry singal-to-noise-ratio performance of the DSN Advanced Receiver compared to current operational DSN systems. The Pioneer 10 spacecraft, which is now out of the solar system, was tracked on foud days. The Advanced Receiver achieved an improvement in telemetry SNR of 1 to 1.5 dB over the operational system. It was demonstrated that the spacecraft carrier signal is stable enough for tracking with a receiver carrier loop bandwidth of 0.5 Hz in the one-way mode and 0.1 Hz in the three-way mode, and that the Advanced Receiver is stable at 0.1 Hz. This reduces tracking threshold by 10 to 15 dB compared to current receivers, which have minimum loop bandwidths of 1 to 3 Hz. Thus, the Advanced Receiver will enable tracking of the Pioneer 10 spacecraft until its power source fails, circa 2000, which would not be possible with the current DSN system.

Hurd, W. J.↗
NASA NTRS1988

Advanced sensible heat solar receiver for space power

NASA Lewis, through in-house efforts, has begun a study to generate a conceptual design of a sensible heat solar receiver and to determine the feasibility of such a system for space power applications. The sensible heat solar receiver generated in this study uses pure lithium as the thermal storage medium and was designed for a 7 kWe Brayton (PCS) operating at 1100 K. The receiver consists of two stages interconnected via temperature sensing variable conductance sodium heat pipes. The lithium is contained within a niobium vessel and the outer shell of the receiver is constructed of third generation rigid, fibrous ceramic insulation material. Reradiation losses are controlled with niobium and aluminum shields. By nature of design, the sensible heat receiver generated in this study is comparable in both size and mass to a latent heat system of similar thermal capacitance. The heat receiver design and thermal analysis were conducted through the combined use of PATRAN, SINDA, TRASYS, and NASTRAN software packages.

Bennett, Timothy J.↗
NASA NTRS1991

Solar dynamic heat receiver technology

A full-size, solar dynamic heat receiver was designed to meet the requirements specified for electrical power modules on the U.S. Space Station, Freedom. The heat receiver supplies thermal energy to power a heat engine in a closed Brayton cycle using a mixture of helium-xenon gas as the working fluid. The electrical power output of the engine, 25 kW, requires a 100 kW thermal input throughout a 90 minute orbit, including when the spacecraft is eclipsed for up to 36 minutes from the sun. The heat receiver employs an integral thermal energy storage system utilizing the latent heat available through the phase change of a high-temperature salt mixture. A near eutectic mixture of lithium fluoride and calcium difluoride is used as the phase change material. The salt is contained within a felt metal matrix which enhances heat transfer and controls the salt void distribution during solidification. Fabrication of the receiver is complete and it was delivered to NASA for verification testing in a simulated low-Earth-orbit environment. This document reviews the receiver design and describes its fabrication history. The major elements required to operate the receiver during testing are also described.

Sedgwick, Leigh M.↗
NASA NTRS1992

A broadband THz receiver for low background space applications

We have developed a sensitive bolometric receiver for low background space applications. In a 10 percent bandwidth at 1 THz, this receiver is approximately 100 times more sensitive than a quantum limited heterodyne receiver with a 1 GHz IF bandwidth. This receiver is designed to be used for the long wavelength band (200-700 microns) in the MIPS instrument on NASA's SIRTF satellite. The bolometers are cooled to 100 mK by an adiabatic demagnetization refrigerator. Roughly 60 g of cesium chrome alum salt is partially demagnetized to 100 mK, followed by a slow regulated downramp to compensate for the heat leak. The hold time of the ADR system is about 18 hours with a temperature stability of delta T(sub rms) approx. equals 10 micro-K. The composite bolometers have electrical responsivities of 10(exp 9)V/W and electrical NEP's of about 3x10(exp -17) W/square root of Hz. The bolometer signals are read out by JFET preamplifiers located on the helium plate and operated at 120 K. We have addressed a number of space qualification issues, such as the development of an analog magnet controller, construction of a cryogenic shake-table for bolometers and selection of the paramagnetic salt CCA which can survive a bakeout at 50 C. The receiver is scheduled to be flown in the spring of 1992 on a balloon telescope. This flight has a dual purpose. One is to provide realistic test of the capabilities of the new receiver. The other is to search for anisotropies in the cosmic microwave background on scales of a few degrees.

Hagmann, C.↗
NASA NTRS1993

A low noise 665 GHz SIS quasi-particle waveguide receiver

Recent results on a 565-690 GHz SIS heterodyne receiver employing a 0.36 micron(sup 2) Nb/AlOx/Nb SIS tunnel junction with high quality circular non-contacting back short and E-plane tuners in a full height wave guide mount are reported. No resonant tuning structures were incorporated in the junction design at this time, even though such structures are expected to help the performance of the receiver. The receiver operates to at least the gap frequency of Niobium, approximately 680 GHz. Typical receiver noise temperatures from 565-690 GHz range from 160K to 230K with a best value of 185K DSB at 648 GHz. With the mixer cooled from 4.3K to 2K the measured receiver noise temperatures decreased by approximately 15 percent, giving roughly 180K DSB from 660 to 680 GHz. The receiver has a full 1 GHz IF pass band and was successfully installed at the Caltech Submillimeter Observatory in Hawaii.

Kooi, J. W.↗
NASA NTRS1997

Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receivers

A parametric study on cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, has been performed. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results in the two-phase regime. Results indicate that parametric changes in receiver gas inlet temperature and receiver heat input effects higher sensitivity to changes in receiver gas exit temperatures.

Hall, Carsie A., III↗
NASA NTRS2004

Navigator GPS Receiver for Fast Acquisition and Weak Signal Space Applications

NASA Goddard Space Flight Center (GSFC) is developing a new space-borne GPS receiver that can operate effectively in the full range of Earth orbiting missions from Low Earth Orbit (LEO) to geostationary and beyond. Navigator is designed to be a fully space flight qualified GPS receiver optimized for fast signal acquisition and weak signal tracking. The fast acquisition capabilities provide exceptional time to first fix performance (TIFF) with no a priori receiver state or GPS almanac information, even in the presence of high Doppler shifts present in LEO (or near perigee in highly eccentric orbits). The fast acquisition capability also makes it feasible to implement extended correlation intervals and therefore significantly reduce Navigator s acquisition threshold. This greatly improves GPS observability when the receiver is above the GPS constellation (and satellites must be tracked from the opposite side of the Earth) by providing at least 10 dB of increased acquisition sensitivity. Fast acquisition and weak signal tracking algorithms have been implemented and validated on a hardware development board. A fully functional version of the receiver, employing most of the flight parts, with integrated navigation software is expected by mid 2005. An ultimate goal of this project is to license the Navigator design to an industry partner who will then market the receiver as a commercial product.

Winternitz, Luke↗
NASA NTRS2000

Adaptive Detector Arrays for Optical Communications Receivers

The structure of an optimal adaptive array receiver for ground-based optical communications is described and its performance investigated. Kolmogorov phase screen simulations are used to model the sample functions of the focal-plane signal distribution due to turbulence and to generate realistic spatial distributions of the received optical field. This novel array detector concept reduces interference from background radiation by effectively assigning higher confidence levels at each instant of time to those detector elements that contain significant signal energy and suppressing those that do not. A simpler suboptimum structure that replaces the continuous weighting function of the optimal receiver by a hard decision on the selection of the signal detector elements also is described and evaluated. Approximations and bounds to the error probability are derived and compared with the exact calculations and receiver simulation results. It is shown that, for photon-counting receivers observing Poisson-distributed signals, performance improvements of approximately 5 dB can be obtained over conventional single-detector photon-counting receivers, when operating in high background environments.

Vilnrotter, V.↗
NASA NTRS1999

Precise Clock Solutions Using Carrier Phase from GPS Receivers in the International GPS Service

As one of its activities as an Analysis Center in the International GPS Service (IGS), the Jet Propulsion Laboratory (JPL) uses data from a globally distributed network of geodetic-quality GPS receivers to estimate precise clock solutions, relative to a chosen reference, for both the GPS satellites and GPS receiver internal clocks, every day. The GPS constellation and ground network provide geometrical strength resulting in formal errors of about 100 p sec for these estimates. Some of the receivers in the global IGS network contain high quality frequency references, such as hydrogen masers. The clock solutions for such receivers are smooth at the 20-p sec level on time scales of a few minutes. There are occasional (daily to weekly) shifts at the microsec level, symptomatic of receiver resets, and 200-p sec-level discontinuities at midnight due to 1-day processing boundaries. Relative clock solutions among 22 IGS sites proposed as "fiducial" in the IGS/BIPM pilot project have been examined over a recent 4-week period. This allows a quantitative measure of receiver reset frequency as a function of site. For days and-sites without resets, the Allan deviation of the relative clock solutions is also computed for subdaily values of tau..

Zumberge, J. F.↗