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NASA NTRS2005

Atmospheric Electron-induced X-Ray Spectrometer (AEXS) Instrument Development

Instrument Development: The membrane properties were investigated in detail due to its critical role. A series of experiments determined that our designed membranes have high electron transmission, yet are capable of isolating high vacuum, are able to withstand differential pressure in excess of one atmosphere, survive vibrational shocks of a magnitude to be expected during a planetary mission. Our initial work has been with a 10 keV source and a 200 nm thick Silicon Nitride (SiN) encapsulation membrane micro-fabricated within a Si support frame (1.5 mm x 1.5 mm window openings. Fig 2 compares the spectra taken with the 10 keV source with spectra taken within SEM. Introduction: This paper describes the progress in the development of the AEXS instrument in our laboratory at JPL. The AEXS is a novel miniature instrument[1-3] based on the excitation of characteristic X-Ray Fluorescence (XRF) and luminescence spectra using a focused electron beam, for non-destructive evaluation of surfaces of samples in planetary ambient atmosphere. In situ operation is obtained through the use of a thin electron transmissive membrane to isolate the vacuum within the AEXS electron source from the outside ambient atmosphere. The impinging electrons excite XRF spectra from the irradiated spots on samples in external atmosphere with high-to-medium (sub-mm to cm-scale) spatial resolution at Mars atmospheric pressure. The XRF spectra are analyzed using an energy-dispersive detector to determine surface elemental composition, or in the case of electron-induced luminescence to identify unusual formations on surface that cathodo-luminescence (CL). The AEXS system (Fig 1) consists of a high-energy (>10keV) electron gun encapsulated by the isolation membrane, an EDX detection and analyzer system to determine the elemental abundance, an optional CL detection system, and a high voltage power supply. The approach to demonstrating a proof of concept of the AEXS has been through 1) demonstrating the viability of micro-fabricated membranes, 2) assembling AEXS setups with increasingly integrated functional components, and 3) simulating the AEXS observational capabilities. This paper will focus on description of the development of the instrument.

Wilcox, J. Z.↗
NASA NTRS2008

Variations of Strahl Properties with Fast and Slow Solar Wind

The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general build solar wind speed could provide some insight into the source, origin, and evolution of the strahl.

Figueroa-Vinas, Adolfo↗
NASA NTRS1995

Integrated Cryogenic Satellite Communications Cross-Link Receiver Experiment

An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies; high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle's 'HitchHiker' carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 2.048 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver's performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology.

Romanofsky, R. R.↗
NASA NTRS1978

Gravitational N-body problem on the accretion process of terrestrial planets

Numerical integration of the gravitational N-body problem has been carried out for a variety of protoplanetary clusters in the range N = 100 to 200. Particles are assumed to coagulate at collisions irrespective of relative velocity and mass ratio of the particles. It is shown graphically how the dispersed N-bodies accumulate to a single planet through mutual collisions. The velocity distribution and size distribution of bodies are also investigated as functions of time in the accretion process. Accretion rates of planets are found to be dependent strongly on the initial number density distribution, the initial size distribution, and the initial velocity distribution of bodies. Formation of satellites of about 10% in the planet mass is common to most cases in the present study. A substantial mass of bodies also escapes from the cluster. Many satellites and escapers formed during the accretion process of planets may be source materials of heavy bombardment in the early history of planets.

Matsui, T.↗
NASA NTRS1959

Some effects of vibration and rotation on the drift of gyroscopic instruments

It is the purpose of this paper to describe and indicate possible analytical approaches to some of the most significant mechanisms by which vibration induced drifts may occur, and to indicate, where possible, some means of alleviating them. In all cases we will not consider gimbal bearing friction, mass unbalance or other sources of steady extraneous torques on the gyro rotor. The mechanisms to be discussed are: Non-Newtonian viscosity in single degree of freedom (SDF) integrating-rate gyros, nonisoelasticity in SDF gyros, noncommutative effects for SDF stabilized platform, gimbal inertia effects, 2 DF gyros, and spin axis torque coupling in 2 DF gyros. High-frequency elastic resonances are not discussed explicitly in detail, because they are a more familiar problem and one which depends strongly on the details of each particular gyro design.

Viscous Torque↗
NASA NTRS1986

Swept frequency technique for dispersion measurement of microstrip lines

Microstrip lines used in microwave integrated circuits are dispersive. Because a microstrip line is an open structure, the dispersion can not be derived with pure TEM, TE, or TM mode analysis. Dispersion analysis has commonly been done using a spectral domain approach, and dispersion measurement has been made with high Q microstrip ring resonators. Since the dispersion of a microstrip line is fully characterized by the frequency dependent phase velocity of the line, dispersion measurement of microstrip lines requires the measurement of the line wavelength as a function of frequency. In this paper, a swept frequency technique for dispersion measurement is described. The measurement was made using an automatic network analyzer with the microstrip line terminated in a short circuit. Experimental data for two microstrip lines on 10 and 30 mil Cuflon substrates were recorded over a frequency range of 2 to 20 GHz. Agreement with theoretical results computed by the spectral domain approach is good. Possible sources of error for the discrepancy are discussed.

Lee, R. Q.↗
NASA NTRS2008

Hyperspectral Fluorescence and Reflectance Imaging Instrument

The system is a single hyperspectral imaging instrument that has the unique capability to acquire both fluorescence and reflectance high-spatial-resolution data that is inherently spatially and spectrally registered. Potential uses of this instrument include plant stress monitoring, counterfeit document detection, biomedical imaging, forensic imaging, and general materials identification. Until now, reflectance and fluorescence spectral imaging have been performed by separate instruments. Neither a reflectance spectral image nor a fluorescence spectral image alone yields as much information about a target surface as does a combination of the two modalities. Before this system was developed, to benefit from this combination, analysts needed to perform time-consuming post-processing efforts to co-register the reflective and fluorescence information. With this instrument, the inherent spatial and spectral registration of the reflectance and fluorescence images minimizes the need for this post-processing step. The main challenge for this technology is to detect the fluorescence signal in the presence of a much stronger reflectance signal. To meet this challenge, the instrument modulates artificial light sources from ultraviolet through the visible to the near-infrared part of the spectrum; in this way, both the reflective and fluorescence signals can be measured through differencing processes to optimize fluorescence and reflectance spectra as needed. The main functional components of the instrument are a hyperspectral imager, an illumination system, and an image-plane scanner. The hyperspectral imager is a one-dimensional (line) imaging spectrometer that includes a spectrally dispersive element and a two-dimensional focal plane detector array. The spectral range of the current imaging spectrometer is between 400 to 1,000 nm, and the wavelength resolution is approximately 3 nm. The illumination system consists of narrowband blue, ultraviolet, and other discrete wavelength light-emitting-diode (LED) sources and white-light LED sources designed to produce consistently spatially stable light. White LEDs provide illumination for the measurement of reflectance spectra, while narrowband blue and UV LEDs are used to excite fluorescence. Each spectral type of LED can be turned on or off depending on the specific remote-sensing process being performed. Uniformity of illumination is achieved by using an array of LEDs and/or an integrating sphere or other diffusing surface. The image plane scanner uses a fore optic with a field of view large enough to provide an entire scan line on the image plane. It builds up a two-dimensional image in pushbroom fashion as the target is scanned across the image plane either by moving the object or moving the fore optic. For fluorescence detection, spectral filtering of a narrowband light illumination source is sometimes necessary to minimize the interference of the source spectrum wings with the fluorescence signal. Spectral filtering is achieved with optical interference filters and absorption glasses. This dual spectral imaging capability will enable the optimization of reflective, fluorescence, and fused datasets as well as a cost-effective design for multispectral imaging solutions. This system has been used in plant stress detection studies and in currency analysis.

Ryan, Robert E.↗
NASA NTRSDate not supplied

Variable Mixing Nozzle Design with Slotted Vortex Generators for Jet Noise Reduction

A new variable geometry turbofan nozzle concept is presented with the dual goals of airport noise reduction and high propulsive efficiency at cruise, while employing only a single moving part. The nozzle utilizes a number of curved vanes to function as vortex generators (VGs) during takeoff and initial climb. Streamwise vortices provide an increase in mixing between the jet and external stream, with a resulting decrease in high frequency noise generation and a noise source distribution which is more amenable to airframe-based shielding. Unlike conventional VGs, the vanes are positioned without transverse incidence, and a pressure difference across the surface of each vane is created via an adjacent slot. During high altitude flight, when nozzle efficiency concerns outweigh any preference for jet noise reduction, all slots may be closed through rotation of a slotted ring inside the nozzle. RANS-based numerical analysis is performed to calculate propulsive metrics, determine noise source characteristics and understand various design parameter sensitivities. A new formulation is developed to approximately correct computed noise intensities for any throttle adjustments required to maintain takeoff thrust, and a rough estimate of shielding effectiveness is proposed by means of integration over a spatially distributed noise source. A total of 19 different nozzle geometries are considered in the present study. Results indicate significant noise benefits at takeoff, including a 2 kHz fly-over noise reduction of roughly 2-3 dB, while allowing for less than 15% of the net thrust reduction at supersonic cruise calculated for a fixed-penetration chevron nozzle.

Jet Noise↗
NASA NTRS1988

Control of the induced microgravity environment of the Man Tended Free Flyer (MTFF)

Induced disturbance sources have been identified on board the Man Tended Free Flyer (MTFF). Vibration responses at sensitive payload/spacecraft interfaces have been predicted by the application of an empirically found spacecraft dynamic transfer function. Vibrations from fluid loops (Freon, water) and of reaction wheels are assessed to be the main contributors to the induced microgravity environment. The expected payload acceleration response amplitudes presented here are more than one hundred times higher than the admissible values given by the MTFF system requirement, not considering the structural striction-friction effects which could be avoided by appropriate design. Real responses will be significantly lower because the derivation of excitation and transmission functions are based on worst case assumptions. The results indicate that future activities must be concentrated on equipment design improvement and the implementation of vibration reduction along the disturbance transmission path. The activities must be accompanied by early equipment and assembly development tests and transmissibility measurements with the integrated spacecraft engineering and structural models in order to improve the accuracy of payload response predictions.

Schlund, Juergen↗
NASA NTRS1993

Software to model AXAF image quality

This draft final report describes the work performed under this delivery order from May 1992 through June 1993. The purpose of this contract was to enhance and develop an integrated optical performance modeling software for complex x-ray optical systems such as AXAF. The GRAZTRACE program developed by the MSFC Optical Systems Branch for modeling VETA-I was used as the starting baseline program. The original program was a large single file program and, therefore, could not be modified very efficiently. The original source code has been reorganized, and a 'Make Utility' has been written to update the original program. The new version of the source code consists of 36 small source files to make it easier for the code developer to manage and modify the program. A user library has also been built and a 'Makelib' utility has been furnished to update the library. With the user library, the users can easily access the GRAZTRACE source files and build a custom library. A user manual for the new version of GRAZTRACE has been compiled. The plotting capability for the 3-D point spread functions and contour plots has been provided in the GRAZTRACE using the graphics package DISPLAY. The Graphics emulator over the network has been set up for programming the graphics routine. The point spread function and the contour plot routines have also been modified to display the plot centroid, and to allow the user to specify the plot range, and the viewing angle options. A Command Mode version of GRAZTRACE has also been developed. More than 60 commands have been implemented in a Code-V like format. The functions covered in this version include data manipulation, performance evaluation, and inquiry and setting of internal parameters. The user manual for these commands has been formatted as in Code-V, showing the command syntax, synopsis, and options. An interactive on-line help system for the command mode has also been accomplished to allow the user to find valid commands, command syntax, and command function. A translation program has been written to convert FEA output from structural analysis to GRAZTRACE surface deformation file (.dfm file). The program can accept standard output files and list files from COSMOS/M and NASTRAN finite analysis programs. Some interactive options are also provided, such as Cartesian or cylindrical coordinate transformation, coordinate shift and scale, and axial length change. A computerized database for technical documents relating to the AXAF project has been established. Over 5000 technical documents have been entered into the master database. A user can now rapidly retrieve the desired documents relating to the AXAF project. The summary of the work performed under this contract is shown.

Ahmad, Anees↗
NASA NTRSDate not supplied

Pyroscopegridding: Geo-Leo Aerosol Data Fusion (an Open-Source Package)

The retrieval of aerosol optical depths (AODs) from sun-synchronous polar orbiting satellites, such as MODISs, VIIRSs, OMI, TROPOMI, etc., has been widely adopted as a method for obtaining information regarding particulate matter (PM) and related atmospheric processes. However, the advent of recently launched geostationary satellites, such as GOES-16/17/18, Himawari-8/9, and Meteosat Third Generation (MTG), has led to an increased temporal resolution of AOD observations (order of 10 minutes), resulting in typically one or more images per hour during daylight hours, compared to the once-per-day observations obtained from LEO satellites. By integrating these observations, the diurnal cycle of global AOD can be characterized at local, regional, and global scales. The scientific community is still examining the novel data from geostationary satellite observations and evaluating methods for effectively merging these observations with differing spatial and temporal resolutions. This presents a significant ""Big Data"" challenge, encompassing not only data storage, but also data discoverability, accessibility, and migration within cloud computing environments. This study presents our attempts at fusing Level 2 aerosol data from six satellites, three of which are geostationary (GOES-16/17 and Himawari-8) and three of which are polar orbiting (TERRA/MODIS, AQUA/MODIS, and SNPP-VIIRS), using the Dark Target aerosol retrieval algorithm. The ability to fuse remote sensing products on demand into desired temporal and spatial domains empowers researchers and practitioners to more efficiently work with satellite and sensor data. It is our hope that through making our open-source package and accompanying functionality available, the scientific community will have improved access to aerosol data processing resources.

Jennifer Wei↗
NASA NTRS2005

Radial Variations in the Io Plasma Torus during the Cassini Era

A radial scan through the midnight sector of the Io plasma torus was made by the Cassini Ultraviolet Imaging Spectrograph on 14 January 2001, shortly after closest approach to Jupiter. From these data, Steffl et al. (2004a) derived electron temperature, plasma composition (ion mixing ratios), and electron column density as a function of radius from L = 6 to 0 as well as the total luminosity. We have advanced our homogeneous model of torus physical chemistry (Delamere and Bagenal, 2003) to include latitudinal and radial variations in a manner similar to the two-dimensional model by Schreier et al. (1998). The model variables include: (1) neutral source rate, (2) radial transport coefficient, (3) the hot electron fraction, (4) hot electron temperature, and (5) the neutral O/S ratio. The radial variation of parameters 1-4 are described by simple power laws, making a total of nine parameters. We have explored the sensitivity of the model results to variations in these parameters and compared the best fit with previous Voyager era models (schreier et al., 1998), galileo data (Crary et al., 1998), and Cassini observations (steffl et al., 2004a). We find that radial variations during the Cassini era are consistent with a neutral source rate of 700-1200 kg/s, an integrated transport time from L = 6 to 9 of 100-200 days, and that the core electron temperature is largely determined by a spatially and temporally varying superthermal electron population.

Delamere, P. A.↗
NASA NTRS2013

Granular Media-Based Tunable Passive Vibration Suppressor

and vibration suppression device is composed of statically compressed chains of spherical particles. The device superimposes a combination of dissipative damping and dispersive effects. The dissipative damping resulting from the elastic wave attenuation properties of the bulk material selected for the granular media is independent of particle geometry and periodicity, and can be accordingly designed based on the dissipative (or viscoelastic) properties of the material. For instance, a viscoelastic polymer might be selected where broadband damping is desired. In contrast, the dispersive effects result from the periodic arrangement and geometry of particles composing a linear granular chain. A uniform (monatomic) chain of statically compressed spherical particles will have a low-pass filter effect, with a cutoff frequency tunable as a function of particle mass, elastic modulus, Poisson fs ratio, radius, and static compression. Elastic waves with frequency content above this cutoff frequency will exhibit an exponential decay in amplitude as a function of propagation distance. System design targeting a specific application is conducted using a combination of theoretical, computational, and experimental techniques to appropriately select the particle radii, material (and thus elastic modulus and Poisson fs ratio), and static compression to satisfy estimated requirements derived for shock and/or vibration protection needs under particular operational conditions. The selection of a chain of polymer spheres with an elastic modulus .3 provided the appropriate dispersive filtering effect for that exercise; however, different operational scenarios may require the use of other polymers, metals, ceramics, or a combination thereof, configured as an array of spherical particles. The device is a linear array of spherical particles compressed in a container with a mechanism for attachment to the shock and/or vibration source, and a mechanism for attachment to the article requiring isolation (Figure 1). This configuration is referred to as a single-axis vibration suppressor. This invention also includes further designs for the integration of the single-axis vibration suppressor into a six-degree-of-freedom hexapod "Stewart"mounting configuration (Figure 2). By integrating each singleaxis vibration suppressor into a hexapod formation, a payload will be protected in all six degrees of freedom from shock and/or vibration. Additionally, to further enable the application of this device to multiple operational scenarios, particularly in the case of high loads, the vibration suppressor devices can be used in parallel in any array configuration.

Dillon, Robert P.↗
NASA NTRS2019

Assessment of Mixer-Ejector Nozzle with Thermal Acoustic Shield for Jet Noise Reduction

A tendency for excessive exhaust jet mixing noise from low bypass ratio turbofan engines is recognized as a key challenge in the design of commercial supersonic aircraft. In this work we investigate a unique combination of two noise mitigation methods as a novel strategy to reduce jet mixing noise. First, a thermal acoustic shield (TAS) is used to reflect high frequency acoustic waves at small angles to the jet axis; second, a mixer-ejector (ME) nozzle is used to mechanically shield noise propagating at large angles to the axis. The ME shroud also provides a convenient location for a TAS nozzle and improves TAS effectiveness by limiting the downstream extent of high frequency noise generation. In an additional benefit for a velocity-matched TAS stream, the ME allows a reduction in strength of the TAS outer shear layer which could serve as a secondary noise source. The present work provides a quantitative assessment of the ME-TAS concept, using a combination of RANS CFD simulations, acoustic analogy calculations for the farfield Green's function, and surrogate-based modeling and parameter space exploration. We first evaluate a subscale configuration, then use scaling arguments to apply subscale results to the systems-level analysis of a flight configuration; the latter configuration includes a generic low bypass ratio turbofan engine with an engine-driven electric generator for supplementary heating of the TAS stream. Additional RANS CFD calculations are performed for a notional ME-TAS geometry based on the full scale configuration, and various modeling assumptions and operational characteristics are evaluated. The ME-TAS concept is shown to provide effective shielding for high frequency jet noise, and should enable comparable noise suppression to a stand-alone ME of considerably greater length, weight and drag. In addition to investigating the integrated ME-TAS system, the present work differs from previous research into TAS and related fluidic shield concepts through the inclusion of modern numerical analysis tools and the systematic numerical examination of various design parameters.

thermal acoustic shield↗
NASA NTRS2003

Instrument for Measuring Cryo CTE

Coefficient of thermal expansion is an integral part of the performance of optical systems, especially for those, which operate at cryogenic temperatures. The measurement of the coefficient of relevant materials has been of continuous interest. Besides commercial measurement sources, development of one-of-a-kind tools have always been of interest due to local needs. This paper describes one such development at the University of Alabama in Huntsville (UAH). The approach involves two vertical rods (one sample and one reference) on a flat platform. A probe bar is held horizontally atop the two samples. A temperature change will generally cause rotation of the probe bar. A mirrored surface on one end of the probe bar is used to measure the rotation using the reflection of an incident laser beam upon it. A position-sensing detector measures the change of the reflected beam spot position. Using other known quantities, the change determines the coefficient of thermal expansion of the sample material as a function of temperature. A parallel measurement of the rotation of the sample support platform is also performed to account for any unwanted background effects. This system has been demonstrated in a cryogenic chamber at the NASA Marshall Space Flight Center X-ray Calibration Facility (XRCF). We present the system details, achievable sensitivity, and up-to-date experimental performance.

Vikram, Chandra S.↗
NASA NTRS1992

Dynamics of atmospheric teleconnections during the northern summer

The mechanisms of northern summertime teleconnections are investigated using a barotropic model. In a series of numerical experiments the atmospheric response over the eastern Pacific-North America to an idealized local divergence source corresponding to the northward displacement of the ITCZ in the eastern Pacific is studied. It is found that the response is much stronger in June than in May and is strongest when the forcing is located north of about 10 deg N. This can be explained in terms of the refractive properties of the climatological summertime subtropical jet stream over North America. In another series of experiments the global response as a function of the longitudinal location of the tropical forcing is examined. A wave train emanating from the subtropics of the western Pacific near the Philippines, arching across the Aleutians and the Gulf of Alaska, and terminating with a high anomaly over the continental United States appears over a wide longitudinal range of local forcing, suggesting the existence of a normal mode for the northern summertime climatological flow. The normal-mode concept is supported by further experiments using extratropical forcings as well as free-mode integrations.

Lau, K.-M.↗
NASA NTRS2003

On the Hilbert-Huang Transform Data Processing System Development

One of the main heritage tools used in scientific and engineering data spectrum analysis is the Fourier Integral Transform and its high performance digital equivalent - the Fast Fourier Transform (FFT). The Fourier view of nonlinear mechanics that had existed for a long time, and the associated FFT (fairly recent development), carry strong a-priori assumptions about the source data, such as linearity and of being stationary. Natural phenomena measurements are essentially nonlinear and nonstationary. A very recent development at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC), known as the Hilbert-Huang Transform (HHT) proposes a novel approach to the solution for the nonlinear class of spectrum analysis problems. Using the Empirical Mode Decomposition (EMD) followed by the Hilbert Transform of the empirical decomposition data (HT), the HHT allows spectrum analysis of nonlinear and nonstationary data by using an engineering a-posteriori data processing, based on the EMD algorithm. This results in a non-constrained decomposition of a source real value data vector into a finite set of Intrinsic Mode Functions (IMF) that can be further analyzed for spectrum interpretation by the classical Hilbert Transform. This paper describes phase one of the development of a new engineering tool, the HHT Data Processing System (HHTDPS). The HHTDPS allows applying the "T to a data vector in a fashion similar to the heritage FFT. It is a generic, low cost, high performance personal computer (PC) based system that implements the HHT computational algorithms in a user friendly, file driven environment. This paper also presents a quantitative analysis for a complex waveform data sample, a summary of technology commercialization efforts and the lessons learned from this new technology development.

Kizhner, Semion↗
NASA NTRS1998

Thermal State-of-Charge in Solar Heat Receivers

A theoretical framework is developed to determine the so-called thermal state-of-charge (SOC) in solar heat receivers employing encapsulated phase change materials (PCMS) that undergo cyclic melting and freezing. The present problem is relevant to space solar dynamic power systems that would typically operate in low-Earth-orbit (LEO). The solar heat receiver is integrated into a closed-cycle Brayton engine that produces electric power during sunlight and eclipse periods of the orbit cycle. The concepts of available power and virtual source temperature, both on a finite-time basis, are used as the basis for determining the SOC. Analytic expressions for the available power crossing the aperture plane of the receiver, available power stored in the receiver, and available power delivered to the working fluid are derived, all of which are related to the SOC through measurable parameters. Lower and upper bounds on the SOC are proposed in order to delineate absolute limiting cases for a range of input parameters (orbital, geometric, etc.). SOC characterization is also performed in the subcooled, two-phase, and superheat regimes. Finally, a previously-developed physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) system is used in order to predict the SOC as a function of measurable parameters.

Hall, Carsie A., Jr.↗