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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 NTRS2005

Quantifying Traversability of Terrain for a Mobile Robot

A document presents an updated discussion on a method of autonomous navigation for a robotic vehicle navigating across rough terrain. The method involves, among other things, the use of a measure of traversability, denoted the fuzzy traversability index, which embodies the information about the slope and roughness of terrain obtained from analysis of images acquired by cameras mounted on the robot. The improvements presented in the report focus on the use of the fuzzy traversability index to generate a traversability map and a grid map for planning the safest path for the robot. Once grid traversability values have been computed, they are utilized for rejecting unsafe path segments and for computing a traversalcost function for ranking candidate paths, selected by a search algorithm, from a specified initial position to a specified final position. The output of the algorithm is a set of waypoints designating a path having a minimal-traversal cost.

Howard, Ayanna↗
NASA NTRS2012

Characterization a single-lens based stereoscopic camera

Traditional stereoscopic vision (3D) is achieved through use of two cameras arranged to emulate human eyes. While this method works on large scale projects, it becomes impractical to use on small scale designs, such as surgical endoscopes, in which the operational area doesn’t allow the immensity of dual camera systems. This project is focused on developing a stereoscopic endoscope using a single camera and Conjugated Multiple-Bandpass Filters (CMBF) to create 3D images. Each filter is designed to allow only a distinct spectrum of light to pass through. The stereoscopic image can be obtained by using filters that reflect and reject wavelengths, complementary to one another. A major concern in all stereovision is crosstalk, defined as the light from one eye image that is present in the other eye image. This incomplete isolation causes deterioration of the 3D image. In our system, the crosstalk comes from imperfect filters. The filter spectrums overlap at certain wavelengths, causing a dim outline of the right eye image to leak into the left eye image and vice versa, a phenomenon known as ghosting. Knowledge of the extent of this phenomenon is critical to creating sustainable, effective stereovision.

Fritz, Eric↗
NASA NTRS1976

Irradiate-anneal screening of total dose effects in semiconductor devices

An extensive investigation of irradiate-anneal (IRAN) screening against total dose radiation effects was carried out as part of a program to harden the Mariner Jupiter/Saturn 1977 (MJS'77) spacecraft to survive the Jupiter radiation belts. The method consists of irradiating semiconductor devices with Cobalt-60 to a suitable total dose under representative bias conditions and of separating the parts in the undesired tail of the distribution from the bulk of the parts by means of a predetermined acceptance limit. The acceptable devices are then restored close to their preirradiation condition by annealing them at an elevated temperature. IRAN was used when lot screen methods were impracticable due to lack of time, and when members of a lot showed a diversity of radiation response. The feasibility of the technique was determined by testing of a number of types of linear bipolar integrated circuits, analog switches, n-channel JFETS and bipolar transistors. Based on the results of these experiments a number of device types were selected for IRAN of flight parts in the MJS'77 spacecraft systems. The part types, screening doses, acceptance criteria, number of parts tested and rejected as well as the program steps are detailed.

Stanley, A. G.↗
NASA NTRS1984

Optimization applications in aircraft engine design and test

Starting with the NASA-sponsored STAEBL program, optimization methods based primarily upon the versatile program COPES/CONMIN were introduced over the past few years to a broad spectrum of engineering problems in structural optimization, engine design, engine test, and more recently, manufacturing processes. By automating design and testing processes, many repetitive and costly trade-off studies have been replaced by optimization procedures. Rather than taking engineers and designers out of the loop, optimization has, in fact, put them more in control by providing sophisticated search techniques. The ultimate decision whether to accept or reject an optimal feasible design still rests with the analyst. Feedback obtained from this decision process has been invaluable since it can be incorporated into the optimization procedure to make it more intelligent. On several occasions, optimization procedures have produced novel designs, such as the nonsymmetric placement of rotor case stiffener rings, not anticipated by engineering designers. In another case, a particularly difficult resonance contraint could not be satisfied using hand iterations for a compressor blade, when the STAEBL program was applied to the problem, a feasible solution was obtained in just two iterations.

Pratt, T. K.↗
NASA NTRS1993

Growth experiment of narrow band-gap semiconductor PbSnTe single crystals in space (M-1)

An experiment on crystal growth of Pb(1-x)Sn(x)Te in microgravity is planned. This material is an alloy of the compound semiconductors PbTe and SnTe. It is a promising material for infrared diode lasers and detectors in the wavelength region between 6 and 30 micron. Since the electrical properties of Pb(1-x)Sn(x)Te depend greatly on the Pb/Sn ratio and crystalline defects as well as impurity concentration, homogeneous, defect-free, high-quality crystals are anticipated. Although many growth methods, such as the pulling method, the Bridgman method, the vapor growth method, etc., have been applied to the growth of Pb(1-x)Sn(x)Te, large, homogeneous, low-defect-density crystals have not yet been grown on Earth. The unsuccessful results were caused by buoyancy-driven convection in the fluids induced by the specific gravity difference between heated and cooled fluids on Earth. A crystal is grown by cooling the melt from one end of the ampoule. In crystal growth from the melt, about 30 percent of the SnTe in the melt is rejected at the solid-liquid interface during solidification. On Earth, the rejected SnTe is completely mixed with the remaining melt by convection in the melt. Therefore, SnTe concentration in the melt, and accordingly in the crystal, increases as the crystal grows. In the microgravity environment, buoyancy-driven convection is suppressed because the specific gravity difference is negligible. In that case, the rejected SnTe remains at the solid-liquid interface and its concentration increases only at the interface. If the growth rate is higher than the PbTe-SnTe interdiffusion rate, the amount of SnTe which diffuses from the interface into the melt increases as SnTe piles up at the interface, and finally it balances the amount of rejected SnTe during solidification, resulting in steady-state SnTe transportation at the interface. By using this principle, compositionally homogeneous crystals can be grown. Furthermore, low-defect-density crystals will be grown in microgravity, because convection causes crystalline defects by mising hot and cold fluids and generating temperature fluctuations in them.

Yamada, Tomoaki↗
NASA NTRS2010

Finned Carbon-Carbon Heat Pipe with Potassium Working Fluid

This elemental space radiator heat pipe is designed to operate in the 700 to 875 K temperature range. It consists of a C-C (carbon-carbon) shell made from poly-acrylonitride fibers that are woven in an angle interlock pattern and densified with pitch at high process temperature with integrally woven fins. The fins are 2.5 cm long and 1 mm thick, and provide an extended radiating surface at the colder condenser section of the heat pipe. The weave pattern features a continuous fiber bath from the inner tube surface to the outside edges of the fins to maximize the thermal conductance, and to thus minimize the temperature drop at the condenser end. The heat pipe and radiator element together are less than one-third the mass of conventional heat pipes of the same heat rejection surface area. To prevent the molten potassium working fluid from eroding the C C heat pipe wall, the shell is lined with a thin-walled, metallic tube liner (Nb-1 wt.% Zr), which is an integral part of a hermetic metal subassembly which is furnace-brazed to the inner surface of the C-C tube. The hermetic metal liner subassembly includes end caps and fill tubes fabricated from the same Nb-1Zr alloy. A combination of laser and electron beam methods is used to weld the end caps and fill tubes. A tungsten/inert gas weld seals the fill tubes after cleaning and charging the heat pipes with potassium. The external section of this liner, which was formed by a "Uniscan" rolling process, transitions to a larger wall thickness. This section, which protrudes beyond the C-C shell, constitutes the "evaporator" part of the heat pipe, while the section inside the shell constitutes the condenser of the heat pipe (see figure).

Juhasz, Albert J.↗
NASA NTRS2011

Non-Nuclear Testing of Compact Reactor Technologies at NASA MSFC

Safe, reliable, compact, autonomous, long-life fission systems have numerous potential applications, both terrestrially and in space. Technologies and facilities developed in support of these systems could be useful to a variety of concepts. At moderate power levels, fission systems can be designed to operate for decades without the need for refueling. In addition, fast neutron damage to cladding and structural materials can be maintained at an acceptable level. Nuclear design codes have advanced to the stage where high confidence in the behavior and performance of a system can be achieved prior to initial testing. To help ensure reactor affordability, an optimal strategy must be devised for development and qualification. That strategy typically involves a combination of non-nuclear and nuclear testing. Non-nuclear testing is particularly useful for concepts in which nuclear operating characteristics are well understood and nuclear effects such as burnup and radiation damage are not likely to be significant. To be mass efficient, a SFPS must operate at higher coolant temperatures and use different types of power conversion than typical terrestrial reactors. The primary reason is the difficulty in rejecting excess heat to space. Although many options exist, NASA s current reference SFPS uses a fast spectrum, pumped-NaK cooled reactor coupled to a Stirling power conversion subsystem. The reference system uses technology with significant terrestrial heritage while still providing excellent performance. In addition, technologies from the SFPS system could be applicable to compact terrestrial systems. Recent non-nuclear testing at NASA s Early Flight Fission Test Facility (EFF-TF) has helped assess the viability of the reference SFPS and evaluate methods for system integration. In July, 2011 an Annular Linear Induction Pump (ALIP) provided by Idaho National Laboratory was tested at the EFF-TF to assess performance and verify suitability for use in a10 kWe technology demonstration unit (TDU). In November, 2011 testing of a 37-pin core simulator (designed in conjunction with Los Alamos National Laboratory) for use with the TDU will occur. Previous testing at the EFFTF has included the thermal and mechanical coupling of a pumped NaK loop to Stirling engines (provided by GRC). Testing related to heat pipe cooled systems, gas cooled systems, heat exchangers, and other technologies has also been performed. Integrated TDU testing will begin at GRC in 2013. Thermal simulators developed at the EFF-TF are capable of operating over the temperature and power range typically of interest to compact reactors. Small and large diameter simulators have been developed, and simulators (coupled with the facility) are able to closely match the axial and radial power profile of all potential systems of interest. A photograph of the TDU core simulator during assembly is provided in Figure 2.

Houts, Michael G.↗
NASA NTRS1977

Thermoelectronic laser energy conversion for power transmission in space

Long distance transmission of power in space by means of laser beams is an attractive concept because of the very narrow beam divergence. Such a system requires efficient means to both generate the laser beam and to convert the light energy in the beam into useful electric output at the receiver. A plasma-type device known as a Thermo-Electronic Laser Energy Converter (TELEC) has been studied as a method of converting a 10.6 micron CO2 laser beam into electric power. In the TELEC process, electromagnetic radiation is absorbed directly in the plasma electrons producing a high electron temperature. The energetic electrons diffuse out of the plasma striking two electrodes with different areas. Since more electrons are collected by the larger electrode there is a net transport of current, and an EMF is generated in the external circuit. The smaller electrode functions as an electron emitter to provide continuity of the current. Waste heat is rejected from the large electrode. A design for a TELEC system with an input 1 MW laser beam was developed as part of the study. The calculated performance of the system showed an overall efficiency of about 42%.

Britt, E. J.↗
NASA NTRS2026

Thermal Cycle and Capacitance Testing of Mezzo Industries Phase Changer Material Heat Capacitor

Effective Thermal management is essential for the safety and performance of human spacecraft, especially during long-duration missions with fluctuating heat loads. Phase Change Material (PCM) heat exchangers offer a compact, efficient solution by storing and releasing thermal energy through latent heat during phase transitions. This allows PCM systems to buffer transient thermal loads without immediate heat rejection, reducing the need for oversized radiators – particularly critical during ascent and re-entry when radiators are stowed. By maintaining stable temperatures in crew cabins and equipment bays, PCM technology enhances crew comfort, protects sensitive systems, and supports long-term mission sustainability with minimal mass and volume impact. A phase change material heat capacitor prototype, designed and built under a NASA Small Business Innovation Research grant by Mezzo Technologies, utilizes a laser welding microtube manufacturing process that promises increased reliability and performance over current manufacturing methods like brazing. This heat exchanger was tested through coolant thermal cycling within the expected flow rates and temperature range of the Orion spacecraft, the crewed spacecraft taking NASA astronauts to the moon under the Artemis Program. The useful heat storage capacitance was measured and compared to Orion spacecraft requirements.

Active Thermal Control Systems↗
NASA NTRS1993

Stray-light suppression in a reflecting white-light coronagraph

An analysis of stray-light suppression in the white-light channel of the Ultraviolet Coronagraph Spectrometer experiment for the Solar and Heliospheric Observatory is reported. The white-light channel consists of a reflecting telescope with external and internal occultation and a polarimeter section. Laboratory tests and analytical methods are used to perform the analysis. The various stray-light contributions are classified in two main categories: the contribution from sunlight that passes directly through the entrance aperture and the contribution of sunlight that is diffracted by the edges of the entrance aperture. Values of the stray-light contributions from various sources and the total stray-light level for observations at heliocentric heights from 1.4 to 5 solar radii are derived. Anticipated signal-to-stray-light ratios are presented together with the effective stray-light rejection by the polarimeter, demonstrating the efficacy of the stray-light suppression design.

Romoli, Marco↗
NASA NTRSDate not supplied

Small Space Craft Materials Evaluation of Commercial Off The Shelf (COTS) Parts

The proliferation of inexpensive small spacecraft involves increasing use of Commercial Off The Shelf (COTS) parts. Often the composition, origin, provenance and/or properties of these parts are unspecified.The use of these materials complicates the evaluation of component suitability for low outgassing, material properties and even functionality. These problems will drive: a) the development of a sequence of gateway acceptability tests that can be used to reject parts before contaminating the usual Thermal Vacuum Chamber (TVAC) and other test equipment; b)the creation of a database for COTS parts that are acceptable for spacecraft use; c) a course of flight hardware training for novice spacecraft builders to limit the recurrence of common mistakes; d)fostering a more experienced, mature and sophisticated community of spacecraft developers that can determine if a proposed approach or material use is appropriate.An especially common spacecraft material issue involves the appropriate and inappropriate use of silicones. This presentation will provide examples of strategic methods used to mitigate the risks of COTS parts.

Small Spacecraft↗
NASA NTRS2013

Automatic Data Filter Customization Using a Genetic Algorithm

This work predicts whether a retrieval algorithm will usefully determine CO2 concentration from an input spectrum of GOSAT (Greenhouse Gases Observing Satellite). This was done to eliminate needless runtime on atmospheric soundings that would never yield useful results. A space of 50 dimensions was examined for predictive power on the final CO2 results. Retrieval algorithms are frequently expensive to run, and wasted effort defeats requirements and expends needless resources. This algorithm could be used to help predict and filter unneeded runs in any computationally expensive regime. Traditional methods such as the Fischer discriminant analysis and decision trees can attempt to predict whether a sounding will be properly processed. However, this work sought to detect a subsection of the dimensional space that can be simply filtered out to eliminate unwanted runs. LDAs (linear discriminant analyses) and other systems examine the entire data and judge a "best fit," giving equal weight to complex and problematic regions as well as simple, clear-cut regions. In this implementation, a genetic space of "left" and "right" thresholds outside of which all data are rejected was defined. These left/right pairs are created for each of the 50 input dimensions. A genetic algorithm then runs through countless potential filter settings using a JPL computer cluster, optimizing the tossed-out data s yield (proper vs. improper run removal) and number of points tossed. This solution is robust to an arbitrary decision boundary within the data and avoids the global optimization problem of whole-dataset fitting using LDA or decision trees. It filters out runs that would not have produced useful CO2 values to save needless computation. This would be an algorithmic preprocessing improvement to any computationally expensive system.

Mandrake, Lukas↗
NASA NTRS2014

Continued Water-Based Phase Change Material Heat Exchanger Development

In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to reject the full heat load requirement. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HXs do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development two full‐scale, Orion sized water‐based PCM HX's were constructed by Mezzo Technologies. These HX's were designed by applying prior research and experimentation to the full scale design. Design options considered included bladder restraint and clamping mechanisms, bladder manufacturing, tube patterns, fill/drain methods, manifold dimensions, weight optimization, and midplate designs. Design and construction of these HX's led to successful testing of both PCM HX's.

Hansen, Scott↗
NASA NTRS1986

Theory of Ostwald ripening in a two-component system

When a two-component system is cooled below the minimum temperature for its stability, it separates into two or more immiscible phases. The initial nucleation produces grains (if solid) or droplets (if liquid) of one of the phases dispersed in the other. The dynamics by which these nuclei proceed toward equilibrium is called Ostwald ripening. The dynamics of growth of the droplets depends upon the following factors: (1) The solubility of the droplet depends upon its radius and the interfacial energy between it and the surrounding (continuous) phase. There is a critical radius determined by the supersaturation in the continuous phase. Droplets with radii smaller than critical dissolve, while droplets with radii larger grow. (2) The droplets concentrate one component and reject the other. The rate at which this occurs is assumed to be determined by the interdiffusion of the two components in the continuous phase. (3) The Ostwald ripening is constrained by conservation of mass; e.g., the amount of materials in the droplet phase plus the remaining supersaturation in the continuous phase must equal the supersaturation available at the start. (4) There is a distribution of droplet sizes associated with a mean droplet radius, which grows continuously with time. This distribution function satisfies a continuity equation, which is solved asymptotically by a similarity transformation method.

Baird, J. K.↗
NASA NTRS2011

Supersonic Mass Flux Measurements via Tunable Diode Laser Absorption and Non-Uniform Flow Modeling

Measurements of mass flux are obtained in a vitiated supersonic ground test facility using a sensor based on line-of-sight (LOS) diode laser absorption of water vapor. Mass flux is determined from the product of measured velocity and density. The relative Doppler shift of an absorption transition for beams directed upstream and downstream in the flow is used to measure velocity. Temperature is determined from the ratio of absorption signals of two transitions (lambda(sub 1)=1349 nm and lambda(sub 2)=1341.5 nm) and is coupled with a facility pressure measurement to obtain density. The sensor exploits wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f) for large signal-to-noise ratios and normalization with the 1f signal for rejection of non-absorption related transmission fluctuations. The sensor line-of-sight is translated both vertically and horizontally across the test section for spatially-resolved measurements. Time-resolved measurements of mass flux are used to assess the stability of flow conditions produced by the facility. Measurements of mass flux are within 1.5% of the value obtained using a facility predictive code. The distortion of the WMS lineshape caused by boundary layers along the laser line-of-sight is examined and the subsequent effect on the measured velocity is discussed. A method for correcting measured velocities for flow non-uniformities is introduced and application of this correction brings measured velocities within 4 m/s of the predicted value in a 1630 m/s flow.

Chang, Leyen S.↗
NASA NTRS1977

Project STOP (Spectral Thermal Optimization Program)

The spectral thermal optimization of solar cell configurations for various solar panel applications is considered. The method of optimization depends upon varying the solar cell configuration's optical characteristics to minimize panel temperatures, maximize power output and decrease the power delta from beginning of life to end of life. Four areas of primary investigation are: (1) testing and evaluation of ultraviolet resistant coverslide adhesives, primarily FEP as an adhesive; (2) examination of solar cell absolute spectral response and corresponding cell manufacturing processes that affect it; (3) experimental work with solar cell manufacturing processes that vary cell reflectance (solar absorptance); and (4) experimental and theoretical studies with various coverslide filter designs, mainly a red rejection filter. The Hughes' solar array prediction program has been modified to aid in evaluating the effect of each of the above four areas on the output of a solar panel in orbit.

Goldhammer, L. J.↗
NASA NTRS2015

Continued Water-Based Phase Change Material Heat Exchanger Development

In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to meet the full heat rejection demands. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HX's do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development two full-scale, Orion sized water-based PCM HX's were constructed by Mezzo Technologies. These HX's were designed by applying prior research on freeze front propagation to a full-scale design. Design options considered included bladder restraint and clamping mechanisms, bladder manufacturing, tube patterns, fill/drain methods, manifold dimensions, weight optimization, and midplate designs. Two units, Units A and B, were constructed and differed only in their midplate design. Both units failed multiple times during testing. This report highlights learning outcomes from these tests and are applied to a final sub-scale PCM HX which is slated to be tested on the ISS in early 2017.

Hansen, Scott W.↗
NASA NTRS1989

H(2)- and H(infinity)-design tools for linear time-invariant systems

Recent advances in optimal control have brought design techniques based on optimization of H(2) and H(infinity) norm criteria, closer to be attractive alternatives to single-loop design methods for linear time-variant systems. Significant steps forward in this technology are the deeper understanding of performance and robustness issues of these design procedures and means to perform design trade-offs. However acceptance of the technology is hindered by the lack of convenient design tools to exercise these powerful multivariable techniques, while still allowing single-loop design formulation. Presented is a unique computer tool for designing arbitrary low-order linear time-invarient controllers than encompasses both performance and robustness issues via the familiar H(2) and H(infinity) norm optimization. Application to disturbance rejection design for a commercial transport is demonstrated.

Ly, Uy-Loi↗