Results for “modulation transfer function” — Page 12

NASA NTRS2011

Test-Anchored Vibration Response Predictions for an Acoustically Energized Curved Orthogrid Panel with Mounted Components

A rich body of vibroacoustic test data was recently generated at Marshall Space Flight Center for a curved orthogrid panel typical of launch vehicle skin structures. Several test article configurations were produced by adding component equipment of differing weights to the flight-like vehicle panel. The test data were used to anchor computational predictions of a variety of spatially distributed responses including acceleration, strain and component interface force. Transfer functions relating the responses to the input pressure field were generated from finite element based modal solutions and test-derived damping estimates. A diffuse acoustic field model was employed to describe the assumed correlation of phased input sound pressures across the energized panel. This application demonstrates the ability to quickly and accurately predict a variety of responses to acoustically energized skin panels with mounted components. Favorable comparisons between the measured and predicted responses were established. The validated models were used to examine vibration response sensitivities to relevant modeling parameters such as pressure patch density, mesh density, weight of the mounted component and model form. Convergence metrics include spectral densities and cumulative root-mean squared (RMS) functions for acceleration, velocity, displacement, strain and interface force. Minimum frequencies for response convergence were established as well as recommendations for modeling techniques, particularly in the early stages of a component design when accurate structural vibration requirements are needed relatively quickly. The results were compared with long-established guidelines for modeling accuracy of component-loaded panels. A theoretical basis for the Response/Pressure Transfer Function (RPTF) approach provides insight into trends observed in the response predictions and confirmed in the test data. The software modules developed for the RPTF method can be easily adapted for quick replacement of the diffuse acoustic field with other pressure field models; for example a turbulent boundary layer (TBL) model suitable for vehicle ascent. Wind tunnel tests have been proposed to anchor the predictions and provide new insight into modeling approaches for this type of environment. Finally, component vibration environments for design were developed from the measured and predicted responses and compared with those derived from traditional techniques such as Barrett scaling methods for unloaded and component-loaded panels.

Frady, Gregory P.↗

NASA NTRS1978

On the calculation of squaring loss in Costas loops with arbitrary arm filters

Specific numerical results for the squaring loss in Costas loop tracking are discussed for cases when the input data were biphase-L, and the Costas loop arm filters were of the n-pole Butterworth type. It is pointed out that a simple scientific calculator may be used for the computations, provided the transfer function of the arm filter has simple poles. The technique can also be used to compute the squaring loss in other modulation forms, such as unbalanced quadriphase-shift-keying (QPSK).

Simon, M. K.↗

NASA NTRS1984

Design and performance of transfer assembly for the infrared telescope for Space Lab 2

The cryogenic design features employed in the case of the Infrared Telescope (IRT) for Spacelab 2 are unique. They involve the delivery of helium gas at a temperature of 2 K to the IR detectors from a superfluid supply dewar which is separate from the telescope/detector unit. This design has the advantage that thermal and mechanical vibration disturbances in the liquid helium bath are decoupled from the IR detector. The interfacing of the storage dewar with the IRT telescope/detector unit (called cryostat) is the function of the subsystem which is called the transfer assembly (TA). The TA design is discussed, taking into account the porous plug module, the plumbing module, the helix module, and the dewar heat exchanger units. Aspects of transfer assembly performance are also considered.

Karr, G. R.↗

NASA NTRS1992

Parameter identification for nonlinear aerodynamic systems

Continuing work on frequency analysis for transfer function identification is discussed. A new study was initiated into a 'weighted' least squares algorithm within the context of the Fourier modulating function approach. The first phase of applying these techniques to the F-18 flight data is nearing completion, and these results are summarized.

Pearson, Allan E.↗

NASA NTRS2003

Detector Apparatus and Method

Transceiver and methods are included that are especially suitable for detecting metallic materials, such as metallic mines, within an environment. The transceiver includes a digital waveform generator used to transmit a signal into the environment and a receiver that produces a digital received signal. A tracking module preferably compares an in-phase and quadrature transmitted signal with an in-phase and quadrature received signal to produce a spectral transfer function of the magnetic transceiver over a selected range of frequencies. The transceiver initially preferably creates a reference transfer function which is then stored in a memory. Subsequently measured transfer functions will vary depending on the presence of metal in the environment which was not in the environment when the reference transfer function was determined. The system may be utilized in the presence of other antennas, metal, and electronics which may comprise a plastic mine detector for detecting plastic mines. Despite the additional antennas and other metallic materials that may be in the environment due to the plastic mine detector, the magnetic transceiver remains highly sensitive to metallic material which may be located in various portions of the environment and which may be detected by sweeping the detector over ground that may contain metals or mines.

Arndt, G. Dickey↗

NASA NTRS1992

Robot Serviced Space Facility

A robot serviced space facility includes multiple modules which are identical in physical structure, but selectively differing in function. and purpose. Each module includes multiple like attachment points which are identically placed on each module so as to permit interconnection with immediately adjacent modules. Connection is made through like outwardly extending flange assemblies having identical male and female configurations for interconnecting to and locking to a complementary side of another flange. Multiple rows of interconnected modules permit force, fluid, data and power transfer to be accomplished by redundant circuit paths. Redundant modules of critical subsystems are included. Redundancy of modules and of interconnections results in a space complex with any module being removable upon demand, either for module replacement or facility reconfiguration. without eliminating any vital functions of the complex. Module replacement and facility assembly or reconfiguration are accomplished by a computer controlled articulated walker type robotic manipulator arm assembly having two identical end-effectors in the form of male configurations which are identical to those on module flanges and which interconnect to female configurations on other flanges. The robotic arm assembly moves along a connected set or modules by successively disconnecting, moving and reconnecting alternate ends of itself to a succession of flanges in a walking type maneuver. To transport a module, the robot keeps the transported module attached to one of its end-effectors and uses another flange male configuration of the attached module as a substitute end-effector during walking.

Purves, Lloyd R.↗

NASA NTRS2022

Mars Terrain Segmentation with Less Labels

Planetary rover systems need to perform terrain segmentation to identify drivable areas as well as identify specific types of soil for sample collection. The latest Martian terrain segmentation methods rely on supervised learning which is very data hungry and difficult to train where only a small number of labeled samples are available. Moreover, the semantic classes are defined differently for different applications (e.g., rover traversal vs. geological) and as a result the network has to be trained from scratch each time, which is an inefficient use of resources. This research proposes a semi-supervised learning framework for Mars terrain segmentation where a deep segmentation network trained in an unsupervised manner on unlabeled images is transferred to the task of terrain segmentation trained on few labeled images. The network incorporates a backbone module which is trained using a contrastive loss function and an output atrous convolution module which is trained using a pixel-wise cross-entropy loss function. Evaluation results using the metric of segmentation accuracy show that the proposed method with contrastive pre-training outperforms plain supervised learning by 2%-10%. Moreover, the proposed model is able to achieve a segmentation accuracy of 91.1% using only 161 training images (1% of the original dataset) compared to 81.9% with plain supervised learning.

Wilson, Brian D↗

NASA NTRS1977

Space station systems analysis study. Part 2, volume 3: Appendixes, Book 2: Supporting data (7 through 18)

Topics discussed include: (1) design considerations for a MARS sample return laboratory module for space station investigations; (2) crew productivity as a function of work shift arrangement; (3) preliminary analysis of the local logistics problem on the space construction base; (4) mission hardware construction operational flows and timelines; (5) orbit transfer vehicle concept definition; (6) summary of results and findings of space processing working review; (7) crew and habitability subsystem (option L); (8) habitability subsystem considerations for shuttle tended option L; (9) orbiter utilization in manned sortie missions; (10) considerations in definition of space construction base standard module configuration (option L); (11) guidance, control, and navigation subsystems; and (12) system and design tradeoffs.

Source record↗

NASA NTRS2006

AEROELASTIC SIMULATION TOOL FOR INFLATABLE BALLUTE AEROCAPTURE

A multidisciplinary analysis tool is under development for predicting the impact of aeroelastic effects on the functionality of inflatable ballute aeroassist vehicles in both the continuum and rarefied flow regimes. High-fidelity modules for continuum and rarefied aerodynamics, structural dynamics, heat transfer, and computational grid deformation are coupled in an integrated multi-physics, multi-disciplinary computing environment. This flexible and extensible approach allows the integration of state-of-the-art, stand-alone NASA and industry leading continuum and rarefied flow solvers and structural analysis codes into a computing environment in which the modules can run concurrently with synchronized data transfer. Coupled fluid-structure continuum flow demonstrations were conducted on a clamped ballute configuration. The feasibility of implementing a DSMC flow solver in the simulation framework was demonstrated, and loosely coupled rarefied flow aeroelastic demonstrations were performed. A NASA and industry technology survey identified CFD, DSMC and structural analysis codes capable of modeling non-linear shape and material response of thin-film inflated aeroshells. The simulation technology will find direct and immediate applications with NASA and industry in ongoing aerocapture technology development programs.

Liever, P. A.↗

NASA NTRSDate not supplied

Gateway Autonomy for Enabling Deep Space Exploration

The Gateway spacecraft is an important stepping-stone to exploration of the solar system, integrating commercial and international partners into a tightly coupled system, enabling cislunar activities, and implementing key technologies for missions to Mars. Autonomy is a capability area necessary to handle long communication outages where intervention from Earth is impossible, to prepare to operate with long communication delays that will be common in interplanetary travel, and to make spaceflight more affordable and accessible by reducing sustaining operations costs. The Gateway Concept of Operations states that one of Gateway’s goals is to “focus on infrastructure and systems that will allow autonomous operations aboard the Gateway with robotics, automated systems, advanced communications, and distributed computing.” Gateway’s Vehicle Systems Manager (VSM) and associated Autonomous Spacecraft Management Architecture (ASMA) are key products towards delivering autonomous capability. The primary functions of the control architecture are Mission Management and Timeline Execution, Resource Management, Fault Management, and Vehicle Control and Operation (VCO). In each of these areas, there is an initial level of capability to be delivered at launch, with plans to continue development and grow to greater capability. The initial deployment of VSM will focus on maintaining vehicle safety by focusing on full fault management capabilities and deploying only enough resource and timeline planning functionality to support that. The final deployment of VSM will add significant planning and control optimization functionality to support nominal operations for up to 21 days without ground support, even accommodating fault and failure conditions. While the VSM is the vehicle-level representation of autonomous reasoning, distributed automation is essential to provide the right scope and abstraction of information to process. Module and system support of automation and simplicity of interfaces are two important design paradigms that Gateway is focusing on to garner a systems approach to autonomy. Distribution of reasoning can increase complexity, so Gateway is also taking a strict hierarchical approach to information flow and decision making. VSM is not the only capability necessary to achieve an autonomous spacecraft. Robotics support for maintenance of the spacecraft will be essential to provide continued vehicle functionality even when crew is not present. Technical and programmatic challenges exist when implementing autonomous robotics operations. These challenges include sufficient network flexibility to support data transfer to the rest of the vehicle to coordinate module-to-module robotic walk-offs and finding the proper interfaces to allow sufficient dexterity. Communication system upgrades planned for Gateway include Delay Tolerant Networking to best utilize the complex network of relays that will be part of mature cislunar operations. Distributed computing and management will provide failure tolerance, robustness, and growth of capabilities while still allowing significant reuse of heritage software on heritage systems as well as reuse of common applications across a spacecraft to minimize new development, but this requires adherence to key standards and interfaces. The Gateway program has demonstrated significant progress towards these capabilities and has identified challenges other spacecraft developers should be aware of from the start.

Molly Anderson↗

NASA NTRSDate not supplied

Gateway Autonomy for Enabling Deep Space Exploration

The Gateway spacecraft is an important stepping-stone to exploration of the solar system, integrating commercial and international partners into a tightly coupled system, enabling cislunar activities, and implementing key technologies for missions to Mars. Autonomy is a capability area necessary to handle long communication outages where intervention from Earth is impossible, to prepare to operate with long communication delays that will be common in interplanetary travel, and to make spaceflight more affordable and accessible by reducing sustaining operations costs. The Gateway Concept of Operations states that one of Gateway’s goals is to “focus on infrastructure and systems that will allow autonomous operations aboard the Gateway with robotics, automated systems, advanced communications, and distributed computing.” Gateway’s Vehicle Systems Manager (VSM) and associated Autonomous Spacecraft Management Architecture (ASMA) are key products towards delivering autonomous capability. The primary functions of the control architecture are Mission Management and Timeline Execution, Resource Management, Fault Management, and Vehicle Control and Operation (VCO). In each of these areas, there is an initial level of capability to be delivered at launch, with plans to continue development and grow to greater capability. The initial deployment of VSM will focus on maintaining vehicle safety by focusing on full fault management capabilities and deploying only enough resource and timeline planning functionality to support that. The final deployment of VSM will add significant planning and control optimization functionality to support nominal operations for up to 21 days without ground support, even accommodating fault and failure conditions. While the VSM is the vehicle-level representation of autonomous reasoning, distributed automation is essential to provide the right scope and abstraction of information to process. Module and system support of automation and simplicity of interfaces are two important design paradigms that Gateway is focusing on to garner a systems approach to autonomy. Distribution of reasoning can increase complexity, so Gateway is also taking a strict hierarchical approach to information flow and decision making. VSM is not the only capability necessary to achieve an autonomous spacecraft. Robotics support for maintenance of the spacecraft will be essential to provide continued vehicle functionality even when crew is not present. Technical and programmatic challenges exist when implementing autonomous robotics operations. These challenges include sufficient network flexibility to support data transfer to the rest of the vehicle to coordinate module-to-module robotic walk-offs and finding the proper interfaces to allow sufficient dexterity. Communication system upgrades planned for Gateway include Delay Tolerant Networking to best utilize the complex network of relays that will be part of mature cislunar operations. Distributed computing and management will provide failure tolerance, robustness, and growth of capabilities while still allowing significant reuse of heritage software on heritage systems as well as reuse of common applications across a spacecraft to minimize new development, but this requires adherence to key standards and interfaces. The Gateway program has demonstrated significant progress towards these capabilities and has identified challenges other spacecraft developers should be aware of from the start.

Molly Anderson↗

NASA NTRS1980

Interaction of oscillations of channel flow and flow separation at duct discontinuities

A two dimensional experiment was used to study the flow fluctuations in the separated region resulting from a wall slot step (convergent step). This geometry corresponds to the geometry present in a segmented solid rocket motor in the region of the ends of adjoining segments. A modulated tunnel flow of controlled oscillation frequency was used, and the effect on flow fluctuations in the separated region was examined by hot wire velocity measurements. The transfer function between free stream oscillations and separated flow fluctuations at the driven frequency was determined over a range of frequencies and main stream flow velocities. The transfer function exhibited a frequency dependence with maximum in the 10 - 25 Hz range, with the maximum occurring at higher frequency when the mean flow velocity was higher.

Price, E. W.↗

NASA NTRS1973

Transmission of radiometer data from the Synchronous Meteorological Satellite

The Synchronous Meteorological Satellite uses a spin scanner radiometer which generates eight visual signals and two infrared signals. These signals are multiplexed and converted into a 28-Mbps data stream. This signal is transmitted to ground by quadriphase modulation at 1686.1 MHz. On the ground, the digital signal is reconstructed to an analog signal. To conserve bandwidth, an analog-to-digital converter with a nonlinear transfer function was used for the visual signals. The size of the quantization step was made proportional to the noise output of the scanner photomultiplier tube which increases as the square root of incident light. The radiometer data transmission link was simulated on a digital computer to determine the transfer function. Some results of the simulation are shown.

Davies, R. S.↗

NASA NTRS1988

Nucleate pool boiling: High gravity to reduced gravity; liquid metals to cryogens

Requirements for the proper functioning of equipment and personnel in reduced gravity associated with space platforms and future space station modules introduce unique problems in temperature control; power generation; energy dissipation; the storage, transfer, control and conditioning of fluids; and liquid-vapor separation. The phase change of boiling is significant in all of these. Although both pool and flow boiling would be involved, research results to date include only pool boiling because buoyancy effects are maximized for this case. The effective application of forced convection boiling heat transfer in the microgravity of space will require a well grounded and cogent understanding of the mechanisms involved. Experimental results are presented for pool boiling from a single geometrical configuration, a flat surface, covering a wide range of body forces from a/g = 20 to 1 to a/g = 0 to -1 for a cryogenic liquid, and from a/g = 20 to 1 for water and a liquid metal. Similarities in behavior are noted for these three fluids at the higher gravity levels, and may reasonably be expected to continue at reduced gravity levels.

Merte, Herman, Jr.↗

NASA NTRS2005

Matlab GUI for a Fluid Mixer

The Test and Engineering Directorate at NASA John C. Stennis Space Center developed an interest to study the modeling, evaluation, and control of a liquid hydrogen (LH2) and gas hydrogen (GH2) mixer subsystem of a ground test facility. This facility carries out comprehensive ground-based testing and certification of liquid rocket engines including the Space Shuttle Main engine. A software simulation environment developed in MATLAB/SIMULINK (M/S) will allow NASA engineers to test rocket engine systems at relatively no cost. In the progress report submitted in February 2004, we described the development of two foundation programs, a reverse look-up application using various interpolation algorithms, a variety of search and return methods, and self-checking methods to reduce the error in returned search results to increase the functionality of the program. The results showed that these efforts were successful. To transfer this technology to engineers who are not familiar with the M/S environment, a four-module GUI was implemented allowing the user to evaluate the mixer model under open-loop and closed-loop conditions. The progress report was based on an udergraduate Honors Thesis by Ms. Jamie Granger Austin in the Department of Electrical Engineering and Computer Science at Tulane University, during January-May 2003, and her continued efforts during August-December 2003. In collaboration with Dr. Hanz Richter and Dr. Fernando Figueroa we published these results in a NASA Tech Brief due to appear this year. Although the original proposal in 2003 did not address other components of the test facility, we decided in the last few months to extend our research and consider a related pressurization tank component as well. This report summarizes the results obtained towards a Graphical User Interface (GUI) for the evaluation and control of the hydrogen mixer subsystem model and for the pressurization tank each taken individually. Further research would combine the two components - mixer and tank, for a more realistic simulation tool.

Barbieri, Enrique↗

NASA NTRSDate not supplied

Gateway bi-propellant refueling development testing and model validation activities

The Gateway is an upcoming long term lunar exploration program to be completed by NASA in partnership with ESA and other US and international partners. The system design of the Gateway contains both a high performance Xenon based Solar Electric Propulsion system, as well as a bi-propellant attitude control system. Both propulsion systems are designed for on-orbit refueling to enable long life performance of the Gateway. The ESPRIT-RM is a module which will expand the pressurized volume of Gateway, while also providing refueling capability for both the Xenon and Bipropellant propulsion systems, therefore extending the Gateway life on orbit. As part of the Gateway bi-propellant refueling system development, a simplified fluidic breadboard system was created to evaluate system performance and response using simulant fluids. The test plan includes verification activities with simulant (water, HFE-7100) to verify joined subsystem behavior in the critical operations, including propellant transfer demonstration between modules, transient tests and venting tests. Integrated testing occurred at TASUK in collaboration with NASA to support joint verification activities to de-risk the major functions of the ESPRIT BTS and the overall CONOPS of the refueling of the Gateway chemical propulsion system. Initially collected test data from the system testing is presented, as well as initial model validation, and correlated to collected high frequency test data and system response is shown. Initially collected data has shown the architected system performance is closing initial design assumptions, but much forward work remains to characterize and develop the system.

Christopher Daniel Radke↗

NASA NTRS1997

Thermophotovoltaic Cell Technology Transferred to the Department of Energy Laboratory and a Commercial Manufacturer

Researchers in the NASA Lewis Research Center's Photovoltaic Branch have developed novel photovoltaic device, called a Monolithically Interconnected Module (MIM), for use in thermophotovoltaic (TPV) power systems. TPV power systems function by heating an emitter to produce light. This light is then converted into electricity by a photovoltaic device or a solar cell. Possible heat sources for the system include concentrated solar energy, the combustion of various fuels, and nuclear decay. NASA has an interest in TPV systems for deep space (nuclear-powered) and near-Sun (solar-powered) missions. There also are many commercial and military applications for TPV, given its potential for high efficiency, low noise, and reliable power. The Monolithically Interconnected Module consists of many small solar cells that are series-interconnected on a common substrate. The cells are fabricated from indium gallium arsenide (InGaAs), which can convert the near-infrared portion of the emitter output spectrum into electricity. The InGaAs devices are deposited on an indium phosphide (InP) substrate that provides electrical isolation. On the bottom the InP substrate is an infrared reflector that returns all the photons that are not converted by the InGaAs device back to the emitter where they are absorbed. This process helps maintain the emitter temperature and dramatically improves the system efficiency. Monolithically Interconnected Module InGaAs thermophotovoltaic cell developed by Lewis. Compared with conventional TPV cells, this TPV device has higher output voltages and lower resistive losses, higher output power density, simplified thermal management, improved reliability, and higher efficiency. The Monolithically Interconnected Module was initially developed under an internally funded effort (Director's Discretionary Fund). Development is now being funded by another government agency, and prototype devices are being produced by a commercial solar cell manufacturer.

Wilt, David M.↗

NASA NTRS1982

Spacelab ground processing

During the Kennedy Space Center ground processing of Spacelab systems, emphasis is placed on verification of physical and functional interfaces aboard the spacecraft. Experiment-related operations consist of the integration of various experiment elements into the flight module. After Spacelab-Space Shuttle interfaces have been verified, the Spacelab cargo is transferred to the Orbiter Processing Facility in a controlled environment. Attention is given to the integrity of all payload-to-Space Shuttle interfaces during final closeout operations. Payload-related activities are minimal at the launch pad stage, since only limited access to the payload module is available through the Space lab Transfer Tunnel.

Scully, E. J.↗