Abiotic and biotic-controlled nanomaterial formation pathways within the Earth’s nanomaterial cycle
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Environmental Sciences & Ecology↗
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Results for “formation control”
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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Solvent structure controlled SeedGel formation investigated using miscible binary solvents
A SeedGel can be formed not only in partially miscible binary solvents but also in miscible binary solvents.
Xi, Yuyin [Center for Neutron Research, National I↗
High-yield implosion modeling using the Frustraum: Assessing and controlling the formation of polar jets and enhancing implosion performance with applied magnetization
Frustraums have a higher laser-to-capsule x-ray radiation coupling efficiency and can accommodate a large capsule, thus potentially generating a higher yield with less laser energy than cylindrical Hohlraums for a given Hohlraum volume [Amendt et al., Phys. Plasmas 26, 082707 (2019]. Frustraums are expected to have less m = 4 azimuthal asymmetries arising from the intrinsic inner-laser-beam geometry on the National Ignition Facility. An experimental campaign at Lawrence Livermore National Laboratory to demonstrate the high-coupling efficiency and radiation symmetry tuning of the Frustraum has been under way since 2021. Simulations benchmarked against experimental data show that implosions using Frustraums can achieve more yield with higher ignition margins than cylindrical Hohlraums using the same laser energy. Hydrodynamic jets in capsules along the Hohlraum axis, driven by radiation-flux asymmetries in a Hohlraum with a gold liner on a depleted uranium (DU) wall, are present around stagnation, and these “polar” jets can cause severe yield degradation. The early-time Legendre mode P4<0 radiation-flux asymmetry is a leading cause of these jets, which can be reduced by using an unlined DU Hohlraum because the shape of the shell is predicted to be more prolate. Magnetization can increase the implosion robustness and reduce the required hotspot ρR for ignition; therefore, magnetizing the Frustraum can maintain the same yield while reducing the required laser energy or increase the yield using the same laser energy—all under the constraint that the ignition margin is preserved. Reducing polar jets is particularly important for magnetized implosions because of the intrinsic toroidal hotspot ion temperature topology.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
X-Band Scanning ARM Precipitation Radar, CF/Radial Formatted, Quality Controlled
The X-band Scanning ARM Precipitation Radar (X-SAPR) is an X-band dual-polarization Doppler weather radar. The X-SAPR operates in a simultaneous transmit and receive (STAR) mode, meaning that the transmit signal is split so that power is transmitted on both horizontal and vertical polarizations at the same time. The X-SAPR transmitter is a 200 kW (peak power) magnetron. The receiver is based upon the Vaisala RVP-900 and runs Vaisala’s IRIS software. In addition to the first three Doppler moments (reflectivity, radial velocity, and spectra width), the X-SAPR also provides differential reflectivity, correlation coefficient, and specific differential phases. The dual-polarization variables enable estimates of rainfall rates and identification of precipitation types. At the Southern Great Plains site, three X-SAPRs surround the Central Facility, allowing the use of multi-Doppler velocity retrievals to estimate wind fields.
xsaprcfrqc↗
Early Archean stromatolites: Paleoenvironmental setting and controls on formation
The earliest record of terrestrial life is contained in thin, silicified sedimentary layers within enormously thick, predominantly volcanic sequences in South Africa and Western Australia. This record includes bacteria-like microfossils, laminated carbonaceous structures resembling flat bacterial mats and stromatolites, and a morphologically diverse assemblage of carbonaceous particles. These structures and particles and their host sediments provide the only direct source of information on the morphology, paleoecology, and biogeochemistry of early life; the nature of interactions between organisms and surface systems on the early earth; and possible settings within which life might have evolved. The three known occurrences of 3.5 to 3.2 billion-year-old stromalites were evaluated in terms of depositional setting and biogenicity.
Lowe, D. R.↗
Data Synchronization Discrepancies in a Formation Flight Control System
Aircraft hardware-in-the-loop simulation is an invaluable tool to flight test engineers; it reveals design and implementation flaws while operating in a controlled environment. Engineers, however, must always be skeptical of the results and analyze them within their proper context. Engineers must carefully ascertain whether an anomaly that occurs in the simulation will also occur in flight. This report presents a chronology illustrating how misleading simulation timing problems led to the implementation of an overly complex position data synchronization guidance algorithm in place of a simpler one. The report illustrates problems caused by the complex algorithm and how the simpler algorithm was chosen in the end. Brief descriptions of the project objectives, approach, and simulation are presented. The misleading simulation results and the conclusions then drawn are presented. The complex and simple guidance algorithms are presented with flight data illustrating their relative success.
Ryan, Jack↗
Kinetic Controls on Formation of Textures in Rapidly Cooled Rocks
The crystallization of silicate melts is a complex process involving melts usually produced by partial melting and cooling environments that are rapid in volcanic lavas or so slow as to be auto-metamorphic in plutonic regimes. The volcanic lavas are amenable to laboratory study as are chondrules that comprise the bulk of chondritic meteorites. Dynamic crystallization studies of basalt and chondrule melts have shown that nucleation has a more profound effect on the final texture than the cooling or crystal growth rates. The sequence of crystal shapes grown at increasing degrees of supercooling (DELTA T) or cooling rate demonstrates the effect of increasing growth rate. Equant or euhedral crystals become skeletal, then dendritic and ultimately spherulitic indicating the nucleation temperature and the DELTA T when growth began. Because crystals cannot grow until they nucleate, cooling rate does not always correlate with crystal growth rate and thus crystal shape. Silicate melts cooled at the same rate can have drastically different textures depending on the temperature of nucleation. A dynamic crystallization study of basaltic rocks shows that basaltic lavas must erupt with sufficient crystals present in the melt to act as nuclei and foster growth. With nuclei present, growth will begin when the temperature drops below the liquidus temperature and typical basaltic textures such as intersertal, intergranular or subophitic will form. If nuclei are not present, crystallization will not begin immediately and the DELTA T will increase until embryos in the melts become nuclei. The DELTA T present when grow begins dictates the growth rate and the crystal shapes and thus the rock texture. If nucleation is delayed, growth will take place at high DELTA T and the crystals will favor skeletal or dendritic shapes. Chondrules are usually considered crystallized melt droplets and clearly some are, but most are not. Most chondrules have porphyritic textures that cannot develop from totally melted droplets because nucleation is delayed during cooling and growth occurs at high DELTA T and the resulting textures are dendritic or spherulitic. The porphyritic textures will develop only if the chondrule is partially molten and begins to crystallize immediately upon cooling. Chondrule compositions are close to komatiites and these studies bear on the origin of their textures as well.
Lofgren, Gary E.↗
Formation Flying Control Implementation in Highly Elliptical Orbits
The Tschauner-Hempel equations are widely used to correct the separation distance drifts between a pair of satellites within a constellation in highly elliptical orbits [1]. This set of equations was discretized in the true anomaly angle [1] to be used in a digital steady-state hierarchical controller [2]. This controller [2] performed the drift correction between a pair of satellites within the constellation. The objective of a discretized system is to develop a simple algorithm to be implemented in the computer onboard the satellite. The main advantage of the discrete systems is that the computational time can be reduced by selecting a suitable sampling interval. For this digital system, the amount of data will depend on the sampling interval in the true anomaly angle [3]. The purpose of this paper is to implement the discrete Tschauner-Hempel equations and the steady-state hierarchical controller in the computer onboard the satellite. This set of equations is expressed in the true anomaly angle in which a relation will be formulated between the time and the true anomaly angle domains.
Capo-Lugo, Pedro A.↗
An Environment for Hardware-in-the-Loop Formation Navigation and Control Simulation
Recent interest in formation flying satellite systems has spurred a considerable amount of research in the relative navigation and control of satellites. Development in this area has included new estimation and control algorithms as well as sensor and actuator development specifically geared toward the relative control problem. This paper describes a simulation facility, the Formation Flying Testbed (FFTB) at NASA's Goddard Space Flight Center, which allows engineers to test new algorithms for the formation flying problem with relevant GN&C hardware in a closed loop simulation. The FFTB currently supports the injection of GPS receiver hardware into the simulation loop, and support for satellite crosslink ranging technology is at a prototype stage. This closed-loop, hardware inclusive simulation capability permits testing of navigation and control software in the presence of the actual hardware with which the algorithms must interact. This capability provides the navigation or control developer with a perspective on how the algorithms perform as part of the closed-loop system. In this paper, the overall design and evolution of the FFTB are presented. Each component of the FFTB is then described in detail. Interfaces between the components of the FFTB are shown and the interfaces to and between navigation and control software are described in detail. Finally, an example of closed-loop formation control with GPS receivers in the loop is presented and results are analyzed.
Burns, Rich↗
Anti-Collision Function Design and Performances of the CNES Formation Flying Experiment on the PRISMA Mission
Within the framework of a partnership agreement, EADS ASTRIUM has worked since June 2006 for the CNES formation flying experiment on the PRISMA mission. EADS ASTRIUM is responsible for the anti-collision function. This responsibility covers the design and the development of the function as a Matlab/Simulink library, as well as its functional validation and performance assessment. PRISMA is a technology in-orbit testbed mission from the Swedish National Space Board, mainly devoted to formation flying demonstration. PRISMA is made of two micro-satellites that will be launched in 2009 on a quasi-circular SSO at about 700 km of altitude. The CNES FFIORD experiment embedded on PRISMA aims at flight validating an FFRF sensor designed for formation control, and assessing its performances, in preparation to future formation flying missions such as Simbol X; FFIORD aims as well at validating various typical autonomous rendezvous and formation guidance and control algorithms. This paper presents the principles of the collision avoidance function developed by EADS ASTRIUM for FFIORD; three kinds of maneuvers were implemented and are presented in this paper with their performances.
Cayeux, P.↗
Formation Flying in Earth, Libration, and Distant Retrograde Orbits
This slide presentation examines the current and future state of formation flying, LEO formations, control strategies for flight in the vicinity of the libration points, and distant retrograde orbit formations. This discussion of LEO formations includes background on perturbation theory/accelerations and LEO formation flying. The discussion of strategies for formation flight in the vicinity of the libration points includes libration missions and natural and controlled libration orbit formations. A reference list is included.
Folta, David C.↗
The formation of the lyman continuum isothermal atmosphere.
Physical processes controlling formation of Lyman continuum of Sun
SOLAR SPECTRUM↗
Expanding Hardware-in-the-Loop Formation Navigation and Control with Radio Frequency Crosslink Ranging
The Formation Flying Testbed (FFTB) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) provides a hardware-in-the-loop test environment for formation navigation and control. The facility continues to evolve as a modular, hybrid, dynamic simulation facility for end-to-end guidance, navigation, and control (GN&C) design and analysis of formation flying spacecraft. The core capabilities of the FFTB, as a platform for testing critical hardware and software algorithms in-the-loop, are reviewed with a focus on recent improvements. With the most recent improvement, in support of Technology Readiness Level (TRL) 6 testing of the Inter-spacecraft Ranging and Alarm System (IRAS) for the Magnetospheric Multiscale (MMS) mission, the FFTB has significantly expanded its ability to perform realistic simulations that require Radio Frequency (RF) ranging sensors for relative navigation with the Path Emulator for RF Signals (PERFS). The PERFS, currently under development at NASA GSFC, modulates RF signals exchanged between spacecraft. The RF signals are modified to accurately reflect the dynamic environment through which they travel, including the effects of medium, moving platforms, and radiated power.
Mitchell, Jason W.↗
Asynchronous switching decentralized controllers for spacecraft formations
A method for the design of decentralized asynchronous controllers for spacecraft formations is presented.
decentralized asynchronous controllers↗
Improved Radiative Control of Ribbon Growth
Shield modifications enhance growth rate while reducing silicon oxide formation. Control of dendritic-web crystal growth requires precise control of web temperature profile. Achieved by using series of thermal radiation shields to control thermal-radiation field in region where melt solidifying onto crystal ribbon being pulled from melt.
Mchugh, J. P.↗
Ground Demonstration of Synchronized Formation Rotations for Precision, Multi-Spacecraft Interferometers
This paper reports the ground demonstration of precision synchronized formation rotations with better than 6 arcmin/5 cm performance in the Formation Control Testbed (FCT). The FCT currently consists of two, five degree-of-freedom, air bearing-levitated robots. The sixth degree-of-freedom, vertical translation, is being added in November 2007. Each robot has a suite of flight-like avionics and actuators, including a star tracker, fiber-optic gyroscopes, reaction wheels, cold-gas thrusters, inter-robot communication, and on-board computers that run the Formation and Attitude Control System software.
ground demonstrations↗
Autonomous Formations of Multi-Agent Systems
Autonomous formation control of multi-agent dynamic systems has a number of applications that include ground-based and aerial robots and satellite formations. For air vehicles, formation flight ("flocking") has the potential to significantly increase airspace utilization as well as fuel efficiency. This presentation addresses two main problems in multi-agent formations: optimal role assignment to minimize the total cost (e.g., combined distance traveled by all agents); and maintaining formation geometry during flock motion. The Kuhn-Munkres ("Hungarian") algorithm is used for optimal assignment, and consensus-based leader-follower type control architecture is used to maintain formation shape despite the leader s independent movements. The methods are demonstrated by animated simulations.
Dhali, Sanjana↗
Partially Decentralized Control Architectures for Satellite Formations
In a partially decentralized control architecture, more than one but less than all nodes have supervisory capability. This paper describes an approach to choosing the number of supervisors in such au architecture, based on a reliability vs. cost trade. It also considers the implications of these results for the design of navigation systems for satellite formations that could be controlled with a partially decentralized architecture. Using an assumed cost model, analytic and simulation-based results indicate that it may be cheaper to achieve a given overall system reliability with a partially decentralized architecture containing only a few supervisors, than with either fully decentralized or purely centralized architectures. Nominally, the subset of supervisors may act as centralized estimation and control nodes for corresponding subsets of the remaining subordinate nodes, and act as decentralized estimation and control peers with respect to each other. However, in the context of partially decentralized satellite formation control, the absolute positions and velocities of each spacecraft are unique, so that correlations which make estimates using only local information suboptimal only occur through common biases and process noise. Covariance and monte-carlo analysis of a simplified system show that this lack of correlation may allow simplification of the local estimators while preserving the global optimality of the maneuvers commanded by the supervisors.
Carpenter, J. Russell↗