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NASA NTRS2009

Validation of Model Forecasts of the Ambient Solar Wind

Independent and automated validation is a vital step in the progression of models from the research community into operational forecasting use. In this paper we describe a program in development at the CCMC to provide just such a comprehensive validation for models of the ambient solar wind in the inner heliosphere. We have built upon previous efforts published in the community, sharpened their definitions, and completed a baseline study. We also provide first results from this program of the comparative performance of the MHD models available at the CCMC against that of the Wang-Sheeley-Arge (WSA) model. An important goal of this effort is to provide a consistent validation to all available models. Clearly exposing the relative strengths and weaknesses of the different models will enable forecasters to craft more reliable ensemble forecasting strategies. Models of the ambient solar wind are developing rapidly as a result of improvements in data supply, numerical techniques, and computing resources. It is anticipated that in the next five to ten years, the MHD based models will supplant semi-empirical potential based models such as the WSA model, as the best available forecast models. We anticipate that this validation effort will track this evolution and so assist policy makers in gauging the value of past and future investment in modeling support.

Macneice, P. J.↗
NASA NTRS2006

Identifying Trends in Deep Space Network Monitor Data

A computer program has been developed that analyzes Deep Space Network monitor data, looking for changes of trends in critical parameters. This program represents a significant improvement over the previous practice of manually plotting data and visually inspecting the resulting graphs to identify trends. This program uses proven numerical techniques to identify trends. When a statistically significant trend is detected, then it is characterized by means of a symbol that can be used by pre-existing model-based reasoning software. The program can perform any of the following functions: Given an expectation that data in a given list should exhibit an upward, downward, constant, or unknown trend, it can determine whether the data do or do not follow such a trend. Given a list of data, it can identify which of the aforementioned trends the data follow. Given two lists of data, it can determine whether or not both follow the same trend. This program can be executed on a variety of computers. It can be distributed in either source code or binary code form. It must be run in conjunction with any one of a number of Lisp compilers that are available commercially or as shareware.

James, Mark↗
NASA NTRS2010

Genesis of Pre-Hurricane Felix (2007): Warm Core Formation, Precipitation Evolution, and Predictability - Part 2

This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm's warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave's pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convective and stratiform precipitation rates increase with time. While stratiform precipitation occupies a larger area even at the tropical storm stage, deep moist convection makes a comparable contribution to the total rain rate at the pregenesis stage, and a larger contribution than stratiform processes at the storm stage. The convergence profile averaged near the pouch center is found to become dominantly convective with increasing deep moist convective activity there. Low-level convergence forced by interior diabatic heating plays a key role in forming and intensifying the near-surface closed circulation, while the midlevel convergence associated with stratiform precipitation helps to increase the midlevel circulation and thereby contributes to the formation and upward extension of a tropospheric-deep cyclonic vortex. Sensitivity tests with different model physics options and initial conditions demonstrate a similar pregenesis evolution. These tests suggest that the genesis location of a tropical storm is largely controlled by the parent wave's critical layer, whereas the genesis time and intensity of the protovortex depend on the details of the mesoscale organization, which is less predictable. Some implications of the findings are discussed.

Wang, zhuo↗
NASA NTRS2012

Approaching Moons from Resonance via Invariant Manifolds

In this work, the approach phase from the final resonance of the endgame scenario in a tour design is examined within the context of invariant manifolds. Previous analyses have typically solved this problem either by using numerical techniques or by computing a catalog of suitable trajectories. The invariant manifolds of a selected set of libration orbits and unstable resonant orbits are computed here to serve as guides for desirable approach trajectories. The analysis focuses on designing an approach phase that may be tied into the final resonance in the endgame sequence while also targeting desired conditions at the moon.

endgame↗
NASA NTRS2013

Geometric Effects on the Amplification of First Mode Instability Waves

The effects of geometric changes on the amplification of first mode instability waves in an external supersonic boundary layer were investigated using numerical techniques. Boundary layer stability was analyzed at Mach 6 conditions similar to freestream conditions obtained in quiet ground test facilities so that results obtained in this study may be applied to future test article design to measure first mode instability waves. The DAKOTA optimization software package was used to optimize an axisymmetric geometry to maximize the amplification of the waves at first mode frequencies as computed by the 2D STABL hypersonic boundary layer stability analysis tool. First, geometric parameters such as nose radius, cone half angle, vehicle length, and surface curvature were examined separately to determine the individual effects on the first mode amplification. Finally, all geometric parameters were allowed to vary to produce a shape optimized to maximize the amplification of first mode instability waves while minimizing the amplification of second mode instability waves. Since first mode waves are known to be most unstable in the form of oblique wave, the geometries were optimized using a broad range of wave frequencies as well as a wide range of oblique wave angles to determine the geometry that most amplifies the first mode waves. Since first mode waves are seen most often in flows with low Mach numbers at the edge of the boundary layer, the edge Mach number for each geometry was recorded to determine any relationship between edge Mach number and the stability of first mode waves. Results indicate that an axisymmetric cone with a sharp nose and a slight flare at the aft end under the Mach 6 freestream conditions used here will lower the Mach number at the edge of the boundary layer to less than 4, and the corresponding stability analysis showed maximum first mode N factors of 3.

Kirk, Lindsay C.↗
NASA NTRS2013

Mixed Integer Programming and Heuristic Scheduling for Space Communication

Optimal planning and scheduling for a communication network was created where the nodes within the network are communicating at the highest possible rates while meeting the mission requirements and operational constraints. The planning and scheduling problem was formulated in the framework of Mixed Integer Programming (MIP) to introduce a special penalty function to convert the MIP problem into a continuous optimization problem, and to solve the constrained optimization problem using heuristic optimization. The communication network consists of space and ground assets with the link dynamics between any two assets varying with respect to time, distance, and telecom configurations. One asset could be communicating with another at very high data rates at one time, and at other times, communication is impossible, as the asset could be inaccessible from the network due to planetary occultation. Based on the network's geometric dynamics and link capabilities, the start time, end time, and link configuration of each view period are selected to maximize the communication efficiency within the network. Mathematical formulations for the constrained mixed integer optimization problem were derived, and efficient analytical and numerical techniques were developed to find the optimal solution. By setting up the problem using MIP, the search space for the optimization problem is reduced significantly, thereby speeding up the solution process. The ratio of the dimension of the traditional method over the proposed formulation is approximately an order N (single) to 2*N (arraying), where N is the number of receiving antennas of a node. By introducing a special penalty function, the MIP problem with non-differentiable cost function and nonlinear constraints can be converted into a continuous variable problem, whose solution is possible.

Lee, Charles H.↗
NASA NTRS2015

Ultrasonic Measurement and Monitoring of Loads in Bolts used in Structural Joints

The paper is an overview of work by the author in measuring and monitoring loads in bolts using an ultrasonic extensometer. A number of cases of bolted joints are covered. These include, a clamped joint with clearance fit between the bolt and hole, a clamped joint with the bolt in an interference fit with the hole, a flanged joint which allows the flange and bolt to bend; and a shear joint in a clevis and tang configuration. These applications were initially developed for measuring and monitoring preload in the NASA Space Shuttle Orbiter critical joints but are also applicable for monitoring loads in other critical bolted joints of structures such as transportation bridges and other aerospace structures. The paper explains how to set‐up a model to estimate the load factor and accuracy for the ultrasonic preload application in a clamped joint with clearance fit. The ultrasonic preload application for clamped joint with bolt in an interference fit can also be used to measure diametrical interference between the bolt shank and hole; and interference pressure on the bolt shank. Model and experimental data are given to demonstrate use of ultrasonic measurements in a shear joint. A bolt in a flanged joint experiences both tensile and bending loads. This application involves measurement of bending and tensile preload in a bolt. The ultrasonic beam bends due to the bending load on the bolt. A numerical technique to compute the trace of ultrasonic ray is presented.

Koshti, Ajay↗
NASA NTRS2015

Combined Structural and Compositional Evolution of Planetary Rings Due to Micrometeoroid Impacts and Ballistic Transport

We introduce improved numerical techniques for simulating the structural and compositional evolution of planetary rings due to micrometeoroid bombardment and subsequent ballistic transport of impact ejecta. Our current, robust code is capable of modeling structural changes and pollution transport simultaneously over long times on both local and global scales. In this paper, we describe the methodology based on the original structural code of Durisen et al. (1989, Icarus 80, 136-166) and on the pollution transport code of Cuzzi and Estrada (1998, Icarus 132, 1-35). We provide demonstrative simulations to compare with, and extend upon previous work, as well as examples of how ballistic transport can maintain the observed structure in Saturn's rings using available Cassini occultation optical depth data. In particular, we explicitly verify the claim that the inner B (and presumably A) ring edge can be maintained over long periods of time due to an ejecta distribution that is heavily biased in the prograde direction through a balance between the sharpening effects of ballistic transport and the broadening effects of viscosity. We also see that a "ramp"-like feature forms over time just inside that edge. However, it does not remain linear for the duration of the runs presented here unless a less steep ejecta velocity distribution is adopted. We also model the C ring plateaus and find that their outer edges can be maintained at their observed sharpness for long periods due to ballistic transport. We hypothesize that the addition of a significant component of a retrograde-biased ejecta distribution may help explain the linearity of the ramp and is probably essential for maintaining the sharpness of C ring plateau inner edges. This component would arise for the subset of micrometeoroid impacts which are destructive rather than merely cratering. Such a distribution will be introduced in future work.

Cassini↗
NASA NTRS2017

Spacecraft Mission Design for the Mitigation of the 2017 PDC Hypothetical Asteroid Threat

This paper presents a detailed mission design analysis results for the 2017 Planetary Defense Conference (PDC) Hypothetical Asteroid Impact Scenario, documented at https://cneos.jpl.nasa.gov/ pd/cs/pdc17/. The mission design includes campaigns for both reconnaissance (flyby or rendezvous) of the asteroid (to characterize it and the nature of the threat it poses to Earth) and mitigation of the asteroid, via kinetic impactor deflection, nuclear explosive device (NED) deflection, or NED disruption. Relevant scenario parameters are varied to assess the sensitivity of the design outcome, such as asteroid bulk density, asteroid diameter, momentum enhancement factor, spacecraft launch vehicle, and mitigation system type. Different trajectory types are evaluated in the mission design process from purely ballistic to those involving optimal midcourse maneuvers, planetary gravity assists, and/or lowthrust solar electric propulsion. The trajectory optimization is targeted around peak deflection points that were found through a novel linear numerical technique method. The optimization process includes constrain parameters, such as Earth departure date, launch declination, spacecraft/asteroid relative velocity and solar phase angle, spacecraft dry mass, minimum/maximum spacecraft distances from Sun and Earth, and Earth/spacecraft communications line of sight. Results show that one of the best options for the 2017 PDC deflection is solar electric propelled rendezvous mission with a single spacecraft using NED for the deflection

Barbee, Brent W.↗
NASA NTRS2017

Spacecraft Mission Design for the Mitigation of the 2017 PDC Hypothetical Asteroid Threat

This paper presents a detailed mission design analysis results for the 2017 Planetary Defense Conference (PDC) Hypothetical Asteroid Impact Scenario, documented at https:cneos.jpl.nasa.govpdcspdc17. The mission design includes campaigns for both reconnaissance (flyby or rendezvous) of the asteroid (to characterize it and the nature of the threat it poses to Earth) and mitigation of the asteroid, via kinetic impactor deflection, nuclear explosive device (NED) deflection, or NED disruption. Relevant scenario parameters are varied to assess the sensitivity of the design outcome, such as asteroid bulk density, asteroid diameter, momentum enhancement factor, spacecraft launch vehicle, and mitigation system type. Different trajectory types are evaluated in the mission design process from purely ballistic to those involving optimal midcourse maneuvers, planetary gravity assists, and/or low-thrust solar electric propulsion. The trajectory optimization is targeted around peak deflection points that were found through a novel linear numerical technique method. The optimization process includes constrain parameters, such as Earth departure date, launch declination, spacecraft, asteroid relative velocity and solar phase angle, spacecraft dry mass, minimum/maximum spacecraft distances from Sun and Earth, and Earth-spacecraft communications line of sight. Results show that one of the best options for the 2017 PDC deflection is solar electric propelled rendezvous mission with a single spacecraft using NED for the deflection.

Barbee, Brent W.↗
NASA NTRS2018

Numerically Simulating an Expanding Continuum Jet into a Surrounding Non-Continuum Region

A numerical technique that simulates the interaction between a continuum jet and a free-molecular, rarefied or transitional flow field is presented and applied. The technique is based on selecting a boundary between the expanding jet plume and interacting flow field defined by the Bird breakdown parameter, P. By properly choosing the boundary, the jet plume computed by computational fluid dynamics (CFD) is uncoupled from the interaction region that is simulated by direct simulation Monte Carlo (DSMC). The mechanics of uncoupling the continuum and non-continuum regions is discussed first. Also, a discussion of expanding continuum plume breakdown and the formulation of the Bird breakdown parameter is presented. To show the usefulness, examples of applying the CFD-DSMC technique are given. Many of the examples were taken from projects worked by the staff of the Aerothermodynamics Branch at the NASA Langley Research Center. These examples show a variety of applications of the technique and allow those examples not previously documented to be formally presented.

Jet interaction↗
NASA NTRS2014

Ghost Imaging of Space Objects

would like to summarize that our "Ghost Imaging of Space Objects" NIAC research effort was successful. As anticipated, its main return has been the newly acquired knowledge and the understanding of the pathways that lead from this knowledge to its applications in observational astronomy. During this research we came across several fundamental insights that were not expected at the beginning. We came to realize that the ghost imaging of dark objects using background thermal light can be treated as a special case of Hanbury Brown and Twiss intensity interferometry in combination with the Babinet's principle for higher-order observables. Extensive recent work performed in this field by other research groups worldwide might seem to detract from the conceptual originality and novelty of our approach; but at the same time it serves as an encouraging indication that the chosen approach is acknowledged in the broader science community as promising. This newly found synergy, acknowledged in the CTA newsletter from May 2014 reporting on the Workshop on Hanbury Brown and Twiss interferometry in Nice, makes us confident that our published and otherwise disseminated results will be integrated into a larger-scale on-going research effort aimed at performing astronomy observations of both bright and dark objects with unparalleled resolution. While we are satisfied with acceptance of our results by the international research community as a contribution to the field of intensity interferometry as well as to the on-going mission-oriented projects, we also have been aiming at receiving support to continue and advance this research at JPL. Several proposals have been submitted in pursuit of this goal. Three of them are still under consideration, and we expect to learn about the funding decisions soon. These new projects would leverage the results of this NIAC study and extend it along well-defined directions that have been discussed above. Shifting the main paradigm of our approach towards intensity interferometry entailed another important realization, that the actual imaging of dark objects, in a sense of mapping the column optical density distribution, is possible by using known numerical techniques, such as the Gerchberg-Saxton approach. This insight was also unanticipated in the beginning and caused a shift of the research focus from the initial plan. While this focus shift has been well-justified and fruitful, it has left several issues unexplored. Some of these issues, too, are included in the future research proposals.

Optics↗
NASA NTRS2016

Periodic Orbit-Attitude Solutions in the Planar Elliptic Restricted Three-Body Problem

The pitch motion of a spacecraft in the planar elliptic restricted three-body system is studied. Previous studies laid the foundation for spacecraft stability analysis with a small perturbation to the zero pitch motion. In this study, a cell mapping approach that combines analytical and numerical techniques is used to study the global behavior of the full nonlinear spacecraft attitude in which coupling between orbital dynamics and attitude occurs. The effect of gravity gradient torques, orbital eccentricity, and the spacecraft configuration at different Lagrangian points is analyzed. Multiple-period periodic solutions and invariant surfaces are presented for different cases. Reference trajectories around the Lagrangian points are also considered to study coupled dynamics.

Koh, Dayung↗
NASA NTRS2019

Gradient-Based Aeroservoelastic Optimization with Static Output Feedback

Static output feedback considers an optimal low-order feedback matrix which directly connects the sensors to the control inputs. This work demonstrates the numerical techniques needed to compute the analytical gradient of the optimal feedback matrix with respect to design variables, which may then be used for gradient-based optimization. The derivatives are demonstrated for aeroservoelastic optimization under a series of closed- loop gust load alleviation constraints, considering a continuous stochastic gust load applied to a transport vehicle configuration, among other design constraints such as utter and maneuver loads. The optimal trade-o s between passive load alleviation and active load alleviation for static output feedback are compared with those from full-state feedback, which may be considered an upper-bound for effective sensor-based control.

Stanford, Bret K.↗
NASA NTRS1995

Planetary-Induced Nutation of the Earth - Direct Terms

Small torques by the planets can alter the direction of the Earth's rotation axis in space. These direct planetary-induced nutations have been computed using a numerical technique. 55 nutation terms with periods between 0.2 and 243 yr are presented. The maximum nutation is 0.5 milliarcseconds. Also given are planetary-induced rates and accelerations of precession and obliquity.

Planetary-Induced↗
NASA NTRSDate not supplied

Buckling Behavior of Conical-Cylindrical Shells and Design Considerations for Launch-Vehicle Applications

Traditionally, launch vehicles are constructed with a series of buckling-prone thin-walled cylindrical and conical shells, in which the buckling behavior of these shells has been well studied and buckling design guidance exists. Conical-cylindrical shell geometry is now being utilized for launch-vehicle stage adapters and payload adapters due to advances in manufacturing and numerical techniques, but there is no available buckling design guidance for this nontraditional combined geometry. In order to provide design recommendations, the buckling behavior and imperfection sensitivity of conical-cylindrical shells and how it differs from the conical and cylindrical components needs to be better understood. From this premise, it is possible to investigate whether or not the buckling knockdown factor guidelines for conical and cylindrical shells outlined in NASA SP-8019 and NASA SP-8007, respectively, are still applicable. The results in this paper will show that the current recommendations are not appropriate in some cases. In addition, it was observed that the large rotations and displacements near the transition between the cone and cylinder can have a larger effect on the buckling load than the presence of radial imperfections for conical-cylindrical shells, which is different than conical and cylindrical shells. More interesting is the fact that design modifications to increase the buckling capability of a conical-cylindrical shell such as adding reinforcement, which may add mass, will make the shell more sensitive to imperfections. The increased imperfection sensitivity may negate the increase in buckling capability that was thought to be achievable. In the end, it may be more beneficial to design a conical-cylindrical shell in which the buckling behavior is dominated by the more predictable geometric nonlinearity, which may lead to an overall lower buckling load, but a lower knockdown factor may be possible since it will not be as sensitive to the less-known radial imperfections.

Buckling↗
NASA NTRSDate not supplied

Autonomous Burn Targeting for a Lunar Sortie Staged From a Near-Rectilinear Halo Orbit

NASA is planning manned lunar landings starting in the mid 2020s as part of its Artemis program. These lunar sortie missions will be staged from a Near-Rectilinear Halo Orbit (NRHO), with a requirement for the lander to autonomously determine the timing and targets for multiple burns so that it can navigate its way back to the staging vehicle in the NRHO. The lander mission profile transitions through multiple gravitational regimes, at times influenced equally by 3rd bodies (Earth and Sun) as much as by the Moon, while at other times the lander is primarily influenced by lunar gravitation. These different gravitational regimes pose challenges to guidance and targeting logic. The present work describes options for autonomous logic for each of several major maneuvers of the lunar sortie, including numerical techniques to incorporate the effect of 3rd bodies. Throughout the development there is an emphasis on simplicity and computational efficiency.

NRHO↗