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NASA NTRS2006

Calculation of Zonal Winds using Accelerometer and Rate Data from Mars Global Surveyor

The Mars Global Surveyor spacecraft was initially placed into a high eccentricity, nearly polar orbit about Mars with a 45-hour period. To accomplish the science objectives of the mission, a 2-hour, circular orbit was required. Using a method known as aerobraking, numerous passes through the upper atmosphere slowed the spacecraft, thereby reducing the orbital period and eccentricity. To successfully perform aerobraking, the spacecraft was designed to be longitudinally, aerodynamically stable in pitch and yaw. Since the orbit is nearly polar, the yaw orientation of the spacecraft was sensitive to disturbances caused by the zonal components of wind (east-to-west or west-to-east) acting on the spacecraft at aerobraking altitudes. Zonal wind velocities were computed by equating the aerodynamic and inertia-related torques acting on the spacecraft. Comparisons of calculated zonal winds with those computed from the Mars Thermospheric Global Circulation Model are discussed.

Mars thermospheric winds↗

NASA NTRS1999

A Comprehensive Orbit Reconstruction for the Galileo Prime Mission in the J2000 System

The Galileo spacecraft arrived at Jupiter in December of 1995 to begin an orbital tour of the Jovian system. The objective of the tour was up close study of the planet, its satellites, and its magnetosphere. The spacecraft completed its 11 orbit prime mission in November of 1997 having had 16 successful close encounters with the Galilean satellites (including two prior to Jupiter orbit insertion). Galileo continues to operate and will have made an additional 10 orbits of Jupiter by the date of this Conference. Earlier papers discuss the determination of the spacecraft orbit in support of mission operations from arrival at Jupiter through the first 9 orbits. In this paper we re-examine those earlier orbits and extend the analysis through orbit 12, the first orbit of the Galileo Europa Mission (GEM). The objective of our work is the reconstruction of the spacecraft trajectory together with the development of a consistent set of ephemerides for the Galilean satellites. As a necessary byproduct of the reconstruction we determine improved values for the Jovian system gravitational parameters and for the Jupiter pole orientation angles. Our preliminary analyses have already led to many of the results reported in the scientific literature. Unlike the Galileo Navigation Team which operates in the EME-1950 coordinate system, we elected to work in the (J2000) International Celestial Reference Frame (ICRF), the reference frame of the current JPL planetary and satellite ephemerides as well as the standard frame of the international astronomical and planetary science community. Use of this frame permits more precise modelling of the spacecraft and satellite observations. Moreover, it is the frame of choice for all other operational JPL missions and will probably be the frame for future missions for some time. Consequently, our adoption of the ICRF will facilitate the combination of our results with any obtained from future missions (e.g. the proposed Europa Orbiter mission). In addition, our results may be used by the science community, without need of a reference frame conversion.

Jacobson, Robert A.↗

NASA NTRS1991

NASA 1990 Multisensor Airborne Campaigns (MACs) for ecosystem and watershed studies

The Multisensor Airborne Campaign (MAC) focus within NASA's former Land Processes research program was conceived to achieve the following objectives: to acquire relatively complete, multisensor data sets for well-studied field sites, to add a strong remote sensing science component to ecology-, hydrology-, and geology-oriented field projects, to create a research environment that promotes strong interactions among scientists within the program, and to more efficiently utilize and compete for the NASA fleet of remote sensing aircraft. Four new MAC's were conducted in 1990: the Oregon Transect Ecosystem Research (OTTER) project along an east-west transect through central Oregon, the Forest Ecosystem Dynamics (FED) project at the Northern Experimental Forest in Howland, Maine, the MACHYDRO project in the Mahantango Creek watershed in central Pennsylvania, and the Walnut Gulch project near Tombstone, Arizona. The OTTER project is testing a model that estimates the major fluxes of carbon, nitrogen, and water through temperate coniferous forest ecosystems. The focus in the project is on short time-scale (days-year) variations in ecosystem function. The FED project is concerned with modeling vegetation changes of forest ecosystems using remotely sensed observations to extract biophysical properties of forest canopies. The focus in this project is on long time-scale (decades to millenia) changes in ecosystem structure. The MACHYDRO project is studying the role of soil moisture and its regulating effects on hydrologic processes. The focus of the study is to delineate soil moisture differences within a basin and their changes with respect to evapotranspiration, rainfall, and streamflow. The Walnut Gulch project is focused on the effects of soil moisture in the energy and water balance of arid and semiarid ecosystems and their feedbacks to the atmosphere via thermal forcing.

Wickland, Diane E.↗

NASA NTRSDate not supplied

Deflection of Solar Energetic Protons by an Ion Thruster

While Galactic Cosmic Rays (GCR) represent a long-term cancer risk to deep space human missions, Solar Energetic Particles (SEP) represent a significant acute radiation hazard to human spaceflight. This work investigates wave-particle interactions caused by the incidence of a beam of energetic protons, representing a notional SEP event, onto a cloud of ions representing a notional ion thruster plume. The resulting electromagnetic ion/ion instability is developed to investigate the degree to which energetic protons can be scattered out of the initial beam. This work includes investigations of deflection rate dependences on incident SEP energy and flux, ion thruster power and orientation relative to SEP incidence, plume ion species, and background plasma. Also investigated are the spectrum and angular distribution of electromagnetic radiation resulting from the wave-particle interactions. The primary objective of this investigation is to develop a technique for active mitigation of SEP radiation threats to spacecraft and crew, by exploring the wave-particle interaction of a SEP event with the plasma plume expelled from an ion thruster. Since the cost in expended fuel restricts this technique to intermittent use during interplanetary flights, effective prediction of when a SEP event might impact the mission is still important, and the observation of conditions that might lead to SEP events, human-in-the-loop space weather analyses, and development of SEP prediction models remain essential to crew safety, spacecraft function, and mission success.

Interplanetary Space Flight↗

NASA NTRS1990

Photovoltaic array space power plus diagnostics experiment

The objective of the Photovoltaic Array Space Power Plus Diagnostics (PASP Plus) experiment is to measure the effects of the interaction of the low- to mid-altitude space environment on the performance of a diverse set of small solar-cell arrays (planar and concentrator, representative of present and future military technologies) under differing conditions of velocity-vector orientation and simulated (by biasing) high-voltage operation. Solar arrays to be tested include Si and GaAs planar arrays and several types of GaAs concentrator arrays. Diagnostics (a Langmuir probe and a pressure gauge) and a transient pulse monitor (to measure radiated and conducted EMI during arcing) will be used to determine the impact of the environment on array operation to help verify various interactions models. Results from a successful PASP Plus flight will furnish answers to important interactions questions and provide inputs for design and test standards for photovoltaic space-power subsystems.

Guidice, Donald A.↗

NASA NTRS1994

Measurement and characterization of force dynamics in high T(sub c) superconductors

Magnetic bearing implementations using more exotic superconducting phenomena have been proliferating in recent years because they have important advantages over conventional implementations. For example, the stable suspension of a six degrees-of-freedom object by superconducting means can be achieved without a control system and with the use of only a single superconductor. It follows that the construction becomes much simpler with decreased need for position sensors and stabilizers. However, it is recognized that the design of superconducting systems can be difficult because important characteristics relating to the 6 degree-of-freedom dynamics of an object suspended magnetically are not readily available and the underlying principles of superconducting phenomena are not yet completely understood. To eliminate some of the guesswork in the design process, this paper proposes a system which can resolve the mechanical properties of suspension by superconductivity and provide position and orientation dependent data about the system's damping, stiffness, and frequency response characteristics. This system employs an actively-controlled magnetically-suspended fine-motion device that can also be used as a six degree-of-freedom force sensor. By attaching the force sensor to a permanent magnet that is being levitated above a superconducting magnet, mechanical characteristics of the superconductor levitation can be extracted. Such information would prove useful for checking the validity of theoretical models and may even give insights into superconducting phenomena.

Higuchi, Toshiro↗

NASA NTRS1993

System identification of the Large-Angle Magnetic Suspension Test Facility (LAMSTF)

The Large-Angle Magnetic Suspension Test Facility (LAMSTF), a laboratory-scale research project to demonstrate the magnetic suspension of objects over wide ranges of attitudes, has been developed. This system represents a scaled model of a planned Large-Gap Magnetic Suspension System (LGMSS). The LAMSTF system consists of a planar array of five copper electromagnets which actively suspend a small cylindrical permanent magnet. The cylinder is a rigid body and can be controlled to move in five independent degrees of freedom. Five position variables are sensed indirectly by using infra-red light-emitting diodes and light-receiving phototransistors. The motion of the suspended cylinder is in general nonlinear and hence only the linear, time-invariant perturbed motion about an equilibrium state is considered. One of the main challenges in this project is the control of the suspended element over a wide range of orientations. An accurate dynamic model plans an essential role in controller design. The analytical model of the LAMSTF system includes highly unstable real poles (about 10 Hz) and low-frequency flexible modes (about 0.16 Hz). Projection filters are proposed to identify the state space model from closed-loop test data in time domain. A canonical transformation matrix is also derived to transform the identified state space model into the physical coordinate. The LAMSTF system is stabilized by using a linear quadratic regulator (LQR) feedback controller. The rate information is obtained by calculating the back difference of the sensed position signals. The reference inputs contain five uncorrelated random signals. This control input and the system reponse are recorded as input/output data to identify the system directly from the projection filters. The sampling time is 4 ms and the model is fairly accurate in predicting the step responses for different controllers while the analytical model has a deficiency in the pitch axis.

Huang, Jen-Kuang↗

NASA NTRS1995

Analysis of Gaspra lightcurves using Galileo shape and photometric models

Galileo-based models for the shape of 951 Gaspra and the global-average photometric behavior of its surface have been used to model a representative subset of the asteroid's telescopic lightcurves. Fitting the synthetic lightcurves to the observed timing of lightcurve extrema, and knowing the orientation of Gaspra's axes at the time of the Galileo flyby, leads to a sidereal rotation period for the asteroid of 7.042024 +/- 0.000020 hr, a slight change from the period reported by Magnusson et al. (1992). Initially, the shapes, amplitudes, and absolute photometry of the synthetic and observed lightcurves agree with each other to within 0.05-0.1 mag. Small modifications to the Gaspra shape model on sides of the asteroid poorly imaged by Galileo (changes of 700 m or less in the southern hemisphere at longitudes 90 deg-270 deg W) reduce the typical discrepancies to approximately 0.05 mag in lightcurve shape and less than 0.03 mag in absolute photometry. The result demonstrates that Earth-based lightcurves can be used to refine the shape of a spacecraft-imaged irregular object in areas that are poorly constrained by the spacecraft observations. The consistency and phase-angle dependence of the Galileo-based model for Gaspra photometry, supports the accuracy of the absolute calibration of the Galileo SSI camera, and confirms the Earth-based determination of the V-filter geometric albedo of the asteroid (0.22 +/- 0.03; Tholen et al., submitted for publication). Remaining discrepancies between the synthetic and observed lightcurves show no indication of systematic latitudinal variations in albedo and also cannot be explained entirely by isolated albedo spots. These discrepancies are most likely caused by (1) small, remaining, hard-to-constrain errors in the Gaspra shape model and/or (2) moderate variations in macroscopic roughness across the asteroid's surface, in particular making longitudes 130 deg to 300 deg W moderately rougher than the opposite hemisphere.

Simonelli, Damon P.↗

NASA NTRS1994

System identification of the Large-Angle Magnetic Suspension Test Fixture (LAMSTF)

The Large-Angle Magnetic Suspension Test Fixture (LAMSTF), a laboratory-scale research project to demonstrate the magnetic suspension of objects over wide ranges of attitudes, has been developed. This system represents a scaled model of a planned Large-Gap Magnetic Suspension System (LGMSS). The LAMSTF consists of a small cylindrical permanent magnet suspended element which is levitated above a planar array of five electromagnets mounted in a circular configuration. The cylinder is a rigid body and can be controlled to move in five independent degrees of freedom. Six position variables are sensed indirectly by using infrared light-emitting diodes and light-receiving phototransistors. The motion of the suspended cylinder is in general nonlinear and hence only the linear, time-invariant perturbed motion about an equilibrium state is considered. One of the main challenges in this project is the control of the suspended element over a wide range of orientations. An accurate dynamic model plays an essential role in controller design. The analytical model is first derived and open-loop characteristics discussed. The system is shown to be highly unstable and requires feedback control for system identification. Projection filters are first proposed to identify the state space model from closed-loop input/output test data in the time domain. This method is then extended to identify linear systems from the frequency test data. A canonical transformation matrix is also derived to transform the identified state space model into the physical coordinate. The LAMSTF system is stabilized by using a linear quadratic regulator (LQR) feedback controller for closed-loop identification. The rate information is obtained by calculating the back difference of the sensed position signals. Only the closed-loop random input/output data are recorded. Preliminary results from numerical simulations demonstrate that the identified system model is fairly accurate from either time domain or frequency-domain data. Experiments will be performed to validate the proposed closed-loop identification algorithms.

Huang, Jen-Kuang↗

NASA NTRS1990

Analysis of MMU FDIR expert system

This paper describes the analysis of a rulebase for fault diagnosis, isolation, and recovery for NASA's Manned Maneuvering Unit (MMU). The MMU is used by a human astronaut to move around a spacecraft in space. In order to provide maneuverability, there are several thrusters oriented in various directions, and hand-controlled devices for useful groups of them. The rulebase describes some error detection procedures, and corrective actions that can be applied in a few cases. The approach taken in this paper is to treat rulebases as symbolic objects and compute correctness and 'reasonableness' criteria that use the statistical distribution of various syntactic structures within the rulebase. The criteria should identify awkward situations, and otherwise signal anomalies that may be errors. The rulebase analysis agorithms are derived from mathematical and computational criteria that implement certain principles developed for rulebase evaluation. The principles are Consistency, Completeness, Irredundancy, Connectivity, and finally, Distribution. Several errors were detected in the delivered rulebase. Some of these errors were easily fixed. Some errors could not be fixed with the available information. A geometric model of the thruster arrangement is needed to show how to correct certain other distribution nomalies that are in fact errors. The investigations reported here were partially supported by The Aerospace Corporation's Sponsored Research Program.

Landauer, Christopher↗

NASA NTRS1994

Cracking characteristics of a habitable module pressure wall following orbital debris penetration

All long-duration spacecraft in low-earth-orbit are subject to high speed impacts by meteoroids and pieces of orbital debris. The threat of damage from such impacts is a significant design consideration in the development of long duration earth-orbiting spacecraft. This report presents the results of a study whose objective was to develop an empirical model to predict the magnitude of the various cracking and through-hole creation phenomena accompanying a habitable module penetration. The significance of the work performed is that the model predictions can be fed directly into a survivability analysis to determine whether or not module unzipping would occur under a specific set of impact conditions. The likelihood of module unzipping over a structure's lifetime can also be determined in such an analysis. In addition, effective hole size predictions can be used as part of a survivability analysis to determine the time available for module evacuation prior to the onset of incapacitation due to air loss. Some of the phenomena considered include maximum petal length, maximum tip-to-tip crack distance, depth of petal deformation, number of cracks formed, orientation of the maximum tip-to-tip distance with respect to the inner wall grain direction, and the effective inner wall hole diameter.

Schonberg, William P.↗

NASA NTRS2002

Synchrotron and Synchrotron Self-Compton Spectral Signatures and Blazar Emission Models

We find that energy losses due to synchrotron self-Compton (BBC) emission in Blazar jets can produce distinctive signatures in the time-averaged synchrotron and SSC spectra of these objects. For a fairly broad range of particle injection distributions, SSC-loss-dominated synchrotron emission exhibits a spectral dependence Fv approximately v (exp -3/2). The presence or absence of this dependence in the optical and ultraviolet spectra of flat-spectrum radio quasars such as PC 279 and in the soft X-ray spectra of high-frequency BL Lac objects such as Mark 501 gives a robust measure of the importance of SSC losses. Furthermore, for partially cooled particle distributions, spectral breaks of varying sizes can appear in the synchrotron and SSC spectra and will be related to the spectral indices of the emission below the break. These spectral signatures place constraints on the size scale and the nonthermal particle content of the emitting plasma, as well as the observer orientation relative to the jet axis.

Chiang, James↗

NASA NTRS2017

Meteorite Material Model for Structural Properties

To assess the threat posed by an asteroid entering Earth's atmosphere, one must predict if, when, and how it fragments during entry. A comprehensive understanding of the asteroid material properties is needed to achieve this objective. At present, the meteorite material found on earth are the only objects from an entering asteroid that can be used as representative material and be tested inside a laboratory setting. Due to complex petrology, it is technically challenging and expensive to obtain reliable material properties by means of laboratory test for a family of meteorites. In order to circumvent this challenge, meteorite unit models are developed to determine the effective material properties including Youngs modulus, compressive and tensile strengths and Poissons ratio, that in turn would help deduce the properties of asteroids. The meteorite unit is a representative volume that accounts for diverse minerals, porosity, cracks and matrix composition. The Youngs Modulus and Poissons Ratio in the meteorite units are calculated by performing several hundreds of Monte-Carlo simulations by randomly distributing the various phases inside these units. Once these values are obtained, cracks are introduced in these meteorite units. The size, orientation and distribution of cracks are derived by extensive CT-scans and visual scans of various meteorites from the same family. Subsequently, simulations are performed to attain stress-strain relations, strength and effective modulus values in the presence of these cracks. The meteorite unit models are presented for H, L and LL ordinary chondrites, as well as for terrestrial basalt. In the case of the latter, data from the simulations is compared with experimental data to validate the methodology. These material models will be subsequently used in fragmentation modeling of full scale asteroids.

Meteorite↗

NASA NTRS1989

Computational methods and software systems for dynamics and control of large space structures

The deployment, assembly and mission-oriented maneuvering of space structures in orbit will trigger large motions of flexible, truss-type structures. In addition, the presence of on-board controls both for attitude stabilization and specified vibration tolerance requirements may further complicate the dynamic behavior of the orbiting structures. Because of safety and cost considerations, the dynamic response of the combined structural and control systems must be predicted reliably. This need can only be met through the development of reliable and efficient simulation capabilities, since there is general agreement that on-orbit experiments should be limited because of cost, time and facility constraints. The long-term objective of this research effort is to develop a next-generation computer simulator for the dynamics and control of large space structures. The simulator will be based on integrating four research thrusts: a new multibody dynamics formulation methodology, modeling capabilities in long/slender truss-beam components with realistic joints, efficient computational procedures that can be implemented either in sequential or concurrent computers, and prototype simulation modules that can be easily processed into a modern large-scale engineering software system such as the NASA/Computational Structural Mechanics (CSM) testbed.

Park, K. C.↗

NASA NTRS2003

HYDRA : High-speed simulation architecture for precision spacecraft formation simulation

e Hierarchical Distributed Reconfigurable Architecture- is a scalable simulation architecture that provides flexibility and ease-of-use which take advantage of modern computation and communication hardware. It also provides the ability to implement distributed - or workstation - based simulations and high-fidelity real-time simulation from a common core. Originally designed to serve as a research platform for examining fundamental challenges in formation flying simulation for future space missions, it is also finding use in other missions and applications, all of which can take advantage of the underlying Object-Oriented structure to easily produce distributed simulations. Hydra automates the process of connecting disparate simulation components (Hydra Clients) through a client server architecture that uses high-level descriptions of data associated with each client to find and forge desirable connections (Hydra Services) at run time. Services communicate through the use of Connectors, which abstract messaging to provide single-interface access to any desired communication protocol, such as from shared-memory message passing to TCP/IP to ACE and COBRA. Hydra shares many features with the HLA, although providing more flexibility in connectivity services and behavior overriding.

formation flying↗

NASA NTRS2008

Similarity Metrics for Closed Loop Dynamic Systems

To what extent and in what ways can two closed-loop dynamic systems be said to be "similar?" This question arises in a wide range of dynamic systems modeling and control system design applications. For example, bounds on error models are fundamental to the controller optimization with modern control design methods. Metrics such as the structured singular value are direct measures of the degree to which properties such as stability or performance are maintained in the presence of specified uncertainties or variations in the plant model. Similarly, controls-related areas such as system identification, model reduction, and experimental model validation employ measures of similarity between multiple realizations of a dynamic system. Each area has its tools and approaches, with each tool more or less suited for one application or the other. Similarity in the context of closed-loop model validation via flight test is subtly different from error measures in the typical controls oriented application. Whereas similarity in a robust control context relates to plant variation and the attendant affect on stability and performance, in this context similarity metrics are sought that assess the relevance of a dynamic system test for the purpose of validating the stability and performance of a "similar" dynamic system. Similarity in the context of system identification is much more relevant than are robust control analogies in that errors between one dynamic system (the test article) and another (the nominal "design" model) are sought for the purpose of bounding the validity of a model for control design and analysis. Yet system identification typically involves open-loop plant models which are independent of the control system (with the exception of limited developments in closed-loop system identification which is nonetheless focused on obtaining open-loop plant models from closed-loop data). Moreover the objectives of system identification are not the same as a flight test and hence system identification error metrics are not directly relevant. In applications such as launch vehicles where the open loop plant is unstable it is similarity of the closed-loop system dynamics of a flight test that are relevant.

Whorton, Mark S.↗

NASA NTRS2024

Growth Rate of Deep Convective System Cloud Shields: Satellite Observations and Km-Scale Radiative Convective Equilibrium Simulations

Deep convection gives rise to large upper level clouds that strongly interact with radiation and are important to the climate energy budget. From an object-oriented perspective, these individual deep cloud systems are characterized by a well depicted cloud shield life cycle, starting with small cloud extents that grow at varying rates before decaying and vanishing. A simple formulation of the growth rate of the cloud shield has been proposed that links together the growth rate on the convective part of the cloud, the mass flux of both the convective and stratiform parts of the cluster and a simple removal sink term (Elsaesser et al., 2022). In this presentation we first show using a suite of satellite observations (infrared from geostationary satellites, GPM radar, etc.) that the functional form of the proposed equation is well suited to quantify the shield growth rate. We then focus on RCE simulations, with deep cloud system objects post processed, to explore the relative role of each term of the growth rate budget. Three different models are used in the same RCEMIP-like configurations. The results show that the budget equation works very well for each model, although the time constants require model-dependent adjustments. We will further show in Vienna the commonalities and the specificities of each model.

Deep convection↗

NASA NTRS1992

A model for ring galaxies - Arp 147-like systems

The galaxy Arp 147 belongs to a class of objects believed to have formed a ring as a result of a collision with a second galaxy. We have produced a combined stellar and gasdynamical computer model of a pair of interacting galaxies which exhibits many of the features seen in Arp 147. In our model, the ring forms in a disk galaxy following the passage of an equal-mass elliptical galaxy approximately perpendicular through the disk, about two radial scale lengths from the center. Some generic features of this type of collision are that (1) 'hot spots' of increased gas density and shocks occur on opposite sides of the ring, away from the nucleus; (2) an incomplete ring forms, with the disk galaxy's remnant nucleus offset from the center and no longer in the plane of the disk; and (3) this nucleus can appear buried in one edge of the ring depending on the orientation relative to the observer.

Gerber, Richard A.↗