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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8

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NASA NTRS1973

Washout circuit design for multi-degrees-of-freedom moving base simulators.

A mathematical framework is presented for designing logic to accept motion-dependent parameters from a simulation, attenuating them ('washing them out'), and generating appropriately limited drive signals. This framework is sufficiently general to encompass six-degree-of-freedom simulators with large motion capability. Emphasis is placed on preserving certain motion cue relations (such as those that would be observed in coordinated flight). Strategies for simulating side forces via tilts are shown. Finally, several specific circuits are shown. These circuits have proven to be readily adaptable to a variety of moving-base simulators.

Conrad, B.↗

NASA NTRS1973

Quasi-optimum design of a six degree of freedom moving base simulator control system

The design of a washout control system for a moving base simulator is treated by a quasi-optimum control technique. The broad objective of the design is to reproduce the sensed motion of a six degree of freedom simulator as accurately as possible without causing the simulator excursions to exceed specified limits. A performance criterion is established that weights magnitude and direction errors in specific force and in angular velocity and attempts to maintain the excursion within set limits by penalizing excessive excursions. A FORTRAN routine for relizing the washout law was developed and typical time histories using the washout routine were simulated for a range of parameters in the penalty- and weighting-functions. These time histories and the listing of the routine are included in the report.

Friedland, B.↗

NASA NTRS1997

Research Related to Multi Degree of Freedom Magnetic Suspensions

This thesis covers the activities associated with (1) recommissioning of the 6-inch Magnetic Suspension and Balance System (MSBS) and (2) enhancing the Annular Suspension and Pointing System (ASPS). These activities continue the program of research in the multi degree of freedom magnetic suspension program at Old Dominion University. The 6-inch MSBS is a large gap magnetic suspension system used as a model support and balance system in wind tunnels. The first stage of recommissioning of the 6-inch MSBS for the 6-inch subsonic wind tunnel is performed. Experimental data and computational results for the magnetic field distribution of the MSBS are given and compared with the estimated magnetic field strength. The comparison indicates that the magnet system is still operating as designed. The Electromagnetic Position Sensor used in the 6-inch MSBS is analyzed before its find reinstatement. The ASPS is a small gap magnetic suspension system providing orientation, mechanical isolation and fine pointing of space payloads. The control system of the ASPS is improved by designing a new code to realize red time control over the system. The original Proportional-Derivative controller is upgraded to a Proportional-Integral-Derivative controller. This progress leads to a system which is more stable and robust with less noise. This new controller is generic and can be adapted to the 6-inch MSBS. Finally, future work on these two systems is proposed.

Britcher, Colin↗

NASA NTRS1991

Six-degree-of-freedom simulation of an astronaut detumble system

The problem of stabilizing the attitude of an untethered astronaut in a three-axis tumble is addressed. A simple six thruster detumbling system mounted on the astronaut's Portable Life Support System backpack is analyzed as a possible solution. A six-degree-of-freedom dynamical model is constructed using the Clohessy-Wiltshire equations, Euler's moment equations, and quaternions. The six thruster system produces both moments and forces when activated. However, it is shown that the thrust forces acting on the body during detumbling do not significantly affect the translational motion.

Fowler, W. T.↗

NASA NTRS1988

Shock spectra applications to a class of multiple degree-of-freedom structures system

The demand on safety performance of launching structure and equipment system from impulsive excitations necessitates a study which predicts the maximum response of the system as well as the maximum stresses in the system. A method to extract higher modes and frequencies for a class of multiple degree-of-freedom (MDOF) Structure system is proposed. And, along with the shock spectra derived from a linear oscillator model, a procedure to obtain upper bound solutions for maximum displacement and maximum stresses in the MDOF system is presented.

Hwang, Shoi Y.↗

NASA NTRS1993

Recent experiences with implementing a video based six degree of freedom measurement system for airplane models in a 20 foot diameter vertical spin tunnel

A model space positioning system (MSPS), a state-of-the-art, real-time tracking system to provide the test engineer with on line model pitch and spin rate information, is described. It is noted that the six-degree-of-freedom post processor program will require additional programming effort both in the automated tracking mode for high spin rates and in accuracy to meet the measurement objectives. An independent multicamera system intended to augment the MSPS is studied using laboratory calibration methods based on photogrammetry to characterize the losses in various recording options. Data acquired to Super VHS tape encoded with Vertical Interval Time Code and transcribed to video disk are considered to be a reasonable priced choice for post editing and processing video data.

Snow, Walter L.↗

NASA NTRS1986

Application of the unsteady vortex-lattice method to the nonlinear two-degree-of-freedom aeroelastic equations

A means of numerically simulating flutter is established by implementing a predictor-corrector algorithm to solve the equations of motion. Aerodynamic loads are provided by the unsteady vortex lattice method (UVLM). This method is illustrated via the obtainment of stable and unstable responses to initial disturbances in the case of two-degree-of-freedom motion. It was found that for some angles of attack and dynamic pressure, the initial disturbance decays, for others it grows (flutter). When flutter occurs, the solution yields the amplitude and period of the resulting limit cycle. The preliminaray results attest to the feasibility of this method for studying flutter in cases that would be difficult to treat using a classical approach.

Strganac, T. W.↗

NASA NTRS2018

Laser Tracker Utilization Methodology in Measuring Truth Trajectories for INS Testing on 6 Degree of Freedom Table at the Marshall Space Flight Center's Contact Dynamics Simulation Laboratory with Lessons Learned

When performing Inertial Navigation System (INS) testing at the Marshall Space Flight Center's (MSFC) Contact Dynamics Simulation Laboratory (CDSL) early in 2017, a Leica Geosystems AT901 Laser Tracker system (LLT) measured the twist & sway trajectories as generated by the 6 Degree Of Freedom (6DOF) Table in the CDSL. These LLT measured trajectories were used in the INS software model validation effort. Several challenges were identified and overcome during the preparation for the INS testing, as well as numerous lessons learned. These challenges included determining the position and attitude of the LLT with respect to an INS-shared coordinate frame using surveyed monument locations in the CDSL and the accompanying mathematical transformation, accurately measuring the spatial relationship between the INS and a 6DOF tracking probe due to lack of INS visibility from the LLT location, obtaining the data from the LLT during a test, determining how to process the results for comparison with INS data in time and frequency domains, and using a sensitivity analysis of the results to verify the quality of the results. While many of these challenges were identified and overcome before or during testing, a significant lesson on test set-up was not learned until later in the data analysis process. It was found that a combination of trajectory-dependent gimbal locking and environmental noise introduced non-negligible noise in the angular measurements of the LLT that spanned the evaluated frequency spectrum. The lessons learned in this experiment may be useful for others performing INS testing in similar testing facilities.

Leggett, Jared O.↗

NASA NTRS2015

Check-Cases for Verification of 6-Degree-of-Freedom Flight Vehicle Simulations

The rise of innovative unmanned aeronautical systems and the emergence of commercial space activities have resulted in a number of relatively new aerospace organizations that are designing innovative systems and solutions. These organizations use a variety of commercial off-the-shelf and in-house-developed simulation and analysis tools including 6-degree-of-freedom (6-DOF) flight simulation tools. The increased affordability of computing capability has made highfidelity flight simulation practical for all participants. Verification of the tools' equations-of-motion and environment models (e.g., atmosphere, gravitation, and geodesy) is desirable to assure accuracy of results. However, aside from simple textbook examples, minimal verification data exists in open literature for 6-DOF flight simulation problems. This assessment compared multiple solution trajectories to a set of verification check-cases that covered atmospheric and exo-atmospheric (i.e., orbital) flight. Each scenario consisted of predefined flight vehicles, initial conditions, and maneuvers. These scenarios were implemented and executed in a variety of analytical and real-time simulation tools. This tool-set included simulation tools in a variety of programming languages based on modified flat-Earth, round- Earth, and rotating oblate spheroidal Earth geodesy and gravitation models, and independently derived equations-of-motion and propagation techniques. The resulting simulated parameter trajectories were compared by over-plotting and difference-plotting to yield a family of solutions. In total, seven simulation tools were exercised.

Murri, Daniel G.↗

NASA NTRS1988

Frequency domain solutions to multi-degree-of-freedom, dry friction damped systems

Dry friction damping has been considered as a means of increasing the passive damping of a variety of systems including large space structures and turbomachinery blades. However, dry friction is highly nonlinear, and hence, analytical investigations are difficult to perform. Here, a multiharmonic, frequency domain solution technique is developed and applied to a multi-degree-of-freedom, dry friction damped system. It is seen that the multiharmonic method is more accurate than traditional, one-harmonic solution methods. The method also compares favorably with time integration. Finally, comparisons are made with experimental results.

Ferri, A. A.↗

NASA NTRS2003

18-Degree-of-Freedom Controller Design for the ST7 Disturbance Reduction System

This paper presents the overall design and analysis process of the spacecraft controller being developed at NASA's Goddard Space Flight Center to close the loop between the GRS and the micro-newton colloidal thrusters. The essential dynamics of the ST7-DRS are captured in a simulation including eighteen rigid-body dynamic degrees of freedom: three translations and three rotations for the spacecraft and for each test mass. The ST7 DRS comprises three control systems: the attitude control system (ACS) to maintain a sun-pointing attitude; the drag free control (DFC) to center the spacecraft about the test masses; and the test mass suspension control. This paper summarizes the control design and analysis of the ST7-DRS 18-DOF model, and is an extension of previous analyses employing a 7-DOF planar model of ST-7.

Markley, F. L.↗

NASA NTRS2003

A Nonlinear, Six-Degree of Freedom Precision Formation Control Algorithm, Based on Restricted Three Body Dynamics

Precision Formation Flying is an enabling technology for a variety of proposed space-based observatories, including the Micro-Arcsecond X-ray Imaging Mission (MAXIM), the associated MAXIM pathfinder mission, and the Stellar Imager. An essential element of the technology is the control algorithm. This paper discusses the development of a nonlinear, six-degree of freedom (6DOF) control algorithm for maintaining the relative position and attitude of a spacecraft within a formation. The translation dynamics are based on the equations of motion for the restricted three body problem. The control law guarantees the tracking error convergences to zero, based on a Lyapunov analysis. The simulation, modelled after the MAXIM Pathfinder mission, maintains the relative position and attitude of a Follower spacecraft with respect to a Leader spacecraft, stationed near the L2 libration point in the Sun-Earth system.

Bauer, Frank↗

NASA NTRS1991

Six-Degree-of-Freedom Test Facility

Shuttle to Space station docking has become an important issue in the last few years. Docking sensors have been proposed that will provide high precision measurements required for the fuel efficient rendezvous and docking of space vehicles. These sensors will also be used for satellite servicing and orbital assembly. The performance of the docking sensors must be tested before they are implemented in a space environment. A Six-Degree-of-Freedom (6-DOF) Test Facility has been developed at the Tracking & Communications Section, Johnson Space Center to test the static and dynamic accuracies of docking sensors. A candidate sensor is evaluated by comparing the sensor's static position and velocity measurements to the more accurate 6-DOF system. The 6-DOF Test Facility's hardware is fully integrated. Software has been developed in-house to support system operation. The system has been tested statically and the operational parameters verified. System accuracies remain to be determined. Dynamic testing of the facility is expected to begin shortly. Several companies such as McDonnell Douglas, Autonomous Technologies, and General Dynamics are scheduled to test sensors in the next few months. The 6-DOF facility will be available for use in November 1991. This presentation describes the subcomponents, operation, and capabilities of the 6-DOF Test Facility. Discussions will be held on system accuracies. Additional applications of the 6-DOF system will also be addressed.

Bittel, Michelle A.↗

NASA NTRS2003

Mars Exploration Rover Six-Degree-Of-Freedom Entry Trajectory Analysis

The Mars Exploration Rover mission will be the next opportunity for surface exploration of Mars in January 2004. Two rovers will be delivered to the surface of Mars using the same entry, descent, and landing scenario that was developed and successfully implemented by Mars Pathfinder. This investigation describes the trajectory analysis that was performed for the hypersonic portion of the MER entry. In this analysis, a six-degree-of-freedom trajectory simulation of the entry is performed to determine the entry characteristics of the capsules. In addition, a Monte Carlo analysis is also performed to statistically assess the robustness of the entry design to off-nominal conditions to assure that all entry requirements are satisfied. The results show that the attitude at peak heating and parachute deployment are well within entry limits. In addition, the parachute deployment dynamics pressure and Mach number are also well within the design requirements.

Desai, Prasun N.↗

NASA NTRS1991

Control algorithm implementation for a redundant degree of freedom manipulator

This project's purpose is to develop and implement control algorithms for a kinematically redundant robotic manipulator. The manipulator is being developed concurrently by Odetics Inc., under internal research and development funding. This SBIR contract supports algorithm conception, development, and simulation, as well as software implementation and integration with the manipulator hardware. The Odetics Dexterous Manipulator is a lightweight, high strength, modular manipulator being developed for space and commercial applications. It has seven fully active degrees of freedom, is electrically powered, and is fully operational in 1 G. The manipulator consists of five self-contained modules. These modules join via simple quick-disconnect couplings and self-mating connectors which allow rapid assembly/disassembly for reconfiguration, transport, or servicing. Each joint incorporates a unique drive train design which provides zero backlash operation, is insensitive to wear, and is single fault tolerant to motor or servo amplifier failure. The sensing system is also designed to be single fault tolerant. Although the initial prototype is not space qualified, the design is well-suited to meeting space qualification requirements. The control algorithm design approach is to develop a hierarchical system with well defined access and interfaces at each level. The high level endpoint/configuration control algorithm transforms manipulator endpoint position/orientation commands to joint angle commands, providing task space motion. At the same time, the kinematic redundancy is resolved by controlling the configuration (pose) of the manipulator, using several different optimizing criteria. The center level of the hierarchy servos the joints to their commanded trajectories using both linear feedback and model-based nonlinear control techniques. The lowest control level uses sensed joint torque to close torque servo loops, with the goal of improving the manipulator dynamic behavior. The control algorithms are subjected to a dynamic simulation before implementation.

Cohan, Steve↗

NASA NTRSDate not supplied

Application of A Dual-Quaternion Six Degree-of-Freedom Guidance to Human-Scale Mars Entry, Descent, and Landing

Landing humans on Mars comes with many challenges, including the execution of a safe and precise entry, descent, and landing (EDL) sequence. Various NASA studies have shown that there are a variety of EDL guidance methods that potentially offer solutions to the human-scale EDL precision landing problem and work is ongoing to assess new and novel methods. As part of these ongoing studies, a dual-quaternion-based six degree-of-freedom guidance algorithm was implemented in the Program to Optimize Simulated Trajectories II (POST2), a NASA-and industry-standard spacecraft trajectory and vehicle design tool. This algorithm considers both translational and rotational dynamics and casts the trajectory optimization problem as a quadratically constrained quadratic program (QCQP) with various constraints at discrete nodes throughout the trajectory. The QCQP problem is solved via an alternating direction method of multipliers (ADMM) approach, and the output is a discretized optimal trajectory. The guidance is applied to a NASA reference human-scale Mars EDL system, and results are compared and discussed.

Optimization↗

NASA NTRSDate not supplied

Application of A Dual-Quaternion Six Degree-of-Freedom Guidance to Human-Scale Mars Entry, Descent, and Landing

Optimization↗

NASA NTRS1993

Six degrees of freedom vibration isolation using electromagnetic suspension

Experimental data are presented for modeling an electromagnet. Control laws are considered with and without flux feedback and with position and orientation information of the suspended body. Base motion and sensor noise are the principal disturbances. Proper selection of the geometrical operating point minimizes the passive coupling above the bandwidth of the control and filtering can attenuate the high frequency content of sensor noise. Six electromagnets are arranged in a configuration which optimizes the load support and provides control over all six degrees of freedom of the suspended body. The design is based on experimental data generated with a specially designed test facility. Application for suspension of a gravity wave antenna is discussed.

Lee, Sang-Il↗