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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Flight Performance Comparison of Bank-Angle Steering and Alpha-Beta Steering for Mars Entry Systems

Alpha-beta steering is an alternative hypersonic steering scheme to state-of-the-art bank-angle steering systems for guided Mars entry vehicles. This study uses opti- mal control to generate steering commands for a large robotic Mars entry vehicle using either a bank-angle or alpha-beta steering system to provide a more equal comparison of these two hypersonic steering options, not dependent on guidance design or the inclusion of conventional bank reversals. Objectives maximizing terminal altitude or minimizing control effort, while also reaching a desired target point are considered for both steering options in nominal and dispersed cases. Re- sults indicate both steering options have similar performance, although alpha-beta steering is shown to have improved targeting performance, particularly for the lati- tude/crossrange. Alpha-beta steering is also able to reach higher terminal altitudes by about 0.25 km, relative to the vehicle using bank-angle steering. The difference in altitude maximization capability grows as the allowable vehicle rates decrease.

Daniel L Engel↗
NASA NTRS1982

Levels of steering control: Reproduction of steering-wheel movements

A schematic description of the steering control process is presented. It is shown that this process can be described in terms of levels of control. Level of control will depend on driver's skill in making use of 'clever' strategies which may be related to knowledge about the path to follow (input) and/or the vehicle under control. This knowledge may be referred to as an internal model of a particular task element. Internal information, as derived from these internal models will probably be used together with proprioceptive feedback. It is hypothesized that the efficiency of the higher levels of control will be dependent on the accuracy of both the internal and proprioceptive information. Based on this research philosophy a series of experiments is carried out. Two primary experiments were done in order to analyse subjects' ability to reproduce steering-wheel positions and movements without visual feedback. Steering-wheel angle amplitude, steering force and movement frequency were involved as independent variables.

Godthelp, H.↗
NASA NTRS2012

Beam Steering Devices Reduce Payload Weight

Scientists have long been able to shift the direction of a laser beam, steering it toward a target, but often the strength and focus of the light is altered. For precision applications, where the quality of the beam cannot be compromised, scientists have typically turned to mechanical steering methods, redirecting the source of the beam by swinging the entire laser apparatus toward the target. Just as the mechanical methods used for turning cars has evolved into simpler, lighter, power steering methods, so has the means by which researchers can direct lasers. Some of the typical contraptions used to redirect lasers are large and bulky, relying on steering gimbals pivoted, rotating supports to shift the device toward its intended target. These devices, some as large and awkward as a piece of heavy luggage, are subject to the same issues confronted by mechanical parts: Components rub, wear out, and get stuck. The poor reliability and bulk not to mention the power requirements to run one of the machines have made mechanical beam steering components less than ideal for use in applications where weight, bulk, and maneuverability are prime concerns, such as on an unmanned aerial vehicle (UAV) or a microscope. The solution to developing reliable, lighter weight, nonmechanical steering methods to replace the hefty steering boxes was to think outside the box, and a NASA research partner did just that by developing a new beam steering method that bends and redirects the beam, as opposed to shifting the entire apparatus. The benefits include lower power requirements, a smaller footprint, reduced weight, and better control and flexibility in steering capabilities. Such benefits are realized without sacrificing aperture size, efficiency, or scanning range, and can be applied to myriad uses: propulsion systems, structures, radiation protection systems, and landing systems.

Source record↗
NASA NTRS2016

Method of Controlling Steering of a Ground Vehicle

A method of controlling steering of a vehicle through setting wheel angles of a plurality of modular electronic corner assemblies (eModules) is provided. The method includes receiving a driving mode selected from a mode selection menu. A position of a steering input device is determined in a master controller. A velocity of the vehicle is determined, in the master controller, when the determined position of the steering input device is near center. A drive mode request corresponding to the selected driving mode to the plurality of steering controllers is transmitted to the master controller. A required steering angle of each of the plurality of eModules is determined, in the master controller, as a function of the determined position of the steering input device, the determined velocity of the vehicle, and the selected first driving mode. The eModules are set to the respective determined steering angles.

Dawson, Andrew D.↗
NASA NTRSDate not supplied

Guidance Performance of Bank-Angle and Alpha-Beta Steering for A Large Robotic Mars Entry Vehicle

Entry performance using Apollo-based entry guidance is assessed with a future entry system for a large robotic payload. Both a traditional bank-angle steering system and an innovative alpha-beta steering concept are considered to compare flight performance. Results indicate alpha-beta steering provides an order of magnitude improvement in crossrange error and mean altitudes up to 1 km higher than bank-angle steering. Results also show alpha-beta steering provides downrange errors with a spread half of that of bank-angle steering. Lastly, alpha-beta steering is found to provide a narrower spread of terminal altitude, Mach number, and dynamic pressure, indicating safer parachute deploy conditions.

Daniel L Engel↗
NASA NTRSDate not supplied

Comparison of Mars Entry Performance Using Bank-Angle and Alpha-Beta Steering Systems

State-of-the-art Mars entry systems havemodulated the bank angle (σ) on blunt-body entry capsulesto steer, providing hypersonic trajectory control. These bank-angle steering vehicles have provided successful entries forboth the Mars 2020 and Mars Science Laboratory missions, achieving landing accuracy on the order of several kilometers. Conventional guidance algorithms for these vehicles choose the bank magnitude to control the longitudinal motionand periodically change the sign of the bank angle to managethe lateral error through open-loop bank reversals. While these bank reversals are relatively simple to implement, they can inject error into the trajectory. More sophisticated steering commands simultaneously considering the lateral and longitudinal motion can potentially obtain higher entry performance, although the high coupling over the lateral and longitudinal motion remains. Bank-angle steering systemsfor Mars entries have achieved a trim angle of attack (α) for steering by offseting the center-of-gravity (CG) usinginert ballast mass and payload packaging. This ballast mass can be a significant, relative to the mass of the payload, reducing the payload mass. Lastly bank-angle steering vehicles typically modulate the bank angle using reactioncontrol system (RCS) thrusters, which can interfere with thehypersonic wake behind the entry vehicle, potentially limitingcontrollability.

Mars↗
NASA NTRSDate not supplied

Structural Sizing of a Tow-Steered Truss-Braced Wing Box Test Article

Tailoring of composite laminates is traditionally performed by changing the orientation of straight fibers in one or more plies. Modern automated fiber placement machines facilitate placement of bundles of curved fibers (tows) in a process called tow-steering, but additional variables must be used to define the shapes of tow-steered fiber paths. In this paper, the design of a tow-steered truss-braced wing test article called the Structural Wing Experiment Evaluating Truss-bracing 15-ft concept (SWEET-15) is discussed. The SWEET-15 test article is scaled to 18.6% of the span length and chord width of a full-scale vehicle. The test article is designed to withstand +2.5-g (positive limit) and -1.0-g (negative limit) maneuvering loads with a factor of safety of 1.5 under strength and buckling constraints. Design studies were performed using commercial finite element analysis and optimization software in conjunction with a tow-steering modeling tool called ATSCOOL (Automated Tool for Steered COmposite Optimizable Laminates) developed at NASA Langley Research center. A 6.4% weight reduction in the upper cover panels was achieved using a tow-steered layup configuration.

Structural Optimization↗
NASA NTRSDate not supplied

Structural Sizing of a Tow-Steered Truss-Braced Wing Box Test Article

Tailoring of composite laminates is traditionally performed by changing the orientation of straight fibers in one or more plies. Modern automated fiber placement machines facilitate placement of bundles of curved fibers (tows) in a process called tow-steering, but additional variables must be used to define the shapes of tow-steered fiber paths. In this paper, the design of a tow-steered truss-braced wing test article called the Structural Wing Experiment Evaluating Truss-bracing 15-ft concept (SWEET-15) is discussed. The SWEET-15 test article is scaled to 18.6% of the span length and chord width of a full-scale vehicle. The test article is designed to withstand +2.5-g (positive limit) and -1.0-g (negative limit) maneuvering loads with a factor of safety of 1.5 under strength and buckling constraints. Design studies were performed using commercial finite element analysis and optimization software in conjunction with a tow-steering modeling tool called ATSCOOL (Automated Tool for Steered COmposite Optimizable Laminates) developed at NASA Langley Research center. A 6.4% weight reduction in the upper cover panels was achieved using a tow-steered layup configuration.

Composites↗
NASA NTRS1972

Analysis of Morgantown vehicle steering control

The proposed Morgantown public transportation system will use a fleet of computer-controlled vehicles operating on a separate dedicated network of roadways called a guideway. An automatic steering system on each vehicle will permit the traversal of the proposed route of various guideway sections. A preliminary study was made to analyze the steering control for the Morgantown vehicles. The primary requirement was to design an automatic steering system that would achieve a smooth ride and eliminate the need for excess margin in the guideway width. Front and rear wheel steering and front and rear sensing capabilities were assumed in the analysis. The system finally adopted front and rear wheel steering and front sensing was shown by computer simulation and vehicle steering experiments to be adequate.

Lin, H. S.↗
NASA NTRSDate not supplied

The Effect of Fiber-Angle Fidelity on the Linear Response of Tow-steered Composite Plates

Composite laminate tailoring is traditionally performed by uniformly changing the in-plane ply orientation to obtain the desired mechanical performance. The emergence of tow-steered plies, where the fibers follow a prescribed curvilinear path, have increased the tailorability of composite laminates. However, characterizing the behavior of tow-steered laminates using finite element analysis is challenging because additional, and often numerous, orientation definitions may be required. The additional orientation definitions detrimentally increase the computational cost and hinder the use of advanced analysis techniques, such as Monte Carlo or uncertainty quantification, in the design process. To reduce computational cost without adversely affecting mechanics-based performance, the results of a parametric study that was used to investigate the effects of fiber-angle fidelity, element size, and tow-steered radius-of-curvature on various loading scenarios for tow-steered composite plates are presented. The three loading scenarios that were analyzed using finite element analysis included an axial tension load, an applied constant through-thickness-direction pressure load, and an axial compression load. Results for mechanics-based metrics of interest are presented and discussed for each loading scenario. Little sensitivity (less than one percent difference) to the effect of fiber-angle fidelity is observed in the mechanics-based metrics until the coarse-end of the considered range. Sensitivity to element size generally dominates the observed results for the mechanics-based metrics. Notable reductions in the preprocessing time are observed for increasingly coarse element size and fiber-rounding parameters. The preprocessing times decreased up to three orders of magnitude from a few thousand seconds to a few seconds without loss of accuracy in the mechanics-based metrics. Such increased computational performance is of particular interest to the structural design and analysis communities that may be conducting large counts of finite-element analyses, such as in other parametric studies, Monte-Carlo analyses, uncertainty quantification, or tow-steered optimization.

tow-steered composites↗
NASA NTRS2023

A Tool for Defining Tow-Steered Laminates for Finite Element Grids

Tailoring of composite laminates is traditionally performed by changing the orientation of straight fibers in one or more plies. Modern automated fiber placement machines facilitate placement of bundles of curved fibers (tows) in a process called tow-steering, but additional variables must be used to define the shapes of tow-steered fiber paths. In this paper, a Python-based tool, called Automated Tool for Steered COmposite Optimizable Laminates (ATSCOOL), is presented for modeling steered tows as chains of circular arcs. The geometry for defining tow path shapes using four input variables is described. The formulae for determining gaps and overlaps between clusters of consecutive tows, called courses, and for determining the number of steered courses needed to cover a rectangular panel are presented. Graphical representation of courses and thickness distribution in an example panel using the ATSCOOL software are presented. Finally, an example of a finite element analysis performed using the property information output from ATSCOOL is shown.

finite element analysis↗
NASA NTRS1981

Steering law for parallel mounted double-gimbaled control moment gyros. Revision A

Mounting of double-gimbaled control moment gyros (CMG's) of unlimited outer gimbal angle freedom with all their outer gimbal axes parallel allows drastic simplification of the CMG steering law development hardware. The advantages of the parallel mounting for the CMG steering law development are such that a law could be developed which is applicable to any number of CMG's with arbitrary angular momentum. Parallel mounting of the CMG's in conjunction with the steering law can therefore be considered a CMG kit suitable for many missions of differing momentum requirements. It also means that increasing momentum demands during the design phase of a space vehicle can be easily met by the addition of one or more CMG's of the original momentum capacity rather than a redesign to a larger momentum capacity. Another advantage of the parallel mounting is that the failure of any CMG can be treated like any other, i.e., only one failure mode is possible. The CMG steering law distributes the CMG momentum vectors such that all inner gimbal angles are equal which reduces the rate requirements on the outer gimbal axes. The steering law also spreads the outer gimbals which ensures avoidance of singularities internal to the angular momentum envelope.

Kennel, H. F.↗
NASA NTRS2012

Analysis of Roll Steering for Solar Electric Propulsion Missions

Nothing is more vital to a spacecraft than power. Solar Electric Propulsion (SEP) uses that power to provide a safe, reliable, and, most importantly, fuel efficient means to propel a spacecraft to its destination. The power performance of an SEP vehicle s solar arrays and electrical power system (EPS) is largely influenced by the environment in which the spacecraft is operating. One of the most important factors that determines solar array power performance is how directly the arrays are pointed to the sun. To get the most power from the solar arrays, the obvious solution is to point them directly at the sun at all times. Doing so is not a problem in deep space, as the environment and pointing conditions that a spacecraft faces are fairly constant and are easy to accommodate, if necessary. However, large and sometimes rapid variations in environmental and pointing conditions are experienced by Earth orbiting spacecraft. SEP spacecraft also have the additional constraint of needing to keep the thrust vector aligned with the velocity vector. Thus, it is important to analyze solar array power performance for any vehicle that spends an extended amount of time orbiting the Earth, and to determine how much off-pointing can be tolerated to produce the required power for a given spacecraft. This paper documents the benefits and drawbacks of perfectly pointing the solar arrays of an SEP spacecraft spiraling from Earth orbit, and how this might be accomplished. Benefits and drawbacks are defined in terms of vehicle mass, power, volume, complexity, and cost. This paper will also look at the application of various solar array pointing methods to future missions. One such pointing method of interest is called roll steering . Roll steering involves rolling the entire vehicle twice each orbit. Roll steering, combined with solar array gimbal tracking, is used to point the solar arrays perfectly towards the sun at all points in the orbit, while keeping the vehicle thrusters aligned in the velocity direction. Roll steering is particularly attractive for a recently proposed mission that involves a spiral trajectory from low Earth orbit (LEO) to the Earth-Moon Lagrange Point 1 (E-M L1). During the spiral, the spacecraft will spend over 300 days experiencing the full spectrum of near-earth environments and solar array pointing conditions. An extensive study of the application of SEP (and roll steering) to this spiral mission is included, highlighting the ultimate goal of reduced vehicle cost and mass. Tools used for this analysis include the Systems Power Analysis for Capability Evaluation (Refs. 1 and 2) (SPACE) electrical power systems code, and SEP trajectory simulation tools developed at NASA Glenn Research Center.

Pederson, Dylan, M.↗
NASA NTRS2019

Safe2Ditch Steer-To-Clear Development and Flight Testing

This paper describes a series of small unmanned aerial system (sUAS) flights performed at NASA Langley Research Center in April and May of 2019 to test a newly added Steer-to-Clear feature for the Safe2Ditch (S2D) prototype system. S2D is an autonomous crash management system for sUAS. Its function is to detect the onset of an emergency for an autonomous vehicle, and to enable that vehicle in distress to execute safe landings to avoid injuring people on the ground or damaging property. Flight tests were conducted at the City Environment Range for Testing Autonomous Integrated Navigation (CERTAIN) range at NASA Langley. Prior testing of S2D focused on rerouting to an alternate ditch site when an occupant was detected in the primary ditch site. For Steer-to-Clear testing, S2D was limited to a single ditch site option to force engagement of the Steer-to-Clear mode. The implementation of Steer-to-Clear for the flight prototype used a simple method to divide the target ditch site into four quadrants. An RC car was driven in circles in one quadrant to simulate an occupant in that ditch site. A simple implementation of Steer-to- Clear was programmed to land in the opposite quadrant to maximize distance to the occupant’s quadrant. A successful mission was tallied when this occurred. Out of nineteen flights, thirteen resulted in successful missions. Data logs from the flight vehicle and the RC car indicated that unsuccessful missions were due to geolocation error between the actual location of the RC car and the derived location of it by the Vision Assisted Landing component of S2D on the flight vehicle. Video data indicated that while the Vision Assisted Landing component reliably identified the location of the ditch site occupant in the image frame, the conversion of the occupant’s location to earth coordinates was sometimes adversely impacted by errors in sensor data needed to perform the transformation. Logged sensor data was analyzed to attempt to identify the primary error sources and their impact on the geolocation accuracy. Three trends were observed in the data evaluation phase. In one trend, errors in geolocation were relatively large at the flight vehicle’s cruise altitude, but reduced as the vehicle descended. This was the expected behavior and was attributed to sensor errors of the inertial measurement unit (IMU). The second trend showed distinct sinusoidal error for the entire descent that did not always reduce with altitude. The third trend showed high scatter in the data, which did not correlate well with altitude. Possible sources of observed error and compensation techniques are discussed.

Petty, Bryan J.↗
NASA NTRSDate not supplied

A Design Framework for Thick and Thin Tow-Steered Composites Using Mechanics of Structure Genome

The design of tow-steered composites is one of the most popular and promising topics under the class of variable stiffness structures. In this work, the authors propose a new design framework and tool for the optimization of tow-steered composites. Mechanics of structure genome (MSG) provides accurate computation of plate/shell section properties including thick and highly curved structures. The computed section properties can be directly used in commercial computer-aided engineering tools. Tow-steered composites are modeled through a design framework wherein tow paths are parameterized in a general way and projected onto a finite element mesh, and MSG calculates the local shell/plate properties. The result is a complete workflow from design parameter input to structural performance evaluation. An open-source optimization software package is used to enable constrained optimization of structural stiffness for the broad tow-steered composite design space. Numerical examples are provided to demonstrate the capabilities of this tool and the promise and potential of tow-steered designs that optimize structural performance while satisfying manufacturing constraints.

Su Tian↗
NASA NTRSDate not supplied

A Design Framework for Thick and Thin Tow-Steered Composites Using Mechanics of Structure Genome

The design of tow-steered composites is one of the most popular and promising topics under the class of variable stiffness structures. In this work, the authors propose a new design framework and tool for the optimization of tow-steered composites. Mechanics of structure genome (MSG) provides accurate computation of plate/shell section properties including thick and highly curved structures. The computed section properties can be directly used in commercial computer-aided engineering tools. Tow-steered composites are modeled through a design framework wherein tow paths are parameterized in a general way and projected onto a finite element mesh, and MSG calculates the local shell/plate properties. The result is a complete workflow from design parameter input to structural performance evaluation. An open-source optimization software package is used to enable constrained optimization of structural stiffness for the broad tow-steered composite design space. Numerical examples are provided to demonstrate the capabilities of this tool and the promise and potential of tow-steered designs that optimize structural performance while satisfying manufacturing constraints.

Su Tian↗
NASA NTRS1972

A comparison of CMG steering laws for High Energy Astronomy Observatories (HEAOs)

A comparison of six selected control moment gyro steering laws for use on the HEAO spacecraft is reported. Basic equations are developed to project the momentum and torque of four skewed, single gimbal CMGs into vehicle coordinates. In response to the spacecraft attitude error signal, six algorithms are derived for controlling the CMG gimbal movements. HEAO performance data are obtained using each steering law and compared on the basis of such factors as accuracy, complexity, singularities, gyro hang-up and failure adaption. Moreover, each law is simulated with and without a magnetic momentum management system. The performance of any steering law is enhanced by the magnetic system. Without magnetics, the gimbal angles get large and there are significant differences in steering law performances due to cross coupling and nonlinearities. The performance of the pseudo inverse law is recommended for HEAO.

Davis, B. G.↗
NASA NTRS1977

A control theoretic model of driver steering behavior

A quantitative description of driver steering behavior such as a mathematical model is presented. The steering task is divided into two levels: (1) the guidance level involving the perception of the instantaneous and future course of the forcing function provided by the forward view of the road, and the response to it in an anticipatory open-loop control mode; (2) the stabilization level whereby any occuring deviations from the forcing function are compensated for in a closed-loop control mode. This concept of the duality of the driver's steering activity led to a newly developed two-level model of driver steering behavior. Its parameters are identified on the basis of data measured in driving simulator experiments. The parameter estimates of both levels of the model show significant dependence on the experimental situation which can be characterized by variables such as vehicle speed and desired path curvature.

Donges, E.↗