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High-fidelity general-purpose robotic simulators are a special class of simulator designed to simulate all the components of a real-world robotics system, including autonomous air vehicles and planetary exploration rovers, so that a real-world system can be tested and verified before/during deployment on the real-world hardware. General-purpose robotic simulators can simulate sensors, actuators, obstacles, terrains, environments, physics, lighting, fluids, and air particles, while also providing a means to verify the system’s autonomous algorithms by using the simulated vehicle in place of the real-world one. General-purpose robotic simulators are typically coupled with an abstract robotic control interface so that autonomous systems evaluated on the simulated vehicles can be deployed, unchanged, on the corresponding real-world vehicles and vice versa. However, the problem with the current technology and research is that neither the robotic simulators nor the robotic control interfaces support Hard Real-Time capabilities, and cannot guarantee that Hard Real-Time constraints will be met. The lack of Hard Real-Time support has major implications on both the utility and the validity of the simulation results and the functioning of the realworld autonomous vehicle. As a solution, this paper will present Hard-RTSim, a novel hard real-time simulation framework that will: 1) Bring Hard Real-Time support to generalpurpose robotic simulators; and 2) Bring Hard Real-Time support to abstract robotic control interfaces. Hard-RTSim guarantees that simulated events in the environment or modeled vehicle are produced and handled with finite (bounded) accuracy and precision. Furthermore it improves these temporal responses to ensure these bounds are representative of temporal requirements for a wide range of scenarios. The Hard-RTSim framework ensures that the simulator and the hard real-time processes will actually get to use the CPU when they request/need it, no matter how many other processes are loaded on the CPU. The experimental results of using the Hard-RTSim framework compared to not using it yield a huge improvement in responsiveness and reliability. There is an improvement of 35% when the CPU is minimally loaded and then as the CPU load is increased the improvement increases as well, all the way up to a 98% improvement when the CPU is loaded at its maximum. These substantial improvements in precision and reliability will help to further the state of space exploration, aerospace technology, and produce better and more reliable autonomous aerial vehicles and planetary exploration rovers.

This paper presents the hysteresis modeling of shape memory alloy actuators (SMA) using Maxwell resistive capacitor (MRC or Maxwell model). The SMA actuators exhibit nonlinearity between electrical input and output displacement. Its hysteretic behavior can cause inaccuracy in tracking if it is not modeled properly. Modified Maxwell model is adopted to compensate for the asymmetric hysteresis loop obtained from the experimental system. Control system design containing inverse Maxwell model is developed and experiments are conducted to verify the effectiveness of the dynamic model and controller.

DIMMACSS-PSG is a free and open-source intelligent robotic middleware that allows a Simulink controller to control a physical real-world multi-agent system or a simulated multi-agent system existing within the Player/Stage/Gazebo general-purpose robotic simulator, using the exact same control system for both in an optimal and efficient manner. A general-purpose robotic simulator, such as Player/Stage/Gazebo, is designed to simulate everything inherent in a real-world robotics experiment, including all types of robotic hardware such as actuators and sensors (stereo-vision camera’s, moving/rotating parts, motors, etc), and provides realistic environments, physics, and sensor data. Intelligent robotic middleware, such as DIMMACSS-PSG, is the class of technologies that sit between a theoretical algorithm/function and the target real-world or simulated devices, and is required in order to actually realize an application such as one implemented on an unmanned aerial vehicle or a surface exploration robot. This paper discusses the motivation for DIMMACSS-PSG, details the important design decisions, and presents a demonstration of a Simulink controller that uses DIMMACSS-PSG to control both a simulated multi-agent system and a real-world multi-agent system.

In orbit dynamics, most perturbations are well modeled, while the inaccuracy of the atmospheric density model turns into the biggest error source in orbit prediction and determination. The commonly used empirical atmospheric density models, such as, Jacchia, MSIS, DTM and Russian GOST, still have a relative error about 10% − 30%. Because of the uncertainty of the density distribution of atmosphere, estimating the atmospheric density by a deterministic model cannot achieve high accuracy. The better way to improve the model precision is calibrating the model with updated measurements. Two-line element set is accessible orbital data of satellite, which can be used in the model calibration. In this paper, an algorithm for calibrating atmospheric density model is developed. First, the density distribution of atmosphere is represented by a power series expansion whose coefficients are denoted by spherical harmonic expansions. Then, the expansion coefficients and the ballistic coefficients of the satellites are identified simultanteneously by solving a nonlinear least squares problem. The simulation results show that the relative error of the atmospheric density is less than 3%, and the relative error of the ballistic coefficient is less than 0.3% after calibration.

Large deployable antennas are used to improve the antenna gain with the development of mobile satellite communication. Large deployable hoop truss antenna (LDHTA) are widely used for its light-weight, high-precision, small launch volume, and high deployment reliability. Its dynamic modeling and analysis are essential in order to improve the mechanical design and the deployment scheme design of the antenna. In this paper, the flexible multibody dynamics model of a LDHTA is developed via the absolute nodal coordinate formulation (ANCF), which results in constant mass matrix without the centrifugal and Coriolis forces. Then the model is applied for the simulation of the non-synchronous deployment phenomena of the LDHTA considering the flexibility of the structure and decay of the driving force. The angular variance is used to evaluate the non-synchronous phenomena. Results show that the non-synchronous deployment can obviously increase the stress of the hoop struts of LDHTA.

DIMMACSS-Stage is a software framework used to control a multi-agent system within the Player/Stage robotic simulator using a controller designed in MATLAB’s Simulink. There is a lot of novel research being done that involves the control of a multi-agent system, and a lot of this research uses robotic simulators, such as Player/Stage, to test and prove the validity of the controller. However, the current trend throughout the published research, even in the top journals and conferences, is that the software framework is constantly being designed from scratch over and over again, and there is little to no discussion regarding how it was actually designed. There are many problems associated with this situation; for example, the solutions are most likely not optimal in their time and space complexities, and there is no way to duplicate or replicate the experimental results of the published work. To this end, this paper provides a method, model, and design regarding how to specifically design a correct and optimal software framework to control a multi-agent system in the Stage robotic simulator using a controller designed in MATLAB’s Simulink. This paper also discusses why optimal solutions are important, and it provides all the information and details necessary to replicate and duplicate the DIMMACSS-Stage framework.

This paper considers Earth-to-Moon low-energy transfers in spatial bicircular four-body problem. Different from these methods based on 2D manifolds, the parking orbit to parking orbit transfers will be obtained directly by utilizing the 3D transit orbits, which can describe the motion near the neck region of the zero velocity curve more accurate. To this end, the low-energy transfer orbits are divided into two stages, the L2 neck region transit stage and the Earth-Moon transfer stage. First, the L2 neck region transit stage is investigated in the Earth-Moon circular restricted three-body problem by using the phase space search method. The boundary of the transit orbits is described by the manifolds of the vertical/horizontal Lyapunov orbits and the transit cones. The relationship between the boundary and the manifolds of libration point orbits is illuminated. Second, the search domain is further reduced by using the perilune properties of these transit orbits, such as the height of perilune and the latitude and longitude of the perilune. Third, the Earth-Moon transfer stage is computed by using backward search technique in the Earth-Moon based Sun perturbed bicircular four-body problem. The height of perigee and the inclination of the parking orbit are also analyzed. Finally, the results are compared with the Hohmann transfer and the results obtained by manifold based methods. Comparing with the manifold based design method, the method introduced in this paper can evaluate the Sun phase angle, time of flight and the total ∆V more accurate, and the results can be refined in the JPL ephemeris model much easier. Moreover, the method can also be adopted in other interplanetary low-energy transfer trajectories design.

Estimation and guidance scheme is presented, which enables two missiles tracking single target cooperatively. Each missile is equipped with an infra-red sensor and measures the LOS angle only. The two missiles form a measuring baseline relative to the target in space and share measured information with each other, enabling that each identies the target state based triangulation method. However, the observability of this double line-ofsight measuring relative navigation method is weak if the separation angle between both line-of-sight vectors is small. This paper proposes a guidance law that modulates the lineof-sight angle through a performance index. Using this guidance law, the missile with large initial ling-of-sight angle maximizes this index. Whereas the other one minimizes it. Simulation results show that the proposed estimation and guidance scheme improves the homing accuracy and can yield hit-to-kill performance.

This paper presents an experimental study on wrinkle reduction in a rectangular membrane structure with elliptical boundary cuts. The structure is subjected to a varying thermal load and wrinkling induced by the thermal expansion of the membrane is measured using a photogrammetry system and the root mean square of the membrane’s surface above a plane of best t. An incremental PI controller is implemented to track a desired atness level when the membrane is subject to either application or removal of a thermal load. Experimental verication is conducted on a membrane structure test facility and the results show that the PI controller is able to track a desired atness level quite well.

This paper presents finite element analysis of a rectangular membrane with elliptical boundary cuts under various loading conditions. A thermo-mechanical analysis investigates the effects of heat loads on the wrinkling and wrinkle reduction using boundary forces. A localized heat load will cause thermal expansion of the membrane close to the heat source while further areas will remain unaffected. The expansion of the heated area will cause compressive stresses where it meets unaffected regions causing wrinkles to form. To remove the wrinkling due to thermal loads, various tension force combinations are analyzed and the results show that it is possible to do so, and an appropriate tension scheme is set up. To try to validate the results from analysis, preliminary experimental data is compared to the results obtained from Abaqus.

This paper presents a vibration control strategy for a flexible manipulator with a collocated piezoelectric sensor/actuator pair. The experimental system is first outlined and then a control law is developed. The proposed vibration controller combines the input shaping technique with multi-mode adaptive positive position feedback. An adaptive parameter estimator based on the recursive least square method is developed to update the system’s natural frequencies which are used by the adaptive positive position feedback. A proportional-derivative controller is combined with the proposed vibration controller to suppress vibration while slewing the manipulator. Experimental results are presented to illustrate the efficacy of the proposed controller.

This paper presents an experimental study on wrinkle reduction in a rectangular membrane structure with elliptical boundary cuts. The structure is subjected to two different heat loads: 145 ◦ Ca nd205 ◦ C. Wrinkling induced by the thermal expansion of the membrane is measured using a photogrammetry system and the root mean square of the membrane’s surface above a plane of best fit. A fuzzy Llogic controller is developed in order to reduce wrinkles due to the thermal disturbance. Experimental study is conducted using our membrane structure test facility and the results show that wrinkles have been reduced significantly and quickly using the proposed fuzzy logic controller.

A vibration suppression strategy is developed for an unconstrained flexible manipulator with a collocated piezoelectric sensor/actuator pair. Dynamic modeling of the flexible manipulator is first shown and then a control law is developed. A proportional derivative (PD) controller is combined with various modified input shapers (MIS) to control the rigid mode and attempt to suppress the vibrations of the flexible mode. In order to suppress vibrations of a strucuture with frequency uncertainties, a positive position feedback (PPF) control law is augmented with an adaptive parameter estimator based on the recursive least squares method which updates the natural frequencies of the structure online.

An active vibration control strategy is developed for a flexible manipulator with a collocated piezoelectric sensor/actuator pair. Dynamic modeling of the flexible manipulator is first shown and then a control law is developed. The positive position feedback (PPF) control law is augmented with an adaptive parameter estimator based on the recursive least squares method which updates the natural frequencies of the structure online. Accurate targeting of the vibrational modes is critical for damping of the vibrations using PPF and simulations are conducted to demonstrate its eectiveness. I. Introduction Active vibration control of a single-link flexible manipulator is a relatively complex problem and has had numerous papers published on it. From a robotics standpoint, a flexible manipulator is desirable due to the fact that existing manipulators are large and heavy due to the need for the manipulator to be sti in order for the precise location of the tip to be known. The flexible manipulator on the other hand, would have the advantages of lighter weight, lower power consumption, and better maneuverability due to smaller size. The drawback to the flexible manipulator is that it faces large vibrations, leading to positional inaccuracy of the tip during and after movement. The same problems occur in large flexible structures for use in space, such as solar panel arrays. Since the size and mass of an object that can be put into space is severely limited, most structures are flexible due to their smaller mass. This can lead to a variety of problems in areas such as high precision attitude control and stability of motions. A significant number of papers have been written on PPF 1‐3 demonstrating its eectiveness in active vibration control. However, the eectiveness of PPF deteriorates when the natural frequencies of the structure are poorly known or changing due to, for example, the presence of a tip mass. There has been significantly less work done on adaptive PPF than there has been on just PPF. Kwak et al. 4 present a method for adaptively tuning the controller frequency of the PPF controller for a single mode of a cantilever beam, and also illustrate their implementation of a real-time controller. Rew et al. 5 propose an adaptive PPF controller for a plate in a fixed-free configuration in which estimated natural frequencies are adjusted at every time step. Baz and Hong 6 present an adaptive modal PPF controller where the AMPPF controller parameters are adjusted in an adaptive manner in order to follow the performance of an optimal reference model (for a cantilever beam). In the first section, development of a finite element model for an Euler-Bernoulli beam to take into account the eect of the sensor and actuator dynamics is presented. This model is created for use in the simulations and is based upon the work of Bandyopadhyay et al. 7 with some modifications. In the second section, a positive position feedback controller is designed for damping of the beam’s vibrations, and then an adaptive online parameter estimator based upon the recursive least squares method with forgetting factor is designed for the first two modes of vibration. Next, the results of using the adaptive estimator to update the estimates of the beam’s first two natural frequencies are presented and their eectiveness demonstrated. Finally, conclusions and possible further areas of investigation are discussed.

This paper involves a thruster hardware setup and Hardware-in-the-Loop (HITL) simulation. The hardware that was used in the simulation is a simple cold gas thruster, which was constructed out of a solenoid valve and a nozzle with N2 gas being fed through air tubing from a compressed tank. The thruster was tested to characterize its performance. The thruster characteristic like time to reach on state, consistency of maximum thrust in steady state, the time it takes to reach an off state, and the input pressure vs. thrust profile were examined. The simulation is comprised of a non-linear dynamic model of two spacecraft formation flying, a Fuzzy Logic controller used to control the relative motion of spacecraft in formation, and an actuator block to fire the thruster and read the thrust measurement. The whole process and results are further explained in the paper.

An adaptive synchronization controller is developed for six-degree-offreedom (6-DOF) spacecraft formation flying based on cross-coupling concept. The proposed strategy allows the attitude and relative position of the follower spacecraft track the desired trajectory, while simultaneously guarantees the motion synchronization among 6 DOFs. The generic synchronization error concept allows to design suitable synchronization error in order to achieve the desired synchronization performance. Simulations of leader-follower spacecraft formation flying are conducted and the results verify the effectiveness of the proposed approach.

This paper presents a flight control system development course project using an innovative, interactive simulation platform. The project integrates design, testing, and flight simulation to give students a close-to-reality engineering development practice. Valuable lessons are learned through “flight testing” experience. It also provides feedback for design fine-tuning and improvement.

In this paper, a synchronized trajectory tracking control strategy is proposed for multiple experimental three-degrees-of-freedom (3-DOF) helicopters. This model-based controller includes a feedforward dynamic term and uses a PD control law as feedback. The convergence is achieved for both trajectory tracking and the motion synchronization. A proposed generalized synchronization concept further improves the transient performance. Numerical simulation results of four helicopters in coordination are presented.