Torque Rods Research Articles

An efficient/accurate multi-scale fatigue prediction method for Metal-Polymer hybrid (MPH) interface

Metal-polymer hybrid (MPH) structures, featuring a micro-structure interlocking design, combine the high strength of metal with the exceptional formability of polymer-based composites and have gained significant attention in automotive load-bearing components. Challenges persist in accurately predicting MPH structure fatigue life using small samples with diverse interlock parameters and swiftly generating static strength and fatigue life response surfaces for automated optimization. We introduce a simplified model for predicting fatigue at the interfaces of MPH structures. Our multi-fidelity prediction method integrates this model with limited high-fidelity data samples to assess both the static strength and fatigue life effectively. This method predicts the deviation with less than 3% error compared to FSR-FEM, achieving a reduction in prediction time of over 60%. Additionally, we elucidate the non-synergistic mechanisms of key interfacial locking parameters between static strength and fatigue life at the micro-scale. Finally, we propose and apply a multi-objective synergistic optimization strategy to the MPH thrust rods in vehicles. By utilizing our optimization method, we achieve a 27.9% weight reduction compared to steel counterparts, while enhancing overall tensile strength by 11.8% and significantly improving fatigue life by 46.7% compared to MPH torque rods lacking an interlock interface.

Distributed magnetic attitude control for large space structures

The utility of distributed magnetic torque rods for the attitude control of a large space structure is investigated. Distributed arrays of actuators offer advantages such as distributing structural loads, increasing fault tolerance, allowing structures to be designed modularly, and additionally the actuators may be integrated with on-orbit fabrication strategies. First, distributed torques are shown to effectively rotate highly flexible structures. This is compared with torques applied to the centre-of-mass of the structure, which cause large surface deformations and can fail to enact a rotation. This is demonstrated using a spring–mass model of a planar structure with embedded actuators. A distributed torque algorithm is then developed to control an individually addressable array of actuators. Attitude control simulations are performed, using the array to control a large space structure, again modelled as a spring–mass system. The attitude control system is demonstrated to effectively detumble a representative 75 × 75 m flexible structure, and perform slew manoeuvres, in the presence of both gravity-gradient torques and a realistic magnetic field model.

우주과학임무를 위한 큐브위성 자기장 청결도 분석

CubeSat is a satellite platform that is widely used not only for earth observation but also for space exploration. CubeSat is also used in magnetic field investigation missions to observe space physics phenomena with various shape configurations of magnetometer instrument unit. In case of magnetic field measurement, the magnetometer instrument should be far away from the satellite body to minimize the magnetic disturbances from satellites. But the accommodation setting of the magnetometer instrument is limited due to the volume constraint of small satellites like a CubeSat. In this paper, we investigated that the magnetic field interference generated by the cube satellite was analyzed how much it can affect the reliability of magnetic field measurement. For this analysis, we used a reaction wheel and Torque rods which have relatively high-power consumption as major noise sources. The magnetic dipole moment of these parts was derived by the data sheet of the manufacturer. We have been confirmed that the effect of the residual moment of the magnetic torque located in the middle of the 3U cube satellite can reach 36,000 nT from the outermost end of the body of the CubeSat in a space without an external magnetic field. In the case of accurate magnetic field measurements of less than 1 nT, we found that the magnetometer should be at least 0.6 m away from the CubeSat body. We expect that this analysis method will be an important role of a magnetic cleanliness analysis when designing a CubeSat to carry out a magnetic field measurement.

Avoid Sign Errors

Sign errors are the most preventable cause of space mishaps, but ironically the leading one as well. This paper recounts the trials and tribulations of several missions, and shows that sign errors can occur anywhere. In every case, engineers overlooked human weaknesses, such as poor communications across functional areas.This paper therefore beseeches the space community members to vigilantly guard against these elementary mistakes. Most generally, they should identify all sign-sensitive items and ensure configuration control at the appropriate level, conduct end-to-end verification, use simple tests to safeguard against gross errors, and validate flight software.The paper also delineates more hands-on lessons in design, manufacturing, testing, and operations: design for unambiguity, plan to quickly correct sign errors during satellite initialization, and avoid taking hasty actions during routine operations.Moreover, this paper prescribes preventive actions for equipment known to be particularly trouble-prone: tantalum capacitors, connectors, actuators such as torque rods, and sensors such as star trackers.These prescriptions look obvious, but when it comes to signs, one should heed the advice of Andy Groves: “Only the paranoid survive. Success breeds complacency; complacency breeds failure.”

The LightSail 2 solar sailing technology demonstration

The LightSail 2 mission is the culmination of a decade-long program sponsored by The Planetary Society to advance solar sailing technology. The objective of LightSail 2 is to demonstrate controlled solar sailing in Earth orbit using a CubeSat platform. The LightSail 2 attitude is controlled using a single-axis momentum wheel and magnetic torque rods. During solar sailing operations, two 90 degree slews are performed each orbit to harness momentum from solar photons. Flight data show that LightSail 2 is successfully controlling its orientation relative to the Sun, and the controlled thrust from solar radiation pressure is measurably reducing the rate of orbital decay. The Planetary Society declared LightSail 2 mission success on July 31, 2019. This paper provides an overview of the LightSail 2 mission implementation, including the design of the flight system and flight software, and the pre-launch testing program. A summary of LightSail 2 mission operations is provided, including a description of the ground system. Solar sailing performance is presented, and anomalies encountered during the mission are discussed. The flight team continues to refine solar sailing performance and conduct on-orbit imaging for engineering purposes and to engage public interest. The LightSail program is entirely donor-funded, with over 50,000 contributors around the globe.

Guidance of magnetic space tug

Magnetic tugging of a target satellite without thrust capacity can be interesting in various contexts, as for example End-Of-Life management, or to complete launchers capabilities. The aim is to gradually modify the orbit of the target by constantly exerting on it a magnetic force. To do so, the chaser is assumed equipped with a steerable magnetic dipole, able to create both forces and torques on the magnetic torque rods carried by the target. The chaser is also supposed to carry electric thrusters, creating a continuous force which modifies the orbit of the whole formation composed of chaser and target.The relative motions of both satellites are derived, in order to assess the feasibility of such a concept. Relative configuration (attitudes and position) trajectories are derived, which are compliant with the dynamics, and enable the chaser to tug the target.Considering targets in Low Earth Orbit (LEO), the magnetic field of the Earth is taken into account, modeled by the International Geomagnetic Reference Field (IGRF). The position of the magnetic torque rod of the target may not be located at its center of mass. This lever-arm is taken into account in the dynamics.As for every Electro-Magnetic Formation Flight concept developed in the literature, satellites involved in magnetic tugging are constantly subjected to torques, created by the Earth magnetic field and by the magnetic fields created by the other satellites in the formation. In this study, the solution chosen to face this problem is to take into account the attitude equilibrium of the satellites early in the guidance phase, in order to avoid having to wave the dipole, as it is generally done.Promising results are presented for different types of orbit, showing that the concept could be feasible in many different scenarios.

Tendon-Sheath Mechanisms in Flexible Membrane Wing Mini-UAVs: Control and Performance

Flexible membrane wings (FMWs) are known for two inherent advantages, that is, adaptability to gusty airflow as the wings can flex according to the gust load to reduce the effective angle of attack and the ability to be folded for compact storage purposes. However, the maneuverability of UAV with FMWs is rather limited as it is impossible to install conventional ailerons. The maneuver relies only on the rudders. Some applications utilize torque rods to warp the wings, but this approach makes the FMW become unfoldable. In this research, we proposed the application of a tendon-sheath mechanism to manipulate the wing shape of UAV. Tendon-sheath mechanism is relatively flexible; thus, it can also be folded together with the wings. However, its severe nonlinearity in its dynamics makes the wing warping difficult to control. To compensate for the nonlinearity, a dedicated adaptive controller is designed and implemented. The proposed approach is validated experimentally in a wind tunnel facility with imitated gusty condition and subsequently tested in a real flight condition. The results demonstrate a stable and robust wing warping actuation, while the adaptive washout capability is also validated. Accurate wing warping is achieved and the UAV is easily controlled in a real flight test.

Verification of Spin Magnetic Attitude Control System using air-bearing-based attitude control simulator

This paper accomplishes one goal and it was to verify and to validate a Spin Magnetic Attitude Control System (SMACS) program and to perform Hardware-In-the-Loop (HIL) air-bearing experiments. A study of a closed-loop magnetic spin controller is presented using only magnetic rods as actuators. The magnetic spin rate control approach is able to perform spin rate control and it is verified with an Attitude Control System (ACS) air-bearing MATLAB® SIMULINK® model and a hardware-embedded LABVIEW® algorithm that controls the spin rate of the test platform on a spherical air bearing table. The SIMULINK® model includes dynamic model of air-bearing, its disturbances, actuator emulation and the time delays caused by on-board calculations. The air-bearing simulator is employed to develop, improve, and carry out objective tests of magnetic torque rods and spin rate control algorithm in the experimental framework and to provide a more realistic demonstration of expected performance of attitude control as compared with software-based architectures. Six sets of two torque rods are used as actuators for the SMACS. It is implemented and simulated to fulfill mission requirement including spin the satellite up to 12degs−1 around the z-axis. These techniques are documented for the full nonlinear equations of motion of the system and the performances of these techniques are compared in several simulations.

Three-Axis Attitude Control Using Redundant Reaction Wheels with Continuous Momentum Dumping

A description of an attitude control system for a three-axis stabilized spacecraft is presented. A globally stabilizing nonlinear feedback control law is derived that enables tracking of an arbitrary time-varying reference attitude. This new control incorporates integral feedback while avoiding any quadratic rate feedback components. A redundant cluster of four or more reaction wheels is used to control the spacecraft attitude, and three magnetic torque rods are used for purposes of continuous autonomous momentum dumping. The momentum dumping strategy can employ general torque rod orientations, and it is developed to take advantage of a redundant set of reaction wheels.

3-Axis magnetic control: flight results of the TANGO satellite in the PRISMA mission

PRISMA implements guidance, navigation and control strategies for advanced formation flying and rendezvous experiments. The project is funded by the Swedish National Space Board and run by OHB-Sweden in close cooperation with DLR, CNES and the Danish Technical University. The PRISMA test bed consists of a fully manoeuvrable MANGO satellite as well as a 3-axis controlled TANGO satellite without any ΔV capability. PRISMA was launched on the 15th of June 2010 on board DNEPR. The TANGO spacecraft is the reference satellite for the experiments performed by MANGO, either with a “cooperative” or “non-cooperative” behaviour. Small, light and low-cost were the keywords for the TANGO design. The attitude determination is based on Sun sensors and magnetometers, and the active attitude control uses magnetic torque rods only. In order to perform the attitude manoeuvres required to fulfil the mission objectives, using any additional gravity gradient boom to passively stabilize the spacecraft was not allowed. After a two-month commissioning phase, TANGO separated from MANGO on the 11th of August 2010. All operational modes have been successfully tested, and the pointing performance in flight is in accordance with expectations. The robust Sun Acquisition mode reduced the initial tip-off rate and placed TANGO into a safe attitude in <30 min. The Manual Pointing mode was commissioned, and the spacecraft demonstrated the capability to follow or maintain different sets of attitudes. In Sun/Zenith Pointing mode, TANGO points its GPS antenna towards zenith with sufficient accuracy to track as many GPS satellites as MANGO. At the same time, it points its solar panel towards the Sun, and all payload equipments can be switched on without any restriction. This paper gives an overview of the TANGO Attitude Control System design. It then presents the flight results in the different operating modes. Finally, it highlights the key elements at the origin of the successful 3-axis magnetic control strategy on the TANGO satellite.

A hybrid attitude controller consisting of electromagnetic torque rods and an active fluid ring

In this paper, a novel hybrid actuation system for satellite attitude stabilization is proposed along with its feasibility analysis. The system considered consists of two magnetic torque rods and one fluid ring to produce the control torque required in the direction in which magnetic torque rods cannot produce torque. A mathematical model of the system dynamics is derived first. Then a controller is developed to stabilize the attitude angles of a satellite equipped with the abovementioned set of actuators. The effect of failure of the fluid ring or a magnetic torque rod is examined as well. It is noted that the case of failure of the magnetic torque rod whose torque is along the pitch axis is the most critical, since the coupling between the roll or yaw motion and the pitch motion is quite weak. The simulation results show that the control system proposed is quite fault tolerant.

Magnetic torque attitude control of a satellite using the state-dependent Riccati equation technique

A non-linear attitude control method for a satellite with magnetic torque rods using the state-dependent Riccati equation (SDRE) technique has been developed. The magnetic torque caused by the interaction with the Earth's magnetic field and the magnetic moment of torque rods plays a role of the control torque. The detailed equations of motion for this system are presented using angular velocity and quaternions. The SDRE controller is developed for the non-linear systems which can be formed in pseudo-linear representations using the state-dependent coefficient (SDC) method without linearization procedure. The aim of this control system is to achieve a stable attitude within 5°, and minimize the control effort. The stability regions for the SDRE controlled satellite system are estimated through the investigation of the stability conditions developed for pseudo-linear systems and the application of Lyapunov's theorem. For comparisons, the Linear Quadratic Regulator (LQR) method using the solution of the algebraic Riccati equation (ARE) is also applied to this non-linear system. The performance of the SDRE non-linear control system demonstrates more robustness and stability than the LQR control system when subjected to a wide range of initial conditions.

A fault-tolerant magnetic spin stabilizing controller for the JC2Sat-FF mission

This paper presents a spin-stabilization algorithm for the Japan Canada Joint Collaboration Satellite-Formation Flying (JC2Sat-FF) mission using magnetic actuation only. It is shown that under a reasonable assumption on the Earth’s magnetic field, the resulting control law is asymptotically stabilizing for an axisymmetric spacecraft, even under the failure of up to two magnetic torque rods and magnetic torque rod saturation. It is also stabilizing under quantization. The satellite motion remains stable under control outages, meaning that the error can be reduced by implementing the control intermittently. The effectiveness of the control law is demonstrated using a high fidelity attitude control system simulator for the JC2Sat-FF satellite.

Meeting science requirements for attitude determination and control in a low-power, spinning nanosatellite

this paper describes the attitude determination and control system for a nanosatellite (30 kg), using geomagnetic field data and solar panels as sun sensors, applied to a spinning nanosatellite (Penn State Univer- sity's LionSat). LionSat will map plasma densities in the ram and wake of the vehicle's path, using two hybrid plasma probes that rotate with the spacecraft. Attitude will be determined using a combination of voltage out- puts from contiguous solar panels and a three-axis magnetometer (TAM). To correct for spin-axis drift due to orbital plane nodal regression (approximately five degrees per day), two magnetic torque rods will provide the necessary control actuation. To avoid corrupting the TAM and plasma probe measurements, periodic quiescent intervals for the torque rods are required. Initial design concepts for this mission employed an extended Kalman filter, implemented onboard to predict attitude during the passive control intervals; making use of digital sun sensors as part of the attitude determination scheme; however, budget limitations have resulted in the need to employ the body-mounted solar panels (sides and end caps) to estimate the sun vector. Simulation results indi- cate that the solar-panel sun sensors (in conjunction with the TAM) can produce the required attitude knowledge for processing the scientific data; the pointing accuracy for spin-axis control (nominally within 5 degrees of or- bit-normal) is degraded to 10 degrees accuracy, but this is still within acceptable limits for the science.

Estimation of a Spacecraft's Attitude Dynamics Parameters by Using Flight Data

An algorithm that uses flight data to estimate the parameters in an attitude dynamics model of a spacecraft has been developed. The new algorithm’s estimates can enhance the fidelity of Euler equation models that are used to implement attitude determination and control functions. The algorithm’s estimation equation is an integrated version of Euler’s equation expressed in inertial coordinates. It uses three-axis attitude data and three-axis rategyro data to yield a set of linear equations in the unknown dynamics parameters, which include moments and products of inertia and scale factors, alignments, and biases for all reaction wheels and magnetic torque rods. The estimation problem statement includes the statistics of unmodeled torques and sensor errors, and it incorporates a scalar quadratic constraint to overcome the unobservability of the parameters’ overall scaling. The sensor errors enter the model equation in a multiplicative fashion, which yields a total least-squares problem. The solution algorithm employs a guarded Newton iteration and recursive factorizations that deal efficiently with the problem’s dynamic structure. The algorithm has been applied to the Wilkinson Microwave Anisotropy Probe spacecraft, and the resulting parameter estimates reduce torque modeling errors by a factor of 5‐7.

Flight Characteristics of Shaping the Membrane Wing of a Micro Air Vehicle

Biologically inspired concepts are rapidly expanding the range of aircraft technology. Consideration is given to merging two biologically-inspired concepts, morphing and micro air vehicles, and the resulting flight characteristics are investigated. Specifically, wing shaping is used to morph the membrane wings of a micro air vehicle. The micro air vehicle has poor lateral control because hinges, and consequently ailerons, are difficult to install on a membrane wing. Instead, a set of torque rods, aligned along the wings, are used to twist the membrane and shape the wing. The resulting morphing is shown to provide significant control authority for lateral dynamics. A set of flight tests are undertaken to determine the flight characteristics by commanding pulses and doublets to the control actuation. The vehicle demonstrates excellent roll performance in response to wing shaping. Futhermore, the vehicle demonstrates several types of spin behavior related to combinations of elevator deflection and the wing shaping.

Failure of steel castings welded to heavy truck axles

Minor changes in steel chemistry can have a significant affect on weld quality. Weld procedures performed in a manufacturing environment are usually developed based on the steel composition required in a material specification. This is done to consistently produce acceptable weld properties without developing a high hardness heat-affected zone (HAZ) in the adjacent base metal. Fatigue cracks were visually detected in cast steel suspension brackets after operators reported noticing looseness in the rear suspension system. These trucks were associated with a particular vocation that resulted in significant loads transferred through the torque rods that position the rear axles. It was discovered that the carbon equivalent (chemistry) in the steel castings had increased slightly over a period of time which ultimately resulted in a higher than expected hardness in the HAZ. Underbead cracks had formed in the HAZ of the casting that subsequently propagated by fatigue that could have resulted in detachment of the castings from the axle housing.

Magnetic Torquer Attitude Control via Asymptotic Periodic Linear Quadratic Regulation

A method of using magnetic torque rods to do 3axis spacecraft attitude control has been developed. The goal of this system is to achieve a nadir pointing accuracy on the order of 0.1 to 1.0 deg without the need for thrusters or wheels. The open-loop system is under-actuated because magnetic torque rods cannot torque about the local magnetic field direction. This direction moves in space as the spacecraft moves along an inclined orbit, and the resulting system is roughly periodic. Periodic controllers are designed using an asymptotic linear quadratic regulator technique. The control laws include integral action and saturation logic. This system's performance has been studied via analysis and simulation. The resulting closed-loop systems are robust with respect to parametric modeling uncertainty. They converge from initial attitude errors of 30 deg per axis, and they achieve steady-state pointing errors on the order of 0.5 to 1.0 deg in the presence of drag torques and unmodeled residual dipole moments.