Small Reaction Wheels Research Articles

Detection and Analysis of Anomalous Behavior in On-Orbit Satellites Using AI Algorithms

The increasing deployment of satellites for essential applications necessitates robust anomaly detection to maintain their operational integrity. Traditional methods, which depend on manual monitoring and predefined thresholds, often prove inadequate in the complex space environment. This paper investigates the application of Artificial Intelligence (AI) algorithms to improve the detection and analysis of anomalous behavior in on-orbit satellites. AI, especially through machine learning (ML) and deep learning (DL), provides advanced capabilities for processing extensive telemetry data and identifying intricate patterns. By leveraging historical data, AI systems can establish normal operational parameters and detect deviations indicating potential anomalies. Techniques such as supervised and unsupervised learning are employed to develop models with high predictive accuracy. Furthermore, AI facilitates root cause analysis by correlating anomalies with operational conditions or external factors, enabling effective corrective measures. The integration of AI also promotes autonomous satellite operations, which are crucial for deep-space missions. This advancement enhances satellite reliability and safety, supporting sustainable and progressive space exploration. In this research, machine learning algorithms were employed to develop the proposed anomaly detection system. The system aims to detect subtle failures in the spacecraft’s attitude dynamics system, particularly in the reaction wheel subsystem, by learning solely from the spacecraft's nominal behavioral data. The system was developed from a small satellite's attitude dynamics control system, which may exhibit bearing failures in the reaction wheels. Two types of anomaly detection systems were introduced: a two-sided learning anomaly detection system and a one-sided learning anomaly detection system. For this study, a two-sided learning anomaly detection system was developed using the Logistic Regression (LR) method. This provided a foundation for the training process using a machine learning approach. By learning from both nominal and failure behaviors of the satellite, the system was designed to detect small reaction wheel friction failures effectively.

On Orbit Demonstration of a Small Reaction Wheel in “TSUBAME”

On Orbit Demonstration of a Small Reaction Wheel in “TSUBAME”

Ensuring of Relative Navigation and Control of Low-Orbital Microsatellites Formation in the Task of Remote Control of Robots

Abstract The article discusses the problem of providing optimal relative navigation and flight control of a group of satellites for remote control of robots operating at a great distance from the command post. It is necessary to provide the intensive data exchange between command post and robot (or several robots) by radio communication without essential delay in signals transmission. The geostationary satellites cannot work without a delay corresponding to their high orbit. That is why the low-orbit micro satellites must be used. To make them smaller and cheaper only one directional antenna is installed at each satellite and it is aimed at the desired point on the earth by the angular orientation of the satellite itself. Three small reaction wheels are used as the actuators for correct functioning of orientation system. For easy radio communication between satellites the distance between them has to be not more than 100m, and the task of keeping such formation is solving automatically with application of several electro-reaction engines. The requirements to all onboard automatic systems and equipment are estimated.

Jitter reduction of a reaction wheel by management of angular momentum using magnetic torquers in nano- and micro-satellites

Nowadays, nano- and micro-satellites, which are smaller than conventional large satellites, provide access to space to many satellite developers, and they are attracting interest as an application of space development because development is possible over shorter time period at a lower cost. In most of these nano- and micro-satellite missions, the satellites generally must meet strict attitude requirements for obtaining scientific data under strict constraints of power consumption, space, and weight. In many satellite missions, the jitter of a reaction wheel degrades the performance of the mission detectors and attitude sensors; therefore, jitter should be controlled or isolated to reduce its effect on sensor devices. In conventional standard-sized satellites, tip-tilt mirrors (TTMs) and isolators are used for controlling or isolating the vibrations from reaction wheels; however, it is difficult to use these devices for nano- and micro-satellite missions under the strict power, space, and mass constraints. In this research, the jitter of reaction wheels is reduced by using accurate sensors, small reaction wheels, and slow rotation frequency reaction wheel instead of TTMs and isolators. The objective of a reaction wheel in many satellite missions is the management of the satellite’s angular momentum, which increases because of attitude disturbances. If the magnitude of the disturbance is reduced in orbit or on the ground, the magnitude of the angular momentum that the reaction wheels gain from attitude disturbances in orbit becomes smaller; therefore, satellites can stabilize their attitude using only smaller reaction wheels or slow rotation speed, which cause relatively smaller vibration. In nano- and micro-satellite missions, the dominant attitude disturbance is a magnetic torque, which can be cancelled by using magnetic actuators. With the magnetic compensation, the satellite reduces the angular momentum that the reaction wheels gain, and therefore, satellites do not require large reaction wheels and higher rotation speed, which cause jitter. As a result, the satellite can reduce the effect of jitter without using conventional isolators and TTMs. Hence, the satellites can achieve precise attitude control under low power, space, and mass constraints using this proposed method. Through the example of an astronomical observation mission using nano- and micro-satellites, it is demonstrated that the jitter reduction using small reaction wheels is feasible in nano- and micro-satellites.

TUGSAT-1/BRITE-Austria—The first Austrian nanosatellite

A nanosatellite to investigate the brightness oscillations of massive luminous stars by differential photometry is currently developed by a Canadian/Austrian team within the BRITE (Bright Target Explorer) project. The first Austrian satellite funded by the Austrian Space Program, called TUGSAT-1/BRITE-Austria, builds on the space heritage of the most successful Canadian CanX-2 and MOST missions. The satellite makes use of recent advances in miniaturized attitude determination and control systems. Precision three-axis stabilization by small reaction wheels and a star tracker provides the necessary accuracy for the photometer telescope to the arcminute level. This will provide to the astronomers photometric data of the most massive stars with unprecedented precision; data which cannot be obtained from the ground due to limitations imposed by the terrestrial atmosphere. The paper describes the spacecraft characteristics and the ground infrastructure being established in support of the BRITE mission which will consist of a constellation of up to four nearly identical satellites allowing to carry out long-term observation of stars (magnitude +3.5) not only with respect to brightness variations, but also in different spectrum ranges.

Solar sail attitude control using small reaction wheels and magnetic torquers

The current paper describes an attitude control system that uses small reaction wheels and magnetic torquers to control the attitude of a large flexible solar sail in low-Earth orbit (LEO). This system is being proposed for the NASA New Millenium Programme Space Technology-9 solar sail technology demonstration mission. Controlling the attitude of a solar sail with these actuators in LEO was previously considered difficult and thus never proposed before. What makes it possible is choosing the right orbit and judiciously constraining the attitude of the solar sail in that orbit. Simulation results are presented that validate this design approach for solar sail attitude control in LEO.

Reaction wheel with HTS bearings for mini-satellite attitude control

We have developed a small reaction wheel, designed to be lightweight, compact and energy efficient. The main innovation is the use of the HTS magnet's bearings that promise low friction so that high momentum storage can be achieved with high spin speed. The bearings consist of seeded growth superconducting discs arranged in rings located above and below the rotating levitated wheel containing ring-magnets embedded at the top and bottom. The reaction wheel is in the shape of a hollow stainless steel cylinder. A brushless dc motor is installed inside the hollow cylinder to provide the necessary torque to the reaction wheel. The maximum design spin speed is 15 000 RPM to store 3.5 J s−1 of angular momentum. Spin-down test of the reaction wheel was performed in air. We have also measured the input power required to sustain rotational speed of the reaction wheel in air. Results from both of these measurements, when extrapolated to full speed in vacuum, indicate that power consumption, even accounting for the needs of the cooling system, is significantly smaller than that for state of the art commercial reaction wheels using mechanical ball bearings.

3327 微小重力下での実時間画像処理を利用した超小型衛星の 3 軸姿勢制御実験

The feasibility study has been conducted to build a small satellite (so called 'nano-satellite'), which has 3-kg mass and less than 30-W power, since October in 1998. A 3-axes attitude control experiment of the nano-satellite under micro-gravity field was carried out at Japan Micro-gravity Center (JAMIC) in 2001. The small reaction wheel was used as an actuator for the attitude control developed by Hokkaido Institute of Technology as one of the important key technologies of the nanosatellite. The 3-axes attitude control by using wireless CCD camera (VHF wave) and image processing was demonstrated under micro-gravity.

Minimum Power Optimum Control of Microsatellite Attitude Dynamics

This paper deals with the attitude dynamics and control of a multimission microsatellite for remote sensing applications. The attitude control system consists of three small reaction wheels and three magnetic torquers. The paper presents a new control technique in which the required control torque is continuouslyredistributed between the reaction wheels and the magnetic torquers to minimize the electric power consumption in the attitude control. The required control torque is computed using proportional derivative control laws and the optimum control theory. Numerical results show that substantial power savings can be obtained while retaining attitude control accuracy adequate for remote sensing applications.

Robust control of the SmArT Microsatellite attitude dynamics

SMART (Scientific Microsatellite for Advanced Research and Technology) is a project of the two Universities of Naples, financed by Regione Campania, aimed at designing and developing a multi-mission microsatellite for remote sensing applications. Since remote sensing requires fine attitude control, the microsatellite is three-axis stabilized with three small reaction wheels. Three magnetic torquers, for initial attitude acquisition and wheel momentum unloading, complete the attitude control subsystem. In this paper the microsatellite attitude control in the case of wheel failure is analyzed. In order to save on-board mass and power, control techniques are developed to automatically re-distribute the required control torque among the operating wheels and the magnetic torquers in the case of failure of one or two wheels. The proposed control is designed in order to maintain the required pointing accuracy. To this end, the control techniques are developed using a mathematical model of the microsatellite attitude dynamics, which considers the variation of the Earth magnetic field magnitude and direction along the orbit. Numerical simulations demonstrate the effectiveness of the proposed techniques.

Aerodynamic and gravity gradient stabilization for microsatellites

When the orbital altitude of a satellite is relatively low, for example, less than 500 km, the method of aerodynamic stabilization can be considered. In particular, this method is very effective when the satellite is small. The aerodynamic restoring torque can be provided by a very light tail stabilizer which is several meters downstream from the main body of the small satellite. An aerodynamic stabilization system has been installed in the Cosmos-149 and another one in the Cosmos-320. One of the disadvantages in using the aerodynamic stabilization is that no rolling stabilization can be achieved. The gravity gradient stabilization method has been used in many satellites. One of the examples is the Eole satellite. In the recent years, many small satellites have adopted this method owing to its long life and continuous Earth pointing characteristics. The main disadvantage is the poor pointing accuracy with respect to the orbiting reference coordinates. This disadvantage can be overcome with the aid of a small reaction wheel. Both pitch and roll orientations can be stabilized. However, no yawing motion stabilization can be achieved by using the pure passive gravity gradient method. The purpose of this paper is to combine the aerodynamic and gravity gradient stabilization methods together so that all the three axes stabilizations can be obtained. We shall consider the attitude motion of a microsatellite under the action of both gravity gradient torque and aerodynamic torque. The set of nonlinear equations of motion will be solved numerically with specified initial condition. The satellite operates in a circular orbit with 500 km altitude. The history of the attitude stabilization will be investigated and discussed in detail.

SMART Attitude Acquisition and Control

This paper deals with the attitude acquisition and control for the Italian Scientific Microsatellite for Advanced Research and Technology. Since the microsatellite is aimed at remote sensing applications, three-axis fine attitude control (0.1°–0.01°) during station keeping is required. The attitude acquisition technique exploits the magnetic control to despin the microsatellite initial tumbling and uses a small reaction wheel to despin the microsatellite residual rotation around the axis perpendicular to the orbit plane, due to the magnetic control. Three-axis attitude control during station keeping is performed by means of three small reaction wheels, whose reaction torque vector is computed using Proportional Derivative control laws and optimum control theory. Coarse attitude control is first performed in which the microsatellite attitude angles are determined by a technique based on the use of sensors with low mass and power consumption. Fine attitude control is then achieved by using a small star tracker for fine attitude measurement. The proposed techniques for attitude acquisition, determination and control during station keeping are numerically tested with a code that simultaneously integrates the microsatellite attitude dynamics and control. Numerical results show that the attitude acquisition is performed in about 20 orbits, after the separation from the launcher, while coarse attitude determination and control during station keeping are achieved with accuracies 0.7° and ±2°, respectively.

High precision active nutation control of a momentum biased spacecraft with flexible appendages

The controller design for the Solar Dynamics Observatory, a momentum biased spacecraft with three flexible appendages, is presented. The pointing of scientific instruments imposes arc-second pointing requirements on the spacecraft bus and meeting these requirements necessitates the use of an active nutation controller, here mechanized with a small reaction wheel oriented along a bus transverse axis. The active nutation controller does its job by orchestrating the transfer of angular momentum out of the bus transverse axes and into the momentum wheel. A simulation study verifies that the controller provides quick, stable, and accurate response.