Attitude control for satellites flying in VLEO using aerodynamic surfaces

This paper analyses the use of aerodynamic control surfaces, whether passive or active, in order to carry out very low Earth orbit (VLEO) attitude maneuver operations. Flying a satellite in a very low Earth orbit with an altitude of less than 450 km, namely VLEO, is a technological challenge. It leads to several advantages, such as increasing the resolution of optical payloads or increase signal to noise ratio, among others. The atmospheric density in VLEO is much higher than in typical low earth orbit altitudes, but still free molecular flow. This has serious consequences for the maneuverability of a satellite because significant aerodynamic torques and forces are produced. In order to guarantee the controllability of the spacecraft they have to be analyzed in depth. Moreover, at VLEO the density of atomic oxygen increases, which enables the use of air-breathing electric propulsion (ABEP). Scientists are researching in this field to use ABEP as a drag compensation system, and consequently an attitude control based on aerodynamic control could make sense. This combination of technologies may represent an opportunity to open new markets. In this work, several satellite geometric configurations were considered to analyze aerodynamic control: 3-axis control with feather configuration and 2-axis control with shuttlecock configuration. The analysis was performed by simulating the attitude of the satellite as well as the disturbances affecting the spacecraft. The models implemented to simulate the disturbances were the following: Gravitational gradient torque disturbance, magnetic dipole torque disturbance (magnetic field model IGRF12), and aerodynamic torque disturbances (aerodynamic model DTM2013 and wind model HWM14).The maneuvers analyzed were the following: detumbling or attitude stabilization, pointing and demisability. Different VLEO parameters were analyzed for every geometric configuration and spacecraft maneuver. The results determined which of the analyzed geometric configurations suits better for every maneuver

NanoSail-D: The First Flight Demonstration of Solar Sails for Nanosatellites

The NanoSail-D mission is currently scheduled for launch onboard a Falcon Launch Vehicle in the late June 2008 timeframe. The NanoSail-D, a CubeSat-class satellite, will consist of a sail subsystem stowed in a Cubesat 2U volume integrated with a CubeSat 1U volume bus provided by the NASA Ames Research Center (ARC). Shortly after deployment of the NanoSail-D from a Poly Picosatellite Orbital Deployer (P-POD) ejection system, the solar sail will deploy and mission operations will commence. This demonstration flight has two primary mission objectives: 1) to successfully stow and deploy the sail and 2) to demonstrate de-orbit functionality. Given a nearterm opportunity for launch, the project was met with the challenge of delivering the flight hardware in approximately six months, which required a significant constraint on flight system functionality. As a consequence, passive attitude stabilization will be achieved using permanent magnets to de-tumble and orient the body with the magnetic field lines and then rely on atmospheric drag to passively stabilize the sailcraft in an essentially maximum drag attitude. This paper will present an introduction to solar sail propulsion systems, overview the NanoSail-D spacecraft, describe the performance analysis for the passive attitude stabilization, and present a prediction of flight data results from the mission

Contributions to the average attitude control of nanosatellites

This work presents contributions with the average control method for the active attitude control of nano-satellites through the use of magnetorquers. Key concepts, constraints, and limitations due to the use of these actuators are presented. Then, based on a previous work employing an adaptive gain, a novel non-adaptive control law is proposed in order to decrease the energy consumption of the overall system without loss of stability. Theoretical guarantees regarding the ultimate bound of closed loop system trajectories are presented through the average method - applied on pre-established regions - and Lyapunov stability theory. Different simulation results illustrate the effectiveness of the proposed approach to achieve the desired attitude for different satellite configurations. A comparison between the new approach to the previous adaptive strategy available in the literature indicates that a considerable energy economy could be reached, with values reaching 70% for some cases. Control signal saturation is considered in some of the simulated scenarios but not mitigated.Este trabalho apresenta contribuições no contexto do método de controle médio para o controle de atitude ativa de nanossatélites através do uso de magnetorquers. Os principais conceitos, restrições e limitações devido ao uso desses atuadores são apresentados. Em seguida, com base em um trabalho anterior empregando um ganho adaptativo, uma lei de controle nova, não adaptativa é proposta para diminuir o consumo de energia do sistema como um todo sem perda de estabilidade. Garantias teóricas referentes às fronteiras das trajetórias do sistema de malha fechada são apresentadas por meio do método de controle médio - aplicado a regiões pré-estabelecidas - e teoria de estabilidade de Lyapunov. Diferentes resultados de simulação ilustram a eficácia da abordagem proposta para alcan- çar a atitude desejada para diferentes configurações de satélite. Uma comparação entre a nova abordagem com a estratégia adaptativa anterior disponível na literatura indica que uma economia considerável de energia pode ser alcançada, com valores chegando a 70 % para alguns casos. A saturação do sinal de controle é considerada em alguns dos cenários simulados, mas não mitigada

CubeSat Design and Attitude Control with Micro Pulsed Plasma Thrusters

This study presents the overall design of a 3U CubeSat equipped with commercial-off-the shelf hardware, Teflon-fueled micro-Pulsed Plasma Thrusters (µPPT) and an attitude determination and control system. The µPPT is sized by the impulse bit and pulse frequency required for continuous compensation of expected maximum disturbance torques at altitudes between 400 and 1000 km, and to perform stabilization of up to 20 deg/s and slew maneuvers of up to 180 degrees. The study involves realistic power constraints anticipated on the 3U CubeSat. Attitude estimation is implemented using the q-method for static attitude determination of the quaternion using pairs of the spacecraft-sun and magnetic field vectors. The quaternion estimate and the gyroscope measurements are used with an extended Kalman filter to obtain the attitude estimates. Proportional and derivative control algorithms use the static attitude estimation in order to calculate the angular momentum required to compensate for the disturbance torques and to achieve specified stabilization and slewing maneuvers or combinations. Two control methods are developed: paired firing method, and separate control algorithm and thruster allocation methods which determines the optimal utilization of the available thrusters and introduces redundancy. Simulations results are presented for a 3U CubeSat under stabilization, pointing, and pointing and spinning scenarios

Drag De-Orbit Device: A New Standard Re-Entry Actuator for CubeSats

With the advent of CubeSats, research in Low Earth Orbit (LEO) becomes possible for universities and small research groups. Only a handful of launch sites can be used, due to geographical and political restrictions. As a result, common orbits in LEO are becoming crowded due to the additional launches made possible by low-cost access to space. CubeSat design principles require a maximum of a 25-year orbital lifetime in an effort to reduce the total number of spacecraft in orbit at any time. Additionally, since debris may survive re-entry, it is ideal to de-orbit spacecraft over unpopulated areas to prevent casualties. The Drag Deorbit Device (D3) is a self-contained targeted re-entry subsystem intended for CubeSats. By varying the cross-wind area, the atmospheric drag can be varied in such a way as to produce desired maneuvers. The D3 is intended to be used to remove spacecraft from orbit to reach a desired target interface point. Additionally, attitude stabilization is performed by the D3 prior to deployment and can replace a traditional ADACS on many missions.This paper presents the hardware used in the D3 and operation details. Four stepper-driven, repeatedly retractable booms are used to modify the cross-wind area of the D3 and attached spacecraft. Five magnetorquers (solenoids) over three axes are used to damp rotational velocity. This system is expected to be used to improve mission flexibility and allow additional launches by reducing the orbital lifetime of spacecraft.The D3 can be used to effect a re-entry to any target interface point, with the orbital inclination limiting the maximum latitude. In the chance that the main spacecraft fails, a timer will automatically deploy the booms fully, ensuring the spacecraft will at the minimum reenter the atmosphere in the minimum possible time, although not necessarily at the desired target interface point. Although this does not reduce the risk of casualties, the 25-year lifetime limit is still respected, allowing a reduction of the risk associated with a hardware failure

Design of the Active Attitude Determination and Control System for the e-st@r cubesat

One of the most limiting factors which affects pico/nano satellites capabilities is the poor accuracy in attitude control. To improve mission performances of this class of satellites, the capability of controlling satellite’s attitude shall be enhanced. The paper presents the design, development and verification of the Active Attitude Determination and Control System (A-ADCS) of the E-ST@R Cubesat developed at Politecnico di Torino. The heart of the system is an ARM9 microcontroller that manages the interfaces with sensors, actuators and the on-board computer and performs the control tasks. The attitude manoeuvres are guaranteed by three magnetic torquers that contribute to control the satellite in all mission phases. The satellite attitude is determined elaborating the data provided by a COTS Inertial Measurement Unit, a Magnetometer and the telemetries of the solar panels, used as coarse Sun sensor. Different algorithms have been studied and then implemented on the microprocessor in order to determine the satellite attitude. Robust and optimal techniques have been used for the controller design, while stability and performances of the system are evaluated to choose the best control solution in every mission phase. A mathematical model of the A-ADCS and the external torques acting on the satellite, its dynamics and kinematics, is developed in order to support the design. After the design is evaluated and frozen, a more detailed simulation model is developed. It contains non-ideal sensors and actuators models and more accurate system disturbances models. New numerical simulations permit to evaluate the behaviour of the controller under more realistic mission conditions. This model is the basic element of the Hardware In The Loop (HITL) simulator that is developed to test the A-ADCS hardware (and also the whole satellite). Testing an A-ADCS on Earth poses some issues, due to the difficulties of reproducing real orbit conditions (i.e. apparent sun position, magnetic field, etc). This is especially true in the case of low cost projects, for which complex testing facilities are usually not available. Thanks to a good HITL simulator it is possible to test the system and its “real in orbit” behaviour to a certain grade of accuracy saving money and time for verification. The paper shows the results of the verification of the ADCS by means of the HITL strategy, which are consistent with the expected values

Project of 1DoF attitude control system of 1U cubesat based on reaction wheel

PLATHONs main mission is to simulate a Networks System of CubeSats that collects information and communicate with other different orbital group satellites using IoT sensors to retrieve the information towards a ground station minimizing delay and maximizing global coverage. The project's overview encompasses an analytical estimation of the worst-case disturbance torques calculations for the mission. Moreover, a detailed control algorithm is developed for fine pointing and coarse pointing modes in the orbit as well as a 3D real-time monitoring interface. Finally, the design of the Reaction Wheel is also made following the technical requirements set by the project specifications. To perform the simulation, the CubeSat is introduced in an Air bearing in the center of a magnetic simulator, which will generate a magnetic field similar to the conditions that the satellite will be subjected in a Low Earth Orbit.El siguiente proyecto se realiza dentro de PLATHON (Plataforma de comunicaciones ópticas en nanosatélites) del proyecto DISEN y del Grupo de Investigación TIEG liderado por el Dr. David González y el Dr. Javier Gago en la ESEIAAT (Escola Superior d’Enginyeries Industrial, Audiovisual i Aeronàutica de Terrassa) de la Escuela Politécnica de Cataluña - BarcelonaTech. La misión principal de PLATHON es simular un Sistema de redes de CubeSats que recoja información y se comunique con otros satélites de diferentes grupos orbitales utilizando sensores IoT para recuperar la información hacia una estación terrestre minimizando el retraso y maximizando la cobertura global. Estudiantes de último curso de grado y máster de varios departamentos son los principales colaboradores del proyecto y la mayoría de los componentes del sistema están diseñados y construidos por los estudiantes. La siguiente tesis comprende una estimación analítica de los cálculos de los pares de perturbación en el peor de los casos para la misión. Además, se desarrolla un algoritmo de control detallado para los modos de apuntamiento fino y grueso en la órbita, así como una interfaz de monitorización 3D en tiempo real. Por último, el diseño de la Rueda de Reacción (RW) también se realiza siguiendo los requisitos técnicos establecidos por las especificaciones del proyecto. La etapa final del proyecto se centra en la realización de pruebas y la simulaciones de los algoritmos de control implementados. Para realizar la simulación, se introduce el CubeSat en un cojinete de aire en el centro de un simulador magnético, que generará un campo magnético similar a las condiciones a las que estará sometido el satélite en una órbita baja terrestre (LEO). El ordenador de a bordo (OBC) del nanosatélite se comunica vía Bluetooth con el ordenador de tierra a la espera de órdenes (en este caso, el ordenador central del laboratorio). La estación de tierra tiene acceso total a la actitud del satélite y control total sobre los distintos modos del satélite (es decir, modo de Detumbling, modo de apuntamiento, modo normal, entre otros). Una vez fijado el campo magnético y otras fuentes de perturbación, las ruedas de reacción y los magnetorquers se activarán para controlar la actitud del CubeSat. Análogamente, estos datos de actitud medidos por la Unidad de Medición Inercial (IMU) del Subsistema de Determinación y Control de Actitud (ADCS) se envían de vuelta al ordenador de la estación de tierra y se visualizan además con un modelo 3D generado por ordenador en tiempo real. El CubeSat está pensado para ser alimentado tanto con paneles solares como con una batería LiPo. La realización de una prueba de software-in-theloop y de hardware-in-the-loop ha demostrado que el sistema requiere algunas modificaciones para lograr resultados más precisos

Development and Experimentation of a CubeSat Magnetic Attitude Control System Testbed

For CubeSats requiring high pointing accuracy and slewing agility, ground-based hardware-in-the-loop simulations are strongly demanded to test and validate spacecraft subsystems and guidance, navigation, and control algorithms. In this article, a magnetic attitude control system (MACS) testbed for a CubeSat is developed utilizing a spherical air bearing and a Helmholtz cage. The design, development, and verification procedure of MACS is presented together with different test scenarios. To generate enough torque with the magnetorquer system in the dynamic testbed, the Helmholtz coil system of the testbed has driven to provide an augmented magnetic field. As an example of experimentation, the B-dot control algorithm was implemented to dissipate the angular momentum of the dynamic MACS testbed. The experimental results were compared with those of the numerical simulations

Design and implementation of an attitude determination and control system for the AntelSat

This thesis describes the design, analysis and construction of the Attitude Determination and Control System (ADCS) for the first Uruguayan nanosatellite, the AntelSat. The AntelSat project is a joint venture between the Electrical Engineering Institute (IIE) of Faculty of Engineering, Universidad de la República (UdelaR University) and Antel, the Uruguayan national telecommunications company. The satellite consists of a two-unit (2U) CubeSat, which implies that the ADCS is designed under tight mass, size, and energy constraints. In addition, these kind of satellites usually have limited sensing, computational and communication capabilities, motivating the need for autonomous and computationally eficient algorithms. Under these strict restraints, developing an effective attitude control system poses a significant challenge. As presented in this thesis, for the attitude determination section of the ADCS, data available from sensors is taken as inputs for the computation of an optimal quaternion estimator. The use of a quaternion implementation of an unscented Kalman filter is also discussed. Additionally, attitude control is based on magnetic actuation with magnetorquers being commanded by pulse width modulation. It is shown that the control system is able to achieve the detumbling of the satellite after separation from the launch interface using the reliable B-dot control law. Nadirpointing control is achieved with the use of a simple Linear Quadratic Regulator. Also pertinent is the simulation environment that was implemented to develop the attitude determination and control algorithms and also to validate their performance. ADCS hardware prototypes and flight versions that were designed and constructed are introduced.Este documento de tesis describe el diseño, análisis y construcción de el Sistema de Determinación y Control de Actitud (ADCS por sus siglas en inglés) del primer satélite uruguayo, el AntelSat. El proyecto AntelSat es una actividad conjunta entre el Instituto de Ingeniería Eléctrica (IIE) de la Facultad de Ingeniería de la Universidad de la República y Antel, la empresa de telecomunicaciones nacional de Uruguay. El satélite consiste en un CubeSat de dos unidades (2U), lo que implica que el ADCS es diseñado bajo estrictas restricciones de masa, tamaño y energía. Además, este tipo de satélites posee una capacidad computacional, de comunicaciones y de medición limitada, lo que motiva la necesidad de lograr algoritmos computacionalmente eficientes. Bajo estas estrictas limitaciones, el desarrollo de un sistema de control de actitud efectivo se traduce en un reto importante. Como se presenta en esta tesis, para el segmento de determinación de actitud del ADCS, la información proveniente de los sensores es tomada como entrada para el cálculo de un estimador de cuaternión óptimo. Se discute también el uso de una implementación con cuaterniones de un filtro de Kalman "unscented". Por otro lado, el control de actitud está basado en actuación magnética con magnetorquers comandados con modulación de ancho de pulso. Se demuestra que el sistema de control es capaz de reducir el valor de velocidad angular del satélite en la fase previa a la separación con la interfaz de lanzamiento, mediante la utilización del algoritmo B-dot. La estabilización de la actitud en modo de apunte al nadir se logra con el uso de un simple regulador lineal cuadrático. Por otra parte, se presenta el entorno de simulación que fue implementado para el desarrollo de algoritmos de determinación y control de actitud, y también para validar el desempeño de los mismos. A su vez, se exhiben el hardware del ADCS que fue diseñado y construido, tanto prototipos como versiones de vuelo