ESTCube-2 asendi- ja orbiidikontrolli süsteemi disain

This thesis presents the design and analysis of the attitude and orbit control system for the ESTCube-2 CubeSat. The objective of the system is to spin up the satellite to high angular rates, perform accurate pointing and should also be able to operate outside of the Earth’s magnetic influences, for example in a Lunar orbit. For this thesis various requirements for the subsystem and payloads of the nanosatellite have been gathered. From these requirements the design drivers for the attitude and orbit control system are identified. Additionally the thesis analyses the ESTCube-1 nanosatellite attitude determination and control performance and presents the lessons learned, which provides input to the design of the ESTCube-2 nanosatellite. Based on the requirements a set of actuators and sensors are presented that fulfil the various ESTCube-2 mission objectives. The thesis also covers the attitude estimation process. This is done by describing the data generation from the simulation environment and the different potential algorithms to be used for sensor fusion. A sensor fusion algorithm for nanosatellite attitude determination is proposed and the first implementation was made to work on the ESTCube-2 microcontroller. Initial results for the algorithm are described and the future improvements are identified

EST-Cube-1 in-orbit attitude determination validation

http://www.ester.ee/record=b448442

Assessment of power characteristics of unmanned tractor for operations on peat fields

Received: June 1st, 2021 ; Accepted: January 3rd, 2022 ; Published: January 11th, 2022 ; Correspondence: [email protected] this article, power characteristics of a state-of-the-art unmanned ground vehicle (UGV) are characterised. It is demonstrated that in terms of power characteristics requirements, purposebuilt computer aided autonomous UGV systems are capable of replacing systems that utilise conventional tractors in peat field operations, with milled peat extraction operations as a case study. The authors demonstrate the viability of the UGV in achieving optimal mobility capabilities in operating on peatland surface. The UGV of interest was assessed for two operations of milled peat extraction: milling and harrowing. For both operations, the power consumption of the UGV and the drawbar pull of the implements (passive miller and harrower) were measured and analysed. The required drawbar pull values of the investigated implements remained in the range of 4–8 kN, which corresponded to the drawbar power of 14–36 kW. It was found that the UGV of interest is capable of carrying out milled peat operations in terms of traction capacity. However, it was found that the power supply capacity to be insufficient, thus requiring an improved solution

Design of a Scientific-Grade Multispectral Imager for Nanosatellites

Applications in agriculture, land-cover change, and vegetation phenology, to name a few, would benefit from more frequent high-quality remote sensing data. However, ”Landsat-class” satellites are too expensive for such applications. Therefore, there is a need to augment larger Earth observation satellites with nanosatellites that use scientific-grade imaging instruments. This paper presents the design for the scientific-grade multispectral imager Theia. It is designed for a 5% radiometric accuracy at a ground sampling distance of 33 m at a 650 km orbit while keeping the modulation transfer function above 0.13 at the Nyquist frequency. The camera has reflective optics with an aluminium optomechanical design to mitigate stress from thermal expansion. Furthermore, the optical path is covered with a mix of black anodization and Acktar Magic Black to suppress stray-light. The sCMOS sensor is back-side illuminated to increase the radio metric quality of the instrument. Furthermore, the imager has a post-launch calibration system for continuous monitoring of the instrument’s quality. The performance is achieved while fitting inside 0.6 CubeSat Units and weighing about 600 g. However, a trade-off between the modulation transfer function and radio metric quality is presented. Such an imager, when deployed on numerous nanosatellites, can enable new kinds of missions that are otherwise too costly. The project is funded by the European Space Agency

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.Peer reviewe

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with - 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.</p

Stabilised LQR control and optimised spin rate control for nanosatellites

This paper presents the design and study of cross product control, Linear-Quadratic Regulator (LQR)optimal control and high spin rate control algorithms for ESTCube-2/3 missions. The three-unit CubeSat is required to spin up in order to centrifugally deploy a 300-m long tether for a plasma brake deorbiting experiment. The algorithm is designed to spin up the satellite to one rotation per second which is achieved in 40 orbits. The LQR optimal controller is designed based on closed-loop step response with controllability and stability analysis to meet the pointing requirements of less than 0.1° for the Earth observation camera and the high-speed communication system. The LQR is based on linearised satellite dynamics with an actuator model. The preliminary simulation results show that the controllers fulfil the requirements set by payloads. While ESTCube-1 used only electromagnetic coils for high spin rate control, ESTCube-2 will make the use of electromagnetic coils, reaction wheels and cold gas thrusters to demonstrate technologies for a deep-space mission ESTCube-3. The attitude control algorithms will be demonstrated in low Earth orbit on ESTCube-2 as a stepping stone for ESTCube-3 which is planned to be launched to lunar orbit where magnetic control is not available.Peer reviewe

Particle swarm optimization for magnetometer calibration with rotation axis fitting using in-orbit data

This article demonstrates the performance of an improved particle swarm optimization (PSO) algorithm with scalar checking and rotation axis fitting objectives using in-orbit data, which is obtained from two CubeSats missions, Aalto-1 and ESTCube-1, as well as simulation as reference. The improved algorithm uses sequential objectives refinement process to combine the two optimization objectives. This improvement addresses some challenges of magnetometer calibration when using in-orbit data. First, the change in the magnetic field vector direction at different points in orbit which is uncorrelated to the rotation of the spacecraft itself. Second, the uncertainty of the rotation axis information used as the reference, e.g., from gyroscope noise. Third, the available data set is heavily affected by the rotation mode of the spacecraft, which imposes some limitation in the rotation axis information needed by the algorithm. The improved PSO algorithm is applied on simulated data in order to analyze the calibration performance under different spacecraft tumbling rates and noise levels. In ideal condition (varying rotation axis during measurements and sufficient sampling rate relative to the spin rate), the rotation axis fitting objective can reach ∼0.1° of correction accuracy.Peer reviewe

Interplanetary Student Nanospacecraft: Development of the LEO Demonstrator ESTCube-2

Nanosatellites have established their importance in low-Earth orbit (LEO), and it is common for student teams to build them for educational and technology demonstration purposes. The next challenge is the technology maturity for deep-space missions. The LEO serves as a relevant environment for maturing the spacecraft design. Here we present the ESTCube-2 mission, which will be launched onboard VEGA-C VV23. The satellite was developed as a technology demonstrator for the future deep-space mission by the Estonian Student Satellite Program. The ultimate vision of the program is to use the electric solar wind sail (E-sail) technology in an interplanetary environment to traverse the solar system using lightweight propulsion means. Additional experiments were added to demonstrate all necessary technologies to use the E-sail payload onboard ESTCube-3, the next nanospacecraft targeting the lunar orbit. The E-sail demonstration requires a high-angular velocity spin-up to deploy a tether, resulting in a need for a custom satellite bus. In addition, the satellite includes deep-space prototypes: deployable structures; compact avionics stack electronics (including side panels); star tracker; reaction wheels; and cold–gas propulsion. During the development, two additional payloads were added to the design of ESTCube-2, one for Earth observation of the Normalized Difference Vegetation Index and the other for corrosion testing in the space of thin-film materials. The ESTCube-2 satellite has been finished and tested in time for delivery to the launcher. Eventually, the project proved highly complex, making the team lower its ambitions and optimize the development of electronics, software, and mechanical structure. The ESTCube-2 team dealt with budgetary constraints, student management problems during a pandemic, and issues in the documentation approach. Beyond management techniques, the project required leadership that kept the team aware of the big picture and willing to finish a complex satellite platform. The paper discusses the ESTCube-2 design and its development, highlights the team’s main technical, management, and leadership issues, and presents suggestions for nanosatellite and nanospacecraft developers