CubeSat Attitude System Calibration and Testing

This thesis concentrates on the development of Aalto-2 CubeSat attitude system calibration and testing methods. The work covers the design and testing phase of the calibration algorithms to the analysis of experimental data in order to verify the performance of the attitude instruments. The instruments under test are two-axis digital Sun sensor, three-axis magnetometer, three-axis gyroscope, and three-axis magnetorquer. These devices are all commercial off-the-shelf components which are selected for their cost-to-performance efficiency. The Sun sensor and gyroscope were calibrated with linear batch least squares method and the results showed that only minor corrections were required for the Sun angle and angular velocity readings, while the brightness readings from the Sun sensor required more corrections. For magnetometer calibration, a specific particle swarm optimization algorithm was developed with novel approach to estimate the full calibration parameters, without having to simplify the sensor model. The calibration results were evaluated with simulation data with satisfying results, while the results from experimental data itself showed heading error improvement from \SIrange[range-phrase=--]{5.24}{13.24}{\degree} to \SIrange[range-phrase=--]{1.9}{7.3}{\degree} for unfiltered data. Besides the magnetometer calibration parameters estimation, the magnetic properties of the spacecraft were also analyzed using inverse multiple magnetic dipole modeling approach, where multiple magnetic dipoles positions and moments are estimated using particle swarm optimization from the magnetic field strength readings around the spacecraft. The estimated total residual magnetic moment of the spacecraft is \SI{58.5}{\milli\ampere\square\meter}, lower than the maximum magnetorquer moment which is \SI{0.2}{\ampere\square\meter} in each axis. The magnetorquer was tested for verifying the validity of magnetic moment generated by the magnetorquer. The result shows that the magnetorquer moment is nonlinear, in contrast to the linear theoretical model

Calibration and testing techniques for nanosatellite attitude system development in magnetic environment

Defence is held on 3.9.2021 12:00 – 15:00 https://aalto.zoom.us/j/62485002135The development of nanosatellites, which are generally defined by its weight ranging between 1kg-10kg, have grown considerably in the academia sector. The most popular form factor for spacecrafts in this category is the CubeSat form factor, as it opens up lower-cost launch opportunities and growing availability of commercial-off-the-shelf solutions for the spacecraft subsystems. For many nanosatellites orbiting in Low Earth Orbit, magnetic environment is an important aspect in its design consideration. This applies to both the platform engineering and mission design, as it influences the attitude system design as well as the design of the relevant scientific instruments. This thesis work contributes in the development of technology and techniques that can help in managing the influence of magnetic environment in spacecraft design, in particular the solution for magnetometers calibration and the detection of spacecraft residual magnetic dipole moment. The magnetometer calibration focuses on the implementation of rotational correction factor, which, in the more conventional techniques, is typically assumed to be in a certain condition. The detection of spacecraft residual magnetic dipole moment focuses on the early development of a machine-vision-assisted test bed that aims to reduce the mechanical and electrical complexity of the more common spacecraft automated magnetic test bed. Several missions, where the spacecraft has been developed and built in Aalto university, has been launched. From the perspective of practical performance of in-orbit spacecraft operation, this thesis work will also discuss the challenges and lessons learned from the operation of Aalto-1 attitude system. This thesis contribution is focused on the attitude analysis and sensors calibration of the Aalto-1 in-orbit operation

Radiation monitor RADMON aboard Aalto-1 CubeSat : First results

The Radiation Monitor (RADMON) on-board Aalto-1 CubeSat is an energetic particle detector that fulfills the requirements of small size, low power consumption and low budget. Aalto-1 was launched on 23 June 2017 to a sun-synchronous polar orbit with 97.4° inclination and an average altitude of somewhat above 500 km. RADMON has been measuring integral particle intensities from October 2017 to May 2018 with electron energies starting at low-MeV and protons from 10 MeV upwards. In this paper, we present first electron and proton intensity maps obtained over the mission period. In addition, the response of RADMON measurements to magnetospheric dynamics are analyzed, and the electron observations are compared with corresponding measurements by the PROBA-V/EPT mission. Finally, we describe the RADMON data set, which is made publicly available.The Radiation Monitor (RADMON) on-board Aalto-1 CubeSat is an energetic particle detector that fulfills the requirements of small size, low power consumption and low budget. Aalto-1 was launched on 23 June 2017 to a sun-synchronous polar orbit with 97.4 degrees inclination and an average altitude of somewhat above 500 km. RADMON has been measuring integral particle intensities from October 2017 to May 2018 with electron energies starting at low-MeV and protons from 10 MeV upwards. In this paper, we present first electron and proton intensity maps obtained over the mission period. In addition, the response of RADMON measurements to magnetospheric dynamics are analyzed, and the electron observations are compared with corresponding measurements by the PROBA-V/EPT mission. Finally, we describe the RADMON data set, which is made publicly available. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.Peer reviewe

Radiation monitor RADMON aboard Aalto-1 CubeSat: First results

The Radiation Monitor (RADMON) on-board Aalto-1 CubeSat is an energetic particle detector that fulfills the requirements of small size, low power consumption and low budget. Aalto-1 was launched on 23 June 2017 to a sun-synchronous polar orbit with 97.4° inclination and an average altitude of somewhat above 500 km. RADMON has been measuring integral particle intensities from October 2017 to May 2018 with electron energies starting at low-MeV and protons from 10 MeV upwards. In this paper, we present first electron and proton intensity maps obtained over the mission period. In addition, the response of RADMON measurements to magnetospheric dynamics are analyzed, and the electron observations are compared with corresponding measurements by the PROBA-V/EPT mission. Finally, we describe the RADMON data set, which is made publicly available.</p

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

CubeSat Attitude System Calibration and Testing

This thesis concentrates on the development of Aalto-2 CubeSat attitude system calibration and testing methods. The work covers the design and testing phase of the calibration algorithms to the analysis of experimental data in order to verify the performance of the attitude instruments. The instruments under test are two-axis digital Sun sensor, three-axis magnetometer, three-axis gyroscope, and three-axis magnetorquer. These devices are all commercial off-the-shelf components which are selected for their cost-to-performance efficiency.The Sun sensor and gyroscope were calibrated with linear batch least squares method and the results showed that only minor corrections were required for the Sun angle and angular velocity readings, while the brightness readings from the Sun sensor required more corrections. For magnetometer calibration, a specific particle swarm optimization algorithm was developed with novel approach to estimate the full calibration parameters, without having to simplify the sensor model. The calibration results were evaluated with simulation data with satisfying results, while the results from experimental data itself showed heading error improvement from 5.24°–13.24° to 1.9°–7.3° for unfiltered data. Besides the magnetometer calibration parameters estimation, the magnetic properties of the spacecraft were also analyzed using inverse multiple magnetic dipole modeling approach, where multiple magnetic dipoles positions and moments are estimated using particle swarm optimization from the magnetic field strength readings around the spacecraft. The estimated total residual magnetic moment of the spacecraft is 58.5mAm2, lower than the maximum magnetorquer moment which is 0.2Am2 in each axis. The magnetorquer was tested for verifying the validity of magnetic moment generated by the magnetorquer. The result shows that the magnetorquer moment is nonlinear, in contrast to the linear theoretical model.Validerat; 20150824 (global_studentproject_submitter

Assessment of a machine-vision-assisted test bed for spacecraft magnetic cleanliness analysis

Small satellites are becoming increasingly popular in several applications, in which attitude systems might require high precision performance. These spacecrafts are susceptible to magnetic disturbances in orbit, such as the interaction between the satellite and Earth’s magnetic field. However, a major disturbance torque is generated by the residual magnetic moment. Therefore, a magnetic cleanliness analysis must be considered in order to meet the requirements for magnetic-sensitive instruments and subsystems. Studies on magnetic environment management are underway for the FORESAIL-1 and FORESAIL-2 missions using the optical magnetic test bed of Aalto University. This is particularly important for FORESAIL-2 which aims to precisely measure the orbital ambient magnetic field with a high sensitivity magnetometer One of the parts of a spacecraft magnetic cleanliness analysis is the modelling of the residual magnetic moment as a set of magnetic dipoles. The dipoles are estimated from the measured magnetic field surrounded by the device-under-test (e.g., complete satellite, or its individual subsystems) using a stochastic estimation algorithm. The measurements are performed in a Helmholtz cage where the device and a low-noise magnetometer are placed, and detected by a smart camera using visual detection markers (ArUco). Information provided by the detection of the markers is then used for representing the position of the magnetometer and measured magnetic field points in the device-under-test coordinate frame. The camera detection accuracy is improved with data fusion from several ArUco markers, and the system performance is assessed by verifying the estimated magnetic moment results using known permanent magnets. Using this methodology for calculating the residual magnetic moment, the system is able to estimate the dipole’s position and magnetic vectors with a mean absolute error of 0.004 ± 9·10-7 m and 0.007 ± 1·10-4 A·m2 respectively. The test bed can be used for the characterization of the magnetic moment when measuring small satellites, or its components, in order to mitigate the residual magnetic moment.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