JOURNAL OF AERONAUTICS AND SPACE TECHNOLOGIES (ISSN : 1304-0448) January 2020 Volume 13 Number 1 www.jast.hho.edu.tr

Research Article Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability Abdelmadjid LASSAKEUR 1 , Craig UNDERWOOD 2 , Benjamin TAYLOR 2 , Richard DUKE2

1 Development Center, Algerian Space Agency, BP 4065, Ibn Rochd USTO, 31130 Oran, Algeria, [email protected], https://orcid.org/0000-0002-4538-6985 2 Surrey Space Centre, University of Surrey, Guildford GU2 7XH, United Kingdom, [email protected], [email protected], [email protected], https://orcid.org/0000-0002-7001-5510, https://orcid.org/0000-0003-3635-003X, https://orcid.org/0000-0003-4450- 7981 Article Info Abstract CubeSats are being increasingly specified and utilized for demanding astronomical and Earth observation missions where precise pointing and stability are critical requirements. Such precision is difficult to achieve in the case of CubeSats, mainly because of their small moment of inertia, this means that even small disturbance torques, such as those due to a residual magnetic moment are an issue and have a significant effect on the attitude of nanosatellites, when a high degree of stability is required. Also, hardware limitations in terms of power, weight and size make the task more challenging. Recently, a PhD research program has been undertaken at the University of Surrey to investigate the Received: July 18, 2019 magnetic characteristics of CubeSats. It has been found that the disturbances may Accepted: November 22, 2019 be mitigated by good engineering practice, in terms of reducing the use of Online: January 23, 2020 permeable materials and minimizing current-loop area. This paper discusses the dominant source nanosatellites disturbances and presents a survey and a short Keywords: ADCS, CubeSats, description of magnetic cleanliness techniques to minimize the effect of the Nanosatellites, Magnetic Disturbances, residual magnetic field. It is mainly intended to supply a guide for CubeSat Magnetic Cleanliness, Magnetic Dipole community to design future CubeSats with improved attitude stability. We Moment determination, Attitude present then our findings to date of a new technique of the residual magnetic Stability. dipole determination for CubeSats and nanosatellites. This method is performed by implementing a network of eight miniature 3-axis on the spacecraft. These are used to determine the strength, the direction and the center of the magnetic dipole of the spacecraft dynamically in-orbit and in real-time. This technique will contribute to reduce the effect of magnetic disturbances and improve the stability of CubeSats. A software model and a hardware prototype using eight magnetometers controlled via a Raspberry-Pi were developed and successfully tested with the boom payload of the Alsat-1N CubeSat and a magnetic air coil developed for validation purposes.

To Cite This Article: A. Lassakeur, C. Underwood, B. Taylor, and R. Duke "Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability," Journal of Aeronautics and Space Technologies, Vol. 13, No. 1, pp. 25-41, Jan. 2020.

1. INTRODUCTION have been launched up to 10th of June 2019 [5]. CubeSats are a demonstration that small size satellite technology CubeSats are nanosatellites built to standard dimensions, developed, mostly, using commercial off-the-shelf with a base unit volume (U) of 10 cm x 10 cm x 10 cm. (COTS) components. CubeSats have recently attracted They can be in different sizes, 1U, 2U, 3U, 6U or even the interest of many national space agencies, professional bigger scale, and the total mass budget is nominally less space-tech companies and universities as a new tool of than 1.33 kg of mass per unit [2]. This concept was space development and research due to their cost and ease proposed by Professor Robert Twiggs from Stanford of technology using COTS components [2]. They can University in November 1999 at the 2nd Space System perform practical space missions, often as university Symposium. It has then been adopted widely by the projects for space engineering students wanting to test out universities and the space industry [3, 4], 1088 CubeSats some new technology or techniques [6]. This class of

25 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability spacecraft is increasingly used for Earth observation and in the spacecraft – both in the wiring harness and in the astronomical applications where precise pointing and layout of the solar panels. Some CubeSats also carry high attitude stability are critical requirements [7, 8]. permanent magnets – e.g., for electric motors – often used in the ADCS systems for momentum wheels [7, 17]. By Knowing the power, volume and cost limitations of contrast, the other typical attitude disturbance sources for CubeSats, many challenges need to be addressed by the spacecraft decrease significantly when the CubeSat engineers. One key challenge is the development become small. of a precise attitude determination and control system (ADCS). As CubeSats are small satellites ,they have less Table 1 represents a quantitative figure on a typical mass, less volume, and less power for sensors, actuators magnitude order of the different disturbance torques in and algorithms processing [9]. Besides, several CubeSats real life mission scenario in low Earth orbit (660km), have been observed to suffer from unwanted magnetic estimated on PRISM nanosatellite [10]. dipole moment (e.g. SNAP1, PRISM, Alsat1-N, etc.) which becomes the dominant source of attitude Table 1. Attitude disturbance in the PRISM mission [10]. disturbances for such a small moment of inertia platforms Disturbance type Value [Nm] [6, 10, 11]. Therefore, to minimize the effect of the magnetic disturbances and achieve the required level of Magnetic disturbance 3.0 ∙ 10−6 attitude control, the source of the magnetic disturbances must be reduced on the ground (e.g., by good design Gravity gradient 8.0 ∙ 10−7 practices) and, ideally, any residual magnetic dipole −8 moment should be cancelled in-orbit using Aerodynamic 3.0 ∙ 10 magnetorquers [7]. Solar pressure 1.0 ∙ 10−8 Surveys of COTS solar arrays and CubeSats subsystems indicate that they are often not designed with magnetic cleanliness in mind [8, 12]. This paper aims to describe Materials which retain their magnetism and are difficult the sources of the residual magnetic moment and evaluate to magnetize or demagnetize are called hard magnetic their effect on the attitude of CubeSats; we then introduce materials. They have a large hysteresis and low methods of magnetic cleanliness on CubeSats to permeability. In contrast, soft magnetic materials have a minimize the sources of the residual magnetic moment low hysteresis and a large magnetic permeability and thus (RMM) and reduce the effect of the magnetic respond very sensitively to the presence of an external disturbances on CubeSats in orbit. We finally discuss the magnetic field – they are easy to magnetize and characterization and estimation methods of the residual demagnetize. Therefore, the use of hard ferromagnetic or magnetic moment. (preferably) non-ferromagnetic materials, such as some forms of stainless steel (e.g. 304 or 316 alloys), aluminum, copper or titanium are recommended for 2. MAGNETIC DISTURBANCE CHALLENGES spacecraft magnetic cleanliness, whereas soft magnetic TO ATTITUDE DETERMINATION AND materials such as iron, nickel and mild steel are not [7, CONTROL SYSTEMS 18].

As CubeSats have tiny moments of inertia (e.g. MIO of Some CubeSats missions use the permanent magnet CSSWE 3U CubeSats 퐽 = 퐷푖푎푔[0.00551, 0.02552, control as the main attitude control, it is also known as a 0.02565] kg ∙ m2) and are usually operating in the low compass mode. It is used when only two-axis stabilization Earth orbits (160km to 2000km), it is found that the is required. The main drawback of this type of internal magnetic moment dominates over other stabilization is that it is not possible to remove the kinetic environmental disturbances (e.g., aerodynamic, Solar energy from the satellite, and the fact that the Earth radiation pressure and gravity-gradient torques) in terms magnetic field varies along the orbit [19, 20]. An example of producing unwanted attitude disturbances [11, 13]. of permanent magnet control applications on 3U This is due to the Geomagnetic field that interacts with CubeSats is the RAX (Radio Aurora Explorer) [21-23] any residual magnetic field of the spacecraft and results and TURKSAT-3USAT [24]. And on 1U CubeSat in a net magnetic dipole moment [14-16]. missions, OUFTI-1 (Orbital Utility For Telecommunications - Technology Innovations) [25], The effect of magnetic disturbances has shown itself by and ITUpSat-1 (Istanbul Technical University the problem of high tumbling rates observed on several PicoSatellite-1) which uses Alnico permanent magnet for CubeSat missions [7, 17]. Post-flight analysis indicates its attitude control [26]. that this is due to the un-modelled dynamically changing magnetic moments mainly caused by the current flowing

LASSAKEUR et. al. 26 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

2.1. Residual Magnetic Moment length dl, the generated magnetic flux density dB at a point (x, y, z) in a Cartesian coordinate system is given The primary sources of current loops in CubeSats that by [1]: generate a dynamic magnetic moment in the satellite come from the layout of the solar panels and the harness µ 퐼 푑푙⃗⃗⃗ × 푟 of the spacecraft. The current flowing in the solar panels ⃗⃗⃗⃗ 0 (2) 푑퐵 = 2 generates a residual magnetic field due to the resulting 4휋 푟 current loops (Figure 1). Many methods are available in the literature, which can reduce these current loops [27], Where: including placing solar cells tracks of opposite current µퟎ is the permeability of free space. flow next to one another or laying the tracks on top of one another in a multilayer PCB (printed circuit board). The battery also generates a current loop that causes some dipole variation when changing the charge or discharge rate [28], but this usually does not have a significant effect compared to other sources [7]. The magnetic torque (T) is generated by the interaction of the spacecraft magnetic dipole (m) with the Geomagnetic field (B) and is given by:

푇⃗ = 푚⃗⃗ × 퐵⃗ (1)

Many CubeSats use magnetorquer coils and solenoids to Figure 1. Magnetic field due to current-carrying wire [1]. deliberately provide a required torque to control the attitude of the spacecraft. This controlled generation of a r is the vector from the current element Idl to the point magnetic dipole is not a problem – it can only be an issue (x, y, z). if the dipole is unexpected or uncontrolled. However, one consequence of the actuation of magnetorquers could be The total field B has three directional components, Bx, that any magnetically permeable material onboard the By, and Bz, and it is obtained by summing over all current satellite becomes magnetized, leaving unwanted residual elements Idl [1, 30]. dipole moment. For this reason, magnetorquer solenoids should make use of low-remanence ferromagnetic cores, The electrical currents on solar arrays and power cables such as Supra-50 alloy [7, 29]. produce current loops that exert undesirable magnetic torques on the satellite. Therefore, it is crucial to reduce The presence of any permanent magnetic material in the this torque by laying out the solar cell circuits and cabling spacecraft generates a permanent source of the magnetic such that the magnetic torques can cancel each other [1]. dipole moment in the spacecraft, which does not vary over time. This source should be known and taken into account by the ADCS and ideally countered on the 3. MAGNETIC CLEANLINESS PROGRAM ground. Some CubeSats use such permanent magnets to provide the primary form of the attitude control system. Spacecraft cannot be integrated without incurring a When coupled to a dissipative mechanism (such as a fluid residual magnetic field generated from contamination loop or simply due to eddy current formation), the spacecraft DC or low-frequency magnetic field. This is magnetic dipole becomes permanently aligned (locked) caused by the wiring and the electronic, with the Earth’s field, thus, making the magnetic dipole electromechanical components or any ferromagnetic axis of the spacecraft track the Geomagnetic field materials onboard the spacecraft [31]. This can be an direction. Without the dissipative mechanism, the system important source of attitude disturbance for the will not settle [7]. spacecraft, and the critical instruments or sensors of the mission (e.g., magnetometers) need to be protected from these spurious magnetic fields if the external field needs 2.1.1. Current Loop to be accurately measured.

The effect of an electric current through wires or To reduce the magnetic sources onboard the satellite and illuminated solar cells and the associated array wiring can its impact on the attitude of the spacecraft, it essential to be illustrated in Figure 1. Due to the current (I) in an run a so-called magnetic cleanliness program on each part elemental conductor (or in an elemental solar cell) of or subsystem of the spacecraft by employing the

LASSAKEUR et. al. 27 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability following plan to achieve acceptable magnetic Several practical methods are available in the literature, cleanliness level by ensuring that the spacecraft magnetic which can reduce these current loops. An example of field stays sufficiently low [32, 33]: these techniques is to minimize the enclosed current loop area and run equal size loops in opposite directions to  Avoid using ferromagnetic materials wherever reduce the induced magnetic moment vectors (Figure2). possible Although many techniques exist which allow minimizing the magnetic fields generated by solar panels, the near  Identify and reduce the current loops in cabling and magnetic field contributions cannot be entirely removed solar panels [32], (e.g. by using the typical method [27]. The near-field limit can be defined by the condition of twisting power and return cables together to 푅 > 퐷, where 퐷 is the largest dimension of the object and reduce the field emission [18, 34]) r is the distance from the object [36-39]. Another example of a vigorous application of magnetic cleanliness  Identify any magnetic sources as early as possible program in the design of solar arrays on CubeSats is Ultra and then minimize them Triple Junction (TASC) and Triangular Advanced Solar (UTJ) solar cells, in which, each cell (or string of cells)  Identify and characterize the magnetic sources by has a pair partner that is rotated by 180 degrees, measuring and modeling their magnetic behavior cancelling the majority of the magnetic field induced by each cell [12].  Measure and calculate the influence of all magnetic sources on the instruments  Use magnetic field compensation methods to minimize the residual magnetic field at the location of the instrumentation [32]. The success of any magnetic cleanliness campaign relies mainly upon the best engineering practices [32, 35] and ensuring that each part on the spacecraft has its residual magnetic field emission has been characterized and compensated. Figure 2. Magnetic Cleanliness practice on TASC solar cell pair [12]. 3.1. Magnetic Cleanliness on Spacecraft Solar Arrays Figure 2 shows a pair of TASC cells, where the majority The current flowing in solar panels (cells and their of the magnetic field produced by each cell current loop associated wiring) always generates a residual magnetic is canceled out by the opposite cell. As can be seen in field [27]. Magnetic cleanliness on solar cell arrays is Figure 3, this type of cells is flown in ELFIN CubeSat affected by their e1ectrical current patterns and by the (Electron Losses and Fields Investigation) developed by presence of any magnetic materials on the array itself. the Earth, Planetary, and Space Sciences department at Magnetic cleanliness on solar cell arrays may be satisfied UCLA (University of California Los Angeles) and th by the following three design features [1]: launched on the 15 of September 2018 [12].

 Use of a solar cell circuit topography which can minimize the magnetic field about a current loop that encompasses the array surface and leads to a magnetically induced dipole.  Arrange solar cells circuits to reduce the local magnetic field at a given location relative to the entire array  Use solar cell circuit designs that are able to Figure 3. TASC and UTJ solar array layouts [12]. minimize the total magnetic field intensity and its Further reductions in the current loops are possible by direction vector such that low energy charged back-wiring” the solar panels so that the return lines of particles in the plasma through which the array the solar cell strings are routed along the backside of the travels are disturbed as minimum as possible.

LASSAKEUR et. al. 28 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability solar cells such that the direction of the current in the solar the size of the shielded part and the frequency of the fields cells is opposite to the direction of current in the back- of interest [43-46] . As it is essential to keep the mass wires [1]. minimized in the case of CubeSats, magnetic shielding is recommended to be used only to shield strong magnetic The method of mutual compensation on solar panels can sources (e.g. ADCS momentum wheel, motors). be extended to Direct Current (DC) magnetic moment compensation, for example, the orientation of motors or other equipment can be chosen to counter any other large 3.3.1. Shielding Effectiveness moment on the satellite. This method was used for the placement of radio-thermal generators (RTGs) on the The electromagnetic field can be reduced by increasing Cassini spacecraft [18, 40]. the shielding effectiveness of the material around the devices [47]. Shielding effectiveness (SE), sometimes called the electric field shielding effectiveness (ESE) or 3.2. Demagnetization of Ferromagnetic Parts of the the magnetic field shielding effectiveness (MSE), is a Spacecraft parameter used for shielding evaluation, and it is typically defined as the ratio between the magnitude of the incident When high accuracy attitude control is required, we apply magnetic field to the barrier, 퐸푖, and the magnitude of the a so-called “Demagnetization” or “Degaussing” transmitted field, 퐸 [48]: techniques on the ferromagnetic parts individually and 푡 prior the assembly in order to reduce the magnetic field → 2 퐸 generated by each part of the spacecraft. Many 푆퐸 = | 푖 | → demagnetization methods are used in the literature and 퐸푡 (3) are described in details in [41]. An example of this is probing the part’s field with magnetic sensors after manufacturing to identify the magnetized regions, 퐸푖 (4) 푆퐸(푑퐵) = 20. log10 | | followed by the placing of small magnets to the structure 퐸푡 to counteract the inherited magnetic fields [41, 42]. Many factors affect the strength of electromagnetic Another technique is exposing the ferromagnetic part to a shielding, including [30, 48]: highly controlled AC degaussing field, as high as 0.06T for a period of time, assuring a lower level of remanent  The incident electromagnetic field frequency magnetization [41]. The components being demagnetized are placed in a controlled AC magnetic field and a  The shield material parameters that include rotating table on three axes as the magnetic field is conductivity, permittivity, and permeability increased and returned to its lowest level. The intensity of the ambient magnetic field during this process must be  The thickness of the shield reduced to near zero (< 0.5 µT) while these parts are being  The electromagnetic field source type (magnetic demagnetized. As this process cannot be achieved in the presence of the earth’s magnetic field, the effective field, electric field, or plane wave) demagnetization can be established either in a 3-axis  The distance between the magnetic source (part) Helmholtz coil system or by placing the parts in an EMC and the shield (Electro-Magnetic Compatibility) test facility [41, 42].  The shield degradation which is caused by any 3.3. Magnetic Shielding shield apertures

Electromagnetic shielding techniques can be used to  The quality of the bond between shielding metal reduce the electromagnetic field generated by any surfaces. electromagnetic device or component by blocking, reflecting, absorbing or redirecting their electric and 3.3.2. Shielding Materials magnetic fields with barriers. Shielding is applied to isolate electrical devices from their surroundings field or Effective shielding can be achieved by a good selection to prevent the magnetic field from infecting the of shielding materials [49]. A variety of advanced spacecraft, sensors or payloads or even electric materials have been developed and used for propulsion devices from the unwanted magnetic field. electromagnetic shielding for various enclosures level, The amount of reduction of the magnetic field depends connector and cable shielding, grounding, bonding, and upon the type of material used for shielding, its thickness, assembling [50].

LASSAKEUR et. al. 29 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

Table 2 shows the electrical properties for typical Table 3 shows the magnetic properties of Mu-Metal: materials used for electromagnetic shielding performed in a steady magnetic fields 150 kHz frequency [43]. The last Table 3. Mu-Metal magnetic properties [52]. two columns of Table 5 represents the absorption loss at 150 kHz for both one milli-metre (mm) and one milli-inch Characteristics Value Units (mil) tick sheet for each of the listed materials. The absorption loss is expressed in decibels (dB) and is Density 8.7 g/cm3 −1 proportional to the shield material thickness and depends Relative Permeability 80000 H*m on the frequency of the electromagnetic wave frequency Young’s Modulus GPA to be shielded against [43]. It is notable that Aluminum is 225

frequently used as a structural material for most Poisson Ratio 0.29 -

CubeSats, and it is one of the worst materials to be used Yield Strength 280 MPa for shielding [49]. Ultimate Tensile Strength 700 MPa W/ (m*K) Table 2. Electrical properties of shielding materials at Thermal Conductivity 19 -5 150 kHz [43]. Linear Expansion 1.2 10 m/m/C

Specific Heat 460 J/ (kg*K) Characteristics Relative Relative Absorption Loss (dB) Melting Point ˚C Conductivity Permeability 1440 σ µ 1mm thick 1mil Resistivity Ω*m thick 55

Silver 1.05 1 51.96 1.32 Note: The cost of Mu Metal varies from 1$ to 10$ for a Copper, annealed 1.00 1 50.91 1.29 small sheet of few inches [52]. Copper, Hard-Drawn 0.97 1 49.61 1.26 Gold 0.70 1 42.52 1.08 Aluminium 0.61 1 39.76 1.01 3.4. The Satellite Layout Optimization Design Magnesium 0.38 1 31.10 0.79 Approach Zinc 0.29 1 27.57 0.70 Brass 0.26 1 25.98 0.66 Cadmium 0.23 1 24.41 0.62 The satellite layout optimization approach can be used to Nickel 0.20 1 22.83 0.58 reduce the dipole moment of the spacecraft considerably Phosphor-Bronze 0.18 1 21.65 0.55 by optimizing the layout of the spacecraft and by Iron 0.17 1000 665.40 16.90 managing properly the residual magnetic moment Tin 0.15 1 19.69 0.50 generated by different electronic components during the Steel, SAE 1045 0.10 1000 509.10 12.90 design of the spacecraft. This method consists of Beryllium 0.10 1 16.14 0.41 measuring or estimating the dipole moment of each part Lead 0.08 1 14.17 0.36 or subsystem of the spacecraft, then designing the layout HyperNick 0.06 80000 3484.0 * 88.50 * of the spacecraft in such a way that the dipole of each part Monel 0.04 1 10.24 0.26 of the spacecraft can be canceled by another one. Mu-metal 0.03 80000 2488.0 * 63.20 * Permalloy 0.03 80000 2488.0 * 63.20 * Few CubeSats have considered this technique, very Steel, Stainless 0.02 1000 224.4 5.70 recently, Chen et al. [53] proposed a new approach called MetShield 0.01 60000 3000.0 * 75.00 * “The satellite layout optimization design” (SLOD) for minimizing the residual magnetic flux density of micro- *Assuming that the material is not magnetically saturated and Nano-satellites. This method aims to reduce the global residual moment of the spacecraft by placing An example for a good and cheap material to be components of the satellite in optimum positions and considered for magnetic shielding is Mu-Metal which is orientations to meet the engineering design requirements, a nickel-iron soft magnetic alloy with a very high such as the alignment of the principal axis of inertia, the permeability making it well suited for numerous constraints on system centroid errors, the minimization of magnetic shielding applications and it is recently used in moments of inertia, the uniform heat distribution of many CubeSat applications. For instance, the new satellite thermal field and mission requirements. The CubeSpace ADCS wheels (CubeWheel) are covered with improved accelerated particle swarm optimization Mu-Metal, to protect the rest of the spacecraft from the (IAPSO) algorithm with gradient-based sequential strong magnets inside the motor of the wheel [51]. quadratic programming (SQP) was developed to search for the optimal layout solution of the spacecraft [53, 54].

LASSAKEUR et. al. 30 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

Although many techniques exist which allow minimizing [10, 58]. However, this technique still has the following the magnetic field of the spacecraft, the near magnetic limitations [10]: field contributions cannot be completely removed, therefore, applying in-orbit dynamic magnetic dipole  The full satellite dynamics (wheel, gyroscopic moment compensation methods is paramount [27, 55]. torques etc.) is not taken into account  The estimator assumes that the magnetorquer compensation is ideal (no cross-coupling effects) 3.5. Characterization of the Satellite Residual Dipole Moment  The magnetic moment disturbance changes are not tracked. To compensate the magnetic disturbance precisely, the Several other methods of the residual magnetic moment residual magnetic dipole has to be measured or estimated estimation and compensation exist in the literature, accurately. Different methods exist in the literature to Inamori, et al. [11] proposed two methods based on the estimate the residual dipole of a spacecraft in orbit. This Kalman Filter. The first method implements an can be done by using magnetic field models for the Earth, Unscented Kalman Filter (UKF) algorithm, it is proposed such as the International Geomagnetic Reference Field for the Japanese Nanosatellite Nano-JASMINE (Nano- (IGRF), and knowledge of the inertial properties of the Japan Astrometry Satellite Mission for Infrared spacecraft (captured in the inertia tensor – i.e. the matrix Exploration). The second approach is based on the comprising the 3 moments of inertia and the 6 products Extended Kalman Filter (EKF). This method is proposed of inertia) [11, 56, 57]. However, difficulties arise when for both Nano-JASMINE and PRISM (Pico-satellite for it comes to physically characterize rather than estimate Remote-sensing and Innovative Space Missions). This the magnetic dipole moment [7]. method is already demonstrated in orbit with PRISM nanosatellite [11] however, the UKF estimation method 3.5.1. In-Orbit Residual Magnetic Moment is demonstrated only using simulation results [14]. The Estimation and Mitigation original launch of Nano-JASMINE was scheduled in August 2011 yet, the launch date has been delayed many The application of the on-ground methods of magnetic times, and Nano-JASMINE will finally be launched in cleanliness discussed in this paper reduces the magnetic around 2021 [59], for in-orbit demonstration and disturbance of the spacecraft considerably but cannot evaluation of UKF method. eliminate them. Thus, it is paramount to apply in-orbit estimation and mitigation methods of the residual Nano-JASMINE is a 35 kg technology demonstration magnetic moment to achieve accurate attitude control of Nanosatellite for astrometry observation application the spacecraft. developed by the National Astronomical Observatory of Japan, and the Intelligent Space Systems Laboratory of The first estimation and mitigation method for the University of Tokyo [60]. PRISM is a remote sensing nanosatellites was applied to SNAP1 (Surrey Nano- nanosatellite launched on the 23rd of January 2009, the satellite Applications Platform). Its mass is only 6.5 kg, objective of the mission is to achieve 30m images and it was launched on the 28th of June 2000 [10]. The resolution in 8.5 kg nanosatellite. The satellite attitude magnetic controller of SNAP1 was initially designed to control is required to stabilize the spacecraft to 0.7˚/s put the satellite into Y-Thomson spin control, however, accuracy in order to orient the telescope payload toward and due to an unmodelled and unexpected permanent the earth [11, 61]. In the design phase of PRISM, the magnetic dipole moment aligned with the Z-axis of the attitude was intended to be passively controlled using spacecraft, a compass mode attitude response was only the gravity gradient torque of the boom extension. observed in orbit right after the launch. The source of the But the attitude stability and control requirement (0.7˚/s) significant magnetic disturbance was a magnetic cannot be satisfied because of the dominance of the remanence in the dual solenoid valves of the propulsion residual magnetic disturbances in orbit, hence reducing thruster [10, 58]. and controlling of the residual magnetic moment is paramount for the success of this mission[11]. The magnetic dipole moment estimation method applied on SNAP1 uses the Kalman Filter (KF) and applies its The attitude of Nano-JASMINE is determined by output to partially compensate the residual magnetic assessing the quality of the star of the mission moment in its counter-direction using the full capacity of telescope onboard the spacecraft, based on how blurred it magnetorquers. This approach was evaluated as the image. This image is mainly used to estimate the satisfactory for the satellite requirements, and the nadir angular velocity of the satellite, and also used to estimate pointing performance was improved to within 3° (1-σ) the residual magnetic moment of the feed-forward

LASSAKEUR et. al. 31 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability controller, the estimated dipole will be then compensated “Classical Electrodynamics” [65]. This is done by using magnetorquers [14, 15, 60]. implementing a network of magnetometers around the spacecraft to characterize and compensate the residual The Unscented Kalman Filter (UKF) algorithm is used magnetic moment on the ground and in real-time in flight. for accurate estimation of the nonlinear dynamics of the Finally, the calculated dipole is then available to the spacecraft, and it does not use the approximation of the ADCS control loop so that this dynamic dipole can be equations and observation models. It uses true nonlinear compensated in orbit and in real-time using the models and the approximate distribution of the random magnetorquers by applying a controlled torque in the state variable. However, only the first-order term of the counter-direction of the calculated magnetic dipole. Taylor series expansion of the nonlinear function is used in the EKF estimator in PRISM nanosatellite, which can The mathematical model described in [18] uses Cartesian introduce the significant errors in the nonlinear coordinates. Where it is possible to take many estimation [11, 14]. measurements of the magnetic field close to the spacecraft at the same time, then the dipole is determined Even though the algorithms based on estimation can [7]. The following equation gives the magnetic field as a achieve accurate attitude control of the satellite to some function of the generated dipole in free space: extent, the effect of the residual magnetic moment on the spacecraft cannot be entirely eliminated due to the performance limitations of estimation algorithms [53]. 휇0 3푟̂(푀⃗⃗ . 푟̂) 푀⃗⃗ 퐵⃗ (푟) = [ − ] 4휋 |푟 |5 |푟 |3 (5) 3.5.2. Residual Magnetic Dipole Moment Where Characterization 퐵⃗ (푟) is the magnetic field at the location P (푥, 푦, 푧) Determination of the spacecraft’s magnetic moment dipole magnitude and direction require accurate 휇0 is the permeability of the free space knowledge of the strength and direction of the 푀⃗⃗ is the magnetic dipole moment surrounding magnetic field of the spacecraft. Many techniques were successfully developed by NASA in the 푟 is the vector from the dipole to (푥, 푦, 푧) early 1960s and are described in detail in [62]. However, these methods have some limitations – for example, one 푟̂ is the unit vector in the direction of 푟 of the techniques used – the resonance technique – is designed only to measure small dipole moments of large After some manipulations of Equation (5), equations (6) spacecraft [63]. to (9) may be derived, which describe each component of the magnetic field: 퐵 , 퐵 and 퐵 as a function of its Three other methods have been used by Intespace and 푥 푦 푧 location (푥, 푦, 푧) and the magnetic dipole location Centre National d'Etudes Spatiales (CNES) in Toulouse, (푎, 푏, 푐). The dipole has an orientation which is described France: by a unit vector 푠̂ with components (푚, 푛, 푝) and a total  The first is the “6 faces” method that involves dipole magnitude of M [33, 66]. measuring the magnetic field at the centre of the 휇 . 푀 3[푚(푥 − 푎) + 푛(푦 − 푏) + 푝(푧 − 푐)]. (푥 − 푎) 푚 퐵 = 0 [ − ] (6) six faces of the (cuboid-shaped) spacecraft and the 푥 4휋 푅5 푅3 equipment then calculates the magnetic moment considering a centred dipole approximation 휇 . 푀 3[푚(푥 − 푎) + 푛(푦 − 푏) + 푝(푧 − 푐)]. (푦 − 푏) 푛 퐵 = 0 [ − ] (7)  The second is the determination of the Fourier 푦 4휋 푅5 푅3 coefficients of three circular magnetic field measurements on the three orthogonal planes (XY, 휇 . 푀 3[푚(푥 − 푎) + 푛(푦 − 푏) + 푝(푧 − 푐)]. (푧 − 푐) 푝 퐵 = 0 [ − ] (8) YZ and ZX) 푧 4휋 푅5 푅3  The third technique was developed in 2012, and it consists of using spherical measurements and R is the distance from the dipole to (푥, 푦, 푧) and is given spherical harmonics modelling [64]. by

We proposed in 2018 [7] a new method designed mainly 푅 = √(푥 − 푎)2 + (푦 − 푏)2 + (푧 − 푐)2 (9) for CubeSats and nanosatellites class. It is fundamentally based on the mathematical model described by Jackson in 1 = 푚2 + 푛2 + 푝2 (10)

LASSAKEUR et. al. 32 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

Given magnetic field measurements at known locations, [퐵푖푥, 퐵푖푦, 퐵푖푧, 푥푖, 푦푖, 푧푖 ] and the solution is six unknowns have to be determined. [푀, 푎, 푏, 푐, 푚, 푛, 푝 ] Amongst many methods tested to solve such a complicated and over-determined nonlinear system of equations (Equation (6) to of Equation (10)), where 25 equations must be solved with seven unknowns for a number of eight magnetometers, we found that the Levenberg-Marquardt; also known as a damped least- squares algorithm (DLS); is the best method to converge to the optimal solution. It is widely used for optimization problems and known as one of the most robust and reliable methods, even if the initial guess is far from the corresponding solution to the minimum of the objective function, this algorithm can still converge toward the best solution. The Levenberg-Marquardt algorithm needs an initial guess to converge to the optimal solution. Therefore, a Figure 4. CubeSat's dipole moment representation. vigorous guess selection is very crucial to minimize the processing time and increase the accuracy of the solution. As the magnetic field of the nanosatellites is assumed to The optimal guess is used to determine the magnetic be a dipole [63, 67, 68], the layout of the magnetometers dipole moment on the ground, can itself be used in-orbit, was initially chosen to be just outside the spacecraft body. as the algorithm is robust and can rapidly converge for a However, the magnetic field of the spacecraft is a multi- small change of the dipole using a fixed guess. pole in the near-field and can only be observed and considered as an equivalent dipole moment in the far- A hardware prototype and a software model based on the field. Hence, the dipole approximation characterization of Levenberg-Marquardt algorithm have been developed the magnetic model of the spacecraft is used (Equation and successfully tested with the engineering model (EM) (5)), and consequently, the layout of the magnetometers of the boom payload of Alsat-1N CubeSat which had to be reconsidered (Figure 4) to respect the far-field represents 1U volume, a magnetic air coil, and permanent scaling. Figure 5 shows the layout of the magnetometers, magnets in a Helmholtz Coil arrangement. For the considering the far-field scaling. hardware configuration, we have used a set of eight HMC1053 magnetometers, and the measurements are synchronized so that the field can be accurately estimated at a particular instant of time. The interface circuit board is developed to connect the magnetometers to the Raspberry Pi 3 Model B computer using the I2C bus. The circuit is capable of reading all eight magnetometers (24 readings) in less than 25ms. The software used to determine the strength, the center and the direction of the dipole of the magnetic source is based on the Levenberg- Marquardt algorithm and is coded in Python then implemented in the Raspberry Pi 3 Model B.

Body Magnetometers Earth’s Magnetic Field Sensor

Figure 5. Far-field magnetometers layout on a typical 3U CubeSat.

For a network of N sensors at known locations, a system of (3*N+1) have to be resolved where the input vector is

LASSAKEUR et. al. 33 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

3.5.2.1. Test Results 0,05 0,04 The ground testing technique described above was 0,03 applied to the engineering model of the boom payload of 0,02 Alsat-1N, which represents a one-unit CubeSat (1U) on 0,01 the 3-Axis Helmholtz Coils (Figure 6). We have chosen 0 to measure the magnetic dipole moment of the Alsat1-N -0,01 -0,02 boom payload as this payload contains permanent (m) -0,03 magnets in its motor and represents the strongest source -0,04

of the magnetic field on Alsat1-N CubeSat. -0,05

2,5

32,5 62,5 92,5

212,5 122,5 152,5 182,5 242,5 272,5 302,5 332,5 362,5 392,5 422,5

Dipole centre position position centre Dipole Time (s) x (m) y (m) z (m)

Figure 8.The Measured center of the dipole of the EM of Alsat-1N boom payload.

0,2 0 -0,2 -0,4 -0,6 -0,8

Figure 6. Dipole determination of the EM of Alsat1-N vector -1 boom payload using the 3-Axis Helmholtz coil test

facility. -1,2

Dipole direction direction Dipole

2,5

32,5 62,5 92,5

152,5 182,5 212,5 242,5 272,5 302,5 332,5 362,5 392,5 422,5 The measurements of this test were made when the 122,5 Time (s) payload is turned off inside the Helmholtz Coil every 2.5 seconds over 7 minutes, and these were used to determine m n p the static magnetic dipole of the boom payload. The results are illustrated in Figure 7, Figure 8 and Figure 9: Figure 9. The Measured dipole direction (m,n,p) vector of the EM of Alsat-1N boom payload.

0,09 Figure 7, Figure 8 and Figure 9 show the magnitude, the ) 2 0,08 position and the direction of the dipole moment of the 0,07 engineering model (EM) of Alsat-1N boom payload 0,06 respectively, computed every 2.5s over 7 minutes period. 0,05 As can be seen in Figure 7, the dipole is hardly varying, 0,04 and its magnitude is consistently equal to 0.064 Am2 (the 0,03 spikes are just measurement noise). The position of the 0,02 calculated center of the dipole (Figure 8) is found to be 0,01 close to the geometrical position of the motor of the boom 0 payload as it contains permanent magnets. The direction

Dipole moment (A*m moment Dipole vector of the dipole is (-0.999, -0.002, -0.013) (Figure 9),

2,5

32,5 62,5 92,5

362,5 152,5 182,5 212,5 242,5 272,5 302,5 332,5 392,5 422,5 122,5 and this direction is dominated by the permanent magnet Time (s) of the motor in the boom payload.

Figure 7. The Measured dipole moment of the EM of Alsat-1N boom payload.

LASSAKEUR et. al. 34 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

3.5.2.2. Validation Method 2 To validate the obtained results, we designed an air coil 1,5 with 11 cm diameter and 93 turns (Figure 10) which can generate up to 2.5 Am2. The dipole can be easily 1 calculated, and it is a function of the number of windings (N) in the coil, its area (A), and the current (I) which is 0,5 put through the coil.

The magnetic dipole moment generated by a magnetic 0 0

2

135 270 405 540 675 810 945

coil is expressed in units of Am and is given by [69]: 67,5

1080

607,5 202,5 337,5 472,5 742,5 877,5 1147,5 Time (s) 1012,5 푚 = 푁퐼퐴 (11) Calculated Dipole M (A*m^2) I Amp Raspberry Pi interface board

Figure 11. The Measured/calculated dipole compared to

the known dipole.

Figure 12 shows the error on the measured dipole compared to the known dipole of each step of graduations. As can be seen, this error is very small and

varies between 0,0003% and 2,24%.

Magnetic air coil Magnetometernetwork 14 Figure 10. The air coil with the set of eight 12 magnetometers inside the Helmholtz coil. 10 8 We used the 3-axis Helmholtz coil test facility to nil out the Earth’s magnetic field. The eight magnetic sensors are 6 put in the same position as the proposed flight 4

configuration for a 3 U CubeSat (Figure 10). This test is % error Dipole 2 performed by putting the air coil in the middle of the 0

magnetometers network system, all inside the Helmholtz 2,5

Coil. Figure 11 shows the dipole moment calculated by 82,5

642,5 162,5 242,5 322,5 402,5 482,5 562,5 722,5 802,5 882,5 962,5 1122,5 the model based on the sensor measurements compared 1042,5 to the theoretically known dipole. These results are Time (s) obtained by changing the input current of the air coil, as shown on the green line, this means that each step of graduations in the graph represents a constant value of Figure 12. The measured dipole error compared to the current and dipole. The experiment was carried out over known dipole. 7 minutes. Figure 13 shows the angle error between the actual and known direction of the dipole, which is in the x-axis direction (-1,0.0) and the dipole calculated by the system for each measurement step.

LASSAKEUR et. al. 35 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

10 dipole (Figure 13) and the small shift in the obtained dipole center (Figure 14) are all due to:

8 )

°  The small errors in the measured position and 6 orientation of the magnetometers 4  Residual offsets and drift of the magnetometers 2  The air coil is not a “perfect” coil in the magnetic

0 sense, as it has some length (5cm) as well as width 0

80 (3cm)

960 160 240 320 400 480 560 640 720 800 880

1040 1120 error angle ( angle error Dipole direction direction Dipole Time (s)  The fact that the 3-axis Helmholtz coil test facility used in these experiments does not entirely cancel Error angle (°) X wrt Z the Earth’s magnetic field. Even though the field is less than 40nT in the middle of the structure, this Error angle (°) X wrt Y value increases when we move away from the centre Figure 13.: Dipole direction error angle.  Levenberg Marquardt algorithm errors, although it Figure 14 shows the calculated center of the dipole based is the best method compared to many methods on the measurements, where the center is located at the used in this research to solve such a complicated center of the coil with a very small error. and overdetermined system of equations. There are always small errors in the solution

0,05 However, as the differences are very small, we consider 0,04 that the results obtained in the last experiments with the 0,03 air coil validate the resultant dipole of the Alsat1-N 0,02 boom payload. The experiments were repeated for 0,01 0 several different positions of the coil and sensors, and -0,01 similar correspondences between the measured dipole -0,02 properties and the theoretically calculated dipoles were -0,03 obtained. -0,04 -0,05

4. SUMMARY

2,5

82,5

882,5 162,5 242,5 322,5 402,5 482,5 562,5 642,5 722,5 802,5 962,5

Dipole centre position centre Dipole 1122,5 1042,5 To achieve acceptable magnetic cleanliness level onboard Time (s) the spacecraft, and considerably reduce the impact of the x (m) y (m) z (m) magnetic disturbances on the attitude of the spacecraft, it is extremely recommended to run the “magnetic Figure 14. Dipole center position. cleanliness program” on each part or subsystem of the spacecraft by employing the following plan (Figure 15)

3.5.2.3. Discussion

The number of magnetometers and their disposition are chosen so that the system can collect as much as magnetic field information in the vicinity of the spacecraft. We found that this layout (Figure 5) and the number of sensors used by the system are optimal; considering the minimum number of the magnetometers is seven; as the system is still capable of providing the same result presented in this paper with only seven sensors instead of eight. However, the accuracy decreases remarkably when less than seven sensors are used. We believe that the small differences in the magnitude of the dipole (Figure 11), the error in the direction of the

LASSAKEUR et. al. 36

Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

mitigation methods of the residual magnetic moment to

1 - Avoid any ferromagnetic materials on spacecraft. achieve precise attitude control of the spacecraft. Design 2 - Minimize any magnetic source. We presented in this paper a new technique of the residual magnetic dipole determination for CubeSats and

Nanosatellites. This method is performed by

Mission 3 - Identify and minimize any magnetic sources implementing a network of eight miniature 3-axis magnetometers on the spacecraft. These are used to

4 - Apply magnetic shielding methods on strong determine the strength, the direction and the center of the magnetic sources magnetic dipole of the spacecraft dynamically in-orbit 5 - Identify and reduce the current loops in and in real-time. A hardware prototype and a software cabling and solar panels model have been developed and successfully tested with Integration 6 - Characterize the residual magnetic field the engineering model of the boom payload of Alsat-1N CubeSat, and a magnetic air coil in a Helmholtz Coil 7 - Use RMM compensation methods to minimize the residual magnetic moment for each subsystem arrangement. The obtained results that are the magnitude, the center of the dipole and its orientation can then be 8 - Demagnetize any ferromagnetic parts of the compensated in orbit and in real time using inbuilt

spacecraft before the launch.

Assembly and Assembly magnetorquers. As a result of the successful outcomes obtained by the method described in this paper to

characterize the dipole moment of the Nanosatellites, we

9 - Use in-orbit residual magnetic moment believe that this method can be generalized to determine Orbit

- determination and compensation methods. the magnetic dipole moment of any magnetic source.

In Ideally, by using a 3-axis Helmholtz coil or putting the device/object which contains the magnetic sources in a Figure 15. Magnetic cleanliness program on spacecraft. uniformed magnetic field, where an external is needed. 5. CONCLUSION 6. ACKNOWLEDGMENT Attitude determination and control systems of CubeSats have always suffered from their limitations, in terms of The authors acknowledge the financial and logistical size, weight, and power constraints. Moreover, CubeSats support for this research provided by The Algerian Space face an unwanted magnetic dipole moment in orbit, which Agency (ASAL) and the UK Space Agency (UKSA), to is the dominant source of attitude disturbances because of whom we are grateful. their small moment of inertia. 7. REFERENCES As discussed in this paper, all spacecraft have an associated magnetic field that depends on its material [1] H. S. Rauschenbach, "Array Design," in Solar properties and the presence of current loops. Solar arrays cell array design handbook: the principles and technology should be designed to minimize the generated magnetic of photovoltaic energy conversion, ed Canada: Van disturbances, including the avoidance of using magnetic Nostrand Reinhold Ltd, 2012, pp. 111-151. materials, and a vigorous application of magnetic field reduction techniques. Surveys of COTS solar arrays and [2] R. Munakata, "CubeSat Design Specification," CubeSats subsystems indicate that they are often not California Polytechnic State University, San Luis Obispo, designed with magnetic cleanliness in mind. Therefore, California, USA2008. magnetic cleanliness program is a necessary step in the development of CubeSats to reduce the dipole moment of [3] N. N. Abbas, H. Xiao, L. Y. Jun, and M. Raza, the spacecraft and prevent the boom-mounted "An Architecture Analysis of ADCS for CubeSat: A magnetometer from the reading of the parasitic magnetic Recipe for ADCS Design of ICUBE," Applied Mechanics field of the spacecraft and eventually improve the attitude and Materials, Vol. 110, pp. 5397-5404, 2012. stability of CubeSats. [4] J. Bouwmeester and J. Guo, "Survey of Even though the application of the magnetic cleanliness worldwide pico- and nanosatellite missions, distributions methods on the ground reduces the magnetic disturbance and subsystem technology," Acta Astronautica, Vol. 67, of the spacecraft considerably, these disturbances cannot pp. 854-862, Oct-Nov 2010. be entirely eliminated on the ground. Thus, it is [5] (2016, 23/06/2016). Nanosatellite Database. paramount to apply in-orbit characterization and Available: http://www.nanosats.eu/

LASSAKEUR et. al. 37 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

[6] T. Inamori, S. Nakasuka, and N. Sako, [16] A. H. De Ruiter, C. Damaren, and J. R. Forbes, "Compensation of time-variable magnetic moments for a "Disturbance Torques on a Spacecraft," in Spacecraft precise attitude control in nano- and micro-satellite Dynamics and Control: An Introduction, ed New York, missions," Advances in Space Research, Vol. 48, pp. 432- USA: John Wiley & Sons, 2012, pp. 227-234. 440, Aug 3 2011. [17] S. Shin-ichiro, F. Yosuke, and S. Hirobumi, [7] A. Lassakeur, C. Underwood, and B. Taylor, "Design and On-Orbit Evaluation of Magnetic Attitude "Enhanced Attitude Stability and Control for CubeSats by Control System for the “REIMEI” Microsatellite," Real-Time On-Orbit Determination of Their Dynamic presented at the the 10th IEEE International Workshop on Magnetic Moment," presented at the the 69th Advanced Motion Control, Trento, Italy, 2008. International Astronautical Congress (IAC), Bremen, Germany, 2018. [18] M. Pudney, "Advances in Spacecraft Magnetic Cleanliness Verification and Magnetometer Zero Offset [8] D. Selva and D. Krejci, "A survey and Determination in anticipation of the Solar Orbiter assessment of the capabilities of Cubesats for Earth Mission," PhD, Department of Physics, Imperial College observation," Acta Astronautica, Vol. 74, pp. 50-68, London, London, UK, 2014. May-Jun 2012. [19] K. F. Jensen and K. Vinther, "Attitude [9] R. Burton, S. Rock, J. C. Springmann, and J. determination and control system for AAUSAT3," Cutler, "Dual attitude and parameter estimation of Master in Intelligent Autonomous Systems, Aalborg passively magnetically stabilized nano satellites," Acta University, Aalborg University, Aalborg, Denmark, Astronautica, Vol. 94, pp. 145-158, Jan-Feb 2014. 2010. [10] W. H. Steyn and Y. Hashida, "In-orbit attitude [20] W. H. Steyn, Y. Hashida, and V. Lappas, "An performance of the 3-axis stabilised SNAP-1 attitude control system and commissioning results of the nanosatellite," presented at the 15th Annual AIAA/USU SNAP-1 nanosatellite," presented at the the 14th Conference on Small Satellites, , Logan, Utah, USA, AIAA/USU Conference on Small Satellites, Logan, Utah, 2001. USA, 2000. [11] T. Inamori, N. Sako, and S. Nakasuka, [21] J. C. Springmann, A. Sloboda, A. Klesh, M. "Magnetic dipole moment estimation and compensation Bennett, and J. Cutler, "The attitude determination system for an accurate attitude control in nano-satellite of the RAX satellite," Acta Astronautica, Vol. 75, pp. missions," Acta Astronautica, Vol. 68, pp. 2038-2046, 120-135, Jun-Jul 2012. 2011. [22] J. C. Springmann, B. Kempke, J. Cutler, and H. [12] C. Shaffer, "A Study on the Usage of TASC and Bahcivan, "Initial flight results of the RAX-2 satellite," UTJ Solar Cells in the Design of a Magnetically Clean presented at the the 26th AIAA/USU Conference on CubeSat," presented at the the 27th AIAA/USU Small Satellites, Logan, Utah, USA, 2012. Conference on Small Satellites, Logan, Utah, USA, 2013. [23] G. Park, S. Seagraves, and N. H. McClamroch, [13] S. Busch, P. Bangert, S. Dombrovski, and K. "A dynamic model of a passive magnetic attitude control Schilling, "UWE-3, in-orbit performance and lessons system for the RAX nanosatellite," in AIAA Guidance, learned of a modular and flexible satellite bus for future Navigation, and Control Conference, Toronto, Ontario pico-satellite formations," Acta Astronautica, Vol. 117, Canada, 2010, pp. 2-5. pp. 73-89, 2015/12/01/ 2015. [24] A. Aslan, H. Yağcı, M. Umit, A. Sofyalı, M. [14] T. Inamori, S. Nakasuka, and N. Sako, "In-orbit Bas, M. Uludag, et al., "Development of a LEO magnetic disturbance estimation and compensation using communication CubeSat," in 2013 6th International UKF in nano-satellite mission," presented at the AIAA Conference on Recent Advances in Space Technologies Guidance, Navigation, and Control Conference, Chicago, (RAST), 2013, pp. 637-641. USA, 2009. [25] F.-L. Vincent, "Study of passive and active [15] T. Inamori and S. Nakasuka, "In-orbit magnetic attitude control systems for the OUFTI nanosatellites," disturbance compensation using feed forward control in Faculty of Applied Sciences,, University of Liège, Liège, Nano-JASMINE mission," presented at the the 22nd Belgium, 2010. AIAA/USU Conference on Small Satellites, Logan, Utha, USA, 2008. [26] A. Sofyali and A. R. Aslan, "Magnetic attitude control of small satellites, a survey of applications and a

LASSAKEUR et. al. 38 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability domestic example," in Proceedings of the 8th symposium [39] C. Christopoulos, Principles and Techniques of on small satellites for Earth observation, 2011. Electromagnetic Compatibility, 2nd ed. Boca Raton, FL, USA: Taylor & Francis Group, LLC, 2007. [27] T. Stern and S. DeLapp, "Techniques for Magnetic Cleanliness on Spacecraft Solar Arrays," [40] K. Mehlem and P. Narvaez, "Magnetostatic presented at the the 2nd International Energy Conversion cleanliness of the radioisotope thermoelectric generators Engineering Conference, Providence, Rhode Island, (RTGs) of Cassini," presented at the IEEE International 2004. Symposium on Electromagnetic Compatability, Seattle, WA, USA, 1999. [28] B. DeKock, D. Sanders, T. VanZwieten, and P. Capo-Lugo, "Design and Integration of an All-Magnetic [41] D. Lovejoy, "Demagnetization," in Magnetic Attitude Control System for Fastsat-Hsv01's Multiple Particle Inspection: A practical guide, ed Dordrecht, Pointing Objectives," Advances in the Astronautical Netherlands: Springer, 1993, pp. 149-169. Sciences, Vol. 141, pp. 127-145, 2011. [42] C. A. Harris, "Magnetic field restraints for [29] D. Miller, "MCubed-2 Magnetic Research," spacecraft systems and subsystems," Goddard Space Michigan Exploration Laboratory2013. Flight Center, Greenbelt, USA1967. [30] R. Bansal, "Magnetostatics," in Fundamentals of [43] L. H. Hemming, Architectural electromagnetic engineering electromagnetics, ed Boca Raton, FL: Taylor shielding handbook: a design and specification guide. & Francis, 2006, pp. 89-122. New York, USA: John Wiley & Sons, 2000. [31] H. Kuegler, "Lessons Learned during the [44] S. Celozzi, R. Araneo, and G. Lovat, Magnetic Cleanliness Programmes of the Cluster Electromagnetic shielding Vol. 192. Canada: John Wiley Projects," presented at the the 4th International & Sons, 2008. Symposium Environmental Testing for Space Programmes, Liege, Belgium, 2001. [45] I. Levchenko, K. Bazaka, Y. Ding, Y. Raitses, S. Mazouffre, T. Henning, et al., "Space micropropulsion [32] W. Ley, K. Wittmann, and W. Hallmann, systems for Cubesats and small satellites: From "Spacecraft Design Process," in Handbook of Space proximate targets to furthermost frontiers," Applied Technology. Vol. 22, ed Chichester, UK: John Wiley & Physics Reviews, vol. 5, 011104, pp. 1-36, 2018. Sons, 2009. [46] A. Tummala and A. Dutta, "An overview of [33] J.-C. P.-M. Terral, "Magnetic cleanliness cube-satellite propulsion technologies and trends," verification of telecommunication satellite payload," Aerospace, Vol. 4, p. 58, 2017. presented at the European Test and Telemetry Conference, Toulouse, France, 2005. [47] D. Micheli, R. Pastore, A. Vricella, R. B. Morles, M. Marchetti, A. Delfini, et al., "Electromagnetic [34] M. Ludlam, V. Angelopoulos, E. Taylor, R. C. characterization and shielding effectiveness of concrete Snare, J. D. Means, Y. S. Ge, et al., "The THEMIS composite reinforced with carbon nanotubes in the Magnetic Cleanliness Program," Space Science Reviews, mobile phones frequency band," Materials Science and Vol. 141, pp. 171-184, Dec 2008. Engineering: B, Vol. 188, pp. 119-129, 2014/10/01/ 2014. [35] M. H. Acuña, "The Design, Construction and Test of Magnetically Clean Spacecraft – A Practical [48] J. W. Gooch and J. K. Daher, "Fundamentals of Guide," Goddard Space Flight Centre2004. Electromagnetic Shielding," in Electromagnetic shielding and corrosion protection for aerospace [36] C. R. Paul, "Introduction to electromagnetic vehicles, ed Atlanta, USA: Springer, 2007, pp. 17-24. compatibility (EMC)," in Introduction to electromagnetic compatibility, 2nd ed. ed Hoboken, N.J., USA: Wiley [49] P. Fortescue, G. Swinerd, and J. Stark, "The Interscience, 1992, pp. 1-48. Spacecraft Environment and its Effect on Design," in Spacecraft systems engineering, ed Chichester, UK: John [37] P. Bienkowski, "The Near Field and the Far Wiley & Sons, 2011, pp. 11-47. Field," in Electromagnetic measurements in the near field, H. Trzaska, Ed., 2nd ed Raleigh, NC: Raleigh, NC [50] X. C. Tong, "Electromagnetic Interference : SciTech Pub., 2012, pp. 11-26. Shielding Fundamentals and Design Guide," in Advanced materials and design for electromagnetic interference [38] D. Weston, Electromagnetic Compatibility: shielding, ed Miami, FL, USA: CRC press, 2016, pp. 1- Principles and Applications, Revised and Expanded. 36. Columbus, Ohio, USA: CRC Press, 2017.

LASSAKEUR et. al. 39 Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

[51] M.-A. Kearney, "CubeADCS User Manual," S. Center, National Aeronautics and Space Administration U. CubeSpace Ed., 3.06 ed. Stellenbosch, South Africa, (NASA), Springfield1969. 2017. [63] B. E. Tossman, "Resonance technique for [52] A. Yadav, "Strong Magnetic Shielding by measurement of satellite magnetic dipole moment," Common Available Material," Int J Adv Tech National Aeronautics and Space Administration (NASA), International Journal of Advancements in Technology, Berwyn, MD, USA1965. Vol. 07, pp. 1-4, 2016. [64] O. Dumond and R. Berg, "Determination of the [53] X. Chen, S. Liu, T. Sheng, Y. Zhao, and W. Yao, magnetic moment with spherical measurements and "The satellite layout optimization design approach for spherical harmonics modelling," presented at the ESA minimizing the residual magnetic flux density of micro- Workshop on Aerospace EMC, Venice, Italy, 2012. and nano-satellites," Acta Astronautica, 05/12/2018 2018. [65] J. D. Jackson, "Magnetostatics, Faraday's Law, Quasi-Static Fields," in Classical electrodynamics, ed [54] X. Chen, W. Yao, Y. Zhao, X. Chen, and X. Hoboken New, Jersey, USA: Wiley, 1999, pp. 174-236. Zheng, "A practical satellite layout optimization design approach based on enhanced finite-circle method," [66] J. C. Springmann, C. James, and B. Hasan, Structural and Multidisciplinary Optimization, Vol. 58, "Magnetic Sensor Calibration and Residual Dipole pp. 2635-2653, December 01 2018. Characterization for Application to Nanosatellites," presented at the AIAA/AAS Astrodynamics Specialist [55] A. Lassakeur and C. Underwood, "Magnetic Conference, Toronto, Ontario, Canada, 2010. Cleanliness Program on CubeSats for Improved Attitude Stability," presented at the the 9th AIAA/IEEE [67] I. Turer and L. Sevgi, "DC magnetic International Conference on Recent Advances in Space compatibility of satellites," International Journal of RF Technologies RAST 2019, Istanbul, Turkey, 2019. and Microwave Computer‐Aided Engineering, Vol. 26, pp. 330-334, 2016. [56] S. Seriani, Y. Brama, P. Gallina, and G. Manzoni, "In-orbit offline estimation of the residual [68] C. Jéger, "Determination and Compensation Of magnetic dipole biases of the POPSAT-HIP1 Magnetic Dipole Moment in Application for a Scientific nanosatellite," Acta Astronautica, Vol. 122, pp. 10-18, Nanosatellite Mission," Master in Aerospace 2016. Engineering, School of Electrical Engineering, KTH ROYAL INSTITUTE OF TECHNOLOGY, Stockholm, [57] M. Lovera and A. Astolfi, "Spacecraft attitude Sweden, 2017. control using magnetic actuators," Acta Astronautica, Vol. 40, pp. 1405-1414, 2004. [69] A. Overlack, J. Kuiper, H. Peter-Contesse, and M. Noca, "Anlaysis of the Attitude Control Stability of [58] K. Miyata and J. C. van der Ha, "Attitude the SwissCube Nano-Satellite," presented at the the 1st Control by Magnetic Torquer," Advances in the International Academy of Astronautics (IAA), Rome, Astronautical Sciences, vol. 134, pp. 1041-1060, 2009. Italy, 2011. [59] N. Gouda and J. w. group, "Outline of Infrared Space Astrometry missions: JASMINE," Proceedings of the International Astronomical Union, Vol. 12, pp. 90-91, 2017. [60] T. Hosonuma, "A precise attitude determination and control strategy for small astrometry satellite “Nano- Jasmine”," presented at the the 26th AIAA/USU Conference on Small Satellites, Logan, Utha, USA, 2012. [61] M. Komatsu and S. Nakasuka, "University of Tokyo Nano Satellite Project “PRISM”," Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan, Vol. 7, pp. 19-24, 2009. [62] S. Schalkowsky, M. Harris, and I. Exotech, "Spacecraft Magnetic Torques," Electronics Research,

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8. VITAE

Abdelmadjid LASSAKEUR received his PhD degree in Ben TAYLOR holds a PhD in Space Environment Electronic Engineering from the Surrey Space Center at Modelling and has worked as a research fellow focusing the University of Surrey in the UK, in 2019. He joined the on Instrumentation and modelling for Earth and Algerian Space Agency in 2006 as a Ground Segment interplanetary missions. Ben moved to UCL to manage Engineer for the Alsat2 Satellites. Abdelmadjid is the scientific instrumentation development for the QB50 currently a researcher at the Satellite Development mission and UCLSat CubeSat project. Ben is currently Center, at the Algerian Space Agency in Oran, Algeria. Development and Systems Lead within the Surrey Space His research is focused on the Attitude Determination and Centre Project Delivery Team, in addition to AIT and Control System (ADCS) of CubeSats. Since 2016, He has management roles working on the AlSat-1N, InflateSail been involved in Alsat-Nano CubeSats project. and RemoveDebris missions.

Craig UNDERWOOD heads the Sensors and Platform Richard DUKE is a spacecraft communications engineer Systems Group within the Surrey Space Centre. He has at the University of Surrey. After starting his career in over 30 years’ experience in space systems engineering control and automation, for the past four years, he has and has worked on numerous small satellite missions. worked on multiple CubeSat missions at the Surrey Space Craig graduated from the University of York in 1982 with Centre. Starting with the development of the spacecraft’s a B.Sc. in Physics with Computer Science. He gained his operating system, he has been involved in the full PhD from the University of Surrey in 1996 with his work lifecycle of the projects working with the spacecraft from on the effects on the ionizing radiation on space concept design through to launch and operations, electronics. Craig is author or co-author of some 200 including management of the centre’s spacecraft scientific papers and teaches modules on the Spacecraft operations facility. Engineering degrees at the University of Surrey.

LASSAKEUR et. al. 41