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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Computational technology for uncertain spacecraft magnetic cleanliness control</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Borys Kuznetsov</string-name>
          <email>kuznetsov.boris.i@gmail.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ihor Bovdui</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Tatyana Nikitina</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Konstantin Chunikhin</string-name>
          <email>kvchunikhin@gmail.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Olena Voloshko</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Valeriy Kolomiets</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Inna Nefodova</string-name>
          <email>inna7str@gmail.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Borys Kobylianskyi</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Anatolii Pidhornyi Institute of Power Machines and Systems of the National Academy of Sciences of Ukraine</institution>
          ,
          <addr-line>Komunalnykiv Str., 2/10, Kharkiv, 61046</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>V. N. Karazin Kharkiv National University</institution>
          ,
          <addr-line>Svobody Sq., 4 , Kharkiv, 61022</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Research presents the development of computational technology for prediction and control by orbital spacecraft magnetic cleanliness based on geometric inverse magneto static problem solution with consideration of magnetic characteristics uncertainty to improve the spacecraft magnetic cleanliness and its controllability in orbit. Geometric inverse problem solution reduced to vector game solution with COMSOL Muliphysics software calculated payof vector. Game solution calculated based on heuristic optimization algorithms from Pareto-optimal solutions taking into account binary preference relations local games solutions. Based on developed computational technology results of prediction and control by «Sich-2» microsatellite family for ensuring microsatellite magnetic cleanliness presented.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;orbital spacecraft</kwd>
        <kwd>magnetic cleanliness</kwd>
        <kwd>uncertainty</kwd>
        <kwd>geometric inverse magneto static problem</kwd>
        <kwd>heuristic optimization algorithms</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        The urgency of the work is due to the need to ensure high accuracy of the magnetic control system for
the angular orientation of the spacecraft in near-Earth space [
        <xref ref-type="bibr" rid="ref1 ref2 ref3">1, 2, 3</xref>
        ]. Among the factors that determine
the accuracy of the angular orientation of the spacecraft: the reliability of current measurements of the
magnetic induction of the Earth magnetic field by the on-board magnetometer of the magnetic control
system; an error in the calculation of the spacecraft magnetic moment with turned on electromagnets,
which are components of the magnetic control system. The initial data of this calculation, along with
magnetic moment value of the electromagnets, also include the spacecraft magnetic moment values;
magnetic induction at the place of installation of the on-board magnetometer of the magnetic control
system.
      </p>
      <p>
        Modern requirements [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] for magnetic control system spacecraft weighing up to 100 kg require,
on the one hand, a reduction of their magnetic moment (to 0.1 *  2), and, on the other hand, high
accuracy of its determination with a distribution capacity of no more than 0.02 *  2. The same
"hard" requirements established for magnetic induction, which formed by the component parts of the
spacecraft at the place of installation of the magnetic control system magnetometer.
      </p>
      <p>
        Technologies for ensuring the spacecraft "magnetic cleanliness" managed by NASA and ESA include
interrelated works of an organizational, technical and metrological nature. The foundation of this
technology is the calculation models of the spacecraft, which allow analytical or numerical prediction of
the spacecraft magnetic characteristics based on the knowledge of the magnetic field of its constituent
parts [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] . At the same time, the magnetic characteristics of the component parts presented in the
format of numerical multiple magnetic dipole models, according to which the corresponding component
part of the spacecraft represented as a set of point magnetic moments with the corresponding location
coordinates.
      </p>
      <p>
        One of the fundamental components of this technology is the organization of metrological support
for determining in the multiple magnetic dipole models format the magnetic characteristics of the
component parts of the spacecraft on specialized magnetic measuring stands [
        <xref ref-type="bibr" rid="ref3 ref4 ref5">3, 4, 5</xref>
        ] . The main
provisions of the organization of work on reducing the magnetic characteristics of spacecraft are
implemented by such leading developers as the National Aeronautics and Space Administration (NASA),
the European Space Agency (ESA), and the Chinese Academy of Space Technologies (CAST). The
presence of these specialized magnetic measuring stands allows them to create spacecraft with high
accuracy of reference to the coordinate system of the Earth surface and to carry out remote sensing of
the Earth surface with high resolution.
      </p>
      <p>Anatolii Pidhornyi Institute of Power Machines and Systems of the National Academy of Sciences
of Ukraine (IPMash of the National Academy of Sciences of Ukraine) has a powerful specialized
experimental base, the basis of which is the unique and unique Magnetodynamic complex in Ukraine,
which is included in the list of scientific objects that constitute the national property of Ukraine. At the
IPMash magnetodynamic complex the experimental part of the fundamental studies of the magnetism
of various technical objects and their physical models (spacecraft, ships, electric power equipment,
building structures, pipelines) is carried out, the analysis of the spatio-temporal structure of their
magnetic field (including ultra-small level - with induction less than 10-8 T). At the IPMash stand
experimental studies of developed methods and means of targeted change of magnetic characteristics of
various technical objects are carried out. Since 2003 year, the magnetometer stand has been providing
tests of all orbital spacecraft launched into near-Earth orbit, namely "Microsat" (2003), "EgiptSat-1"
(2007), "Sich-2" (2011), "Sich-2-30" (2022).</p>
      <p>
        During space engineering testing in accordance to latest standards of the European Space Agency
ECSS-E-HB-20-07A [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] it is necessary to take into account test conditions, input tolerances and
measurement uncertainties. The main uncertainties of the spacecraft magnetic cleanliness are the changing
values of the magnetic moments of the spacecraft elements when the spacecraft operating modes
changing [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. In particular, the magnetic moments change most strongly when the polarization relays
operate in the “on” and “of” positions, when the battery operates in the “charge” or “discharge” mode,
during operation of high-frequency valves etc. Therefore, an urgent problem is develop of method to
improve spacecraft magnetic cleanliness which is robust to the spacecraft elements magnetic moments
uncertainties.
      </p>
      <p>This work is devoted to the development of computational technology for control by orbital spacecraft
magnetic cleanliness based on geometric inverse magneto static problem solution with consideration of
magnetic characteristics uncertainty to improve the spacecraft magnetic cleanliness and its
controllability in orbit.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Mathematical model of the spacecraft magnetic field</title>
      <p>
        When designing a mathematical model of the spacecraft magnetic field the Gauss equation [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] for the
scalar magnetic potential of the source in the surrounding space written the following form in spherical
coordinates , ,  :
 =
1 ∑∞︁ 1 ∑︁ (  + ℎ)(),
4 =1 +1 =0
(1)
where  is the radius of the sphere on which the potential is determined; , ℎ - constant
coeficients. The magnetic field strength, calculated from (1) determined by the equations:
 =
      </p>
      <p>∞ 1 
1 ∑︁ ( + 1) +2 ∑︁ ( cos() + ℎ sin())(cos );
4 =1 =0
(2)
 =
 =
1 ∑∞︁ 1 ∑︁ ( sin() − ℎ  cos() (cos )
4 =1 +2 =0 sin 
41 ∑∞=︁1 1+2 ∑=︁0 ( cos() + ℎ sin()) sin1  · . . .
;
·( −  + 1) +1(cos ) − ( + 1) cos 
(cos ).</p>
      <p>The solution of equation (2) with respect to the coeficients , ℎ represents spacecraft multipole
mathematical model.</p>
      <p>
        The mathematical model of spacecraft magnetic field in the form of a multipole model (2), proposed
by K. Gauss in the study of Earth magnetism [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], makes it possible to describe the distribution of the
spacecraft’s magnetic field at any point in space. However, to date, there are insuficiently developed
methods that would allow in practice to use the spatial harmonics of the magnetic field of a spacecraft.
The need to develop such methods confirmed by one of the latest standards of the European Space
Agency ECSS-E-HB-20-07A [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ], which recommends using spherical harmonics as integral characteristics
of the spatial distribution of the magnetic field to ensure the magnetic purity of the spacecraft [
        <xref ref-type="bibr" rid="ref2 ref4 ref5">2, 4, 5</xref>
        ].
      </p>
      <p>
        As follows from the analysis of expressions (2) the spacecraft magnetic field at distances is greater
than three of its maximum overall dimensions are determined mainly by members of the first degree
series, i.e. the first three multipole coeficients [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Therefore, if the measurement of the spacecraft
magnetic field performed at a distance greater than three of its maximum overall dimensions, then
it can be limited to the construction of the spacecraft mathematical model in the form of a multiple
magnetic dipole model [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ].
      </p>
      <p>All spacecraft elements undergo strict control for magnetic cleanliness and, as a rule, their preliminary
demagnetization is performed. The components , ,  – of the spacecraft magnetic moment
elements are measured before installation and meet the stringent requirements of magnetic cleanliness.</p>
      <p>
        Then, the components  ,  ,  of technical object magnetic field at any point  of space
with coordinates , ,  in the form of the multiple magnetic dipole models (MDM) of the spacecraft
with the magnetic moment , ,  of  dipole located at the points of the space of the
spacecraft with coordinates (, , ) calculated [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]
⎡ ⎤ 
⎣ ⎦ =  0 ∑︁
 =1
      </p>
      <p>1
4 ′5 ⎣
⎡2′2 −  ′2 −  ′2
3′′
3′′
... 3′′
· · · 2 ′2 −  ′2 −  ′2
... 3′′
3′′
3′′
2′2 −  ′2 −  ′2
⎤ ⎡⎤
⎦ · ⎣⎦ (3)

Here the designations are introduced</p>
      <p>=  −  ,  =  −  ,  =  −  ,
′ = (( −  )2 + ( −  )2 + ( −  )2) 21 .</p>
    </sec>
    <sec id="sec-3">
      <title>3. Statement of the problem</title>
      <p>All Ukrainian spacecraft after installing all the elements are examined for magnetic cleanliness at the
magnetic measuring stand Anatolii Pidhornyi Institute of Mechanical Engineering Problems of the
National Academy of Sciences of Ukraine. According to real measurements, the spacecraft magnetic
moment and the magnetic field at the installation point of the onboard magnetometer are calculated.
For this purpose, according to the data of measurements of the magnetic field in the near zone of the
spacecraft, the real values of the moment vectors of the dipoles of the received  are restored. In
this case, it is assumed that the coordinates of the location of the dipoles in the space of the spacecraft
remain unchanged.</p>
      <p>If the spacecraft multiple magnetic dipole model (3) obtained based on the vector  of measured
magnetic field is too rough, then on the basis of the vector  of the measured magnetic field, not
only the magnetic moments , ,  of the dipoles, but also their position in the space of the
technical object with coordinates , ,  can be calculated.</p>
      <p>Let us consider the design of the technical object multiple magnetic dipole models only based on
the vector  of the measured magnetic field. Let us introduce the vector of desired parameters ,
the components of which are the desired values magnetic moments , ,  of the dipoles and
coordinates , ,  of their position in the space of the spacecraft.</p>
      <p>
        We also introduce the vector  of uncertainty parameters of the magnetic moments of the spacecraft
the components of which are the deviations during the operation of the spacecraft of the magnetic
moments of the spacecraft elements from their central values, taken in the design of the control system
for the magnetic field of the spacecraft [
        <xref ref-type="bibr" rid="ref2 ref4 ref5">2, 4, 5</xref>
        ]. Then, based on (3), the initial nonlinear equation for
the spacecraft multiple magnetic dipole model can be obtained.
      </p>
      <p>=  (, ).
(4)</p>
      <p>Here, the vector nonlinear function (, ) obtained on the basis of expression (3) with respect
to the vector  of unknown variables, whose components are the desired values magnetic moments
, ,  of the dipoles and coordinates , ,  of their position in the space of the spacecraft
and the vector  of the parameters of the uncertainties of the magnetic moments of the elements of the
technical object.</p>
      <p>In nonlinear equation (4) the number of unknown components of the vector  equal to six times the
number  of dipoles, and the number of equations is equal to three times the number  of measurement
points.</p>
      <p>Let us introduce the  vector of the discrepancy between the vector  of the measured magnetic
ifeld and the vector   of the predicted by model (4) magnetic field</p>
      <p>(, ) =  −   (, ) =  −  (, ).</p>
      <p>We write the objective nonlinear function as the weighted sum of squared residuals between the
measured and predicted by the model (4) values of the magnetic field
 (, ) = ((, ))  (, ).
(5)
(6)</p>
      <p>The nonlinear objective function (6) obtained on the basis of expression (2) with respect to the vector
 of unknown variables, whose components are the desired values magnetic moments , , 
of the dipoles and coordinates , ,  of their position in the space of the spacecraft and the vector
 of the parameters of the magnetic moments uncertainties of the spacecraft elements.</p>
      <p>As a rule, when optimizing the nonlinear objective function (6)
 · =  (, ), · =  (, ),
(7)
it is necessary to take into account restrictions on the values of magnetic moments , , 
of the dipoles and coordinates , ,  of their position in the space of the spacecraft.</p>
      <p>Let’s consider another approach to the design of spacecraft multiple magnetic dipole models. Usually
the designer of the spacecraft knows the  of the elements of the spacecraft, which are the main sources
of the initial magnetic field of the technical object. These are polarization relays, batteries and
highfrequency valves. The technical object designer knows the number  of these elements, the coordinates
, ,  of their location in the spacecraft space, as well as the nominal values , ,  of
their magnetic moments. Then the vector  of the magnetic field components  ,  ,  at the
given points  of the space with coordinates , ,  can be calculated based on spacecraft multiple
magnetic dipole model (3).</p>
      <p>Note that the values , ,  of the magnetic moments of these  main elements of the
spacecraft can be refined on the basis of the vector   of the measured magnetic field.</p>
      <p>As a rule, the spacecraft multiple magnetic dipole models obtained in this way is a rather rough
approximation to the actual magnetic range of the spacecraft. To refine this model, consider the
following approach. Let’s introduce more  dipoles wits magnetic moment , ,  located
at the points  of the spacecraft with coordinates , , . Let us introduce the vector of desired
parameters , the components of which are the desired values magnetic moments , , 
of the  dipoles and coordinates , ,  of their position in the space of the spacecraft. We
also introduce the vector  of uncertainty parameters of the magnetic moments of the spacecraft.
Then, based on the spacecraft multiple magnetic dipole models (4) calculated the vector (, ) of
additional magnetic field, generated by only  additional dipoles at the measurement points.
(, ) = (, ).
(8)</p>
      <p>We introduce the vector  of the initial magnetic field of the spacecraft, the components of which
are the components of the magnetic field of the spacecraft calculated in this way at the measurement
points generated by the main  elements of the technical object with known values of the magnetic
moments and the coordinates of their location in the space of the spacecraft.</p>
      <p>Then one can calculate the vector  of resulting magnetic field generated by  dipoles with known
magnetic moments nominal values , ,  and coordinates , ,  of their location in
the technical object space and generated by  additional dipoles with unknown magnetic moments
, ,  and unknown coordinates , ,  of their location in the spacecraft space
(, ) =  + (, ).
(9)</p>
      <p>Then the problem (7) of calculated the vectors of unknown parameters of additionally introduced
 dipoles solved similarly to the problem (9) of calculated the vector of unknown parameters of 
dipoles for design of the spacecraft multiple magnetic dipole model.</p>
      <p>
        Usually, the spacecraft magnetic cleanliness requirements presented in the form of restrictions on
the total magnetic moment of the spacecraft and the magnitude of the magnetic field at the installation
point of the onboard magnetometer [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. If the magnetic properties of the spacecraft do not satisfy
the overall magnetic cleanliness requirements magnetic compensation tests conducted. According to
the spacecraft multiple magnetic dipole models obtained in the form (8), it is possible to calculate the
spacecraft far magnetic field components  ,  ,  , and in particular, at the point of installation
of the onboard magnetometer and technical object magnetic moments , , . Let us now
consider the application of the developed technical object multiple magnetic dipole models to ensure
the spacecraft magnetic cleanliness by introducing additional magnetic dipoles to compensate for the
far magnetic field of the spacecraft, in particular, at the point of the onboard magnetometer installation
[
        <xref ref-type="bibr" rid="ref3 ref4 ref5">3, 4, 5</xref>
        ].
      </p>
      <p>To compensate for the initial magnetic field of the spacecraft we introduce  magnetic dipoles
with unknown magnetic moments , ,  located at  points  with unknown coordinates
, , .</p>
      <p>
        Let us introduce the vector  of the desired parameters for solving the problem of compensating the
initial magnetic field of the technical object, whose components are the oblique values of the magnetic
moments , ,  and coordinates , ,  of the location of the compensating magnetic
dipoles in the spacecraft space. Then, for a given value of the vector  of the desired parameters
of the compensating dipoles, the vector  () of the compensating magnetic field generated by all
compensating dipoles at the installation point of the onboard magnetometer and the vector  () of
the compensating magnetic moment generated by all compensating dipoles calculated [
        <xref ref-type="bibr" rid="ref6">6, 7, 8</xref>
        ].
      </p>
      <p>Then we calculated the vector (, ) of resulting magnetic moment and vector (, )
of resulting magnetic field generated at the installation point of the onboard magnetometer by the
spacecraft elements and all compensating dipoles</p>
      <p>(, ) =  () +  (), (, ) = () +  ().</p>
      <p>Then the problem of calculated the coordinates , ,  of spatial arrangement and magnetic
moments , ,  of the compensating dipoles can be reduced to solving the problem of vector
minimax optimization of resulting magnetic moment of the spacecraft and the resulting magnetic field
at the installation point of the onboard magnetometer
(10)
(11)
(12)
(13)
(14)</p>
      <p>Note that this approach is standard when designing of robust control, when the coordinates of the
spatial arrangement and the magnitudes of the magnetic moments of the compensating dipoles are
found from the conditions for minimizing the modulus of spacecraft magnetic field at the magnetometer
installation point for the “worst” values of the magnetic moments of the elements of the spacecraft
[9, 10, 11, 12].</p>
    </sec>
    <sec id="sec-4">
      <title>4. The problem solving method</title>
      <p>The solution of the vector minimax optimization problem wits vector objective function (11) and (12)
is the set of unimprovable solutions – the Pareto set of optimal solutions if only one vector objective
function given [13, 14, 15]. Such a statement of the optimization problem is an ill-posed problem, since
the solution in the form of a Pareto optimal set of unimprovable solutions is devoid of engineering sense
from the point of view of practical application [16]. In addition to the vector optimization criterion (10),
it is also necessary to have information about the binary relations of preference of local solutions to
each other in order to correctly solve the problem of multi-criteria optimization. This approach makes
it possible to significantly narrow the range of possible optimal solutions to the original multi-criteria
optimization problem [17, 18, 19].</p>
      <p>The problem of finding a local minimum at one point of the considered space is, as a rule,
multiextreme, containing local minima and maxima, therefore, for its solution, it is advisable to use algorithms
of stochastic. Currently, the most widely used are multi-agent stochastic optimization methods that use
only the speed of particles. To find the solution of minimax vector optimization problem (11) from
Paretooptimal decisions [20, 21, 22] taking into account the preference relations, we used special nonlinear
algorithms of stochastic multi-agent optimization. First-order methods have good convergence in the
region far from the local optimum, when the first derivative has significant values [23].</p>
      <p>The main disadvantage of first-order search methods, which use only the first derivative – the speed
of particles, is their low eficiency of the search and the possibility of getting stuck in the search near
the local minimum, where the value of the rate of change of the objective function tends to zero. The
advantage of second-order algorithms is the ability to determine not only the direction of movement,
but also the size of the movement step to the optimum, so that with a quadratic approximation of the
objective function, the optimum found in one iteration [24, 25, 26].</p>
      <p>To search the components  () optimal values of the vector  of the desired parameters minimizing
vector optimization criterion (11) and (12) for calculating velocities  () and accelerations  () of 
particle of  swarm using the following steps [27, 28, 29, 30]
· = (, ), · = (, ),
· = (, ), · = (, ),
 ( + 1) = 1  () + 1 1 ()(1 () −  1 ()) [ () −   ()] +</p>
      <p>2 2 ()(1 () −  2 ()) [︀ * () −   ()]︀ .
 ( + 1) = 2  () + 3 3 ()(3 () −  3 ()) [ () −   ()] +</p>
      <p>4 4 ()(4 () −  4 ()) [︀ * () −   ()]︀ .</p>
      <p>Here,  () and * () – the best–local and global positions  (),  () and * () – the best-local
and global velocity  () of the –th particle, found respectively by only one –th particle and all the
particles of  swarm.</p>
      <p>Random numbers  (),  () and constants  ,  ,  are tuning parameters,  – Heaviside
function.</p>
      <p>To search the components  () optimal values of the vector  of the parameters of the uncertainty of
the control object of the system of active silencing maximizing the same vector optimization criterion (10)
for calculating velocities  () and accelerations  () of  particle of  swarm using the steps similarly
(13), (14). However, unlike (13), (14), the best local and global position and velocity components are
those that lead not to a decrease in the corresponding components of the vector objective function (10),
but vice versa to their increase. This is where the “malicious” behavior of the vector  of uncertainties
of the designed system manifested.</p>
      <p>The use of the Archimedes algorithm for calculating minimax vector optimization problem (10)
solutions with binary preference relations it possible to reduce the calculating time.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Experimental research</title>
      <p>Anatolii Pidhornyi Institute of Power Machines and Systems of the National Academy of Sciences of
Ukraine (IPMash of the National Academy of Sciences of Ukraine) has the magnetodynamic complex
includes premises with a total area of about 20002 and consists of a magnet measuring stand with an
area of 4502 equipped with unique world-class magnetometric equipment, a technological plot of
land with an area of 5.3ℎ, which ensures a "magnetic silence" mode, power supply systems with a
capacity of 800  and others engineering systems and structures.</p>
      <p>The measurements procedure of components of the spacecraft magnetic moment involves
compensation of the Earth magnetic field in three orthogonal directions ,  and . The procedure for
determining the components of the magnetic moment of the test object involves the alternating influence
on it of the magnetic field of the windings in three orthogonal directions ,  and  with induction
40 . Measurements of the spacecraft magnetic moment according to the existing technology, involves
the stationary installation of twelve magnetometer "Magnetomat 1.782" at the corresponding points of
the sphere with a radius of 2 m. For measuring the magnetic moment of the component parts (blocks)
of the spacecraft magnetometer "Magnetoscop 1.069" used.</p>
      <p>Figure 1 shows the spacecraft "SICH-2-1" on the measuring stand.</p>
      <p>Ensuring the high accuracy of the MSU operation, with modern trends in the reduction of spacecraft
mass, requires the minimization of its magnetic moment and high accuracy of its determination.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Simulation results</title>
      <p>Let us consider the application of the developed method for solving the problem of ensuring the magnetic
cleanliness of the «Sich-2-1» spacecraft. Experimental measurements of the magnetic characteristics of
the «Sich-2-1» spacecraft carried out at the Anatolii Pidhornyi Institute of Power Machines and Systems
of the National Academy of Sciences of Ukraine stand. Based on these measurements, we calculate the
model of the «Sich-2-1» spacecraft. The experimentally measured value of the total magnetic moment
of spacecraft is equal  = [0.24, 0.5, 0.4]. The dispersion of the magnetic field prediction error in this
case is  = 7560.6. The value of the experimentally measured magnetic moment of the spacecraft
implies the presence of several dipoles located in the space of the spacecraft. In the calculation it is
assumed that the model of the magnetic field of the spacecraft represents one dipole located at the
origin of the spacecraft.</p>
      <p>Based on the experimental measured magnetic field at first the spacecraft magnetic field model
presented as a single dipole located in the center of the spacecraft. Based on the vector of the measured
magnetic field of the spacecraft   , the moments of this single dipole  = [0.24, 0.5, 0.4] were
calculated. The dispersion of the magnetic field prediction error in this case is  = 7272.7.</p>
      <p>Let us now consider the mathematical model of the magnetic field of the spacecraft in the form of a
single dipole, the location coordinates of which in the space of the spacecraft also need to be calculated.
For the calculated value of the moment  = [0.2664, 0.1641, 0.1434] and coordinates  = [0.2158, -0.4136,
0.0859] of the location of such a single dipole, the prediction error variance is  = 3239.8. Note that
the location of the only dipole not at the origin of the coordinates, but at the point with the optimal
coordinates made it possible to reduce the dispersion of the magnetic field prediction by a factor of
2.3337.</p>
      <p>If, when solving the problem of optimizing the values of the magnetic moments and the coordinates
of the location of one dipole, we introduce restrictions on the magnitude of the dipole moments in
the form of restrictions [-0.8, -0.8, -0.8] ≤  ≤ [0.8, 0.8, 0.8], optimal values of the moments  =
[0.2388, 0.1921, 0.1258] and coordinates  = [0.2056, -0.4146, 0] of the location of such a single dipole,
the prediction error variance is  = 3325.1. Thus, under restrictions on the magnitude of the dipole
moments, the optimum values of the magnetic moments are at the limits and, in this case, the dispersion
increases by a factor of 2.2738.</p>
      <p>Let us now consider the model of the spacecraft magnetic field in the form of two dipoles. If, when
solving the problem of optimizing the values of the magnetic moments and the coordinates of the
location of two dipoles, we introduce restrictions on the magnitude of the dipole moments in the form
of restrictions [-0.8, -0.8, -0.8] ≤  ≤ [0.8, 0.8, 0.8], optimal values of the moments  1 = [0.3538,
-0.0326, -0.0345] and  2 = [-0.6137, 0.6695, -0.2802] and the coordinates  1 = [0.3090, -0.3080, 0.0867]
and  2 = [-0.0657, -0.0789, -0.3908] of the location of two dipoles, the dispersion the prediction error
is  = 1203.4. Thus, under restrictions on the magnitude of the two dipoles moments, the optimum
values of the magnetic moments are at the limits and, in this case, the dispersion increases by a factor
of 6.2827.</p>
      <p>The simplest satellite multiple magnetic dipole models is a model consisting of two dipoles with
magnetic dipoles
and coordinates
 1 = [︀ 1.8404 −0.4147 0.1316 ]︀ ,  2 = [︀ −1.9641 1.3347 −0.3664
 1 = [︀ 0.2173 −0.1625 −0.0366
︀] ,  2 = [︀ 0.1609 −0.0306 −0.1397
︀] ,
︀] .
deviations for spacecraft mathematical model in the form of two dipoles.</p>
      <p>Based on this model, we calculate the spacecraft magnetic moment as the sum (8) of the magnetic
moments of the dipoles
and magnetic field
 = [︀ −0.1237
at the installation point of the onboard magnetometer. The simplest solution to the problem of
compensating the initial satellite magnetic moment is to place this one compensating dipole with a magnetic
moment
  = [︀ 0.1237 −0.92
opposite to the satellite moment. Even with the location of this compensating dipole at the origin of
the spacecraft coordinates, the magnetic field induction
 = [︀ 1.6155
at the point of installation of the magnetometer decreases by a factor 6.23. The location coordinates of
this compensating dipole calculated from the condition of minimizing the resulting magnetic field at
magnetometer installed point. Optimal position coordinates of the compensating dipole
and at the same time the induction level at the installation point of the magnetometer
 1 = [︀ 0.5</p>
      <p>0.5 −0.5 ]︀
 = [︀ 0.8903</p>
      <p>Thus, due to the installation of a compensating dipole at the optimal point, the magnetic field induction
module at the magnetometer installation point decreased by 3.15 times compared with the magnetometer
installation in the middle of the spacecraft and decreased by 19.8 times compared to the satellite without
compensation. A more accurate compensation of the spacecraft magnetic moment is achieved by
placing two compensation dipoles with magnetic moments
 1 = [︀ −1.8404 0.4147 −0.1316</p>
      <p>
        ︀] ,
 2 = [︀ 1.9641 −1.3347 0.3664 ]︀ ,
whose location coordinates in the spacecraft space are calculated by minimizing the magnetic field at
onboard magnetometer installation point taking into account design constraints. Note that in the work
[
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] the spacecraft model was accepted as adequate to real measurements when 29 dipoles were taken
into account, and when “only” 26 dipoles were taken into account, the spacecraft magnetic field model
was insuficiently adequate to real measurements.
      </p>
    </sec>
    <sec id="sec-7">
      <title>7. Conclusions</title>
      <p>Computational technology for prediction and control by orbital spacecraft magnetic cleanliness based
on geometric inverse magneto static problem solution with consideration of magnetic characteristics
uncertainty to improve the spacecraft magnetic cleanliness and its controllability in orbit developed.</p>
      <p>Geometric inverse problem solution reduced to vector game solution with COMSOL Muliphysics
software calculated payof vector. Game solution calculated based on heuristic optimization algorithms
from Pareto-optimal solutions taking into account binary preference relations local games solutions.</p>
      <p>Results of prediction and control by «Sich-2» microsatellite family for ensuring microsatellite
magnetic cleanliness based on developed computational technology presented.</p>
    </sec>
    <sec id="sec-8">
      <title>Declaration on Generative AI</title>
      <p>The author(s) have not employed any Generative AI tools.
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