Method for controlling the attitude in survival mode of a satellite carrying an instrument sensitive to solar radiation

Abstract

A method for controlling the attitude of a satellite in low orbit in survival mode is described, the satellite comprising an instrument sensitive to solar radiation, the method comprising: implementing attitude control (100) using a control law according to which: magneto-couplers are controlled to limit variations in the Earth's magnetic field, an internal kinetic moment is controlled along a determined axis, the method being characterized in that it further comprises: measuring an inertial rotation speed (200) of the satellite, by equipment for measuring an inertial rotation speed of the satellite and at least when the standard of the measured inertial rotation speed is less than a predetermined trigger threshold, controlling (300) inertial actuators adapted to form internal kinetic moments in said satellite frame, to increase the standard of the inertial rotation speed of the satellite.Abstract Figure: Figure 2.

Description

Title of the invention: Method for controlling the attitude in survival mode of a satellite carrying an instrument sensitive to solar radiation Technical field

[0001] The present disclosure relates to the field of attitude control of satellites in geocentric orbit, and more particularly relates to the attitude control of satellites in survival mode in low orbit, where the satellite carries an instrument sensitive to solar radiation. Prior art

[0002] In the present application, the term "survival mode" means any mode of attitude control of a satellite aiming, from an initial disturbed state, to ensure sufficient sunlight for the solar generators to guarantee the electrical autonomy of a platform of said satellite until its restoration to a state close to the nominal operational conditions.

[0003] Thus, the survival mode can be implemented immediately after separation from the launcher for the initial acquisition of the Sun and / or after the satellite mission has begun in its mission orbit, in the event of any incident requiring the mission to be interrupted, such as, for example, a failure of equipment such as a thruster.

[0004] For a satellite in survival mode in low orbit, equipped with both magneto-couplers and flywheels, it is known from patent application EP 0778201 A1 to control the attitude by using in particular a magneto-coupler control law called "B point", to indicate that it involves the derivative of the Earth's magnetic field B.

[0005] According to this B-point law, the Earth's magnetic field is measured along the three axes of a satellite reference frame, the measurements are derived with respect to time, then the derivatives are multiplied by a gain and a current representative of the result is passed through magneto-couplers to create internal magnetic moments which tend to stop the variations of the Earth's magnetic field in the satellite reference frame, so that the satellite follows the lines of the Earth's magnetic field. Thus, for a polar orbit, the B-point law finally causes the satellite to rotate on itself at a speed equal, in an inertial reference frame, to twice the orbital pulsation (i.e. the satellite makes two turns on itself per orbit) around an axis orthogonal to the plane of the orbit.

[0006] Furthermore, the flywheels are controlled to form an internal angular momentum, called "survival angular momentum", along a predetermined axis in the satellite reference frame. Due to this survival angular momentum formed by the flywheels, and the fact that the B-law is used to control the magneto-couplers, the satellite will naturally orient itself so as to rotate on itself around the axis of the survival angular momentum. In other words, the satellite orients itself so as to have the axis of the survival angular momentum orthogonal to the plane of the satellite's orbit. In order to maximize the average sunlight of the solar generators, the axis of the survival angular momentum can be predetermined according to the local time of the satellite's orbit.

[0007] Also known from patent EP 3 921 235 B1 is a method for controlling a satellite orbit in survival mode also implementing a B-point law and further comprising a step of searching for the Sun by means of a solar sensor, making it possible to detect whether the satellite is in the Sun's visibility phase and, when a Sun's visibility phase is detected, an attitude control step implementing a B-point magnetocoupler control law, and during which the inertial actuators are also controlled to form torques aimed at placing and maintaining the satellite in an attitude in which the satellite's sun generator is directed towards the Sun.

[0008] In the case where the satellite comprises at least one instrument sensitive to solar radiation, and in particular an optical instrument, the implementation of these attitude control laws may present a risk of damage to the instrument, linked to dazzling of the instrument at low speed. Indeed, the implementation of a B-point law typically has the effect of reducing the inertial rotation speed of the satellite, until it converges to the rotation speed equal to twice the orbital pulsation, as indicated above. During this period, the orientation of the satellite varies, and it may in particular happen that the line of sight of the optical instrument is oriented towards the sun, which causes dazzling of the instrument.

[0009] The glare of an instrument is defined as a period when the solar flux, direct or reflected, is incident on a sensitive area of ​​the instrument (typically, in the case of an optical instrument, the sensitive area may include optical components such as lenses and mirrors, as well as electronic components, including optoelectronic sensors). However, in the case of glare at low speed, the duration during which the instrument is dazzled increases and may result in a thermal increase that is detrimental to the instrument. Summary

[0010] The present disclosure aims to remedy all or part of the limitations of the solutions of the prior art, in particular those set out above, by proposing attitude control of a satellite in survival mode carrying an instrument sensitive to solar radiation, which greatly reduces the risk of damage to the on-board instrument linked to slow, i.e. too long, glare of the on-board instrument.

[0011] In this regard, a method is proposed for controlling the attitude of a satellite in low orbit in survival mode, the satellite comprising an instrument sensitive to solar radiation, the method comprising: - the implementation of attitude control using a control law according to which: • magneto-couplers, adapted to form internal magnetic moments in a satellite reference frame, are controlled according to a measurement of the Earth's magnetic field by magnetometers, to limit variations in the Earth's magnetic field, • an internal kinetic moment is controlled along a determined axis, the internal kinetic moment being of a minimum standard function of at least the inertia of the satellite, the method being characterized in that it further comprises: - the measurement of an inertial rotation speed of the satellite, by equipment for measuring an inertial rotation speed of the satellite and - at least when the measured inertial rotation speed standard is lower than a predetermined trigger threshold, the control of inertial actuators adapted to form internal kinetic moments in said satellite frame, to increase the inertial rotation speed standard of the satellite.

[0012] Thus, the proposed attitude control method comprises measuring the inertial rotation speed of the satellite by means of a gyroscope, and, in the event of detection of a low inertial rotation speed, controlling the inertial actuators to increase this inertial rotation speed.

[0013] This method is implemented regardless of the orientation of the instrument, and therefore does not require knowledge of the position of the sun relative to the instrument. However, it eliminates the risk of damage to the instrument due to glare, by ensuring a minimum inertial rotation speed for the satellite. Thus, when glare occurs, controlling the inertial rotation speed makes it possible to reduce the exposure time of the sensitive components of the instrument to a duration that is sufficiently short to avoid the risk of overheating or damage.

[0014] Since the control of the inertial actuators only takes place when the inertial rotation speed is lower than a determined trigger threshold, and it is carried out according to the inertial rotation speed of the satellite, the control of the actuators remains little disruptive on the final attitude of the satellite. The attitude control according to the invention remains in particular without impact on the expected long-term behavior of a B-point law.

[0015] In embodiments, when the measured inertial rotational speed is less than the predetermined trigger threshold, the inertial actuators are controlled to generate an incremental angular momentum of determined norm and direction.

[0016] In embodiments, the norm of the incremental angular momentum is a decreasing function of the measured speed, between a maximum increment value and a zero value when the measured inertial rotation speed is equal to the trigger threshold.

[0017] In embodiments, the decreasing function of the measured speed is continuous in the inertial rotational speed value corresponding to the trigger threshold on at least two derivative orders. For example, the decreasing function of the measured speed is a power function of order at least 2 or an exponential function.

[0018] In embodiments, the norm of the incremental angular momentum is constant and equal to the maximum value when the measured inertial rotational speed is less than or equal to a second threshold, less than the trigger threshold.

[0019] In embodiments, the value of the inertial rotation speed corresponding to the trigger threshold is determined as a function of a maximum authorized time of exposure of the optical instrument to the sun.

[0020] In embodiments, the steps of measuring and controlling the inertial actuators are iterative, and the direction of the incremental angular momentum is equal to the satellite inertia multiplied by the direction of natural rotational speed of the satellite, corresponding to the direction of the measured inertial rotational speed of the satellite from which the incremental angular momentum applied to the previous iteration of the step of controlling the inertial actuators is deduced.

[0021] In embodiments, the steps of measuring and controlling the inertial actuators are iterative and, when the measured inertial rotation speed is less than a safety threshold less than the trigger threshold, the direction of the incremental angular momentum is the last direction of incremental angular momentum determined during a previous iteration of the step of controlling the inertial actuators.

[0022] In embodiments, when the measured inertial rotational speed becomes greater than the safety threshold, the direction of the incremental angular momentum is determined by time interpolation between the last direction of momentum incremental kinetics controlled by inertial actuators and the natural rotation speed direction of the satellite.

[0023] In embodiments, the control law is a biased B-point law.

[0024] According to another object, there is provided a satellite intended to be placed in low orbit inclined, comprising at least one instrument sensitive to solar radiation, magneto-couplers adapted to form internal magnetic moments in a satellite frame, inertial actuators adapted to form internal kinetic moments in said satellite frame and magnetometers adapted to measure the Earth's magnetic field, said satellite being characterized in that it further comprises equipment for measuring an inertial rotation speed of the satellite and a module for controlling the magneto-couplers and the inertial actuators, said control module being configured to implement an attitude control method in survival mode according to the preceding description.

[0025] In embodiments, the inertial actuators are reaction wheels.

[0026] In embodiments, the equipment for measuring a rotational speed The satellite's inertial system is a gyroscope.

[0027] According to another object, a computer program product is described, characterized in that it comprises a set of program code instructions which, when executed by a processor of a control module of a satellite, configure said control module to implement the attitude control method in survival mode according to the preceding description. Brief description of the drawings

[0028] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig.l

[0029] [Fig.l] is a schematic representation of one embodiment of a satellite. Fig. 2

[0030] [Fig.2] schematically represents the main stages of a control process attitude in survival mode according to an embodiment Fig. 3

[0031] [Fig.3] represents an example of evolution of the speed increment standard brought to the satellite according to the measured inertial speed. Fig. 4a

[0032] [Fig.4a] represents an example of the trajectory of the Sun relative to a cone glare of an instrument, without the implementation of the attitude control process. Fig. 4b

[0033] [Fig.4b] represents the trajectory of the Sun relative to a glare cone of an instrument, from similar initial kinematic conditions, with the implementation of the attitude control method. Description of the embodiments

[0034] The present invention relates to the attitude control of a satellite 10 in survival mode in low geocentric orbit.

[0035] As indicated previously, in the present application, the survival mode is an attitude control mode implemented immediately after separation from the launcher and / or after the mission of the satellite 10 has begun, in the event of any incident requiring the mission to be interrupted (collision with a meteorite, failure of a thruster, etc.)

[0036] By “low orbit” is meant that the maximum altitude of the satellite 10 is such that the local Earth magnetic field is not negligible and allows the implementation of magneto-couplers to control the attitude of said satellite. In practice, this condition is verified in particular when the maximum altitude of the satellite is less than 2000 kilometers.

[0037] In the following, the concept of inertial reference frame is used, i.e. a reference frame in which the principle of inertia, according to which any free point body persists in a uniform rectilinear motion, is verified. In practice, for a satellite in orbit around the Earth, it can be considered by approximation that a geocentric reference frame, i.e. a reference frame centered on the center of the Earth, and comprising three orthogonal axes pointing towards three stars sufficiently far from the Earth to appear fixed (for the period of time considered during the implementation of the method), is an inertial reference frame. A heliocentric reference frame can also be considered as an inertial reference frame, i.e. a reference frame centered on the center of the Sun, and comprising three orthogonal axes pointing towards three stars sufficiently far from the Sun to appear fixed (for the period of time considered during the implementation of the method).

[0038] [Fig.l] schematically represents an exemplary embodiment of a satellite 10 according to the invention.

[0039] A satellite reference frame is associated with the satellite 10, for example centered on a center of mass O of the satellite 10, comprising three axes X, Y and Z orthogonal to each other. The satellite reference frame is linked to the satellite 10, that is to say that it is entirely defined by the geometry of the satellite 10, and that any rotation of the satellite in an inertial reference frame results in an equivalent rotation of the satellite reference frame in an inertial reference frame.

[0040] The satellite comprises a body 11. In the non-limiting example shown in [Fig. 1], the body 11 is substantially in the shape of a rectangular parallelepiped. The satellite also comprises at least one solar generator 12, and typically two solar generators arranged on either side of said body. The number of solar generators carried by the satellite is however not limiting.

[0041] The satellite also comprises at least one instrument 14 sensitive to solar radiation. For example, the instrument 14 may be an optical instrument. When the satellite is in position, the line of sight of the optical instrument may be oriented towards the Earth, for an Earth observation mission. However, as indicated above, during survival mode, the rotations of the satellite in inertial reference may cause the solar radiation-sensitive components of the instrument 14 - in particular, for an optical instrument, the line of sight - to be oriented towards the Sun, thus causing dazzling and heating of these sensitive components.

[0042] The satellite also comprises several actuators implemented for attitude control. In particular, the satellite comprises a set of magneto-couplers 15 adapted to form an internal magnetic moment of any axis in the satellite frame.

[0043] The satellite also comprises a set of inertial actuators 16, such as reaction wheels or gyroscopic actuators, adapted to form internal kinetic moments in the satellite frame.

[0044] Furthermore, the satellite comprises equipment 17 for measuring the inertial speed of the satellite, for example a gyroscope. Alternatively, the equipment 17 may also be a star sensor, adapted to measure the coordinates of one or more stars in the satellite reference frame, allowing the measurement of an inertial speed of the satellite from the displacement of the targeted stars measured by the sensor.

[0045] The satellite 10 further comprises a control module (not shown in the figures) adapted to control the magneto-couplers and the inertial actuators.

[0046] The control module comprises for example at least one processor and at least one memory in which a computer program product is stored, in the form of a set of program code instructions to be executed to implement the different steps of a method for controlling the attitude of the satellite in survival mode described below. In a variant, the control module comprises one or more programmable logic circuits of the FPGA, PLD, etc. type, and / or specialized integrated circuits (ASIC) adapted to implement all or part of the steps of the method 50 for controlling the attitude of said satellite 10 in survival mode.

[0047] In other words, the control module comprises a set of means configured in software (specific computer program product) and / or hardware (FPGA, PLD, ASIC, etc.) to implement the method for controlling the attitude of the satellite 10 in survival mode.

[0048] With reference to [Fig.2], we will now describe the main steps of a method for controlling the attitude in survival mode of the satellite 10 according to embodiments.

[0049] Attitude control in survival mode includes steps of: - Implementation 100 of an attitude control using a control law, - Measure 200 of an inertial rotation speed of the satellite during the setting implementation of the said control law, and - Increase 300 of the standard of the inertial rotation speed of the satellite when this, obtained at the measurement stage, becomes lower than a predetermined trigger threshold.

[0050] During step 100, the control law that is implemented comprises the control of the magneto-couplers 15, as a function of local values ​​of the Earth's magnetic field, to form internal magnetic moments in the satellite reference frame, aiming to limit the variations of the Earth's magnetic field in the satellite reference frame. The local values ​​of the Earth's magnetic field can be provided by measurements carried out by one or more magnetometers (not shown in the figures), or by estimates provided by a model of the Earth's magnetic field which receives as input the position of the satellite 10. This position can be estimated by means of a GNSS receiver ("Global Navigation Satellite System") such as a GPS receiver ("Global Positioning System"), not shown in the figures.

[0051] The control law also comprises the control of the generation of an internal kinetic moment in the satellite along a determined axis, and of a minimum norm depending on at least the inertia of the satellite. This internal kinetic moment can for example be generated by the inertial actuators of the satellite. Due to this kinetic moment along a predetermined axis, and the internal magnetic moments generated by the magneto-couplers 15, the satellite naturally orients itself so as to rotate on itself around the axis of the kinetic moment.

[0052] In embodiments, the control law is a so-called biased B-point law, or using a biased B-point law.

[0053] According to the biased B-point law, the internal magnetic moment generated by the magneto-couplers 15 comprises a term proportional to the derivative of the local values ​​of the Earth's magnetic field, and a bias, which is a term proportional to a vector product between the local Earth's magnetic field and a determined vector, the gain of which is determined as a function of the rotation speed on itself that we want to achieve for the satellite.

[0054] The biased B-point law can for example be expressed as follows:

[0055] _ JZ F db, y î] MMTQ - ■ l dt + œCTRL XJ

[0056] Expression in which: - MuTrn corresponds to the internal magnetic moment formed by the magneto-couplers, - Kg corresponds to a strictly positive predetermined gain, - db is the derivative of the measured or estimated unit Earth magnetic field dt in the satellite frame, which is equal to ÿ / ||g|| where B is the Earth's magnetic field measured or estimated in the satellite frame, - ^CTRL is a predetermined vector, and x denotes the vector product.

[0057] In the absence of the bias, the application of the law at B point causes the satellite to rotate on itself at a speed equal, in inertial reference, to twice the orbital pulsation around the axis of the kinetic moment. The bias increases this rotation speed. The gain ^ctrl (which is the norm of the vector) can be determined to result in a rotation speed of the satellite on itself in inertial reference of norm strictly greater than 2. | w0| and equal to or less than 4. | w()|, being the orbital pulsation of the satellite 10 in inertial reference. Of course, this speed is reached at the end of a convergence period, during which the inertial rotation speed of the satellite is variable, being able to take values ​​respectively lower, or even zero, or values ​​higher than this speed reached at the end of the convergence period.

[0058] During step 200, the inertial rotation speed of the satellite, along the three axes of the inertial reference frame, is measured. Measuring the inertial speed makes it possible to obtain information on the relative speed of movement between the Sun and the satellite. This measurement is advantageously carried out by a gyroscope 17, the measurement of which has a high level of precision, and the response time is low, i.e. of the order of less than 100 milliseconds, and therefore allows a low reaction time for the implementation of step 300.

[0059] The measurement of the inertial rotation speed of the satellite is implemented repeatedly at a determined frequency during the implementation of the control law 100 described above. For example, the acquisition frequency of this speed is advantageously at least once per second, it can for example be between 1 Hz and 20 Hz.

[0060] The standard of the inertial rotation speed thus measured is, at each iteration of step 200, compared to a so-called trigger threshold Tb for the implementation of step 300, which comprises the control of the inertial actuators 16 so as to increase the standard of the inertial rotation speed of the satellite 10, when the standard of the speed is or becomes lower than this trigger threshold.

[0061] The trigger threshold Ti is defined by an inertial rotation speed value of the satellite. In embodiments, this value corresponds to a value minimum inertial rotation speed below which exposure of the instrument to the Sun would be too long and therefore likely to damage the instrument. Advantageously, the value of the trigger threshold Ti is therefore determined based on a maximum authorized time of exposure of the instrument to the Sun, possibly with the addition of a safety margin. As a non-limiting example, the speed value corresponding to the trigger threshold Ti can be between 5 and 15 mrad / s, for example.

[0062] During step 300, the inertial actuators are controlled to generate an incremental kinetic moment (i.e. which is added to the kinetic moment already generated by these actuators where applicable), of determined norm and direction, to increase the norm of the inertial rotation speed. Increasing the norm of the speed therefore corresponds to adding, to the measured speed, a speed increment of determined norm, and the direction of which corresponds to that of the instantaneous inertial rotation speed of the satellite. Thus, the axis of rotation of the satellite is not modified, and the rotation is therefore not disturbed but only accelerated if it reaches the trigger threshold.

[0063] In the sequence Acoinc is the vector corresponding to the satellite speed increment. Considering a target Acoinc increment of rotation speed for the satellite, this increment is linked to the increment vector AHmom of the kinetic moment commanded to the inertial actuators as follows:

[0064] ÀHMom — ^,z\nc

[0065] Where is the incremental angular momentum increment, and Isat is the inertia matrix of the satellite.

[0066] In embodiments, and with reference to FIG. 3, the norm of the kinetic momentum increment, denoted (and therefore the norm of the speed increment) is a decreasing function of the measured speed, between a maximum increment value, reached for example for a zero speed, and a zero value, which is reached when the measured inertial rotation speed is equal to the trigger threshold Tp In other words, considering a satellite 10 whose inertial rotation speed gradually decreases until reaching the trigger threshold Ti, the norm of the incremental kinetic moment [| AH^J) commanded to the inertial actuators 16 gradually increases as the rotation speed of the satellite decreases, so as to achieve a stronger correction of the speed if it becomes too low.

[0067] In embodiments, this function is a continuous function, on at least two orders of derivation, at the point where the value of the inertial rotation speed is equal to the trigger threshold Tb. For example, the function may be a function power of order 2 or higher, or an exponential function. This allows for gradual acceleration and avoids excessively sudden speed variation phenomena, which could have the effect of damaging certain equipment on board satellite 10.

[0068] In embodiments, and as shown in the example of [Fig. 3], the norm of the kinetic moment increment is constant, and equal to the maximum increment value, when the norm of the inertial rotation speed is less than a second threshold T2, less than the trigger threshold, i.e. when this norm is between 0 and T2. In other words, - between speeds between T and T2. The lower the speed of the satellite, the higher the norm of the kinetic moment increment, - between speeds between 0 and T2: the norm of the kinetic moment increment is constant and maximum.

[0069] Thus, the application of a maximum increment is ensured for all speeds between 0 and T2, which makes it possible to ensure very rapid correction for a speed range where the risk of damage in the event of dazzling is particularly high.

[0070] The norm of the increment of the kinetic moment is thus determined.

[0071] The direction of the increment of the angular momentum, denoted uMom, is given by uMom - with lsat the satellite inertial matrix and uRate the direction of the desired speed increment. is chosen equal to the direction of the natural rotation speed of the satellite, noted ^nat, which corresponds to the last measured inertial rotation speed of the satellite, from which is deduced the incremental kinetic moment AU^p^ applied to the previous iteration of step 300 of controlling the inertial actuators:

[0072] COnat — ^satll” ^inc.prev

[0073] It can be observed from the above equation that in certain cases, where the inertial rotation speed of the satellite is too low, the direction of the increment of the kinetic moment may not be determinable due to divergence of the calculation. In this case, the method advantageously provides that when the measured inertial rotation speed is lower than a safety threshold Ts, the direction of the incremental kinetic moment is not recalculated, but the last direction of the incremental kinetic moment determined during a previous iteration of the step 300 of controlling the inertial actuators is used. A locking 310 of the direction of the kinetic moment increment is thus carried out until an inertial rotation speed of the satellite is found which allows the calculation of this direction again. The threshold of safety Ts is lower than the threshold Ti for triggering the increase in satellite speed. For example, it is lower than Imrad / s.

[0074] In embodiments, when the inertial rotation speed of the satellite becomes higher than the safety threshold Ts, the direction calculated at least for the next implementation of step 300 can be determined 320 by temporal interpolation between the last direction of incremental kinetic momentum commanded to the inertial actuators (i.e. during the previous iteration of step 300, including in the event of locking 310 as indicated above) and the direction of natural rotation speed of the satellite described above. In embodiments, this method of calculating the direction is used for more than one implementation of step 300 following the return of the inertial rotation speed to a level higher than the threshold Ts. It can for example be used for a determined period of time or for a determined number of iterations of this step.This makes it possible to exit the 310 direction lock state by ensuring a progressive change of direction of the rotation speed increment, and makes it possible to limit disturbances to the control law as well as the risks of damage to the equipment on board the satellite.

[0075] The interpolation 320 can for example be a linear interpolation (LERP) or spherical linear interpolation (SLERP) which are conventional interpolation techniques.

[0076] With reference to Figures 4a and 4b, an example of the trajectory of the Sun is shown relative to an optical instrument mounted on a satellite implementing attitude control respectively with and without the increase in the standard of the inertial rotation speed of the satellite when it becomes lower than the trigger threshold Tp. In these figures, the trajectory of the Sun is represented by a curve, on a sphere which represents the set of spherical coordinates around the instrument, shown in the center. The dotted circle centered on the line of sight corresponds to the glare cone of the optical instrument, which must not be oriented towards the Sun beyond a determined duration. The shades of gray of the trajectory of the satellite correspond to values ​​of the inertial rotation speed of the satellite, so that the darker the trajectory, the slower the speed, and therefore the longer the time spent at the position considered.

[0077] In the case of [Fig.4a], we note that part of the Sun's trajectory passes through the glare cone, and for low speed values, therefore potentially detrimental to the instrument. In the case of [Fig.4b], we note that the Sun's speed remains in high values, thanks to the acceleration provided according to the preceding description. Thus, even if the Sun passes through the cone glare from the optical instrument, it does so at a speed high enough not to damage the instrument.

[0078] The proposed method therefore makes it possible, by applying an increase in the inertial rotation speed of the satellite 10 each time it becomes lower than a predetermined threshold, to avoid risks of dazzling, without needing to know the position of the instrument relative to the sun. Indeed, this increase in speed is implemented without knowledge or condition applied to the orientation of the instrument.

Claims

Claims

1. Method for controlling the attitude of a satellite in low orbit in survival mode, the satellite comprising an instrument sensitive to solar radiation, the method comprising: - implementing (100) an attitude control using a control law according to which: • magneto-couplers, adapted to form internal magnetic moments in a satellite frame, are controlled as a function of a measurement of the Earth's magnetic field by magnetometers, to limit variations in the Earth's magnetic field, • an internal kinetic moment is controlled along a determined axis, the internal kinetic moment being of a minimum standard which is a function of at least the inertia of the satellite, the method being characterized in that it further comprises: - measuring (200) an inertial rotation speed of the satellite,by equipment for measuring an inertial rotation speed of the satellite and - at least when the standard of the measured inertial rotation speed is lower than a predetermined trigger threshold, the control (300) of inertial actuators adapted to form internal kinetic moments in said satellite frame, to increase the standard of the inertial rotation speed of the satellite.,

2. The method of claim 1, wherein when the measured inertial rotational speed is below the predetermined trigger threshold, the inertial actuators are controlled (300) to generate an incremental angular momentum of determined norm and direction.

3. A method according to claim 1 or 2, wherein the norm of the incremental angular momentum is a decreasing function of the measured velocity, between a maximum increment value and a zero value when the measured inertial rotation speed is equal to the trigger threshold.

4. Method according to claim 3, in which the decreasing function of the measured speed is continuous in the inertial rotation speed value corresponding to the trigger threshold on at least two derivation orders.

5. The method of claim 4, wherein the decreasing function of the measured speed is a power function of order at least 2 or an exponential function.

6. Method according to one of claims 3 to 5, in which the norm of the incremental kinetic moment is constant and equal to the maximum value when the measured inertial rotation speed is less than or equal to a second threshold, less than the trigger threshold.

7. Method according to one of the preceding claims, in which the value of the inertial rotation speed corresponding to the trigger threshold is determined as a function of a maximum authorized time of exposure of the instrument to the sun.

8. Method according to one of claims 2 to 7, in which the steps of measuring (200) and controlling (300) the inertial actuators are iterative, and the direction of the incremental kinetic moment is equal to the satellite inertia multiplied by the direction of natural rotation speed of the satellite, corresponding to the direction of the measured inertial rotation speed of the satellite from which the incremental kinetic moment applied to the previous iteration of the step of controlling the inertial actuators is deduced.

9. Method according to one of the preceding claims, in which the steps of measuring (200) and controlling (300) the inertial actuators are iterative and, when the measured inertial rotation speed is lower than a safety threshold (Ts) lower than the trigger threshold, the direction of the incremental kinetic moment is the last direction of incremental kinetic moment determined during a previous iteration of the step of controlling the inertial actuators.

10. A method according to claim 10, wherein, when the measured inertial rotational speed becomes greater than the safety threshold (Ts), the direction of the incremental angular momentum is determined by time interpolation between the last moment direction incremental kinetics controlled by inertial actuators and the natural rotation speed direction of the satellite.

11. Method according to one of the preceding claims, in which the control law is a biased B-point law.

12. Satellite (10) intended to be placed in inclined low orbit, comprising at least one instrument (14) sensitive to solar radiation, magneto-couplers (15) adapted to form internal magnetic moments in a satellite frame, inertial actuators (16) adapted to form internal kinetic moments in said satellite frame and magnetometers adapted to measure the Earth's magnetic field, said satellite (10) being characterized in that it further comprises equipment (17) for measuring an inertial rotation speed of the satellite and a module for controlling the magneto-couplers and the inertial actuators, said control module being configured to implement an attitude control method in survival mode according to any one of the preceding claims.

13. Satellite according to the preceding claim, in which the inertial actuators (16) are reaction wheels.

14. Satellite according to claim 12 or 13, wherein the equipment (17) for measuring an inertial rotation speed of the satellite is a gyroscope.

15. Computer program product, characterized in that it comprises a set of program code instructions which, when executed by a processor of a control module of a satellite, configure said control module to implement the attitude control method in survival mode according to any one of claims 1 to 11.

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