System and method for monitoring space objects in orbit

Abstract

A monitoring system (1) for an orbiting space object (5) comprising a ground-based radar system (2) (7) including an antenna (6) with a controllable pointing direction for moving a space observation window (11) within a field of view (12), the pointing direction having a predetermined value (Zref) associated with the space object (5), the monitoring system (1) comprising ground-based optical sensors (3) (7) and a control unit (4) configured to determine a first orbital restitution (O1) from first positions (P1) of the space object (5) measured by the optical sensors (3), and, if the first orbital restitution (O1) crosses the field of view (12) of the radar system (2) outside the space observation window (11) associated with the predetermined value (Zref) of the pointing direction, to determine a command for the pointing direction of the antenna (6). Abstract figure: Figure 1

Description

Title of the invention: System and method for monitoring space objects in orbit. Technical field

[0001] The present invention relates to the field of monitoring space objects in orbit, and in particular active space objects capable of maneuvering in space, such as satellites.

[0002] It is known to use ground-based radar systems to monitor orbiting space objects, typically low-Earth orbit satellites located between 200 km and 2000 km above the ground. Such a radar system classically comprises an array of transmitters of incident radio waves at high frequencies above 100 MHz and an array of receivers of radio waves reflected by the space object. The position of the space object at different times is determined, in particular, from the reception time of the reflected radio waves and the angle formed between the directions of the incident and reflected radio waves. It is thus possible to estimate the trajectory of the space object, known to those skilled in the art as the "orbital restitution," in order to assess a potential risk of collision with other space objects.

[0003] It is particularly known to equip such radar systems with directional and controllable antennas. Such antennas are adapted to emit a narrow beam of radio waves, or "main lobe," defining a space observation window. The pointing direction of such antennas can be changed, notably by mechanical or electronic scanning, to move the space observation window within a wide field of view. This gives radar systems both a precise and comprehensive view, enabling them to be used for both surveillance, i.e., the detection of space objects, and tracking. Furthermore, such radar systems are operable in all weather conditions, unlike optical sensors, particularly telescopes, which require darkness for measurements and that space objects be illuminated to be visible.

[0004] In practice, the exceptional growth in the number of space objects increases the number of objects to be monitored and the risks of collision, tending to saturate the resources of radar systems. To remedy this, one solution would be to deploy a larger number of ground-based radars to increase available resources. However, such a solution is too costly to be feasible. Another solution would be to increase the observation window of radar systems. This, however, would generate an undesirable loss of accuracy that would necessitate cross-referencing measurements from several radar systems are needed to compensate for it. Such a solution is therefore also just as costly.

[0005] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0006] The invention relates to a monitoring system for at least one orbiting space object comprising: • At least one ground-based radar system comprising at least one antenna configured to emit a beam of waves defining a space observation window, the antenna comprising a controllable pointing direction to move the space observation window within a predetermined field of view, the pointing direction having a predetermined value associated with the space object, • A plurality of ground-based optical sensors, each covering a spatial area extending beyond the radar system's field of view, • At least one control unit connected to the radar system and the plurality of optical sensors, the control unit being configured to: • Determine a plurality of first positions of the spatial object in at least one of the spatial areas from at least one of the plurality of optical sensors, • Determine an initial orbital reconstruction of the space object based on the initial positions, • If the first orbit restitution crosses the radar system's field of view outside the space observation window associated with the predetermined pointing direction value, determine a radar system antenna pointing direction command from the first orbit restitution, to determine at least a second position of the space object within the space observation window from the radar system.

[0007] The surveillance system according to the invention combines optical sensors with radar systems in such a way as to synergistically exploit the low-cost, comprehensive vision of optical sensors and the precise and reliable vision of radar systems. The optical sensors advantageously allow for the comprehensive monitoring of space traffic in the extended space area, in particular all active space objects capable of maneuvering, such as satellites. This makes it possible to obtain a first, low-cost, coarse orbital reconstruction of each space object, sufficient to identify among them space objects of interest not following a Keplerian motion, typically a satellite performing a maneuver. It is thus possible to reduce the workload of the radar system so that it can be focused on the precise and reliable tracking of space objects of interest, which represent only about 60% of active space objects. The invention can also be used to alert other sensors.

[0008] According to one aspect of the invention, the space object is adapted for maneuvering and is located at an altitude above the ground greater than 200 km, and preferably less than 2000 km. The monitoring system according to the invention is particularly suitable for observing active space objects in low Earth orbit, typically satellites.

[0009] According to one aspect of the invention, the field of view of the radar system has a length and width at least five times smaller than the length, preferably at least ten times smaller than the length. Preferably, the field of view is rectangular, a sector of a ring, or conical. Thanks to measurements from the optical sensors, the control unit can correctly position the radar system's antenna to ensure effective tracking of an object of interest, without requiring a more time-consuming and resource-intensive watch. This is particularly advantageous for radar systems with a narrow field of view where the spatial object appears only for a short time.

[0010] According to one aspect of the invention, the wave beam emitted by the radar system antenna has a width of less than 5°, preferably less than 2°, ensuring high measurement accuracy.

[0011] According to one aspect of the invention, the plurality of optical sensors are in the form of cameras, preferably adapted to operate in the visible or infrared range, allowing for low-cost global monitoring of space traffic.

[0012] According to one aspect of the invention, the monitoring system comprises at least one auxiliary ground-based optical sensor covering an auxiliary spatial area extending at least partially within the field of view of the radar system, the control element being configured to: • Determine at least one initial auxiliary position of the spatial object within the auxiliary spatial area using the auxiliary optical sensor, • Determine the first orbital restitution of the space object from the first auxiliary position.

[0013] Advantageously, the area covered by the optical sensors is located outside the radar system's field of view so as to detect the space object before it enters the radar system's field of view. This makes it possible to predict where the space object will appear within the radar system's field of view. The auxiliary optical sensors, in addition to the optical sensors, allow for lower-cost monitoring of the space object when it is within the radar system's field of view. This is particularly useful in cases of late detection or when radar system resources are limited.

[0014] The invention also relates to a method for monitoring at least one space object in orbit using the monitoring system as described above, the monitoring method consisting of: • Determine the plurality of first positions of the spatial object in at least one of the spatial areas from at least one of the plurality of optical sensors, • Determine the first orbital reconstruction of the space object from the initial positions, • If the first orbit restitution crosses the radar system's field of view outside the space observation window associated with the predetermined pointing direction value, determine the radar system antenna pointing direction command from the first orbit restitution, to determine the second position of the space object in the space observation window from the radar system.

[0015] According to one aspect of the invention, the monitoring method also consists of determining a second orbital reconstruction of the space object from the first and second positions. Thanks to the precision of the radar system measurements, the second orbital reconstruction is advantageously more precise than the first orbital reconstruction. This allows for optimal tracking of space objects of interest, and in particular makes it possible to reliably predict a potential collision risk.

[0016] According to one aspect of the invention, the monitoring method also consists, if the first orbital restitution crosses the space observation window associated with the predetermined value of the pointing direction, of observing the space object solely with the plurality of optical sensors. This saves the radar system's resources by devoting them only to observing objects of interest.

[0017] According to one aspect of the invention, the step of determining the second position of the space object within the space observation window from the radar system is also implemented if the first orbital restitution crosses the space observation window associated with the predetermined value of the pointing direction. Optical sensors advantageously allow confirmation that the antenna's pointing direction is correct for tracking the space object, without requiring the system to operate in standby mode. The radar system's tracking mode is advantageously less costly in terms of time and resources than standby mode.

[0018] The invention also relates to a computer program-type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by this processor, triggers the execution of the steps of the monitoring process as previously described.

[0019] The invention further relates to a computer-readable medium containing the computer program-type product as described above. PRESENTATION OF FIGURES

[0020] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0021] Fig. 1 is a schematic representation of the monitoring system according to a first embodiment of the invention.

[0022] Fig. 2 is a schematic representation of the optical sensors of the monitoring system of Fig. 1.

[0023] Fig. 3 is a schematic representation of the monitoring system of Fig. 1 in the case of a space object during maneuvering.

[0024] Fig. 4 is a schematic representation of the monitoring system of Fig. 1 in the case of a space object following a Keplerian motion.

[0025] Fig. 5 is a schematic representation of the monitoring method according to a first embodiment of the invention.

[0026] Fig. 6 is a schematic representation of the monitoring system according to a second embodiment of the invention.

[0027] Fig. 7 is a schematic representation of the monitoring method according to a second embodiment of the invention.

[0028] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0029] The invention relates to a system and a method for monitoring space objects, particularly those located in low Earth orbit between 200 km and 2000 km above the ground. The invention is particularly applicable to active space objects, namely those adapted to maneuver in space, such as satellites.

[0030] According to the invention and with reference to Figures 1 and 2, the surveillance system 1 comprises one or more ground-based radar systems 2 7 and a set of ground-based optical sensors 3 7, which are connected by a control unit 4. Each radar system 2 comprises one or more antennas 6 configured to emit a beam of waves 10 defining a spatial observation window 11 and comprising a controllable pointing direction to move the spatial observation window 11 in a predetermined field of view 12. Each optical sensor 3 covers a spatial area 13 extending outside the field of view 12 of the radar system 2.

[0031] With reference to [Fig. 1], for each space object 5, the pointing direction of the antenna(s) 6 of the radar system 2 has a predetermined value Zref so as to observe the space object 5 during its next passage through the field of view 12. The predetermined value Zref is typically obtained from predetermined measurements and / or theoretical data of the space object 5, assuming that the space object 5 follows a Keplerian trajectory. The predetermined value Zref is typically expressed as an angle in the frame of reference of the radar system 2.

[0032] According to the invention and with reference to [Fig. 1], the control element 4 is configured to: • Determine initial positions PI of the spatial object 5 in at least one of the spatial areas 13 from at least one of the optical sensors 3, • Determine a first orbit reconstruction 01 of the space object 5 from the first positions PI, • If the first orbit restitution 01 crosses the field of view 12 of the radar system 2 outside the space observation window 11 associated with the predetermined value Zref of the pointing direction (see [Fig.3]), determine a command C of the pointing direction Z of the antenna 6 of the radar system 2 from the first orbit restitution 01, to determine one or more second positions P2 of the space object 5 in the space observation window 11 from the radar system 2.

[0033] The surveillance system 1 according to the invention combines optical sensors 3 with radar systems 2 in such a way as to synergistically exploit the low-cost, comprehensive view provided by the optical sensors 3 and the precise and reliable view provided by the radar systems 2. The optical sensors 3 cover a set of spatial areas 13 in which they together monitor space traffic by detecting the rough position of a large number of space objects 5. This makes it possible to obtain a first rough orbital reconstruction 01 of the space objects 5 at a lower cost, sufficient to verify whether the space objects 5 are following the expected trajectory, typically a Keplerian orbit. For space objects 5 with a non-Keplerian orbit, typically during or after a satellite maneuver, the optical sensors 3 advantageously help to position the radar system 2 without it having to perform a time- and resource-intensive monitoring operation.The radar system 2 can thus focus on tracking space objects 5, in order to determine their trajectory accurately and reliably.

[0034] As will be seen later, according to a first mode that maximizes resource efficiency for the radar system 2, the radar system 2 observes only non-Keplerian orbital space objects 5, while the optical sensors 3 provide coarse tracking of Keplerian orbital space objects 5 that do not require special attention. According to a second mode, the radar system 2 prioritizes tracking non-Keplerian orbital space objects 5 but also tracks Keplerian orbital space objects 5 for comprehensive and precise monitoring of space traffic.

[0035] As illustrated in Figures 1 and 2, the optical sensors 3 are ground-based 7 and distributed individually and / or in groups across different ground sites. The number of ground sites is preferably greater than 3, with several optical sensors 3 per ground site. The optical sensors 3 are preferably in the form of cameras comprising a lens typically operating in the visible or infrared range. The optical sensors 3 are preferably fixed. Such optical sensors 3 are inexpensive and easy to install.

[0036] As illustrated in Figures 1 and 2, the spatial area 13 observed by each optical sensor 3 is a function of the terrestrial position, the viewing angle b and the orientation of the optical sensor 3. The spatial areas 13 of the optical sensors 3 can be completely distinct from each other or overlap, as illustrated in [Fig. 1], or even coincide.

[0037] With further reference to Figures 1 and 2, each optical sensor 3 is adapted to acquire one or more images R at different times t1, t2 of the corresponding spatial area 13. In practice, and as illustrated in [Fig. 2], the optical sensors 3 are only operational during night Y, i.e., when the terrestrial site on which they are positioned is not illuminated by the Sun. Optical sensors 3 located on illuminated terrestrial sites, i.e., during day X, are therefore generally unusable. Furthermore, space objects 5 are only visible to the optical sensors 3 when they are illuminated, typically by the Sun. Thus, at a given time t1, t2, only a portion of the optical sensors 3 are operational. According to a preferred configuration, the optical sensors 3 are distributed across the Earth to provide a global view at all times.

[0038] As illustrated in [Fig. 1], the spatial areas 13 covered by the optical sensors 3 extend beyond the field of view 12 of the radar system 2. The optical sensors 3 thus make it possible to detect a space object 5 and, if necessary, to assist in repositioning the antenna 6 of the radar system 2, before the space object 5 enters the field of view 12 of the radar system 2. The spatial areas 13 are also complementary to the field of view 12, which advantageously provides greater coverage of the Earth's atmosphere for global surveillance. Do not Providing optical sensors 3 to observe the field of view 12 of the radar system 2 is also economical.

[0039] According to another aspect of the invention illustrated in [Fig. 6], the surveillance system 1 also includes auxiliary optical sensors 3' on the ground 7 covering an auxiliary spatial area 13' extending at least partially into the field of view 12 of the radar system 2. The auxiliary optical sensors 3' are preferably identical to the optical sensors 3. The auxiliary optical sensors 3' preferably have the same function as the optical sensors 3, namely, to determine one or more first positions PI' of a space object 5 in the auxiliary spatial area 13'. The first auxiliary positions PI' and the first positions PI together allow the determination of the first orbital reconstruction 01. The auxiliary optical sensors 3' are particularly useful in the event of late detection or when the resources of the radar system 2 are limited.

[0040] With reference to [Fig. 1], each radar system 2 is ground-based, preferably at a different ground site from those of the optical sensors 3. The surveillance system 1 preferably comprises a small number of radar systems 2 to reduce costs, typically less than 10. A single radar system 2 is described hereafter by way of example.

[0041] As illustrated in Figures 1 and 3, the radar system 2 comprises one or more transmitters with one or more antennas 6 configured to emit a beam 10 of incident radio waves Se, typically at high frequencies above 100 MHz, and preferably below 10 GHz. The radar system 2 also comprises one or more receivers of the radio waves reflected Sr by the space object 5. The radar system 2 is of the directional antenna type 6, i.e., the emitted wave beam 10 has a dominant main lobe and weak or non-existent side lobes. The width of the emitted wave beam 10, namely the width of the main lobe, defines a space observation window 11, known as the "field of regard (FOR)," of the space objects 5 in the Earth's atmosphere.The radar system 2 is also of the type with controllable antenna(s) 6, i.e. the pointing direction Z of the antenna 6 can be oriented by mechanical or electronic scanning to move the spatial observation window 11 into a predetermined field of view 12, known as the "field of view (FOV)".

[0042] Preferably, the field of view 12 covers the low Earth orbit located at an altitude between 200 km and 2000 km above the ground. Also preferably, the field of view 12 has a width a at least five times less than its length e, preferably at least ten times less. Such a field of view 12, typically rectangular in this example or in the shape of a ring sector, has a large amplitude along its length, allowing the antenna 6 to point in many directions. However, an object A spatial object 5 crossing the field of view 12 along its width is only visible for a short time to the radar system 2. Optical sensors 3 detecting the spatial object 5 before it enters the field of view 12 advantageously allow the radar system 2 to estimate its pointing direction. The field of view 12 could alternatively have another shape, such as circular, conical, or similar. Preferably, the wave beam 10 defining the spatial observation window 11 also has an angular width f of less than 5°, preferably less than 2°.

[0043] With reference to Figures 1, 3, and 4, the control unit 4 is connected to the radar system 2 and the optical sensors 3 and is typically ground-based 7. In this single example, the control unit 4 is shown at a different ground location than the radar system 2 and the optical sensors 3. However, it is understood that the control unit 4 could also be located at the same ground location as the radar system 2 or the optical sensors 3. Furthermore, the control unit 4 could also have a modular architecture with modules physically distributed across several ground locations. The control unit 4 is typically in the form of a computer.

[0044] In practice, the control unit 4 is particularly suited to managing the resources of the radar system 2 by determining a sequence of instructions in the form of a query table. Each instruction sequence includes the mode of the radar system 2, namely the "standby" mode, in which the antenna 6 scans the field of view 12, or the "tracking" mode, also known as "pursuit," in which the antenna 6 has a predetermined pointing direction. The standby mode is more energy-intensive than the tracking mode, as it requires a longer transmission and reception time range than the tracking mode, as well as a more energy-intensive wave beam to cover a wider area than the tracking mode. The operation of the control unit 4 is detailed later in the description of the monitoring method according to the invention.

[0045] With reference to [Fig. 5], the monitoring method according to the invention is implemented using the monitoring system 1 described above. Only one space object 5 is considered in this example, but it is understood that the monitoring method aims to enable global monitoring of space traffic in the Earth's atmosphere.

[0046] With reference to [Fig. 5], a first step consists of determining several first positions PI of the spatial object 5 in one or more spatial areas 13 from one or more of the optical sensor set 3. According to a preferred aspect, step 1 also includes determining one or more auxiliary first positions PI' from the auxiliary optical sensors 3'. As illustrated in [Fig. 1], one or more optical sensors 3, 3' acquire one or more photos R at Several instants t1, t2 of the space object 5 in the space zone(s) 13, 13'. The optical sensors 3, 3' correspond to those that are operational, namely located on a terrestrial site not illuminated by a celestial body and with the space object 5 within their field of view b. The photos R are transmitted to the control unit 4. From the photos R, the control unit 4 determines the position of the space object 5 at each instant t1, t2, such positions being referred to as "first positions PI, PI'". Such first positions PI, PI' are conventionally obtained by astrometry, initial orbit determination (IOD) and orbit determination (OD). The first positions PI, PI' are typically expressed as a right ascension and a declination in the equatorial coordinate system.

[0047] With reference to [Fig. 5], a second step consists of determining E2 a first orbit reconstruction 01 of the space object 5 from the first positions PI, PI'. The first orbit reconstruction 01 is a first trajectory estimation of the space object 5 determined by the control unit 4 from the first positions PI, PI' at times t1, t2 determined previously.

[0048] As illustrated in [Fig. 5], from the first orbit reconstruction 01, it is determined where the space object 5 will be visible in the field of view 12 of the radar system 2 to determine whether the predetermined value Zref of the pointing direction Z of the radar antenna 6 is suitable for observing the space object 5. The predetermined value Zref is specific to a space object 5 and has been previously obtained, typically from theoretical or measured data of the space object 5, assuming that the space object 5 follows a Keplerian orbit. An orbit is said to be Keplerian in that its motion relative to the Earth satisfies Kepler's three laws, typically in the form of an ellipse with one of its foci coinciding with the center of mass of the Earth.

[0049] As illustrated in [Fig. 4], if the first orbit reconstruction 01 crosses the field of view 12 of the radar system 2 within the spatial observation window 11 associated with the predetermined value Zref of the pointing direction, the space object 5 does not require special attention and monitoring by the optical sensors 3 is sufficient. With reference to Figures 4 and 5, the subsequent procedure therefore preferably consists of observing the space object 5 E7 solely with the optical sensors 3, 3', determining new initial positions Pl(t4), in order to conserve the resources of the radar system 2.

[0050] As illustrated in Figures 3 and 5, if the first orbit restitution 01 crosses the field of view 12 of the radar system 2 outside the space observation window 11 associated with the predetermined value Zref of the pointing direction Z, the space object 5 has a non-Keplerian trajectory, typically characterized by a past or present maneuver, which should be observed more precisely with the radar system 2. A third step then consists of determining E3 a command C of the pointing direction Z of the antenna 6 of the radar system 2. The command C of the pointing direction Z of the antenna 6 is determined by the control element 4 so that the space observation window 11 is correctly positioned to observe the space object 5. At the end of the fourth step, the antenna 6 has been moved so that its pointing direction Z corresponds to the command C.

[0051] According to a preferred aspect illustrated in Figures 3 and 5, a fourth step then consists of determining E4 one or more second positions P2 of the space object 5 in the space observation window 11 from the radar system 2. The radar system 2 emits a beam 10 of incident radio waves Se in the pointing direction Z of the control C and receives the radio waves reflected Sr by the space object 5. The control element 4 determines the second position(s) P2 at a given time t3 of the space object 5 based in particular on the reception time of the reflected radio waves Sr and the angle formed between the direction of the incident radio waves Se and the reflected radio waves Sr. The second positions P2 are typically expressed in the frame of reference of the radar system 2.

[0052] According to a preferred aspect illustrated in Figures 3 and 5, a fifth step then consists of determining E5 a second orbit reconstruction 02 of the space object 5 from the second positions P2, and preferably the first positions PI, PI'. The second orbit reconstruction 02 is determined by the control unit 4 in a manner analogous to the first orbit reconstruction 01. The second orbit reconstruction 02 is a more precise estimate of the trajectory of the space object 5 than the first orbit reconstruction 01 thanks to the acquisition means used, the radar systems 2, which are more accurate and reliable than the optical sensors 3. Furthermore, the radar systems 2 can be used in all weather conditions, unlike the optical sensors 3.

[0053] The invention thus makes it possible to track space traffic precisely, reliably, and without risk of saturation. The optical sensors 3 advantageously allow for comprehensive and cost-effective monitoring of significant space traffic and the identification of space objects 5 of interest, such as a satellite undergoing maneuvers. Thanks to the optical sensors 3, the pointing direction of the radar system 2 can be determined without resorting to standby mode, which is time-consuming and energy-intensive, thereby saving the resources of the radar system 2.

[0054] Furthermore, in the example of [Fig. 5], the tracking mode of radar system 2 is dedicated to space objects 5 of interest, namely those with non-Keplerian trajectories, which represent less than 60% of space traffic, thus further conserving the resources of radar system 2. According to another embodiment illustrated in [Fig. 7], radar system 2 also determines second positions P2 of space objects 5 having a Keplerian orbit, in order to have global and precise monitoring of all space traffic.

[0055] Faced with the increase in space traffic, the surveillance system 1 according to the invention can also be easily adapted without significant additional cost by increasing the number of optical sensors 3.

Claims

Demands

1. A monitoring system (1) for at least one orbiting space object (5) comprising: • At least one ground-based radar system (2) (7) comprising at least one antenna (6) configured to emit a beam of waves (10) defining a space observation window (11), the antenna (6) comprising a controllable pointing direction (Z) to move the space observation window (11) within a predetermined field of view (12), the pointing direction (Z) having a predetermined value (Zref) associated with the space object (5), • A plurality of optical sensors (3) on the ground (7), each covering a spatial area (13) extending beyond the field of view (12) of the radar system (2), • At least one control unit (4) connected to the radar system (2) and to the plurality of optical sensors (3), the control unit (4) being configured to: • Determine a plurality of first positions (FP) of the spatial object (5) in at least one of the spatial areas (13) from at least one of the plurality of optical sensors (3), • Determine a first orbit reconstruction (01) of the space object (5) from the first positions (PI), • If the first orbit restitution (01) crosses the field of view (12) of the radar system (2) outside the space observation window (11) associated with the predetermined value (Zref) of the pointing direction (Z), determine a command (C) of the pointing direction (Z) of the antenna (6) of the radar system (2) from the first orbit restitution (01), to determine at least a second position (P2) of the space object (5) in the space observation window (11) from the radar system (2).

2. A surveillance system (1) according to claim 1, wherein the space object (5) is adapted to maneuver and is located at a altitude above ground greater than 200 km, and preferably less than 2000 km.

3. Surveillance system (1) according to any one of claims 1 and 2, wherein the field of view (12) of the radar system (2) has a length (e) and a width (a) at least five times less than the length (e), preferably at least ten times less than the length (e).

4. Surveillance system (1) according to any one of claims 1 to 3, wherein the wave beam (10) emitted by the antenna (6) of the radar system (2) has an angular width (f) of less than 5°, preferably less than 2°.

5. Surveillance system (1) according to any one of claims 1 to 4, wherein the plurality of optical sensors (3) are in the form of cameras, preferably adapted to operate in the visible or infrared range.

6. Surveillance system (1) according to any one of claims 1 to 5, comprising at least one ground-based auxiliary optical sensor (3') (7) covering an auxiliary space area (13') extending at least partially into the field of view (12) of the radar system (2), the control member (4) being configured to: • Determine at least one first auxiliary position (PI') of the space object (5) in the auxiliary space area (13') from the auxiliary optical sensor (3'), • Determine the first orbit restitution (01) of the space object (5) from the first auxiliary position (13').

7. A method for monitoring at least one orbiting space object (5) using the monitoring system (1) according to any one of claims 1 to 6, comprising: • Determining (E1) the plurality of first positions (FP) of the space object (5) in at least one of the space zones (13) from at least one of the plurality of optical sensors (3), • Determining (E2) the first orbital recovery (01) of the space object (5) from the first positions (FP), • If the first orbital recovery (01) crosses the field of view (12) of the radar system (2) outside the space observation window (11) associated with the value predetermined (Zref) of the pointing direction (Z), determine (E3) the command (C) of the pointing direction (Z) of the antenna (6) of the radar system (2) from the first orbit restitution (01), to determine (E4) the second position (P2) of the space object (5) in the space observation window (11) from the radar system (2).

8. A monitoring method according to claim 7, also consisting of determining (E5) a second orbital restoration (02) of the space object (5) from the first positions (PI) and the second position (P2).

9. A monitoring method according to any one of claims 7 and 8, also consisting, if the first orbit restitution (01) crosses the space observation window (11) associated with the predetermined value (Zref) of the pointing direction (Z), of observing (E6) the space object (5) only with the plurality of optical sensors (3).

10. A monitoring method according to any one of claims 7 and 8, wherein the step of determining (E4) the second position (P2) of the space object (5) in the space observation window (11) from the radar system (2) is also implemented if the first orbit restitution (01) crosses the space observation window (11) associated with the predetermined value (Zref) of the pointing direction (Z).

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