Method and device for referencing an artificial satellite in a star ephemeris for the detection of GNSS decoy.

Abstract

This method (PREF) makes it possible to reference at least one artificial satellite (SAT) in a star catalog (CTG) comprising the position of at least one star projected onto a celestial sphere (SC). It comprises: - a step (E10) of obtaining coordinates of an observation location of said at least one artificial satellite (SAT) and orbital parameters (TLE) of said at least one artificial satellite (SAT); - a step (E50) of projecting the satellite (SAT) onto said celestial sphere (SC) according to a direction of view determined from said orbital parameters (TLE) and the observation location; - a step (E80) of recording, in said catalog (CTG), coordinates of the satellite (SAT) projected onto the celestial sphere (CS), the coordinates of the stars and of said at least one artificial satellite (SAT) being expressed in the same geocentric reference frame, called the star catalog reference frame. Fig. 3

Description

Title of the invention: Method and device for referencing an artificial satellite in a star ephemeris for the detection of GNSS decoy.

[0001] The present invention relates to a method and a device for detecting GNSS (Global Navigation Satellite System) decoys, such systems making it possible to determine in particular the position and speed of objects equipped with GNSS receivers using signals emitted by satellites in orbit around the Earth.

[0002] The invention can in particular be used to detect spoofing, namely an attack aimed at deceiving such a positioning system by sending falsified signals to a receiver.

[0003] There are currently decoy detection systems that use a star ephemeris to detect the presence of falsified GNSS signals, for example by comparing the received GNSS signals with the expected positions of these stars, as calculated from the star ephemeris. A decoy device can, for example, be detected if the received signals do not correspond to the expected positions.

[0004] Unfortunately, star finders or other observation devices used to observe stars have optronic performances, generally limited by the technology of the detector used (CMOS), which only allow the observation of the brightest stars, for example of magnitude less than 4. Consequently, current detection systems can only exploit a limited number of stars, which negatively impacts the availability and precision of their measurements.

[0005] The invention aims at a method for improving the detection of decoying, or more generally for improving the detection of a malfunction of a global positioning system. Subject matter and summary of the invention

[0006] [Fig.l] presents geocentric or topocentric reference frames known to those skilled in the art of star or satellite observation and which will be used in certain embodiments of the invention.

[0007] The International Terrestrial Reference Frame [ITRF] is an Earth-bound reference frame, identical to the [WGS84] reference frame, within a few centimeters. The [WGS84] reference frame is created from coordinates of a large number of measuring stations, in a similar way to the [ICRF] reference frame but in an Earth-bound reference frame. This Terrestrial reference frame is used to define geographic longitude and latitude, used in GPS. Its origin is placed at the Earth's center of mass. Its x1TRF axis is oriented along the International Earth Rotation and Reference meridian Systems Service (IERS), a meridian almost equivalent to the Greenwich meridian to within 5.3 arcseconds. Its z1TRF axis is collinear with the axis of revolution of the ellipsoid. The y1TRF axis is defined to define a direct orthonormal reference frame.

[0008] The Terrestrial Intermediate Reference System (TIRS) or Pseudo-Earth Fixed (PEF) reference frame is defined at date t by the equator of the Celestial Intermediate Pole (CIP), i.e. the true celestial pole, and an origin for longitude called the Terrestrial Intermediate Origin (TIO) and noted m. It is a reference frame rotating with the Earth. The PEF reference frame is a geocentric reference frame whose zPEF axis follows the movements of the poles on the Earth's crust. This reference frame is obtained by rotating the ITRF reference frame around the x1TRF and y1TRF axes so that the zPFF axis follows the movement of the poles. Its principal plane PPFF is defined as the true equator at a date t and its xPFF axis defines the intermediate terrestrial origin TIO.

[0009] The TEME (True Equator Mean Equinox) reference frame: a geocentric mean celestial reference frame used to track satellite trajectories around the Earth. Its principal plane PTeme is the true equator at date t and its xTEme axis points towards the mean vemal point (vernal point which does not take nutation into account). Its z teme axis is aligned with the Earth's mean rotation axis, in the direction of the North Pole.

[0010] The SEZ (South-East-Zenith) topocentric reference frame: reference frame linked to the observation location whose axes point towards the South, the East and the Zenith. Its origin Osez corresponds to the position of the observer. Its zSEz axis is aligned with the local vertical in the sense of the WGS84 model, it points towards the zenith of the observer. The SFZ e axis is aligned towards the east, and points in the direction of the horizon to the east of the observer. The sSEz axis is aligned towards the south and points in the direction of the horizon to the south of the observer. Its principal plane PSEZ is tangent to the reference ellipsoid.

[0011] The J2000.0 reference frame: geocentric reference frame Mean Equator / Mean Equinox on January 1, 2000 at 12:00. Star catalogs are expressed in this reference frame. Its xJ2Ooo axis is defined as the vector from the center of the Earth to the mean vemal point at J2000.0 (specific date corresponding to January 1, 2000 at 12:00). Its z nooo axis is the mean celestial pole at J2000.0. It is aligned with the Earth's rotation axis at J2000.0 and points approximately towards the North Polar Star.

[0012] The ICRF (International Celestial Reference Frame) reference system, a 1TCRS project, is constructed from observations of distant quasars by VLB1 (Very Long Baseline Interferometry). Its origin is the barycenter of the solar system, and its axes are fixed relative to these distant objects, quasars, which are assumed to have no angular motion perceptible from Earth.

[0013] The axes of this frame are “non-rotating”, although its center moves over time: it is a pseudo-inertial frame of reference.

[0014] The direction of the axes of the ICRF and J2000.0 reference frames are almost identical to 0.02 arcseconds. The transformation matrix to go from one to the other is called the bias matrix and is:

[0015] ' 1 - daQ 1 . ^0 1

[0016] where da0 = - 14.6 mas (offset on the origin of the right ascension of the ICRS reference frame with respect to the equinox J2000.0), = - 16.6170 mas, and — -6.8192 mas, where 1 mas equals approximately 4.848 136 811 095 4x109 radians).

[0017] The GCRS (Geocentric Celestial Reference System) is today the standard geocentric celestial reference system. It corresponds to a translation of the ICRS heliocentric reference frame constructed from the observation of distant quasars. The xGCRs, yGGRs and zGCRs axes are fixed relative to these distant objects. The xGCRS axis is defined as the direction from the center of the Earth to the intersection of the celestial equator and the GCRS meridian plane. The yGGRs axis is defined as being perpendicular to the xGCRS axis in the GCRS meridian plane, pointing towards the vernal point. The zGCRS axis is defined as being perpendicular to the GCRS meridian plane, pointing towards the north celestial pole.

[0018] The axes of the ICRF and GCRF frames are the same. Only the center changes: GCRF is centered on the Earth, ICRF is centered on the barycenter of the solar system. There is no rotation between the two frames.

[0019] The axes of the GCRS reference frame are close to those of the J2000.0 reference frame at 0.02 arc-seconds. Those skilled in the art may refer in particular to the document “Relativistic celestial mechanics of the solar System, Kopeikin, Efroimsky, & Kaplan, 2011, p. 773” or to the document “Fundamentals of astrodynamics and applications, 4th edition, David. A. Vallado, 2013.” Star catalogs express the coordinates of stars in the J2000.0 or ICRF reference frames in particular.

[0020] According to a first aspect, the invention relates to a method for referencing at least one artificial satellite in a star catalog, this catalog comprising the position of at least one star projected onto a celestial sphere. This method comprises:

[0021] - a step of obtaining coordinates of an observation location of said at least one artificial satellite and orbital parameters of said at least one artificial satellite;

[0022] - a step of projecting the satellite onto said celestial sphere in a direction of aim determined from said orbital parameters and the observation location;

[0023] - a step of recording, in said catalog, coordinates of the projected satellite on the celestial sphere, the coordinates of the stars and of said at least one artificial satellite being expressed in the same geocentric reference frame, called the star catalogue reference frame.

[0024] Correlatively, the invention relates to a device for referencing at least one artificial satellite in a star catalog comprising the position of at least one star projected onto a celestial sphere, this device comprising:

[0025] - a module for obtaining coordinates of an observation location of said at least one artificial satellite and orbital parameters of said at least one artificial satellite;

[0026] - a module for projecting the satellite onto said celestial sphere in a direction of aim determined from said orbital parameters and the observation location;

[0027] - a module for recording, in said catalog, satellite coordinates projected onto the celestial sphere, the coordinates of the stars and of said at least one artificial satellite being expressed in the same reference frame, called the star catalogue reference frame.

[0028] As is known, the celestial sphere is an astronomical concept that allows distant stars to be represented on a sphere of very large arbitrary radius, regardless of their actual distance. For example, but not limited to, a radius of one light year can be used for the celestial sphere.

[0029] Thus, and in general, the invention proposes to exploit the orbital coordinates of artificial satellites to complete a star catalog or ephemeris.

[0030] In a particular embodiment, the geocentric reference frame of the star catalog is the J2000.0, ICRS or GCRS reference frame.

[0031] For example, for ephemerides using the J2000.0 reference system, the equatorial coordinates (a, 5) of the stars are given at a specific date called J2000.0: January 1, 2000 at 12:00, Earth Time. Note that Earth Time differs from the coordinated universal time (UTC) used in everyday life by a certain number of whole seconds called leap seconds, which change each year. The number of stars reported varies depending on the type of catalog; it can reach several million. The transition from the equatorial coordinates of a star at the date J2000.0 to another date and time of observation is done by physical corrections of the movement of the Earth (precession, nutation) and of the stars themselves (proper movement) which are detailed in particular in the article by Meeus, J. (1998) entitled "Astronomical Algorithms" published by "Willmann-Bell".These physical corrections are not detailed here.

[0032] On the other hand, the position of artificial satellites is known in the Earth's geocentric reference frame and is defined by the two-line orbital parameters (TLEs) which correspond to a standardized representation of the orbital parameters of objects in Earth orbit and which are widely disseminated by NORAD (North American Aerospace Defense Command) and NASA.

[0033] In a particular embodiment, the referencing method comprises:

[0034] - a step of determining the coordinates of the artificial satellite in the reference frame TEME from orbital parameters and a date of said observation;

[0035] - a step of determining coordinates of said artificial satellite in the re ITRF reference from the coordinates of the artificial satellite in the TEME reference system, and the position of the Earth's poles;

[0036] - a determination step, from the coordinates of the artificial satellite in the re ITRF reference, of coordinates of the artificial satellite in a topocentric reference frame centered on said observation location;

[0037] - a step of projection of the artificial satellite onto a projection point of the sphere celestial according to a direction of view defined from said coordinates of the artificial satellite in the topocentric reference frame;

[0038] - a step of determining coordinates of said projection point in the re geocentric ITRF ferential; and

[0039] - a step of determining the coordinates of the artificial satellite in the reference frame geocentric of the catalog from said coordinates of said projection point in the ITRF reference system.

[0040] The invention also relates to a star catalog comprising:

[0041] - for at least one object consisting of a star; and

[0042] - for at least one object constituted by an artificial satellite;

[0043] the position of these objects projected onto a celestial sphere,

[0044] the coordinates of the positions of these objects being expressed in the same geocentric reference frame.

[0045] This star catalog can be used in a decoy detection method. It advantageously makes it possible to improve the performance of such methods in that it makes it possible to exploit a much larger number of landmarks, that is to say not only stars but also artificial satellites, in a coordinate system compatible with ephemerides.

[0046] Consequently, and according to another aspect, the invention relates to a method for detecting deception, this method comprising:

[0047] - at least one step of targeting an object recorded in a catalog such as mentioned above, said object being targeted using the coordinates of the position of said object as recorded in said catalog; and

[0048] - if the targeted object is not observed at said position, a step of triggering a decoy alert.

[0049] This target object may be a star or an artificial satellite referenced by a referencing method as presented above.

[0050] Correlatively, the invention relates to a decoy detection device comprising:

[0051] - a module for aiming and observing an object recorded in a catalog such as mentioned above, said object being targeted using the coordinates of the position of said object as recorded in said catalog; and

[0052] - a module for triggering an alert if the object (targeted) is not observed at said position.

[0053] In a particular embodiment, the different steps of the referencing method or the decoy detection method are determined by computer program instructions or are implemented by a silicon chip which comprises transistors adapted to constitute logic gates of non-programmable hard-wired logic.

[0054] Consequently, the invention also relates to a computer program on an information medium, this program being capable of being implemented in a controller computer, this program comprising instructions adapted to the implementation of the steps of a referencing method and / or a decoy detection method as described above.

[0055] This program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0056] The invention also relates to a computer-readable information medium, and comprising instructions of a computer program as mentioned above. The information medium may be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a ROM, a non-volatile memory of the flash type or even a magnetic recording means, for example a hard disk. Furthermore, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention may in particular be downloaded from a network such as the Internet. Alternatively, the information medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question. Brief description of the drawings

[0057] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not in any limiting nature. In the figures:

[0058] [Fig.l] The [Fig.l] already described presents reference systems used in certain embodiments of the invention.

[0059] [Fig.2] [Fig.2] illustrates the projection of an artificial satellite onto a celestial sphere seen from two observation points;

[0060] [Fig.3] [Fig.3] illustrates in the form of a flowchart, the main stages of a a referencing method and a decoy detection method according to embodiments of the invention;

[0061] [Fig.4] [Fig.4] represents the functional architecture of a reference device listing in accordance with a particular embodiment of the invention;

[0062] [Fig.5] [Fig.5] represents the functional architecture of a detection device of decoy conforming to a particular embodiment of the invention;

[0063] [Fig.6] [Fig.6] represents the hardware architecture of a reference device listing in accordance with a particular embodiment of the invention;

[0064] [Fig.7] [Fig.7] represents the hardware architecture of a detection device of decoy in accordance with a particular embodiment of the invention. Detailed description of embodiments

[0065] In the remainder of the description, the coordinates which correspond to the geocentric equatorial coordinates of the targeted object if it were projected onto the celestial sphere from the observation location will be called "equatorial coordinates of the projected object". These coordinates are similar to the standard geocentric equatorial coordinates for stars which are far from the Earth.

[0066] [Fig.2] illustrates, in the ITRF reference system, the projection of an artificial satellite S AT onto a celestial sphere SC seen from two observation points LOI, LO2 of the Earth's surface T.

[0067] In this [Fig.2], we have referenced CT the center of the Earth T and CEI, CE2, the equatorial coordinates of the satellite SAT projected onto the celestial sphere CS from the two observation locations LOI, LO2.

[0068] It appears clearly that these equatorial coordinates CEi are extremely different depending on the observation point LOi.

[0069] [Fig. 3] represents the main steps of a method for referencing at least one satellite in accordance with a particular embodiment of the invention. The referencing of a satellite will be described here, but it can be used in the same way to reference several satellites.

[0070] In the embodiment described here, this method implements a loop comprising steps E10 to E70 to calculate the equatorial coordinates of the satellite projected onto the celestial sphere from an observation point in the same reference frame as the star catalogs and update the CTG catalog (step E80) with these coordinates.

[0071] Note that these coordinates do not correspond to the actual equatorial coordinates of the satellite in the catalog reference system (J2000.0 for example). If these coordinates can be confused for distant stars, for satellites ar In fact, the equatorial coordinates of the projected object depend directly on the observation location.

[0072] This loop is for example implemented every second of observation so as to keep the satellite's referencing up to date in real time. A satellite can thus be treated as a star with zero proper motion for stellar navigation. It is recalled that the proper motion of stars corresponds to their apparent movement on the celestial sphere seen from Earth. The coordinates of stars evolve over time by this proper motion given in star catalogs.

[0073] Subsequently, we will designate R2&t R3 respectively the rotations of axes x, y and z.

[0074] During a step E10, we obtain: - the coordinates of the observation location of the artificial satellite SAT. These coordinates include, for example, the geodetic latitude ^^of this location, its longitude 2 and its altitude; - the current date of observation f^rc in the Coordinated Universal Time (UTC) format; - the two-line TLE orbital parameters of the artificial satellite as updated daily by NORAD; the position of the poles XP and PP on the Earth's crust at that time, as determined by TIERS (International Earth Rotation and Reference Systems Service).

[0075] During a step E20, the coordinates of the artificial satellite SAT are determined in the TEME reference frame, from the orbital parameters TLE and the observation date in coordinated universal time. For this, we use, for example, the SGP4 algorithm provided by David Vallado, and available at http: / / celestrak.org / software / vallado-sw.php.

[0076] Those skilled in the art may also refer to the algorithm (C code) detailed in the reference Vallado, David A.; Paul Crawford; Richard Hujsak; TS Kelso (August 2006). “Revisiting Spacetrack Report #3”. Astrodynamics Specialist Conference or to the document “Félix R. Hoots, Ronald L. Roehrich, SPACETRACK REPORT NO. 3 Models for Propagation of NORAD Element Sets. December 1980” which presents the SGP4 algorithm from a theoretical point of view.

[0077] We will note t the instant of observation. This instant can be expressed in different time scales, indicated by subscript, according to the definition of the time considered in the different changes of reference points: in UTC time scale noted Turkish, in terrestrial time scale noted Fr.

[0078] By noting Turkish the coordinated universal time civil time and TLE the orbital parameters of the artificial satellite in Turkish time we obtain the coordinates rTEME{ / ) of the satellite in the TEME reference frame:

[0079] rTEME{ t) = SGP4(TLE, tUTC) (D

[0080] During a step E30, from the coordinates of the artificial satellite in the TEME reference frame, and from the position of the poles XP and PP, the coordinates of the satellite in the ITRF reference frame are calculated.

[0081] We first perform a rotation of angle Qgmst along the axis zTEME of angle GMST (in English Greenwich Mean Sidereal Time) calculated at the instant of observation, to bring the axis xTEME towards xPEE.

[0082] It is recalled that the GMST angle (mean sidereal time) corresponds to the angle between the mean vemal point and the Greenwich meridian.

[0083] In this embodiment, the equation provided by the book “Fundamentals of Astrodynamics and Application” by David A Vallado (1997), page 188 is used:

[0084] 0cwsr= (67310.54841+ (8766000*3600 + 8640184.812866)* 7OTI + 0.093104^,-6.210^^,)¾¾ (2)

[0085] With:

[0086] - &GMst in rac^

[0087] - TUTl the date in Julian centuries since January 1, 2000, expressed as a function of the Julian date UTl

[0088] T _ 77),,^,-2451545.0 1 UT - 36525

[0089] The coordinates rPEE( t ) of the satellite in the PEF reference frame are obtained by a rotation R3 along the axis zTEME of angle Oqmst

[0090] rpEF(t}—

[0091] The coordinates r1TRE( t ) of the satellite are obtained by a rotation of the RPEE reference frame along the yPEE and xPEE axes by angles ~xp and Ap to bring the zPEE axis perpendicular to the true equator towards the mean axis of rotation of the Earth considered in ITRF.

[0092] Eitrf ( / ) = -y -XpjrPE^

[0093] During a step E40, the coordinates of the satellite are defined in a topocentric reference frame relative to the observation location (for example LOI). As explained with reference to [Fig.2], the viewing angles impact the equatorial coordinates of the projected satellite.

[0094] In one embodiment, we place ourselves in the SEZ topocentric reference frame.

[0095] Alternatively, we place ourselves in another topocentric reference frame, for example in the Northwest-Zenith reference.

[0096] We first calculate the ITRF vector defined by the center of the Earth and the observation location as a function of the latitude, longitude and altitude of this location. We then calculate the vector 1 iTRFt<>P<> going from the observation location to the artificial satellite:

[0097] rITRFtopo—rITRF~ rsite^

[0098] We then apply a rotation to this vector around the z1TRF axis by an angle 2, the longitude of the observation location to align the x1TRF axis with the south axis.

[0099] A rotation is then performed along the y1TRF axis by an angle of 90 - with the geodesic latitude of the observation location to align the z1TRF axis with the zenith axis. [° 10 °l ( t )= R^R^ - ¢)

[0101] where rSE^t) corresponds to the vector connecting the observation location to the satellite expressed in the South-East-Zenith topocentric reference frame.

[0102] During a step E50, the artificial satellite SAT is projected onto the celestial sphere SC in the direction of sight. The topocentric SEZ vector is arbitrarily multiplied by 1 light year to obtain the coordinates in the SEZ reference frame of the projected satellite. [01031

[0104] In [Fig.2], the direction of sight is the straight line (LOI, SAT).

[0105] During a step E60, the change of reference frame is then carried out in reverse to that carried out in step E40 to determine the coordinates of the point targeted by the SEZ vector extended in the ITRF geocentric reference frame.

[0106] The coordinates thus determined are the geocentric ITRF coordinates of the satellite projected onto the celestial sphere SC from the observation location. These coordinates allow it to be assimilated to a star in the context of stellar navigation at the observation location.

[0107] nTRFpr.{>) )7?3(-2)rsEZ^,(0 +rsiteS^

[0108] The addition of 7 sites in the equation is actually not important. After extension of the SEZ vector, the geocentric and topocentric vectors of the projected satellite become assimilable.

[0109] Therefore, equivalently:

[0110] rITRFf,fO,(î) -(f -0g))^3(-^)^2,,,,, / (^)

[0111] During a step E70, the coordinates of the satellite projected onto the celestial sphere SC are obtained in a coordinate system used by the star catalogs.

[0112] For example, the coordinates of the satellite are determined in the GCRS reference frame. We note that this GCRS reference frame is close to the J2000.0 reference frame at 0.02 arc seconds. In the context of satellite tracking where this position precision is not achieved, these two reference frames can be confused.

[0113] In the embodiment described herein, this conversion is performed using the Ter2Cel algorithm from the Novas (Naval Observatory Vector Astrometry Software) library, Kaplan et al. (2012), available at https: / / ascl.net / 1202.003. Other methods described in the Kaplan (2011) or Meeus (1998) references mentioned above can be used.

[0114] This algorithm allows to move from the ITRF reference frame to the GCRS reference frame according to the position of the celestial poles XP and y P relative to the terrestrial poles, the precession, the nutation (parameters Ô8, Ôip provided by TIERS), the Turkish coordinated universal time and the terrestrial time G provided by TIERS.

[0115] Two equivalent methods are possible to achieve this change of reference by Ter2Cel: Equinox-based transformation and ClO-based transformation. A different change of reference can be applied depending on the desired final reference. [01 16] rGCRsJ$ = Ter2CelNOVJ^ Xp, yp, tUT, &, <9)

[0117] In the embodiment described here, the coordinates of the artificial satellite SAT are stored in the star catalog CTG during a step E80. This satellite SAT can thus be treated as a star with zero proper motion for stellar navigation.

[0118] The CTG catalog can be used by a PDL decoy detection method according to the invention.

[0119] In accordance with the invention, this catalog includes both positions of stars (natural celestial objects) and positions of artificial satellites SAT projected onto the celestial sphere CS. The coordinates of these different objects OBJi are expressed in the same reference frame.

[0120] During a step E90, an observation instrument (star finder, telescope, etc.) obtains the coordinates of an object (star or artificial satellite) recorded in the catalog and aims at this object according to the coordinates of this object recorded in the CTG catalog to observe it.

[0121] When the targeted object is detected at the expected position, the result of a test E100 is positive, and another object from the catalog is targeted during a new iteration of step E90.

[0122] On the contrary, if the targeted object is not in the expected position, the result of the test E100 is negative, a decoy alert is triggered during a step E1 10, because jamming signals may be the cause of the disturbance of the instrument's measurements.

[0123] [Fig.4] represents the functional architecture of a DREF referencing device according to the invention. It makes it possible to reference artificial satellites in a star catalogue (or ephemeris) which includes the position of at least one star projected onto a celestial sphere.

[0124] This DREF device comprises an M10 input module configured to obtain the pa parameters necessary for the implementation of the invention, and in particular the coordinates / l) of an observation location of an artificial satellite, its orbital parameters TLE, and the observation date.

[0125] The DREF device also comprises a module M50 configured to determine the coordinates of the artificial satellite in the different reference frames, using for example the equations (1) to (9) described previously. This module M50 is in particular configured to calculate the projection of an artificial satellite onto the celestial sphere according to a direction of view determined from its orbital parameters TLE and the observation location.

[0126] The DRE device further comprises an M80 module for recording in a star catalogue, the coordinates of the satellite projected onto the celestial sphere, the coordinates of the stars and of said at least one artificial satellite being expressed in the same geocentric reference frame.

[0127] [Fig.5] represents the functional architecture of a DDL decoy detection device according to the invention.

[0128] The DDL device comprises an M90 module for aiming and observing an object recorded in a star catalogue comprising objects consisting of stars and artificial satellites.

[0129] The DDL device comprises a module Ml 10 to trigger an alert if the targeted object is not observed at the position recorded in the star catalog.

[0130] [Fig. 6] represents the hardware architecture of a DREF referencing device according to the invention. In the embodiment described here, the DREF referencing device has the hardware architecture of a computer. It comprises a processor 10, a ROM type read-only memory 11, a random access memory 12, a rewritable non-volatile memory 13 and communication means 14.

[0131] The ROM type read-only memory 11 constitutes a recording medium within the meaning of the invention. It comprises a computer program PGREF comprising instructions for executing the steps of a referencing method in accordance with the invention when this program is executed by the processor 10.

[0132] [Fig. 7] represents the hardware architecture of a DDL decoy detection device according to the invention. In the embodiment described here, the DDL decoy detection device has the hardware architecture of a computer. It comprises a processor 20, a ROM type read-only memory 21, a random access memory 22, a rewritable non-volatile memory 23 and communication means 24.

[0133] The ROM type read-only memory 21 constitutes a recording medium within the meaning of the invention. It comprises a PGDL computer program comprising instructions for executing the steps of a decoy detection method in accordance with the invention when this program is executed by the processor 20.

Claims

Claims

1. Method (PREF) for referencing at least one artificial satellite (SAT) in a star catalogue (CTG) comprising the position of at least one star projected onto a celestial sphere (SC), this method comprising: - a step (E10) of obtaining coordinates of an observation location of said at least one artificial satellite (SAT) and orbital parameters (TLE) of said at least one artificial satellite (SAT); - a step (E50) of projecting the satellite (SAT) onto said celestial sphere (SC) according to a direction of view determined from said orbital parameters (TLE) and the observation location; - a step (E80) of recording, in said catalogue (CTG), coordinates of the satellite (SAT) projected onto the celestial sphere (CS), the coordinates of the stars and of said at least one artificial satellite (SAT) being expressed in the same geocentric reference frame, called the star catalogue reference frame.

2. Method (PREF) of referencing according to claim 1, characterized in that said geocentric reference frame of the star catalog is the J2000.0, ICRS or GCRS reference frame.

3. Method (PREF) of referencing according to claim 1 or 2, characterized in that it comprises: - a step (E20) of determining coordinates ) of said artificial satellite (SAT) in the TEME reference frame from said orbital parameters (TLE) and a date ( of said observation; - a step (E30) of determining coordinates (rjTRF) of said artificial satellite (SAT) in the ITRF reference frame from the coordinates ) of the artificial satellite in the TEME reference frame, and the position (xP-> PP) of the poles of the Earth; - a step (E40) of determining, from the coordinates (r1TFp) of said artificial satellite (SAT) in the ITRF reference frame, coordinates (rSEz) of the artificial satellite (SAT) in a topocentric reference frame centered on said observation location;- a step (E50) of projecting the artificial satellite (SAT) onto a projection point of the celestial sphere (SC) according to a direction of sight defined from said coordinates (rSEZ) of the artificial satellite (SAT) in the topocentric reference frame; - a step (E60) of determining coordinates sr \ of said projection point in the ITRF geocentric reference frame; and - a step (E70) of determining coordinates rçGCRS of the artificial satellite (SAT) in the geocentric reference frame of the catalog (CTG) from said coordinates 1 of said ITRF projection point in the ITRF reference frame.

4. Star catalog (CTG) comprising: - for at least one object (OBJ;) consisting of a star; and - for at least one object (OBJ;) consisting of an artificial satellite (SAT); the position of said objects (OBJ;) projected onto a celestial sphere (SC), the coordinates of the positions of said objects (OBJ;) being expressed in the same geocentric reference frame.

5. Method (PDL) for detecting decoying comprising: - at least one step (E90) of targeting an object (OBJi) recorded in a catalog according to claim 4, said object (OBJi) being targeted using the coordinates of the position of said object (OBJi) as recorded in said catalog (CTG); and - if the targeted object (OBJi) is not observed at said position, a step (E100) of triggering a decoy alert.

6. Device (DREF) for referencing at least one artificial satellite (SAT) in a star catalogue (CTG) comprising the position of at least one star projected onto a celestial sphere (SC), this device comprising: - a module (M10) for obtaining coordinates 2^ of an observation location of said at least one artificial satellite (SAT) and orbital parameters (TLE) of said at least one artificial satellite (SAT); - a module (M50) for projecting the satellite (SAT) onto said celestial sphere (SC) according to a direction of view determined from said orbital parameters (TLE) and the observation location; - a module (M80) for recording, in said catalogue (CTG), coordinates of the satellite (SAT) projected onto the celestial sphere (CS), the coordinates of the stars and of said at least one artificial satellite (SAT) being expressed in the same geocentric reference frame, called the reference frame of the star catalogue.

7. Device (DDL) for detecting decoy comprising: - a module (M90) for aiming and observing an object (OBJi) recorded in a catalog according to claim 4, said object (OBJi) being aimed using the coordinates of the position of said object (OBJi) as recorded in said catalog (CTG); and - a module (M1 10) for triggering an alert if the object (OBJi) aimed at is not observed at said position.

8. Computer program (PGREF, PGDL) comprising instructions for executing the steps of the referencing method according to any one of claims 1 to 3 and / or instructions for executing the steps of the decoy detection method according to claim 5 when said program is executed by a computer.

9. Computer-readable recording medium (11, 21) on which a computer program (PGREF, PGDL) according to claim 8 is recorded.

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