FR3056305A1 - FLIGHT IN TRAINING OF AEROSPATIAL VEHICLES - Google Patents

Abstract

Flight in aerospace vehicle formation A primary aerospace vehicle (SM), capable of communicating with one or more secondary aerospace vehicles (SE1, SE2, ..., SEi, ..., SEN) of an aerospace vehicle formation (10). ), comprising an antenna configured to receive GNSS signals, a digitizer configured to digitize the GNSS signals received by the antenna, a communication system configured to receive data including GNSS signals digitized by one or more secondary aerospace vehicles, and transmitting data including flight instructions for one or more secondary aerospace vehicles and an on-board GNSS signal processor configured to determine a training navigation state based on the digitized GNSS signals from the digitizer as well as those from, via the communication system, one or more aerospace vehicles of the f raining. The invention will be of interest to all stakeholders interested in aerospace training flights.

Description

Technical Field [0001] In general, the invention relates to aerospace vehicles designed to be able to fly in formation under the supervision of a particular aerospace vehicle.

Technological background The realization of a formation flight by aerospace vehicles is a subject which is very much studied at present. In particular, training flights in complete safety and independently could open the way to the realization of a multitude of applications such as, for example, space or airborne telescopes with a large aperture, very spaceborne or airborne interferometers precise, synthetic aperture radars, complex maneuvers by aerospace vehicles, etc.

Document US 2010/0032528 describes a system for controlling the deployment of at least two spacecraft intended to move in formation under the control of ground stations. Each machine is connected to a ground station by a communication link. The maneuvers to be performed by each spacecraft are determined on the ground in order to place the formation in a chosen configuration. The instructions for carrying out the maneuvers are sent separately to each machine by the ground stations.

The objective of the present invention is to overcome the drawbacks of existing solutions.

General description of the invention [0005] According to one aspect of the invention, aerospace vehicles are configured to allow a global approach to the supervision and / or management of training so that the implementation of the control system as well as the training management is not significantly more complicated or expensive than that of a single aerospace vehicle.

In the context of this document, the expression "aerospace vehicles" includes space vehicles (eg satellites, probes, etc.) as well as aeronautical vehicles (eg drones, planes , etc.). The term "primary aerospace vehicle" refers to an aerospace vehicle responsible for one or more other aerospace vehicles assigned to it, called "secondary aerospace vehicles". Secondary aerospace vehicles can be supervised and / or managed by the primary aerospace vehicle. The aerospace vehicles covered by this document are designed to fly in formation, that is, to perform a coordinated flight. Preferably, the secondary aerospace vehicles of the formation are distant, at most 500 km, preferably at most 100 km, more preferably at most 50 km, even more preferably at most 10 km, from the primary aerospace vehicle.

A first aspect of the present invention relates to a primary aerospace vehicle, capable of communicating with one or more secondary aerospace vehicles of an aerospace vehicle formation. The primary aerospace vehicle includes an antenna configured to receive radio navigation signals also called GNSS signals (GNSS ("Global Navigation Satellite System" in English)), a digitizer configured to digitize the GNSS signals received by the antenna, a configured communication system for receiving data comprising GNSS signals digitized by the one or more secondary aerospace vehicles and for transmitting data comprising flight instructions for the one or more secondary aerospace vehicles and an onboard GNSS signal processor. The on-board GNSS signal processor is configured to determine a navigation state of the formation on the basis of the digitized GNSS signals coming from the digitizer as well as those coming, via the communication system, from one or more aerospace vehicles of the formation. .

A GNSS signal corresponds to a radio navigation signal emitted by a GNSS satellite (GPS, GLONASS, Galileo, ...) in a certain frequency band. The GNSS signal includes a carrier modulated by a code, data (except in the case of a pilot signal), and, optionally, a subcarrier. The carrier is sinusoidal at a certain frequency (for example at a frequency of 1575.42 MHz in the frequency band L1). The code is a pseudo-random binary code (“Pseudo-Random Noise (PRN) sequences” or “PRN code” in English) identifying the transmitting satellite. The data include navigation data comprising, for example and among others, ephemerides of the transmitting GNSS satellite and “almanac” type data on the GNSS constellation. The modulation of the carrier by the pseudo-random binary code and the data causes the spectrum to be spread around the (central) frequency of the carrier (for example, for a signal of GPS code C / A, the spread around the center frequency is 1575.42 ± 1.023 MHz for the main lobe). The pseudo-random codes of the different GNSS satellites are orthogonal, which results in a code division multiple access (TDMA) system to the frequency resource shared by all GNSS satellites (i.e.

carrier frequency).

On reception (in our case at the level of a primary or secondary aerospace vehicle), the GNSS signals emanating from the “visible” GNSS satellites (ie.

not eclipsed from the receiving antenna) are mixed. Their reception and processing includes several stages, the first comprising digitization (possibly after transposition to an intermediate frequency) by a radio frequency head stage ("RF front end" in English) equipped with an analog-digital converter. After digitization follows the acquisition and tracking step, which is carried out on several processing channels in parallel for different GNSS signals, and which produces observables, eg code observables, phase observables, etc. . Observables are processed in a navigation stage, configured to estimate position, speed and / or time.

In the context of the present invention, the GNSS signals digitized and transmitted by the one or more secondary aerospace vehicles correspond to the GNSS signals delivered by an analog-digital converter of the radiofrequency head stage, before any subsequent processing of acquisition or prosecution. The data packets containing the digitized GNSS signals transmitted to the primary aerospace vehicle of the formation can be understood as "snapshots" of the GNSS signals received raw in a certain frequency band, taken by the secondary aerospace vehicles of the formation during a certain interval of time. In practice, GNSS signal processing equipment on board an aerospace vehicle can be limited to an antenna and a radiofrequency head stage ("RF front end") equipped with an analog-digital converter.

The communication system can be any wireless communication system suitable for communication between aerospace vehicles. According to one embodiment of the invention, the communication can be carried out on a radiofrequency band, through radiofrequency antennas present on each aerospace vehicle of the formation. According to a preferred embodiment of the invention, the communication system of the primary aerospace vehicle is an optical communication system, comprising a laser for transmitting the data and an optical receiver for receiving the data. The data to be transmitted to one or more secondary aerospace vehicles may include, for example, flight instructions. Flight instructions may include, for example, controls for propulsion system actuators, solar panel actuators to deploy the panels in a certain direction, etc. The data, coming from one or more secondary aerospace vehicles, to be transmitted to the primary aerospace vehicle notably include the digitized GNSS signals (the "snapshots" mentioned above).

By "navigation state" of the formation, we mean all the positions of the aerospace vehicles of the formation. Optionally, the navigation state can also include, among other things, speeds and / or accelerations of one or more (and preferably all) aerospace vehicles of the formation. According to one embodiment of the invention, the physical quantities related to the navigation state (positions, speeds, etc.) are relative quantities with respect to a reference aerospace vehicle of the formation. The reference vehicle is preferably the primary aerospace vehicle. It will be appreciated that the navigation state of the formation is determined centrally on the primary aerospace vehicle. In fact, any processing of GNSS signals relating to the determination of the navigation state of the formation (eg acquisition / pursuit stages, etc.) downstream of the digitization of GNSS signals (which is carried out on all training vehicles), is executed centrally on the primary aerospace vehicle. In other words, only the primary aerospace vehicle has a full GNSS receiver. It goes without saying that the GNSS receiver is more developed than a standard GNSS receiver, since it must be able to support the GNSS signals received by all the antennas

GNSS distributed on aerospace training vehicles.

According to one embodiment of the invention, the aerospace vehicles of the formation each include several antennas configured to receive GNSS signals in space. The use of several GNSS antennas on an aerospace vehicle of the formation makes it possible to determine the attitude (the orientation iso in space) of this aerospace vehicle within the framework of the determination of the navigation state of the formation.

Preferably, the GNSS signal processor of the primary aerospace vehicle is configured to determine the navigation state using known constraints on training. A determination under constraints makes it possible, among other things, to limit the number of possible solutions for the navigation state. In other words, a determination of the navigation state of the training under constraints makes it possible to significantly increase the precision of the determined navigation state. These constraints may include, for example, previous positions of aerospace vehicles in the formation, positions obtained by ancillary systems (for example by telemetry and / or through the optical communication means). According to one embodiment of the invention, the constraints include approximate positions and speeds (absolute or relative) of the aerospace vehicles of the formation.

The determination of the navigation state may include a demodulation of the GNSS signals received in order to obtain code and phase observables. The different GNSS signals can be combined to obtain observables of other types. E.g. there are possibilities of making “iono-free” observables. Estimation of navigation status may also include the use of differences between GNSS signals received by different aerospace vehicles in the formation (simple differences between receivers). Another example of relative navigation state determination includes making differences between GNSS signals from different GNSS satellites (simple differences between GNSS satellites). There is also the possibility of observing "double differences" corresponding to differences between GNSS signals from different GNSS satellites and different receivers.

According to one embodiment of the invention, the signal processor

GNSS of the primary aerospace vehicle is configured to determine the navigation state of the formation by the real-time kinematic method. This method uses doubly differentiated carrier phase observables. The kinematic method in real time can be the variant with mobile base îo ("Moving baseline real-time kinematics (RTK)" in English) or the variant with fixed base, if there is a reference station on the ground. The carrier signal being at high frequency, it makes it possible to achieve high accuracy in determining the navigation state. The RTK method determines relative physical quantities (for example the relative positions) with respect to a reference station (which can be an aerospace vehicle of the formation). In the case where the aerospace vehicle of the formation serves as the reference station, it is preferable to combine, as part of the determination of the navigation state, the RTK method with a determination of at least the absolute position from the reference station.

According to one embodiment of the invention, the primary aerospace vehicle comprises an on-board computer configured to communicate, via the communication system, with the one or more secondary aerospace vehicles of the training in order to coordinate and / or supervise the training based, among other things, on the navigation status of the training. Coordination of training can include, for example, "day-to-day" management of training in accordance with higher level guidelines. These higher level instructions can be, for example, a particular geometry (static or dynamic) to be observed. Such instructions can be set and transmitted by a ground station and the primary aerospace vehicle then acts so as to maintain this geometry. The primary aerospace vehicle can, for example, send instructions to a secondary aerospace vehicle to deploy its solar panels in a certain direction. The primary aerospace vehicle may also, for example, request a report on the operational and / or health status of a component of a secondary aerospace vehicle (eg on its propulsion). It will be appreciated that the primary aerospace vehicle can be considered as the nerve center of the formation, at least as regards the coordination of the formation flight.

According to one embodiment of the invention, the on-board computer of the primary aerospace vehicle is configured to assign (add) a secondary aerospace vehicle to the training or to decommission (remove) a secondary aerospace vehicle from the training, optionally based on data relating to the operating state of the secondary aerospace vehicle considered.

The primary aerospace vehicle preferably comprises a single internal clock, shared with each of its components, and an on-board computer or the on-board GNSS signal processor. The unique shared clock provides a time stamp for events taking place on board the aerospace vehicle (e.g. scientific measurements, reports of operations) in a consistent and unique way to the aerospace vehicle. The on-board computer or on-board GNSS signal processor is configured to determine a bias between a clock in an aerospace vehicle (primary or secondary) of the formation and a reference clock. According to an advantageous embodiment of the invention, this bias can be determined by virtue of the GNSS signals received by the vehicles of the formation (i.e. thanks to the stereotypes of the GNSS signals received by the formation). Preferably, all the biases between the clocks and the reference clock are determined. According to a preferred embodiment of the invention, the reference clock is the clock of the primary aerospace vehicle. According to another embodiment of the invention, the reference clock can be that of a secondary aerospace vehicle of the formation. The clock on the primary aerospace vehicle is adapted to the restrictions imposed by aerospace vehicles. It can be, for example, a quartz clock or an atomic clock (for example a maser, an ion trap, etc.) or the like.

A second aspect of the present invention relates to a secondary aerospace vehicle, capable of communicating with a primary aerospace vehicle of an aerospace vehicle formation, comprising an antenna configured to receive GNSS signals, a digitizer configured to digitize the GNSS signals received by said antenna, a communication system configured to transmit data comprising digitized GNSS signals to the primary aerospace vehicle and to receive data comprising flight instructions from the primary aerospace vehicle. According to an advantageous embodiment of the invention, the digitizer is configured to dynamically adapt its operating parameters, such as its sampling frequency, in order to free up, for example, bandwidth for other data to be transmitted. (for example data collected by an instrument forming part of the payload of the secondary aerospace vehicle).

According to one embodiment of the invention, the communication system of the secondary aerospace vehicle is an optical communication system comprising a laser for transmitting data comprising GNSS signals and an optical receiver for receiving data comprising instructions for theft of the primary aerospace vehicle.

Preferably, the secondary aerospace vehicle comprises an on-board computer as well as a single internal clock, shared with the components of the secondary aerospace vehicle. The on-board computer is preferably configured to time stamp, using the clock, the data to be transmitted. The time stamp may include, for example, a number of ticks since the clock was put into service, GNSS signals received, etc. The clock on the secondary aerospace vehicle is adapted to the restrictions imposed by aerospace vehicles. It can be, for example, a quartz clock or an atomic clock (for example a maser, an ion trap, etc.) or the like. According to a preferred embodiment of the invention, all the data that the secondary aerospace vehicles transmit to the primary aerospace vehicle are time-stamped.

According to a preferred embodiment of the invention, each aerospace vehicle (primary or secondary) of the formation is equipped with a single internal clock. This configuration allows each aerospace vehicle to time stamp all the measurements or observations made there using this clock.

In particular, each aerospace vehicle is preferably configured to time stamp the GNSS signals digitized using this clock. As the digitized GNSS signals allow GNSS time to be determined, it will be possible to precisely determine the bias of each clock with respect to time

GNSS and therefore indicate the GNSS time for any measurement carried out on any of the training vehicles. Thanks to this configuration, a major problem of distributed measurement systems is therefore resolved or at least considerably reduced.

A third aspect of the present invention relates to software for controlling the formation of aerospace vehicles, stored on a computer support, comprising commands, which, when executed by computer hardware comprising a processor. GNSS signals, cause the GNSS signal processor to implement a method comprising determining the navigation state of a formation of aerospace vehicles on the basis of digitized GNSS signals originating from the formation. Computer equipment may also include an on-board computer.

According to one embodiment of the invention, the software further comprises commands, which, when executed by the computer hardware, cause the computer hardware to determine a bias between a single internal clock present on an aerospace vehicle and a reference clock.

Preferably, all the biases between each clock of the formation and the reference clock are determined.

A fourth aspect of the invention relates to aerospace vehicle training which comprises a primary aerospace vehicle according to the first aspect of the invention, one or more secondary aerospace vehicles according to the second aspect of the invention. In addition, the on-board computer of the primary aerospace vehicle is preferably configured to execute software, according to the third aspect of the invention, loaded into computer hardware.

According to one embodiment of the invention, the formation of primary and secondary aerospace vehicles is a formation of planes or drones.

According to another preferred embodiment of the invention, the formation of primary and secondary aerospace vehicles is a formation of satellites.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and characteristics of the invention will emerge from the detailed description of certain advantageous embodiments presented below, by way of illustration, with reference to the appended drawings which show:

Fig. 1: a constellation of satellites flying in formation comprising several slave satellites under the control of a master satellite;

Fig. 2: a possible structure of a master satellite and a slave satellite;

Fig. 3: a schematic representation of the different processing channels of the GNSS signal processor present on the master satellite;

îo Fig. 4: a graphical representation of measurements made on different satellites of the formation and the determination of the delays between each clock of the formation and the clock of the master satellite.

Detailed description of several embodiments of the invention [0029] FIG. 1 illustrates a constellation 10 of satellites flying in formation 18.

According to a preferred embodiment of the invention, this constellation 10 comprises a primary or master satellite and one or more secondary or slave satellites. In the following, and without limiting the scope of the invention, a preferred embodiment of the invention will be described in which the constellation 10 is composed of Λ / slave satellites SE), SE2, ..., SE /,. .., SE / v, numbered from 1 to N (where Λ / is a positive integer, i = 1, 2, N). The master satellite SM is responsible for the management and / or supervision of the training 18. In other words, the master satellite coordinates the constellation. The slave satellites SE / relay to the master satellite SM, via a wireless communication link 22, all the raw data relating to them, for example, the state of health and / or functioning of their components, one or more indicators of their positioning, received and digitized radio navigation signals, etc. All the data is processed on the master satellite SM, which, as a function of this data, sends, via a wireless communication link 22, flight instructions to the slave satellites SE / of the formation 18. These instructions may include, for example , instructions for the propulsion actuators in order to correct a deviation of the position of one or more satellites to the desired geometry of the formation 18. By way of example in FIG. 1, the SE / v satellite deviates from the formation 18. The constellation is said to be “autonomous”, in the sense that the management is carried out and centralized by the master satellite SM and not satellite by satellite, for example, by agents in ground stations, or as described in document US 2010/0032528. According to a particular embodiment of the invention, the geometry of the formation 18 is a star, the master satellite SM being at the center of the formation 18 (as shown in FIG. 1). According to a particular embodiment of the invention, the SE slave satellites; are arranged around the master satellite SM on an ellipse. According to a preferred embodiment of the invention, the geometry of the formation 18 is a close formation ("cluster training" in English). In the close formation considered in the preferred embodiment of the invention, the distance between the satellites is typically a few kilometers.

The master satellite SM comprises a radiofrequency antenna 12 for establishing and / or maintaining a communication link 20 with a ground station 16 also comprising a radiofrequency antenna 14. Even if the constellation 10 is autonomous, a station at ground 16 can communicate with it and in particular send it instructions through the master satellite SM in order to, for example, change the formation geometry 18. It will be appreciated that, from the point of view of the ground station 16, the constellation 10 can be managed as a single satellite.

SE slave satellites; can be designed in such a way as to embark only the bare minimum outside the payload ("payload" in English) so that their design and launch are as inexpensive as possible. This reduction in mass also offers the advantage of increasing the chances of being able to launch these SE slave satellites; in slots reserved for satellites called nanosatellites or microsatellites. The absence of a control center on board the SE slave satellites; provides a better payload to total mass ratio of the satellite. Control is delegated to the master satellite SM. A slave satellite SE; is therefore unable to function alone and even less manage, alone, its formation flight within a constellation. It will be appreciated below that the delegation of control is advantageous for the coordination of the constellation 10. It will also be appreciated below that the delegation of control is advantageous for reducing the redundancies of components in the training (for example Λ / processors GNSS signals, Λ / protective boxes for GNSS processors, etc.).

The payload as well as the other components of the SE slave satellites; are determined according to the function and / or mission within the constellation 10. The satellites can include, for example, a telescope, cameras (IR, UV, ...), a radar, a propulsion module specific to their needs , etc. Provided that the navigation state of constellation 10 is precisely known, the elements of the payload, for example the telescopes, can work together to achieve equivalent performance and probably exceeding that of a single satellite comprising a single large telescope (ie a satellite with a large payload). Indeed, disturbances (for example vibrations) coming from ancillary components in the payload of the single satellite (for example a very powerful propulsion necessary to maintain in orbit) can hinder other components (telescopes, interferometers, ...) . The constellation 10 of satellites is also much more diverse because the geometry of the formation 18 thereof can change, if necessary.

The master satellite SM can be considered as the nerve center of training 18. Indeed, the master satellite centralizes all the data received, generated, captured, etc. by formation 18. In particular, the master satellite SM centralizes all the GNSS signals 24 received by formation 18 after digitization. On the basis, inter alia, of these GNSS signals received 24, the master satellite determines the navigation state of the formation 18. The navigation state comprises, among other things, the positions and the speeds of the satellites of the formation 18. Optionally , the navigation state can also include the acceleration of the satellites in formation 18.

[0034] FIG. 2 shows a possible structure of a master satellite SM and a slave satellite SE ;. Each satellite in the constellation can include a power supply module 32 comprising, for example, solar panels, batteries, etc. Each satellite can also include an environmental control module 34 having the function of facilitating or prohibiting heat exchanges passively or actively, a propulsion system 36 and a system of control of orbit and altitude 38 ( SCOA for "Altitude and Orbital Control

System (AOCS) "in English) including, for example, solar collectors, star collectors, reaction wheels, etc. According to another embodiment of the invention, the satellites of the constellation comprise only part of the components mentioned in the preferred embodiment. According to another embodiment of the invention, the components (including the payload 42) may be different from satellite to satellite of the constellation and include other or none of the components mentioned above.

The determination of the navigation state of the constellation is based on the reception of GNSS 24 signals emitted by transmitters of an positioning system (for example satellites of the GPS constellation, Galileo,

GLONASS, ...) and their interpretation. To do this, the satellites in the constellation each include a radio frequency antenna 26 receiving GNSS signals 24. The GNSS signals 24 received are digitized in an RF head stage 30. The slave satellites SE / transmit to the master satellite SM, via a link communication 22 established by a communication system 28, the GNSS signals 24 received and digitized. The GNSS signal processor 48, present on the master satellite SM deduces the navigation state of the constellation on the basis of the GNSS signals 24 received by the constellation. Alternatively, all GNSS signals can be transferred, via the radio frequency antenna (12, see Fig. 1) from the master satellite SM, to the ground station for determining the navigation state of the constellation. It should be noted that the master satellite SM can also send, via the radio frequency antenna (12, see Fig. 1), data other than the GNSS signals 24 received for processing on the ground by the station. In this case, the master satellite SM acts as an aggregator of information for the satellite constellation.

The constellation satellites include a radio frequency (RF) head stage 30 (“RF front end” in English), connected to the antenna 26 which receives the GNSS signals 24 in one or more frequency bands used for the signal transmission, reduces the frequency of signals (normally to an intermediate frequency) and converts them to digital format using an analog-to-digital converter. The converter is preferably configured to dynamically adapt its operating parameters (such as the sampling frequency or the number of frequencies sampled) according to the available bandwidth of the communication system. According to a preferred embodiment of the invention, the RF head stage 30 reduces the central frequency of the GNSS signals 24 to an intermediate frequency (Fl, "IF" in English). According to embodiments of the invention, the bit rate of the digitized GNSS signals can vary between 2 M bits / s and 1200 M bits / s depending, among other things, on the operating parameters of the converter. The raw GNSS signals 24, received by a slave satellite SE / of the constellation and passed through the RF head stage 30, are sent to the master satellite SM via the communication system 28.

The determination of the navigation state, comprising the processing of the raw GNSS signals coming from the slave satellites of the constellation, is, therefore, deported to the master satellite SM, on which is embedded a GNSS signal processor 48 The master satellite SM receives all the signals

GNSS raw of the constellation through the communication system 28. The GNSS 48 signal processor determines the navigation state. It includes a baseband processing stage including GNSS signal acquisition / tracking channels. The baseband processing stage determines a set of GNSS observables (for example, carrier phase measurements, code measurements) through demodulation of the carrier and, among other things, the use of the pseudo-random binary code. GNSS observables are determined in parallel on the different channels. The number of channels of the GNSS signal processor 48 can be chosen high enough to allow the processing of all GNSS signals of the constellation simultaneously. Alternatively, the number of channels of the GNSS signal processor 48 can be chosen according to the one or more missions to be performed by the constellation satellites. A schematic representation of the channels 44 for processing GNSS signals is given in FIG. 3.

Downstream of the acquisition / tracking stage is a stage called the navigation stage or navigator. At this stage, observables and possibly navigation data extracted from GNSS signals are combined (eg in an extended Kalman filter or by a least squares method, etc.) to provide an estimate of the navigation state. 46. That includes, eg, position, speed, and time, etc. of each satellite in the constellation.

The number of channels allocated to one satellite may be different from the number of channels allocated to another (for example M channels for the master satellite and p channels for the first slave satellite, see FIG. 3) according to, among other things, the number of signals received by the satellite in question. For example, 32 double channels for the GPS and Galileo navigation systems, could process the GNSS signals received by the master satellite SM and each time 8 channels, for the GPS navigation system, could process the GNSS signals received by io the SE / slave satellites. Channel allocation can change over time, as needed. It will be appreciated that an advantage of the invention lies in the fact that a single cryptographic module for all the training is sufficient to determine the navigation state of the training on the basis of encrypted GNSS signals.

A priori knowledge of constraints on the formation, for example on the geometry of the constellation (ie a priori knowledge of the approximate positions of each satellite of the constellation) makes it possible to substantially increase the precision of the estimation of the navigation state 46 of the constellation. As an example, the navigation stage could implement a Kalman filter (extended) whose model supplemented by the set of constraints and / or a priori knowledge of the constellation allows the increase in the precision of the results given in the browser. It will be appreciated that the determination of the navigation state of the constellation is made in a global manner, and not in isolation satellite by satellite. According to a preferred embodiment of the invention, the position and the speed of the master satellite is determined in a terrestrial or geocentric reference frame and the positions as well as the speeds of the slave satellites are determined relatively with respect to the master satellite.

The determination of the navigation state 46 for the slave satellites of the constellation may be based (among other things) on the kinematic method in real time. The carrier signal is at a higher frequency than the code signals allowing a more precise determination of the navigation state of the constellation. This embodiment of the invention can be particularly advantageous in the event of close formation, in which the satellites generally have the same GNSS satellites in view. Optionally, measurements with ancillary systems, for example telemetry measurements, can be used to increase the accuracy, for example, of the positioning of the constellation satellites.

With reference to FIG. 2 and according to an advantageous and preferred embodiment of the invention, the communication system 28 is an optical communication system comprising a laser and an optical receiver. The benefit of an optical communication system is twofold. In fact, compared to radiofrequency communication, optical communication makes it possible, first of all, to avoid interference with radiofrequency signals and therefore to increase electromagnetic compatibility (“Electromagnetic compatibility (EMC)” in English) as well. both locally at the constellation of satellites and globally at the level of international management of the radio frequency spectrum. Secondly, this communication system makes it possible to achieve high data rates for a size, weight and reduced and / or low power (“low Size, Weight and Power” or “low SWaP” in English). to the radio frequency system.

The onboard computer 40 of the master satellite SM is also configured to determine flight instructions to be executed by the slave satellites SE /. These instructions are determined based, among other things, on the navigation status of the constellation. The instructions may include, for example, commands to restore conformity of the actual geometry of the formation with the desired geometry. These commands may include, for example, an actuation order for the actuators of a propulsion system of a slave satellite SE / in order to restore the conformity of the geometry of the formation. The instructions determined on the master satellite SM are sent by the master satellite to the slave satellites SE / via the communication system 28. The instructions are executed by an on-board computer 40 of the slave satellite SE /.

Preferably, the onboard computer of the master satellite SM is configured to deactivate a slave satellite SE / on the basis, among other things, of information on the state of health transmitted by the slave satellite SE /. Indeed, when the slave satellite SE / is no longer able to perform its function (for example when its propulsion 36 is faulty), it becomes useless in training and the master satellite decommissioned the SE satellite, from training. The on-board processor is configured to assign a new SEy slave satellite (/ # /) available for training and give it, for example, the position of the old faulty SE satellite, in the constellation.

Preferably, each satellite of the constellation includes an internal clock 50, unique and shared with each component of the satellite. All components of a satellite have access to the same clock to time stamp, for example, scientific measurements 49, data describing the state of health of a component, a signal notifying a defective RF antenna, etc., and , in particular, the GNSS signals received and digitized 52. All the events taking place on a formation satellite are therefore time-stamped by the on-board computer in a coherent and unique manner. Fig. 4 represents measurements 49 of components of two satellites SE, and SEy over time thanks to the time stamp 51 provided by their respective internal clocks 50. The data transmitted to the master satellite, via the communication system 54, includes, in the illustrated case, scientific measurements 49 and the digitized GNSS signals 52 received in parallel with the measurements 49. Preferably, the on-board computer time stamps all the data to be transmitted .

The processor of the onboard computer 40 of the master satellite SM performs synchronization of the internal clocks of all the satellites. This synchronization is possible because the digitized GNSS signals transmitted by each slave satellite make it possible to determine exactly the instant of their reception on the antenna in GNSS time (eg in GPS time) and therefore also the moment of their reception. timestamp using the internal clock. All the internal clocks of the satellites are thus referenced with respect to GNSS time (i.e. their biases and possibly their drifts are known with respect to a clock indicating GNSS time). As shown in FIG. 4, the processor of the on-board computer 40 can optionally determine a bias Δ (56 between the internal clock 50 of a slave satellite SE, of the constellation and the clock of the master satellite SM. In this case the clock of the master satellite SM can serve as a reference clock, which is also calibrated on GNSS time. Optionally, the clock of the master satellite SM could be set on GNSS time by a loop of The clocks of the slave satellites could also be set to GNSS time or be slaved to the clock of the master satellite. In this case, the clock corrections (the adjustment commands) would be determined by the computer's processor. on board 40 of the master satellite SM and transmitted to the slave satellites SE via the communication means. When all the clocks are synchronized (ie when all the biases of the clocks 50 are determined és), all measurements 49 and events recorded by the formation (on any satellite thereof) are dated (or at least datable) in a single time reference io (GNSS time and / or the time indicated by l 'reference clock).

While particular embodiments have just been described in detail, those skilled in the art will appreciate that various modifications and alternatives to these can be developed in the light of the overall teaching provided by the present disclosure of the invention. Consequently, the specific arrangements and / or methods described herein are intended to be given by way of illustration only, without the intention of limiting the scope of the invention.

Claims (15)

Claims 1. A primary aerospace vehicle (SM), capable of communicating with one or more secondary aerospace vehicles (SEi, SE2, SE /, SE / v) of a formation of aerospace vehicles (10), comprising an antenna (12) configured for receiving GNSS signals (24); a digitizer (30) configured to digitize the GNSS signals received by said antenna; a communication system (28) configured to receive data comprising GNSS signals (24) digitized by the one or more secondary aerospace vehicles (SE1, SE2, SE /, ..., SEn) and to transmit data comprising instructions flight for one or more secondary aerospace vehicles; and an on-board GNSS signal processor (48) configured to determine a navigation state of said formation based on digitized GNSS signals from the digitizer as well as those from, via the communication system, one or more aerospace vehicles of said training. 2. The primary aerospace vehicle (SM) according to claim 1, in which the determination of the navigation state of the formation is made using known constraints on the formation (10). 3. The primary aerospace vehicle (SM) according to any one of claims 1 and 2, configured to determine the navigation state by the kinematic method in real time with a mobile base. 4. The primary aerospace vehicle (SM) according to any one of claims 1 to 3, wherein said communication system (28) is an optical communication system comprising a laser for transmitting data comprising flight instructions to one or more several secondary aerospace vehicles and an optical receiver for receiving data comprising digitized GNSS signals coming from one or more secondary aerospace vehicles (SEî, SE2, ..., SE /, ..., SE / v). 5. The primary aerospace vehicle (SM) according to any one of claims 1 to 4, comprising an on-board computer (40) configured to communicate, via the communication system (28), with the one or more secondary aerospace vehicles ( SEî, SE2, ..., SE /, ..., SEn) of said formation in order to coordinate said formation on the basis, inter alia, of said navigation state of the formation. 6. The primary aerospace vehicle (SM) according to claim 5, wherein the on-board computer (40) is configured to decommission a secondary aerospace vehicle (SEî, SE2, SE /, SEn) of said formation or to assign an aerospace vehicle secondary to said training. 7. The primary aerospace vehicle (SM) according to any one of claims 1 to 6, comprising a single internal clock (50) and in which the on-board computer (40) or the on-board GNSS signal processor (48) are configured so as to determine a bias between a clock of an aerospace vehicle of said formation and a reference clock, the reference clock preferably being the clock of the primary aerospace vehicle. 8. A secondary aerospace vehicle (SE1, SE2, ..., SE /, ..., SEn), capable of communicating with a primary aerospace vehicle (SM), according to any one of claims 1 to 7, d ' an aerospace vehicle formation (10), comprising an antenna (26) configured to receive GNSS signals (24); a digitizer configured to digitize the GNSS signals received by said antenna; a communication system (28) configured to transmit data including digitized GNSS signals to the primary aerospace vehicle (SM) and to receive data including flight instructions from the primary aerospace vehicle (SM). 9. The secondary aerospace vehicle (SEî, SE2, ..., SE /, ..., SEn) according to claim 8, wherein said communication system (28) is an optical communication system comprising a laser for transmitting data comprising GNSS signals and an optical receiver for receiving data comprising flight instructions from the primary aerospace vehicle (SM). 10. The secondary aerospace vehicle (SEî, SE2, ..., SE /, ..., SEn) according to any one of claims 8 and 9, comprising an on-board computer (40) as well as a single internal clock (50), the on-board computer (40) being configured to time stamp, thanks to the clock (50), the data to be transmitted. 11. A computer program product comprising program code instructions stored on a computer-readable medium, comprising: 5 - computer-readable programming means for determining the navigation state of an aerospace vehicle formation (10) on the basis of digitized GNSS signals originating from said formation, when said program operates on a computer comprising a GNSS signal processor (48). 10 12. The computer program product of claim 11, further comprising program code instructions recorded on a computer readable medium comprising - computer-readable programming means for determining a bias between a single internal clock (50) present on a vehicle 15 aerospace and a reference clock, when said program is running on said computer comprising a GNSS signal processor (48). 13. An aerospace vehicle formation (10) characterized in that it comprises 20 a primary aerospace vehicle (SM) according to any one of claims I to 7; and one or more secondary aerospace vehicles (SEî, SE2, .... SE /, ..., SE / v) according to any one of claims 8 to 10; wherein an on-board computer of the primary aerospace vehicle (40) is 25 configured to run software according to any one of claims II and 12, loaded into computer hardware. 14. The formation of aerospace vehicles (10) according to claim 13, in which the primary (SM) and secondary aerospace vehicles (SEî, SE2, SE /, .... SE / v) are airplanes or drones. 30 15. The formation of aerospace vehicles (10) according to claim 13, in which the primary (SM) and secondary aerospace vehicles (SEî, SE2 ..... SE /, ..., SE / v) are satellites. 1/4