EP0986728B1 - Method for detecting a projectile point or moment of impact - Google Patents

Description

The invention relates to a method and a system. for the detection of the point or instant of impact of a projectile.

It is often useful to know the position of the point impact of a projectile. This point of impact is usually the ground. However, it can be constituted by another mobile.

The position of the point of impact can be calculated at from the characteristics of the projectile and the conditions of launch. However, in some cases, this calculation is not easy or does not provide satisfactory results. For example, the trajectory of a bomb dropped from an airplane is difficult to calculate. Anyway it is always useful to know, to know preferably in real time, the exact position of the point of impact.

We have already proposed, for staff training, a point of impact detection system for a dropped bomb of an airplane that uses acoustic means. But system is not always reliable, especially because noise of the plane risks disturbing the detection of noise caused by the impact.

Location systems have also been proposed direction finding, using for example three directional antennas rotating, to identify the direction from each antenna where a radio source seems to be emitting, and to locate the point emission by calculation of the point of intersection of the three directions identified. These direction finding methods are very imprecise and require several reception facilities.

Note that it is known from patent application FR-A-2490 802 a goniometry point of impact detection system in which a projectile emits signals until its impact. He is also known to coarse subscriber location systems in satellite communication (US 5,543,813).

The invention allows the realization of a system of detection, in real time, of the point of impact of a projectile which does not have the disadvantages mentioned above and that is with good accuracy.

The system according to the invention is characterized in that the projectile has a device for receiving signals GPS or the like and for transmitting received GPS signals to a remote receiver, and in that the receiver, for example at ground, includes means for periodically determining the position of the mobile from GPS or similar signals received and to detect the position of the impact by extrapolation from, on the one hand, the determination of the moment when the signals from the projectile, and, on the other hand, previous position measurements.

Such a detection system is of course not sensitive to impact noise. The measurement period is by example between 100 ms and 1 second.

By GPS or similar signals is meant here signals which come from satellites or beacons, these signals serving to determine the position and speed of mobiles thanks to the measure the distance between this mobile and satellites or beacons whose positions are known. Each distance is measured from the time between the instant of emission of a signal by a satellite or beacon, from the moment of reception of the same signal by the mobile. The signal from each satellite or tag has a carrier frequency whose value is a parameter used for determining speeds.

It can be noted that today there are two networks of satellites, one of which is assigned to the GPS system itself ("Global Positioning System") and the other to the GLONASS system ("Global Orbiting Navigation Satellite System"). he is also considered the use of geostationary satellites and fixed beacons on the ground.

In each of these systems the satellite emits a signal at a specific time, this instant being a data transmitted by the satellite. The distance is proportional to the time between the instant of emission, supplied by the satellite signal, from the instant of reception by the mobile.

In the GPS system, which will be referred to mainly below, each satellite transmits on a carrier frequency L ₁ equal to 1,575.42 MHz as well as on an auxiliary carrier frequency L ₂ at 1,227.06 MHz.

The carrier frequency, which is also used for speed determination, is modulated by a binary sequence repetitive pseudo-random according to a phase modulation of the type BPSK ("Binary Phase Shift Keying"). Each sequence constitutes a code which, in the case of GPS, has a length of 1023 bits. These codes are issued at a frequency of 1.023 MHz. They coexist with other codes issued at ten times the frequency: 10.23 MHz. The codes, called C / A, at 1.023 MHz allow in principle an approximate position determination while the codes, called P, at a frequency ten times higher, allow a precise location.

The role of each code is threefold: on the one hand, it identifies the transmitting satellite, on the other hand, it facilitates detection and demodulation of signals which are drowned in very high noise, detection being carried out by correlation between the code received from the satellite and an identical code locally produced, and secondly finally, it is used to measure time shifts for calculating distances.

The carrier frequency L ₁ is also coded by other binary data which represent, in particular, the date of transmission of the signal. The satellite being identified and the date of emission of the signal being known, the position of this satellite at the time of emission of the signal is then known with great precision.

For the record, it will be indicated here that in the GLONASS system the carrier frequency L ₁ constitutes the identification of the satellite. It therefore differs from one satellite to another. The frequencies L ₁ range from approximately 1600 MHz to 1615 MHz. A pseudo-random code is also provided in this GLONASS system, but its usefulness is limited to extracting the signal in noise and determining time differences for measuring the distances between receiver and satellite.

The invention also relates to the determination of the instant of impact of a non-destructible projectile.

As for the detection of the point position impact, a device is provided on the projectile reception of GPS or similar signals and re-transmission of these signals to a remote receiver, the remote receiver comprising means for periodically determining the position of the projectile. This projectile and / or the reception and retransmission of non destructible GPS signals during the impact, the moment of impact is extrapolated from the position of the point of impact and at least one position measured previously.

Extrapolation is, in any case, necessary because position determinations are not made continuously but periodically, the period being at least of the order of 100 ms. This sampling period is either fixed or variable. It depends on the speed characteristics and / or projectile acceleration.

On the projectile there are preferably two antennas, namely an antenna for receiving GPS signals at the rear and a transmitting antenna so arranged that the radiation pattern is preferably directed towards forward. The projectile can take orientations variables, in one embodiment, the antenna diagram is strongly omnidirectional.

In an embodiment intended for a projectile drive, the latter has a shell material plastic and it is shaped to participate in the diagram emission radiation. During experiments carried out in within the scope of the invention, it has been found that with an antenna at the rear, the plastic fuselage - which constitutes a dielectric - can increase omni-directionality of the radiation diagram.

• la figure 1 est un schéma d'un projectile avec une antenne pour la réception et la réémission de signaux GPS,
• la figure 2 est un schéma analogue à celui de la figure 1, mais pour deux variantes,
• la figure 3 est un diagramme montrant une interpolation effectuée pour déterminer la position de l'impact d'un projectile,
• la figure 4 est un schéma d'un dispositif destiné à équiper un projectile dont on veut détecter la position de l'impact, et
• la figure 5 est un schéma pour la réception de signaux fournis par un dispositif du type de celui de la figure 4.

Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:

• FIG. 1 is a diagram of a projectile with an antenna for receiving and re-transmitting GPS signals,
• FIG. 2 is a diagram similar to that of FIG. 1, but for two variants,
• FIG. 3 is a diagram showing an interpolation carried out to determine the position of the impact of a projectile,
• FIG. 4 is a diagram of a device intended to equip a projectile whose position of impact is to be detected, and
• FIG. 5 is a diagram for the reception of signals supplied by a device of the type of that of FIG. 4.

The example that we will describe, in relation to the figures, concerns the detection of the impact position of a training projectile such as a bomb dropped from an airplane (not shown).

This training bomb 10 (Figure 1) presents the general shape of a rocket with an elongated body 12 narrowed in point shape 14 forward and fins 16 toward the rear.

Since the path of bomb 10 is from the top downwards the antenna 18, intended to receive the signals of the GPS satellites, is arranged at the back, that is to say towards the high.

In this example, a quadrifilar antenna is provided composed of helically wound wires. We know that such an antenna has good omni-directionality qualities. Alternatively, using a "PATCH" type antenna, formed by one or more conductors on a support.

The GPS antenna is also used to retransmit signals to a ground station (not shown in Figure 1). Although the transmitting antenna is placed at the rear of the bomb 10 when it has to transmit forward, this antenna gives, despite everything, good results because we found that the structure plastic insulator of the bomb 10 participates in the radiation pattern of the transmitting antenna. These results are due to dielectric coupling.

The circuits 20 associated with the antenna 18 are found in the same housing 22 as the antenna 18, at the rear of the bomb 10, substantially along its axis.

In the variant shown in Figure 2, which is preferably provided for emission frequencies higher than 2 GHz approximately, the 18 'antenna for receiving signals GPS satellites are arranged in the same way as the antenna 18 in Figure 1 but the transmit antenna, 24 or 26, is separate of the receiving antenna 18 '.

In a first embodiment, the antenna 24 has the form a belt surrounding the shell 10 at the front of the antenna 18 ', between the latter and the middle zone 28. Such an antenna allows an almost omnidirectional emission without variation of phase or level even if the projectile revolves around its axis. You can also use a plurality of antennas elementary (or "patch") coupled.

In a second embodiment, an antenna 26 is provided. near the nose 14 of the bomb 10, around the hull. This antenna 26 is formed by several elementary antennas coupled. You can also use a belt type antenna. In both cases, the arrangement of the antenna on the part conique avant favors forward transmission.

To determine, on the ground, the location of the impact of the bomb 10, using the signals retransmitted by the antenna 18, or by antenna 24 or 26, we proceed as follows:

A GPS signal receiver, which will be described later in relation to FIG. 5, periodically determines, by example every 200 ms, the position of the mobile and, depending of the measured positions, the path 32 of the mobile. In the example shown in figure 3 the trajectory is in a vertical plane, the Oz axis being vertical and the Ox axis horizontal. For each point of the calculated path 32 we keep in memory the corresponding time as well as the speed and acceleration.

The impact of the mobile on the ground will generally have consequence of destroying the reception electronics and re-transmission of GPS signals. The moment of impact is thus determined by the disappearance of the signals received on the ground.

Detection of the instant of disappearance of signals GPS is carried out using a circuit located either downstream processing circuits providing the GPS signals either upstream of processing, on the carrier of the received signal.

In the first case (downstream of the treatment), a means is provided for continuously measuring the signal-to-noise ratio and the instant of impact corresponds to the instant the signal-to-noise ratio drops below one determined threshold.

In the second case (upstream of the treatment), a circuit is provided which, before treatment, and before correlation, determines the signal level, for example the level of automatic gain control and instant of impact corresponds to the moment when the signal drops below a threshold predetermined, or when automatic gain control exceeds a predetermined limit.

From the trajectory calculated during the reception of GPS signals on the ground and other calculated parameters (speed and acceleration), one can extrapolate the trajectory between the last instant t ₁ of measurement and the instant td of disappearance of the signals GPS. This extrapolation therefore provides the position of the point of impact of the mobile on the ground. Of course the calculation and the extrapolation are carried out in real time.

Alternatively, when the receiver-transmitter circuits GPS signals from the mobile are resistant and are not therefore not destroyed by impact on the ground, the invention makes it possible to simple determination of the moment of impact. Indeed, in in this case, the position of the impact is known. extrapolation will therefore relate to the determination of time and not to the determination of the position.

FIG. 4 represents an exemplary embodiment of reception and retransmission circuits on board the mobile.

In this example, the antenna 18 for receiving GPS signals supplies a signal to the amplifier 112. This amplified signal is applied to the first input 114 ₁ of a member 114, such as a frequency change mixer, of which the second input 114 ₂ receives a local signal supplied by the output 116 ₁ of a generator 116. The local signal applied to the input 114 ₂ has a frequency of 1580 GHz while the signal detected by the antenna 18 is the signal from the GPS carrier at the frequency 1,575.42 MHz.

The signal appearing on the output 114 ₃ of the mixer 114 is at a frequency equal to the difference between the frequencies of the signals applied to the inputs 114 ₁ and 114 ₂ . This signal is applied to a second amplifier 118, then is transmitted to a filter 120 and, from there, is connected to the transmitting antenna 18, directed towards the GPS receiver on the ground.

Figure 5 shows the installation on the ground.

It includes a conventional GPS receiver.

Processing means allow the calculation of the trajectory and the instant of impact and, therefore, the location of this point of impact.

In the example shown, the installation on the ground includes a receiving antenna 142 whose signal is applied to a telemetry receiver 144 which performs functions filtering and amplification classics. The receiver output 144 is connected to a circuit 146 for calculating the trajectory of the mobile.

Furthermore, the installation includes a so-called receiver 148 with its own antenna 150. In a way known, the reference receiver allows, at all times, the comparison between, on the one hand, the distance measured between this receiver on the ground and the satellite and, on the other hand, the distance, known a priori, between this receiver and the satellite. This comparison is used to correct the measurements provided by the cellphone. This type of correction, which allows great precision of the location of the mobile, is called a GPS system differential.

The reference receiver 148 has a clock output 148 ₁ connected to a corresponding clock input 146 ₁ of the circuit 146. It also has an output 148 ₂ providing the reference data on a corresponding input of a calculation circuit 152 of position, speed, acceleration and time, which, with circuit 146, makes it possible to calculate the trajectory. The circuit 146 further comprises an input 146 ₂ receiving a help signal (inertial for example), to improve the performance of attachment and tracking of GPS signals.

Claims (12)

1. Method for determining the position of the impact of a projectile (10), characterized in that, the projectile being equipped with a reception/transmission device for, on the one hand, receiving satellite-positioning signals, transmitted by a group of satellites, which are used to determine the position of the projectile by measuring the distance between it and the satellites, whose positions are known, and, on the other hand, transmitting the received signals to a remote receiver (142-152), the following are determined in the remote receiver:

   periodically, the position of the mobile,

   the time (td) at which the signals transmitted by the transmission device of the mobile disappear, and

   on the basis of at least one position measurement and of measuring the time at which the signals disappear, by extrapolation, the position of the impact.
2. Method according to Claim 1, characterized in that the positions are determined with a period of between 100 ms and 1 second.
3. Method according to Claim 1 or 2, characterized in that the extrapolation used for determining the position of the impact also involves velocity and acceleration.
4. Method according to any one of Claims 1 to 3, characterized in that the time at which the received signals disappear is determined by comparing these signals with a threshold, the time of disappearance corresponding to the moment when a received signal falls below the threshold.
5. Method according to any one of the preceding claims, characterized in that the position-determination signals are of the GPS type or the like.
6. Projectile for implementing the method according to any one of Claims 1 to 5, characterized in that it has a satellite-signal reception antenna (18, 18') which is arranged at the rear of this projectile.
7. Projectile for implementing the method according to any one of Claims 1 to 5, characterized in that it has a signal transmission antenna (18; 24; 26) arranged in such a way that it transmits the signals forwards from the projectile.
8. Projectile according to Claim 7, characterized in that the transmission antenna (18) is arranged at the rear and is coupled to the front by a dielectric.
9. Projectile according to Claim 8, characterized in that the dielectric constitutes the outer casing of this projectile.
10. Projectile according to Claim 7, characterized in that the transmission antenna forms a belt (24) or a ring enclosing the projectile.
11. Projectile according to Claim 10, characterized in that the transmission antenna (26) is arranged at the front of the projectile.
12. Method for determining the time of the impact of a projectile or mobile, characterized in that, the projectile or mobile being equipped with a reception/transmission device for, on the one hand, receiving satellite-positioning signals, transmitted by a group of satellites, which are used to determine the position of the mobile by measuring the distance between it and the satellites, whose positions are known, and, on the other hand, transmitting the received signals to a remote receiver, the following are determined in the remote receiver:

    periodically, the position of the mobile, and

    on the basis of these periodic measurements and of the position of the immobilized mobile, by extrapolation, the time of the impact.

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