Solid propellant thruster with integrated control means and thruster aging control system

Abstract

The invention relates to a solid propellant thruster comprising a casing (12) housing a propellant charge (14), an axial channel (16) being formed in the propellant charge (14) and allowing the combustion of the propellant charge (14), the casing (12) carrying a propellant specimen (24) disposed in the channel (16) and a transducer (28) disposed outside the casing (12) and opposite the specimen (24) so ​​as to allow the emission of a vibrational stimulus through the specimen (24) and the transmission of a response thereto. Figure for the abstract: Fig. 1.

Description

Title of the invention: Solid propellant thruster with integrated control means and thruster aging control system

[0001] The invention relates to a solid propellant thruster with integrated control means and a thruster aging control system.

[0002] Many rocket-type ballistic devices employ the combustion of a solid propellant to deliver a thrust force ensuring their movement.

[0003] Ballistic missiles, after their manufacture, can be stored for periods that are sometimes very long, even several years. It is important to know the condition of the propellant before its use in order to verify that it is fit to perform its function, and to assess the level of safety inherent in its operation.

[0004] It is possible to define the apparent age of the propellant corresponding to a level of aging actually observed. This makes it possible to evaluate the remaining service life of the ballistic missile using the propellant.

[0005] Solid propellants contain both a fuel and an oxidizer, and knowledge of certain mechanical characteristics of the propellant, such as Young's modulus or shear modulus, makes it possible to estimate its apparent age. These mechanical characteristics can be determined from the material's response to vibrational stress.

[0006] It is known, notably from document FR 2 954 498 A1, to implement a test device containing, in a housing, a propellant sample and a vibratory system. The test device can be placed near the ballistic missile or even inside it, in order to attempt to obtain comparable aging for the ballistic missile and the test device.

[0007] However, the test device described in document FR 2 954 498 A1 is not suitable for industrial use. The applicant has identified several drawbacks: - The device is heavy and bulky inside the propulsion unit. - The environmental conditions of the propellant sample in the test device are not the same as those of the propellant in the engine due to the sample being confined within the test device housing. In particular, the oxidation of the sample does not occur at the same rate as that of the propellant in the engine. - The installation of the test device inside the thruster results in the presence of an electrical power source within the thruster. This presents a risk of the thruster igniting during a sample testing phase. - The presence of components other than propellant inside the propulsion unit can disrupt its operation.

[0008] The invention aims to overcome all or part of the problems mentioned above by proposing a solid propellant thruster equipped with a test specimen allowing, from outside the thruster, to emit a vibratory stimulus through the specimen and to transmit a response.

[0009] To this end, the invention relates to a solid propellant thruster comprising a casing housing a propellant charge, an axial channel being made in the propellant charge and allowing the combustion of the propellant charge, the casing carrying a propellant test specimen disposed in the channel and a transducer disposed outside the casing and opposite the test specimen so as to allow the emission of a vibratory stimulus through the test specimen and to transmit a response thereto.

[0010] Advantageously, the channel extends between two axial ends of the propellant, the envelope having a passage orifice for the test specimen communicating with the channel at one of its ends.

[0011] Advantageously, the propellant further comprises a disc fixed to the casing at the orifice and having an inner face oriented towards the channel and on which the test specimen is fixed, and an outer face oriented opposite the channel and on which the transducer is fixed.

[0012] Advantageously, the casing has a cylindrical recess in which the disc is housed, the passage orifice of the test specimen being provided in the bottom of the cylindrical recess.

[0013] Advantageously, the test specimen is fixed to an inner face of the disc by means of an adhesive.

[0014] The propellant charge may include a polymer binder and the glue is advantageously based on the same polymer binder.

[0015] Advantageously, the propellant of the test specimen is identical to that of the load.

[0016] Advantageously, the transducer includes electrical connections allowing to receive a first signal configured so that the transducer emits the vibratory stimulus and allowing to recover a second signal representative of the response of the specimen to the vibratory stimulus.

[0017] The invention also relates to an aging control system for a propulsion system according to the invention, comprising an electronic module configured to: - temporarily connect to the transducer, - to emit an initial signal towards the transducer, enabling it to generate the vibratory stimulus, - receive a second response signal from the transducer, - deduce from the received signal a parameter representative of an aging state of the propellant charge.

[0018] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which:

[0019] [Fig.1] schematically represents a solid propellant propulsion system according to the invention;

[0020] [Fig.2] represents in more detail components allowing testing of the propellant of the [Fig.1] engine.

[0021] For the sake of clarity, the same elements will bear the same references in the different figures.

[0022] Figures 1 and 2 schematically represent a propellant 10, for example, used in a ballistic missile. The propellant 10 comprises, within a casing 12, a solid propellant charge 14. The solid propellant contains both a fuel and an oxidizer. The propellant is, for example, a composite propellant based on a polyurethane binder, as described in French patent FR 3 108 331 B3 filed in the name of the applicant. The invention is not limited to this type of propellant, and any type of propellant can be used within the scope of the invention.

[0023] The combustion of the propellant provides the thrust of the propulsion unit, and the casing 12 must withstand the pressure and temperature due to combustion. To withstand the combustion temperature, thermal protection can be integrated between the casing 12 and the propellant charge. To withstand the pressure, various materials can be used, such as a metallic material like steel or a carbon fiber-based material. Other materials can be used, and other constraints besides pressure and temperature may be considered later for the implementation of the invention.

[0024] A longitudinal channel 16, extending along an axis 18, is made in the propellant charge 14. The channel 16 extends between two axial ends 20 and 22 of the propellant 10. One of the ends 20 of the channel 16 is here obstructed by a disk 26 and the other end 22 of the channel 16 forms a nozzle through which the combustion products of the propellant providing the propulsion are ejected.

[0025] According to the invention, the propellant 10 comprises a propellant test specimen 24 disposed in the channel 16 and fixed here on an inner face 27 of the disc 26. The propellant test specimen 24 is advantageously made of the same propellant as that of the propellant loading 14. Alternatively, it is possible to use for the test specimen 24 a propellant different from that of the loading 14 but having similar physical properties, in particular in terms of aging.

[0026] The propellant 10 further includes a transducer 28 fixed to an outer face 30 of the disk 26 and positioned opposite the test specimen 24 so as to allow the emission of a vibrational stimulus through the specimen 24 and the transmission of a response. The channel 16 can be directly formed in the propellant charge 14. In this case, the test specimen 24 is advantageously bare. More precisely, the propellant in the specimen 24 as well as that in the charge 14 are directly exposed to the air in the channel 16. Thus, the propellant in the charge 14 and that in the test specimen 24 react in the same way to the environment of the channel 16. More specifically, during the storage of the propellant 10, variations in temperature and humidity may occur. These two parameters are crucial in the aging of the propellant. Other parameters may also come into play, such as pressure, but are a priori less decisive.However, exposing the propellant of load 14 and that of test specimen 24 to the same environment allows for the consideration of all types of environmental parameters. This identical exposure also makes it possible to adapt to different propellant compositions that may age differently depending on the environment; by using the same material for the propellant of load 14 and that of test specimen 24, they will age similarly because they are exposed to the same environmental conditions.

[0027] Figure 2 shows in more detail the transducer 28, the disk 26, and the test specimen 24. The transducer 28 is located on the outer face 30 of the disk 26, which carries the test specimen 24 on its inner face 27, here parallel to the outer face 30, and is configured to induce a vibrational stimulus in the test specimen 24. The vibrational stimulus is obtained, for example, by means of an ultrasonic acoustic wave emitted by the transducer 28 and passing through the disk 26 and the test specimen 24. A steel disk 26, in particular, has good properties for transmitting an ultrasonic vibrational stimulus. More generally, the material of the insert formed by the disk 26 is chosen so that it can transmit a mechanical stimulus while being less subject to the risk of aging, unlike the propellant.

[0028] The test specimen 24, in the example shown in Figures 1 and 2, has two parallel faces, one 32 in contact with the inner face 27 of the disk 26 and the other 34 free and exposed to the air present in the channel 16. The vibrational stimulus emitted by the transducer 28 passes through the test specimen 24 for the first time from its face 32 to its face 34, is reflected at least partially on the face 34, passes again through the disk 26 to be received by the transducer 28. The path of the vibrational stimulus, called the forward path, from face 32 to face 34 is indicated by an arrow 36, and the path of the vibrational stimulus, called the return path, from face 34 to face 32 is indicated by an arrow 38. Other shapes of the test specimen 24 are possible for implementation the invention. Faces 32 and 34 may be non-parallel. Faces 32 and 34 are not necessarily flat. For example, the inner face 27 of the disk 26 on which the specimen 24 is placed may not be flat and it is advantageous that the face 32 of the specimen 24 conforms to the shape of the inner face 27 in order to promote the transmission of the vibratory stress directly from the disk 26 to the specimen 24 without passing through a possible air gap that may be between the inner face 27 of the disk 12 and the face 32 of the specimen 24.

[0029] The thickness of the disc 12 allows it to withstand the temperature / pressure couple prevailing in the combustion chamber but, as needed, a thermal protection sheet can be interposed between these two faces 27 and 32 to thermally protect the disc 26, without this fundamentally disturbing the acoustic principle of the system.

[0030] Advantageously, the test specimen 24 is bonded to the inner face 27 of the disk 26, while the transducer 28 is bonded to the outer face 30 of the disk 26. Thus, no mechanical component likely to disturb the vibrational stress is present in the fixings of the test specimen 24 and the transducer 28. The bonding also limits the formation of an air gap between the inner face 27 of the disk 26 and the face 32 of the test specimen 24 by completely diffusing between faces 27 and 32. The same applies on the side of the transducer 28. The propellant may comprise a polymer binder, as described, for example, in French patent FR 3 108 331 B3. It is then advantageous to use an adhesive 39 based on the same binder as that used in the propellant to fix the test piece 24 on the inner face 27 of the disc 26, or even the transducer 28 on its opposite face 30.This type of adhesive helps to minimize disruption to the propagation of vibrational stress at the interface between the adhesive and the propellant.

[0031] Alternatively, bonding the test specimen 24 directly onto the inner face of the envelope 12 is conceivable with an envelope obstructing the end 20 of the channel 16.

[0032] The disc 26 can be attached to the casing in various ways. Here, it is housed in a cylindrical recess 29 in the casing 12 and fixed to it by screwing (not shown in the figures for the sake of simplicity). The bottom 31 of the recess 29 has an opening 33 to allow the test specimen 24 to pass through. Alternatively, it is also possible to mechanically clamp the disc 26 to the outer face of the casing 12.

[0033] A sealing gasket 35 is also interposed between the disc 26 and the casing 12, being housed here in a groove 37 made in the disc 26.

[0034] In Figures 1 and 2, the transducer 28 is shown as a single-piece component configured to emit a vibrational stimulus and to receive a response to the emitted vibrational stimulus. In practice, it is possible to distinguish the The device has two functions: transmission and reception of the vibrational stimulus. A first component transmits the stimulus, and a second receives the vibrational stimulus reflected by face 34 after passing through specimen 24. The transducer 28 can generate the vibrational stimulus using a piezoelectric ceramic. This type of ceramic also receives the reflected wave, which forms the response to the vibrational stimulus, and outputs a corresponding electrical signal.

[0035] In the illustrated embodiment, the transducer 28 includes electrical connections 40 for temporarily connecting the transducer 28. The electrical connections 40 and the transducer 28 are located outside the enclosure 12, thus preventing any electrical signal from entering the enclosure to operate the transducer 28. Only the vibrational signal enters the enclosure 12. The electrical connections 40 allow connection to an electronic module 42, shown here as a personal computer. The electronic module 42 can be connected to the transducer 28 by means of a cable 44. Alternatively, the electronic module 42 can be connected to the transducer 28 by means of a wireless link.

[0036] The electronic module 42 is configured to generate and transmit a signal to the transducer 28, enabling it to induce vibration. The electronic module 42 is also configured to receive a response signal from the transducer 28, a signal corresponding to the vibration response of the test specimen 24.

[0037] The electronic module 42 is configured to analyze the response signal from the transducer 28 and deduce a parameter representative of the aging state of the propellant in the test specimen 24, and therefore of the aging state of the propellant in the load 14. This deduction is made, for example, by comparing the received signal with stored signals representative of different aging states. It is also possible to determine certain mechanical parameters of the propellant, such as its Young's modulus or its shear modulus, from the vibrational response. The changes in these mechanical parameters provide information on the aging state of the propellant.

[0038] It will be noted in this regard that the provisions according to the invention make it possible to determine the remaining service life of a propellant without in particular needing to know the conditions in which the propellant was stored in order to determine the aging state of the propellant.

Claims

Claims

1. Solid propellant thruster comprising a casing (12) housing a charge of propellant (14), an axial channel (16) being made in the charge of propellant (14) and allowing the combustion of the charge of propellant (14), the casing (12) carrying a test piece (24) of propellant arranged in the channel (16) and a transducer (28) arranged outside the casing (12) and facing the test piece (24) so ​​as to allow the emission of a vibratory stress through the test piece (24) and to transmit a response therefrom.

2. Propellant according to claim 1, in which the channel (16) extends between two axial ends (20, 22) of the propellant (10), the casing (12) having an orifice (33) for the passage of the test piece (24) communicating with the channel (16) at one of its ends (20).

3. A thruster according to claim 2, further comprising a disc (26) fixed to the casing (12) at the orifice (33) and having an internal face (27) oriented towards the channel (16) and on which the test piece (24) is fixed as well as an external face (30) oriented away from the channel (16) and on which the transducer (28) is fixed.

4. Propellant according to claim 3, in which the casing (12) has a cylindrical recess (29) in which the disc (26) is housed, the orifice (33) for the passage of the test piece being formed in the bottom (31) of the cylindrical recess (29).

5. Propellant according to one of claims 3 and 4, in which the test piece (24) is fixed on an internal face (27) of the disc (26) by means of an adhesive (39).

6. A propellant according to claim 5, wherein the propellant charge (14) comprises a polymer binder and wherein the glue (39) is based on the same polymer binder.

7. Propellant according to one of the preceding claims, in which the propellant of the test piece (24) is identical to that of the charge (14).

8. Propellant according to one of the preceding claims, in which the transducer (28) comprises electrical connections (42) making it possible to receive a first signal configured so that the transducer (28) emits the vibratory stress and making it possible to recover a second signal representative of the response of the test piece (24) to the vibratory stress.

9. System for controlling the aging of a thruster (10) according to one of the preceding claims, comprising an electronic module (42) configured to: - temporarily connect to the transducer (28), - emit a first signal to the transducer (28) allowing it to form the vibratory stress, - receive a second response signal from the transducer (28), - deduce from the received signal a parameter representative of an aging state of the load (14) of the thruster (10).

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