TECHNICAL FIELD

The present invention concerns a solid propellant rocket motor.

BACKGROUND ART

As is known, solid propellant motors are used both in the military field and in the field of space launchers.

In both applications, the known motors comprise an outer casing, which houses a predefined annular mass of solid propellant and is closed at the opposite ends by two closing heads distinct from the casing.

One of said heads carries an ignition device for igniting the solid propellant while the other supports a nozzle for outlet of the exhaust gases resulting from combustion of the propellant inside the casing.

Loading of the solid propellant in the casing, assembly of the heads and connection of the heads to the casing and any subsequent storage are generally performed in sites or on different platforms normally well away from the launch platform.

Both in the storage period and during transport towards the launch platform and in any case for the entire launch preparation phase on the same platform, external causes such as an increase in temperature, an impact or an electrostatic discharge, for example, can cause a sudden and uncontrolled ignition of the solid fuel with devastating effects in terms of financial losses or loss of human life. For this reason, the heads are initially coupled to the casing by means of distinct temporary connecting elements with predefined breaking points which, in the event of spontaneous ignition, rupture due to the action generated by the pressure of the gases inside the casing, permitting an increase in the outflow section of the gases towards the outside. This reduces the pressure inside the motor combustion chamber and, consequently, the thrust generated.

When all the preparatory operations have been positively completed on the launch platform, the temporary connecting elements are removed and replaced with permanent structural elements which permanently connect the heads to the casing, enabling the motor for flight.

The removal of the temporary connecting elements and assembly of the permanent ones involves complications and obliges the technicians in charge to work in difficult conditions exposed to risks.

A condition of safety at spontaneous ignition is never fully achieved when several motors are stacked on top of one another, as in the case of multistage launchers. In said cases, in fact, the permanent connecting elements must be inserted before stacking one motor on top of the motor below which, at this point, is ready for ignition and therefore has the same problems as described before concerning prevention of the effects of spontaneous ignition.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a solid propellant rocket motor which solves the above problems simply and inexpensively.

According to the present invention, a solid propellant rocket motor is provided, as claimed in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting implementation example thereof, in which:

figure 1 illustrates, schematically and in section, a preferred embodiment of the solid propellant rocket motor according to the present invention;

figure 2 is a view according to the arrow A of figure 1 ;

figure 3 is a perspective view, on a highly enlarged scale, of a detail of figures 1 and 2;

figure 4 is a section, on an enlarged scale, according to the line IV- IV of figure 2 ;

figures 5 and 6 are figures analogous to figure 4 and illustrate a detail of figure 4 in two different functional positions ;

figure 7 illustrates, on an enlarged scale, a detail of figure 3 ; and

figure 8 illustrates schematically, in a perspective view and on an enlarged scale, a further detail of figure 3.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, the number 1 indicates, as a whole, a solid propellant rocket motor.

The motor 1 comprises, in the particular example described, an elongated cylindrical tubular casing 3, which has a longitudinal axis 4 and houses, in a per se known manner, a mass 5 of solid propellant delimiting a central channel 6 defining an elongated combustion chamber along the axis 4.

The casing 3 comprises, in turn, a lateral wall 7 and two frontal walls 8 and 9, which delimit respective passages 10 closed by respective heads 11 and 12.

The head 11 carries an ignition assembly 14, known per se and not described in detail, arranged in an end section of the duct 6 to ignite the solid propellant 5, while the head 12 carries a nozzle 15 for outlet of the exhaust gases resulting from combustion of the propellant 5 inside the casing 3, also known per se and not described in detail.

The heads 11 and 12 are connected to the respective frontal walls 8 and 9 by respective connection assemblies 16 that can be configured from the outside to arrange the motor 1 in an operating or launching configuration or in a safety condition, or in an assembly condition, as will be described in detail below .

With reference to figures 2 and 3, each connection assembly 16 comprises a circumferential groove 18 obtained coaxially to the axis 4 inside the respective wall 8,9 through a surface 8A, 9A delimiting the relative opening. Expediently, each groove 18 has in radial semi-section a rectangular shape elongated in a radial direction and is delimited by a bottom surface 19 and by an axial abutment surface 20.

With reference to figures 3 to 6, each connecting assembly 16 further comprises an open circular annular body 21, which extends coaxially to the axis 4 and to the outside of the relative head 11,12 and is made of elastically deformable material, for example steel or aluminium alloy. Specifically, the body 21 is shaped like an ordinary Seeger ring, is deformable on a plane orthogonal to the axis 4 and comprises a curved intermediate portion 22 and two free end portions 23 adjacent to and facing each other.

Preferably, the annular body 21 has, in radial semi-section, a shape complementary to the groove 19 and external dimensions such as to engage the groove 19 itself sliding in a radial direction .

Specifically, the annular body 21 is laterally delimited by a cylindrical perimeter surface 24 facing the bottom wall 19 of the groove 18 and axially by two flat surfaces 25 and 26 parallel to each other and orthogonal to the axis 4, the surface 26 of which is arranged abutting against the relative head 11,12, while the surface 25 is adapted to be arranged abutting against, or on the outside of, the surface 20 according to the deformation of the annular body 21.

Again with reference to figures 3 to 6, the body 21 carries a plurality of radial appendixes 28, which are distributed at a predefined pitch on the perimeter surface 24, protrude from the surface 24 and in this specific case constitute with the annular body 21 part of a body made in one single piece.

Alternatively, according to a variation, the appendixes 28 are welded on the surface 24.

Each appendix 28 has a resistant radial section which is smaller than the section of the annular body 21, as can be clearly seen from figure 7, and is axially delimited by two axial surfaces 29 and 30 coplanar with the surface 25 and with the surface 26 respectively (fig. 7) .

Each appendix 28 is then laterally delimited by a cylindrical surface 31 parallel to and facing the bottom surface 19 of the groove 18.

In the particular example described, each appendix 28 has in radial section an upturned L shape and comprises two curved walls 33 and 34 orthogonal to each other and delimiting with the surface 24 a curved axial channel 32 having an axial opening facing outwards.

With reference to figures 2, 3 and 8, each assembly 16 further comprises a device 35 for inflexion or elastic deformation of the annular body 21. In the particular example described, each device 35 is arranged between the relative end portions 23 and outside the relative head 11,12. Each device 35 comprises an actuation assembly 36, in turn comprising a frame 37 permanently connected to the relative head 11,12 between the terminal portions 23, a worm 40 coupled to the frame 37 to rotate about an axis 41 orthogonal to the axis 4 and a helical wheel 38 engaging with the worm 40 and revolving about an axis 39 tangential and orthogonal to the axes 4 and 41. Conveniently, the worm 40 is manually activated by an operator from the outside of the casing 37 and the head 11,12 by means of an appropriate wrench, not illustrated, which is inserted in the hollow hub of the worm 40.

Alternatively, according to a variation, the worm 40 is driven by an electric, hydraulic or pneumatic motor controlled by a dedicated control unit, not illustrated, which can be activated in remote mode.

The opposite axial ends of the wheel end 39 protrude outside the casing 37 and are each connected to a relative end portion 23 by means of a respective corner joint 43, for example of cardan type, and via a relative screw/screw-nut assembly 44.

Each assembly 44 comprises a screw 45 angularly integral with the relative joint 43 and a screw-nut 46 hinged to the respective portion 23 in a position angularly fixed by means of a pin 47 parallel to the axis 4.

Again with reference to figure 3, the assembly 16 comprises, lastly, a plurality of pairs 48 of elastic fins 49 arranged along the outer periphery of the annular body 21 between two consecutive appendixes.

The fins 49 of each pair 48 of fins are curved fins with concavity facing towards the surface 24 of the annular body 21 and are integrally connected to the surface 24 itself, for example, by welding or bolting. In a non-deformed condition, the fins 49 of each pair 48 of fins extend from the surface 24 towards each other and towards the outside, whereas in a condition of maximum deformation they envelop the surface 24 without coming into contact with each other. The fins 49 have, in a direction parallel to the axis 4, dimensions such as to engage by sliding in the groove 18 to maintain, when arranged in a non-deformed or partially deformed condition, the annular body 21 in an assembly position, illustrated in figure 4, in which the annular body 21 extends in a position coaxial to the axis 4 and the appendixes 28 are arranged outside the groove 18.

Operation of the devices 16 will now be described considering the head 11, analogous considerations obviously apply to the head 12, and starting from the assembly condition illustrated in figure 4, in which the solid propellant material is accommodated in the casing 3, the head 11 is inserted in the passage 10, the annular body 21 is maintained by the device 35 in a practically non-deformed condition with its surface 26 in contact with the head 11, the fins 49 are partially accommodated in the groove 18 and abutting against the surface 19 and the appendixes 28 are arranged on the outside of the groove 19.

Starting from said assembly condition, when it is necessary to set the motor 1 to a safe condition, for example in order to be stored, transported, positioned on the launch platform and/or coupled to the unit to be transported, acting from the outside on the device 35, the annular body 21 is progressively deformed spacing its end portions 23 from each other. Following said spacing, the fins 49 elastically deform, moving progressively closer to the annular body 21 and the appendixes 28 are progressively inserted inside the groove 18. The deformation of the annular body 21 continues until the walls 33 are completely arranged abutting against the surface 20 and the channels 32 communicate axially with the outside, as illustrated in figure 5. Having reached this position which is indicated, in the particular example described, by a section of the screws 45 coloured green and directly visible from the outside, the motor 1 is arranged in a safe condition in which it is not able to develop the maximum rated power. In said condition, in fact, the head 11, while closing to seal the casing 3, is blocked with respect to the casing 3 by deliberately weakened or breakable portions, so that a sudden pressure increase inside the casing 3 resulting from accidental ignition of the solid propellant 5 is interrupted, allowing the head 11,12 to disengage from the casing 3 when the pressure value inside said casing 3 exceeds a threshold value at the preset design stage, expediently in the order of 10 bar or equal to a predefined percentage of the motor operating pressure.

In this way, the propellant continues to burn but with reduced combustion speed and, above all, without providing the necessary thrust for flight and therefore in conditions of greater safety for the personnel in charge.

When all the operations for preparation of the motor 1 and connection of the same to the units to be moved have been positively completed, the motor 1 is set to a propulsion position by spacing, again via device 35, the portions 23 from each other and elastically deforming the body 21 until bringing an outer perimeter portion 21A of the annular body 21 inside the groove 18, abutting against the surface 20 of the groove 18, as indicated in figure 6.

Once said position has been reached, indicated by a coloured section, for example red, of the screws 45, the head 11 is permanently blocked with respect to the casing 3 regardless of the pressure present inside the casing 3 since the annular portion 21A has a much bigger resistant section than the resistant section of the appendixes 28. In said condition, the motor 1 is ready to be used.

From the above it therefore appears obvious that, with respect to the known solutions, the devices 16 described allow the motor 1 to be configured extremely rapidly and particularly easily. In particular, the devices 16 allow the motor 1 to be set to a safe condition or a propulsion operating condition in addition to an assembly position by simply operating an actuator assembly arranged on the outer periphery of the casing 3 and, therefore, without the need to disassemble elements and re-fit others in their place, as in the solutions known today.

The above is essentially a consequence of the fact that in the devices 16 described, the portions with different strength are all carried by one single body which performs the dual function of support and movement and said portions replace one another by means of a simple radial forward movement within a circumferential groove which is not only delimited by a common supporting surface but is such as to accommodate the weakened appendixes 28 when the heads 11,12 are blocked by the portion 21A.

The use of the devices 16 described is particularly advantageous in cases in which two or more motors 1 are stacked on top of one another since, unlike the known solutions, the various motors are set to their operating condition simultaneously and only after all the other assembly and preparation operations have been completed, thus increasing safety on the launch platform.

From the above, it is obvious that modifications and variations can be made to the devices 16 described. In particular, the appendixes 28 and the portion 21A could be carried by a support and movement body different in construction terms from the elastic body 21 but always such as to selectively arrange the blocking portions with different strength between at least one of the heads 11,12 and the casing 3. Furthermore, both the weakened appendixes 28 and the fins 49 provided to maintain the portions with different strength in a reference position around the axis 4 could be different in terms of geometry and/or number. Lastly, also the casing 3 and the device 35 for deformation of the annular body 21 could be different from those indicated, likewise the manner of indicating to an operator the instantaneous functional configuration of the motor 1 could be different .

Lastly, it is obvious that the motor 1 described could comprise one single configurable device 16.