FR2573858A1 - Method and device for masking a target such as a tank using smoke- producing material - Google Patents

Abstract

From the target, and on the observation side, there is spread 30, 32 in aerosol form 39 a liquid 36 capable of initially reacting with the ambient air in order, at least in the short term, to be an absorber of contrast in the infra-red range, while in the short and medium term being an absorber of contrast in the visible range, and there is spread 41, 44, 50 a granulometry powder 55 chosen to be, at least in the medium term, an absorber of contrast at least in the infra-red range.

Description

 The invention relates to the masking of a target, in particular but not exclusively of a tank, against observations in the field of electromagnetic radiation in particular visible and / or infrared, even distant.

 One of the modes of action of a tank consists in advancing in hostile zone to carry out a rapid offensive action there (shooting of one or more shots on a target, for example). The tank is then very exposed to the enemy's defense, and is likely to be spotted in visible or infrared observation. To increase its chances of withdrawal without hindrance, it is desirable that the tank has means of masking its position.

Of course, it is necessary to hide not only the tank itself, but also a large area around it (which is in the tens of meters), and this quickly (implementation in a second to more), and durable (several tens of seconds).

 The effective realization of such a masking poses serious problems, especially since it is necessary to take into account the influence of atmospheric conditions (temperatures, pressure, humidity, wind speed, in particular). This problem naturally extends to other types of targets, mobile or static.

 The present invention provides solutions to these problems.

 The first object of the invention is to achieve rapid and lasting masking, and this over a wide band of wavelengths covering the visible and infrared range, even far (some infrared detectors operate in lengths of wave up to 14 microns).

 Another object of the invention is to create such a masking which is sufficiently effective for targets of the tank type, offering particularly radiant zones such as their engine or their exhaust.

 Yet another object of the invention is to create a mask which has a homogeneous masking power over its entire surface, and which is able to "stick to the ground", so as to avoid diffraction effects which would annihilate the action of masking.

 The invention also aims to make the masking effect as much as possible independent of atmospheric circumstances.

 For this, the invention provides a masking process using specific smoke materials, and a device for the implementation of this process.

The masking process extends, in a particular version, to a mode of dispersion of the device.

The method of the invention consists in carrying out the following steps, from the target and in the direction of observation (in visible or infrared radiation) a) developing in the form of an aerosol a liquid capable of
initially interact with the ambient air to be at
less short-term contrast absorber in the
infrared range, while being short and medium
term contrast absorber in the visible range, and b) developing a powder of particle size chosen for
at least in the medium term, absorbing contrast
at least in the infrared range.

 Preferably, the initial interaction of the aerosol with ambient air produces a significant and substantially uniform infrared emission.

 It appears interesting to entrust the aerosol with an initial mission of absorbing contrast (preferably with emission) in the infrared domain, while choosing it capable of forming lasting fog (contrast absorber) in the visible domain. Subsequently, the powder will in particular supplement the possible decrease in the infrared properties of the aerosol, by its own ability to absorb contrast.

 In addition, the rapid infrared effect of the liquid aerosol is well suited for masking the engine and exhaust of a very advanced tank while it begins to fold.

 I1 also appeared that the two clouds of liquid and powder, launched at the same place, have a certain tendency to stabilize one another, and to cooperate for the obtaining of a significant and effective absorption of contrast.

 Advantageously, the liquid contains at least one compound capable of reacting exothermically with the humidity of the air, as well as establishing a mist. It is advantageous to use for this purpose a chlorinated compound, in particular titanium tetrachloride and boron trichloride.

 We thus obtain, initially, a kind of "boiling cloud" of fog, which can stick to the ground, while being subjected to convection movements; this prevents any visual or infrared perception through the cloud, and is well suited as a contrast absorber over the entire wavelength band of perception.

 Thereafter, the effect of the aerosol in infrared may tend to fade while the effect in the visible remains longer. However, the cloud cools which tends to compensate for its tendency to expand under the effect of shoring factors, given the wind. Again the effect is beneficial for masking.

 Conversely, the above-mentioned provisions make it possible to maintain the granulometry of the liquid droplets in a lasting manner, and to maintain an effective fog in the visible for a long time.

 For its part, the powder is advantageously of varied but controlled particle size, less than about 10 microns, and preferably situated in the range going from 0.3 microns to 5 microns, or better still from 0.5 microns to 3 microns.

 Very advantageously, the powder is developed in combination with a gaseous propellant (freon and / or carbon dioxide in particular).

 I1 appeared that the gaseous propellant not only allows the development of the powder in a cloud, but also by relaxing, cooling the entire cloud (powder aerosol). This avoids excessive movements of the aerosol in its convection phase, by facilitating its "sticking" to the ground, and also avoids the heating of the powder particles.

 Furthermore, it is possible to choose a gaseous propellant containing one or more gases which are themselves opacifying in the infrared and / or visible fields. An interesting example is ammonia.

The powder preferably consists of one or more of the following materials
metals in powders of the transition metals series
(Group IVB to IIB of the Mendeleiev Table as well as
Aluminum, Boron, Silicon, Antimony, Tin, Lead,
Bismuth and alloys of these metals,
transition metal oxides as well as
Boron, Barium Oxide, Strontium Oxide, Oxide
Copper,
carbon in the form of graphite.

The invention also offers a countermeasure device in the field of infrared and / or visible radiation, allowing the implementation of the above method in its various variants. This device comprises - a substantially sealed enclosure, - in this enclosure, a liquid housing comprising
on one side a piston able to push on command the
liquid, and on the other a connection to a first
nozzle capable of opening towards the outside of the enclosure, - a second nozzle capable of opening towards the outside of the enclosure
the enclosure, and communicating with the rest of the enclosure, - in the rest of the enclosure a powder and an agent
pressurized gas propellant, and - means for triggering the thrust on the liquid and
jointly allow the expulsion of gas and powder
by the second nozzle.

In general, the two above conditions must be fulfilled, namely a) the liquid is able to interact initially with the air
ambient to be at least short-term absorber of
contrast in the infrared range, while being
short and medium term contrast absorber in
the visible range, and b) the powder has a particle size chosen to be absorbed
contrast beuse at least in the infrared range.

In a particular embodiment, the enclosure comprises - a cartridge of gas under pressure, and suitable members
releasing the pressurized gas at a selected point of
the enclosure, - a dip tube having an open end in
the enclosure, substantially opposite the point chosen, and
another end which communicates with the second nozzle, and the powder fills the rest of the enclosure.

 Very advantageously, the two nozzles are close to each other, in particular when the device has to operate on the ground, the two nozzles facing upwards.

 However, it can also be envisaged that, after launching, the device functions or begins to operate on its trajectory. The arrangement of the nozzles can then be different.

 In a preferred variant, the two nozzles are coaxial, the first nozzle being in the axis.

 According to another aspect of the invention, at least when it is removed, the enclosure is inscribed in a substantially spherical outer envelope, with respect to which the region of the nozzles is more curved, and the opposite zone less curved, this the latter being the closest to the center of gravity of the device.

 Preferably, the triggering means are pyrotechnic means.

 To obtain an ammunition launched from the target (the tank), the enclosure is of generally cylindrical shape, and housed in an envelope whose socket bottom houses an impeller capable of causing the deposition of the envelope, as well as transmitting fire triggering means, which are then pyrotechnic delays.

 According to an advantageous characteristic of the device, for the operation on the ground, between the cylindrical walls of the enclosure and of the envelope, are housed arched fins, foldable, integral with the enclosure, these fins having on the bottom side of socket a more pronounced convexity than on the side of the nozzles, opposite; the center of gravity of the device is located below the point at vertical tangent of the fins when they are unfolded.

 Finally, the invention proposes a particular implementation of the above method, using the above device. This consists in firing from the target, at low site and at low speed, a beam of these devices, with in particular a low site (angle less than 150), a low speed (15 to 25 ms 1) and a trajectory length of a few tens of meters, and extended impacts also over a few tens of meters.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, as well as in the accompanying drawings. The detailed description and the drawings are intended to give, by way of nonlimiting example, three embodiments of the present invention which are currently considered to be preferred. In the drawings - Figures 1 to 1B are shown schematic sectional views
of a particular embodiment of the device according to
the invention, and two interesting variants - Figure 2 is an external view of the device, taken out
of its launch envelope, and fins deployed
and - Figure 3 is a top view corresponding to the
Figure 2, showing the same fins deployed.

 We will first describe the countermeasure device according to the invention, in its embodiments of FIGS. 1 and 1A. These particular embodiments involve the device in a launched version.

 In FIG. 1, an envelope of generally cylindrical shape, open at one of its ends, is defined by a cylindrical wall 12, formed in one piece with a flat bottom of the sleeve 11.

 The socket bottom 11 houses an impeller 13, which is advantageously initiated electrically. At the periphery, the socket bottom 11 also houses a ring forming a supply contact 14, surrounded by an insulating material 15, and mounted on a screwable ring 16. The electrical circuit of the initiator of the impeller 13 is therefore taken between the mass of the socket bottom 11 and this supply contact 14. The impeller 13 ejects the device from its launcher tube (not shown), and activates a pyrotechnic delay 17 (of very short duration, of the order of a few tenths of seconds). This delay communicates with the interior of the envelope.

 Internally, the envelope houses an enclosure forming the active device proper. This enclosure, which is substantially sealed, is defined by a lower bottom 21, provided with a radial projection with seal 27. On this bottom is fixed a cylindrical side wall 22, closed in turn at the other end by a cap 23. When the enclosure is in its envelope, FIG. 1 shows that the extreme edges of the cylindrical wall 12 of the envelope are crimped onto suitable housings of the cap 23.

 The enclosure firstly comprises a housing for a liquid, this housing being defined by a cylindrical wall 34 forming a bore for a piston 32 provided with sealing means 33. At its other end, the bore 34 is closed by a fixed flange 35, provided with a nozzle 37, ensuring the connection from the interior of the liquid housing to a tube 38, which in turn communicates with a first nozzle 39.

 It will be noted in FIGS. 1 and 3 that the cap 23 is provided with a recessed cell, a flat bottom and a circular section for example. This cell is normally closed by a plug 25 provided with sealing means 26. The divergence of the first nozzle 39 is closed by this plug 25. A pressure, developed in the cell 30 formed behind the piston 32, pushes the liquid . After having ejected the plug, the liquid emitted by the first nozzle 39 can therefore develop outside the enclosure defined by the walls 21 to 23.

 Still in the enclosure is a cartridge 50 of pressurized gas. This cartridge is provided with connection and expansion means illustrated in 51. These means terminate in 52 with a closing spangle, capable of being pierced. The end 51 of the cartridge will be screwed into a support sleeve, generally designated by 42. This support sleeve defines a bore opposite the paillet 52, in which slides a piston 44 provided with sealing means 55, as well as a beveled tip 46 apS to pierce the straw 52. Between the surface of the piston and the straw 52, the bore defined inside the sleeve 42 communicates through an orifice 47 with a tube 48, which comes to point 49, in top of the enclosure, just under the cap 23.This therefore makes it possible to release gas under pressure under the cap (pressure from 4 to 6 bars, for example).

 The enclosure also comprises a dip tube, generally designated by 56. This dip tube ends with an open end, at 59, in the lower part of the enclosure, substantially opposite point 49 where the gas under pressure is released. . (To simplify the drawing, the liquid housing and the dip tube 56 have been shown in the same section. In fact, these two elements are in separate planes, and the tube 56 effectively extends with a constant cross section up to its end 59).

 The other end of the tube 56 communicates with a second nozzle 57, which also opens towards the outside of the enclosure, under the plug 25.

 In the embodiment of Figure 1, the two nozzles are adjacent to each other. And the pipes that open out are vertical or substantially vertical. When an action of the device is desired during the trajectory, it may be desirable to place the nozzles in more spaced locations.

 In the rest of the enclosure, there is placed a powder, of controlled and selected particle size. It is immediately understood that the gas released at 49 will produce a pressurization of the powder, and travel within it to the bottom at 59 where the orifice of the dip tube 56 is located. The gas will then invade the dip tube, cause the expulsion of the stopper 25 if the expulsion of liquid has not already done so, and entrain the powder by the nozzle 57 in a violent jet towards the outside.

 It will naturally be the same for the liquid through its clean nozzle 39, under the effect of a displacement of the piston 32.

 The device also includes means 31 and 41 for jointly triggering the thrust on the liquid and the release of the gas under pressure. We then obtain the joint development of a cloud of liquid and a cloud of powder entrained by the gas.

As previously indicated, it is intended that: a) the liquid is capable of interacting initially with
ambient air to be at least short-term absorber
contrast in the infrared range, while being
short and medium term contrast absorber in
the visible field, and b) the powder has a particle size chosen to be
contrast absorber at least in the field
infrared.

In the preferred embodiment, the triggering means 31 and 41 are pyrotechnic means.
Under these conditions, the housing defined by the cylindrical side wall 34 is placed in a recess in the bottom 21 of the envelope. The concave shape of the piston 32 leaves a place 30 which is used to house a pyrotechnic charge capable of generating a high gas pressure, in a manner controlled by the delay device 31 placed between the cavity 30 and a recess 28 placed on the other side from the bottom 21, in communication with the delay 17 already mentioned.

 In the same way, the sleeve 42 comes to thread in another place on the bottom 21, to communicate by a passage 40 with the recess 28. The sleeve 42 also includes a fire transmission delay 44.

 Finally, the recess 28 receives a load of deposition, which will allow the device to be removed from its envelope, at the same time as the deployment of its fins, as will be seen below.

 Figure 1A shows a preferred variant of the device of Figure 1. Many elements are common. They bear the same reference numbers and will not be described again.

 Other elements, similar, but slightly different in shape, carry numerical references increased by 100 units. For the most part, they will not be described again either.

 The essential difference between the two figures concerns the arrangement of the nozzles, which are coaxial in FIG. 1A.

 The tube 38 now goes to a connector 160, followed by a pipe 161, then by a convergent-divergent tube 162 which results in sealing on an area 163 of the plug 25. The area 163 is made of material capable of withstanding the action possible corrosive of the liquid 36. All of this is housed in the internal conical part 165 of a part 166, the external part 167 of which folds around the internal part to join (as an integral part) the recess 24 of the cap 23.

 Between the internal 165 and external 167 parts is defined an annular divergent 170, which terminates under the plug 25.

 This divergent 170 communicates with a connector 157, mounted on an orifice formed in the external part 167.

Finally, the. connector 157 is connected to tube 156, a hidden part of which goes to the opposite bottom of the enclosure.

 Note, moreover, that the tube 149 ends here in a more central area under the cap 23 than in FIG. 1. Finally, the non-return device for the pyrotechnic delay 31 is visible in FIG. 1A.

 We will now focus on Figure 1B, which shows another variant, very advantageous. Again, the elements already described have the same reference numeral, possibly increased by 200 if their embodiment has changed.

 The basis of the device remains the same. The bottom 221 is now screwed onto a monobloc assembly, which can be molded with lost wax and includes the side walls 234, 222, the cap 223, the two coaxial pipes 282 and 285, with their extensions 265 and 267 towards the ex. - interior, and the thick internal partition 281, V-shaped open upwards.

 This internal partition 281 is axially pierced with an orifice 237 which communicates with the passage 238 of the inner tube 282. The latter ends at the nozzle 262. The partition 281 defines, with a reinforced zone 234 (in the lower part of the cylindrical wall 222 ), the bore of the piston 232, the upper face of which is in a V-shape homologous to that of the partition 281. The lower face of the piston 232 is dimpled at 230, to receive the pyrotechnic charge for pushing the liquid. This charge is started by the delay 31, provided with a non-return, as before. We thus find, for the liquid, the same operation as above, but with a symmetry of revolution in the material, and a large mass at the bottom.

 A plug 225 is clipped onto a bead 295 formed at the end of the extension 267. This plug internally houses an elastic sealing mass, which closes the orifice 296 of the nozzle 262, and the annular orifice 297 which is coaxial with it. The cap is ejected when the liquid is pressurized.

 The annular tube 285 which extends the cap 223 and the lips 267 penetrates into the enclosure, until 259, in the hollow of the V defined by the thick partition 281. There is therefore above this partition, a sealed enclosure 255 , closed at the top of the annular passage 256 by the mass 263 of the plug 225. (This enclosure corresponds to the "rest of the enclosure" referred to above, the liquid enclosure being set aside).

 According to this variant, the mixture of powder and gaseous propellant according to the invention is placed in the sealed space 255. The mixing is therefore carried out here during construction, and introduced by a suitable plug shown diagrammatically at 290.

 The operation is as follows: the plug 225 is ejected by the liquid, and the gas-powder mixture, immediately released, is ejected by the divergent 297, coaxial with the liquid nozzle 262, in a manner comparable to the case of the figure 1A.

 Of course, the modifications of FIGS. 1 1A and 1B are for the most part interchangeable, it being observed in particular that the arrangement of FIGS. 1A and 1B makes it possible to further lower the center of gravity.

 The following description applies to the three embodiments.

 Figures 2 and 3 show that between the cylindrical walls of the enclosure 22 and the envelope 12 are housed fins A1 to A8, in an arc, foldable, and integral with the lateral part 22 of the enclosure.

 With these fins in the deployed position, the enclosure is part of an outer envelope of substantially spherical outline. The cap 23, in which the nozzles are located, has a more convex convexity than this spherical contour. Conversely, the bottom 21, which is substantially flat, is less domed than said spherical contour. Furthermore, the center of gravity G is preferably closer to the bottom 21.

 The fins also make it possible to connect the surfaces of the cap 23 and the bottom 21.

 To this end, the arcuate shape of these fins has a more pronounced convexity on the side of the socket bottom 21 than on the side of the nozzles, namely opposite.

In addition, as shown in FIGS. 1 and 2, the center of gravity G of the device is located below the vertical tangent point of the fins, when the latter are unfolded.

The device can then be launched by a mortar, in a relatively short trajectory, then fall on the ground where it will naturally tend to stabilize on its bottom 21. (The fins give it a property of "culbuto")
This will be the case even if the ejection of material by the two nozzles results in oscillatory movements imprinted on the device
The preferred mode of implementation of the device consists in pulling it from a tank, at a low site and at low speed, and of course in the form of a bundle of devices fired substantially at the same time, so as to obtain an almost cloud continuous, completely masking the tank over a large geographic area.

Numerical values of the elevation and speed angles have already been indicated, as well as values concerning the desirable size for the cloud overall obtained.

 For example, up to 12 rounds of ammunition are fired over a range of 30 m radius for 40 m deployment. In doing so, it has been observed that the wind spreads the tail of the cloud without moving its forehead, which facilitates the constitution of the same cloud from several devices.

In the embodiment currently considered to be preferred, the liquid is tetrachloride of
Titanium, or at least based on Titanium tetrachloride.

 I1 has been observed that this component, diffused through a nozzle whose opening has a diameter of the order of a millimeter, and under a pressure of 10 to 15 bars, can form a jet of range up to 10 m, and made up of liquid droplets of very fine particle size (0.5 to 5 microns).

 This aerosol constitutes a very opaque mist in the field of visible radiation, and this for a period of several tens of seconds. Such a fog is by nature absorbing contrast, and prevents the limits of any object placed behind it from being perceived.

 At the same time, the liquid reacts with the humidity of the air, in an exothermic way, to give in particular hydrochloric acid, and titanium oxide, which is accompanied by absorption of contrast in the infrared at the same time as a substantially uniform infrared emissivity. The latter participates in the masking of the target in the manner of a "noise".

 Alternatively, boron trichloride can also be used, which undergoes comparable chemical reactions, together with the generation of a mist. Naturally, other types of chlorinated compounds can also be used in the context of the present invention.

 More generally, the liquid may contain one or more compounds capable of reacting exothermically with the humidity of the air, while having the property of establishing a fog in the visible range.

 For its part, the powder is important first of all by its particle size, for which numerical values have already been indicated above.

 It can be a metallic powder.

 Aluminum has interesting properties, provided that the cloud is cold enough to avoid the pyrophoric effects observed with this metal.

In this sense, the use of a propellant capable of relaxing with strong cooling, in particular freon or carbon dioxide, is likely to cool the cloud sufficiently to allow the use of a aluminum-based powder.

 Brasside, copper and / or iron powders are less sensitive to temperature and very effective. One can naturally envisage other powders in the families already mentioned.

On the other hand, it has proved advantageous for certain applications to constitute the powder from graphite, at least in part, as well as on the other hand from copper oxides of boron, barium or
Strontium. Mixtures can be made.

 According to another aspect of the invention, and a priori unexpectedly, it seems that the joint use of a liquid dispersed in the form of fine droplets, and of a powder propelled preferably from a gas, produced clouds which have good mixing properties, and tend to stabilize in a collocated manner. This is particularly important to ensure good cloud stability in the presence of a high speed wind.

 Furthermore, although the phenomena are not yet fully explained, it seems that the joint dispersion of a liquid and a powder according to the present invention produces, at least in the infrared range, a synergistic effect which gives properties of unexpected absorption of contrast, in addition with excellent homogeneity, and good continuity over time both in the short term and in the medium term.

 Finally, it is naturally possible to use a propellant gas or a mixture of propellant gases which themselves have contrast absorption properties in the infrared and / or visible light range. In this sense, ammonia, or even hydrochloric gas, can be used as the propellant gas (at least for FIGS. 1 and 1A).

 Furthermore, the degradation products of the chlorinated compound (here in principle Ti Cl4) will interact with the powder, which is particularly true for hydrochloric acid. This allows on the one hand the synergy already mentioned. On the other hand, this facilitates the long-term neutralization of hydrochloric acid.

Claims (27)

 1. Masking process using smoke material.  at least in the infrared range.  be at least in the medium term, absorbent- of contrast  contrast absorber in the visible range, and b) a powder of particle size chosen for  infrared, while being short and medium term  short-term contrast absorber in the field  initially interact with the stirring air to be at least of a target, in particular a tank, against observations in the field of infrared and / or visible electromagnetic radiation, characterized in that from the target, and from the side of the observation a) a liquid is developed in the form of an aerosol  2. Method according to claim 1, characterized in that the initial interaction of the liquid with the ambient air produces an infrared emission  substantially uniform.  3. Method according to claim 2, characterized in that the liquid contains at least one compound capable of reacting exothermically with the humidity of the air, as well as establishing a fog in the visible range.  4. Method according to claim 3, characterized in that the liquid contains a chlorinated compound.  5. Method according to claim 4, characterized in that the liquid contains titanium tetrachloride.  6. Method according to claim 4, characterized in that the liquid contains tri boron chloride.  7. Method according to one of claims 1 to 6, characterized in that the powder is of varied particle size, less than about 10 microns.  8. Method according to claim 7, characterized in that the powder is of varied particle size in the range from 0.3 microns to 5 microns.  9. Method according to one of claims 1 to 8, characterized in that the powder is associated with at least one propellant gas.  10. Method according to claim 9, characterized in that the propellant comprises freon.  11. Method according to claim 9, characterized in that the propellant gas comprises carbon dioxide.  12. Method according to claim 9, characterized in that the propellant gas comprises ammonia.  13. Method according to one of claims 1 to 10, characterized in that the powder contains at least one of the following materials - powdered metals from the series of transition metals  (Group IVB to IIB of the Mendeleiev Table as well as  Aluminum, Boron, Silicon, Antimony, Tin, Lead,  Bismuth and alloys of these metals, - oxides of transition metals as well as boron oxide,  Barium oxide, Strontium oxide, Copper oxide, - carbon in the form of graphite.  14. Method according to claim 13, characterized in that the powder contains Aluminum, Brass, Copper or Iron.  15. The method of claim 13, characterized in that the powder contains an oxide of Copper or Boron.  16. Method according to claim 13, characterized in that the powder contains graphite.  17. Countermeasure device in the field of infrared and / or visible radiation, allowing the implementation of the method according to one of the preceding claims, characterized in that it comprises: - a substantially sealed enclosure (21, 22, 23) - in this enclosure, a housing (34) of liquid com  carrying on one side a piston (32) capable of pushing on  controls (31) the liquid, and on the other a connection  (37, 38) to a first nozzle (39) capable (25) of  open to the outside of the enclosure (21 - 23), - a second nozzle (57) capable (25) of opening towards  outside the enclosure, and communicating with the  rest of the enclosure, - in the rest of the enclosure a powder and an agent  pressurized gas propellant, and - means (31, 41) for triggering the thrust on the  liquid and jointly allow the expulsion of gas  and powder by the second nozzle (57), and by the fact that a) the liquid is capable of interacting initially with the air  ambient to be at least short-term absorber of  contrast in the infrared range, while being  short and medium term contrast absorber in  the visible range, and b) the powder has a particle size chosen to be  contrast absorber at least in the field  infrared.  18. Device according to claim 17, charac terized in that the enclosure comprises - a cartridge (50-51) of gas under pressure, and  organs (41 to 49) capable of releasing the gas under pressure  at a selected point (49) of the enclosure, - a dip tube (56) having an open end  (59) in the enclosure, substantially opposite the point  chosen (49), and another end which communicates  with the second nozzle (57), and by the fact that the powder fills the rest of the enclosure.  19. Device according to claim 17, characterized in that the enclosure is subdivided into a liquid housing (236) and, in the rest, a housing (255) of powder mixture and gaseous propellant.  20. Device according to one of claims 17 to 19, characterized in that the bottom (281) of the powder housing is V-shaped with a concavity facing this housing, and that the dip tube (256) ends in the hollow of this V shape.  21. Device according to one of claims 17 to 20, characterized in that the two nozzles (39, 57) are adjacent to each other.  22. Device according to claim 21, characterized in that the two nozzles (39, 57) are coaxial, the first nozzle (39) being in the axis.  23. Device according to one of claims 17 to 22, characterized in that at least when it is removed, the enclosure is inscribed in a substantially spherical outer envelope, with respect to which the region (23) of the nozzles is more curved, and the opposite zone (21) less curved, the latter being the closest to the center of gravity of the device.  24. Device according to one of claims 17 to 23, characterized in that the triggering means (31, 41) are pyrotechnic means.  25. Device according to one of claims 17 to 24, characterized in that the enclosure (21, 22, 23) is of generally cylindrical shape, and housed in an envelope (11, 12) whose socket bottom ( 11) houses an impeller (13) capable of causing (17) the stripping of the envelope, as well as transmitting the fire to the triggering means (31, 41), which are pyrotechnic delays.  26. Device according to claim 25, taken in combination with claim 23, characterized in that between the cylindrical walls of the enclosure (22) and of the envelope (12) are housed fins (A1-A8) in an arc, foldable, integral with the enclosure (22), these fins having on the side (21) of the socket bottom a more pronounced convexity than on the side (23) of the nozzles, and by the fact that the center of gravity (G ) of the device is located below the vertical tangent point of the fins when they are unfolded.  27. Masking method according to one of claims 1 to 16, characterized in that it consists in firing from the target, at low site and at low speed, a bundle of devices according to one of claims 17 to 26 .