Space system for the cryogenic cooling of an item of equipment to be cooled and method for separating a thermal coupling between a cryogenerator and an item of equipment to be cooled

Abstract

The invention relates to a cryogenic cooling space system with a system (1) for managing a thermal coupling between a thermal link (4) and a finger (2; 3) of a cryogenerator or an item of equipment to be cooled, the space system comprising: - a fastening system (5) configured to provide, in a pretensioned state, a direct coupling between the finger (2; 3) and the thermal link (4), in a coupling configuration; - a separation system (6) configured to reduce or eliminate the pretensioned state of the fastening system (5) in order to reduce or eliminate the coupling between the finger (2; 3) and the thermal link (4), in a separation configuration.

Description

Description SPACE CRYOGENIC COOLING SYSTEM FOR EQUIPMENT TO BE COOLED AND METHOD FOR SEPARATING A THERMAL COUPLING BETWEEN A CRYOGENERATOR AND EQUIPMENT TO BE COOLED Technical field

[0001] The present disclosure relates to the field of thermomechanics, in particular cryogenic cooling of space equipment. The present disclosure can be applied to any cooling system having redundancy of the cryogenic machine. In particular, the present disclosure relates to a system for managing a thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled as well as a space cryogenic cooling system comprising such a management system. Prior art

[0002] It is known, to cool space equipment, to implement a cooling system comprising a cryostat and two cryogenerators, also called cryocoolers or cryorecoolers.

[0003] The presence of two cryogenerators is a safety precaution in the event of failure of one of the two cryogenerators and constitutes what is commonly called redundancy.

[0004] Both cryogenerators can operate according to the principle known as cold redundancy. In this case, one of the two cryogenerators provides 100% of the cooling energy while the other cryogenerator is only used in the event of a failure.

[0005] Another operating principle of the two cryogenerators is referred to as hot redundancy. This principle consists of operating the two cryogenerators simultaneously, for example, to each provide 50% of the cooling energy. In the event of failure of one of the two cryogenerators, the other of the two cryogenerators is then called upon to provide 100% of the cooling energy. The present disclosure relates in particular to a cryogenic cooling system operating according to this hot redundancy principle.

[0006] A problem that arises in particular in the implementation of cold redundancy is the parasitic thermal leakage linked to the coupling of the non-operational cryogenerator. In the case of hot redundancy, this leakage appears only in the event of a cryogenerator failure. For both redundancy principles, this parasitic leakage is a major parameter in the performance of a cooling system present in cryogenic instruments on board spacecraft such as Earth observation satellites or scientific mission satellites. This leakage alone typically represents 30% of the cryogenic power required to maintain the equipment to be cooled, in particular the detection system, at its operational temperature.This leak is generated by the non-operational cryogenerator, i.e. faulty or not used, which, not being in service, generates a direct link between the equipment to be cooled, for example at 60K, and the rest of the instrument, for example at 293K. The leak can. possibly degrade the performance of the instrument and necessarily induce oversizing of the cryogenerators.

[0007] To solve the problem of thermal leakage in case of hot redundancy, thermal switch solutions have been considered, described in W02007116157 and FR2985004.

[0008] W020071 16157 proposes a brittle material, typically sapphire, on the thermal path between the cryogenerator and the equipment to be cooled. When the cryogenerator fails, the brittle material is broken so as to interrupt the thermal path and therefore the leak. However, its presence degrades the nominal thermal coupling, particularly across its two contact surfaces. In addition, its brittleness may be unsuitable for the mechanical environments to which the instrument will be subjected during launch or in orbit.

[0009] FR2985004 proposes a thermal switch based on the fusion of an integrated solder between the cryogenerator and the equipment to be cooled, with a heating system allowing the rupture of this solder. This solution is not very suitable for space cryogenic instruments because the fusion of the solder necessarily occurs at too high a temperature which presents a high risk of heating the equipment to be cooled and degrading it. Furthermore, this solder introduces a thermal resistance on the conductive thermal path between the cryogenerator and the equipment to be cooled, degrading the nominal thermal coupling.

[0010] There is therefore a need for a cryogenic cooling space system implementing hot redundancy in particular, to improve its performance. Summary

[0011] This disclosure improves the situation.

[0012] A spatial cryogenic cooling system for equipment to be cooled is proposed, comprising: at least two cryogenerators each being in an operational or non-operational state, the cryogenerators being redundant and configured to generate cold simultaneously in their operational state, each cryogenerator comprising a cold finger, the cold fingers being connected to at least one interface with the equipment to be cooled, in their operational state, a management system associated with each cryogenerator and controlled as a function of the operational or non-operational state of the associated cryogenerator, each management system ensuring, when the associated cryogenerator is in the operational state, a thermal coupling between the cold finger of the associated cryogenerator and said interface;the system being characterized in that each management system comprises: a fixing system configured to ensure, in a pre-tensioned state of the fixing system, direct coupling with the finger or said interface, in the operational state of the associated cryogenerator; a separation system configured to reduce or eliminate the pretension state of the attachment system in order to reduce or eliminate the thermal coupling with the finger or said interface, in the non-operational state of the associated cryogenerator, the attachment system being arranged on either side of the finger or said interface and neutrally with respect to a conductive path connecting the finger and said interface, each finger being connected to said interface via a thermal link belonging to the conductive path.

[0013] According to a feature of the invention, the coupling between the finger or the interface on the one hand and the thermal link on the other hand is carried out at an interface plane between the finger or the interface and the thermal link.

[0014] Alternatively, the coupling between the finger and the thermal link may be achieved at a cylindrical contact surface between the finger and the thermal link. The fastening system may comprise, for example, a terminal configured to surround the thermal link and the finger. The terminal may comprise, for example, an open ring portion comprising an opening and surrounding the thermal link and the finger and a clamping portion comprising two free ends extending from this opening. The rod may, for example, pass through the two free ends at least in the coupling configuration. The terminal may, for example, comprise an elastic return function intended to separate the free ends in the separation configuration.

[0015] According to another feature of the invention, at least one of the thermal links is arranged on either side of the finger or the interface, the management system comprising an elastic return function configured to separate the finger or the interface and said thermal link arranged on either side of the finger or the interface, in a separation configuration.

[0016] According to another feature of the invention, the elastic return function comprises a spring tending to separate the portions of said thermal link arranged on either side of the finger or the interface, the spring being compressed in the coupling configuration.

[0017] According to another feature of the invention, the elastic return function comprises a stiffness of said thermal link arranged on either side of the finger or the interface, said thermal link arranged on either side of the finger or the interface having an orientation tending to separate from each other the portions of said thermal link arranged on either side of the finger or the interface, in the absence of mechanical constraints.

[0018] According to another feature of the invention, the fixing system comprises a rod and a clamping ring, the rod being in said pre-tensioned state in the coupling configuration.

[0019] According to another feature of the invention, the rod comprises a weak point and the separation system is configured to break the rod at the weak point, the separation system comprising a heating device and a component comprising a material, of the shape memory material type, capable of changing dimension when heated to a predetermined temperature.

[0020] According to another feature of the invention, the shape memory material is arranged in the fixing system, at least in the coupling configuration, and comes to bear against at least one head at the end of the rod or against the clamping ring.

[0021] According to another feature, the cryogenic cooling space system according to the invention comprises a bolt catcher configured to retain at least one of a portion of the rod and the clamping ring in a separation configuration.

[0022] Another object of the invention relates to a method for separating a coupling of a finger or an interface of equipment to be cooled connected to one of the cryogenerators which is faulty, to reduce or cut a conductive path between said faulty cryogenerator and the equipment to be cooled in a space cooling system (100) according to any one of the preceding claims, comprising: a. detecting failure of the cryogenerator; b. activating the separation system so as to reduce or eliminate the thermal coupling at the finger or the interface. Brief description of the drawings

[0023] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:

[0024] [Fig. 1] shows schematically, in side view and in longitudinal section, an example of a spatial cooling system comprising an example of a system for managing a thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled.

[0025] [Fig. 2] shows schematically, in section, an example of a management system, the finger and the thermal link being in a coupling configuration.

[0026] [Fig. 3] is a view similar to Fig. 2 of the exemplary management system of Fig. 2, with the finger and thermal link in a separation configuration.

[0027] [Fig. 4] shows schematically, in section, an example of a management system, the finger and the thermal link being in a coupling configuration.

[0028] [Fig. 5] is a view similar to Fig. 4 of the exemplary management system of Fig. 4, with the finger and thermal link in a separation configuration.

[0029] [Fig. 6] shows schematically, in section, an example of a management system, the finger and the thermal link being in a coupling configuration.

[0030] [Fig. 7] is a view similar to Fig. 6 of the exemplary management system of Fig. 6, with the finger and thermal link in a separation configuration.

[0031] [Fig. 8] shows schematically, in section, an example of a management system, the finger and the thermal link being in a coupling configuration.

[0032] [Fig. 9] is a view similar to Fig. 8 of the exemplary management system of Fig. 8, with the finger and thermal link in a separation configuration. Description of the embodiments

[0033] In the various figures, the same references designate identical or similar elements. For the sake of brevity, only the elements which are useful for understanding the embodiment described are shown in the figures and are described in detail below.

[0034] Reference is now made to Figure 1. This represents a spatial cryogenic cooling system 100 for equipment to be cooled 50, for example a detector or detection system or a measuring system, for example optical. The equipment to be cooled 50 may be part of an instrument of which only a part, called equipment to be cooled, needs to be cooled to a temperature below 200K, in particular below 150K, or even to a temperature below 70K.

[0035] The space cooling system 100 has a so-called hot redundancy of the cryogenic machine.

[0036] The spatial cooling system 100 comprises a cryostat 101, shown in dotted lines, which is by definition a passive enclosure whose role is to limit as much as possible thermal leaks to the environment. The spatial cooling system 100 comprises two cryogenerators 40 configured to generate cold, for example using a compressor or other dilution system, the cryogenerators 40 further comprising a finger 2, which is a cold finger 2. Only a part of each cryogenerator 40, namely the cold finger 2, has been shown for the sake of clarity of the drawing.

[0037] For each cryogenerator 40, the spatial cooling system 100 comprises a thermal link 4 and a management system 1 for a thermal coupling between the thermal link 4 and the cold finger 2 of each cryogenerator 40 or an interface 3 of the equipment to be cooled 50. In the example illustrated, the management system 1 acts at the level of the thermal coupling between each thermal link 4 and the cold finger 2 of each cryogenerator 40. The thermal link 4 may be a thermal braid. It is a conductive element, metallic for example, or carbon for certain less cold applications, that is to say over a temperature range between 150K and 200K. The interface 3 of the equipment to be cooled 50 forms an interface of the focal plane with the two thermal links 4 coupled moreover respectively to the two cryogenerators 40. The interface 3 is for example connected to a focal plane 51 of the equipment to be cooled 50 to be maintained at a temperature for example lower than 70K.

[0038] The management system 1 comprises a fixing system 5 configured to ensure, in a pretensioned state, a direct coupling between the finger 2 or the interface 3, in this example the cold finger 2 of the cryogenerator 40, and the thermal link 4, in a coupling configuration, illustrated in FIG. 1. The management system 1 also comprises a separation system 6 configured to reduce or eliminate the pretensioned state of the fixing system 5 in order to reduce or eliminate the thermal coupling at the cold finger 2 or the interface 3, in a coupling configuration, illustrated in FIG. separation, not illustrated in this example, but which will be detailed later, in another example.

[0039] The thermal link 4 may, for example, comprise a thermal braid. The thermal link may, for example, comprise one or more heat pipes. The thermal link may, for example, comprise a thermal seal. The thermal link may, for example, comprise a finger end. The finger 2 is, for example, at least partly movable or flexible. The interface 3 is, for example, at least partly movable or flexible. The thermal link 4 is, for example, at least partly movable or flexible. The flexibility allows a spacing, for example, of a few micrometers.

[0040] Subsequently, the thermal coupling management systems described can be applied indifferently to the cold finger or to the interface of the instrument to be cooled.

[0041] The fixing system 5 is arranged in this example on either side of the cold finger 2 and the thermal link 4. Furthermore, the fixing system 5 is arranged neutrally with respect to a conductive path C connecting the cold finger 2 and the interface 3 via the thermal link 4. In other words, it is arranged in parallel with this conductive path C and is not part of it.

[0042] In this example, the fastening system 5 comprises a rod 7, which is a threaded rod in this example, and a clamping ring 8, which is a nut in this example, the rod 7 being in said pretensioned state in the coupling configuration illustrated in FIG. 1. This means that the rod 7 and the clamping ring 8 which surround the cold finger 2 and the thermal link 4 are screwed tight so as to ensure a mechanical and therefore thermal coupling between the cold finger 2 and the thermal link 4 at an interface plane 15, thus creating an optimal thermal path in nominal mode. The distance between the cold finger 2 and the thermal link 4 is zero at the interface plane 15, in the coupling configuration.

[0043] The rod 7 has a weak point 9. Such a weak point 9 may be the result of machining the rod 7 so as to create a constriction forming a weak point in terms of structural strength. The separation system 6 is configured to break the rod 7 at the weak point 9, which is therefore a precise location, at a predetermined temperature. It should be noted that this break is definitive. It is thus not possible to switch from the separation configuration to the coupling configuration without changing the rod 7, that is to say without carrying out a maintenance operation on land.

[0044] To create this rupture of the rod 7 at the weak point 9, the separation system 6 comprises in this example a heating device 10 and a component 11 comprising a material, of the shape memory material type, capable of changing dimension when it is heated to a predetermined temperature.

[0045] The shape memory material of the component 11 is arranged in the fixing system 5, at least in the coupling configuration, and bears against at least one head 12 at the end of the rod 7 or against the clamping ring 8, in this example at the end of the rod 7. The triggering of the heating device 10 causes the change in dimension of the component 11, creating a force aimed at moving the head 12 away from the thermal link 4, which causes the breakage of the rod 7 at the weak point 9. The pretension is removed and, in this example, the previously coupled thermal link 4 and cold finger 2 are then separated. The distance between the thermal link 4 and the cold finger 2, at least in certain places, is non-zero, being for example of the order of a tenth of a millimeter. The mechanical coupling is broken, thereby reducing or breaking the thermal coupling. The conductive path C is thus interrupted. There is therefore no thermal leakage, or this thermal leakage is minimal, in the case where there remains contact between the cold finger 2 and the thermal link 4. The cryogenerators therefore do not need to be oversized. It should be noted that the fact that the management system 1 is arranged in parallel with the conductive path, and not on the path of this conductive path, makes it possible not to deteriorate the performance of the spatial cooling system 100 in nominal mode.

[0046] The shape memory material is advantageously an alloy, typically chosen from Ni-Ti (Nickel-Titanium) or Cu-Al-Ni (Copper-Aluminum-Nickel) alloys. Its intrinsic properties induce a sudden change in the arrangement of the material, in particular of the atoms, which creates a change in dimension when it is heated to a temperature within a range of values ​​of at most a few degrees Celsius. This makes it possible to know precisely and therefore control the change of state temperature at which the material will pass from a first state to a second state by changing the arrangement of the material. By controlling the heating device 10, it is therefore easy and in a controlled manner to cause a change of state of the shape memory material so as to reduce or eliminate the pretension in the fixing system 5. In practice, the activation temperature can be defined over a range of less than 1 °C, that is to say precisely.No overheating of the equipment to be cooled 50 above its maximum permissible temperature is generated by the management system 1.

[0047] Other materials may be considered apart from shape memory materials, in particular materials with differential expansion, used for example to produce the rod 7 for one and to produce the clamping ring 8 for the other. For example, the rod 7 could be made of TA6V type titanium (CTE 7 um / m / K) and the clamping ring 8 could be made of A4-70 type steel (CTE 16 um / m / K). Thus, when heated, the clamping ring 8 expands more than the rod 7 and slippage occurs, causing the pretension, or preload, to be lost.

[0048] In the example illustrated in Figure 1, the cold finger 2 and the thermal link 4 each comprise a through hole, respectively 41 and 42. At least in the coupling configuration, the rod 7 passes through the cold finger 2 and the thermal link 4 by extending into the through holes 41 and 42 which are aligned with each other. The weak point 9 is arranged in this example within the cold finger 2 near the interface plane 15.

[0049] As explained, the interface between the cold finger 2 and the thermal link 4 is flat, in the example of figure 1, and forms the interface plane 15.

[0050] In the example of figures 2 and 3, the coupling between the cold finger 2 and the thermal link 4 is carried out at a cylindrical contact surface 16 forming the interface between the cold finger 2 and the thermal link 4.

[0051] Furthermore, in this example, the fixing system 5 comprises a terminal 18 configured to surround the thermal link 4 and the cold finger 2. The terminal 18 comprises an open ring portion 19 comprising an opening 20 and surrounding the thermal link 4 and the cold finger 2 and a clamping portion 21 comprising two free ends 22 extending from said opening 20. In this example, the rod 7 passes through, via corresponding through holes, the two free ends 22 at least in the coupling configuration. Figure 2 illustrates the coupling configuration, in nominal mode, the mechanical and therefore thermal coupling between the cold finger 2 and the thermal link 4 being ensured at the level of the cylindrical contact surface 16 so as to create the desired conductive path in this configuration.Figure 3 illustrates the separation configuration, after rupture of the weak point 9, the mechanical and therefore thermal coupling between the cold finger 2 and the thermal link 4 no longer existing.

[0052] Still in this example, the terminal 18 comprises, in itself, by its stiffness for example, an elastic return function aimed at separating the free ends 22 from each other in the separation configuration, so as to ensure that any contact between the cold finger 2 and the thermal link 4 is reduced or even eliminated. In the same way, the thermal link 4 can be configured to comprise an elastic return function aimed at separating it from the cold finger 2 in the separation configuration.

[0053] Still in this example, the management system 1 comprises a bolt catcher 25 configured to retain at least one of a portion of the rod 7 and the clamping ring 8 in the separation configuration. In this example, there are two bolt catches 25, one, referenced 25a, being configured to retain a portion of the rod 7 and the head 12, and the other, referenced 25b, being configured to retain the clamping ring 8 secured to another portion of the rod 7. Thus, in the separation configuration, no element escapes freely into the enclosure of the cryostat.

[0054] In the example of Figures 4 and 5, the spatial cooling system 100 comprises two thermal links 4, denoted 4a and 4b, arranged on either side of the cold finger 2 and comprising an elastic return function 31 configured to separate the cold finger 2 and the thermal link 4, in the separation configuration, this elastic return function 31 comprising in this example a spring 32 connecting the two thermal links 4a and 4b, the spring 32 being compressed in the coupling configuration. As soon as the pretension is reduced or removed, the spring 32 acts to separate the thermal links 4 to reduce or remove the contact of the thermal links 4a and 4b with the cold finger 2.

[0055] Alternatively or additionally, the elastic return function 31 may comprise a stiffness of the thermal links 4a and 4b, the thermal links 4a and 4b having an orientation tending to separate them from each other in the absence of mechanical constraints.

[0056] The spring 32 may connect the thermal link(s) 4 to other structural parts of the space cooling system 100.

[0057] Figures 2 and 3 as well as Figures 4 and 5 illustrate the coupling configuration and the separation configuration.

[0058] The transition from one to the other is done using the implementation of the method of separating a coupling between a finger 2 or an interface 3 of one of the cryogenerators 40 which is faulty or of the equipment to be cooled 50, and a thermal link 4 ensuring the conductive path C between said faulty cryogenerator 40 and the equipment to be cooled 50 in a spatial cooling system 100.

[0059] Such a method firstly comprises the detection of failure of one of the cryogenerators 40. This detection can be carried out by detecting a rise in temperature of the equipment to be cooled 50 which, after investigation, can be associated with a faulty cryogenerator.

[0060] In this case, the method then comprises activating the separation system 6 so as to reduce or eliminate the coupling between the faulty cryogenerator 40 or the equipment to be cooled 50 via the finger 2 or the interface 3, and the thermal link 4. This operation comprises, in the examples illustrated, controlling the heating device 10 so as to cause the change of state of the shape memory material in order to break the rod 7 at its weak point 9. After this operation, which is not reversible, as explained above, all or part of the thermal leak generated by the faulty cryogenerator 40 is eliminated. These steps can be controlled from Earth, remotely from the space cooling system 100. This thus meets a need to thermally disconnect a faulty cryogenerator which becomes a source of thermal leak penalizing performance.

[0061] In the example of Figures 6 and 7, the management system 1 differs from that of Figures 2 and 3 in that the terminal 18 comprises an elastic return function intended to separate the free ends 22 from each other in the separation configuration illustrated in Figure 7. This elastic return function takes in this example the form of a spring 33 arranged in the opening 20 extending between the two portions of the clamping part 21, in a compressed state in the coupling configuration illustrated in Figure 6. This spring 33 is configured to deploy in the separation configuration illustrated in Figure 7 so as to separate the ends 22 of the clamping part 21 in order to release the clamping of the thermal link 4 against the cold finger 2.

[0062] It should also be noted in this example that the thermal link 4 forms two thermal links 4a and 4b forming annular portions connected to each other by springs 34 in the compressed state in the coupling configuration in FIG. 6 and deployed in the separation configuration in FIG. 7, because they are freed from their stress, and so as to separate the thermal links 4a and 4b from each other and thus separate the thermal links 4a and 4b from the cold finger 2.

[0063] The example illustrated in Figures 8 and 9 differs from that of Figures 4 and 5 in that the fixing system 5 comprises two threaded rods 7 arranged parallel to each other, passing through through holes of the corresponding thermal links 4 and cold finger 2.

[0064] Furthermore, in this example, two springs 32 are provided on either side of the cold finger 2 to separate, in the separation configuration, the thermal links 4a and 4b away from the cold finger 2 once the pretension has been removed by the breaking of the rods 7 at their weak point 9.

[0065] Of course, this disclosure is not limited to the examples just described.

[0066] In particular, component 11 may comprise a material other than a shape memory material.

[0067] The rod 7 may not be broken but released in the transition to the separation configuration. In this case, we have a shock-free solution.

[0068] The rod 7 may be an unthreaded rod, for example if a rivet is used.

[0069] The management system 1 can be located at the interface 3 of the equipment to be cooled 50, the interface 3 forming the interface of the equipment to be cooled 50. In this case, compared to the system illustrated in figure 1, the interface 3 is duplicated to break the conductive path C only with one of the cryogenerators via the thermal link 4.

Claims

Claims

1. A spatial cryogenic cooling system (100) for equipment to be cooled, comprising: at least two cryogenerators each being in an operational or non-operational state, the cryogenerators being redundant and configured to generate cold simultaneously in their operational state, each cryogenerator comprising a cold finger (2), the cold fingers being connected to at least one interface (3) with the equipment to be cooled, in their operational state, a management system (1) associated with each cryogenerator and controlled as a function of the operational or non-operational state of the associated cryogenerator, each management system ensuring, when the associated cryogenerator is in the operational state, a thermal coupling between the cold finger (2) of the associated cryogenerator and said interface (3);the system being characterized in that each management system (1) comprises: a fixing system (5) configured to ensure, in a pre-tensioned state of the fixing system, a direct coupling with the finger (2) or said interface (3), in the operational state of the associated cryogenerator; a separation system (6) configured to reduce or eliminate the pre-tensioned state of the fixing system (5) in order to reduce or eliminate the thermal coupling with the finger (2) or said interface (3), in the non-operational state of the associated cryogenerator, the fixing system (5) being arranged on either side of the finger (2) or said interface (3) and neutrally with respect to a conductive path (C) connecting the finger (2) and said interface (3), each finger (2) being connected to said interface (3) via a thermal link (4) belonging to the conductive path (C).;

2. System according to claim 1, in which the coupling between the finger (2) or the interface (3) on the one hand and the thermal link (4) on the other hand is carried out at an interface plane (15) between the finger (2) or the interface (3) and the thermal link (4).

3. System according to claim 1 or 2, in which at least one of the thermal links (4; 4a, 4b) is arranged on either side of the finger (2) or the interface (3), the management system comprising an elastic return function (31) configured to separate the finger (2) or the interface (3) and said thermal link (4) arranged on either side of the finger (2) or the interface, in separation configuration.

4. System according to claim 3, in which the elastic return function (31) comprises a spring (32) tending to separate the portions of said thermal link arranged on either side of the finger (2) or the interface, the spring (32) being compressed in the coupling configuration.

5. System according to claim 3 or 4, in which the elastic return function (31) comprises a stiffness of said thermal link (4) arranged on either side of the finger (2) or of the interface, said thermal link (4) arranged on either side of the finger (2) or of the interface having a orientation tending to separate from each other the portions of said thermal link arranged on either side of the finger (2) or the interface, in the absence of mechanical constraints.

6. System according to one of claims 1 and 2, in which the fixing system comprises a rod (7) and a clamping ring (8), the rod (7) being in said pre-tensioned state in the coupling configuration.

7. System according to claim 6, wherein the rod (7) has a weak point (9) and wherein the separation system (6) is configured to break the rod (7) at the weak point (9), the separation system (6) comprising a heating device (10) and a component (11) comprising a material, of the shape memory material type, capable of changing dimension when heated to a predetermined temperature.

8. System according to the preceding claim, in which the shape memory material is arranged in the fixing system (5), at least in the coupling configuration, and comes to bear against at least one head (12) at the end of the rod (7) or against the clamping ring (8).

9. System according to one of claims 6 to 8, comprising a bolt catcher (25) configured to retain at least one of a portion of the rod (7) and the clamping ring (8) in the separation configuration.

10. A method of separating a coupling of a finger (2) or an interface of equipment to be cooled (50) connected to one of the cryogenerators (40) which is faulty, to reduce or cut a conductive path (C) between said faulty cryogenerator (40) and the equipment to be cooled (50) in a space cooling system (100) according to any one of the preceding claims, comprising: a. detecting failure of the cryogenerator (40); b. activating the separation system (6) so as to reduce or eliminate the thermal coupling at the finger (2) or the interface (3).

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