System for managing thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled

Abstract

A thermal coupling management system (1) for a thermal link (4) and a finger (2; 3) of a cryogenerator or equipment to be cooled, comprising: a fastening system (5) configured to ensure, in a pre-tensioned state, a direct coupling between the finger (2; 3) and the thermal link (4), in a coupling configuration; and a separation system (6) configured to reduce or eliminate the pre-tensioned 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. Abstract figure: Figure 1

Description

Title of the invention: System for managing thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled technical field

[0001] This disclosure falls within the field of thermomechanics, specifically cryogenic cooling of space equipment. This disclosure can be applied to any cooling system with redundancy of the cryogenic machine. In particular, this disclosure relates to a system for managing thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled, as well as a cryogenic cooling space system incorporating such a management system. Previous technique

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

[0003] The presence of two cryogenerators provides security in case of failure of one of the two cryogenerators and constitutes what is commonly called redundancy.

[0004] The two 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 case of failure.

[0005] Another operating principle for the two cryogenerators is known as hot redundancy. This principle involves operating both cryogenerators simultaneously, for example, each providing 50% of the cooling energy. If one of the two cryogenerators fails, the other is then called upon to provide 100% of the cooling energy. This disclosure relates in particular to a cryogenic cooling system operating according to this hot redundancy principle.

[0006] One problem that arises particularly in the implementation of cold redundancy is the parasitic heat leakage related to the coupling of the non-operational cryogenerator. In the case of hot redundancy, this leakage only occurs in the event of a cryogenerator failure. For both redundancy principles, this parasitic heat leakage is a major parameter affecting the performance of a cooling system present in cryogenic instruments onboard spacecraft such as Earth observation satellites or scientific mission satellites. This leakage typically accounts for 30% of the cryogenic power required to maintain the equipment being cooled, particularly the detection system, at its operating temperature. This leakage is generated by the non-operational cryogenerator—that is, one that is faulty or not in use—which, being out of service, creates a direct link between the equipment being cooled, for example at 60 K, and the rest of the instrument, for example at 293 K. The leakage can potentially degrade the instrument's performance and necessarily leads to oversizing of the cryogenerators.

[0007] To solve the problem of thermal leakage in the case of hot redundancy, thermal switch solutions have been considered, described in WO2007116157 and FR2985004.

[0008] WO2007116157 proposes a fragile material, typically sapphire, on the The thermal path between the cryogenerator and the equipment to be cooled is a complex process. When the cryogenerator fails, the brittle material breaks, interrupting the thermal path and thus the heat leak. However, its presence degrades the nominal thermal coupling, particularly through its two contact surfaces. Furthermore, its fragility 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 a solder Integrated between the cryogenerator and the equipment to be cooled, with a heating system that breaks the brazing joint. This solution is poorly suited to cryogenic space instruments because the brazing necessarily occurs at too high a temperature, which presents a high risk of overheating and damaging the equipment. Furthermore, this brazing introduces thermal resistance along the conductive thermal path between the cryogenerator and the equipment, degrading the nominal thermal coupling.

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

[0011] This disclosure improves the situation.

[0012] A system for managing thermal coupling between a thermal link and a finger of a cryogenerator or equipment to be cooled is proposed, comprising: - a fastening system configured to ensure, in a pre-tensioned state, a direct coupling between the finger and the thermal link, in a coupling configuration; - a separation system configured to reduce or eliminate the pretension state of the fastening system in order to reduce or eliminate the coupling between the finger and the thermal bond, in a separation configuration.

[0013] The features described in the following paragraphs may optionally be implemented independently of each other or in combination with each other:

[0014] The fastening system can be arranged on either side of the finger and the thermal link and in a neutral manner with respect to a conductive path linking the finger and the thermal link.

[0015] The fastening system may include a rod, which may be a threaded rod, and a clamping ring, which may be a nut, the rod being in said pre-tensioned state in the coupling configuration.

[0016] The rod may, for example, have a weak point. In this case, the separation system can be configured to break the rod at the weak point. The separation system may, for example, include a heating device and a component comprising a material, in particular a shape-memory material, capable of changing dimensions when heated to a predetermined temperature.

[0017] If the component includes a shape-memory material, the shape-memory material may be arranged in the fastening system, at least in the coupling configuration. The shape-memory material may bear against at least one head at the end of the rod or against the clamping ring.

[0018] At least in the coupling configuration, the rod can pass through the finger and the thermal link, each having a through hole.

[0019] The coupling between the finger and the thermal link can be achieved at the level of an interface plane between the finger and the thermal link.

[0020] Alternatively, the coupling between the finger and the thermal link can be achieved at a cylindrical contact surface between the finger and the thermal link.

[0021] In this case, the fastening system may include a lug configured to surround the thermal link and the finger. The lug may include an open ring portion having an opening and surrounding the thermal link and the finger, and a clamping portion having two free ends extending from this opening. The stem may pass through both free ends, at least in the coupling configuration.

[0022] The lug may include an elastic return function aimed at separating the free ends in the separation configuration.

[0023] The management system may include a bolt catcher configured to retain at least one of a portion of the rod and the clamping ring in separation configuration.

[0024] According to another aspect, a cryogenic cooling space system for equipment to be cooled is proposed in combination with the above, comprising two cryogenerators configured to generate cold, and, for each cryogenerator, a thermal link and a management system as defined above.

[0025] The spatial cooling system may include two thermal links disposed on either side of the finger and having an elastic return function configured to separate the finger and the thermal link in the separation configuration. This elastic return function may include a spring connecting the two thermal links, the spring being compressed in the coupling configuration.

[0026] The elastic restoring function may include a stiffness of the thermal links, the thermal links having an orientation tending to move them away from each other in the absence of mechanical constraints.

[0027] According to another aspect, a method is proposed, in combination with the above, for separating a coupling between a finger of one of the cryogenerators that is faulty or of the equipment to be cooled, and a thermal link ensuring the conductive path between said faulty cryogenerator and the equipment to be cooled in a cooling system as defined above, comprising: a. cryogenerator failure detection; b. activation of the separation system so as to reduce or eliminate the coupling between the finger and said thermal bond. Brief description of the drawings

[0028] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings, on which:

[0029] [Fig. 1] schematically shows in side view and in longitudinal section an example of a space cooling system comprising an example of a thermal coupling management system between a thermal link and a finger of a cryogenerator or of equipment to be cooled.

[0030] [Fig.2] schematically shows, in cross-section, a management system according to another example, the finger and the thermal link being in a coupling configuration.

[0031] [Fig.3] is a view similar to [Fig.2] of the example management system of [Fig.2], the finger and the thermal link being in a separation configuration.

[0032] [Fig.4] schematically shows, in cross-section, another example of a management system, the finger and the thermal link being in a coupling configuration.

[0033] [Fig.5] is a view similar to [Fig.4] of the example management system of [Fig.4], the finger and the thermal link being in a separation configuration.

[0034] [Fig.6] schematically shows, in cross-section, another example of a management system, the finger and the thermal link being in a coupling configuration.

[0035] [Fig.7] is a view similar to [Fig.6] of the example management system of [Fig.6], the finger and the thermal link being in a separation configuration.

[0036] [Fig.8] schematically shows, in cross-section, another example of a management system, the finger and the thermal link being in a coupling configuration.

[0037] [Fig.9] is a view similar to [Fig.8] of the example management system of [Fig.8], the finger and the thermal link being in a separation configuration. Description of embodiments

[0038] In the various figures, the same reference numerals designate identical or similar elements. For the sake of brevity, only the elements that are useful for understanding the described embodiment are shown in the figures and are described in detail below.

[0039] Reference is now made to [Fig. 1]. This figure represents a cryogenic space cooling system 100 for equipment to be cooled 50, for example, a detector or detection system or a measurement system, for example, optical. The equipment to be cooled 50 may be part of an instrument of which only a part, called the equipment to be cooled, needs to be cooled to a temperature below 200 K, in particular below 150 K, or even below 70 K.

[0040] The space cooling system 100 has a redundancy, called hot, of the cryogenic machine.

[0041] The space cooling system 100 includes a cryostat 101, shown in dashed lines, which is by definition a passive enclosure designed to minimize heat loss to the environment. The space cooling system 100 includes two cryogenerators 40 configured to generate cold, for example using a compressor or other dilution system. The cryogenerators 40 also include a finger 2, which is a cold finger 2. Only a portion of each cryogenerator 40, namely the cold finger 2, is shown for the sake of clarity in the drawing.

[0042] For each cryogenerator 40, the space cooling system 100 comprises a thermal link 4 and a management system 1 for thermal coupling between the thermal link 4 and the cold finger 2 of each cryogenerator 40 or a finger 3, which is an interface, of the equipment to be cooled 50. In the illustrated example, 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 can be a thermal braid. It is a conductive element, metallic for example, or carbon for certain less cold applications, i.e., over a temperature range between 150 K and 200 K. The finger 3 of the equipment to be cooled 50 forms a focal plane interface with the two thermal links 4, which are also coupled respectively to the two cryogenerators 40. The finger 3 is connected to a focal plane 51 of the equipment to be cooled 50 to be maintained at a temperature for example below 70K.

[0043] The control system 1 includes a fastening system 5 configured to ensure, in a pre-tensioned state, a direct coupling between the finger 2 or 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 control system 1 further includes a separation system 6 configured to reduce or eliminate the pre-tensioned state of the fastening system 5 in order to reduce or eliminate the coupling between the cold finger 2 and the thermal link 4, in a separation configuration not illustrated in this example, but which will be detailed later in another example.

[0044] In this example, the fastening system 5 is arranged on either side of the cold finger 2 and the thermal link 4. Furthermore, the fastening system 5 is arranged in a neutral manner with respect to a conductive path C connecting the cold finger 2 and the finger 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.

[0045] 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 the pre-tensioned state in the coupling configuration illustrated in [Fig. 1]. This means that the rod 7 and the clamping ring 8 surrounding the cold finger 2 and the thermal link 4 are screwed tightly so as to ensure 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.

[0046] The rod 7 has a weak point 9. Such a weak point 9 can be the result of machining the rod 7 to create a necking that forms a weak point in terms of structural integrity. 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 permanent. It is therefore not possible to switch from the separation configuration to the coupling configuration without changing the rod 7, i.e., without performing a maintenance operation on land.

[0047] To create this break in the rod 7 at the weak point 9, the separation system 6 in this example comprises a heating device 10 and a component 11 comprising a material, of the shape memory type, capable of changing dimensions when heated to a predetermined temperature.

[0048] The shape-memory material of component 11 is arranged in the fastening 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 rod 7. Activation of the heating device 10 causes a change in the dimensions of component 11, creating a force that pushes the head 12 away from the thermal link 4, causing the rod 7 to break at the weak point 9. The pre-tension 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 some places, is non-zero, being, for example, on 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. Therefore, there is no thermal leakage, or this thermal leakage is minimal, in the case where contact remains between the cold finger 2 and the thermal link 4. Cryogeners 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, prevents the performance of the spatial cooling system 100 from being degraded in nominal mode.

[0049] 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 matter, particularly atoms, which creates a change in dimensions when heated to a temperature within a range of a few degrees Celsius. This makes it possible to know precisely, and therefore control, the phase change temperature at which the material will transition from a first state to a second state by changing the arrangement of matter. By controlling the heating device 10, it is therefore easy and controllable to induce a phase change in the shape memory material in order to reduce or eliminate the pretension in the fastening system 5. In practice, the activation temperature can be defined within a range of less than 1°C, i.e., precisely.No overheating of the equipment to be cooled 50 above its maximum permissible temperature is generated by the management system 1.

[0050] Other materials besides shape-memory materials can be considered, particularly materials with differential expansion, used, for example, to make the rod 7 in one application and the clamping ring 8 in the other. For example, the rod 7 could be made of TA6V type titanium (CTE 7 µm / m / K) and the clamping ring 8 could be made of A4-70 type steel (CTE 16 µm / m / K). Thus, when heated, the clamping ring 8 expands more than the rod 7, and slippage occurs, causing a loss of preload.

[0051] In the example illustrated in [Fig. 1], the cold finger 2 and the thermal link 4 each have a through hole, 41 and 42 respectively. At least in the coupling configuration, the rod 7 passes through the cold finger 2 and the thermal link 4 in extending into the through holes 41 and 42, which are aligned with each other. The weak point 9 is located in this example within the cold finger 2, near the interface plane 15.

[0052] As explained, the interface between the cold finger 2 and the thermal link 4 is planar, in the example of [Fig.1], and forms the interface plane 15.

[0053] In the example of figures 2 and 3, the coupling between the cold finger 2 and the thermal link 4 is achieved at the level of a cylindrical contact surface 16 forming the interface between the cold finger 2 and the thermal link 4.

[0054] Furthermore, in this example, the fastening system 5 comprises a lug 18 configured to surround the thermal link 4 and the cold finger 2. The lug 18 comprises an open ring portion 19 having an opening 20 and surrounding the thermal link 4 and the cold finger 2, and a clamping portion 21 having two free ends 22 extending from said opening 20. In this example, the rod 7 passes, through corresponding through holes, through at least the two free ends 22 in the coupling configuration. [Fig. 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 cylindrical contact surface 16 so as to create the desired conductive path in this configuration. [Fig.[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.

[0055] Still in this example, the lug 18 has, 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 reduce or even eliminate any contact between the cold finger 2 and the thermal link 4. In the same way, the thermal link 4 can be configured to have an elastic return function aimed at separating it from the cold finger 2 in the separation configuration.

[0056] Still in this example, the control system 1 includes 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 catchers 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 attached to another portion of the rod 7. Thus, in the separation configuration, no element escapes freely into the cryostat enclosure.

[0057] 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 a separation configuration, this elastic return function 31 comprising in this example a spring 32 connecting the two links thermal links 4a and 4b, with spring 32 compressed in the coupling configuration. As soon as the pretension is reduced or removed, spring 32 acts by separating the thermal links 4 to reduce or eliminate the contact of the thermal links 4a and 4b with the cold finger 2.

[0058] Alternatively or additionally, the elastic restoring function 31 may include a stiffness of the thermal links 4a and 4b, the thermal links 4a and 4b having an orientation tending to move them away from each other in the absence of mechanical stresses.

[0059] The spring 32 can connect the thermal link(s) 4 to other structural parts of the space cooling system 100.

[0060] Figures 2 and 3, as well as Figures 4 and 5, illustrate the coupling configuration and the separation configuration.

[0061] The transition from one to the other is achieved by means of implementing the method of separating a coupling between a finger 2 or 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 space cooling system 100.

[0062] Such a process first involves detecting the 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 failing cryogenerator.

[0063] In this case, the process then includes 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 3, and the thermal link 4. This operation includes, in the illustrated examples, 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 leakage generated by the faulty cryogenerator 40 is eliminated. These steps can be controlled from Earth, remotely from the space cooling system 100. This addresses the need to thermally disconnect a faulty cryogenerator that becomes a source of thermal leakage penalizing performance.

[0064] In the example of Figures 6 and 7, the control system 1 differs from that of Figures 2 and 3 in that the lug 18 has an elastic return function designed to separate the free ends 22 from each other in the separation configuration illustrated in [Fig. 7]. This elastic return function takes the form, in this example, of a spring 33 disposed in the opening 20 extending between the two portions of the clamping part 21, in a compressed state in the coupling configuration illustrated. on [Fig.6]. This spring 33 is configured to deploy in the separation configuration illustrated on [Fig.7] so as to spread apart the ends 22 of the clamping part 21 in order to release the clamping of the thermal link 4 against the cold finger 2.

[0065] 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 on the [Fig.6] and deployed in the separation configuration on the [Fig.7], because they are freed from their constraint, 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.

[0066] The example illustrated in Figures 8 and 9 differs from that in Figures 4 and 5 in that the fastening system 5 comprises two threaded rods 7 arranged parallel to each other, passing through through holes in the corresponding thermal links 4 and cold finger 2.

[0067] Furthermore, in this example, two springs 32 are provided on either side of the cold finger 2 to separate, in 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.

[0068] Of course, this disclosure is not limited to the examples just described.

[0069] In particular, component 11 may comprise a material other than a shape memory material.

[0070] The rod 7 can be released rather than broken during the transition to the separation configuration. In this case, a shock-free solution is obtained.

[0071] The rod 7 can be an unthreaded rod, for example if a rivet is used.

[0072] The management system 1 can be located at the finger 3 of the equipment to cool 50, the finger 3 forming the interface of the equipment to be cooled 50. In this case, compared to the system illustrated in [Fig.1], the finger 3 is duplicated so as to break the conductive path C only with one of the cryogenerators via the thermal link 4.

Claims

1.

2.

3. Demands Cryogenic space cooling system (100) for equipment to be cooled, comprising: - at least two cryogenerators, each in an operational or non-operational state, the cryogenerators being redundant and configured to generate cold simultaneously in their operational state, - at least two thermal links, each connecting one of the cryogenerators, in its operational state, to the equipment to be cooled via at least one finger, - a management system (1) associated with each cryogenerator and controlled according to 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 thermal link (4) of the associated cryogenerator and a finger (2; 3) of the associated cryogenerator or of the equipment to be cooled, The system is characterized in that each management system comprises: - a fastening system (5) configured to ensure, in a pre-tensioned state of the fastening system, a direct coupling between the finger (2; 3) and the thermal link (4), in the operational state of the associated cryogenerator; - a separation system (6) configured to reduce or eliminate the pretension 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 the non-operational state of the associated cryogenerator. System according to claim 1, wherein the fastening system (5) is disposed on either side of the finger (2; 3) and the thermal link (4) and in a neutral manner with respect to a conductive path (C) connecting the finger (2; 3) and the thermal link (4). System according to claim 1 or 2, wherein the fastening system comprises a rod (7) and a clamping ring (8), the rod (7) being in said pretensioned state in the coupling configuration.

4. System according to claim 3, 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 type, capable of changing dimensions when heated to a predetermined temperature.

5. System according to the preceding claim, wherein the shape memory material is disposed in the fastening 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).

6. System according to any one of the preceding claims, wherein the coupling between the finger (2; 3) and the thermal link (4) is achieved at the level of an interface plane (15) between the finger (2; 3) and the thermal link (4).

7. System according to claim 3 and possibly any of the preceding claims, comprising a bolt catcher (25) configured to retain at least one of a portion of the rod (7) and the clamping ring (8) in separation configuration.

8. A space cooling system (100) according to any one of the preceding claims, comprising two thermal links (4; 4a, 4b) disposed on either side of the finger (2; 3) and comprising an elastic return function (31) configured to separate the finger (2; 3) and the thermal link (4), in the separation configuration, this elastic return function (31) comprising a spring (32) connecting the two thermal links (4; 4a, 4b), the spring (32) being compressed in the coupling configuration.

9. Space cooling system (100) according to the preceding claim, wherein the elastic restoring function (31) comprises a stiffness of the thermal links (4; 4a, 4b), the thermal links (4; 4a, 4b) having an orientation tending to move them away from each other in the absence of mechanical stresses.

10. Method of separating a coupling between a finger (2; 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 cooling system (100) according to any one of the preceding claims, comprising: a. cryogenerator failure detection (40); b. activation of the separation system (6) so as to reduce or eliminate the coupling between the finger (2; 3), and said thermal link (4).

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