Cryogenic propellant tank for a spacecraft engine

Abstract

Cryogenic propellant tank for a spacecraft engine. The invention relates to a cryogenic propellant tank for a spacecraft engine, comprising a wall delimiting a storage volume for the cryogenic propellant, the wall being made of a composite material and comprising a fibrous reinforcement in the form of a fiber stack (110) which is densified by an organic matrix, the fiber stack comprising at least in succession in this order in the direction of the thickness (E) of the wall: (a) a first ply (113) of unidirectional fibers oriented at an angle of –α, (b) a second ply (115) of unidirectional fibers oriented at an angle of -β°, (c) a third ply (117) of unidirectional fibers oriented at an angle of +α, and (d) a fourth ply (119) of unidirectional fibers oriented at an angle of +β°, with α between 5° and 20°. and β between 40° and 50°, each angle being taken with respect to a longitudinal axis of the reservoir.Figure for the summary: Fig. 4.

Description

Title of the invention: Cryogenic propellant tank for a spacecraft engine. Technical field

[0001] The present disclosure relates to a cryogenic propellant tank made of composite material for a spacecraft engine having improved mechanical properties and sealing at low temperatures. Previous technique

[0002] Space launcher engines typically consume cryogenic propellants stored in dedicated tanks. Cryogenic propellants are maintained at very low temperatures, on the order of 90 K for oxygen, 20 K for hydrogen, or 110 K for methane.

[0003] Composite materials have been proposed as an attractive alternative to metallic materials for reducing the mass of the tank. However, it is possible to improve existing composite solutions in terms of maintaining leak-tightness and preserving mechanical properties at the low temperatures involved. Description of the invention

[0004] The present description relates to a cryogenic propellant tank for a spacecraft engine, comprising a wall delimiting a storage volume for the cryogenic propellant, the wall being made of composite material and comprising a fibrous reinforcement in the form of a fibrous stack which is densified by an organic matrix, the fibrous stack comprising at least in succession in this order in the direction of the thickness of the wall: (a) a first ply of unidirectional fibers oriented at an angle of -a, (b) a second ply of unidirectional fibers oriented at an angle of -|3, (c) a third ply of unidirectional fibers oriented at an angle of +a, and (d) a fourth ply of unidirectional fibers oriented at an angle of +[3, with a between 5° and 20° and [3 between 40° and 50°, each angle being taken with respect to a longitudinal axis of the tank.

[0005] The first and third plies, having the + / - orientation described above, are relatively well aligned with each other, which gives the tank wall good resistance to the stresses exerted when the tank is filled and cooled. The inventors nevertheless observed that using only the first and third plies could lead to a loss of tank seal if matrix cracks appeared, which could then generate a network of long cracks in the affected plie as well as in the adjacent plies. To overcome this drawback, the invention proposes adding to the stack the second and fourth folds described above which are sufficiently disoriented with respect to the first and third folds to limit the opening of matrix cracks by minimizing interactions between adjacent folds, but whose disorientation remains limited so as not to generate excessive thermomechanical stresses when the tank is cooled.

[0006] In an example embodiment, a is between 13° and 17°, for example is approximately equal to 15°.

[0007] In an example embodiment, [3 is between 43° and 47°, for example is substantially equal to 45°.

[0008] Such a characteristic advantageously makes it possible to further limit the opening of matrix cracks, without generating excessive thermomechanical stresses during cooling.

[0009] In one embodiment, the fiber stack further comprises an additional ply of unidirectional fibers oriented at an angle of +a, and the first ply being located between said additional ply and the second ply.

[0010] Such a characteristic advantageously makes it possible to further limit the rate of cracking within the wall.

[0011] In one embodiment, each ply of the fibrous stack has a thickness less than or equal to 150 pm, for example less than or equal to 100 pm.

[0012] The use of thin plies makes it possible to further delay the initiation of matrix cracking.

[0013] In one embodiment, the fibrous stack is made of carbon fibers.

[0014] In one embodiment, the organic matrix is ​​an epoxy matrix.

[0015] In one embodiment, the internal volume contains dihydrogen in the state liquid. Alternatively, the storage volume contains dioxygen in liquid form.

[0016] The invention also relates to a spacecraft engine comprising a cryogenic propellant tank as described above. Brief description of the drawings [Fig.1] Fig.1 illustrates, schematically and partially, the interaction effect of cracks between adjacent superimposed folds in the context of a reservoir outside the invention. [Fig.2] Fig.2 illustrates, schematically and partially, the effect of crack opening within adjacent superimposed folds under tensile loading in the context of a tank outside the invention. [Fig.3] Fig.3 illustrates, schematically and partially, an example of a tank according to the invention. [Fig.4] Fig.4 illustrates, schematically and partially, an example of fibrous stacking forming the reinforcement of the wall of the tank in Fig.3. Description of the implementation methods

[0017] The invention is now described by means of figures, which are present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0018] Figures 1 and 2 relate to a composite tank outside the invention whose reinforcement comprises only a stack of plies 10 of unidirectional fibers oriented at an angle of -a, and plies 30 of unidirectional fibers oriented at an angle of +a, with a between 5° and 20° and each angle being taken with respect to a longitudinal axis of the tank.

[0019] With respect to thermomechanical stresses (induced by the cooling of the tank), the stackings designed to minimize stresses in the different plies consist of plies with the closest possible orientation (i.e., most favorable case: two adjacent plies with the same orientation; most unfavorable case: two adjacent plies with orientations a° and a°+90°). Indeed, in the case of unidirectional composites, thermal expansion is highly anisotropic: in the direction of the fibers, the material expands very little, while it expands significantly in the direction perpendicular to the fibers.Thus, when stacking layers that are highly misaligned with each other, a significant temperature variation, such as in the case of tank cooling, will generate very significant internal stresses, reducing the stack's capacity to withstand mechanical forces (internal tank pressure).

[0020] Also, with regard to the initiation of matrix cracks that can lead to leaks in the tank, it would be desirable to minimize the angle between two adjacent plies. However, if these cracks are initiated, their propagation generates a network of long cracks in the affected plie and initiates cracks in adjacent plies. Figure 1 illustrates this interaction effect by designating the matrix crack propagating in plie 30 as FM30, and the matrix crack initiated in plie 10 adjacent to plie 30 as FM10. These cracks result in an increase in the number of leak points, and thus significantly degrade the tank's leak-tightness, especially since no fiber prevents their opening under internal pressure. Figure 2 illustrates this crack opening, denoted OFM, under the effect of the tensile flow FT.

[0021] Figure 3 illustrates an example of a tank 100 according to the invention containing a cryogenic propellant 108, in particular liquid dihydrogen, in the storage volume V, it being understood that the invention can be applied to the storage of other cryogenic fluids. By way of illustration, the internal pressure within the volume V can be at least 10 bar.

[0022] The reservoir 100 includes a wall 102 which delimits the volume V. The wall 102 is The structure is made of an organic matrix composite material and includes a fibrous reinforcement, the structure of which will be described in more detail in relation to [Fig. 4]. The wall defines a body 103, here generally cylindrical in shape, which is integral with ends 104. The ends 104 may be monolithic (one-piece) with the body 103. The reservoir 100, as well as the body 103, extends along a longitudinal axis X. The ends 104 delimit the reservoir along the X axis.

[0023] In the illustrated example, one of the ends 104 is provided with a port 106 which is, in a manner known per se, intended to be in communication with a circuit (not shown) comprising a turbopump capable of transmitting the cryogenic propellant 108 from the tank 100 to a combustion chamber, when the tank 100 is integrated within a spacecraft engine. This communication is represented by arrow C in [Fig. 3]. The engine may further include a second tank containing a second cryogenic propellant which is intended to be delivered to and react with the first propellant in the combustion chamber to generate thrust. By way of example, the first propellant may be dihydrogen and the second propellant dioxygen.

[0024] The wall 102 comprises a fibrous reinforcement, for example of carbon fibers, which is densified by an organic matrix, such as an epoxy matrix. The fibrous reinforcement is, in the illustrated example, in the form of a fibrous stack 110 formed by a superposition of plies of unidirectional fibers having particular orientations.

[0025] The stack 110 comprises, in succession in this order along the thickness E of the wall 102: - a first 113-fold of unidirectional fibers oriented at an angle of -a, - a second ply 115 of unidirectional fibers oriented at an angle of -|3, in contact with the first ply 113, - a third ply 117 of unidirectional fibers oriented at an angle of +a, in contact with the second ply 115, and - a fourth ply 119 of unidirectional fibers oriented at an angle of +[3, in contact with the third ply 117, with a between 5° and 20° and [3 between 40° and 50° and, in the illustrated example, equal to 45°, each angle being taken with respect to the X axis.

[0026] In the illustrated example, the stack 110 further comprises an additional ply 111 of unidirectional fibers oriented at an angle of +a, in contact with the first ply 113, the first ply 113 being located between said additional ply 111 and the second ply 115. Thus, the illustrated stack comprises, in succession in this order along the thickness E of the wall 102: - the additional fold 111, - the first fold 113 in contact with the additional fold 111, - the second fold 115 in contact with the first fold 113, - the third fold 117 in contact with the second fold 115, and - the fourth fold 119 in contact with the third fold 117.

[0027] According to an unillustrated variant, the additional fold 111 can be dispensed with. According to an unillustrated variant, the stacking just described can be repeated in the direction of the thickness E of the wall 102 with a mirror symmetry (symmetry with respect to a median layer of the stacking).

[0028] Whatever the example considered, a may be between 13° and 17° and / or [3 may be between 43° and 47°.

[0029] Regardless of the example considered, each ply 111-119 of the stack 100 can have a thickness ep less than or equal to 150 pm, for example less than or equal to 100 pm.

[0030] Generally, the stack 110 can be manufactured by manual draping or by automated fiber placement (AFP) on a mandrel having the shape of the desired reservoir 100. The stack 110 can then be impregnated with a resin to form the organic matrix. This impregnation can be carried out by a technique known per se, such as resin transfer molding (RTM) or infusion. In one embodiment, the stack 110 is made from plies pre-impregnated with the resin. The resin can be thermoplastic or thermosetting. In the latter case, a heat treatment to crosslink the resin is carried out after impregnation.

[0031] Tank 100 can be a first-stage or second-stage space launcher tank.

[0032] The effect of the invention on the permeability of the material under load was observed during "bulge test" type tests. These tests aim to pressurize composite specimens in a cryogenic environment (up to 20K) and identify the point at which the helium leakage rate increases significantly.

[0033] The tests were carried out on two types of composites representative of a tank wall. The first, outside the scope of the invention, comprised only an alternation of unidirectional plies at -a and +a, with 5° < a < 20°. The second, according to the invention, comprised a stacking as illustrated in [Fig. 4]. In each of the composites, the plies had a thickness of 76 µm. The plies were made of carbon fibers marketed under the reference HexTow® IMA by Hexcel and densified with an M56 epoxy resin from Hexcel.

[0034] A significant premature leak (at 3 bars), due to matrix cracks of significant length compared to the useful area of ​​the test specimens, was observed for the first composite outside the invention.

[0035] The onset of the leak was significantly delayed for the second composite according to the invention. In this case, the leak pressure was predicted to be between 9 and 14 bar and This was measured at 13 bars for one specimen and 15 bars for another specimen. Furthermore, although a leak was observed during these tests, no cracks were detected during post-mortem tomographic analyses with a resolution of 40 pm. The resulting crack network therefore appeared to consist of very short cracks that likely closed during the depressurization of the specimen.

[0036] The expression "between ... and ..." should be understood as including the bounds.

Claims

Demands

1. A cryogenic propellant reservoir (100) for a spacecraft engine, comprising a wall (102) delimiting a storage volume (V) for the cryogenic propellant, the wall being made of a composite material and comprising a fibrous reinforcement in the form of a fiber stack (110) that is densified by an organic matrix, the fiber stack comprising at least in succession in this order in the direction of the thickness (E) of the wall: (a) a first ply (113) of unidirectional fibers oriented at an angle of -α, (b) a second ply (115) of unidirectional fibers oriented at an angle of -α, (c) a third ply (117) of unidirectional fibers oriented at an angle of +α, and (d) a fourth ply (119) of unidirectional fibers oriented at an angle of +α, with α between 5° and 20° and α between 20° and 20°. 40° and 50°, each angle being taken with respect to a longitudinal (X) axis of the tank.

2. Reservoir (100) according to claim 1, in which a is between 13° and 17°.

3. Reservoir (100) according to claim 1 or 2, in which [3 is between 43° and 47°.

4. Reservoir (100) according to any one of claims 1 to 3, wherein the fibrous stack (110) further comprises an additional ply (111) of unidirectional fibers oriented at an angle of +a, and wherein the first ply (113) is located between said additional ply and the second ply (115).

5. Reservoir (100) according to any one of claims 1 to 4, wherein each ply (111-119) of the fibrous stack (110) has a thickness (ep) less than or equal to 150 pm.

6. Reservoir (100) according to any one of claims 1 to 5, wherein the fibrous stack (110) is made of carbon fibers.

7. Reservoir (100) according to any one of claims 1 to 6, wherein the organic matrix is ​​an epoxy matrix.

8. Tank (100) according to any one of claims 1 to 7, in which the storage volume (V) contains dihydrogen in liquid form.

9. Tank (100) according to any one of claims 1 to 7, in which the storage volume (V) contains dioxygen in liquid form.

10. Spacecraft engine comprising a propellant tank (100) cryogenic according to any one of claims 1 to 9.

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