FR3159152A1 - Cryogenic propellant tank for a spacecraft engine - Google Patents

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 composite material and comprising a fibrous reinforcement in the form of a fibrous stack (110) which is densified by an organic matrix, the fibrous 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 relative to a longitudinal axis of the tank. Figure for abstract: Fig. 4.

Description

Cryogenic propellant tank for a spacecraft engine

This disclosure relates to a composite cryogenic propellant tank for a spacecraft engine having improved mechanical properties and sealing at low temperatures.

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

Composite materials have been proposed as an attractive alternative to metallic materials in order to reduce the mass of the tank. However, it is possible to improve existing composite solutions in terms of maintaining watertightness and preserving mechanical properties at the low temperatures involved.

The present disclosure 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 with an angle of –α, (b) a second ply of unidirectional fibers oriented with an angle of –β, (c) a third ply of unidirectional fibers oriented with an angle of +α, and (d) a fourth ply of unidirectional fibers oriented with an angle of +β, with α between 5° and 20° and β between 40° and 50°, each angle being taken relative to a longitudinal axis of the tank.

The first and third plies having the orientation +/- α described above are relatively little disoriented with respect to each other, which gives the wall of the tank a good absorption of the forces which are exerted when the tank is filled and brought to a cold state. The inventors have nevertheless noted that the use of the first and third plies alone could lead to a loss of tightness of the tank if matrix cracks appeared which could then generate a network of cracks of significant length in the ply concerned as well as in the adjacent ply or plies. To overcome this drawback, the invention proposes adding to the stack the second and fourth plies described above which are sufficiently disoriented with respect to the first and third plies to limit the opening of the matrix cracks by minimizing the interactions between adjacent plies, but whose disorientation remains limited so as not to generate excessively high thermomechanical stresses when the tank is brought to a cold state.

In an exemplary embodiment, α is between 13° and 17°, for example is substantially equal to 15°.

In an exemplary embodiment, β is between 43° and 47°, for example is substantially equal to 45°.

Such a characteristic advantageously makes it possible to further limit the opening of matrix cracks, without generating excessive thermomechanical stresses during cold setting.

In an exemplary embodiment, the fibrous stack further comprises an additional ply of unidirectional fibers oriented at an angle of +α, and the first ply being located between said additional ply and the second ply.

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

In an exemplary embodiment, each ply of the fibrous stack has a thickness less than or equal to 150 µm, for example less than or equal to 100 µm.

The use of fine folds further delays the initiation of matrix cracking.

In an exemplary embodiment, the fiber stack is made of carbon fibers.

In an exemplary embodiment, the organic matrix is an epoxy matrix.

In an exemplary embodiment, the internal volume contains dihydrogen in the liquid state. Alternatively, the storage volume contains dioxygen in the liquid state.

The invention also relates to a spacecraft engine comprising a cryogenic propellant tank as described above.

Brief description of the drawings
FIG. 1 There FIG. 1 illustrates, schematically and partially, the effect of interaction of cracks between adjacent superimposed folds in the context of a reservoir outside the invention.
FIG. 2 There FIG. 2 illustrates, schematically and partially, the effect of crack opening within adjacent superimposed folds under tensile loading in the context of a reservoir outside the invention.
FIG. 3 There FIG. 3 illustrates, schematically and partially, an example of a reservoir according to the invention.
FIG. 4 There FIG. 4 illustrates, schematically and partially, an example of a fibrous stack forming the reinforcement of the wall of the tank of the FIG. 3 .

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

Figures 1 and 2 relate to a composite tank outside the invention, the reinforcement of which comprises only a stack of plies 10 of unidirectional fibers oriented at an angle of –α, and plies 30 of unidirectional fibers oriented at an angle of +α, with α between 5° and 20° and each angle being taken relative to a longitudinal axis of the tank.

With regard to stresses of thermomechanical origin (induced by the cold setting of the tank), the stacks that allow the constraints in the different plies to be limited as much as possible are made up of plies with the closest possible orientation (i.e. the most favorable case: two adjacent plies with the same orientation; the most unfavorable case: two adjacent plies with orientations α° and α°+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 plies that are highly misoriented relative to each other, a significant temperature variation, as in the case of the cold setting of the tank, will generate very significant internal stresses, reducing the stack's capacity to absorb the forces of mechanical origin (internal pressure of the tank).

Also, with regard to the initiation of matrix cracks which could lead to the non-tightness of the tank, it would be desirable to minimize the angle between two adjacent folds. However, in the event of initiation of these cracks, their propagation generates a network of cracks of significant length in the fold concerned and initiates cracks in the adjacent folds. FIG. 1 illustrates this interaction effect by designating FM30 as the matrix crack propagating in fold 30, and FM10 as the matrix crack initiated in fold 10 adjacent to fold 30. These cracks result in an increase in the number of leak points, and then significantly degrade the tightness of the tank, especially since no fiber blocks their opening under internal pressure. FIG. 2 illustrates this opening of cracks, noted OFM, under the effect of the traction flow FT.

There FIG. 3 illustrates an example of a tank 100 according to the invention which contains a cryogenic propellant 108, in particular dihydrogen in the liquid state, 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 prevailing within the volume V can be at least 10 bar.

The tank 100 comprises a wall 102 which delimits the volume V. The wall 102 is made of organic matrix composite material and comprises a fibrous reinforcement whose structure will be described in more detail in connection with the FIG. 4 The wall defines a body 103, here of generally cylindrical shape, which is integral with bottoms 104. The bottoms 104 can be monobloc (in one piece) with the body 103. The reservoir 100, as well as the body 103, extend along a longitudinal axis X. The bottoms 104 delimit the reservoir along the axis X.

In the illustrated example, one of the bottoms 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 shown by the arrow C at FIG. 3 The engine may further comprise a second tank containing a second cryogenic propellant which is intended to be supplied and react with the first propellant in the combustion chamber to generate thrust. For example, the first propellant may be dihydrogen and the second propellant dioxygen.

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

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

In the example illustrated, the stack 110 further comprises an additional ply 111 of unidirectional fibers oriented at an angle of +α, 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 stack illustrated comprises in succession in this order in the direction of the thickness E of the wall 102:
- 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.

According to a variant not illustrated, the additional fold 111 can be dispensed with. According to a variant not illustrated, the stack which has just been described can be repeated in the direction of the thickness E of the wall 102 with mirror symmetry (symmetry with respect to a middle layer of the stack).

Whichever example is considered, α can be between 13° and 17° and/or β can be between 43° and 47°.

Whatever the example considered, each ply 111-119 of the stack 100 may have a thickness ep less than or equal to 150 µm, for example less than or equal to 100 µm.

Generally speaking, the stack 110 can be manufactured by manual draping or by automatic placement of fibers (“Automated Fiber Placement”; “AFP”) on a mandrel having the shape of the reservoir 100 to be obtained. The stack 110 can then be impregnated with a resin intended 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. According to a variant, the stack 110 is produced from plies pre-impregnated with the resin. The resin can be thermoplastic or thermosetting. In the latter case, a heat treatment for crosslinking the resin is carried out after the impregnation.

Tank 100 may be a first-stage or second-stage space launcher tank.

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 moment when the helium leak rate increases significantly.

The tests were carried out on two types of composites representative of a tank wall. The first, outside the invention, only included an alternation of unidirectional folds at -α and +α, with 5° < α < 20°. The second, according to the invention, included a stack 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 the company Hexcel and densified by an epoxy resin M56 from the company Hexcel.

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

The onset of the leak was significantly delayed for the second composite according to the invention. In this case, the leak pressure was expected to be between 9 and 14 bars and 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 could be observed during post-mortem tomographic analyses with a resolution of 40 µm. The crack network generated therefore appeared to consist of cracks of very short length and probably closed during depressurization of the specimen.

The expression “between … and …” must be understood as including the limits.

Claims (10)

Tank (100) of cryogenic propellant for a spacecraft engine, comprising a wall (102) delimiting a storage volume (V) for the cryogenic propellant, the wall being made of composite material and comprising a fibrous reinforcement in the form of a fibrous stack (110) which is densified by an organic matrix, the fibrous 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 with an angle of –α, (b) a second ply (115) of unidirectional fibers oriented with an angle of –β, (c) a third ply (117) of unidirectional fibers oriented with an angle of +α, and (d) a fourth ply (119) of unidirectional fibers oriented with an angle of +β, with α between 5° and 20° and β between 40° and 50°, each angle being taken relative to a longitudinal axis (X) of the tank. Tank (100) according to claim 1, wherein α is between 13° and 17°. Tank (100) according to claim 1 or 2, wherein β is between 43° and 47°. Reservoir (100) according to any one of claims 1 to 3, in which the fibrous stack (110) further comprises an additional ply (111) of unidirectional fibers oriented at an angle of +α, and in which the first ply (113) is located between said additional ply and the second ply (115). Reservoir (100) according to any one of claims 1 to 4, in which each ply (111-119) of the fibrous stack (110) has a thickness ( ep ) less than or equal to 150 µm. Tank (100) according to any one of claims 1 to 5, in which the fibrous stack (110) is made of carbon fibers. A reservoir (100) according to any one of claims 1 to 6, wherein the organic matrix is an epoxy matrix. Tank (100) according to any one of claims 1 to 7, in which the storage volume (V) contains dihydrogen in the liquid state. Tank (100) according to any one of claims 1 to 7, in which the storage volume (V) contains dioxygen in the liquid state. Spacecraft engine comprising a tank (100) of cryogenic propellant according to any one of claims 1 to 9.