WO2008066486A1

WO2008066486A1 - Micro system based solid state gas storage

Info

Publication number: WO2008066486A1
Application number: PCT/SE2007/050913
Authority: WO
Inventors: Lars Stenmark
Original assignee: Åstc Aerospace Ab
Priority date: 2006-11-28
Filing date: 2007-11-28
Publication date: 2008-06-05

Abstract

The present invention provides a gas storage system (1) comprising individually addressable igniters (23) arranged as a two dimensional array in an igniter module (20) and fuel elements (2) extending from an end surface (21) of the igniter module (20). By igniting a fuel element (2) using an adjacent igniter (23), a decomposition of a solid propellant (9) in the fuel element (2) generates a gas (15). Deflection shields (28) may be arranged about the fuel elements (2) to thermally shield adjacent fuel elements (2) and to provide structural support. The gas storage system (1) may further comprise a tank (40) having a gas outlet (41); a filter module (50); and a control module (60). Thanks to the invention it is possible to provide a solid state gas storage system (1) having a high gas storage capacity per mass unit.

Description

MICRO SYSTEM BASED SOLID STATE GAS STORAGE

Technical field of the invention

The present invention relates to gas storage, and in particular gas storage in mass critical applications using a solid chemical compound.

Background of the invention

The most common way to store the gas is in gaseous phase under high or very high pressure. This has some major disadvantages. One disadvantage is the shape of the tank. A high pressure vessel should be spherical to obtain maximum efficiency, i.e. highest wt-% stored gas, or cylindrical if a factor of 2 reduced wt% stored gas is acceptable. Another disadvantage is the mass and cost of the required support components, such as valves, pressure regulators, fittings, etc., needed for high pressure gas handling. Yet another disadvantage with high pressure storage is the risk for catastrophic failure, which makes handling, testing and qualification a major issue.

Another common way to store gas is in a liquid phase at low temperature in cryogenic tanks. This gives potentially very high storage capacity per mass unit. Major disadvantages with this method are related to the low temperature. Cryogenic storage is difficult in general, and in particular unavoidable gas boil-off during long term storage is a problem due to limited thermal insulation.

An alternative method is to store gas in solid chemical compounds that can be decomposed to release the gas. In order to avoid the need for a large collecting volume when the gas is released it is necessary to only release a small amount of the gas at each time. In conventional solid state gas storage devices a number of individual cartridges are connected in parallel. Each cartridge is filled with the chemical compound to be decomposed and an individual igniter. The whole battery of gas cartridges is arranged in a common buffer tank. The gas is usually released in small quantities by decomposing the chemical compound of individual cartridges on demand to the buffer tank. Thus the working pressure can be kept at a low, but stable level, which allows simpler support components and reduces the demands on the tank as compared to high pressure storage. One disadvantage is that conventional solid state gas storage devices become quite bulky and not very efficient with respect to mass and volume. There is a need for high gas storage capacity per mass unit. Moreover there is a safety issue and a maintenance issue coupled to this need. Therefore the solid state gas storage is an interesting alternative. For example in the development of a new generation of small but high performance spacecraft gas storage has become one of the limiting factors for further miniaturization.

Summary of the invention

Obviously the prior art has drawbacks with regards to being able to provide gas storage devices having sufficiently high gas storage capacity per mass unit.

The object of the present invention is to overcome the drawbacks of the prior art. This is achieved by the device as defined in the independent claim.

In a first aspect the present invention provides a gas storage system that comprises fuel elements and igniters. Each fuel element comprises a volume of a solid propellant and an adjacent igniter for ignition of the solid propellant, which, when ignited, decompose and releases a gas volume of a gas that is larger than the volume of the solid propellant of the fuel element. The individually addressable igniters are arranged as a two dimensional array in an igniter module and the fuel elements are extending from an end surface of the igniter module. Preferably, the fuel elements are rod-shaped and arranged in parallel. The solid propellant may be stored in a tube-shaped propellant cartridge of the fuel element, and the gas is released through exhaust openings in the cartridge.

In a second aspect the present invention provides a deflection shield arranged about a fuel element and covering an exhaust opening. Released gas is thereby deflected away from an adjacent fuel element. The deflection shield provides structural support and thermal isolation.

The gas storage system may further comprise a tank having a gas outlet, as well as a filter module and a control module.

Thanks to the invention it is possible to provide a low pressure solid state gas storage system having a high gas storage capacity per mass unit. It is a further advantage of the invention to provide a cost effective solid state gas storage system due to the integrated igniter module and the replaceable sub-units.

It is yet a further advantage of the invention to provide a solid state gas storage system having high reliability during transport and operation due to the supportive deflection shields and optionally also the suspended mounting of the fuel elements.

Embodiments of the invention are defined in the dependent claims. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims.

Brief description of the drawings

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein

Fig. 1 is a schematic diagram of the operation of a gas storage system according to the present invention,

Fig. 2 is a schematic perspective drawing of a gas storage device according to the present invention,

Fig. 3 is a schematic top view of a gas storage device according to the present invention,

Fig. 4 is a schematic cross sectional view of a gas storage device according to the present invention,

Fig. 5a is a schematic cross sectional view of an igniter according to the present invention,

Fig. 5b is a schematic top view of a gas storage device comprising a redundant igniter matrix according to the present invention,

Fig. 6a-e are cross sectional views of different fuel elements according to the present invention, Fig. 7 is a schematic illustration of a fuel element comprising exhaust openings according to the present invention,

Fig. 8a-b are schematic illustrations of a deflection shield arranged about a fuel element according to the present invention,

Fig. 9 is a schematic cross section of a fuel element comprising a deflection shield according to the present invention,

Fig. 10 is an illustration of close-packed fuel elements according to the present invention, and

Fig. 1 1 is a close-up of the close-packed fuel elements of Fig. 10.

Detailed description of embodiments

The basis for the innovation is that a pressure tight volume, e.g. a tank, is filled with a large number of individual fuel elements. Other denotations, such as gas generators or fuel rods, may also be used interchangeably for the fuel elements. The fuel element represents a fraction of a total charge in a gas storage system. Each fuel element can be individually addressed and fired autonomously or on command from a control system outside the tank. In an autonomous mode an integrated pressure sensor is used to determine when it is time to activate a fuel element to boost the tank pressure. AU dead volumes inside the tank, including burned-out fuel elements act as the working pressure gas storage volume or plenum, i.e. the volume becomes consequently larger as new fuel rods are decomposed. In Fig. 1 a typical tank pressure versus time graph is depicted. After reloading and leak testing the tank is filled with a start pressure. At a given time the gas consumption starts resulting in lowering of the tank pressure. After a while the minimum acceptable tank pressure is reached and the first fuel element is ignited releasing gas enough to reach the maximum tank pressure. As the gas consumption goes on the pressure is decreased again until the minimum tank pressure is reached for the second time at which the second fuel rod is ignited. This time the pressured reaches a little lower as the system dead volume has increased. This procedure will continue until the last fuel rod is used. The absolute valve of the pressure increase due to decomposition of one fuel element depends on the number fuel elements used in the system. Thus a larger number of fuel elements yields a smaller incremental pressure increase. The pressure increase will also gradually decrease for a given fuel element size as used fuel elements contribute to the internal storage volume in the tank. The dynamic range of the output pressure from the tank is very small, at least a magnitude less than for a high pressure tank. Because of this, the requirement on a pressure regulator is also small. A single stage pressure regulator is most likely quite sufficient to give a stable secondary pressure to the end user in the system. Hence, if the gas storage elements may be densely packed, the gas mass fraction of the total system mass has the potential to be higher than for a conventional high pressure gas storage system. The total system mass is defined as the mass of all components needed in a system which provides a useful secondary pressure. The present invention provides a dense packing of the fuel elements and further provides a compact integration of different subsystems of a solid state gas storage system.

Referring to Fig. 2, one embodiment of the present invention is a gas storage system 1 comprising fuel elements 2 and igniters 23. Each fuel element 2 comprises a volume of a solid propellant 9 and an adjacent igniter 23 for ignition of the solid propellant 9, which, when ignited, decompose and releases a gas volume of a gas 15 that is larger than the volume of the solid propellant 9 of the fuel element 2. The individually addressable igniters 23 are arranged as a two dimensional array 24 in an igniter module 20 and the fuel elements 2 are extending from an end surface 21 of the igniter module 20.

As illustrated in Fig. 2, in one embodiment of the present invention the fuel elements 2 are rod-shaped and arranged in parallel on the end surface 21 of the igniter module 20. Each fuel element, or fuel rod, has an adjacent igniter 23 for ignition of the solid propellant 9 integrated in the igniter module 20.

Referring to Fig. 3, the igniters 23 are arranged in a two dimensional array 24 in the igniter module 20. As shown in the cross sectional view in Fig. 3, the fuel elements 2 may be close-packed in the same pattern as the igniters 23 on the end surface 21 of the igniter module 20. One advantage with the present invention is that the fuel elements 2 can be fired in a certain order to maintain the centre of mass of the system 1 approximately in the same position all the time. Conventional systems wherein the fuel elements are decomposed serially will not be able to compensate for this. In one embodiment of the present invention the igniter module 20 comprises two independent igniters 23 for each fuel element 2.

Fig. 4 illustrates a gas storage system 1 according to the present invention wherein the igniter module 20 and the fuel elements 2 are accommodated inside a tank 40. The tank 40 may further accommodate other sub-systems as well. By way of example the tank 40 has a cylindrical shape with a hermetic electrical connector 43 in one end and a gas outlet 41 with an integrated outlet valve in the other end. The fuel elements 2 are for example pen-shaped fuel rods. The fuel elements 2 form a package that is held together by the igniter module 20 in one end and an end cap 42 together with a filter module 50 in the other end. By way of example a honeycomb shaped end cap may be used to simplify the mounting. The modules 20, 50 may be held together by nine long, thin pin bolts, three located in the centre and six around the outer diameter. A control module 60 is placed in between a hermetic connector 43 and the igniter module 20. Since the pressure levels are fairly low the tank may be thin walled. As shown in Fig. 3, a large number of fuel elements 2 may be packed in an ordered manor inside the tank 40. The diameter of each individual fuel element 2 should be small compared to the tank 40 diameter in order not to produce too much local heat during the solid propellant 8 decomposition that nearby fuel elements are affected to such a degree that an uncontrolled decomposition starts. A small well-defined gap is maintained around each fuel element 2 for thermal insulation reasons. It should be understood that the integration of three miniaturized modules, i.e. the igniter module 20, the control module 60 and the filter module 50, contributes very efficiently to one of the unique features of the system. This is the high wt % of stored gas, which partly is due to the fact that most of connectors, harness, fittings, etc. are eliminated in the highly integrated system. The fabrication of any of the miniaturized modules 20, 50, 60 may comprise micromachining, e.g. photolithography and etching of e.g. a silicon wafer.

Referring to Fig. 5a, in one embodiment of the present invention an igniter 23 of the igniter module 20 comprises a pyrotechnical charge 34 enclosed in a cavity 35. The cavity is sealed by a membrane 36. By way of example the cavity 36 may be formed in a micromachined silicon wafer or in a stack of micromachined silicon wafers. A heater element 37 is integrated with the membrane 36. The heater element 37 may be deposited on either side of the membrane 36 or formed within the membrane, e.g. by doping of a semiconducting membrane. By activating the heater element 37 the pyrotechnical charge 34 is ignited and due to an intensive combustion of the pyrotechnical charge 34, the membrane 36 breaks and a flame of the pyrotechnical charge 34 hits the fuel element 2, whereby the solid propellant 9 starts decomposing and a constant flux of the desired gas 15 is generated.

By forming the igniter module using microelectromechanical systems (MEMS) or microsystems technology (MST) technologies a highly integrated module having a densely packed igniter array 24 may be formed. This also allows integration of electronic features within the igniter module itself, i.e. control system electronics can be integrated as well.

Referring to Fig. 5b, in embodiment of the present invention two redundant integrated diode matrixes are used to decode a fire command. The command is given as a row and column number from a control system. The control module electronics is divided in two identical totally independent parts. Each part contains the following electronics. A power bus interface with a small power converter to the CAN-bus electronics, the interface includes also EMS filtering circuitry. A small microprocessor with an integrated CAN-bus node and an electro optical interface to the spacecraft CAN-bus system constitutes the CAN interface. Out from the processor an 8-bit parallel data word gives a 4-bit row and 4-bit column information to a decoder and heater element driver circuit. An integrated pressure sensor and/ or a temperature sensor may, together with a stored list of fired fuel rods, give the necessary housekeeping information back to the system user. Fig. 5b illustrates how an individual igniter 23 may be addressed by applying two independent signals to the individual igniter 23 from a first control signal connection 64 and a second control signal connection 65. The first and the second control signal connections 64, 65 are arranged in a row and a column, respectively. By applying a signal in a connection of 64, 65 of the row and the column simultaneously a specific igniter 23 may be activated.

In one embodiment of the present invention a filter module 50 is mounted between the fuel elements 2 and the gas outlet 41. The filter module is preferably easily replaceable when the fuel elements 2, and optionally also the igniter module 20, is removed. The filter module 50 may be sealed with a sealing gasket 51, such as O-rings, which also serves as a soft end stop for the fuel elements. The sealing gasket 51 serves an additional function of eliminating thermal stress caused by different CTE:s in the system. The filter module 50, which may consist of a stack of bonded micromachined silicon wafers 56, may contain also at least one safety burst disc 53 and a safety gas outlet 54, in order to give a good overpressure protection.

Referring to Fig. 6a-e, in one embodiment of the present invention the fuel element 2 comprises a propellant cartridge 8, which at least partly is filled with a solid propellant 9.

Fig. 6a illustrates a fuel element 2 comprising a tube-shaped propellant cartridge 8 completely filled with solid propellant according to one embodiment of the present invention.

Referring to Fig. 6b, in one embodiment of the present invention the propellant cartridge 8 is a thin walled tube, which is filled with a solid propellant 9 from one end towards a porous end plug 68 pressed into the other end of the tube. A small cavity 69 is left in the filling end to give room for an igniter flame to expand and ignite the solid propellant. By way of example the tube is made of a metal or metal alloy such as stainless steel, titanium, or similar.

Referring to Figs. 6c-d, a propellant cartridge 8 according to the present invention may be coated with either or both a heat conductive coating 12 and a low emission coating 13. One example of a heat conductive coating is a plated copper coating, and one example of a low emission coating 13 is a plated gold coating, however not limited to this. The heat conductive coating 12 is conducting the heat generated by decomposition along an longitudinal axis of the propellant cartridge 8. The low emission coating 13 minimizes thermal emittance.

Fig. 6e illustrates a fuel element 2 according to the present invention that comprises a pyrotechnical charge 34 integrated in an end portion of the propellant cartridge 8 adjacent to the igniter 23. This design allows the fuel element 2 to be ignited by the heater element 37 of the igniter 23. Accordingly, one embodiment of the present invention comprises an igniter module 20 having an igniter 23 comprising only a heater element 37. The heater element 37 may be e.g. a resistive element and it may be deposited on the end surface 21 or formed in the surface layer of the igniter module 20. The gas generating fuel can be a mixture between e.g. a nitrogen rich solid chemical, such as sodium azide, if nitrogen is the desired gas, and a pyrotechnical material, which supplies the necessary energy, required for decomposing the nitrogen chemical. The mixture composition is such that the decomposition rate is low to permit the released nitrogen to transpire through the porous fuel mixture. The released gas cools down in the transpiration process.

In one embodiment of the present invention the solid propellant 9 comprises a pyrotechnical material, which supplies additional energy. This may be needed for some compounds, such as the nitrogen chemical mentioned above, to be able to decompose them.

Referring to Fig. 7, as the relation between length and diameter is relatively unfavorable for a gas transpiration process through the porous solid propellant 9 a propellant cartridge 8 of one embodiment of a gas storage system 1 according to the present invention comprises a number of exhaust openings or slots 17. In order to protect surrounding fuel elements 2 from hot exhaust gases 15 from a fuel element 2 in decomposition the exhaust openings 17 may be concentrated in groups of 3 (120° apart) along an longitudinal axis of the fuel element 2.

Referring to Fig. 7a, in one embodiment of the present invention the gas storage system 1 comprises a deflection shield 28 arranged about the fuel element 2. The deflection shield covers an exhaust opening 17 in order to deflect the hot released gas 15 away from an adjacent fuel element 2 and along a longitudinal axis of the fuel element 2. As illustrated in Fig. 7a the deflection shield 28 may partly cover the fuel element 2. This covered section may comprises e.g. three exhaust opening separated by 120° around the propellant cartridge 8, as mentioned above.

Fig. 7b illustrates an alternative design of the deflection shield 28, which covers two or more exhaust openings distributed along the longitudinal axis of the fuel element 2. In one embodiment of the present invention the gas storage system 1 comprises at least a fuel element 2 having a deflection shield 28 extending substantially along the full length of the fuel element 2. Fig. 7c and 7d illustrates perspective drawings of the fuel element 2/deflection shield 28 arrangement of Fig. 7a and 7b, respectively.

In one embodiment of the present invention the deflection shield 28 provides structural support for the fuel element 2. Such a structural support may be needed e.g. in transport and launching of a space aircraft.

One embodiment of the present invention is a gas storage system 1 comprising fuel elements 2 and igniters 23. Each fuel element 2 comprises a volume of a solid propellant 9 and an adjacent igniter 23 for ignition of the solid propellant 9, which, when ignited, decompose and releases a gas volume of a gas 15 that is larger than the volume of the solid propellant 9 of the fuel element 2. The individually addressable igniters 23 are arranged as a two dimensional array 24 in an igniter module 20 and the fuel elements 2 are extending from an end surface 21 of the igniter module 20. A deflection shield 28 is arranged about each fuel element 2. The deflection shield 28 comprises at least two dents 29, 30, 31 along a longitudinal axis of the fuel element 2 forming an intermediate bulge 25, 26, 27 over an exhaust opening 17. The bulge 25, 26, 27 of the deflection shield 28 of a fuel element 2 is preferably arranged on a dent 29, 30, 31 of an adjacent deflection shield 28.

One reason for the grouping mentioned above is that the exhaust openings 17 should be covered by a deflection shield 28 formed e.g. from a piece of larger diameter metal tube.

Fig. 9 illustrates a deflection shield 28 according to the present invention. The exhaust opening 17 should be covered by a deflection shield 28, to prevent that a narrow concentrated beam of hot gases heats up and eventually ignites the surrounding fuel elements 2, in particular when the decomposition front passes the exhaust openings 17.

The deflection shield 28 may be preformed by pressing a thin walled tube over a pre- shaped plug, by help of a hydraulic "3-yaw" chuck. As three dents (29, 30, 31) are produced on the deflection shield 28, the fuel elements can be densely packed, and in addition giving each other mechanical support during vibration. The packing principle is illustrated in Fig. 10. The dents 29, 30, 31 lock also the rotational orientation of each fuel element 2. The deflection shield 28 can be fixed to the propellant cartridge 8 e.g. by laser spot welding, soft bonding with a suitable ceramic adhesive, soldering etc.

The deflection shields 28 are only in direct thermal contact with the propellant cartridge 8 along three lines as far away from the exhaust openings as possible. The hot gases 15 coming out from an exhaust opening 17 is deflected up-and downward the fuel element 2. The deflection prevents the hot gas stream from heating up a small spot on an adjacent fuel element 2 located just in front of the exhaust opening 17, which otherwise could start an unwanted decomposition in the adjacent fuel element 2. An unwanted decomposition could in worst case lead to an uncontrolled chain reaction in the whole system 1.

The deflection shields 28 have a second as important function, in particular if the length-to-diameter-ratio is high for the fuel elements 2 involved. The function is to provide mechanical support for each fuel element 2 making the system resistant to high vibration (i.e. launch loads if used onboard a spacecraft). An unsupported very long extremely thin walled tube filled with a heavy compound can easily experience a transverse vibration mode breaking the propellant 9 in parts or in the worst case the tube itself. Figure 10 schematically illustrates how adjacent fuel elements 2 and their associated deflection shields 28 support each other. The dents 29, 30, 31 in the deflection shields 28 also prevent each individual fuel element 2 from rotating. If a first fuel element 2 is fixed, a second fuel element 2 is resting against the first fuel element with a dent 29 of the deflection shield 28 arranged in a mating relationship on a bulge 25 of the first fuel element 2.

Fig. 11 illustrates a cross-section through two deflection shields 28 in contact with each other. The purpose is to illustrate the mechanical contact points and the possible flow paths for the heat flux from one fuel element 2 to another. Hot decomposition gases 15 from the solid propellant 9 are expelled through the exhaust opening 17 hitting a local area on the deflection shield 28. From the heated local area the heat flux in the deflection shield material is flowing to the contact point between adjacent deflection shields 28, which also receive some heat flux from the contact point between the deflection shield 28 and the propellant cartridge 8. The different radius of the bulge that comprises the hot local area and the dent 29 in the adjacent deflection shield 28 gives a dead volume 32, which results in that all heat flux from the heated deflection shield 28 has to pass the two contact points to reach the other deflection shield 28, which in turn only has thermal contact at three points with the propellant cartridge 8 around the non-ignited fuel element 2. This means that the heat flux from the solid propellant 9 in one fuel element to any solid propellant 9 in the surrounding six fuel elements 2 is very low. Thermal radiation can be neglected, particularly if relevant surfaces are e.g. gold plated to give them low thermal emissivity. The temperatures involved are also typically relatively low, maximum a few hundreds degree Celsius, which means that the thermal radiation levels are quite low.

Components designed for an operational pressure between 20-60 MPa are by nature heavy and expensive. Such components are tanks, F/D valves, isolation valves, pressure transducers, pressure regulators, etc. In particular for a small spacecraft the mass of the conventional components is quite disturbing and any of these that can be replaced by a low mass alternative should be replaced.

As the system can be integrated and transported without being pressurized and as no high pressure filling is required at the launch site the integration procedure is simplified. The gas system down line the tank assembly can be tested by filling the tank to operational pressure from an external feed line.

During long periods of storage or standby even a small leakage in a high pressure tank assembly can create a significant problem. This is totally avoided as the gas is stored in the chemical composition of the solid propellant in the fuel elements and only released when a fuel element rod is decomposed.

Although the modules (20, 50, 60) have been described as cylindrical the present invention is not limited to this. In fact, a gas storage system according to the present invention may have essentially any shape since the pressure levels are relatively low, and thus the shape of the modules (20, 50, 60) rectangular. Furthermore, an igniter module 20/fuel element 2 assembly may be stacked.

Although the shape of the fuel elements 2 and the deflection shields 28 primarily have been presented as having the exhaust openings 17 and the dents 29, 30, 31 120° apart, respectively, other designs are possible, e.g. having the exhaust openings spaced 90° apart. However, the degree of packing is advantageous with the design presented above.

The present invention has preferentially been described with space applications in mind. However, the present invention is not limited to this. A gas storage system of the invention may be used in different application areas. In particular, mass critical applications would benefit from the invention, but virtually all applications may benefit from a lighter, simpler and more reliable system.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, on the contrary, is intended to cover various modifications and equivalent arrangements within the appended claims.

Claims

1. A gas storage system (1) comprising fuel elements (2) and igniters (23), each fuel element (2) comprising a volume of a solid propellant (9) and an adjacent igniter (23) for ignition of the solid propellant (9), and, when ignited, decomposition of the solid propellant (9) of an fuel element (2) releases a gas volume of a gas (15) that is larger than the volume of the solid propellant (9) of the fuel element (2), characterised in that the igniters (23) are arranged as a two dimensional array (24) in an igniter module (20); the igniters (23) are individually addressable; and the fuel elements (2) are extending from an end surface (21) of the igniter module (20).

2. A gas storage system (1) according to claim 1 , wherein the fuel elements (2) are rod-shaped and arranged in parallel.

3. A gas storage system (1) according to claim 1 or 2, wherein the solid propellant (9) comprises a pyrotechnical material (10).

4. A gas storage system (1) according to any of the preceding claims, wherein the fuel element (2) comprises a propellant cartridge (8).

5. A gas storage system (1) according to claim 4, wherein the propellant cartridge (8) is tube-shaped.

6. A gas storage system (1) according to claim 4 or 5, wherein the propellant cartridge (8) comprises a heat conductive coating (12).

7. A gas storage system (1) according to any of claims 4-6, wherein the propellant cartridge (8) comprises a low emission coating (13).

8. A gas storage system (1) according to any of claims 4-7, wherein the propellant cartridge (8) comprises exhaust openings (17) distributed along a longitudinal axis (4) of the fuel element (2).

9. A gas storage system (1) according to claim 8, wherein the exhaust openings ( 17) are arranged in rows ( 18) along the longitudinal axis of the fuel element (2).

10. A gas storage system (1) according to claim 8 or 9, wherein a deflection shield (28) is arranged about the fuel element (2), and the deflections shield (28) at least covers an exhaust opening (17) to deflect the released gas (15) away from an adjacent fuel element (2).

1 l .A gas storage system (1) according to claim 10, wherein the deflection shield

(28) provides structural support for the fuel element (2).

12. A gas storage system (1) according to claim 10 or 1 1, wherein the deflection shield (28) is fixed to the fuel element (2).

13. A gas storage system (1) according to any of claims 10-12, wherein the deflection shield (28) comprises at least two dents (29, 30, 31) along a longitudinal axis of the fuel element (2) forming an intermediate bulge (25, 26, 27) at least over an exhaust opening (17).

14. A gas storage system (1) according to claim 13, wherein the bulge (25, 26, 27) of the deflection shield (28) is arranged on a dent (29, 30, 31) of an adjacent deflection shield (28) in a mating relationship.

15. A gas storage system (1) according to claim 14, wherein a dead volume (32) is enclosed in between the adjacent deflection shields (28) which are arranged in a mating relationship.

16. A gas storage system () according to claim 1, wherein an igniter (23) comprises a pyrotechnical charge (34) for ignition of the fuel element (2).

17. A gas storage system (1) according to claim 16, wherein the pyrotechnical charge (34) is enclosed in a cavity (35) by a membrane (36).

18. A gas storage system () according to any of claims 1 and 16-17, wherein the igniter (23) comprises a heater element (37) for ignition.

19. A gas storage system (1) according to any of claims 1 and 16- 18, wherein ignition of an igniter (23) of the two dimensional array (24) is individually controlled by two redundant control signal connections (64, 65).

20. A gas storage system () according to any of claims 1 and 16-19, wherein the igniter module (20) comprises a micromachined silicon wafer.

21. A gas storage system (1) according to any of the preceding claims, further comprising a tank (40) having a gas outlet (41).

22.A gas storage system (1) according to claim 21, wherein the tank (40) comprises a removable end cap (42) and at least the fuel elements (2) are replaceable.

23.A gas storage system (1) according to any of the preceding claims, further comprising a filter module (50) arranged on an end portion (6) of the fuel elements (2).

24.A gas storage system (1) according to claim 23, wherein the filter module (50) and the igniter module (20) holds the fuel elements (2).

25.A gas storage system (1) according to claim 23 or 24, wherein a sealing gasket (51) holds the filter module (50) and provides a soft end stop for the fuel elements (2).

26.A gas storage system (1) according to claim 24 or 25, wherein the filter module (50) is removable.

27.A gas storage system (1) according to any of claims 24-26, wherein the filter module (50) comprises a micromachined silicon wafer.

28.A gas storage system (1) according to any of claims 23-27, wherein the filter module (50) comprises a safety burst disc (53) and a separate safety gas outlet (54) for overpressure protection.

29.A gas storage system (1) according to claim 21, further comprising a control module (60) for ignition control.

30. A gas storage system (1) according to claim 29, wherein the control module (60) comprises a pressure sensor (61).

31. A gas storage system (1) according to claim 29 or 30, wherein the control module () comprises a temperature sensor (62).