JP2010229853A - Catalyst decomposition type thruster for space vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst decomposition type thruster for a space vehicle, for producing high thruster output even when using HAN (Hydroxylammonium Nitrate) based liquid propellant for one liquid propulsion system. <P>SOLUTION: The catalyst decomposition type thruster for the space vehicle includes a hollow tank for storing the liquid propellant, a combustor for decomposing the liquid propellant and injecting reactive gas, and a flow path for supplying the liquid propellant from the tank to the combustor. The tank has a section in which the liquid propellant is filled, and includes a piston for delivering the liquid propellant to the combustor. The combustor includes a catalyst layer having a catalyst to be used for combusting the liquid propellant, a heating device for heating the catalyst layer, and an injector for supplying the liquid propellant to the catalyst layer. With predetermined pressure applied to the piston, the injector sprays the liquid propellant to the catalyst layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalytic decomposition type thruster for space vehicles. In particular, the present invention relates to a catalytic decomposition type thruster that can be suitably used for a one-component propulsion system used in a space vehicle.

As a propulsion system used to control the attitude and orbit of a spacecraft such as a spacecraft in outer space, a propelling force has been conventionally achieved by decomposing a liquid propellant with a catalyst and injecting the resulting reaction gas. Catalytic cracking thrusters, which are so-called one-part propulsion systems, have been used.
Hydrazine is often used as a fuel for a one-component propulsion system for space vehicles. Hydrazine is an excellent fuel because of its high reactivity, but it is dangerous to handle. Therefore, in recent years, hydroxylammonium nitrate (“HAN”)-based liquid propellants have attracted attention as low-toxic liquid propellants that can replace hydrazine.
For example, Japanese Patent Application Laid-Open No. 2007-023135 discloses hydroxylammonium nitrate as a highly safe liquid oxidizing agent used for a monopropellant (single liquid propellant) that is a propellant that functions only with one liquid. HAN) and hydrazinium nitrate (HN) are dissolved in water (H ₂ O), and a liquid oxidizer containing 10% by weight or less of a fuel component is disclosed. A hot gas generation method is disclosed in which liquid fuel is stored separately and mixed or brought into contact immediately before use to ignite and generate hot gas.
Japanese Patent Laid-Open No. 2004-340148 discloses that a HAN group propellant is introduced into a reactor, the propellant is decomposed so as to dissociate at least most of the HAN in the propellant, and the output of the reactor is burned. A method is disclosed in which the output of the reactor is combusted in the combustor such that the dissociated HAN dissociation product is combusted with unreacted fuel in the propellant.

As the catalytic decomposition type thruster when hydrazine is used as the fuel, for example, the one shown in FIG. 1 can be considered. In this catalytic decomposition type thruster 10, a liquid propellant such as hydrazine is stored in a propellant tank 11 and is sent to a combustor 13 through a flow path 12. The combustor 13 includes a catalyst layer 14 that catalytically decomposes a liquid propellant such as hydrazine. The liquid propellant such as hydrazine conveyed from the flow path 12 is released by the injector 15 toward the catalyst layer 14 like a plurality of rod-shaped water streams.
For example, Japanese Patent Application Laid-Open No. 2004-331425 discloses a HAN / HN-based monolith comprising a HAN / HN mixed oxidant containing hydroxylammonium nitrate (HAN), hydradium nitrate (HN) and water and a fuel component. A hot gas generating method is disclosed in which a propellant is sprayed directly onto a catalyst to generate a hot gas.

JP 2007-023135 A JP 2004-340148 A JP 2004-331425 A

In the case of the conventional catalytic decomposition type thruster as shown in FIG. 1, a liquid propellant such as hydrazine discharged like a rod-shaped water flow from the injector 15 toward the catalyst layer 14 is a catalyst in which a part of the liquid propellant collides with the water flow. Although it remains in the vicinity of the catalyst in the layer 14, most of it remains in the vicinity of the inner wall of the combustor 13 between the injector 15 and the catalyst layer 14 or between the catalyst layer 14 and the nozzle. The unreacted liquid propellant staying between the catalyst layer 14 and the nozzle causes liquid injection.
Further, the catalytic decomposition type thruster as shown in FIG. 1 causes a further problem when a HAN liquid propellant is used instead of hydrazine. That is, although the HAN liquid propellant is superior in terms of low toxicity as compared with hydrazine, the reactivity is low. For this reason, in order to catalytically decompose the HAN liquid propellant, it is necessary to heat the catalyst in the catalyst layer in advance to increase the activity of the catalyst at a high temperature. In such a case, if the HAN-based liquid propellant is discharged from the injector like a rod-shaped water stream and collides with a catalyst layer that has been activated at a high temperature in advance, the catalyst in which the liquid propellant has been intensively touched This part is cooled by the liquid propellant, and the temperature locally decreases. As described above, the reactivity of the HAN-based liquid propellant depends on the temperature of the catalyst. For this reason, a significant bias occurs in the catalytic reaction between the preheated portion in the catalyst layer and the portion where the temperature of the liquid propellant collides and the temperature is lowered. Similarly, a liquid propellant that stays near the inner wall of the combustor also significantly reduces the temperature of the catalyst in the catalyst layer and reduces the catalytic activity.
As described above, it is not desirable that the unreacted liquid propellant stays or that the catalytic reaction is biased because it leads to a decrease in the output of the catalytic decomposition thruster.

  Accordingly, an object of the present invention is to provide a catalytic decomposition type thruster capable of obtaining a high thruster output even when a HAN liquid propellant is used in a single liquid propulsion system.

  In supplying the liquid propellant to the catalyst layer in the combustor of the catalytic decomposition type thruster by the injector, the present inventors spray and spray the liquid propellant toward the catalyst layer and spray it onto the catalyst. By preventing unreacted liquid propellant from staying in the combustor, and preventing the local temperature drop of the catalyst and the occurrence of bias in the catalytic reaction, maintaining a high thruster output, The present invention has been achieved based on the knowledge that the above problems can be solved.

  That is, the present invention is a catalytic decomposition type thruster for a spacecraft, which obtains a propulsive force by injecting a reaction gas obtained by decomposing a liquid propellant with a catalyst, and is a hollow for containing a liquid propellant. A tank for decomposing the liquid propellant and injecting a reaction gas, and a flow path for supplying the liquid propellant from the tank to the combustor. The tank is further filled with the liquid propellant. And a piston for delivering the liquid propellant to the combustor, the combustor further comprising a catalyst layer having a catalyst for catalytic decomposition of the liquid propellant, and heating for heating the catalyst layer A catalytic decomposition type thruster comprising an apparatus and an injector for supplying a liquid propellant to the catalyst layer, wherein the injector sprays the liquid propellant on the catalyst layer by applying a predetermined pressure to the piston; Subjected to.

  According to the present invention, the liquid propellant is made fine by an injector and uniformly diffused and sprayed onto the catalyst layer, so that a large amount of liquid propellant concentrates and collides with a specific portion, and the local catalyst layer is formed. The temperature drop can be prevented and the unevenness of the catalytic reaction in the catalyst layer is eliminated. Further, the sprayed liquid propellant has an increased unit surface area that contributes to the reaction, and the contact surface area with the catalyst also increases, so that the reactivity is improved. Furthermore, since the heat of reaction due to catalytic decomposition of the liquid propellant can be efficiently obtained, the self-decomposability of the liquid propellant can be enhanced.

It is a cross-sectional schematic diagram of a conventional catalytic decomposition type thruster. It is a cross-sectional schematic diagram of the catalytic decomposition type thruster by this invention. It is a cross-sectional schematic diagram of the tank employ | adopted by this invention. It is a figure which shows the result of the ground injection test obtained by one Embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view of the catalytic decomposition type thruster according to the present invention. The catalytic decomposition type thruster 1 is a catalytic decomposition type thruster 1 that obtains a driving force by injecting a reaction gas obtained by decomposing a liquid propellant with a catalyst. This catalytic combustion type thruster 1 includes a hollow tank 2 for containing liquid propellant, a combustor 4 for burning the liquid propellant and injecting combustion gas from the nozzle 3, and burning the liquid propellant from the tank 2. And a flow path 5 to be supplied to the container 4.

a. Tank FIG. 3 is a schematic sectional view of a tank employed in the present invention.
Here, a cylindrical tank 2 is shown. For example, a cylindrical tank having an inner diameter of 50 mm can be used, but the shape and dimensions of the tank 2 are not limited thereto. In view of the fact that the HAN liquid propellant is strongly acidic, it is desirable that the material of the tank 2 be stainless steel or titanium material that has been confirmed to be compatible by a material compatibility test.
The tank 2 includes a piston 9, and the piston 9 forms a compartment in which the liquid propellant L is filled inside the tank 2. Further, as will be described later, the liquid propellant L is delivered to the combustor 4 by the operation of the piston 9. In FIG. 3, the push gas G for moving the piston by applying a predetermined pressure and the liquid propellant L are separated via the piston 9. A gas such as nitrogen or helium can be used as the push gas G, and the liquid propellant L is discharged from the tank 2 by pushing the piston 9 with the gas pressure of the push gas G.
The fact that the tank in the catalytic decomposition type thruster of the present invention is equipped with such a gas-liquid separation mechanism such as a piston is extremely important in that the catalytic decomposition type thruster of the present invention is used for a space vehicle. That is, without providing a gas-liquid separation mechanism inside the tank as in the present invention to form a section filled with liquid propellant, the liquid part and the gas part are not separated inside the tank. When used in a space environment, the liquid propellant becomes unevenly distributed near the inner wall of the tank under zero gravity. If it is attempted to discharge the liquid propellant from the tank in such a state, the gas will be discharged, making it impossible to efficiently discharge the liquid propellant, resulting in a decrease in the output of the catalytic decomposition thruster. End up. By providing a gas-liquid separation mechanism inside the tank as in the present invention, it is possible to prevent such problems from occurring. From the viewpoint of resistance to the HAN liquid propellant, it is desirable that the piston 9 as the gas-liquid separation mechanism is also made of a material having compatibility with materials such as stainless steel and polymer material.
The inner surface of the tank 2 has a mirror finish. In view of pushing the piston 9 with the gas pressure of the pushing gas G in the space environment, the tank 2 has a safety factor of at least twice (a safety factor of at least four times in the ground combustion test) and an internal pressure of about 3 MPa. It has a pressure-resistant structure that can sufficiently withstand the pressure assumed in the orbit of the spacecraft.
When the liquid propellant L is filled in the tank 2, a so-called vacuum filling method generally used as a liquid propellant filling method in the spacecraft can be adopted as follows.
In FIG. 3, first, the liquid port P _L is opened. At this time, the piston 9 is located at a location in contact with the bottom surface of the tank 2 on the liquid port P _L side. Then, when the evacuation by the vacuum pump through the gas port P _G, the piston 9 moves toward the inside of the tank 2 to the gas port P _G side. Then, after closing the gas port P _G, evacuated from the liquid port P _L. Thereafter, the liquid port P _L is closed, and the liquid port P _L is connected to a propellant transport container (not shown). Then, the liquid propellant is filled into the tank when opening the liquid port P _L.
Since the HAN propellant can be stored for a long time, the liquid propellant can be stored in a state where the tank 2 is filled.

b. Combustor Returning to FIG. 1, the combustor 4 is preferably made of a stainless alloy material. The material of the combustor 4 may be selected as long as it is compatible with the high temperature (1000 ° C. or higher) reaction gas and the strongly acidic unreacted liquid propellant. The shape of the combustor 4 may be a general pressure-resistant shape used in a space vehicle, and may be, for example, a cylindrical shape. The structure of the combustor 4 is a structure that can sufficiently withstand the pressure of the reaction gas, which is less than 1 MPa. Further, in the ground combustion test, a safety factor of 4 or more is ensured for safety (space). It is desirable to use a design such as a safety factor of 2 for flying vehicles.
As a thrust force obtained by the combustor 4, it is desirable to obtain about 15N. The magnitude of the obtained thrust force can be changed by adjusting the thruster shape.
As the nozzle 3 of the combustor 4, it is possible to employ a type normally used in space vehicles. As for the nozzle 3, the reaction gas is choked at the throat of the nozzle 3, whereby the pressure of the reaction gas can be measured, and the thruster performance can be evaluated from the measurement result. A nozzle system that can be choked can be selected based on the evaluated thruster performance.
The process of obtaining the driving force by discharging the reaction gas from the nozzle 3 is that the reaction gas is choked at the throat of the nozzle 3, passes through the throat at the speed of sound, and then expands properly, thereby obtaining the driving force. Is.

c. Flow path The flow path 5 is usually made of a pipe material having material compatibility and high temperature resistance such as stainless alloy, and can be made of, for example, 1/8 pipe. The shape of the flow path 5 is generally a straight pipe. As the structure / performance of the flow path 5, the structure / performance of a general stainless steel pipe is sufficient.
In the catalytic decomposition type thruster of the present invention, as shown in FIG. 3, the liquid propellant L employs a structure in which the piston 9 is pushed by the gas G that pressurizes the tank 2 and the liquid propellant L is sent out. Can do. As shown in FIG. 2, the liquid propellant L is supplied from there to the flow path 5, and the supply of the liquid propellant L is controlled by the propellant valve upstream of the combustor 4 through the flow path 5 constituted by a stainless steel pipe or the like. And supplied to the combustor 4.
Further, the combustor 4 includes a catalyst layer 6 having a catalyst for catalytically decomposing the liquid propellant, a heating device 7 for heating the catalyst layer 6, and an injector for supplying the liquid propellant to the catalyst layer 6. 8 and. Then, by applying a predetermined pressure to the piston 9, the injector 8 sprays the liquid propellant onto the catalyst layer 6.

d. Catalyst Layer The catalyst layer 6 has a distance from the tip of the injector 8 to the catalyst layer 6 so that the liquid propellant sprayed from the injector 8 is sprayed over the entire catalyst layer 6 in the combustor 4 without excess or deficiency. Optimize and place. For example, the catalyst layer 6 can be disposed at a position of about 50 mm from the tip of the injector 8.
The reaction gas of the liquid propellant decomposed in the catalyst layer 6 is completely decomposed in a region downstream of the catalyst layer 6 in the combustion chamber, and is discharged from the nozzle 3. Graphite is used as the heat-resistant material on the inner surface of the part involved in this process in the combustor 4.
As the catalyst used for the catalyst layer 6, for example, an alumina carrier catalyst on which iridium such as S405 is supported can be used. The type of the catalyst is not particularly limited as long as it is a catalyst usually used for a one-part propulsion system of a space vehicle. As the size and shape of the catalyst, it is preferable to use particles having a particle size of about 0.5 mm or less. The catalyst layer 6 can be configured by sandwiching the catalyst with a stainless steel wire mesh having a fine mesh to such an extent that such a catalyst does not spill. Further, for holding the catalyst layer 6, it is desirable to use a stainless alloy wire mesh as a heat and pressure resistant material and to use carbon fiber and a ceramic material as a reinforcing material.
As a liquid propellant decomposed | disassembled with the catalyst of the catalyst layer 6, what mixed ammonium nitrate, water, and methanol by the mass ratio 95: 5: 8: 21 can be used, for example. The liquid propellant having such a composition has a specific gravity of 1.4 and a freezing point of −68 ° C.
The mechanism of obtaining a driving force by decomposing such a HAN liquid propellant with the catalyst of the catalyst layer 6 is that the HAN liquid propellant is decomposed by the catalyst and decomposed into nitrogen, hydrogen, etc. It is explained that the fuel component methanol burns in the combustor 4 and is discharged from the nozzle during the reaction process.

e. Heating device There is no restriction | limiting in particular as the heating device 7, For example, the tape heater which processed the heating wire in tape shape can be used. Such a heater, for example, generates heat by applying a voltage of 24V to a 10Ω heating wire. When the tape heater is used, the heating device 7 can be applied by winding the tape heater around the outside of the combustor 4 near the catalyst layer 6. And the catalyst layer 6 is heated using the heat transfer of the combustor 4 made of stainless steel.

f. Injector It is desirable that the injector 8 is also made of a material having material compatibility and high-temperature resistance such as stainless steel and titanium for the same reason as other elements. The injector 8 is a sprayer disposed upstream of the catalyst layer 6 in the combustor 4. In order for the liquid propellant sprayed from the injector 8 to be sprayed uniformly on the catalyst of the catalyst layer 6, it is considered that the spray diffusion angle is preferably set to 50 ° from the measurement.
The particle size of the liquid propellant droplet sprayed by the injector is preferably about 0.1 mm to 0.7 mm, and more preferably about 0.3 mm to 0.5 mm. In order to hold the powdered catalyst in the catalyst layer 6, the catalyst is usually sandwiched from both sides using a metal net. It is extremely difficult to spray the liquid propellant directly on the catalyst of the catalyst layer 6 having such a structure. On the other hand, a metal mesh for holding a catalyst used to fix a granular catalyst having a particle size of about 0.5 mm or less as described above is usually about 0.2 mm in wire diameter and about 40 mesh. Therefore, if the droplet is too larger than this size, it will collide with the metal wire constituting the wire mesh, making it difficult for the droplet to reach the catalyst. On the other hand, a droplet that is too small has a small inertial force and a moving speed is lowered, so that it becomes difficult for the liquid propellant to reach the catalyst layer 6 efficiently and the surface tension becomes very large. It becomes difficult to pass through and cause a large amount of unreacted liquid propellant to be formed. Large quantities of unreacted liquid propellant droplets become large lumps, resulting in a decrease in catalyst temperature, while also having the risk of causing an explosion by reacting suddenly. Furthermore, droplets that are too fine exhibit a sensitive reaction, and when the catalyst holding wire mesh that is heated at the same time as the catalyst is heated, it also reacts and melts the holding wire mesh. . Therefore, when the catalyst layer 6 of a type using a metal mesh for holding the catalyst is adopted, the droplet diameter of the sprayed liquid propellant is 70 to 120% of the mesh interval of the metal mesh. It is desirable to make it.
The catalytic decomposition type thruster according to the present invention is such that the injector 8 sprays the liquid propellant onto the catalyst layer 6 by applying a predetermined pressure to the piston 9. At that time, it is desirable that the pressure applied to the piston 9 is 0.75 MPa or more in consideration of the viscosity of the liquid propellant. If the pressing pressure is too low, the liquid propellant is not sprayed and becomes a water stream. Further, the upper limit of the pressing pressure is considered to be about 4 MPa from the viewpoint of use in the space environment.

A catalytic decomposition type thruster according to the present invention having a structure as shown in FIGS. 2 and 3 is prepared, and the supply pressure of the liquid propellant applied by the piston is adjusted to a constant 0.75 MPa for 5 seconds. Combustion experiments were carried out by supplying propellant continuously. The performance of the catalytic cracking thruster was evaluated by measuring the flow rate of the propellant and the internal pressure of the combustor. For comparison, a catalytic decomposition type thruster having a structure as shown in FIG. 1 was prepared and the same experiment was performed. The results are shown in FIG.
From FIG. 4, the combustion efficiency of the catalytic decomposition type thruster having the conventional structure is about 53%, whereas the catalytic efficiency type thruster having the structure of the present invention has a combustion efficiency of about 83%, which is about the comparison with the conventional case. It can be seen that the improvement is 1.6 times.

1 Thruster 2 Tank 3 Nozzle 4 Combustor 5 Flow path 6 Catalyst layer 7 Heating device 8 Injector 9 Piston

Claims (1)

A catalyst-decomposable thruster for space vehicles, which obtains propulsive force by injecting a reaction gas obtained by decomposing a liquid propellant with a catalyst,
A hollow tank for containing the liquid propellant;
A combustor that decomposes the liquid propellant and injects a reactive gas;
A flow path for supplying the liquid propellant from the tank to the combustor;
With
The tank further includes a piston that forms a compartment filled with the liquid propellant in the tank and delivers the liquid propellant to the combustor,
The combustor further includes
A catalyst layer having a catalyst for catalytically decomposing the liquid propellant;
A heating device for heating the catalyst layer;
An injector for supplying the liquid propellant to the catalyst layer;
The catalytic decomposition type thruster, wherein the injector sprays the liquid propellant on the catalyst layer by applying a predetermined pressure to the piston.

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