Propulsion system for a spacecraft and method for propelling a spacecraft

Abstract

Method for propelling a spacecraft in which at least a first propulsion device (38, 46) of a propulsion system (1) of the spacecraft is operated by combustion of a premixed flammable fluid (14) containing a hydrocarbon as fuel and N2O as oxidizer, wherein the flammable fluid (14) is stored in a storage device (12) in a premixed state and wherein the first drive device (18, 38, 46) is supplied with the flammable fluid (14) by means of a first supply line (31) arranged between the storage device (12) and the drive device (38, 46), wherein the storage device (12) and the drive device (38, 46) are in flow communication with each other by means of a piping system (28) of the first supply line (31) arranged between them, characterized by that the flammable fluid (14) is essentially completely liquid in the storage device (12), wherein the temperatures within the storage device (12) are below the boiling points of the individual components of the flammable fluid at a certain pressure, and is drawn from it in liquid form and conveyed in gaseous form to the drive device (18, 38, 46), wherein the flammable fluid (14) is vaporized within the first supply line (31) by means of at least one vaporization arrangement, the vaporization arrangement comprising a throttling device (30) which is arranged in the piping system (28) downstream of the storage device (12) and comprising at least one heat supply device (50) in which the flammable fluid is, if necessary, further vaporized and the pressure in the supply line (31), between the storage device (12) and the drive device (38, 46), is increased to a delivery pressure, and wherein the flammable fluid (14) can be stored in an intermediate volume (34) in the piping system (28) downstream of the throttling device (30) and fluctuations in the composition are homogenized by the intermediate volume (34), wherein the heat supply device (32, 50) is arranged on and / or in the intermediate volume (34) in thermal contact with the flammable fluid (14) and / or on and / or in the piping system (28) downstream of the throttling device (30).

Description

[0001] The invention relates to a propulsion system for a spacecraft, comprising at least a first propulsion device that can be operated with a premixed flammable fluid containing a fuel and oxidizer, a storage device for storing the flammable fluid in a premixed state, and a first supply line for supplying the first propulsion device with the flammable fluid, which is arranged with a piping system between the storage device and the propulsion device for their flow connection. The invention further relates to a method for propelling a spacecraft.

[0002] Such a drive system is specified in WO 2013 / 105988 A2.

[0003] JP 2011-183840 A describes a tank for storing liquid fuel, whereby the fuel is supplied to an engine in a gaseous state. The fuel vaporizes within the storage device in which the liquid fuel is stored.

[0004] A propulsion system for operation with gaseous fuel is specified in KR 10 2012 0 062 288 A. In this system, the fuel is stored in gaseous form in a storage tank. A constant supply pressure for a thrust generator is achieved by placing a collection tank between the storage tank and the thrust generator.

[0005] Other propulsion systems for spacecraft, in which several storage devices are available for the separate storage of different propellant components, e.g. fuel and oxidizer, are known, for example, from GB 2 293 627 A, US 2016 / 0 108 855 A1 and GB 1 210 601 A.

[0006] A fuel that can serve as a combustible fluid in the aforementioned propulsion system is shown, for example, in US 2009 / 0 133 788 A1.

[0007] US Patent 6,968,673 B1 describes various designs for so-called cold gas engines, in which a working fluid is heated by the addition of heat and thereby expands to generate thrust. The heat is generated by combustion or catalytic decomposition of the fluid.

[0008] The KR 10 2012 062 288 A discloses a fuel supply system, more precisely a cold gas system, for conveying gaseous fuel, with a high-pressure tank for pressure equalization.

[0009] WO 2012 / 172 238 A1 shows a cryogenic propulsion unit with two cryogenic tanks for each holding a propellant, in particular liquid hydrogen and liquid oxygen.

[0010] US Patent 5,746,050 A describes a system for delivering a gaseous product into a reaction chamber. The system includes a tank in which a hypergolic propellant is stored in liquid form.

[0011] US patent 2016 / 0237952A1 describes a propulsion system for a spacecraft with two tank systems, for example, for the separate storage of liquid hydrogen and oxygen. Each tank has its own pressurization device to return propellant in gaseous form to the tanks, thus achieving self-pressurization.

[0012] US 2009 / 0 007 541 A1 shows a propulsion system for operation with nitrous oxide and a fuel. The nitrous oxide can also serve as a pressurizing gas for self-pressurization.

[0013] The invention is based on the objective of providing a propulsion system that can be operated within small and very small thrust classes and is precisely controllable, and a corresponding method for propelling a spacecraft.

[0014] The problem is solved for the method with the features of claim 1 and for the drive system with the features of claim 2.

[0015] The drive system is designed to carry out the method according to claim 1, wherein the storage device is designed such that the flammable fluid is essentially completely liquid in it and can be removed in liquid form, and that the first supply line has at least one evaporation arrangement for evaporating the flammable fluid.

[0016] The flammable fluid is a propellant mixture for the rocket engine, which ignites upon application of ignition energy. The fuel and oxidizer are premixed in the storage device. According to the invention, the propellant is a mixture of nitrous oxide (N₂O) as the oxidizer and hydrocarbons, such as ethene (C₂H₄) or an alcohol (mixture) (e.g., ethanol), or even ammonia, as the fuel. The terms "flammable fluid" and "propellant" are used synonymously here. Advantageously, the components of the flammable fluid exhibit a sufficiently high vapor pressure at a given temperature, which corresponds at least to the required delivery pressure within the piping system. This ensures the safe delivery of the flammable fluid in gaseous form to the propulsion device, even in its gaseous state.

[0017] The propulsion system is designed for operation with gaseous combustible fluid and is specifically assigned to a small (e.g., up to 200 N) and / or very small (e.g., less than 1 N) thrust class. Since the energy density of gas is lower than that of liquid, the energy input into the propulsion system and converted into thrust is easier and / or more precisely controllable in these small or very small power ranges than with liquid-fueled engines. Thus, thrust can be precisely controlled even within these small and / or very small thrust classes using such propulsion systems. In this way, propulsion maneuvers requiring only small or very small propulsion energy, such as attitude control maneuvers, can be precisely controlled.

[0018] The energy density of the liquid phase of a flammable fluid is higher than that of the gas phase. Therefore, liquid storage allows for the advantageous storage and transport of larger quantities of energy within the storage device than gaseous storage.

[0019] Evaporation outside the storage device makes it possible to largely forgo evaporation within the device. This advantageously prevents continuous segregation or shifts in the mixing ratio of the combustible fluid within the storage device: In a non-azeotropic mixture, as is usually the case, components of the fuel mixture transition into the gas phase at different rates under identical external conditions. If combustible fluid is gradually withdrawn and further evaporated, for example, for withdrawal purposes or to maintain a specific pressure in the storage device, the mixing ratio within the liquid phase changes. As the storage device is increasingly depleted, this shift in the mixing ratio of the combustible fluid can lead to significant performance losses in the propulsion system.By extracting the fluid in its liquid state and (completely) evaporating the flammable fluid outside the storage device, a constant, controlled mixing ratio can be ensured within the storage device until it is emptied.

[0020] The pressure and / or temperature within the storage device are, in particular, below the critical points of the components of the flammable fluid. Depending on the fill quantity and density, the pressure can be, for example, up to 100 bar, and according to the invention, the temperatures are below the boiling points of the individual components of the flammable fluid at a given pressure. Pressures of up to 20 or 25 bar, with correspondingly low (maximum) temperatures (e.g., below -25 °C (20 bar) for ethene, or below 8 °C (25 bar) for nitrous oxide), have proven advantageous for a comparatively low pressure load on the storage device and the subsequent piping system.

[0021] According to the invention, the evaporation arrangement comprises a throttle device, in particular an adjustable one, which is arranged in the piping system downstream of the storage device. This allows for a rapid, continuous pressure reduction in the mass flow of combustible fluid required for operating the drive device. The mass flow can be interrupted as needed by completely closing the throttle device. Via the throttle device, the combustible fluid is, for example, reduced to a pressure below its vapor pressure, e.g., from 20 bar to 10 bar, and can subsequently be at least partially in a gaseous state. For a uniform composition in the gas phase, it is also advantageous to reduce the pressure to such an extent that the combustible fluid is liquid downstream of the throttle device and is, for example, (completely) evaporated further downstream by the addition of heat.The presence of the throttling device allows the pressure in the piping system and / or in the storage device to be advantageously kept at a lower level than with purely heat-based evaporation.

[0022] According to the invention, the evaporation arrangement comprises at least one heat supply device, which is arranged, in particular, downstream of the throttling device. Energy in the form of heat is introduced into the extracted and, if necessary, previously expanded combustible fluid via the heat supply device. This ensures that the combustible fluid, which may initially have only partially transitioned into the gas phase via the throttling device, is completely re-evaporated. Furthermore, the introduction of energy in the form of heat increases the pressure in the supply line to a delivery pressure that depends, for example, on the operating pressure of the drive device and the components or piping system arranged downstream in the supply line. The temperature is thereby increased, for example, by 10 K, depending on the fuel mixture, to achieve a pressure increase of approximately 3 to 4 bar.The thermal energy used can be obtained from various sources, such as solar, nuclear, or electrical sources, or by utilizing internal waste heat (generated within the drive system). In particular, the combination of a throttling device and a heat input device in an evaporation arrangement allows for good, flexible adjustment and control of the state variables of the combustible fluid (especially pressure and temperature) to bring them from storage conditions in the storage device to a state required for the operating conditions of the drive device. Thus, the contributions of the throttling device and the heat input to the transition to the gaseous state can be optimized, for example, depending on the operating conditions. Optimization can also be carried out by considering and, if necessary, adjusting the pressure and temperature in the storage device.For example, if a low mass flow rate is required, evaporation could be largely carried out via the throttling device, thus saving thermal energy.

[0023] According to the invention, a uniform delivery pressure or supply pressure for the drive device is achieved by arranging an intermediate volume for storing gaseous flammable fluid in the piping system downstream of the throttling device, wherein a valve device is arranged, in particular, at or downstream of its outlet opening in the piping system. The intermediate volume can be formed, in particular, by means of a buffer storage tank and / or a tank. The pressure within the intermediate volume, or the withdrawal of the mass or volume flow of flammable fluid from the intermediate volume, can be controlled and / or regulated via the valve device, wherein the pressure in the intermediate volume corresponds, for example, to a maximum of the pressure after the introduction of heat energy downstream of the throttling device, e.g., between 13 and 14 bar.In addition, the intermediate volume advantageously smooths out any fluctuations in the composition that might occur during the transition to the gas phase via the throttling device.

[0024] According to the invention, the heat supply device is arranged on and / or in the piping system downstream of the throttling device. In this way, the extracted flow of flammable fluid can be continuously heated to a specific temperature and a corresponding specific pressure level. The upstream, at least partial, expansion of the flammable fluid via the throttling device advantageously reduces the heat energy required for (complete) vaporization.

[0025] Alternatively or additionally, according to the invention, the heat supply device is arranged on and / or in the intermediate volume in thermal contact with the combustible fluid. This allows for an additional or different operating mode, whereby, for example, the intermediate volume is filled with liquid combustible fluid and evaporation occurs partially or completely by introducing thermal energy through the heat supply device. This can be advantageous, for example, if a larger amount of usable heat is available from an energy source, e.g., so large that a quantity or flow rate of combustible fluid required for operating the drive device is completely evaporated. It would also be possible that, depending on the availability of thermal energy from the energy source, the transition to the gas phase is at least partially carried out via the throttling device and, depending on the availability of thermal energy, shifted to the heat supply device.It is possible for the vaporized flammable fluid to be temporarily stored in the intermediate volume at a pressure and temperature where the components are gaseous (e.g., 20 bar and 0 °C). This allows for the input of thermal energy at the point in time when it is generated and the subsequent storage of the input energy in the intermediate volume within the flammable fluid as a carrier medium. In this way, the input and the energy utilization (utilization within the drive device) can be advantageously decoupled in time. This can be particularly advantageous when using a thermal energy source that is available discontinuously (for example, using solar energy or waste heat recovery). Additionally, such an operating mode can advantageously ensure a uniform (target) composition of the flammable fluid in the gas phase.

[0026] In a specific exemplary embodiment of the aforementioned variant, the evaporation arrangement comprises the heat supply device and the intermediate volume. The throttling device could be omitted or replaced, for example, by a shut-off valve to control the filling of the intermediate volume.

[0027] An advantageous increase in the efficiency of the propulsion system is possible if the heat supply device is assigned to a heat exchanger, forming a first heat exchanger. A second heat exchanger is coupled to a component of the propulsion system with a temperature higher than the target temperature of the combustible fluid, in particular to at least one propulsion device, for the thermal utilization of its waste heat. The two heat exchangers are in thermal contact with each other. This constitutes a heat source utilizing internal waste heat within the propulsion system. The propulsion device is, for example, a gas-powered engine or a liquid-fueled engine, where the combustible fluid is used energetically through a combustion process.

[0028] In an advantageous embodiment, two sub-lines branch off from the intermediate volume, each assigned to a drive device for operation with gaseous combustible fluid. Separate valve devices are arranged in the sub-lines, allowing independent control of the gas withdrawal from the intermediate volume. In particular, the drive devices can be assigned to different thrust classes and / or drive technologies: these can be, for example, thrust classes for small thrusts (up to 200 N) and for very small thrusts (less than 1 N), and / or drive technologies that utilize the combustible fluid for energy through combustion and the pressure level through expansion, as a so-called "cold gas drive." Due to system constraints, the assignment to a thrust class often coincides with the assignment to a drive technology.In this way, a kind of “dual-mode” drive system is available, which allows different drive maneuvers to be carried out in an optimized manner.

[0029] If at least one of the pipe sections contains an additional heat supply device, the different drive devices can advantageously be operated at different pressure levels. For example, if one drive device is a cold gas drive, the pressure level for operating the cold gas drive can be deliberately increased compared to the pressure level for operating the other drive device. This can increase the thrust range that can be covered by the drive devices.

[0030] Precisely coordinated propulsion maneuvers, e.g. for precise attitude control of a spacecraft, are feasible if the (possibly second) propulsion device is formed by a cold gas propulsion system.

[0031] Preferably, a second supply line is coupled to the storage device, by means of which a further propulsion device, in particular a liquid-propellant engine, is in flow communication with the storage device for its supply. Propulsion maneuvers requiring higher thrusts, especially more than 200 N, can advantageously be performed via the liquid-propellant engine. In this way, a propulsion system can be obtained that is advantageously equipped with adapted propulsion devices for different propulsion maneuvers, using a single storage device. In addition to the liquid-propellant engine for high thrusts, for example, a propulsion device for low thrusts (less than 200 N) and / or for very low thrusts (less than 1 N) can be provided.A propulsion device that utilizes energy from the combustion of the gaseous combustible fluid (in addition to the combustion of the liquid combustible fluid in the liquid-fueled engine) and / or by utilizing the stored pressure level as a cold gas propulsion system. In this way, a type of "dual-" or "triple-mode" propulsion system is available, with which different propulsion maneuvers can be carried out in an optimized manner.

[0032] Preferably, a pressure storage device is in flow communication with the storage device (particularly in the gas phase region), by means of which the pressure in the storage device is kept constant. The pressure storage device contains a pressure storage gas, in particular helium. The storage device can, in particular, be a membrane storage device, wherein a separation device, in particular a membrane, is arranged for the material separation between the (pressure-regulating) gas phase and the combustible fluid as a liquid phase. The external pressure thus obtained can at least largely prevent evaporation of the combustible fluid within the storage device. This counteracts a change in the composition in the liquid phase and helps to ensure that the target composition of the combustible fluid is maintained until the storage device is emptied.This counteracts performance losses due to a shift in the mixing ratio within the flammable fluid.

[0033] It is also possible for the storage device to contain a mixture of the flammable fluid and a pressurized fluid, where the (saturation) vapor pressure of the pressurized fluid is higher than the (saturation) vapor pressure(s) of the components of the flammable fluid. This could be, for example, CO2, which is advantageously an inert gas. This design allows for internal pressurization of the storage device using the pressurized fluid, without an external pressure storage unit and / or separation device, thus reducing system complexity without causing (significant) segregation of the flammable fluid, which is (almost) entirely in the liquid phase. A mixture of N2O and C2H6 (ethane) as the flammable fluid and CO2 as the pressurized fluid is advantageous, for example.It is also conceivable to mix the flammable fluid of N₂O and C₂H₆ at the azeotropic point of the mixture, then without a separate pressurized fluid, as long as this mixture is ignitable and delivers good performance. In this case, the pressurized fluid is formed from the flammable fluid.

[0034] For increased system safety, the design can be such that a further storage device is arranged upstream of the storage device and coupled to it in a flow-connected manner, with a valve device, in particular a safety valve device, arranged between the further storage device and the storage device. In the further storage device, the fuel can initially be stored separately from the oxidizer, which is preferably located in the storage device. Thus, for example, during the launch maneuver of the launch vehicle, no ignitable mixture is present in the storage device. Via the valve device, the components of the flammable fluid can be combined, e.g., shortly before operation of the propulsion device, and in particular the fuel can be fed to the oxidizer for premixing in the storage device.Both the secondary storage device and the storage device itself can be designed, for example, as membrane storage devices. External pressurization can be achieved, for example, via a common pressure storage device (containing a pressurized storage gas, e.g., helium, nitrogen, or carbon dioxide) that can be brought into flow contact with both the gas phase of the secondary storage device and the gas phase of the storage device, particularly by opening a valve in each case. Alternatively, pressurization could be achieved with a pressurized fluid present in each storage device, with the pressure in the secondary storage device being higher than in the storage device itself.

[0035] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawings. The drawings show: Fig. 1 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a first embodiment, Fig. 2 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a second embodiment, Fig. 3 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a third embodiment, Fig. 4 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a fourth embodiment, Fig. 5 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a fifth embodiment, Fig. 6 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a sixth embodiment, Fig. 7 a flow diagram of a drive system with an evaporation arrangement in a supply line according to a seventh embodiment, Fig. 8 a flow diagram of a drive system based on the seventh embodiment with a storage device modified compared to the one shown and Fig. 9 a flow diagram of part of a drive system, wherein the storage device is in flow connection with another storage device.

[0036] Fig. Figure 1 shows a flow diagram of a propulsion system 1 for propelling a spacecraft, such as that which may be present on a satellite as an auxiliary thruster for its attitude and / or orbital control in space. The propulsion system 1 includes a storage device 12 in which a flammable fluid 14 is stored.

[0037] Furthermore, the propulsion system 1 comprises a propulsion device 38, which is designed to propel the spacecraft by utilizing energy stored in the flammable fluid 14, wherein the flammable fluid 14 is introduced in a gaseous state. Such propulsion devices 38, or thrusters, are generally assigned to small or very small thrust classes (e.g., small thrusts up to 200 N or very small thrusts down to 1 N) and are used, for example, for attitude control of a satellite. The energy can be released, in particular, by combustion of the flammable fluid 14. However, it is also possible to utilize the pressure energy by expanding the flammable fluid 14 in a cold gas propulsion system.

[0038] The flammable fluid 14 is a propellant mixture for the rocket engine, which is ignitable upon application of ignition energy. The fuel and oxidizer are already premixed in the storage device 12. According to the invention, the propellant is a mixture of nitrous oxide (N₂O) as the oxidizer and one or more hydrocarbons, e.g., ethene (C₂H₄), as the fuel.

[0039] The drive system 1 further comprises a piping system 28 for conveying the flammable fluid 14 from the storage device 12 to the drive device 38. The piping system 28 is arranged between the individual components of the drive system 1, in particular between the storage device 12 and the drive device 38.

[0040] The piping system 28, also associated with the drive system 1, includes a throttle device 30, a heat supply device 32, an intermediate volume 34, in particular a buffer storage tank or a tank, and a valve device 36. Further components not shown here, such as additional valve devices, sensors, control devices and / or the like, may be present or integrated.

[0041] The throttling device 30 and the heat supply device 32 are associated with an evaporation arrangement. The heat supply device 32 advantageously ensures complete and uniform evaporation. The presence of the throttling device 30 advantageously allows the pressure level in the piping system 28 and / or in the storage device 12 to be maintained at a lower level. The evaporation arrangement may include further components not shown here, such as a control device, temperature sensors, a heat source, etc.

[0042] The throttling device 30 is arranged downstream of a withdrawal point 24, through which the flammable fluid 14 is withdrawn from the storage device 12. The heat supply device 32 is arranged downstream of the throttling device 30 and upstream of the intermediate volume 34 such that it can transfer thermal energy to the flammable fluid 14 flowing past it.

[0043] The storage device 12 is designed to store the flammable fluid 14 in a liquid state. Specifically, the storage device 12 is a diaphragm tank. The storage device 12 is coupled, for example, to a pressure accumulator 10 via a controllable flow connection, by means of which the pressure in the storage device 12 is kept essentially constant. The pressure in the storage device 12 can be, for example, approximately 20 to 25 bar, depending also on the operating pressure of the drive device 38 and the pressure loss within the supply line 31. The pressure within the pressure accumulator 10 is higher than the vapor pressure in the storage device, e.g., greater than 200 bar. External pressurization, e.g., by means of a pump, would also be conceivable.A valve device 20 is arranged between the pressure storage device 10 and the storage device 12. This valve device allows the pressure charging of the storage device 12 to be controlled by regulating the flow of a pressurized gas (generally helium) from the pressure storage device 10. The pressure storage device 10 maintains a substantially constant pressure in the gas environment 22 within the storage device 12. A separating device 26, for example a membrane, is arranged between the flammable fluid 14 and the gas environment 22 for material separation.

[0044] During operation, the flammable fluid 14 is drawn in liquid form from the storage device 12 via the extraction point 24 and flows into the piping system 28. Within the storage device 12, (continuous) evaporation of the flammable fluid is preferably prevented, at least to a large extent, for example by means of external pressure and / or by means of the membrane. In this way, continuous segregation or shifting of the mixing ratio within the flammable fluid 14 is advantageously prevented. Further examples of the storage device 12 with such an effect are described in the Fig. 8 and Fig. Figure 9 shows that by extracting the flammable fluid 14 in its liquid state and (completely) transferring it into the gas phase outside the storage device 12, a constant, controlled mixing ratio of the flammable fluid 14 is ensured until the storage device 12 is emptied. At the same time, the energy density of the liquid phase is higher than that of the gas phase, so that a greater amount of energy can be stored and carried within the storage device 12 by means of the flammable fluid 14 in its liquid state than when stored in its gaseous state.

[0045] The flammable fluid 14 is drawn off in liquid form via the outlet 24 and first conveyed through the piping system 28 over the throttle device 30. The flammable fluid 14 is depressurized via the throttle device 30, e.g., from 20 bar to 10 bar, and may be at least partially gaseous downstream of the throttle device 30. For a more uniform gaseous composition, it is also advantageous to depressurize the fluid to a pressure such that it remains liquid downstream of the throttle device 30 and is only (completely) vaporized further downstream by the application of heat. The throttle device 30 is adjustable, allowing the subsequent pressure level and / or mass flow rate to be varied and adapted, for example, to different operating modes.

[0046] Downstream of the throttling device 30, energy is supplied to the combustible fluid 14 to increase the pressure, in particular to a required delivery pressure within the piping system 28, which, however, is below the vapor pressure (or vapor pressures of the components) of the gaseous combustible fluid. The delivery pressure depends in particular on the operating pressure of the drive device 38 and can, for example, be between 10 and 15 bar. Advantageously, energy is supplied in the form of heat via the heat supply device 32. The thermal energy used by the heat supply device 32 can advantageously be obtained from various sources, for example, from solar, nuclear, or electrical sources and / or by utilizing internal waste heat. The pressure of the combustible fluid 14 within the heat supply device 32 can be further increased, and, if necessary, the conversion to the gas phase can be completed.

[0047] The continuous conversion of the combustible fluid 14 into the gas phase via the evaporation arrangement comprising the throttling device 30 and the heat supply device 32 advantageously ensures a complete or homogeneous phase change of the combustible fluid 14 from liquid to gaseous. The gas phase thus obtained has the defined mixture ratio of fuel and oxidizer.

[0048] The increase in volume of the continuously expanded or vaporized mass flow of flammable fluid 14 is dampened in the intermediate volume 34. This ensures a defined (delivery) pressure downstream of the intermediate volume 34. The intermediate volume 34 can also serve as an intermediate storage for gaseous flammable fluid 14 when, for example, the drive device 38 is not in operation. The drive device 38 can be connected to and disconnected from the flow connection via the controllable valve device 36.

[0049] Fig. Figure 2 shows a second embodiment of the drive system 1. In addition to the embodiment shown in Figure 2, the following embodiment is shown: Fig. In the drive system 1, a second supply line 15 is provided. The second supply line 15 establishes a flow connection between the storage device 12 and, optionally, a further drive device 18. The drive device 18 is designed for operation with flammable fluid 14 in a liquid state. Such drive devices 18 are, for example, assigned to higher thrust classes, for example, with thrusts of more than 200 N. The second supply line 15 includes, upstream of the drive device 18, a valve device 16 for connecting and disconnecting the drive device 18 from the flow connection with the flammable fluid 14. In this way, two drive devices 38, 18 of different thrust classes are advantageously combined in the drive system, which are operated with the flammable fluid 14 in different states of matter (drive device 38: gaseous, further drive device 18: liquid).

[0050] Fig. Figure 3 shows a third embodiment of the drive system 1. Compared to the embodiment according to Fig. The first supply line 31 varies. In addition to the drive devices 38 and 18, there is a further drive device 46, which is operated with gaseous flammable fluid 14. The drive device 46 can, for example, be a cold gas drive in which no combustion takes place, but the pressure level of the flammable fluid 14 is used energetically to generate minute thrusts (e.g., in the range of µN to 1 N). To supply the drive device 46 with the flammable fluid 14, the first supply line 31 downstream of the intermediate volume 34 splits into a first sub-line 40 and a second sub-line 42. The first sub-line 40 with a first partial line 27 corresponds in its design, for example, to the section of the supply line 31 downstream of the intermediate volume 34 according to Fig. 1 and Fig. 2. The second sub-pipe 42 with a second sub-pipe 29 includes a valve device 44 for connecting and disconnecting the drive device 46 to and from the flow connection with the intermediate volume 34. A further heat supply device could be installed in the second sub-pipe 42 upstream of the valve device 44 to further increase the pressure level of the combustible fluid 14 in the second sub-pipe 42.

[0051] Fig. 4 shows another embodiment variant, based on the embodiment shown in the illustration. Fig. 2 (or possibly Fig. 3) The heat supply device 32 is arranged in the intermediate volume 34. This embodiment allows for discontinuous evaporation of the combustible fluid 14 and its storage to supply the drive device 18 (and, if present, the drive device 46, not shown here), which is operated with gaseous combustible fluid. Evaporation can, for example, take place exclusively via the heat supply device 32, with the throttle device 30 open and not contributing to evaporation. The intermediate volume 34 is closed when the valve device 36 (and, if present, the valve device 44, cf.) is closed. Fig. 3) filled with (liquid) flammable fluid 14. After filling is complete, the throttling device 30 is fully closed, whereby the quantity introduced into the intermediate volume 34 is sufficiently small to allow complete evaporation of the flammable fluid 14. Heat energy is introduced into the intermediate volume 34 via the heat supply device 32 until complete evaporation of the flammable fluid 14 is achieved. In this embodiment, the evaporation arrangement thus comprises the heat supply device 32 and the intermediate volume 34. The throttling device 30 could also be omitted and, for example, a simple closing valve device could be used instead.

[0052] Fig. Figure 5 shows another design variant, based on an example of Fig. 2 with a variation of the evaporation arrangement or the heat supply device 32. The heat supply device 32 is associated with a heat exchange device 48 and forms a first heat exchanger 50 of the heat exchanger 48. The heat exchanger 48 further comprises a second heat exchanger 52. The first heat exchanger 50 and the second heat exchanger 52 are thermally coupled. Here, the heat exchanger 48 serves as an example for utilizing the waste heat from the drive device 38 as a heat source for the evaporation of the combustible fluid 14 in the intermediate volume 34. In this way, energy can be advantageously saved and the overall efficiency of the drive system 1 can be improved.

[0053] Fig. Figure 6 shows another design variant, based on the heat exchange principle according to Fig. 5. In this case, the second heat exchanger device 52 is thermally coupled to the drive device 18 instead of to the drive device 38.

[0054] Fig. Figure 7 shows another design variant based on an example of Fig. 6, wherein the first heat exchanger 50 is in thermal contact with the piping system 28 instead of the intermediate volume 34, and the flammable fluid 14 is evaporated or heated there. It would also be possible to omit the first and second heat exchangers 50, 52 and to design the piping system 28 such that the flammable fluid 14 is guided past the drive device 18 in direct thermal contact. In this case, the heat exchanger 48 would be formed by a section of the piping system 28 and a heat-emitting part of the drive device 18.

[0055] Fig. 8 is based on Fig. Figure 7 shows a variant of the storage device 12. The storage device 12 comprises a single chamber without a separating device or membrane. The chamber contains a mixture 14.1 of the combustible fluid and a pressurized fluid, for example, CO2. The (saturation) vapor pressure of the pressurized fluid is higher than the (saturation) vapor pressure of the components of the combustible fluid. This allows pressurization by means of the pressurized fluid without an external pressure storage device and / or separating device, thus reducing system complexity without causing (significant) segregation of the combustible fluid, which is (almost) entirely in the liquid phase.

[0056] Fig. Figure 9 shows a part of a drive system comprising the storage device 12. For increased system safety, a further storage device 11 is provided, which is coupled upstream of the storage device 12 and can be brought into flow communication with it via the piping system 28. A safety valve device 21 is arranged between the further storage device 11 and the storage device 12. In the further storage device 11, the fuel (for example, a hydrocarbon) is initially located separately from the oxidizer (for example, N₂O), which is preferably located in the storage device 12. Shortly before operation of the drive device, which requires the flammable fluid as fuel, the components are combined by opening the safety valve device 21, whereby, in particular, the fuel is supplied to the oxidizer. In this way, the premixed flammable fluid 14 is obtained.Both the additional storage device 11 and the storage device 12 can, for example, be designed as membrane storage devices. External pressurization can be achieved, as shown here by way of example, via a common pressure storage device 10 (containing a pressure storage gas, e.g., helium, nitrogen, or carbon dioxide), which can be brought into flow contact with both the gas phase of the additional storage device 11 and the gas phase of the storage device 12. For example, the additional storage device 11 is first pressurized with the pressure storage gas under control via the valve device 20. After the additional storage device 11 has been emptied or the storage device 12 has been filled, the storage device 12 is pressurized between the pressure storage device 10 and the storage device 12 under control via the valve device 20.It would also be conceivable to apply pressure fluid to each of the respective storage devices 11 and 12, with the pressure in the further storage device 11 being higher than in the storage device 12, in order to generate the pressure differential required for joining the components. Downstream of the storage device 12, the drive system 1 can, for example, be configured according to one of the embodiments described above.

[0057] The valve devices 16, 20, 20.1, 36 and 44 shown here, and any other valve devices that may be present, can be at least partially formed by control valves. In this way, the mass flows and thus the thrusts of the actuator 38 and, if present, 18 and / or 46, can be controlled.

[0058] It is understood that the different design variants shown can be combined with one another. For example, the heat exchange principle can be implemented in different configurations in the design of drive system 1 according to Fig. 1 will be provided.

[0059] The inventive design of the drive system 1 and the inventive method for propelling the spacecraft support, on the one hand, reliable operation of the drive system 1, whereby precise thrust control is advantageously possible even in small and very small thrust classes. This enables operation without loss of performance until the storage device 12 is emptied. Furthermore, the liquid storage of the flammable fluid 14 allows a higher amount of energy to be stored and carried on the spacecraft in the same volume compared to gaseous storage.

Claims

[1] Method for propelling a spacecraft wherein at least a first propulsion device (38, 46) of a propulsion system (1) of the spacecraft is operated by combustion of a premixed flammable fluid (14) containing a hydrocarbon as fuel and N2O as oxidizer, wherein the flammable fluid (14) is stored in a storage device (12) in a premixed state and wherein the first drive device (18, 38, 46) is supplied with the flammable fluid (14) by means of a first supply line (31) arranged between the storage device (12) and the drive device (38, 46), wherein the storage device (12) and the drive device (38, 46) are in flow communication with each other by means of a piping system (28) of the first supply line (31) arranged between them, characterized by , that the flammable fluid (14) is essentially completely liquid in the storage device (12), wherein the temperatures within the storage device (12) are below the boiling points of the individual components of the flammable fluid at a certain pressure, and is drawn from it in liquid form and conveyed in gaseous form to the drive device (18, 38, 46), wherein the flammable fluid (14) is vaporized within the first supply line (31) by means of at least one vaporization arrangement, the vaporization arrangement comprising a throttling device (30) which is arranged in the piping system (28) downstream of the storage device (12) and comprising at least one heat supply device (50) in which the flammable fluid is, if necessary, further vaporized and the pressure in the supply line (31), between the storage device (12) and the drive device (38, 46), is increased to a delivery pressure, and wherein the flammable fluid (14) can be stored in an intermediate volume (34) in the piping system (28) downstream of the throttling device (30) and fluctuations in the composition are homogenized by the intermediate volume (34), wherein the heat supply device (32, 50) is arranged on and / or in the intermediate volume (34) in thermal contact with the flammable fluid (14) and / or on and / or in the piping system (28) downstream of the throttling device (30). [2] Propulsion system (1) for a spacecraft configured to perform the method according to claim 1, comprising - at least a first propulsion device (38, 46) which can be operated by combustion of a premixed flammable fluid (14) containing a hydrocarbon as fuel and N2O as oxidizer, - a storage device (12) for storing the flammable fluid (14) in a premixed state and - with a first supply line (31) for supplying the first drive device (18, 38, 46) with the flammable fluid (14), which is arranged with a piping system (28) between the storage device (12) and the drive device (38, 46) for their flow connection, wherein the storage device (12) is designed such that the flammable fluid (14) is essentially completely liquid in it and can be removed in liquid form, wherein the first supply line (31) has at least one evaporation arrangement for evaporating the flammable fluid (14), wherein the evaporation arrangement comprises a throttling device (30) which is arranged in the piping system (28) downstream of the storage device (12) and comprises at least one heat supply device (50) for post-evaporation and pressure increase in the supply line (31) to a delivery pressure, and wherein an intermediate volume (34) for storing gaseous flammable fluid (14) and homogenizing fluctuations in the composition is arranged in the piping system (28) downstream of the throttling device (30), wherein the heat supply device (32, 50) is arranged on and / or in the intermediate volume (34) in thermal contact with the flammable fluid (14) and / or on and / or in the piping system (28) downstream of the throttling device (30). [3] Drive system (1) according to claim 2, characterized by, that the evaporation arrangement comprises the heat supply device (32) and the intermediate volume (34). [4] Drive system (1) according to one of claims 2 or 3, characterized by , that the heat supply device (32, 50) is associated with a heat exchange device (48) and thereby forms a first heat exchange device (50), wherein a second heat exchange device (52) of the heat exchange device (48) is coupled to a component of the drive system (1) with a higher temperature than the target temperature of the combustible fluid (14). [5] Drive system (1) according to any one of claims 2 to 4, characterized by , that from the intermediate volume (34) two partial lines (27, 29) branch off, each of which is assigned to a drive device (38, 46) for operation with gaseous flammable fluid (14). [6] Drive system (1) according to claim 5, characterized by , that in at least one of the partial lines (27, 29) a further heat supply device (32) is arranged. [7] Drive system (1) according to any one of claims 2 to 6, characterized by , that the drive device (38, 46) is formed by a cold gas drive. [8] Drive system (1) according to any one of claims 2 to 7, characterized by , that a second supply line (15) is coupled to the storage device (12), by means of which a further drive device (18) is in flow connection with the storage device (12) for its supply. [9] Drive system (1) according to any one of claims 2 to 8, characterized by , that a pressure storage device (10) is in flow communication with the storage device (12), by means of which the pressure in the storage device (12) is kept constant. [10] Drive system (1) according to any one of claims 2 to 9, characterized by, that the storage device (12) contains a mixture (14.1) of the combustible fluid (14) and a pressure fluid, wherein the vapor pressure of the pressure fluid is higher than the vapor pressure of the components of the combustible fluid. [11] Drive system (1) according to claim 9 or 10, characterized by , that upstream of the storage device (12) a further storage device (11) is arranged which is coupled to the storage device (12) in a way that allows it to be brought into flow communication, wherein a valve device is arranged between the further storage device (11) and the storage device (12).

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