Rocket methane subcooling filling system and control method

Abstract

This invention relates to the field of rocket cryogenic propellant refueling technology, specifically disclosing a methane subcooled refueling system and control method for rockets. The system is connected to the rocket's liquid oxygen tank for methane refueling and includes a methane storage tank and a methane refueling pipeline. The end of the methane refueling pipeline is equipped with a series-connected end-of-refueling valve and a one-way valve. The one-way valve conducts unidirectionally from the methane storage tank to the rocket's methane storage tank. This invention, while ensuring continuous flow of subcooled methane throughout the process and avoiding pipeline freezing, physically eliminates the problem of methane backflow from the storage tank caused by sequence differences at the end of refueling. It does not rely on valve synchronization control precision, offering high safety, strong reliability, and good engineering adaptability. Simultaneously, it can be equipped with discharge and recovery pipelines, addressing the needs of stopping refueling to prevent freezing, refueling conditions, and propellant recovery and reuse, significantly improving the safety and economy of the methane subcooled refueling process.

Description

Technical Field

[0001] This invention relates to the field of rocket cryogenic propellant refueling technology, specifically to a rocket methane supercooling refueling system and control method. Background Technology

[0002] With the rapid development of commercial space technology, liquid oxygen-methane rockets have become the mainstream development direction in the field of space launch vehicles due to their advantages such as low propellant cost, non-toxicity and pollution-free operation, reusability, and excellent overall carrying capacity. As the main propellant, the performance of liquid methane directly determines the rocket's carrying capacity, launch reliability, and mission safety. Among these technologies, supercooled liquid methane refueling technology, by cooling liquid methane to a near-freezing state, can significantly increase propellant density, reduce vaporization losses during refueling, and increase the upper limit of tank capacity. It is one of the core technologies for improving the carrying capacity of liquid oxygen-methane rockets.

[0003] Liquid methane has a freezing point of -182.5℃ and a boiling point of -161.5℃ at normal pressure. The temperature of the liquid methane used for subcooled refueling is usually controlled in the range of -180℃ to -170℃, very close to its freezing point. This places extremely stringent requirements on the temperature control and fluid flow state of the refueling pipeline. During subcooled refueling, if the subcooled liquid methane in the pipeline stops flowing, the heat leaking in from the external environment will quickly cause the liquid methane to heat up and vaporize, leading to gas blockage in the pipeline, a sudden pressure increase, and in extreme cases, even freezing and blocking the pipeline, causing the refueling system to fail. Therefore, the subcooled liquid methane must maintain a continuous flow state throughout the entire refueling process, and dead spaces without flow paths are strictly prohibited.

[0004] Based on the above characteristics, existing rocket methane subcooled refueling systems must adhere to a mandatory operating sequence during the shutdown phase after the initial refueling: first, open the vent valve to discharge the methane from the pipeline, then close the final refueling valve to cut off the refueling path. This involves first providing a continuous flow of subcooled liquid methane through the vent valve to prevent flow interruption and freezing; only after the vent path is completely clear is the final refueling valve closed to complete the shutdown. However, this operating sequence has an inherent, insurmountable flaw: there is inevitably a time difference, ranging from milliseconds to seconds, between opening the vent valve and closing the final refueling valve.

[0005] Within the aforementioned time window, the opening of the discharge valve causes a sudden drop in pressure in the main refueling pipeline, while the rocket propellant tanks remain at the high pressure level they were in after refueling. This creates a significant pressure inversion, causing the high-pressure liquid methane in the rocket propellant tanks to backflow into the low-pressure main refueling pipeline via the partially closed unfilled valve, resulting in propellant backflow. This backflow problem can lead to a series of serious consequences: First, it can cause inaccurate propellant loading in the rocket propellant tanks, directly affecting the rocket's orbital insertion accuracy and even causing launch mission failure. Second, the backflow of cryogenic liquid methane can cause severe pressure fluctuations and water hammer in the refueling pipeline, easily damaging core equipment such as refueling pumps and precision valves, and even causing pipeline seal failure, methane leakage, and posing a risk of flammability and explosion. Third, the backflow of liquid methane can cause temperature fluctuations in the pipeline, increasing the risk of vaporization and freezing, affecting the normal execution of subsequent refueling operations.

[0006] To address the aforementioned backflow problem, existing technological solutions mainly fall into three categories: First, by optimizing the program logic of the refueling control system to minimize the time difference in valve action, this solution can only alleviate the degree of backflow, not fundamentally eliminate the time difference, and cannot cope with fault conditions such as valve jamming and action delay, resulting in inherent reliability shortcomings. Second, by adding complex pressure interlocks and emergency shut-off protection devices to the refueling system, but these solutions all rely on the normal operation of the electrical control system and cannot cope with extreme conditions such as power outages and signal failures, which does not conform to the design principle of "passive redundancy and intrinsic safety" in aerospace systems. Third, by coordinating the shut-off with the isolation valve at the rocket's propellant tank refueling port, but the rocket's isolation valve is a core safety component during rocket flight, designed to be opened and closed very infrequently. Frequent opening and closing in coordination with the ground refueling sequence can cause wear and shrinkage failure of the cryogenic sealing surface, and when the pipeline is disconnected before launch, there is a high risk of fatal leakage due to sealing failure. Furthermore, the control authority of the rocket system and the ground refueling system is isolated, making it impossible to achieve millisecond-level timing coordination, thus failing to fundamentally solve the backflow problem.

[0007] Chinese invention patent CN 119737559 B discloses an online fully subcooled methane refueling system and its refueling method. This system, through a combination of dual methane storage tanks, a subcooler, and a loop pipeline, maintains stable methane flow rate in the subcooler tube side and stable liquid nitrogen level in the shell side, preventing methane icing due to level instability and achieving stable online subcooled refueling at different flow rates. However, this solution only focuses on stable control of subcooling temperature and flow rate, without proposing any protective structure to address the methane backflow problem caused by differences in refueling timing. Furthermore, existing methane subcooled refueling systems struggle to simultaneously address the requirements for propellant backflow prevention and recycling: to achieve propellant recovery after rocket ignition testing and mission cancellation, the refueling system needs a parallel recovery pipeline. However, in existing solutions, opening and closing the recovery pipeline easily causes pressure fluctuations in the refueling pipeline, further exacerbating the backflow risk, making it impossible to reliably prevent backflow while achieving controllable propellant recovery.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned deficiencies in existing rocket methane subcooling refueling technology by providing a rocket methane subcooling refueling system and control method. Under the premise of strictly meeting the mandatory process requirement of continuous flow of subcooled liquid methane throughout the entire process, this invention fundamentally and reliably solves the core pain point of propellant backflow caused by valve action timing differences, while also taking into account the need for propellant recovery and reuse, thus comprehensively improving the inherent safety, operational reliability, and engineering practicality of the refueling system.

[0010] To achieve the above objectives, this invention discloses a methane subcooling refueling system for a rocket, connected to a rocket methane tank for refueling methane, comprising: Methane storage tanks are used to store subcooled liquid methane. The methane refueling pipeline is connected at one end to the methane storage tank and at the other end to the rocket methane storage tank. The discharge pipeline is connected to the methane refueling pipeline; The methane refueling pipeline is equipped with a final refueling valve and a one-way valve connected in series at the end. The one-way valve is unidirectionally open from the methane storage tank to the rocket methane storage tank. The connection point between the discharge pipeline and the methane filling pipeline is located upstream of the unfilled valve and the check valve.

[0011] It should be noted that the final filling valve, also known as the end filling valve, end filling shut-off valve, or replenishment valve, specifically refers to a controllable shut-off valve that is connected in series at the end of the filling pipeline and is closest to the rocket tank filling port in the ground filling system. It is used to precisely control the opening and closing of the filling passage to realize the normal filling, stopping, and replenishment of propellant.

[0012] Furthermore, the one-way valve is located upstream or downstream of the unadded valve; Preferably, the one-way valve is located downstream of the unadded valve.

[0013] Furthermore, the one-way valve is arranged adjacent to the unadded valve; Preferably, the unadded valve is a cryogenic emergency shut-off valve; Preferably, the one-way valve is a cryogenic swing check valve or a cryogenic vertical check valve.

[0014] Furthermore, the discharge pipeline is equipped with a discharge valve, one end of the discharge pipeline is connected to the methane injection pipeline, and the other end is connected to the discharge recovery unit or the methane storage tank; Preferably, the emission recovery unit is a ground-based cryogenic methane recovery storage tank or a launch site flare combustion system.

[0015] Furthermore, it also includes a recovery pipeline, which is connected to a methane refueling pipeline downstream of the one-way valve.

[0016] Preferably, one end of the recovery pipeline is connected to the methane filling pipeline downstream of the one-way valve, and the other end is connected to the methane filling pipeline upstream of the one-way valve.

[0017] Preferably, one end of the recovery pipeline is connected to the methane filling pipeline upstream of the unfilled valve and the check valve, and the other end is connected to the methane filling pipeline downstream of the unfilled valve and the check valve.

[0018] Furthermore, a backflow valve is provided on the recovery pipeline.

[0019] This invention also provides a control method for a rocket's methane subcooling refueling system, comprising the following steps: S1 Refueling Stage: Subcooled liquid methane in the methane storage tank is injected into the rocket's methane storage tank via the methane refueling pipeline, the final refueling valve, and the check valve; S2: The betting phase ends after the raise. The discharge valve opens, and the subcooled liquid methane in the methane refueling pipeline continues to flow through the discharge pipeline. Then the final valve is closed to stop the refueling. During this process, the check valve prevents the methane in the rocket's methane tank from flowing back into the upstream of the methane refueling pipeline.

[0020] Preferably, in step S2, the time interval between the full opening of the discharge valve and the beginning of the closing of the unfilled valve is not less than 200ms.

[0021] Furthermore, it also includes: S3 Replenishment Stage: The discharge valve is opened to maintain the continuous flow of subcooled liquid methane in the methane refueling pipeline. First, the final refueling valve is opened, and then the discharge valve is closed to refuel the subcooled liquid methane into the rocket's methane storage tank, thus completing the replenishment.

[0022] Preferably, in step S3, the time interval between the unfilled valve being fully opened and the discharge valve starting to close is not less than 200ms.

[0023] The present invention has at least the following beneficial effects: 1. Completely eliminates the propellant backflow problem caused by timing differences. This invention uses a one-way valve connected in series with the unfilled valve at the end of the refueling pipeline to physically lock the reverse passage from the rocket tank to the upstream of the refueling pipeline with a purely passive mechanical structure. It completely eliminates the need to rely on the synchronization of valve actions or the control precision of the electronic control system, thus fundamentally preventing the propellant backflow problem within the refueling and stopping timing difference window. This completely eliminates the fatal risks caused by backflow, such as inaccurate refueling volume, water hammer impact in the pipeline, equipment damage, and methane leakage and explosion. It solves the industry problem that existing technologies can only alleviate, but cannot eliminate, the risks.

[0024] 2. While achieving the core function of preventing backflow, it fully retains the safe operating sequence that must be followed when adding supercooled methane, ensuring continuous flow of methane throughout the entire process of adding, stopping, standing by, and replenishing. This fundamentally avoids ultra-low temperature operating condition failures such as pipeline dead space, vaporization blockage, and freezing blockage, and completely solves the core contradiction between preventing freezing and preventing backflow.

[0025] 3. This invention uses a purely passive mechanical structure as the core safety redundancy, without the need to add complex electrical control interlocking devices. It can still reliably lock the return flow path under extreme working conditions such as power failure, signal failure, and valve jamming.

[0026] 4. This invention, through a recovery pipeline and a return valve arranged in parallel with the refueling end section, achieves controllable closed-loop recovery and reuse of propellant in scenarios such as rocket ignition testing, launch mission cancellation, and tank overpressure relief, without interfering with the core anti-backflow effect of the one-way valve. This avoids the safety risks of direct discharge of flammable and explosive methane and significantly reduces propellant waste. Simultaneously, it completely solves the problem of pressure fluctuations exacerbating backflow caused by opening and closing the recovery pipeline in existing technologies, significantly reducing launch costs while ensuring safety.

[0027] 5. The system structure of this invention is extremely simple. All innovations and improvements are concentrated on the ground refueling system. There is no need to modify the existing structure of the rocket, the refueling interface and the control logic. It can be directly adapted to the existing launch site refueling system and the entire series of liquid oxygen methane rockets. It is highly compatible with the existing aerospace refueling operation procedures, has low modification costs, and has extremely high engineering implementation and promotion application value. Attached Figure Description

[0028] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is one of the schematic diagrams of the methane subcooling refueling system for a rocket in Embodiment 1 of the present invention; Figure 2 This is the second schematic diagram of the methane subcooling refueling system for the rocket in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the methane supercooling refueling system for the rocket in Embodiment 2 of the present invention.

[0029] Attached reference numerals: 1. Methane storage tank; 10. Methane filling pipeline; 101. Final filling valve; 102. Check valve; 11. Discharge pipeline; 111. Discharge valve; 12. Recovery pipeline; 121. Return valve; 2. Rocket methane storage tank; 010-First filling line, 011-Subcooling unit, 012-Input line, 013-Output line, 014-First control valve; 015-Second control valve, 016-Third control valve, 017-Regulating valve; 020-Second filling line, 030-Connecting line, 031-On / off valve.

[0030] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0031] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Those skilled in the art will understand that the following embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0032] Reference Figure 1 First, it should be noted that all expressions of "upstream" and "downstream" in this specification are based on the unique and fixed reference standard of the main medium flow direction in the corresponding pipeline design, as defined below: 1. The main medium flow direction of the methane refueling pipeline 10 is: methane storage tank 1 → rocket methane storage tank 2. Along this direction, the first position through which the medium flows is the upstream position, and the last position through which it flows is the downstream position. Example 1

[0033] like Figure 1 As shown, in this embodiment, a rocket methane subcooling refueling system is connected to the rocket methane storage tank 2 to achieve the refueling of subcooled liquid methane. The system includes: Methane storage tank 1, used to store subcooled liquid methane; The methane refueling pipeline 10 is connected at one end to the methane storage tank 1 and at the other end to the rocket methane storage tank 2; The discharge pipeline 11 is connected to the methane refueling pipeline 10; The methane filling pipeline 10 is provided with a final filling valve 101 and a one-way valve 102 connected in series at the end. The one-way valve 102 is unidirectionally open from the methane storage tank 1 to the rocket methane storage tank 2. The connection point between the discharge pipeline 11 and the methane injection pipeline 10 is located upstream of the final injection valve 101 and the one-way valve 102.

[0034] Among them, methane storage tank 1 is a ground-based cryogenic storage device used to store subcooled liquid methane with a temperature close to the freezing point of methane. For example, the temperature of the subcooled liquid methane can be controlled in the range of -180℃ to -170℃. Preferably, methane storage tank 1 adopts a high-vacuum multi-layer insulated cryogenic storage tank with a daily evaporation rate of no more than 0.3%, which can maintain the low temperature state of subcooled liquid methane for a long time and avoid the medium temperature rise and vaporization before filling.

[0035] The methane refueling pipeline 10 is the main channel for transporting subcooled liquid methane. Its first end is connected to the outlet of the methane storage tank 1, and its last end is sealed to the refueling port of the rocket methane storage tank 2 through a ground-to-rocket docking mechanism, forming a complete refueling path from the ground storage tank to the rocket storage tank. Preferably, the methane refueling pipeline 10 is made of austenitic stainless steel resistant to ultra-low temperatures, and the outer wall of the pipeline is covered with a multi-layer vacuum insulation structure. The multi-layer vacuum insulation structure is composed of alternating stacked aluminum foil reflective layers and glass fiber insulation layers, with a heat leakage rate of no more than 0.5 W / (㎡・K), which can minimize the transfer of heat from the external environment into the pipeline and prevent the subcooled liquid methane from temperature rise and vaporization during transportation. The last section of the methane refueling pipeline 10 is equipped with a final refueling valve 101 and a one-way valve 102 connected in series, which together constitute the core unit for on / off control and backflow prevention of the refueling path.

[0036] The discharge pipeline 11 is connected to the methane filling pipeline 10. The discharge pipeline 11 is equipped with a discharge valve 111 for controlling the opening and closing of the branch. The connection point between the discharge pipeline 11 and the methane filling pipeline 10 is located upstream of the final filling valve 101 and the check valve 102, ensuring that when the discharge valve 111 is open, it can directly provide a medium flow path to the main pipeline upstream of the final filling valve 101 and the check valve 102, avoiding flow interruption and freezing. In some embodiments, the discharge valve 111 is selected as a cryogenic shut-off valve adapted to subcooled liquid methane, with remote electronic control function, and can achieve time-sequential interlock control with the final filling valve 101. Its nominal pipe diameter is consistent with that of the discharge pipeline 11. Preferably, the pipe diameter of the discharge pipeline 11 is 1 / 3 to 1 / 10 of the pipe diameter of the methane filling pipeline 10, which satisfies the discharge flow rate requirements while avoiding additional cold loss and external heat transfer caused by a large pipe diameter.

[0037] Furthermore, the connection point between the discharge pipeline 11 and the methane filling pipeline 10 is preferably located at the lower part of the pipeline. This location allows for gravity-driven drainage of the supercooled liquid methane in the pipeline, preventing residual liquid methane at the bottom of the pipeline from freezing and maximizing the efficiency of liquid medium discharge. It also facilitates pipeline laying and avoids medium retention and dead space caused by pipeline bends.

[0038] Furthermore, in some specific embodiments, the final valve 101 is selected as a cryogenic emergency shut-off valve adapted to ultra-low temperature conditions of -180℃ to -160℃. The valve body is made of austenitic stainless steel, the same material as the methane filling pipeline 10. The valve stem adopts an extended stem design to adapt to the thickness of the pipeline insulation layer, avoiding frostbite caused by personnel contact with the cryogenic pipeline during operation. It has dual operation functions of remote electric control and on-site manual operation, with an opening and closing response time of no more than 200ms. It can quickly cut off the filling passage in emergency conditions to ensure the safety of the filling system. Its forward flow resistance does not affect the rated filling flow rate, and its reverse sealing has zero leakage, which can form a precise match with the one-way valve 102.

[0039] The one-way valve 102 is a purely passive mechanical valve, requiring no electrical control drive. It automatically opens and closes solely based on the pressure difference of the medium within the pipeline. Its conduction direction is unidirectional, flowing from the methane storage tank 1 to the rocket methane storage tank 2, and completely blocking in the reverse direction. Preferably, the one-way valve 102 is a cryogenic swing check valve or cryogenic vertical check valve adapted to the temperature range of supercooled liquid methane. Its forward opening pressure is no greater than 0.05 MPa, enabling low-resistance forward conduction during refueling without affecting the refueling flow rate and efficiency. The reverse sealing leakage rate is zero, the reverse pressure resistance level is no less than 1.5 times the rated working pressure of the methane refueling pipeline 10, and the opening and closing response time is no greater than 10 ms. It can quickly lock the reverse passage the moment pressure inversion occurs, completely preventing propellant backflow.

[0040] Furthermore, the one-way valve 102 can be disposed upstream or downstream of the unfilled valve 101; preferably, the one-way valve 102 is disposed in series downstream of the unfilled valve 101.

[0041] In one specific embodiment, the one-way valve 102 is connected in series downstream of the final filling valve 101, that is, on the methane filling pipeline 10 between the final filling valve 101 and the rocket methane storage tank 2. This scheme is a preferred embodiment of the present invention, and its advantages are as follows: the one-way valve 102 is located closest to the rocket methane storage tank 2, which can lock the reverse passage from the very end of the filling passage. Within the timing difference window when filling ends and stopping, if the high-pressure methane in the rocket storage tank wants to flow back, the first step will be completely blocked by the one-way valve 102, and even the final filling valve 101 and the upstream methane filling pipeline 10 cannot make contact. Physically, it completely eliminates the harmful backflow caused by the timing difference, and the backflow prevention effect is optimal. At the same time, this installation method can completely prevent the backflowing methane from entering the final filling valve 101, prevent the valve sealing surface from shrinking and wearing due to low-temperature methane backflow, and extend the service life and sealing reliability of the final filling valve 101.

[0042] In another embodiment, the one-way valve 102 is connected in series upstream of the final refueling valve 101. This solution is an alternative embodiment of the present invention and can be adapted to the modification scenarios of existing refueling pipelines in some launch sites. It does not require adjustment of the original layout of the final refueling valve 101 and the docking mechanism on the rocket. Only the addition of the one-way valve 102 upstream of the final refueling valve 101 is needed to achieve the anti-backflow function of the present invention. The modification cost is low and the adaptability is strong. Its anti-backflow logic is as follows: within the timing difference window, when methane in the rocket tank flows back to the upstream of the final refueling valve 101, it will be completely locked by the one-way valve 102 and cannot enter the upstream main section of the methane refueling pipeline 10, thus avoiding backflow impact on core equipment such as the refueling pump and flow meter, and achieving the core anti-backflow effect.

[0043] Furthermore, one end of the discharge pipeline 11 is connected to the methane injection pipeline 10, and the other end is connected to the discharge recovery unit or the methane storage tank 1. The discharge pipeline 11 is equipped with a discharge valve 111 for controlling the opening and closing of the branch.

[0044] In some embodiments, the emission recovery unit can select two independently implementable schemes according to the actual layout of the launch site: one is a closed recovery scheme, in which the emission recovery unit is a ground-based cryogenic methane recovery storage tank. When the emission valve 111 is opened, the supercooled liquid methane in the methane filling pipeline 10 can be recovered through the emission pipeline 11 to the cryogenic storage tank for reuse, without any media waste. The entire process is sealed and there is no risk of flammable and explosive methane leakage, which is the preferred scheme of the present invention; the other is an open emission scheme, in which the emission recovery unit is the launch site flare combustion system, which can be adapted to emergency depressurization, pre-cooling emission and other scenarios, to transport the gaseous methane in the pipeline to the flare system for safe combustion, avoiding direct emission of methane to the launch pad area to form an explosive mixture, and ensuring operational safety.

[0045] In another specific embodiment, the other end of the discharge pipeline 11 is directly connected to the methane storage tank 1 for scenarios such as pre-cooling before filling, depressurization after filling, and pipeline circulation temperature regulation. This allows the subcooled liquid methane in the methane filling pipeline 10 to be directly returned to the methane storage tank 1 for recycling, eliminating the need for an additional recovery tank, simplifying the system structure, reducing equipment costs, and maintaining the medium in a low-temperature, closed environment throughout the process, with no risk of temperature rise, vaporization, or leakage.

[0046] Furthermore, the methane subcooling refueling system of the rocket of the present invention also includes a recovery pipeline 12, which is at least connected to the methane refueling pipeline 10 downstream of the one-way valve 102, so as to realize the closed-loop circulation and cooling of subcooled methane and the controllable recovery of propellant without interfering with the backflow prevention function of the one-way valve 102.

[0047] In some embodiments, one end of the recovery line 12 is connected to the methane filling line 10 downstream of the one-way valve 102, and the other end can be connected to any upstream location of the methane filling line 10, the methane storage tank 1, or other recovery unit.

[0048] Furthermore, one end of the recovery pipeline 12 is connected to the methane filling pipeline downstream of the one-way valve 102, and the other end is connected to the methane filling pipeline upstream of the one-way valve 102.

[0049] In another embodiment, the one-way valve 102 is located downstream of the unfilled valve 101. One end of the recovery pipeline 12 is connected to the methane filling pipeline 10 between the unfilled valve 101 and the one-way valve 102, and the other end is connected to the methane filling pipeline 10 downstream of the one-way valve 102. This can realize local small-scale recovery and circulation, reduce volume, and improve the circulation and cold preservation response speed.

[0050] In another embodiment, one end of the recovery pipeline 12 is connected to the methane storage tank 1, and the other end is connected to the methane filling pipeline 10 downstream of the one-way valve 102. The supercooled liquid methane in the arrow tip and end pipeline can be directly returned to the methane storage tank 1 without going through the upstream filling pipeline, making the recovery path simpler.

[0051] In another embodiment, one end of the recovery pipeline 12 is connected to a ground-based cryogenic methane recovery storage tank or a launch site recovery and processing unit, and the other end is connected to a methane refueling pipeline 10 downstream of the one-way valve 102, thereby realizing external classification, recovery, and safe processing of propellant.

[0052] In a preferred embodiment of the present invention, the recovery pipeline 12 is arranged in parallel with the end section of the methane filling pipeline 10 where the final filling valve 101 and the one-way valve 102 are located, forming a parallel structure. Specifically, one end of the recovery pipeline 12 is connected to the methane filling pipeline 10 upstream of the final filling valve 101 and the one-way valve 102, and the other end is connected to the methane filling pipeline 10 downstream of the final filling valve 101 and the one-way valve 102. A return valve 121 for controlling the opening and closing of the branch is connected in series on the recovery pipeline 12.

[0053] The core advantages of this parallel configuration are as follows: Firstly, it enables closed-loop cooling during the standby phase before replenishment. During standby, the final filling valve 101 is fully closed and the return valve 121 is fully open, allowing the subcooled liquid methane in methane storage tank 1 to circulate continuously through methane filling pipeline 10 and the recovery pipeline 12 where the return valve 121 is located. This keeps the entire final filling pipeline in a low-temperature pre-cooled state, eliminating any static dead space and completely preventing freezing blockage. Simultaneously, there is no need to open the discharge valve 111 for direct discharge, resulting in no media waste, no safety risks, and seamless switching to replenishment mode at any time. Secondly, it enables controllable closed-loop recovery of rocket propellant. In scenarios requiring the release of propellant from rocket tanks, such as rocket ignition tests or launch mission cancellations, the final filling valve 101 is fully closed and the return valve 121 is fully open, allowing the high-pressure subcooled liquid methane in rocket methane storage tank 2 to circulate continuously through the recovery pipeline 12 and the methane filling pipeline 10. The propellant can be controlled to flow back to the ground methane storage tank 1, realizing the recovery and reuse of propellant and significantly reducing launch costs. At the same time, the recovery process does not pass through the main refueling branch where the one-way valve 102 and the unfilled valve 101 are located, so it will not impact the core equipment of the main refueling branch. Furthermore, the one-way valve 102 can completely avoid reverse backflow caused by pressure fluctuations during the recovery process, thus taking into account both the recovery function and the backflow prevention safety.

[0054] Furthermore, a drain valve 121 is connected in series on the recovery pipeline 12 to control the opening and closing of the recovery pipeline 12 and to regulate the flow rate.

[0055] Furthermore, the diameter of the recovery pipeline 12 matches the diameter of the methane filling pipeline 10, ensuring that when the return valve 121 is open, the flow rate of subcooled liquid methane in the methane filling pipeline 10 is not lower than the minimum critical flow rate for antifreeze blockage, thus ensuring that there are no stagnant dead spaces in the pipeline and completely preventing the vaporization and freezing of subcooled methane. In some embodiments, the return valve 121 is selected as a cryogenic regulating valve adapted to subcooled liquid methane, which can precisely control the circulation flow rate through opening adjustment, has remote electronic control function, and can achieve time-series interlock control with the final filling valve 101 and the discharge valve 111.

[0056] This invention also provides a control method for the above-mentioned rocket's methane subcooling refueling system. This method strictly follows the forced process requirement of continuous flow of subcooled liquid methane throughout the entire process, forming a dual guarantee of "active timing control + passive physical protection" with the passive backflow prevention function of the one-way valve. Specifically, it includes the following steps: S1 Refueling Stage: With discharge valve 111 fully closed and final refueling valve 101 fully open, the subcooled liquid methane in methane storage tank 1 is refueled into rocket methane storage tank 2 via methane refueling pipeline 10, final refueling valve 101, and check valve 102. During this process, check valve 102 is fully open under the action of forward medium pressure difference, and has no additional flow resistance effect on the refueling process, which can stably achieve high flow rate and high precision refueling.

[0057] S2 Refueling Completion and Shutdown Phase: When the liquid level in the rocket methane tank 2 reaches the rated refueling volume, a shut-down operation is performed, strictly following the mandatory sequence of "opening the discharge valve first, then closing the final refueling valve": First, the discharge valve 111 is opened. After the discharge valve 111 is fully open and the discharge passage is unobstructed, the final refueling valve 101 is closed, completing the shut-down process. During this process, the one-way valve 102 prevents the methane in the rocket methane tank 2 from flowing back upstream of the methane refueling pipeline 10.

[0058] Preferably, in step S2, the time interval between the full opening of the discharge valve 111 and the beginning of the closing of the final filling valve 101 is not less than 200ms. This ensures that the discharge path is completely unobstructed before cutting off the main filling line, thus completely avoiding dead spaces without flow paths within the methane filling pipeline 10 and preventing the supercooled methane from stopping and freezing. Within the timing window of this process, the opening of the discharge valve 111 will cause a sudden drop in upstream pressure in the methane filling pipeline 10, creating a pressure inversion with the rocket methane storage tank 2. The one-way valve 102 can automatically lock the reverse path the moment the pressure inversion occurs, completely preventing the high-pressure methane in the rocket methane storage tank 2 from flowing back upstream into the methane filling pipeline 10, thus eliminating a series of safety risks caused by backflow at the source.

[0059] Furthermore, in some embodiments, the control method further includes a replenishment stage S3: when the liquid level in the rocket methane tank 2 drops due to methane vaporization and replenishment is required, a replenishment operation is performed, strictly following the sequence of "opening the final replenishment valve first, then closing the discharge valve": first, the discharge valve 111 is kept open to allow the subcooled liquid methane in the methane refueling pipeline 10 to flow continuously, maintaining the pipeline in a low-temperature pre-cooled state; then, the final replenishment valve 101 is opened, and after the final replenishment valve 101 is fully open and the refueling passage is completely unobstructed, the discharge valve 111 is closed to cut off the continuous flow passage, allowing the subcooled liquid methane to be stably refueled into the rocket methane tank 2, completing the replenishment.

[0060] Preferably, in step S3, the time interval between the full opening of the final addition valve 101 and the beginning of the closing of the discharge valve 111 is not less than 200ms, ensuring that methane flows continuously throughout the replenishment process without the risk of flow interruption or freezing.

[0061] In some embodiments, the control method further includes S4, a standby cycle cooling stage before replenishment: during the standby waiting stage before replenishment, the final replenishment valve 101 is fully closed, the return valve 121 is fully closed, and the discharge valve 111 is fully open. The subcooled liquid methane in the methane storage tank 1 flows continuously through the methane filling pipeline 10 and the discharge pipeline 11, keeping the entire filling pipeline in a low-temperature pre-cooled state throughout, completely avoiding the vaporization and freezing of subcooled methane. At the same time, it can be seamlessly switched to the replenishment condition at any time without re-pre-cooling the pipeline and without delaying the launch window.

[0062] In other embodiments, the control method further includes a controlled methane recovery stage (S5): In scenarios requiring the release of propellant from the rocket's fuel tanks, such as rocket ignition tests or launch mission cancellations, the final loading valve 101 is fully closed and the return valve 121 is fully open. The subcooled liquid methane in the downstream methane loading pipeline 10 and / or the high-pressure subcooled liquid methane in the rocket's methane fuel tank 2 are controllably returned to the ground methane storage tank 1 via the downstream methane loading pipeline 10, the recovery pipeline 12, and the upstream methane loading pipeline 10, completing the closed-loop recovery and reuse of the propellant; or it is controllably returned to the methane storage tank 1 or the ground cryogenic methane recovery tank via the discharge pipeline 11. During this process, the one-way valve 102 completely locks the reverse passage of the main loading branch, thoroughly avoiding harmful backflow caused by pressure fluctuations during recovery, thus balancing recovery efficiency and system safety.

[0063] like Figure 2 As shown, in some exemplary embodiments, to meet the actual engineering requirements of staged refueling of multiple sections such as the first and second stages of a liquid oxygen-methane rocket, the methane refueling pipeline 10 adopts a staged branch structure design, including a main refueling pipe and at least one set of branch refueling pipes. The first end of the main refueling pipe is connected to the methane storage tank 1, serving as the main channel for transporting subcooled liquid methane. The inlet end of each set of branch refueling pipes is connected to the main refueling pipe, and the outlet end is connected to the rocket methane storage tank 2 of different sections of the rocket. At the end of each set of branch refueling pipes, a final refueling valve 101 and a one-way valve 102 are connected in series. Each set of branch refueling pipes is also connected to an independent discharge pipe 11 and a recovery pipe 12, enabling independent refueling, independent backflow prevention, independent pressure relief and discharge, and independent propellant recovery for each section's refueling branch. The branches do not interfere with each other, eliminating blind spots in system operation and simultaneously adapting to the differentiated refueling requirements of multiple rocket sections. Example 2

[0064] Based on Example 1, this embodiment provides a more detailed description of the rocket's methane subcooling refueling system, specifically for engineering applications involving parallel supply from multiple methane storage tanks and staged refueling in multi-stage rocket tanks, in conjunction with Figure 3.

[0065] This embodiment uses at least two independent methane storage tanks as the supply source of subcooled liquid methane. Independent refueling is carried out to multiple methane storage tanks, such as the first and second stages of the rocket core, via staged parallel refueling pipelines, as shown in Figure 3. The methane refueling pipeline 10 includes a first refueling pipeline 010 and a second refueling pipeline 020 arranged in parallel. One end of the first refueling pipeline 010 is connected to the first methane storage tank, and the other end is connected to the rocket tank 2 (first stage). The second refueling pipeline 020 has the same structure as the first refueling pipeline 010, with one end connected to the second methane storage tank and the other end connected to the rocket tank 2 (second stage).

[0066] Each filling pipeline is equipped with a subcooling unit 011, which is connected in parallel with the filling pipeline. The subcooling unit 011 is connected to the filling pipeline through an input pipeline 012 and an output pipeline 013. A first control valve 014 is installed on the input pipeline 012, a second control valve 015 is installed on the output pipeline 013, and a third control valve 016 is installed on the section of the filling pipeline connected in parallel with the subcooling unit 011.

[0067] At the end of each refueling pipeline, a final refueling valve 101 and a one-way valve 102 are connected in series. Each refueling pipeline is also connected to an independent discharge pipeline 11 and a recovery pipeline 12. This enables independent refueling, independent backflow prevention, independent pressure relief and discharge, and independent propellant recovery for each section's refueling pipeline. At the same time, it achieves redundant supply from multiple storage tanks, independent control of graded flow rates, and significantly improves system redundancy, refueling stability, and mission adaptability in large-scale refueling scenarios for high-thrust rockets.

[0068] Furthermore, to address the technical issues of interrupted refueling tasks at the corresponding level and lack of redundant support capabilities between multi-level pipelines in existing rocket cryogenic propellant refueling systems due to single-point equipment failures (especially supercooler failures) caused by the staged independent architecture, this embodiment also provides a connecting pipeline 030 between the first refueling pipeline 010 and the second refueling pipeline 020.

[0069] The connection point between the connecting pipeline and the filling pipeline is located downstream of the connection point between the output pipeline and the filling pipeline. On each filling pipeline, a regulating valve 017 is also installed downstream of the connection point between the connecting pipeline and the filling pipeline. An on / off valve 031 is installed on the connecting pipeline 030 to control the on / off state of the connecting pipeline.

[0070] The first control valve 014 is located on the input line 012 (upstream of the subcooling unit) and controls the channel through which propellant enters the subcooling unit. It is open during normal operation to allow propellant to flow into the subcooling unit for cooling; it is closed when the subcooling unit malfunctions or requires isolation maintenance to cut off the source of the fault and prevent insufficiently subcooled or uncooled propellant from entering the downstream line.

[0071] The second control valve 015 is located on the output line 013 (downstream of the subcooling unit) and controls the channel through which the subcooled propellant flows out of the subcooling unit. During normal operation, it is open, allowing the subcooled propellant to flow into the refueling line. In redundant switching mode, when it is necessary to introduce subcooled propellant from an adjacent refueling line, this valve remains open, serving as an inlet channel for introducing propellant, allowing the subcooled propellant from the adjacent side to enter the refueling line on this side through the output line.

[0072] The third control valve 016 is located on the section of the refueling pipeline connected in parallel with the subcooling unit. It controls whether the propellant bypasses the subcooling unit and flows directly through the refueling pipeline. Under normal operation, it is closed, and the propellant is forced to flow through the subcooling unit. When the subcooling unit fails and non-subcooled propellant refueling is permitted, this valve opens, allowing the propellant to flow directly through the parallel pipeline section, bypassing the faulty subcooling unit, thus enabling continuous non-subcooled refueling.

[0073] Through the coordinated control of the three valves, the system can flexibly switch between "subcooled mode," "straight-through mode," and "redundant mode" according to fault conditions and mission requirements, meeting the needs of different refueling scenarios. When the subcooled unit fails, the first control valve closes to quickly isolate the fault source, preventing the fault from escalating and ensuring system safety. The second control valve serves as the inlet for introducing subcooled propellant from the adjacent side during redundancy switching, ensuring that the introduced propellant can smoothly enter the refueling pipeline on this side, and is precisely controlled by the regulating valve 017 on this side. By closing the three valves in coordination, the subcooled unit can be completely isolated, enabling online maintenance without interrupting the operation of the entire refueling system. The regulating valve 017 is used to precisely control the refueling flow rate and pressure entering the tank.

[0074] Under normal operating conditions, the first refueling pipeline 010 and the second refueling pipeline 020 operate independently. Both the first control valve 014 and the second control valve 015 are open, the subcooling unit 011 subcools the propellant passing through, and the regulating valve 017 adjusts its opening according to refueling requirements, refueling the first-stage and second-stage propellant tanks of the rocket respectively. At this time, the on / off valve 031 on the connecting pipeline 030 is closed, and the two pipelines do not interfere with each other.

[0075] When a malfunction is detected in the supercooling unit 011 on the first refueling line 010, the control system immediately closes the first control valve 014 on the first refueling line 010 to cut off the source of the malfunction. Simultaneously, the on / off valve 031 on the connecting line 030 is opened, allowing the supercooled propellant in the second refueling line 020 to be diverted to the first refueling line 010 via the connecting line 030. The diverted propellant then flows through the regulating valve 017 on the first refueling line 010, where the flow rate and pressure are adjusted according to the refueling requirements of the rocket's first-stage propellant tank, maintaining stable refueling parameters.

[0076] During this process, the regulating valve 017 on the second refueling pipeline 020 is adjusted simultaneously to balance the refueling flow of the two pipelines, ensuring that the refueling mission of the second refueling pipeline 020 to the rocket's second-stage propellant tank is not affected.

[0077] After the second refueling line 020 completes the refueling of the second stage propellant tank, if the first stage propellant tank has not yet been refueled, the on / off valve 031 on the connecting line 030 remains open, and the second refueling line 020 continues to supply supercooled propellant to the first refueling line 010 through the connecting line 030 until the first stage propellant tank is refueled.

[0078] This embodiment achieves redundant support between the two-stage refueling pipelines by setting up connecting pipeline 030 and corresponding control valves. When a subcooling unit fails, the adjacent normally operating subcooling unit can provide subcooled propellant, ensuring the refueling task can be carried out continuously, which significantly improves the reliability of the system.

[0079] As another implementation, it can be further extended to the refueling application of three-stage rockets. The system includes a first refueling line 010, a second refueling line 020, and a third refueling line.

[0080] The first refueling line 010 is connected to the first stage propellant tank of the rocket, the second refueling line 020 is connected to the second stage propellant tank of the rocket, and the third refueling line is connected to the third stage propellant tank of the rocket. Connecting lines 030 are respectively provided between the third refueling line and the first and second refueling lines 010 and 020, and each connecting line 030 is equipped with an on / off valve 031.

[0081] The subcooling units and control valves on the first filling pipeline 010, the second filling pipeline 020, and the third filling pipeline are configured the same as in Embodiment 1.

[0082] Under normal operating conditions, the three refueling pipelines operate independently, refueling the first, second, and third stage propellant tanks of the rocket respectively.

[0083] When the supercooling unit 011 on the first refueling line 010 fails, supercooled propellant support can be provided by the second refueling line 020 through the connecting line 030 between the first refueling line 010 and the second refueling line 020.

[0084] When the supercooling unit 011 on the first refueling line 010 and the second refueling line 020 fails simultaneously, the third refueling line can be activated. Through the two connecting lines 030 between the third refueling line and the first refueling line 010 and the second refueling line 020, supercooled propellant support can be provided to the first-stage and second-stage propellant tanks of the rocket.

[0085] This embodiment achieves multiple redundancy support between multiple pipelines by setting up multiple connecting pipelines. When multiple subcooling units fail at the same time, the remaining normally operating subcooling units can still be used to ensure the completion of the filling task, which greatly improves the system's task continuity capability under complex failure scenarios.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A methane subcooling refueling system for a rocket, connected to a rocket methane tank for refueling methane, characterized in that, include: Methane storage tanks are used to store subcooled liquid methane. The methane refueling pipeline is connected at one end to the methane storage tank and at the other end to the rocket methane storage tank. The discharge pipeline is connected to the methane refueling pipeline; The methane refueling pipeline is equipped with a final refueling valve and a one-way valve connected in series at the end. The one-way valve is unidirectionally open from the methane storage tank to the rocket methane storage tank. The connection point between the discharge pipeline and the methane filling pipeline is located upstream of the unfilled valve and the check valve.

2. The methane subcooling refueling system for a rocket according to claim 1, characterized in that, The one-way valve is located upstream or downstream of the unadded valve.

3. The methane subcooling refueling system for a rocket according to claim 1, characterized in that, The one-way valve is located downstream of the unadded valve.

4. The methane subcooling refueling system for a rocket according to claim 1, characterized in that, One end of the discharge pipeline is connected to the methane injection pipeline, and the other end is connected to the discharge recovery unit or the methane storage tank. The discharge pipeline is equipped with a discharge valve.

5. The methane subcooling refueling system for a rocket according to claim 4, characterized in that, The emission recovery unit is either a ground-based cryogenic methane recovery storage tank or a launch site flare combustion system.

6. The methane subcooling refueling system for a rocket according to claim 1, characterized in that, It also includes a recovery pipeline, which is connected to a methane injection pipeline downstream of the one-way valve.

7. The methane subcooling refueling system for a rocket according to claim 6, characterized in that, One end of the recovery pipeline is connected to the methane filling pipeline downstream of the one-way valve, and the other end is connected to the methane filling pipeline upstream of the one-way valve.

8. The methane subcooling refueling system for a rocket according to claim 6, characterized in that, One end of the recovery pipeline is connected to the methane filling pipeline upstream of the unfilled valve and the check valve, and the other end is connected to the methane filling pipeline downstream of the unfilled valve and the check valve.

9. A control method for a methane subcooling refueling system of a rocket as described in any one of claims 1-8, comprising the following steps: S1 Refueling Stage: Subcooled liquid methane in the methane storage tank is injected into the rocket's methane storage tank via the methane refueling pipeline, the final refueling valve, and the check valve; S2 Refueling End and Refueling Stop Phase: The discharge valve opens, and the subcooled liquid methane in the methane refueling pipeline continues to flow through the discharge pipeline. Then, the final refueling valve is closed to complete the refueling stop. During this process, the check valve prevents the methane in the rocket's methane storage tank from flowing back upstream into the methane refueling pipeline.

10. The control method according to claim 9, characterized in that, Also includes: S3 Replenishment Stage: The discharge valve is opened to maintain the continuous flow of subcooled liquid methane in the methane refueling pipeline. First, the final refueling valve is opened, and then the discharge valve is closed to refuel the subcooled liquid methane into the rocket's methane storage tank, thus completing the replenishment.

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