Vapor propellant management system

A propellant management device (PMD) may reduce or prevent liquid propellant from entering a thruster manifold (TM) or gas venting manifold (GVM) while allowing propellant vapor and/or gas to pass through the PMD to allow for thrust or venting.

FIELD

The present invention relates to satellite propulsion, and more particularly, to a propellant management device.

BACKGROUND

In satellite propulsion systems, the propulsion management device traditionally uses surface tension (e.g., vanes, sponges on the bottom of a tank) to facilitate the delivery of liquid propellant to the propulsion manifold and thrusters. During launch, the liquid propellant is isolated from the thrusters via valves. See, for example,FIG.1, which is related art illustrating a conventional propulsion management device100. InFIG.1, (A) shows liquid in a tank in a gravity environment, where gravity forces the liquid to the bottom of the tank, and therefore, flow from the exit port is purely liquid. (B), on the other hand, shows the same tank in a microgravity environment, where without the assistance of gravity, the flow out of the tank will be a mixture of liquid and gas. Most propulsion systems are not equipped to handle a mixture of liquid propellant and gas and this can lead to engine failure. (C) shows the tank in a microgravity environment with a propellant management device (PMD). While this illustration shows veins and a sump that draws liquid to the bottom port, other versions of liquid PMDs exist, and all are intended to deliver liquid, not gas or vapor, to the exit port.

These PMDs are designed to facilitate the flow of liquid into the propulsion manifold and to prevent vapor or gas from entering the manifold. The thrusters in these systems are designed to run on liquid and gas ingestion can result in catastrophic failure.

For thrusters designed to run on the vapor phase of the propellant, a propellant management device designed to deliver liquid and prevent gas/vapor delivery is completely ineffective.

Accordingly, the invention of a new propellant management device designed for a vapor-fed propulsion system is necessary.

SUMMARY

Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully identified, appreciated, or solved by current propellant management device technologies. For example, some embodiments of the present invention pertain to a propellant management device configured to prevent liquid propellant from entering the thruster or venting manifolds while allowing propellant vapor to pass through to produce thrust and gas products of decomposing propellant or excess propellant vapor or gas to vents via vent relief valves (VRVs).

In an embodiment, a propellant management system includes a PMD configured to reduce or prevent liquid propellant from entering a thruster manifold (TM) or gas venting manifold (GVM) while allowing propellant vapor and/or gas to pass through the PMD to allow for thrust or venting.

In another embodiment, a propellant management system includes a PMD placed inside of a tank. The PMD is configured to reduce or prevent liquid propellant from entering a TM or GVM while allowing propellant vapor and/or gas to pass through the PMD to allow for thrust or venting. The propellant management system includes a shaft connecting the PMD to a TM and a GVM. The shaft allows the propellant vapor and/or gas to pass through to the TM or GVM.

In yet another embodiment, a propellant management system includes a PMD configured to reduce or prevent liquid propellant from entering a TM or GVM while allowing propellant vapor and/or gas to pass through the PMD to allow for thrust or venting. The PMD includes a junction on the inside of a tank, with the junction being constructed with hydrophobic material. The hydrophobic material configured to create low interfacial tension between the junction and the liquid propellent, repelling the liquid propellant from a surface of the junction.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Some embodiments of the present invention pertain to a propellant management system. The propellant management system includes a PMD configured to prevent liquid propellant from entering the thruster or venting manifolds while allowing (1) propellant vapor or gas to pass through to produce thrust and (2) gas product of decomposing propellants (e.g., oxygen for a hydrogen peroxide propellant) or undesired excess propellant vapor (e.g. nitrous dioxide vapor for a nitrogen dioxide propellant) to vents via VRVs. In an embodiment, the PMD may be inside of a tank and may include a junction constructed with hydrophobic material (e.g. Teflon) on the inside of the tank. The hydrophobic material results in low interfacial tension between the junction and the liquid, effectively repelling the liquid from the surface. Interfacial (surface) tension may be defined as adhesive forces (tension) between the liquid phase of one substance and either a solid, liquid, or gas phase of another substance. Hydrophobic behavior is observed by surfaces with critical surface tensions less than 35 dynes per centimeter. An example of this is how PTFE has a critical surface tension of 18.5 dynes per centimeter, making it hydrophobic in nature. The PMD uses the junction to connect entry ports of the GVM and TM. The junction in some embodiments contains small holes of a predefined diameter designed to additionally limit liquid transfer by taking advantage of the liquids' cohesive properties. Necessary hole diameter to limit liquid passage may depend on several parameters including but not limited to molecular properties, surface material, and pressure. The combination of the hydrophobic material and the controlled hole size results in the inability of liquid to enter the junction and therefore the propellant manifold. Severe environments could be critical factors in the design of the junction. These environments include, but are not limited to impact, vibration, and thermal.

In certain embodiments, the junction is placed in the center of the tank. When the tank is filled half full of liquid, whether in a gravity or microgravity environment, some of the holes are exposed to the gas and/or vapor phase, no matter the tank orientation. In gravity, the liquid is forced in the downward direction, leaving half of the holes exposed. In microgravity, the liquid will be drawn to the side of the tank and away from the hydrophobic junction, limiting the liquid interaction with the holes.

The liquid propellant passage through the PMD, at any temperature and pressure, would be nonexistent or negligible, which would be the only pathway to the manifolds. Instead, only propellant vapor or gas decomposition byproducts moves through the holes, keeping the manifolds safe from the liquid propellant. The junction holes lead to a central flow shaft that allows the gas/vapor to access the manifolds.

In some embodiments, a GVM fed from the junction may prevent over-pressurization. An over-pressurization event occurs when the pressure inside of the tank passes the maximum allowable system pressure causing a leak or structural failure. This can be catastrophic for the propulsion system and the satellite. The GVM may facilitate the flow of vapor and/or gas from the junction and central flow shaft within the tank out of the VRVs when the designated pressure is reached, all while keeping liquid inside of the tank. Due to the configuration of the junction and central flow shaft, the manifolds may always be at tank pressure. Therefore, if the designated pressure is reached, the VRVs within the GVM open allowing excess pressure to be released. When pressure is again below the designated pressure, the valve closes. This may be done with a purely mechanical VRV or with an actuated VRV.

In some embodiments, the propellant flow or TM may facilitate the flow of vapor and/or gas through the nozzle when valves are opened, all while keeping liquid inside of the tank. The vapor and/or gas flow may produce thrust. The propellant vapor may react on a reacting surface to create hot product gases that could then be used for higher efficiency thrust.

In some embodiments, the PMD may be made of multiple parts to allow for easier construction.

Put simply, some embodiments include a system that includes a PMD, a GVM, and a TM for thrust.

FIG.2is a diagram illustrating a cross-section view of a tank205containing PMD210. In this diagram, a 50 percent liquid fill fraction in a gravity environment is shown. Arrows show the path gas and/or vapor can travel, i.e., either to the GVM or the TM, by way of flow shaft220. Even when the holes on junction215are exposed to liquid, as shown in the illustration, the liquid stays in tank205and does not traverse the holes due to surface tension and the lack of pressure differential between tank205and manifolds. Surface tension may be defined as the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the molecule. The gas in junction215and in tank205are at the same pressure, and therefore, there is no pressure differential, negligible pressure differential, or negligible pressure force exerted on the liquid.

The pressure in tank205and PMD210remains the same at all times. If pressure venting is necessary, VRVs in the GVM open and the pressure in PMD210and tank205is released. Some liquid propellants may slowly decompose and create product gases (e.g. hydrogen peroxide) and/or have substantial vapor phase pressure (e.g. nitrogen dioxide) that could result in higher pressure in tank205than desired over time. That pressure, in some instances, should be relieved to prevent component or system failure.

If thrust is desired, valves in the TM open and the gas and/or vapor is flowed to the thruster for either reactive or non-reactive thrust. Thrust may be used for satellite station-keeping, orbit transfers, reaction control, or other maneuvers.

FIG.3is a diagram illustrating a perspective view of a tank305and a propellant management system300, according to an embodiment of the present invention. In some embodiments, propellant management system300include a tank305. Tank305includes a PMD310, which includes junction315and flow shaft320. PMD310ensures that propellant (e.g., hydrogen peroxide) vapor travels into the TM (not shown) and GVM (not shown) while preventing the liquid propellant from passing through. In this embodiment, junction315features holes330, being 0.01″ in diameter distributed on the sides, top, and bottom (not shown). All of holes330lead to a central tube325, so the gas and/or vapor can travel down the shaft320to either the TM or the GVM. Although the number and the size of holes330vary, often times it may be beneficial to balance total flow path and associated pressure drop and machining difficulty and associated cost. In this embodiment, PMD310is constructed of Teflon and is made of two parts for easier machining. The two parts press fit and seal together. The two ends of the shaft press fit and seal to either side of the interior of the tank, allowing gas passage into the manifolds.

In some embodiments, TM may be in the downward direction and the GVM may be in the upward direction. Cut-outs335in cylindrical junction315are not required, but do not hinder the embodiments and are a product of a specific application. For example, this embodiment is used for a high concentration hydrogen peroxide vapor propulsion system. The configuration allows for excess pressure from hydrogen peroxide decomposition to be safely vented through the GVM automatically and without the need for human intervention. This keeps the system within designed pressure limits. It also allows for propellant vapor and gas to travel through the TM to a catalyst and nozzle, allowing for higher efficiency thrust, when satellite maneuvering is desired.

FIG.4is a diagram400illustrating a cross-section of tank405with PMD410press fit inside, according to an embodiment of the present invention. In this embodiment, PMD410is press fit into tank405, such that there is a seal for the 2 parts of the PMD and at the top (A) and bottom (B) of tank405. In this embodiment, top (A) of tank405leads to the TM, and the bottom (B) of tank405to the GVM.

FIG.5is a diagram illustrating a perspective view of a PMD500, according to an embodiment of the present invention. In this embodiment, PMD500includes cut-outs505. It should be noted that cut-outs505in cylindrical junction are not necessary, but do not hinder, the embodiments and are a product of a specific application. For example, this embodiment may be used for a propulsion system that is filled half-full of propellant and uses the junction in the center of the tank. The cut-outs allow for the insertion of additional propellant management features, such as veins, as well as additional structural elements such as screws.

FIG.6is a diagram illustrating PMD500ofFIG.5, according to an embodiment of the present invention. For example, PMD500can be constructed of 2 parts, which allows for easier machining. These two parts include top600(a) and bottom600(b). When top600(a) and bottom600(b) are pressed together, the tight fit prevents leakage and creates a full, complete PMD500.

FIG.7is a diagram illustrating a prospective view of a PMD700without cutouts, according to an embodiment of the present invention. It should be noted that the number of holes705and the diameter of hole705may depend on the configuration of the satellite propulsion system. The shape of junction710and distribution of holes705will vary based on application.

FIG.8is a diagram illustrating a cross-section of PMD700ofFIG.7within a tank805, according to an embodiment of the present invention. In this embodiment, path815shows how the gas and/or vapor travel through small holes810into central flow shaft820.

In practice, when tank805is filled with liquid propellant up to 50 percent capacity (e.g., 20 mL for the example embodiment inFIG.3), at least half of holes810are exposed to propellant vapor and/or decomposition byproduct gas, even under the influence of gravity in any vehicle orientation. With microgravity or a lower fill fraction, additional holes810may be exposed as the liquid propellant, which seeks the side wall and corners of tank805in microgravity. Due to cohesion and hydrophobicity, only propellant vapor or gas passes through PMD700and into central flow shaft820.

This was verified in development testing of the embodiment of the invention shown inFIG.3. It should be noted that the PMD and tank, as part of a full propulsion system (including TM and GVM), were violently shook on a table used for simulation of launch loads. They were then placed in an oven used for simulation of orbital temperature fluctuations. This simulated the intense launch and orbital environments that the propulsion system would experience getting to and operating in low earth orbit (LEO). These are the environments that could result in liquid being forced in the manifolds and cause (1) a thruster failure and/or (2) an over-pressurization event if the vapor propulsion management system is not functional.

FIG.9is a graph900illustrating the vacuum hot fire test for an embodiment of the propulsion system after the environmental testing described above, according to an embodiment of the present invention. In graph900, at 46 seconds, the data shows the VRVs venting as they reach the set pressure of approximately 75 psi. At 1876 seconds, the valves in the TM are opened allowing gas and propellant vapor to travel to the reacting surface and out the nozzle into vacuum. The immediate rise in catalyst temperature within the data and the lack of liquid spray out of the nozzle (verified via viewport on vacuum chamber), indicate no liquid traversed the junction and entered the TM. If liquid were present in the TM, a visible spray would be evident in the viewport and the catalyst temperature data profile would be erratic. This was witnessed in a prior test without the invention.

As shown inFIG.2, the bottom of flow shaft leads to the TM. See, for example,FIG.10, which is a diagram illustrating a propellant vapor flow manifold or TM1000, according to an embodiment of the present invention. The top of flow shaft however leads to an over-pressurization manifold or GVM. See, for example,FIG.11, which is a diagram illustrating an over-pressurization manifold or GVM1100, according to an embodiment of the present invention.

FIG.10is a diagram illustrating a TM1000, according to an embodiment of the present invention. The liquid propellant vapor and/or gas flows from the center inlet through two valves1005a,1005band onto the thruster to produce thrust. In this embodiment, two pressure sensors1010a,1010bare placed ahead of the valves1005a,1005bto take measurements of tank and PMD pressure.

FIG.11is a diagram illustrating an GVM1100, according to an embodiment of the present invention. The gas and/or vapor flows from central inlet1005to two parallel vent relief valves1010a,1010bset to a crack pressure of 75 psi. If the VRVs read a pressure of 75 psi or greater, VRVs1010a,1010bopen allowing the gas and/or vapor to vent. Once the pressure is less than 75 psi, VRVs1010a,1010breseat. In this embodiment, VRVs1010a,1010bautomatically actuate when the set pressure is reached, allowing for over-pressurization protection without human interaction. In this embodiment, a perforated copper box surrounds the VRV as a secondary protection against liquid hydrogen peroxide leaving the system. Any trace peroxide would be trapped and decompose into water and oxygen.