Multimode propellant feed system and method of use

Abstract

A propellant feed system and method for testing on a propulsion thruster that includes a multimode propellant feed component that has at least a first operational mode, a second operational mode, and a third operational mode. A propellant supply component is configured to supply one or more of a plurality of different propellants to the multimode propellant feed component. The first operational mode is configured to feed pure gas selected from the plurality of different propellants to an anode and a cathode of the propulsion thruster. The second operational mode is configured to feed mix gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster. The third operational mode is configured to feed condensable gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster.

Description

MULTIMODE PROPELLANT FEED SYSTEM AND METHOD OF USECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Application Serial No. 63 / 659,669, filed June 13, 2024, and entitled Multimode and In-Situ Propellant Feed System, the entire contents of which are herein incorporated by reference.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under FA9300-22-C-6006 awarded by U.S. Air Force. The government has certain rights in the invention.BACKGROUND

[0003] Multimode and in-situ propellants and propulsion systems have garnered recent interest for use in electric propulsion (EP) devices. Multimode propulsion systems can include two separate propulsion architectures that can, for example, be integrated on a common spacecraft platform and can share a common propellant. The two propulsion devices, e g., chemical and electric, can allow for a spacecraft to operate in either a high-efficiency or high-thrust mode without the additional cost, weight, and complexity of two entirely independent propulsion systems. In-situ propellants, on the other hand, can include propellants that are harvested in space, either in orbit or on various planetary bodies. In-situ propellants can be useful in that the propellant can be harvested and resupplied away from Earth, which allows spacecraft to carry less propellant on the initial launch and extend their operational lifetime in space.

[0004] There are multiple arrangements of thruster and propellant combinations that can be used for multimode and in-situ systems, but one of the common propellants that has gained attention in recent years across both areas is water. Water is beneficial in that an electrolysis process can separate it into hydrogen and oxygen constituents, which are prominent fuels for bi-propellant chemical propulsion systems in high-thrust multimode applications. Furthermore, water stores at a relatively high density compared to other gaseous propellants and maintains a high specific impulse due to its low particle mass, which are both beneficial for a high-efficiency multimodeapplication. Water is also found on a myriad of planetary bodies in the universe, making water ideal for in-situ propellant harvesting on deep space missions.

[0005] Many EP devices, such as Hall effect thrusters (EIETs), rely on gaseous products to operate, but at room temperatures and pressures water tends to condense. Along with condensability risks, water in its liquid state maintains a relatively high surface tension compared to other condensable liquids due to its intermolecular hydrogen bonding. These characteristics of water pose challenges to developing and operating a propellant feed system for EP ground testing, especially in maintaining steady flow over time.

[0006] Another common in-situ propellant is air, which can be harvested for satellite propulsion in very low Earth orbit (VLEO), which is generally defined as orbits less than 450 km. Harvesting air in VLEO could provide an indefinite supply of propellant, which would greatly extend the lifetime of satellites in this orbit. VLEO is an attractive orbit due to its close positioning to Earth, offering better latency of communication systems and higher resolution ground imaging along with numerous other benefits. The VLEO environment is complex, where the atmospheric composition changes as a function of altitude, time of day, time of year, and solar activity. These factors can cause the input propellant composition to consistently change in a VLEO in-situ electric propellant thruster, resulting in varying performances and efficiencies.SUMMARY

[0007] A propellant feed system for testing on a propulsion thruster that may comprise a multimode propellant feed component that may comprise at least a first operational mode, a second operational mode, and a third operational mode. A propellant supply component configured to supply one or more of a plurality of different propellants to the multimode propellant feed component via a plurality of propellant lines. The first operational mode can be configured to feed pure gas selected from the plurality of different propellants to an anode and a cathode of the propulsion thruster. The second operational mode can be configured to feed mix gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster. The third operational mode can be configured to feed condensable gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster.

[0008] In certain aspects, at least one of the plurality of propellant lines is an independent cathode path line configured to feed cathode gas from the plurality of different propellants to the cathode; the cathode gas is xenon or krypton; one or more metering devices are positioned in one or more of the plurality of propellant lines, the one or more metering devices being configured to regulate a flow rate of propellant in the one or more of the plurality of propellant lines; at least one of the one or more metering devices is positioned in the independent cathode path line; each of the one or more metering devices is a mass flow controller; a pressure regulator is provided upstream of the at least one metering device, the pressure regulator being configured to regulate a pressure of propellant going to the at least one metering device; and / or the one or more metering devices are configured to provide a mass flow range of 0.5-10 mg / s.

[0009] In other aspects, at least one calibration device is coupled to one or more of the plurality of propellant lines, the at least one calibration device is configured to calibrate a flow of propellant in the one or more of the plurality of propellant lines; a plenum can be connected to one or more of the plurality of propellant lines feeding to the anode; in the first operational mode at least one of the plurality of propellant lines is an anode propellant line that is configured to feed pure gas from the plurality of different propellants directly to the anode; at least one metering device is provided in the anode propellant line to regulate a flow rate of the pure gas in the anode propellant line; and / or at least one of the plurality of propellant lines is a shared gas line that feeds to the anode propellant line and to a cathode propellant line that feeds the pure gas to the cathode.

[0010] In some aspects, in the second operational mode, the plurality of propellant lines comprise at least a primary anode propellant line configured to feed a primary anode gas of the plurality of different propellants to the anode and a second anode propellant line configured to feed a secondary anode gas of the plurality of different propellants to the anode; the primary anode propellant line and the secondary propellant line feed to a plenum that is configured to mix the primary and secondary anode gases; the primary anode gas is oxygen and the secondary anode gas is nitrogen; each of the primary and secondary anode propellant lines includes a metering device configured to regulate a flow rate of the primary and secondary anode gases, respectively, to the anode.; and / or each of the primary and secondary anode propellant lines includes a pressure regulator upstream of the respective metering device.

[0011] In other aspects, in the third operational mode, at least one of the plurality of propellant lines is a condensable gas propellant line that is configured to feed vaporized gas to the anode; a flow control device is coupled to the condensable gas propellant line to control a flow of condensable gas through the condensable gas propellant line; the flow control device is a syringe pump; a pressure regulator is disposed in the condensable gas propellant line that is configured to regulate pressure on the flow control device by the condensable gas; first and second calibration columns are in fluid communication with the condensable gas propellant line, the first and second calibration columns being configured to measure condensation of the condensable gas; the condensable gas propellant line includes an in-line heater configured to vaporize condensable gas from the plurality of different propellants; at least a portion of one or more of the plurality of propellant lines is heat insulated; a series of in-line pressure transducers and thermocouples are provided throughout a heated section of the condensable gas propellant line to ensure the condensable gas remains in a vapor state to the anode; and / or the multimode propellant feed component comprises a first heating circuit encompasses the in-line heater, a second heating circuit configured to covers heated propellent lines outside a vacuum chamber feedthrough to the anode, and a third heating circuit that regulates heated lines inside the vacuum chamber feedthrough.

[0012] A method of testing a range of propellants a propulsion thruster, comprising selecting one operational mode from multiple operational modes of a single propellant feeding system, the multiple operational modes comprising at least first, second, and third operational modes; supplying one or more propellants from a plurality of different propellants that correspond to the one operational mode selected from the multiple operational modes; and feeding the one or more propellants selected from a plurality of different propellants to an anode and cathode of the propulsion thruster, wherein the first operational mode is configured to feed pure gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster, wherein the second operational mode is configured to feed mix gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster, and wherein the third operational mode is configured to feed condensable gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster.

[0013] In certain embodiments, the method comprises metering a flow rate of the one or more propellants through one or more propellant lines of the single propellant feed system; the methodcomprises calibrating of the one or more propellants through the one or more propellant lines; the method comprises validating a mass flow rate of the one or more propellants through the one or more propellant lines; the method comprises verifying no condensation of the one or more propellants when in the third operational mode; when in the third operational mode, further comprising separately metering water from the plurality of different propellants and vaporizing the water using an in-line heater; and the method comprising real-time monitoring of pressures and temperatures of the single propellant feed system.

[0014] This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide an overview or framework to understand the nature and character of the disclosure.BRIEF DESCRIPTION OF THE FIGURES

[0015] The accompanying drawings are incorporated in and constitute a part of this specification. It is to be understood that the drawings illustrate only some examples of the disclosure and other examples or combinations of various examples that are not specifically illustrated in the figures may still fall within the scope of this disclosure. Examples will now be described with additional detail through the use of the drawings, in which:

[0016] FIG. 1 illustrates an overall diagram of an exemplary multimode feed system according to the disclosure;

[0017] FIG. 2 illustrates an exemplary overall configuration of the feed system of FIG. 1, with colors representing flow paths in various operating modes;

[0018] FIG. 3A illustrates an example configuration of one operational mode of the feed system of FIG. 1;

[0019] FIG. 3B illustrates an example configuration of another operational mode of the feed system of FIG. 1 ;

[0020] FIG. 3C illustrates an example configuration of yet another operational mode of the feed system of FIG. 1;

[0021] FIG. 4 illustrates an example user interface of the feed system of FIG. 1;

[0022] FIG. 5 illustrates a water condensation validation test of the feed system of FIG. 1 using a calibration column and a mass flow rate;

[0023] FIG. 6 illustrates an example laboratory thruster operating in various operational modes, e.g. pure gas mode (a)(b), gas mixture mode (c), and water vapor mode (d) using the feed system of FIG. 1; and

[0024] FIG. 7 illustrates example data of the feed system of FIG. 1, showing water vapor start-up pressures.DETAILED DESCRIPTION

[0025] The present disclosure relates to a multimode and in-situ propellant feed system and method of use designed for ground testing of propellants on electric propulsion (EP) thrusters. The feed system of the disclosure is capable of supplying a variety of different propellants - including pure gases, gas mixtures, and condensable vapors like water vapor - to a single feed system at controlled and steady flow rates. The feed system of the disclosure can be applied, for example, to research and development in alternative and in-situ propellants, such as for space propulsion, supporting both high-efficiency and high-thrust operational modes. The feed system can operate in several modes, supplying pure gases, gas mixtures, and condensable vapors. Thus, the feed system can serve, for example, as a testbed for various alternative propellants in EP devices.

[0026] The feed system can be designed to deliver propellants at wider mass flow rates ranging from, for example, 0.5 to 10 mg / s, with a maximum mean flow rate uncertainty of ±2%, for example, and a maximum peak-to-peak oscillation of ±5% of the setpoint, for example. For specific operational modes, the mass flow rate uncertainty can be even lower (e.g., ±0.56% for condensable gases). In an aspect, the feed system of the disclosure can feature independent metering for each propellant constituent, with dedicated calibration methods to ensure accuracyand to verify that condensable vapors do not condense within the system. In an aspect, the design of the feed system can address several risks associated with alternative propellants, such as condensation, high surface tension of liquids, flammability, corrosion, and pressure / temperature management. For example, water can be metered separately and vaporized using an in-line heater, with heated and insulated lines to prevent condensation. In an aspect, the feed system of the disclosure can include real-time monitoring of pressures and temperatures throughout, with a user interface for live data plotting and control. This can ensure steady-state operation before thruster ignition and provides comprehensive system oversight. In an aspect, the feed system of the disclosure can undergo validation, including leak testing, condensation checks, and hot-fire tests. The feed system presents stable operation across all operational modes, with flow rate oscillations within required or pre-determined limits.

[0027] It is to be understood that the figures and descriptions of the present disclosure may have been simplified to illustrate elements that are relevant for a clear understanding of the present disclosure, while eliminating, for purposes of clarity, other elements found in a typical propellant feed system or propulsion system. Those of ordinary skill in the art will recognize that other elements may be desirable and / or required in order to implement the present disclosure. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present disclosure, a discussion of such elements is not provided herein. It is also to be understood that the drawings included herewith only provide diagrammatic representations of the presently preferred structures of the present disclosure and that structures falling within the scope of the present disclosure may include structures different than those shown in the drawings. Reference will now be made to the drawings wherein like structures are provided with like reference designations.

[0028] Before explaining at least one embodiment in detail, it should be understood that the inventive concepts set forth herein are not limited in their application to the construction details or component arrangements set forth in the following description or illustrated in the drawings. It should also be understood that the phraseology and terminology employed herein are merely for descriptive purposes and should not be considered limiting.

[0029] It should further be understood that any one of the described features may be used separately or in combination with other features. Other invented devices, systems, methods, features, and advantages will be or become apparent to one with skill in the art upon examining the drawings and the detailed description herein. It is intended that all such additional devices, systems, methods, features, and advantages be protected by the accompanying claims.

[0030] FIG. 1 illustrates a diagram of the overall multimode and in-situ propellant feed system 100, according to an example of the disclosure, which is configured to feed propellant to an EP thruster 10. The feed system 100 facilitates ground testing and captures the capabilities and performances of water, air, and other propellants in an EP device. The disclosure relates to the design, calibration, and verification of the feed system 100 informed by risks and constraints imposed by the various propellant constituents. As seen in FIG. 1, the feed system 100 may generally comprise a propellant supply component 110, a multimode propellant feed component 120, and a control 130 for controlling supply and flow of the propellants and operation of the system. The feed system 100 of this disclosure can serve as a testbed for various alternative propellants used in an EP capacity. The feed system 100 according to an aspect of this disclosure can operate on water vapor and a mix of gaseous propellants, such as air; however, this use case can be expanded to include other condensable propellants and gaseous mixtures as the field of alternative propellants continues to evolve.

[0031] The multimode propellant feed component 120 of the feed system 100 can operate in several modes, such as first operational mode A that can feed pure gases (e.g., xenon and / or nitrogen) to thruster 10, a second operational mode B that can feed gas mixtures (e.g., air, and / or krypton / argon) to thruster 10, and a third operational mode C that can feed condensable gas (e.g., water vapor) to thruster 10.

[0032] One example of thruster 10 that the feed system and method of the disclosure can be used with is a Hall effect thruster (HET). A Hall effect thruster (HET) uses a combination of electric and magnetic fields to ionize and accelerate a propellant to generate thrust. The basic components of an HET are an anode, cathode, discharge channel, and magnetic circuit. The anode, e.g. anode 30 (FIG. 1), serves as a positive electrode and also acts as the gas distributor, introducing the propellant into the discharge channel. The cathode, e.g. cathode 32 (FIG. 1), serves as the negativeelectrode and emits electrons into the discharge channel. The cathode emits electrons into the discharge channel. These electrons are necessary for ionizing the propellant and for neutralizing the ion beam as it exits the thruster. The discharge channel is the region between the anode 30 and the exit plane of the thruster 10. The magnetic circuit contains magnets that are arranged around the discharge channel to create a radial magnetic field for trapping electrons and creating the Hall effect for operation of the thruster 10.

[0033] A variety of propellants can be used with the thruster 10, such as xenon gas, krypton, argon, nitrogen, and water vapor (in vaporized form). The propellant can be injected into the discharge channel via the anode. Once inside, it is ionized by collisions with energetic electrons emitted from the cathode. The resulting ions are then accelerated out of the thruster by the electric field, producing thrust. The Hall effect thruster works by the magnetic field in the discharge channel being arranged so that it is perpendicular to the electric field between the anode and cathode. Electrons emitted from the cathode are trapped by the magnetic field and forced to spiral around the channel, creating a circulating Hall current. This circulation increases the probability of electron-atom collisions, enhancing ionization efficiency. The ions, being much heavier than electrons, are not significantly affected by the magnetic field and are accelerated straight out of the channel by the electric field, producing thrust.

[0034] In an example, the feed system 100, can be designed based on ease of use, calibration capability, safety, and material compatibility and influenced from the NASA Preferred Practices Design Considerations for Fluid Tubing Systems document (NASA PD-ED- 1224).

[0035] In certain aspects of the disclosure, the feed system 100 can operate with pure gas, water vapor, and gaseous mixture constituents; the feed system 100 can supply all products in a gaseous form; the feed system can supply a gas, independent from the anode and non-corrosive, to the cathode; the feed system 100 can supply constituents in a mass flow rate range of 0.5-10 mg / s; the feed system can supply constituents with a maximum mean flow rate uncertainty of ± 2% of the operational setpoint; the feed system 100 can a steady mass flow rate of constituents with a maximum peak-to-peak oscillation of ±5% of the flow rate setpoint; the feed system 100 can avoid a propellant leak greater than 0.5 seem on nitrogen at 30 psi; the feed system 100 can avoid safetyrisk for operators; and / or the feed system 100 can be constructed of materials compatible with water and oxygen.

[0036] The feed system 100 can be designed to mitigate risks, particularly the risk that water is condensable at standard pressures and temperatures. Other risks that the feed system 100 can be designed to address may include that liquid water has high surface tension causing potentially unsteady flow rate control, and oxygen and water can cause corrosive risks. For example, to address the risk that the water is condensable, the feed system 100 and method can be configured to meter the water and gaseous constituents separately, to incorporate a heating system for water vaporization, to include pressure transducers and thermocouples that can verify water vapor remains in a vapor state, and / or to incorporate an additional calibration method to ensure water vapor does not condense.

[0037] Other design features of the feed system 100 and method of the disclosure which optimize operation and / or address the inherent risks, may include, the feed system 100 can have an independent flow path to run to the cathode 32, such as on xenon or krypton; all installed flow devices can be rated for the mass flow rate range of 0.5-10 mg / s; all propellant constituents can have an independent calibration method to validate flow rate uncertainty; the feed system 100 can contain a plenum (FIG. 2) to mitigate water flow rate oscillations; a leak check procedure can be implemented to verify the leak rate goal; the feed system 100 can have the capability to record the flow rate of all constituents in real-time; oxygen operation can be performed with an installed oxygen flame arrestor; heated lines of the feed system 100 can have insulation to reduce outside temperatures; the feed system 100 can have a relief valve (FIG. 2) to maintain safe working pressures; oxygen-wetted surfaces can be maintained at a temperature significantly below metal ignition temperatures; and / or water and oxygen-wetted surfaces can be constructed with stainless steel.

[0038] FIG. 2 illustrates an overview of an exemplary configuration of the feed system 100 according to aspects of this disclosure. In FIG. 2, the flow paths for each operational mode A, B, and C of the feed component 120 are highlighted in different colors to distinguish the hardware and devices used in each mode.

[0039] First operational mode A of the feed component 120 of the feed system 100 can be a pure gas mode, as seen in FIGS. 2 and 3A. The pure gas mode supplies a pure gas propellant 40 (also referred to as “pure gas” or “cathode gas”) from the propellent supply component 110. The pure gas 40 can be a cathode gas or gases (e.g. xenon and / or nitrogen), as seen in FIGS. 2 and 3A. In an aspect, the pure gas 40 may be a single, non-condensable gas supplied to and shared by the anode 30 and cathode 32, such as xenon supplied to both the anode 30 and the cathode 32, or can be distinct gases between the two, such as nitrogen to the anode 30 and xenon to the cathode 32. A shared gas flow path line 140 (shown in light blue in FIG. 2) can direct the propellant to the anode 30 and cathode 32. In an aspect, the shared gas flow path line 140 can have an anode propellant line 142 directly to the anode 30 (bypassing the plenum) and a cathode propellant line 144 directly to cathode 32. The term “propellant line” may also be referred to as “path line” or “path”. A first metering device, such as mass controller (MFC) 150a, can be provided in the cathode propellant line 144 and a second metering device, such as mass flow controller (MFC) 150b, can be provided in the anode propellant line 142. The MFCs 150a and 150b are configured to meter and regulate the flow of propellant through the propellant lines 142 and 144 to the cathode and anode. A pressure regulator 152a can be incorporated into the shared gas flow path line 140 upstream of the MFCs 150a and 150b. The MFCs 150a and 150b can have a resultant uncertainty of 1% of the flow rate setpoint, leading to a maximum test uncertainty of ±0.10 mg / s at a 10 mg / s setpoint flow rate. In an aspect, the operational flow rates of the anode and cathode propellant lines 142 and 144 can be independently calibrated. This provides the system with the ability to measure and adjust the flow rates of propellant gases in two separate paths: the anode path 142 and the cathode path 144. This independent calibration ensures that both paths can be optimized for their specific requirements. Control of these flow rates optimizes efficiency and stable performance of the propulsion thruster. In an aspect, the calibration can be done uses a device, such as a MesaLabs DryCal 800, that used for calibrating flow rates. This device provides accurate measurements of gas flow, which ensures the propulsion system operates correctly. By using the DryCal 800, the flow rates can be verified and adjusted in the anode and cathode paths to meet a desired specification.

[0040] Second operational mode B of the feed component 120 of the feed system 100 can be a gas mixture mode, as seen in FIGS. 2 and 3B, which can include supplying a variable mixture of non-condensable gases 42, such as an air mixture, from propellent supply component 110. The gas mixture 42 can be supplied via a primary anode propellant line 142a’ and a secondary anode propellant line 142b’ to eventually feed the gas mixture to the anode 30. The primary anode propellant line 142a’ can supply a primary anode gas (e.g. oxygen) of the gas mixture 42 and the secondary anode propellant line 142b’ can supply a secondary anode gas (e.g. nitrogen) of the gas mixture 42. The primary anode propellant line 142a’ and the secondary propellant line 142b’ feed the primary and secondary anode gases to a plenum 160 for mixing. In an aspect, the plenum 170 can be a 0.5L plenum formed of stainless steel. The mixed gases then exit the plenum 160 and are directed to the anode 30 via anode line 162. In an aspect, one of the gases in the mixture 42 or a third, independent gas can be supplied to the cathode 32. The cathode gas 40 can be supplied to the cathode 32 via cathode path 144 similar to first operational mode A with MFC 150a metering the gas flow.

[0041] The primary anode gas can be metered and regulated using the mass flow controller 150b in the primary anode propellant line 142a’ . The secondary anode gas can be metered and regulated using a third metering device, such as MFC 150c, provided in the second anode propellant line 142b’. Pressure regulator 152a can be incorporated into the cathode gas flow path 144 upstream of the MFCs 150 similar to first operational mode A. Second and third pressure regulators 152b and 152c can be provided upstream in the primary and secondary anode paths 142a’ and 142b’, respectively. For gas mixtures 42 containing oxygen, an oxygen flame arrest 170 can be installed on the primary anode gas path 142a’ to prevent flame propagation given an ignition event. In an aspect, a needle valve 172a can be installed in primary anode path 142a’ downstream of MFC 150b and upstream of the plenum 170 and another needle valve 172b can be install in secondary anode path 142b’ downstream of MFC 150c and upstream of the plenum 170 to impose a pressure gradient to prevent the gases from back streaming into the opposing fluid path. The complete / combined gas mixture then flows out of the plenum 170 and continues to the anode 30. Because both anode primary and secondary gases can be actively controlled using MFCs 150b and 150b, the mixture ratio of gas mixture 42 can be changed throughout the course of a test, simulating various atmospheric conditions, such as in a VLEO environment.

[0042] MFC 150c located in the secondary anode path 142b’ can also be independently calibrated with a calibration device, such as MesaLabs DryCal 800. Pressure transducers 152b and 152c canbe incorporated in the primary and second anode paths 142a’ and 142b’, respectively, upstream of both MFCs 150b and 150c to ensure steady flow from both gas constituents, e g. the primary and secondary anode gases. If the flow of each of the primary and second anode gases is steady, constituent back streaming is mitigated, and there are no mass loss mechanisms, the final mixture composition of gas mixture 42 can remain constant in the gas mixture. The gas mixture operational mode B can present a flow rate and composition uncertainty of 1.4% of the flow rate setpoint, leading to a maximum test uncertainty of ±0.14 mg / s at a 10 mg / s setpoint flow rate.

[0043] Third operational mode C of the feed component 120 of the feed system 100 can be a condensable gas mode, as seen in FIGS. 2 and 3C, which can include supplying condensable gases 44, such as water vapor, from propellent supply component 110. Third operational mode C can include supplying water vapor to the anode 30 and an independent, non-condensable gas, such as pure gas 40, to the cathode 32. Gas 40 can be supplied to the cathode 32 via cathode propellant line 144 similar to first and second operational modes A and B. Secondary anode gas (also referred to as “purge gas”) can optionally be supplied via a secondary anode propellant line 142b”.

[0044] The condensable gas or water vapor 44 can be supplied to the plenum 160 via a condensable gas propellant line 146 (also referred to as the “water path line” or “water path”). In aspect of the disclosure, water can be independently supplied and metered from the rest of the gas constituents. A liquid water flow control technique can be used, for example, to meter the water. This technique maintains the water flow rate using a liquid-based mass flow controller. To isolate the liquid MFC from vacuum, a flow restrictor, such as a backpressure regular or capillary tube can be used downstream of the liquid MFC. Flow control for a water vapor thruster application can be performed with a capillary as a flow restrictor.

[0045] Within the liquid flow control technique, various flow controller types can be used, such as Coriolis, thermal -based, micro pump fed, or syringe pump. In an example, the feed system 100 of the disclosure can utilize a syringe pump configuration 180 as a flow control device. In an example, the pump 180 may be a Cole Parmersix-channel syringe pump configured to allow operation of multiple syringes simultaneously, and operating with KD Scientific 50ml stainless steelgas-tight syringes, Syringe pump 180 can be advantageous due to the relatively low cost, high flow rate range, and high accuracy. The syringe pump 180 can operate by using a high-precisionlinear stepper motor to compress a plunger of a gas-tight syringe pre-loaded with deionized water. The speed of the linear stepper motor and the diameter of the syringe can dictate the resultant water flow rate. Due to the adaptability of operating with different syringe diameters and linear pusher speeds, the syringe pump can operate with a flow rate range anywhere from / iL / hr to mL / s with less than 1% uncertainty. The syringe pump also excels with viscous liquids and liquids with a high surface tension, making them advantageous elements of the feed system according to aspects of this disclosure. In an aspect, the condensable gases 44 can be a deionized water component that is metered in liquid form using pump 180. Pressure can be regulated on the pump 180, such as by using a backpressure regulator 182. In an example, the backpressure regulator 182 can be an Equilibar ZF1SNN8 backpressure regulator, with a pressure set at 30 psi, for example.

[0046] Upstream of the backpressure regulator 182, the water path line 146 can have a region that is liquid-locked with water, which can cause increases in pressure with the actuation of the pump 180. To mitigate pressure spikes due to actuation of pump 180, a relief valve 184, such as a 40 psid relief valve, can be installed in the liquid-locked region, where an air pocket is held between a ball valve 186 and the relief valve 184. The air allows for a quick release of pressure and acts as a spring to slow the rate of pressure rise. The pressure can rise in the liquid-locked region until it reaches a certain pressure, such as 30 psi, verified by an installed pressure transducer?, at which point the water can pass through the backpressure regulator 182 at a rate equal to the supply rate of the pump 180.

[0047] Once the water constituent exits the backpressure regulator 182, it can pass through a first heater 190 incorporated in the path 146 upstream of the backpressure regulator 182 to vaporize the water. In an example, the first heater 190 can be a Watlow FluentFLC-2 in-line heater, which is can be configured to force the water over a series of heated baffles to vaporize the liquid water. The water can be maintained in a vapor state through the feed component 120 until it reaches the anode 32. The vaporization process may create some pressure oscillations, which can be damped as the water vapor passes through the plenum 170. To ensure the water vapor does not condense, the remainder of the propellant lines of path 146, after the in-line heater 190, can be coated in a thermal transfer compound, wrapped in heater wire, and insulated using fiberglass and alumina insulation.

[0048] The control 130 can be configured to maintain the in-line heater 190 and heated lines at a constant, set temperature. A series of pressure transducers P and in-line thermocouples T are provide in path line 146 throughout the heated section to the water constituent remains in a vapor state. The pressure transducers P in the vapor region can serve an additional function of acting as live flow rate monitors. Because the anode 30 has a fixed cross-sectional area and the water vapor is maintained at a constant temperature, the water vapor flow rate into the anode 30 is directly a function of the upstream pressure. If this pressure is constant, and the water is not condensing anywhere, the vapor flow rate into the anode 30 is equal to the commanded flow rate from the pump 180.

[0049] Prior to flowing water vapor to the anode 30, the feed system 100 can undergo a calibration process to ensure the pump 180 is outputting the correct flow rate and the water vapor is not condensing in the system. The pump flow rate can be calibrated using a calibration device, such as a first calibration column (denoted as calibration column 1 in FIG. 3C). The first calibration column can be, for example, a 100 mL Koflo calibration column, in fluid connection with the pump. The calibration column may generally comprise a calibration column body with end caps and a protective shield. The calibration column can be connected to the pump system via the end caps. The pump is then operated to deliver fluid into the column. As the pump delivers fluid, the fluid level rises in the column. The graduated scales allow measurement of the flow rate in mL / min or GPH over a set period. Based on the observed flow rate, adjustments can be made to the pump to achieve the desired flow rate. This process ensures that the pump operates efficiently and accurately.

[0050] A second calibration column (demoted as calibration column 2 in FIG. 3C) can be used to ensure the water vapor does not condense in the feed system 100. The second calibration column 2 can be in fluid connection with the anode propellant line 162 upstream of the plenum 160 and positioned just before a vacuum chamber propellant feedthrough 164 that leads to anode 30. Tubing just before the second calibration column 2 can be equipped with a water chiller sleeve and the bottom of second calibration column 2 can be fitted with a stack of Peltier plates and a heat sink, where both regions are held at 1°C. The water vapor will re-condense in calibration column 2. If the steady state flow rate measured in calibration column 2 is equal to that measured in calibration column 1, then there is no water condensation between the two calibration columnsand no condensation of the water vapor is verified. That can ensure a flow rate uncertainty of 0.56% of the flow rate setpoint, leading to a maximum test uncertainty of ±0.056 mg / s at a 10 mg / s flow rate.

[0051] The heaters in the feed component 120 can be controlled using an on / off control of the control 130 with a relay board to regulate power to the heaters. The heaters can be divided into three different circuits, as shown in FIG. 2 and 3C, where heating circuit 1 encompasses the inline heater 190, heating circuit 2 covers all the heated lines outside the vacuum chamber propellant feedthrough 164, and heating circuit 3 regulates the heated lines inside the vacuum chamber propellant feedthrough 164. Each heating circuit can use a control thermocouple T to provide the control input.

[0052] FIG. 4 shows an example user interface 200 of the feed system 100. A user can control the setpoint temperature and monitor the pressure transducer P and thermocouple T data in the feed system 100 via the control 130, such as a Lab VIEW VI control, which can communicate to the feed system 100, such as via a MODBUS serial communication. Live data plotting can be provided that allows the operator to determine when the propellant, particularly the water vapor component, is in a steady state prior to starting the thruster 10. The live system monitoring presents a holistic view of the feed system 100, including pressures and temperatures throughout the system 100 and when each heater is engaged. Data from all sensors can be recorded and saved.Example Validation and Verification Tests

[0053] To verify the design and operation of this feed system, multimode and in-situ propellant feed system 100 of this disclosure were tested using delivery of xenon, nitrogen, a krypton / argon mixture, and water vapor in a hot-fire test with a 5-kW P5 HET. The feed system 100 of this disclosure was tested with a series of validation tests to ensure nominal operation.

[0054] One validation test sought to verify system adherence to the requirement that the leak rate of the system shall be less than 0.5 seem on nitrogen at 30 psi. To perform this leak test, the propellant line was disconnected from the thruster and the end capped. The primary anode MFC 150b was fed upstream with 30 psi nitrogen and pressurized the system until the system reached a pressure balance across the MFC 150b. At this point, the MFC flow rate dropped to zero,indicating the system had no discernable leaks, and any remaining leakage in the feed system was much less than 0.5 seem. As a secondary test, leak detection fluid was used while the system was at pressure to ensure no visible leaks.

[0055] Another validation test verified that the feed system 100 ensures water will not condense within the feed system 100. The water condensation test ensured water did not condense between the two calibration columns 1 and 2. This region can be the highest-pressure region in the feed system 100 and can be the most likely region for water to condense. Chilling calibration column 2 causes the water to re-condense, allowing for the effective measurement of the water vapor flow rate through this section. If the flow rate measured in calibration column 2 is lower than that supplied by the syringe pump 180 and measured in calibration column 1, that indicates that water vapor mass is lost somewhere in the feed system 100 by either a leak path or by condensation.

[0056] Water is the most likely to condense at the highest operating pressures, which can occur at a maximum designed flow rate condition, such as 10 mg / s. Due to that, a water condensation validation test at a 10 mg / s flow rate can define the designed flow rate range of the feed system 100. The condensation validation test occurred at steady state until the syringe pump delivered 10 mb of water, which occurred in 16.67 min at the 10 mg / s flow rate. FIG. 5 illustrates a water condensation validation test of the feed system 100 using calibration column 2 and a mass flow rate for the validation test is 10 mg / s. FIG. 5 presents before and after results from the condensation validation test. As seen in FIG. 5, 10 mb of water condensed in calibration column 2 in X number of minutes, e.g. 16.67 min, within 1% uncertainty, thus validating negligible condensation of water in the multimode and in-situ propellant feed system.

[0057] A further validation test of the feed system 100 was to test the functionality of each operational mode A, B, and C, during a hot-fire test on a laboratory HET. Specifically, this test sought to verify system adherence to ensuring stable operation of the HET using the feed system 100. The inventors selected the P5 HET, which is a 5-kW laboratory thruster, to perform the hot- fire validation test. The P5 operated on xenon and nitrogen to verify operation in the pure gas mode A, a krypton and argon mixture to verify operation in the gas mixture mode B, and water vapor to verify operation in the water vapor mode C. All setpoints from the hot-fire test arepresented in Table 1 , below. These setpoints capture the stable operating point of the P5 on each propellant.Table 1: Hot-fire HET operational setpoints

[0058] All testing was performed in a vacuum test facility and all operational chamber pressures were below 5 x I O5Torr, corrected for the respective propellant. The P5 operated for at least two consecutive hours at each setpoint. FIG. 6 illustrates an example laboratory thruster (P5) operating in pure gas mode (a)(b), gas mixture mode (c), and water vapor mode (d) using the multimode and in-situ propellant feed system, where: (a) has xenon through the anode and cathode, (b) has nitrogen through the anode and xenon through the cathode (b), (c) has a krypton / argon mixture through the anode and krypton through the cathode, and (d) has water vapor through the anode and xenon through the cathode. FIG. 6 presents the P5 HET operating on each of the propellants supplied with the feed system 100 operating in its various propellant supply modes. The P5 reached thermal and discharge stability, classified by a thruster body temperature variation lessthan 2 °C / hr and an average discharge current variation less than 1% over five minutes, running on each of the propellants in the hot-fire validation test. The successful thruster stability conditions using each of the feed system operational modes validate that the metering of water and gaseous constituents can be separate. In the validation of ensuring the peak-to-peak oscillations of the propellant flow rate remain under ±10% deviation from the mean, the water vapor constituent demonstrated the largest oscillations.

[0059] A sample start-up profile of the water vapor constituent, illustrating these oscillations, is shown in FIG. 7. In the figure, the pressure transducer P directly upstream of the backpressure regulator 182 records the liquid water pressure, and the pressure transducer P directly downstream of the plenum 170 captures the plenum pressure. Example locations of these pressure transducers P are shown in FIG. 2. The flow rate of water vapor to the thruster scales by the square root of plenum pressure for a fixed anode cross section and water vapor temperature as mentioned in ISO 516717. Thus, the resultant peak-to-peak oscillation in the water vapor flow rate is determined by analyzing the peak-to-peak oscillation in plenum pressure. The maximum measured peak-to-peak oscillation of the plenum pressure is ±8.6%, which results in an approximate maximum peak-to- peak oscillation of the delivered water vapor flow rate of ±4.2%, thereby meeting the stability requirement and validating that the system can contain a plenum to mitigate water flow rate oscillations. Additional plenum volume and operation at a higher water vapor mass flow rate can further mitigate these remaining water vapor oscillations.

[0060] The operational mode seen to produce the largest oscillations is the condensable gas mode C, seen with approximate peak-to-peak flow rate oscillations of ±4.2% while running on water vapor at a flow rate of 5 mg / s. Those oscillations can be further mitigated by increasing the plenum volume or adding additional flow-dampening hardware to the feed system 100.

[0061] Aspects of this disclosure are directed to a feed system 100 used in ground-testing for space electric propulsion thrusters. It acts as a testbed to supply a multitude of propellant combinations including pure gases (such as xenon), gas mixtures (such as nitrogen and oxygen), condensable gases (such as water vapor), and condensable gas mixtures (such as air and water vapor). This feed system can also feature a calibration method for condensable gases involving a recondensation process after the highest pressure region in the propellant feed system. This systemcan also have a live flow rate monitoring system that allows for more accurate and steadier flow rates than what has been published thus far.

[0062] The feed system 100 of the disclosure can have following capabilities: ability to flow pure gas, pure gas mixture, condensable gas, and condensable gas mixture using the same feed system as opposed to separate feed systems for each application. This has not been shown to be done before; a novel calibration technique to verify that condensable gases do not condense in the feed system. This technique is more robust than other existing methods; and ability to record live flow rate measurements of condensable gases to ensure steady flow. Other existing feed systems use a time-averaged approach, which offers much greater uncertainty. This feed system 100 can be designed to flow condensable gases over a much wider mass flow rate range than other existing feed systems. For water vapor, this feed system 100 can be designed to meter in the range of 0.5 mg / s to 10 mg / s where competing feed systems can flow at a maximum of only approximately 2.5 mg / s.

[0063] The system and method of the present disclosure is designed to be versatile in that it can supply a variety of propellant, e g. pure gases, gas mixtures, and condensable vapors, using a single integrated feed system, rather than separate systems for each propellant type. The system of the present disclosure can provide advanced calibration in that it introduces a calibration technique for condensable gases, involving re-condensation after the highest-pressure region to verify no condensation occurs within the system. The feed system 100 can be designed to provide enhanced flow control in that it can provide live, real-time flow rate measurements for condensable gases, improving accuracy and stability over traditional time-averaged methods. The system 100 can be configured for a wider flow range as it is capable of metering condensable gases, like water vapor, over a much broader flow rate range (0.5-10 mg / s) than conventional systems.

[0064] The feed system 100 and method of the disclosure can serve as a flexible testbed for ground-based electric propulsion research, enabling the study and development of alternative and in-situ propellants, such as those that could be harvested in space or on planetary bodies. The feed system 100 can support the advancement of multimode propulsion systems, which can switch between high-efficiency and high-thrust modes, and can be suited for validating new propellant concepts, such as for future space missions.

[0065] The system’s ability to operate in multiple modes— supplying pure gases, gas mixtures, condensable vapors (such as water vapor), and condensable gas mixtures— offers significant advantages for research and development in electric propulsion (EP), such as:• Comprehensive Testing Platform: Researchers can use a single feed system to test a wide variety of propellants and combinations, including those relevant for both traditional and emerging EP technologies. That eliminates the need for multiple, specialized feed systems, streamlining experimental setups and reducing costs and complexity.• Support for Alternative and In-Situ Propellants: The system can be specifically designed to handle propellants that are of growing interest in the field, such as water (which can be electrolyzed into hydrogen and oxygen) and air (for very low Earth orbit applications). This supports the development and validation of propulsion concepts that utilize resources harvested in space or on planetary bodies, a key area of innovation for long-duration and deep-space missions.• Simulation of Real -World Conditions: The system’s ability to mix gases and adjust mixture ratios in real time allows researchers to simulate varying atmospheric compositions, such as those encountered in very low Earth orbit (VLEO) or on other planetary bodies. This helps with understanding thruster performance under realistic, dynamic conditions.

[0066] The system’s capability to meter propellants— especially condensable gases like water vapor— over a broad flow rate range, e.g. (0.5 to 10 mg / s, compared to the ~2.5 mg / s limit of competing systems) provides several key benefits:• Broader Applicability: The wide flow range accommodates the testing needs of both low- power and high-power EP thrusters, such as Hall effect thrusters (HETs) operating at different power levels. This flexibility is essential for developing propulsion systems for a variety of spacecraft sizes and mission profiles.• Enabling High-Fidelity Experiments: The ability to deliver steady, precisely controlled flows at both low and high rates allows for detailed performance mapping and optimization of thrusters across their full operational envelope. This is helpful for characterizing efficiency, stability, and lifetime under different propellant flow conditions.• Facilitating Scale-Up and Down: As propulsion concepts move from laboratory-scale experiments to flight-ready systems, the need to test at different flow rates becomes critical. The system’s range supports this transition, enabling seamless scaling of experiments without the need for new hardware.

[0067] By providing a single, adaptable platform for a wide array of propellants and flow conditions, the system of the disclosure reduces barriers to experimentation and iteration. Researchers can more rapidly test new ideas, validate models, and refine designs. The feed system’s advanced calibration and live monitoring capabilities ensure high accuracy and low uncertainty in flow delivery, which translates to more reliable experimental data. This helps with developing predictive models and for qualifying new thruster technologies for spaceflight. The ability to test with in-situ and alternative propellants under controlled, ground-based conditions helps identify and mitigate risks before flight, supporting the safe and successful adoption of new propulsion technologies.

[0068] The versatility and wider flow range of the multimode and in-situ propellant feed system 100 enhances the scope, quality, and efficiency of research and development in electric propulsion. The system 100 enables comprehensive, high-fidelity testing of a broad spectrum of propellants and thruster types, supports the advancement of innovative propulsion concepts, and accelerates the path from laboratory research to operational space systems.

[0069] It will be apparent to those skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings that modifications, combinations, subcombinations, and variations can be made without departing from the spirit or scope of this disclosure. Likewise, the various examples described may be used individually or in combination with other examples. Those skilled in the art will appreciate various combinations of examples not specifically described or illustrated herein that are still within the scope of this disclosure. In this respect, it is to be understood that the disclosure is not limited to the specific examples set forth and the examples of the disclosure are intended to be illustrative, not limiting.

[0070] As used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise. Similarly, the adjective“another,” when used to introduce an element, is intended to mean one or more elements. The terms “comprising,” “including,” “having” and similar terms are intended to be inclusive such that there may be additional elements other than the listed elements. Additionally, where a method described above or a method claim below does not explicitly require an order to be followed by its steps or an order is otherwise not required based on the description or claim language, it is not intended that any particular order be inferred. Likewise, where a method claim below does not explicitly recite a step mentioned in the description above, it should not be assumed that the step is required by the claim. It is noted that the description and claims may use geometric or relational terms, such as right, left, above, below, upper, lower, top, bottom, linear, arcuate, elongated, parallel, perpendicular, etc. These terms are not intended to limit the disclosure and, in general, are used for convenience to facilitate the description based on the examples shown in the figures. In addition, the geometric or relational terms may not be exact. For instance, walls may not be exactly perpendicular or parallel to one another because of, for example, roughness of surfaces, tolerances allowed in manufacturing, etc., but may still be considered to be perpendicular or parallel.

Claims

WHAT IS CLAIMED IS:

1. A propellant feed system for testing on a propulsion thruster, comprising: a multimode propellant feed component comprising at least a first operational mode, a second operational mode, and a third operational mode; and a propellant supply component configured to supply one or more of a plurality of different propellants to the multimode propellant feed component via a plurality of propellant lines, wherein the first operational mode is configured to feed pure gas selected from the plurality of different propellants to an anode and a cathode of the propulsion thruster; wherein the second operational mode is configured to feed mix gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster, and wherein the third operational mode is configured to feed condensable gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster.

2. The propellant feed system of claim 1, wherein at least one of the plurality of propellant lines is an independent cathode path line configured to feed cathode gas from the plurality of different propellants to the cathode.

3. The propellant feed system of claim 2, wherein the cathode gas is xenon or krypton.

4. The propellant feed system of claim 2, further comprising one or more metering devices positioned in one or more of the plurality of propellant lines, the one or more metering devices being configured to regulate a flow rate of propellant in the one or more of the plurality of propellant lines.

5. The propellant feed system of claim 4, wherein at least one of the one or more metering devices is positioned in the independent cathode path line.

6. The propellant feed system of claim 4, wherein each of the one or more metering devices is a mass flow controller.

7. The propellant feed system of claim 4, wherein a pressure regulator is provided upstream of the at least one metering device, the pressure regulator being configured to regulate a pressure of propellant going to the at least one metering device.

8. The propellant feed system of claim 4, wherein the one or more metering devices are configured to provide a mass flow range of 0.5-10 mg / s.

9. The propellant feed system of claim 1, wherein at least one calibration device is coupled to one or more of the plurality of propellant lines, the at least one calibration device being configured to calibrate a flow of propellant in the one or more of the plurality of propellant lines.

10. The propellant feed system of claim 2, further comprising a plenum connected to one or more of the plurality of propellant lines feeding to the anode.

11. The propellant feed system of claim 2, wherein in the first operational mode at least one of the plurality of propellant lines is an anode propellant line that is configured to feed pure gas from the plurality of different propellants directly to the anode.

12. The propellant feed system of claim 11, wherein at least one metering device is provided in the anode propellant line to regulate a flow rate of the pure gas in the anode propellant line.

13. The propellant feed system of claim 11, wherein at least one of the plurality of propellant lines is a shared gas line that feeds to the anode propellant line and to a cathode propellant line that feeds the pure gas to the cathode.

14. The propellant feed system of claim 2, wherein in the second operational mode, the plurality of propellant lines comprise at least a primary anode propellant line configured to feed a primary anode gas of the plurality of different propellants to the anode and a second anode propellant line configured to feed a secondary anode gas of the plurality of different propellants to the anode.

15. The propellant feed system of claim 14, wherein the primary anode propellant line and the secondary propellant line feed to a plenum that is configured to mix the primary and secondary anode gases.

16. The propellant feed system of claim 15, wherein the primary anode gas is oxygen and the secondary anode gas is nitrogen.

17. The propellant feed system of claim 14, wherein each of the primary and secondary anode propellant lines includes a metering device configured to regulate a flow rate of the primary and secondary anode gases, respectively, to the anode.

18. The propellant feed system of claim 17, wherein each of the primary and secondary anode propellant lines includes a pressure regulator upstream of the respective metering device.

19. The propellant feed system of claim 2, wherein in the third operational mode, at least one of the plurality of propellant lines is a condensable gas propellant line that is configured to feed vaporized gas to the anode.

20. The propellant feed system of claim 19, wherein a flow control device is coupled to the condensable gas propellant line to control a flow of condensable gas through the condensable gas propellant line.

21. The propellant feed system of claim 20, wherein the flow control device is a syringe pump.

22. The propellant feed system of claim 20, wherein a pressure regulator is disposed in the condensable gas propellant line that is configured to regulate pressure on the flow control device by the condensable gas.

23. The propellant feed system of claim 20, further comprising first and second calibration columns in fluid communication with the condensable gas propellant line, the first and second calibration columns being configured to measure condensation of the condensable gas.

24. The propellant feed system of claim 19, wherein the condensable gas propellant line includes an in-line heater configured to vaporize condensable gas from the plurality of different propellants.

25. The propellant feed system of claim 24, wherein at least a portion of one or more of the plurality of propellant lines is heat insulated.

26. The propellant feed system of claim 24, wherein a series of in-line pressure transducers and thermocouples are provided throughout a heated section of the condensable gas propellant line to ensure the condensable gas remains in a vapor state to the anode.

27. The propellant feed system of claim 24, wherein the multimode propellant feed component comprises a first heating circuit encompasses the in-line heater, a second heating circuit configured to covers heated propellent lines outside a vacuum chamber feedthrough to the anode, and a third heating circuit that regulates heated lines inside the vacuum chamber feedthrough.

28. A method of testing a range of propellants for a propulsion thruster, comprising: selecting one operational mode from multiple operational modes of a single propellant feeding system, the multiple operational modes comprising at least first, second, and third operational modes; supplying one or more propellants from a plurality of different propellants that correspond to the one operational mode selected from the multiple operational modes; and feeding the one or more propellants selected from a plurality of different propellants to an anode and cathode of the propulsion thruster, wherein the first operational mode is configured to feed pure gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster,T1wherein the second operational mode is configured to feed mix gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster, and wherein the third operational mode is configured to feed condensable gas selected from the plurality of different propellants to the anode and the cathode of the propulsion thruster.

29. The method of claim 28, further comprising metering a flow rate of the one or more propellants through one or more propellant lines of the single propellant feed system.

30. The method of claim 29, further comprising calibrating of the one or more propellants through the one or more propellant lines.

31. The method of claim 29, further comprising validating a mass flow rate of the one or more propellants through the one or more propellant lines.

32. The method of claim 29, further comprising verifying no condensation of the one or more propellants when in the third operational mode.

33. The method of claim 29, wherein when in the third operational mode, further comprising separately metering water from the plurality of different propellants and vaporizing the water using an in-line heater.

34. The method of claim 28, further comprising real-time monitoring of pressures and temperatures of the single propellant feed system.

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