POST LAUNCH INERT GAS PRODUCTION AND UTILIZATION SYSTEM AND METHOD

Abstract

A gas production and utilization system includes an ionic liquid having an electrochemical window and engineered to produce a specific gas. A power supply is configured to apply a voltage potential across electrodes disposed in the ionic liquid at a level higher than the electrochemical window of the ionic liquid to decompose the ionic liquid. The resultant gas is delivered to a pressure vessel and may be utilized in a variety of different ways.

Description

GOVERNMENT RIGHTS

This invention was made with U.S. Government support under Contract No. FA9300-10-C-2101 awarded by AFRL/Edwards AFB. The Government may have certain rights in the invention

FIELD OF THE INVENTION

This application pertains to spacecraft gas production, utilization, and storage.

BACKGROUND OF THE INVENTION

In space applications, a liquid propellant may be delivered under pressure to a thruster using a gas expulsion tank containing a gas under pressure. See, for example, U.S. Pat. No. 5,471,833 incorporated herein by this reference.

Such gas expulsion tanks can be heavy, occupy significant real estate, and can impose hazards to a launch since it can be dangerous to store and/or transport gasses at high pressures. If the propellant is pressurized before and during launch and leaks, the result can also be disastrous. Using a mechanical pump system to pressurize the propellant post launch requires power and can be prone to various failure modes.

Certain gasses can be generated post-launch, but energy (e.g., heat) is usually required and such gas generation techniques can be dangerous onboard a spacecraft. Also, some gasses, for example oxygen, can be generated by electrolysis. But, other dangerous gasses such as hydrogen in excess, for example, are also generated. Also, it is desirable that only inert gasses be used for certain subsystems such as for propellant pressurization. Moreover, the gas used for propellant pressurization must be at a sufficiently high pressure, for example 350 psi.

Ionic liquids (salt with a low melting temperature, for example molten salts composed of anions and cations with a melting point below about 100° C.) have been used as electrolytes in batteries, for example. Typically, any gas production by electrolysis of an ionic liquid used as an electrolyte is undesirable and is to be avoided.

Finally, U.S. Pat. No. 7,563,308, incorporated herein by this reference proposes using ionic liquids to store various gases. See also U.S. Pat. No. 7,297,289 incorporated herein by this reference.

SUMMARY OF THE INVENTION

Provided in various aspects of the invention is an innovative post-launch propellant pressurization subsystem which is shelf storable, easily scalable, and contains few moving parts as a safe and low cost alternative to prior systems. The system is easily scalable to accommodate propulsion systems of various types and sizes without the safety concern of filled high-pressure gas tanks.

The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

Featured is a post-launch inert gas production method. An ionic liquid is engineered to produce a given inert gas, e.g., CO₂. The ionic liquid is decomposed by electrolysis to produce the inert gas at a given pressure. The pressurized inert gas can then be utilized in a variety of ways.

In preferred examples, the ionic liquid has an electrochemical window and electrolysis includes applying a voltage potential across the ionic liquid at a voltage above the electrochemical window of the ionic liquid. Preferably, the ionic liquid resides in a housing with at least first and second electrodes therein connected to a power supply. In one preferred design, the power supply is configured to provide AC power to the electrodes at a voltage of 6-16 volts.

The interior of the housing may include an electrically insulative material. Also, there can be a plurality of electrodes in an array. The housing is typically coupled to an outlet conduit. A filter allows the inert gas produced to exit the housing via the outlet while retaining the ionic liquid in the housing. In one example, the filter includes a porous frit material.

Utilizing the pressurized gas may include delivering the pressured gas to a pressure vessel. In one design, the pressure vessel includes a propellant therein delivered to a thruster. In another example, utilization of the pressurized gas includes delivering the pressurized gas directly to a cold-gas thruster.

Also featured is a post-launch inert gas production method comprising decomposing an ionic liquid by electrolysis to produce a pressurized inert gas by applying a voltage potential to the ionic liquid at a voltage above the electrochemical window of the ionic liquid and utilizing said pressurized inert gas by delivering the pressurized inert gas to a pressure vessel.

One gas production and utilization system includes a housing including spaced electrodes therein, an ionic liquid in the housing, a power supply configured to apply a voltage potential across said electrodes at a level sufficient to decompose the ionic liquid and produce a pressurized gas, and a pressure vessel for storing the pressurized gas so produced.

In one design, a gas production and utilization system comprises a housing including spaced electrodes therein, an ionic liquid in the housing having an electrochemical window and engineered to produce a specific gas, a power supply configured to apply a voltage potential across said electrodes at a level higher than the electrochemical window of the ionic liquid to decompose the ionic liquid and produce the specific gas under pressure, and a pressure vessel for the pressurized gas.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features, and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic view of a prior art propellant pressurization system;

FIG. 2 is a schematic diagram showing several of the primary components associated with a post launch gas production and utilization system in accordance with the invention; and

FIG. 3 is a schematic view showing another example of an electrolysis module in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

FIG. 1 shows a source 10 of propellant 12 delivered to thruster 14 via gas expulsion tank 16 containing pressurized gas 18 delivered to propellant 12 via valve 19. Such a system results in a heavy, fairly large tank 16. This source of pressurized gas can be dangerous during launch of a space craft employing thruster 14. In other prior art designs the propellant is pressurized and similar inherent dangers exist.

In one example of the invention, housing 20 (e.g., stainless steel) includes spaced electrodes 22a and 22b therein connected to power supply 24 configured to apply a voltage of, for example, 6-16 volts (at, for example, 0.1 amps) to electrodes 22a and 22b. An ionic liquid such as 2-hydroxyethylammonium formate (2-HEAF) (an equimolar mixture of formic acid and 2-hydroxyethylamine) is used in housing or module 20. Other possible ionic liquids include 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) or 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4). Compared to EMI-TFSI and EMI-BF4, the 2-HEAF ionic liquid has a much narrower electrochemical window (e.g., 0.1-1.1V). Preferably, the ionic salt chosen fills the interior of housing 20 and has an electrochemical window typically in the range of 0-5 volts. Electrochemical window typically refers to the potential difference between oxidation potential (anodic limit) and the reduction potential (cathodic limit). An electrochemical window may be defined as the voltage range between which a substance is neither oxidized nor reduced.

Post launch, by applying a voltage potential at a voltage level above the electrochemical window of the ionic liquid, the ionic liquid decomposes (e.g., 2-HEAF) at least in the area proximate the electrodes 22a, 22b and produces a pressurized inert gas (e.g., mainly CO₂) which can be utilized, for example, by delivering the pressurized inert gas to pressure vessel 30 shown in this particular example with bladder 32 (or a piston) used to pressurize propellant 34 on the other side of bladder 32 to be delivered to and used in thruster 36. Controller 40 (e.g., a microcontroller, or the like) can be employed to operate power source 24 and valve 42 in the conduit 44 between housing 20 and pressure vessel 30 based on the pressure inside housing 20 as measured by pressure sensor 42. In other examples, the gas produced is delivered to a separate pressure vessel and then, for example, to a propellant vessel.

The result is a low cost, lightweight, small inert gas production system which produces pressurized gas with very little power input. An AC power supply is preferred to prevent degradation of electrodes 22a and 22b. In one example, a small housing 20 containing just 20 cc of ionic liquid which produced a gas sufficient to pressurize 280 cc of propellant to 350 psi for 30 minutes of operation of thruster 36.

The interior 50 of housing 20 may include (e.g., a coating of) an electrically insulative material such as a ceramic. Filter 52 (e.g., made of a porous frit material such as stainless steel or titanium) may be disposed at outlet 52 to trap the ionic liquid in housing 20 but allow the pressurized gas produced by electrolysis to exit.

In FIG. 3, ionic liquid 26 in module 20′ is maintained in contact with an array of electrodes 22 connected to power supply 24 by using spring loaded plate 60. A power supply which provides an alternating current voltage is preferably used. Spring 62a and 62b urge plate 60 downward in the figure and keep the ionic liquid dispersed about the electrodes in low or zero gravity operations. Other mechanisms for maintaining the ionic liquid about the electrodes may be used and the electrodes may be designed to attract the ionic liquid thereto by surface tension for low gravity operations. Also, in this particular example, the gas produced by the decomposition of the ionic liquid is supplied directly to cold gas thruster 70 by valve 72.

When the ionic liquid 2-HEAF was tested after electrolysis, a gaseous mixture composed primarily of CO₂ was produced. As the 2-HEAF ionic liquid decomposes, the gas is pressurized and can be utilized by a variety of different types of subsystems.

Because the pressurized gas is generated in-situ, the system can be stored and launched unpressurized as opposed to previous systems where tanks of high pressure gas were required to be stored and launched. This new system is low cost because there are few moving parts which also reduces the likelihood of failure. The preferred gasses generated are relatively non-toxic, do not react with the fuel/oxidizer, and are stable which reduces the potential risk of a rupture or other failure occurs during use or testing. The power supply can be operated a various power levels depending on the required pressurization rate and available electrical power. Tests have demonstrated that a minimum input power of 0.5-1 W reaches a gas pressurization of 300 psig. Tests have demonstrated that a minimum input power of 0.5-1 W produces over 200 standard CCs of gas from only 4 mL of ionic liquid.

In another test, the ionic liquid EMI-IM was used in an 11 ml stainless steel test cell housing with opposing 1.6 mm diameter platinum rods. Utilizing the ionic liquid 2-HEAP, however, resulted in a gas production on the order of magnitude greater than when the EMI-IM ionic liquid was used. Thus, the ionic liquid chosen in the preferred embodiment is preferably engineered to maximize gas production for a given power consumption. Another benefit of 2-HEAF is that it decomposes into relatively safe, inert substances. The composition of the product gas was confirmed to be 90% CO₂ and 10% CO and possibly a fraction of hydrogen.

The pressurization process can begin as soon as power is available to the system, typically when the spacecraft solar array is deployed. The reaction can be stopped and restarted at any time in order to divert power to other systems as needed. Because the product gasses are non-corrosive, no exotic materials are needed and typically commercial off the shelf valves and sensors can be utilized.

By purposely decomposing an ionic liquid via AC electrolysis in reaction housing 20, FIG. 2, the product gas or gasses can be utilized in various applications which require a pressurized gas. Preferably, the gasses are generated for utilization in situations where space for storing gas is limited or where it is dangerous to transport or store gasses at high pressures. The specific ionic liquid chosen should decompose to gas from liquid in high fractions to minimize the volume and mass of the ionic liquid required. Furthermore, toxicity, condensation temperatures of gasses produced, and neutrality of the gasses may be important factors in choosing the appropriate ionic liquid. An ionic liquid which does not thermally decompose may be favored. The electrodes may exist in an array as shown. In one test a ⅛″ electrode, gap was used for 1-2 cc of the ionic liquid. Use of an AC voltage prevents electrode fouling. In a test where the produced gas was used in a cold gas thruster, electrolysis was performed on 4 cc of the 2-HEAF ionic liquid at 16 volts AC at 60 Hz using a 0.060″ electrode gap. Gas was generated at a pressure of approximately 180 psia. A valve was opened and the working gas was delivered to non-pressurized tubing reducing the pressure to 120 psia. The average thrust measured was 124.4 mN for a duration of 0.75 seconds. Using the ionic liquid 2-HEAF, the best gas production rate was achieved at 16 volts at 10 Hz. Testing with electrode gaps of 0.030, 0.060, and 0.090″ demonstrated the gas generation rates increased with greater electrode gaps and gaps generation efficiency remains relatively consistent despite changes in gap size. During one test, 204 sec gas was generated from 4 cc of 2-HEAF ionic liquid during 294 hours of electrolysis with a consistent gas generation efficiency averaging 0.43 scc/kJ. This amount of gas would be sufficient to pressurize a 10 cc vessel to 300 psig. The ionic liquid 2-HEAF was tested and appears to be largely compatible with platinum, aluminum, macor ceramic, and Teflon. The gas generation rate of 7.5 sec/hr and a maximum gas generation efficiency of 5 scc/kJ was noted.

In the electrolysis process of the 2-HEAF ionic liquid, the ethanol ammonium cation will first adsorb on the electrode and then be reduced to ethanolamine and hydrogen. The format anion will also first adsorb on the electrode and then be oxidized to form CO2 and protons. For the present application, the 2-HEAF ionic liquid is a good candidate because of the carboxylate anion which will preferably generate CO2 gas. In addition, this particular ionic liquid also has a relative short alkyl chain in the cation which can prevent the formation of excess gaseous hydrocarbon. Other ionic liquids can be chosen for use based on the same or similar criteria.

Utilization of the gas produced by the electrolysis method may further include using the gas in pneumatic actuators (valves, cylinders, and the like), pneumatic motors, compressors, cold-gas thrusters, and other examples such as tire inflation systems and insect traps (if CO₂ is the produced gas). Typically, the gas is used for a broad range of thrusters, mono- and bi-propellant rockets, electric propulsion and cold-gas thrusters, and the like.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.

Other embodiments will occur to those skilled in the art and are within the following claims.

Claims

1. A post-launch inert gas production method comprising:

choosing an ionic liquid engineered to produce a given inert gas;

decomposing the ionic liquid by electrolysis to produce the inert gas at a given pressure; and

utilizing said pressurized inert gas.

2. The method of claim 1 in which the ionic liquid is engineered to produce CO2.

3. The method of claim 1 in which the ionic liquid has an electrochemical window and electrolysis includes applying a voltage potential across the ionic liquid at a voltage above the electrochemical window of the ionic liquid.

4. The method of claim 3 in which the ionic liquid resides in a housing with at least first and second electrodes therein connected to a power supply.

5. The method of claim 4 in which the power supply is configured to provide AC power to said electrodes.

6. The method of claim 5 in which AC power is provided to said electrodes at a voltage of 6-16 volts.

7. The method of claim 4 in which the interior of the housing includes an electrically insulative material.

8. The method of claim 4 in which there are a plurality of electrodes in an array.

9. The method of claim 4 in which the housing is coupled to an outlet conduit.

10. The method of claim 9 further including a filter allowing the inert gas produced to exit the housing via the outlet while retaining the ionic liquid in the housing.

11. The method of claim 10 in which the filter includes a porous frit material.

12. The method of claim 1 in which utilizing the pressurized gas includes delivering the pressured gas to a pressure vessel.

13. The method of claim 12 in which the pressure vessel includes a propellant therein delivered to a thruster.

14. The method of claim 1 in which utilization of the pressurized gas includes delivering the pressurized gas to a cold-gas thruster.

15. A post-launch inert gas production method comprising:

decomposing an ionic liquid by electrolysis to produce a pressurized inert gas by applying a voltage potential to the ionic liquid at a voltage above the electrochemical window of the ionic liquid; and

utilizing said pressurized inert gas by delivering the pressurized inert gas to a pressure vessel.

16. A gas production and utilization system comprising:

a housing including spaced electrodes therein;

an ionic liquid in the housing;

a power supply configured to apply a voltage potential across said electrodes at a level sufficient to decompose the ionic liquid and produce a pressurized gas; and

a pressure vessel for storing said pressurized gas.

17. The system of claim 16 in which the ionic liquid is engineered to produce CO2.

18. The system of claim 16 in which the ionic liquid has an electrochemical window and the power supply is configured to apply a voltage potential across said electrodes at a voltage above the electrochemical window of the ionic liquid.

19. The system of claim 16 in which the power supply is configured to provide AC power to said electrodes.

20. The system of claim 19 in which the power supply is configured to provide AC power at a voltage of 6-16 volts to said electrodes.

21. The system of claim 16 in which the interior of the housing includes an electrically insulative material.

22. The system of claim 16 in which there are a plurality of electrodes in an array disposed within the housing.

23. The system of claim 16 in which the housing includes an exit filter allowing the inert gas produced to exit the housing while retaining the ionic liquid in the housing.

24. The system of claim 23 in which the filter includes a porous frit material.

25. The system of claim 16 in which the pressure vessel includes a propellant therein pressurized by the pressurized gas.

26. A gas production and utilization system comprising:

a housing including spaced electrodes therein;

an ionic liquid in the housing having an electrochemical window and engineered to produce a specific gas;

a power supply configured to apply a voltage potential across said electrodes at a level higher than the electrochemical window of the ionic liquid to decompose the ionic liquid and produce said specific gas under pressure; and

a pressure vessel for said pressurized gas.