Patent Application
20160060768
This application pertains to spacecraft gas production, utilization, and storage.
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.
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.
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:
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.
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.
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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,
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.
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
