WO2017023383A1

WO2017023383A1 - Liquid fueled pulsed plasma thruster

Info

Publication number: WO2017023383A1
Application number: PCT/US2016/031006
Authority: WO
Inventors: Shae WILLIAMS; Wayne N. Sawka; Michael D. Mcpherson
Original assignee: Digital Solid State Propulsion, Inc.
Priority date: 2015-05-05
Filing date: 2016-05-05
Publication date: 2017-02-09

Abstract

In one aspect and one example, a liquid fueled pulsed plasma thruster includes an ionic liquid propellant and electrodes disposed to at least partially cause electrolytic decomposition of the ionic liquid propellant. The ionic liquid propellant may include a Hydroxylammonium Nitrate (HAN)-based Green Electric Monopropellant (GEM). Further, the electrodes may be disposed in various orientations within the thruster, including parallel or coaxial orientations. In another example, a dual mode combustion thruster is provided, allowing a thruster to selectively operate either chemically for high thrust or in a pulsed plasma mode for high efficiency.

Description

LIQUID FUELED PULSED PLASMA THRUSTER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisional patent application serial

No. 62/157,352, filed May 5, 2015, entitled "LIQUID FUELED PULSED PLASMA

THRUSTER," which is hereby incorporated by reference in its entirety for all purposes.

[0002] This application is further related to previously filed U.S. patent application serial No. 12/989,639, entitled "ELECTRODE IGNITION AND CONTROL OF

ELECTRICALLY IGNITABLE MATERIALS," filed on January 7, 2011, which is hereby incorporated by reference herein in its entirety. Further, this application is related to previously filed U.S. patent application serial No. 12/993,084, entitled "FAMILY OF MODIFIABLE HIGH PERFORMANCE ELECTRICALLY CONTROLLED PROPELLANTS AND EXPLOSIVES," filed on May 15, 2009, which is hereby incorporated by reference herein in its entirety.

FEDERAL FUNDING

[0003] Aspects of this description were made with Government support under Small

Business Innovative Research Contracts: HQ0147-13-C-7206 and HQ0147-13-C-7608, awarded by the Missile Defense Agency. The Government may have certain rights in the invention.

BACKGROUND

[0004] Pulsed plasma thrusters are currently used, but with inert propellants (both solid and liquid). Teflon is the most common propellant, with other materials such as water, dimethylether , and other plastics commonly used. Fig. 1 illustrates a conventional liquid pulsed plasma thruster showing multiple required circuits and a specialized ignition electrode.

SUMMARY

[0005] Described herein are liquid and solid propellants based on ionic liquids, and a thruster that uses the propellant' s properties to create a high-efficiency, low power pulsed plasma thruster (PPT) relative to conventional liquid pulsed plasma thrusters. [0006] In one aspect and one example, a liquid fueled pulsed plasma thruster includes an ionic liquid propellant and electrodes disposed to at least partially cause electrolytic decomposition of the ionic liquid propellant. The ionic liquid propellant may include Hydroxylammonium Nitrate (HAN)-based Green Electric Monopropellant (GEM). Further, the electrodes may be disposed in various orientations within the thruster, including parallel or coaxial orientations.

[0007] In another example, a dual mode combustion thruster is provided, e.g., allowing for a thruster to either burn chemically for high thrust or fire in a pulsed plasma mode for high efficiency.

[0008] According to another aspect a satellite is provided which comprises or is coupled to a liquid pulsed plasma thruster as described, which may include a single or dual mode combustion thruster.

[0009] According to another aspect, a process for the stoichiometric combustion of ionic liquid propellants is provided. In some examples, the process is performed in the exemplary thruster systems described, and may result in enhanced ionization and electrothermal-chemical burning at lower voltages (<600V) and reduced power processing unit size relative to conventional pulsed plasma thrusters.

[0010] Additionally, systems, electronic devices, processes, and non-transitory computer readable storage medium (the storage medium including programs and instructions for carrying out one or more processes described) for providing or operating ionic liquid pulsed plasma thrusters are described.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present application can be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.

[0012] FIG. 1 illustrates an exemplary liquid pulsed plasma thruster showing multiple required circuits and a specialized ignition electrode.

[0013] FIG. 2 illustrates an exemplary ionic liquid pulsed plasma thruster according to one example. [0014] FIG. 3 illustrates an exemplary dual mode thruster block diagram providing for different levels of thrust and efficiency with common tankage and plumbing, providing increased flexibility without increased weight.

[0015] FIG. 4 illustrates a comparison of state of the art propulsion systems with predictions for an exemplary ionic liquid-fueled (e.g., GEM-fueled) pulsed plasma thruster.

[0016] FIGs. 5A and 5B illustrate isometric and cross-sectional views, respectively, of an exemplary ionic liquid pulsed plasma thruster design according to another example.

DETAILED DESCRIPTION

[0017] The description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the present technology. Thus, the disclosed technology is not intended to be limited to the examples described herein and shown, but is to be accorded the scope consistent with the claims.

[0018] Described herein are liquid and solid propellants based on ionic liquids, and a thruster that uses the propellant' s properties to create a high-efficiency, low power pulsed plasma thruster (PPT) that operates in ways no other thruster currently operates. When a small amount of propellant is located between two electrodes, either parallel or coaxial orientation, voltage is applied between the electrodes across the propellant. This causes the propellant to undergo electrolytic decomposition, which generates a highly conductive gas on the surface of the propellant; the remaining power then arcs through that conductive gas, which superheats and partially ionizes the gas into an energetic plasma. The plasma then accelerates out the back of the thruster both via thermodynamic expansion and

electromagnetic expansion, yielding fuel efficiencies greater than conventional chemical thrusters can offer at the cost of lower thrust.

[0019] Certain examples provided herein may provide several key advantages. For instance, the ionic liquid nature of the propellant described herein is a key feature. The ionic liquid based propellant ionizes at a much lower voltage than conventional inert propellants. For example, the ionic liquid propellant can be ionized as propellants at as low as 300 V, while conventional pulsed plasma thrusters typically require greater than 1,000 V to ionize. This is a benefit because it allows for the electronics needed to fire the subsystem to be lighter and more compact, e.g., by a factor of 2, relative to conventional electronics.

[0020] Another benefit of the propellant being based on an ionic liquid is that the propellant is sufficiently conductive so as to not require an extra system to begin ionizing the propellant. Conventional PPTs typically require either a second circuit to initiate or a special 'spark plug' electrode near the propellant surface to act as a focus for electric fields. FIG. 1 illustrates a conventional liquid pulsed plasma thruster with separate electronic systems for ignition and acceleration. In contrast, FIG. 2 illustrate an exemplary liquid PPT 200, according to one example, that only requires one pair of electrodes 202 and one circuit connection to ignite and accelerate ionic liquid plasma. In operation, ionic liquid plasma enters the thruster via valve 210 and exits after combustion via valve 212. The single pair of electrode and circuit connection greatly simplifies, lightens, and economizes on eventual propulsion system.

[0021] Exemplary liquid propellant is also a combustible monopropellant, which also yields advantages. For example, in addition to the energy delivered by the electronic pulse, the heated plasma can also burn as it travels down the thruster. This adds more energy to the exhaust plume, which in turn adds thrust to the system' s potential performance. Typical fuels like Teflon cannot combust in this manner.

[0022] Another benefit is that the stoichiometric combustion of these ionic liquids enhances ionization and electro-thermal-chemical burning at lower voltages (<600V), rather than the spalling, vaporing, and/or ablating the chemical species for ionization at high voltages (> 1500V). This reduces the power processing unit size.

[0023] This combustibility allows for a thruster to either burn chemically for high thrust or fire in the mode outlined above for high efficiency. The chemical mode is described in greater detail, e.g., in U.S. Publication No. 2014/0109788, entitled, "Liquid Electrically Initiated and Controlled Gas Generator Composition," filed on September 27, 2013, the entire content of which is incorporated herein by reference. An exemplary PPT described herein can be combined with a chemical mode to provide a "dual-mode" thruster with selectable efficiency levels and a common propellant as illustrated in FIG. 3. Such a design may offer different levels of thrust and efficiency with common tankage and plumbing, giving users more flexibility without increased weight.

[0024] The combustible nature of the propellant also provides multiple options for

'afterburner' functionality where additional systems can be added to increase thrust after the primary firing is complete. As such, one can either add an electromagnetic focusing system for the high efficiency thrusters, or also potentially add in a more typical afterburner where unburnt fuel is dumped into the nozzle once the superheated plasma slug is away; the plasma will combust the fresh fuel and add thrust to the system. Conventional electric propulsion systems do not have the ability to perform thrust augmentation in this way.

[0025] Another feature of examples provided herein is that the liquid PPT propellant is space storable and does not need to be in a pressurized tank. The most common liquid PPT propellant is water, with either pure or with ionic salts added to increase conductivity. These propellants need to be kept isolated from vacuum exposure unlike the exemplary propellants describe herein, which increases the tankage mass and complexity.

[0026] Exemplary propellant composition may further be augmented with heavy metal species to increase thrust at the cost of efficiency, either alone or in ionic salt solutions, or light metal species such as lithium to augment efficiency at the cost of thrust again either alone or in ionic salt solutions. This provides an unprecedented ability to tailor propellant for the specific needs of a mission.

[0027] In one example of a PPT as described, the PPT uses Hydroxylammonium

Nitrate (HAN)-based Green Electric Monopropellant (GEM) as the liquid propellant. In one example, a PPT enables microsatellites to perform missions with delta-v's of greater than 1 kilometer per second. A GEM-fueled PPT is able to do this better than conventional electric propulsion options because GEM's ionic liquid main ingredient ionizes at low voltages, which allows a correspondingly low-mass power processing unit (PPU) while maintaining high specific impulse. This combination will make ambitious missions possible with satellites as small as 3U CubeSats. Further, GEM's high density, compared to many propellants used in electric propulsion, allows for a very high impulse density, critical to volume-limited systems. Exemplary GEM propellant delivers these advantages while remaining space-storable, and has low toxicity and low sensitivity unlike many other energetic materials. [0028] In one example, a system as described can deliver higher efficiency, higher thrust, and a higher specific impulse than conventional electrospray or Teflon-fueled PPTs, while having a small enough PPU and thruster size to fit into a CubeSat form factor (see, e.g., FIG. 4, which illustrates a comparison of conventional CubeSat propulsion systems with predictions for an exemplary GEM-fueled PPT described herein. The predicted GEM PPT is higher in both thrust and ISP than conventional PTFE PPTs and state of the art

electrosprays.).

[0029] The ability to ionize and sustain electromagnetic acceleration has already been demonstrated in known Electric Solid Propellant (ESP) thrusters operating with specific impulses approaching 1000 seconds. Since the formulations of the solid and liquid forms of the propellant are similar, it is expected that GEM will be as ionizable as the spaceflight- proven solid formulation. Initial studies have shown evidence of this; empty solid thruster bodies were filled with GEM and fired using the ESP Power Processing Unit (PPU). Using this configuration, it was verified that GEM using the ESP PPU could deliver from 0.5 mN up to 0.5N of thrust from the 40J output of the ESP PPU.

[0030] Electric propulsion thrusters deliver extremely high specific impulses that allow for large changes in velocity, orbital transfers, and other deep space missions. For a given mission, the use of a mature electric propulsion thruster translates to significantly higher payload capacity to support the mission of a spacecraft. For example, NASA's stated goals are for a thruster that can provide 1000 m/s or potentially more delta-v to a CubeSat launched as a secondary payload using green propulsion. To illustrate the density-specific impulse of a GEM-fueled PPT to deliver 1 km/sec of delta-v, the volume of required propellant for different sizes of CubeSat can be seen in Table 1.

Spacecraft Volume Required GEM Required GEM volume

(U) volume (cc) as a percentage of total

spacecraft volume

3 (4 kg) 189 6.3%

6 (12 kg) 566 9.4%

12 (20 kg) 943 7.9%

Table 1: Volume of required GEM propellant to deliver 1000 m/s of delta- v to a CubeSat using a GEM-fueled PPT with a specific impulse of 1300 sec.

[0031] GEM also demonstrates high density (1.7 g/cc) relative to other common working fluids and will not need high pressure to feed the fuel to the PPT due to capillary action. Also, GEM allows for easier testing due to lack of contaminants in the exhaust, so that vacuum chambers firing GEM need very little cleaning to be ready for another test fire. Because the fuel of the GEM-based PPT is liquid, the same thruster hardware could be utilized on a wide array of microsatellite sizes by simply scaling the propellant tank.

Accordingly, in one example, a GEM-fueled PPT system may offer the specific impulse of a Teflon-fueled PPT with a lower system mass to meet a wide range of mission requirements.

[0032] An exemplary PPT design includes a coaxial thruster based on an ESP thruster configuration, utilizing an axisymmetric design with a refractory metal center electrode to resist arc ablation. The exemplary hardware may include a commercial-off-the-shelf (COTS) valve taken from the inkjet printer industry, with the intention of designing and acquiring a custom valve for a flight system (Error! Reference source not found., which illustrate isometric (FIG. 5A) and cross-section (FIG. 5B) views of an exemplary Liquid PPT design. In this example, the valve is a COTS inkjet printer valve and combined with a coaxial design similar to a ESP thruster.

[0033] Related U.S. patent publications, which describe various aspects of electrically ignitable propellants, grain structures, housings, and the like, which may be used in conjunction or as part of the devices described herein, include the following: U.S. Publication No. 2014/0109788, entitled, "Liquid Electrically Initiated and Controlled Gas Generator Composition"

U.S. Publication No. 2011/0067789, entitled "Family of Modifiable High

Performance Electrically Controlled Propellant and Explosives"

U.S. Publication No. 2012/0103479, entitled "High Performance Electrically

Controlled Solution Solid Propellant"

U.S. Publication No. 2011/0259230, entitled "Electrode Ignition and Control of Electrically Ignitable Materials" and

U.S. Publication No. 2012/0137912, entitled "Controllable Digital Solid State Cluster Thrusters for Rocket Propulsion and Gas Generation"

all of which are hereby incorporated by reference in their entirety.

[0034] Various exemplary embodiments are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the disclosed technology. Various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the various embodiments. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the various embodiments. Further, as will be appreciated by those with skill in the art, each of the individual variations described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the various embodiments. All such modifications are intended to be within the scope of claims associated with this disclosure.

[0035] While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.

Claims

CLAIMS We claim:

1. A liquid fueled pulsed plasma thruster, comprising:

an ionic liquid propellant; and

electrodes disposed to at least partially cause electrolytic decomposition of the ionic liquid propellant.

2. The liquid fueled pulsed plasma thruster of claim 1, wherein the ionic liquid propellant comprises Hydroxylammonium Nitrate.

3. The liquid fueled pulsed plasma thruster of claim 1, wherein the ionic liquid propellant comprises a green electric monopropellant.

4. The liquid fueled pulsed plasma thruster of claim 1, wherein the electrodes are disposed in a parallel orientation.

5. The liquid fueled pulsed plasma thruster of claim 1, wherein the electrodes are disposed in a coaxial orientation.

6. The liquid fueled pulsed plasma thruster of claim 1, further comprising a dual mode combustion thruster.

7. A liquid fueled pulsed plasma thruster as described herein.

8. A satellite comprising a liquid fueled pulsed plasma thruster as described herein.

9. A method for the stoichiometric combustion of descried ionic liquid

propellants for enhanced ionization and electro-thermal-chemical burning at lower voltages (<600V) and reduced power processing unit size.