Joshua L. Rovey

Ionic Liquid Dual-Mode Spacecraft Propulsion Assessment

Analytical and numerical investigations of the performance of a series of potential dual-mode propulsion systems using ionic liquids are presented. A comparison of the predicted specific impulse of ionic liquids with hydrazine and unsymmetrical dimethylhydrazine shows that ionic liquid fuels have a 3–12% lower specific impulse when paired with a nitrogen tetroxide oxidizer. However, when paired with hydroxylammonium nitrate oxidizer, the specific impulse of the ionic liquids is 1–4% lower than that of hydrazine and unsymmetrical dimethylhydrazine paired with nitrogen tetroxide. Analytical investigation of an electrospray electric propulsion system shows that ion extraction in the pure ion regime provides a very high specific impulse, outside the optimum range for potential missions. Results suggest a deceleration grid, a lower ion fraction, or emission of higher solvated states is required. Analysis of a dualmode ionic-liquid-propelled spacecraft shows that the electric propulsion component determines the overall feasibility comparedwith current technology. Results indicate that the specific power for an ionic liquid electrospray systemmust be at least 15 W=kg in order for a dual-mode ionic liquid system to compete with traditional hydrazine and Hall thruster technology.

Simple Penning ion source for laboratory research and development applications

A simple Penning ion generator (PIG) that can be easily fabricated with simple machining skills and standard laboratory accessories is described. The PIG source uses an iron cathode body, samarium cobalt permanent magnet, stainless steel anode, and iron cathode faceplate to generate a plasma discharge that yields a continuous 1 mA beam of positively charged hydrogen ions at 1 mTorr of pressure. This operating condition requires 5.4 kV and 32.4 W of power. Operation with helium is similar to hydrogen. The ion source is being designed and investigated for use in a sealed-tube neutron generator; however, this ion source is thoroughly described so that it can be easily implemented by other researchers for other laboratory research and development applications.

Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster

The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5kW Hall thruster operating over the range of 300–500V and 5–10mg∕s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of 4.4×10−4Pa Xe (3.3×10−6Torr Xe) to 1.1×10−3Pa Xe (8.4×10−6Torr Xe) in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operatin...

Thrust measurement of dielectric barrier discharge plasma actuators and power requirements for aerodynamic control

Plasma-based aerodynamic actuators can modify a flow field without the need for moving control surfaces or a source of pressurized air. Actuator power consumption and thrust production were measured for driving frequencies between 1 and 18 kHz, and for driving voltages of 6 and 9 kV peak to peak. The actuator consumed between 3 and 22 W, and produced thrust levels between 0.05 and 0.2 mN per meter span. A comparison of results showed good agreement between this work and previous authors’ results. The actuator effectiveness (thrust produced per watt of power input) was found to range between 0.017 and 0.11 mN/W. The continuous power consumption of a DBD actuator-based control system was then estimated by modeling the actuators as jet flaps. The elevator jet flap strength required to trim a small aircraft in flight was determined. A 0.5 kg aircraft with 0.76 m 2 wing area required between 0.47 and 2.22 kW of power for trim. A 3 kg aircraft with 1.27 m 2 wing area required between 13.6 and 54.6 kW of power for trim. In the most challenging circumstances, flight at stall or max velocity, current battery capacities would allow these aircraft to maintain trimmed flight for only 73 seconds.

Assessment of Imidazole-Based Ionic Liquids as Dual-Mode Spacecraft Propellants

Imidazole-based ionic liquids are investigated in terms of dual-mode chemical monopropellant and electrospray rocket propulsion capabilities. A literature review of ionic liquid physical properties is conducted to determine an initial, representative set of ionic liquids that shows favorable physical properties for both modes, followed by numerical and analytical performance simulations. The ionic liquids 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium nitrate, and 1-ethyl-3-methylimidazolium ethyl sulfate meet or exceed the storability properties of hydrazine, and their electrochemical properties indicate that they may be capable of electrospray emission in the purely ionic regime. These liquids are projected to have 13–23% reduced monopropellant propulsion performance in comparison to hydrazine due to the prediction of solid carbon formation in the exhaust. The use of these ionic liquids as a fuel component in a binary monopropellant mixture with hydroxylammonium nitrate shows a 1–4...

Experimental Investigation of Time-Resolved Electron Beam Energy Distributions Generated in a Transient Hollow Cathode Discharge

In this paper, a retarding potential energy analyzer (RPEA) specific for pulsed electron beams within the pressure range of tens of mTorr is developed and used to investigate the energy of transient hollow cathode discharge produced electron beams. This RPEA has been applied in a pseudospark-based electron beam source at applied potential up to 20 kV. Experimental investigations under applied potential of 5 kV, 10 kV, 15 kV, and 20 kV were carried out and the time-resolved electron energy distributions are constructed. The numbers of electrons within various energy groups are calculated from the time-resolved electron energy spectra. Results show that the maximum number of electrons is emitted within the energy range of 40%–60% of the full applied potential on the pseudospark device, and varies from 22.5 ± 2.0% to 38.9±2.0% of the total number of emitted electrons. Additionally, the energy transformation efficiency of stored electrical energy to electron beam energy is calculated from presented data. The ...

Fundamental Processes of DBD Plasma Actuators Operating at High Altitude

Dielectric barrier discharge (DBD) plasma actuators are active flow control devices being investigated for implementation on future aircraft. This paper provides the details of a high altitude analysis done on a plasma actuator operating at altitudes from 0 to 18288 meters (60000 feet) in order to qualitatively determine the fundamental processes that lead to increased power consumption and decreased force production. The actuator is driven with a 5 kHz sine wave with a peak-peak voltage of 13.4 kV at pressures of 760, 429, 321, 226, and 88 Torr. A passive measurement technique called the capacitive V-dot probe is adapted to the actuator in order to resolve the spatiotemporal evolution of the surface potential on the dielectric surface. At low pressures, where there is up to 800% more plasma than at sea level, the electric field is at or very near zero for approximately 80% of the dielectric surface, compared to just 55% at sea level. This implies that at lower pressures increased actuator power is spent making plasma and not accelerating it. Measurements also show that the location of the peak physical charge deposition corresponds closely with the location of the peak surface potential, indicating that the primary mechanism for building potential on the dielectric surface is due to physical charge deposition and not from the capacitive voltage division/polarization effects of the actuator.

Dual-Mode Propellant Properties and Performance Analysis of Energetic Ionic Liquids

Imidazole-based energetic ionic liquids capable of dual-mode chemical monopropellant or bipropellant and electric electrospray rocket propulsion are investigated. A literature review of ionic liquid physical properties is conducted to determine an initial set of ionic liquids that show favorable physical properties for both modes, followed by numerical and analytical performance simulations. Of the ionic liquids considered in this study, [Bmim][dca], [Bmim][NO3], and [Emim][EtSO4] meet or exceed the storability properties of hydrazine and their electrochemical properties are comparable to [Emim][Im], the current state-of-the-art electrospray propellant. Simulations show that these liquids do not perform well as chemical monopropellants, having 10-22% lower specific impulse due to their lack of oxidizing species. The ionic liquids show acceptable bipropellant performance when burned with standard oxidizers, having specific impulse 6-12% lower than monomethylhydrazine and nitrogen tetroxide combination. Considering these ionic liquids as a fuel component in a binary monopropellant mixture with hydroxyl ammonium nitrate shows 1-3% improved specific impulse over some green monopropellants, while retaining a higher molecular weight, reducing the number of electrospray emitters required to produce a given thrust level. More generally, ionic liquids with oxidizing anions perform well as chemical monopropellants while retaining high molecular weight desirable for electrospray propulsion missions.

Pre-Ionization Plasma in an FRC Test Article

Pulsed plasma systems, specifically field reversed configuration devices, show great potential for future space propulsion systems. The fundamental formation process of heavygas plasma necessary for propulsion application is not well understood. The following study is focused on characterizing the pre-ionization stage of a field reversed configuration test article. Specifically, flux loop and B-dot probe data are presented and used calculate the magnetic flux and magnetic field strengths within MPX. Finally, plasma images collected with a high speed camera are presented. Tests are conducted at 15 and 20 kV using both air and argon over a pressure range of 2 – 70 mTorr and at atmosphere. Discharges with no plasma present have a frequency of 464 kHz while a discharge that produces plasma resonates at approximately 490 kHz. Details of probe construction and calibration are also presented. A maximum magnetic field of 882 G is observed for a 20 kV discharge with fill pressure of 45 mTorr of air near the edge of the theta coil. A maximum magnetic flux of 2.17 mWb is observed for a 20 kV discharge with a fill pressure of eight mTorr. The largest amount of energy absorbed by the plasma is 30.3 J and occurs during a 20 kV discharge in air at 60 mTorr. Peak magnetic fields, magnetic flux, and formation times as functions of gas species, pressure, and voltage are also presented. Maximum energy absorption into plasma occurs at 65 mTorr of air at a discharge voltage of 20 kV.

Capillary Extraction of the Ionic Liquid (Bmim)(DCA) for Variable Flow Rate Operations

The ionic liquid [Bmim][DCA] is a propellant candidate in a standalone electrospray thruster or in a dual-mode propulsion system consisting of a chemical system and an electrospray system. Since limited published data exists for [Bmim][DCA], the electrospray characteristics are relatively unknown. Emission testing of the ionic liquid has been conducted to characterize the [Bmim][DCA] electrospray plume for both an external flow titanium needle and internal flow capillary. Mass spectrometric, retarding potential, and angle distribution measurements were collected for the positive polarity ions emitted from [Bmim][DCA] wetted emitters with nominal extraction voltages between ~1 kV to ~2.5 kV. The titanium needle operated at a sizably reduced liquid flow rate in comparison to the capillary. As such, only the major species of Bmim + ([Bmim][DCA])n with n=0,1 were identifiable in the quadrupole measurement range of 0-1000 amu and were formed at or near the needle potential. A typical needle angle distribution was found in these measurements. For the capillary emitter, flow rates from 0.27 nL/s to 2.18 nL/s were used to investigate corresponding alterations in the electrospray beam. The aim of the investigation was to ascertain the ability to “tune” or “dial-in” an electrospray thruster to specific ion or droplet sizes and thus specific performance levels. Unlike the limited species observed from the needle emission, the capillary measurements indicated the presence of n=0,1,2,3,4 cation species with large mass droplet contributions. The lowest flow rates indicated the highest levels of ions in the measurement range of 0-1000 amu with a mix of large mass droplets. For increasing flow rate, species < 500 amu ceased to exist leaving only the n=2,3,4 species mixed with large mass droplets in the electrospray beam. All ion species exceeded the quadrupole mass range at the upper flow rates. Ions emitted from the capillary were formed at levels below the emitter potential. Ohmic losses in the ionic liquid are likely the cause for the less energetic ions. Angular distribution measurements indicated broadening of the beam current and mass distribution for increasing flow rates.