P.O. Box 131460
Ann Arbor, MI, 48113-1460
734-786-1434, fax 734-786-3235
Hybrid Chemical-Electrical Propulsion
(HCEP)
Phase I STTR
Christopher Davis, Ph.D.
Senior Engineer
ElectroDynamic Applications, Inc. (EDA)
Professor Michael Micci
The Pennsylvania State University (PSU)
OVERVIEW
This Phase I effort seeks to develop a dual-mode Hybrid Chemical–Electric Propulsion
thruster concept design based on the extensive microwave torch/arcjet experience of
PSU and Hall and ion thruster experience of EDA. The primary focus of the Phase I
effort will be demonstrate the operation of an ionic liquid (IL) microwave thruster in the
high-thrust-to-power regime and the basic operation of a Hall and/or ion thruster on an IL
simulant. The overall effort (Phases I, II, and III) will advance the TRL level of a dualmode hybrid chemical–electric propulsion thruster technology for immediate use on a
government demonstration mission.
The HCEP thruster concept using an IL propellant and input microwave power is shown
in Figure 1 and Figure 2. The central chamber consists of a microwave resonant cavity,
sized to the selected microwave frequency, with a converging–diverging nozzle exit. It is
surrounded by an annular electrostatic thruster such as an ion or Hall thruster. Both
chambers use the same IL
propellant. The
microwave energy can be
used in one or a
combination of three
ways: 1) The first use
would be to ignite and
bring to complete
combustion the energetic
IL within the central
chamber without the use
Figure 1, Schematic of Variable Isp IL Electric Thruster. Microwaves are
used either to ignite and heat the IL propellant or to vaporize and ionize it
for electrostatic acceleration.
P.O. Box 131460
Ann Arbor, MI, 48113-1460
734-786-1434, fax 734-786-3235
of a catalyst, providing for the high chemical Isp mode. 2) Subsequent to this process,
additional heating of the combustion product gases can be accomplished via a
microwave-generated plasma, approximately doubling the chemical specific impulse to
generate the low electric Isp mode (< 1000 s). 3) For the high Isp mode, the microwave
energy is used to vaporize and ionize the IL propellant. The ions are then accelerated
electrostatically in the annulus around the central chamber. The microwave power is
input to the thruster via a coaxial transmission line, and a microwave switch would direct
the power to the appropriate section(s) of the thruster.
In the low Isp electric mode, a
thrust level of at least 3 N could be
achieved with 25 kW of input
microwave power while operating
at a thruster efficiency of 50% or
higher, an efficiency that has
already been validated on a thrust
stand for a low power microwaveheated thruster using molecular
propellants such as ammonia and
simulated hydrazine
Figure 2, Schematic of Variable Isp IL Electric Thruster.
Central chamber is used for high thrust mode while outer
annulus serves as a dual-charge Isp electrostatic thruster.
decomposition products.
In the high Isp electric mode,
recent work has shown that molecular propellants perform well in both ion and Hall
thrusters and are able to produce specific impulses up to the 3000 second range.
OBJECTIVES
The proposed development of a HCEP will involve four objectives in Phase I. The
primary technical objective of this program is the successful operation of two small-scale
experiments to validate the principal two unknown technologies involved in the thruster.
P.O. Box 131460
Ann Arbor, MI, 48113-1460
734-786-1434, fax 734-786-3235
Table 1: Summary of Phase I Technical Objectives
#
Objective
1
Evaluation of the previous and current Dual-Mode EP devices and mission analysis
for Responsive Space Missions
2
Validation of PSU Microwave Igniter and Electrothermal Concept for low-Isp and
high-Thrust operation on an ionic liquid propellant.
3
Validation of EDA high-Isp low-Thrust EP concepts on simulated ionic liquid
components
4
Development of a conceptual HCEP thruster design
Objective 1: Evaluation of the Previous and Current Dual-Mode EP devices and Mission
Analysis for Responsive Space Missions
The first objective of the Phase I effort is the detailed study of previous and ongoing
research into the development of “dual-mode” or “multi-mode” EP devices. The HCEP
team will examine possible mission scenarios that a dual-mode EP system would enable
for government and commercial interest.
Objective 2: Validation of PSU Microwave Igniter and Electrothermal Concept for lowIsp and high-Thrust operation on Ionic Liquid Propellants
The second objective of the Phase I effort is to conduct an experimental campaign that
will validate the use of microwave energy to ignite a flowing IL, such as AF-M315E.
The Penn State surface-wave plasma torch will be modified to introduce a flow of an IL
and input microwave power will be increased until IL ignition is achieved. This smallscale experiment will be used to determine the microwave power required to ignite and,
after IL ignition is achieved, to sustain the combustion of a representative IL as a function
of flow rate.
An additional aspect of this objective will be to operate a microwave electrothermal
thruster with representative combustion products of an IL, such as H2O, CO2 and N2O,
and quantify the performance increase in terms of specific impulse and thrust.
Objective 3: Validation of EDA high-Isp low-Thrust EP Concepts on Simulated Ionic
Liquid Propellants
The third objective of the Phase I effort is to conduct an experimental campaign that will
validate the use of IL, or simulated products of an IL, on an existing well-characterized
electrostatic Hall and/or ion thruster in order to validate the acceleration process for these
propellants. The HCEP team will accomplish this by examining the most efficient path to
P.O. Box 131460
Ann Arbor, MI, 48113-1460
734-786-1434, fax 734-786-3235
demonstrate the high-Isp operation and will chose the best path forward in either
conducting the test on EDA’s HHT or HPHT ion thrusters.
Objective 4: Development of Conceptual Design of a HCEP Thruster
The fourth objective of the Phase I effort is the conceptual design of a 30-kW HCEP
thruster. Based on the results of the two small-scale technology validation experiments,
the preliminary design of a complete variable Isp HCEP thruster system will be
undertaken. A particular means of electrostatic acceleration will be chosen and
implemented in an annular region around the central microwave resonant cavity.
Methods to extract charges of both signs from the microwave ionizer and accelerate them
in separate channels will be examined, with one being selected for implementation in the
design. The design will also need to address the means to switch the input microwave
power between the central chamber and the outer propellant vaporizer/ionizer using, if
possible, commercially available microwave switches.
PROGRESS
Kick-Off Meeting
A kick-off telecom was held with ElectroDynamic Applications (EDA), Penn State
University (PSU) and the AFRL program manager of the project, 2Lt. Anne Sheppard on
July 26th, 2012. A summary of the project objectives and work plan were presented.
Hall Thruster Testing
Work is being done to set up a Hall thruster for testing with simulated ionic liquid
components. The initial test will be done using Nitrogen and Carbon Dioxide. Initial
testing will begin in September 2012 based on chamber availability. The thruster
operating conditions and plume properties will be compared to previous tests run with
Xenon.
Microwave Ignition Testing
Microwave waveguide components and an IL propellant feed and metering system were
procured and are being assembled. A microwave electrothermal thruster operating at
2.45 GHz for the additional heating of the IL combustion products is also under
assembly.
PLANS
During the next 2 month period we expect to do the following:
 Initial Hall Thruster testing with Nitrogen and Carbon Dioxide (EDA).
 Complete experimental setup for characterization of microwave ignition of AF315E (PSU).
 Initial Microwave Electrothermal Thruster testing of representative IL propellant
combustion products; H2O, CO2, and N2O.