Session B5
Paper # 6009
Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the
University of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is
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THE EFFICACY OF THE HALL-EFFECT THRUSTER IN SPACE TRAVEL
Ben Harper, bjh87@pitt.edu, Lora 4:00, Christian Marble, cdm63@pitt.edu, Lora 6:00
Abstract—For the past 50 years satellites and spacecraft
have utilized the technology of an electrical propulsion
system to maintain their orbit path or travel in space. Many
of these electrical propulsion systems use a specific type of
engine called a Hall-Effect Thruster. A Hall-Effect thruster
is an electrostatic ion thruster that creates thrust by
accelerating ions with an electric field.
Hall-Effect thrusters provide a unique option for deep
space travel because they generate thrust over a long period
of time and attain very high speed to reach the far areas of
outer space. Their fuel efficiency and economy exceeds that
of chemically propelled engines due to a marked reduction
of propellant required resulting in an increased payload.
Currently, high-powered Hall-Effect thrusters are being
tested to be used in NASA’s Asteroid Redirect Mission,
targeted for 2020, to redirect an asteroid so it can be studied
by astronauts. The success of this mission, using Hall-Effect
thrusters in conjunction with Solar Electric Propulsion,
could establish the foundation to enable cost-effective trips
to Mars.
This paper will discuss the concept of electric propulsion
focusing on the Hall-Effect thruster. Through the use of
diagrams and formulas regarding rocket propulsion and
electromagnetic principles the paper will explain the
construction and operation of the Hall-Effect thruster. New
advancements in Hall-Effect thruster technology will be
explored, and the economic and ethical implications of the
use of Hall-Effect thrusters in geosynchronous satellites and
space travel will be examined.
Key Words--Deep Space Travel, Electric Propulsion, HallEffect Thruster, NASA’s Asteroid Redirect Mission,
Satellites
ELECTRIC PROPULSION SYSTEMS AND
HALL-EFFECT THRUSTERS: AN
OVERVIEW
The Evolution of Electric Propulsion and Hall-Effect
Thrusters
University of Pittsburgh Swanson School of Engineering
2016-03-04
The concept of electric propulsion was first described by
Dr. Robert Goddard, an American physicist, while
conducting experiments with discharge tubes in 1906.
Goddard observed that charged particles accelerated to great
velocities due to the electric fields created within the tube
while the walls of the tube remained cool; this was in
contrast to chemical means that required high temperatures
to propel gas at similar speeds. Goddard theorized that high
velocity streams of negative and positive particles could be
energized by solar electric power supplies to provide thrust
for an interplanetary spacecraft [1].
A critical milestone in the development of electric
propulsion was reached in 1954 when the first
comprehensive study of the major components associated
with an electrically propelled spacecraft was completed by
Dr. Ernst Stuhlinger, a German-American rocket scientist.
Stuhlinger defined the relationship between the optimum
exhaust velocity, the desired delta-v (change in velocity),
and the specific mass of the power source necessary for the
operation of an electric propulsion system. He also
identified Mercury or Xenon as the propellants of choice for
use in an electric propulsion engine because their large
mass-to-charge ratio permitted a reduction in the size of the
ion engine to achieve a specific thrust level [1].
Stuhlinger’s work with electric propulsion advanced the
technology from a theoretical stage to an operational one. In
the following decade, research programs dedicated to
electric propulsion were instituted in the United States and
Soviet Russia. The primary objective of this research was to
develop electric propulsion technology for satellite stationkeeping and deep-space propulsion applications [2]. The
United States concentrated its research on ion thrusters,
culminating in the first successful space-flight test of an ion
thruster with the Space Electric Rocket Test I (SERT I)
spacecraft in 1964. Concurrently, the Soviets focused on
increasing the thrust efficiency and flight readiness of HallEffect thrusters for use in station-keeping on
communications satellites [3].
The end of the Cold War in the early 1990’s facilitated
the spread of the Soviet’s optimization of Hall-Effect
thruster technology to the United States and Europe. Soon
the western nations were conducting their own research to
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increase the power and lifetime of Hall-Effect thrusters.
Since 1971 over 240 Xenon Hall thrusters have flown in
space with a 100% success rate [4]. The aforementioned
statistic attests to the reliability of this type of electrostatic
thruster. In 2003 the European Space Agency used a solar
electric propulsion system with a Hall-Effect thruster on its
Small Missions for Advanced Research and Technology-1
(SMART -1) mission. The SMART-1 spacecraft orbited the
Moon for three years and achieved its mission objectives of
investigating lunar geochemistry, searching the south lunar
pole for the potential presence of ice, and testing solar
electric propulsion [5]. The success of the SMART-1
mission demonstrated the viability of solar electric
propulsion for future extended space missions.
Electric Propulsion and Hall-Effect Thrusters: An
Alternative to Chemical Propulsion
Electric propulsion and Hall-Effect thruster technology
has been developed for applications in deep space travel and
satellite station-keeping because they offer a more economic
and efficient alternative to chemically propelled rockets.
Rocket systems are rated on their efficiency by a parameter
known as the specific impulse (Isp) that is measured in
seconds. The Isp for a chemical propulsion system is 500
seconds compared to 1500 seconds for an electric propulsion
system using a Hall-Effect thruster [6]. Electric propulsion
systems consume less propellant than chemical propulsion
systems permitting more room for payloads such as
passengers and cargo on the spacecraft and a reduction in
cost for the mission [7]. Any reduction in cost is significant
because the price of putting one pound of payload into the
Earth’s orbit is $10,000 [8]. The economy of fuel and the
efficiency of the electric propulsion system qualify it as an
appropriate option for use in extended journeys into space.
The National Aeronautics and Space Administration
(NASA) has planned a launch in 2020 using Solar Electric
Propulsion (SEP) and Hall-Effect thrusters for its Asteroid
Redirect Mission. During this mission a robotic spacecraft
will capture a boulder from the surface of a near-earth
asteroid and move it into a stable orbit around the Moon to
be explored in the future by astronauts [9]. The performance
of the SEP system will be tested in the Asteroid Redirect
Mission and if reliable, this propulsion system could be
considered to support future missions to Mars.
solar panels may create electrical energy directly from
sunlight.
Once the energy source is determined, there are three
types of electric propulsion that may be used. Collectively,
they are called ion thrusters due to the commonality of the
ionization of the propellant into a plasma. Ion thrusters are
classified as electrostatic, electrothermal, or electromagnetic.
Electrostatic thrusters primarily accelerate ions in the
direction of an established electric field. Electrothermal
thrusters heat the propellant to impart greater thermal energy
that is changed into thrust by focusing the propellant out of a
nozzle.
Electromagnetic thrusters accelerate ions by
electromagnetic fields [2].
The Hall-Effect thruster is an electrostatic ion thruster,
and the electrical propulsion system for its operation is
composed of five parts: the power source, the power
processing unit, the propellant management system, the
control computer, and of course, the Hall-Effect thruster
[10]. The power processing unit converts the electrical
power into the power needed for the operation of the HallEffect thruster. Contained in the thruster are powerful
electromagnets which trap electrons generated by an external
hollow cathode tube that are attracted to an internal anode.
The trapped electrons form a spiraling path towards the
anode known as a Hall current. Then Xenon gas, used as the
propellant, is injected into the thruster’s channel by the
propellant management system. The trapped electrons
collide with the atoms of the propellant and form ions. The
propellant ions accelerate out of the thruster creating the
thrust needed for propulsion [11]. Finally, the control
computer monitors and controls the performance of the HallEffect thruster system.
THE HALL-EFFECT THRUSTER
The Science Underlying the Creation of Thrust in a HallEffect Thruster
ELECTRIC PROPULSION TECHNOLOGY
Electric propulsion can be defined as the conversion of
electrical energy into thrust. The electrical energy used for
propulsion is usually generated from either a nuclear
powered or solar-powered source. A compact nuclear
reactor can generate thermal energy to be converted to the
necessary electrical energy through turbines, or arrays of
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FIGURE 1 [2]
Schematic of a Hall-Effect thruster
As an electrostatic form of electric propulsion, the HallEffect thruster derives its name from the Hall Current
established within the thruster. To understand the physics
behind it, Figure 1 provides a cross-section of a cylindrical
Hall-Effect thruster. First, the external hollow cathode
generates a dense plasma from a small amount of propellant,
(Xenon) by heating the gas. Electrons are emitted from the
cathode and establish a negative electric potential at the end
of the thruster. The electrons are attracted to the anode that
is at a positive electric potential in the innermost part of the
thruster. Then the electrons experience a force from right to
left caused by the electric field created because of the
difference in electric potentials given by the equation:
Where the thrust is a vector given in millinewtons with Ib as
the current flow of Xenon ions and Vb as the voltage
difference that created the electric field [2].
The Efficiency of Hall-Effect Thrusters
To produce thrust, an electric propulsion system must
generate ions to be expelled as exhaust. The electrical
energy input to receive the kinetic energy as thrust, the
specific impulse, and the factors that influence the lifetime
of a system all contribute to the efficiency of that system.
𝐹⃗𝑒 = 𝑞𝐸⃗⃗
Where q is the charge on an electron and E is the vector with
the direction and magnitude of the electric field.
As the electrons enter the thruster, they experience a
magnetic field from the electromagnets in the rim radially
inward to the other electromagnets in the center. Due to the
movement of electrons through this magnetic field, they also
experience a magnetic force by:
⃗⃗
𝐹⃗𝑒 = 𝑞𝑣⃗ × 𝐵
Where q is the charge on an electron, v is the velocity of an
electron and B is the vector with the direction and magnitude
of the magnetic field. The combined force on the electrons
can then be expressed as the Lorentz Force:
⃗⃗ )
𝐹⃗𝑒 = 𝑞(𝐸⃗⃗ + 𝑣⃗ × 𝐵
From the Lorentz force, the Hall Current is formed with
electrons moving in the azimuthal direction (spiraling)
towards the anode.
Near the anode, the propellant gas (Xenon) is released.
The Xenon atoms collide with the accelerating electrons and
become ionized. This produces positively charged Xenon
ions and more electrons [10].
𝑦𝑖𝑒𝑙𝑑𝑠
𝑋𝑒 + 𝑒 − →
𝑋𝑒 + + 2𝑒 −
The newly charged ions experience the same force
accelerating the electrons, except the force is in the opposite
direction. So the force exerted on the ions to accelerate out
of the thruster is equal to the thrust. A final equation for
thrust is given as:
⃗⃗ = 1.65𝐼𝑏 √𝑉𝑏 [𝑚𝑁]
𝑇
FIGURE 2 [2]
Table of efficiency values among several types of
propulsion
The table in Figure 2 provides a comparison of
parameters that are used to determine the efficiencies
between different forms of propulsion. From this data,
electric propulsion systems typically require up to 4.5
kilowatts of power to produce thrust and the specific
impulse, which is the amount of thrust per the weight flow.
Both the thrust and specific impulse increase as the system
uses more power. Electrostatic forms of electric propulsion
generally have greater efficiencies in the percentage of
kinetic energy produced per energy consumed. Electrostatic
forms also produce the greatest specific impulses as
compared to electrothermal and electromagnetic.
When comparing the types of electrostatic forms of
electric propulsion, ion thrusters can operate at higher
efficiencies and achieve greater specific impulses than those
of Hall-Effect thrusters. However, Hall thrusters produce
larger thrusts per power used than ion thrusters, and Hall
thrusters are simpler in design [2].
Hall thrusters have exhaust velocities that can range from
“10-50 kilometers per second and thrust from 40-600
millinewtons” [12]. To achieve thrust, the ions are expelled
at high velocities and the thruster must run for long periods.
However, speeds of up to 112,000 miles per hour can be
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attained when Hall thrusters operate for an extended time
[10]. A major obstacle for thruster lifetimes is the
degradation of the channel wall that separates the
electromagnets from the electric field. Two variations of
Hall-Effect thrusters exist and affect the lifetimes of the
thruster. The Stationary Plasma Thruster (SPT) and Thruster
with Anode Layer (TAL) are two types of Hall thrusters
[10].
In SPT Hall thrusters, the channel wall between the
electric field and electromagnets is composed of a dielectric
material. This material is vulnerable to sputtering, a process
by which electrons traveling towards the anode hit into the
channel wall and degrade it over time, reducing efficiency.
The TAL Hall thruster attempts to decrease the effects of
sputtering through the replacement of dielectric material
with metallic walls which may also change the magnetic
field. With metallic walls, the magnetic field constrains
electrons to a narrower path of travel so fewer electrons may
hit into the channel wall. This extends the operable lifetime
to the range of tens of thousands of hours [2].
Thus, chemical rockets are the current ideal option for
launching spacecraft [7].
On, the other hand, electric thrusters are ideal for other
scenarios. To begin, electric systems are very maneuverable
compared to chemical propulsion. Their propellant is
emitted in a low-thrust stream, so precise movement is
practical. This is especially useful for satellites, which are
often affected by disturbances in the gravity between the
sun, earth, and moon [7]. Finally, electric propulsion is
extremely efficient. This makes it the best option for deep
space exploration and inter-planetary transfers. Due to the
nature of the design of electric thrusters, they can achieve
much higher velocities than chemical thrusters with the same
amount of fuel. This relates back to the previouslymentioned specific impulses of the two types of propulsion.
With the same load, a Hall thruster could achieve about ten
times the speed compared to a monopropellant rocket [7].
APPLICATIONS OF HALL-EFFECT
THRUSTERS IN SATELLITES AND
SPACECRAFT
A Comparison between Electric and Chemical
Propulsion Systems
The Hall thruster must compete with chemical
propulsion systems in addition to the aforementioned forms
of electric propulsion. The fundamental principles by which
both forms of propulsion operate are similar: accelerate
particles in the opposite direction of where you want to go.
However, they function by performing that task very
differently. Because of this, each form of propulsion is
suited for different types of missions. Fundamentally,
electric and chemical propulsion systems differ in their
safety, specific impulse and thrust, maneuverability, and
efficiency [7].
First, electric propulsion systems are safer than chemical
systems. This is due to the fact that chemical rockets rely on
complex arrangements of pipes, valves, and precise control
mechanisms [7]. The risk of a component failing is quite
large in relation to an electric thruster. Ion propulsion
systems, like the Hall thruster, are relatively simple and do
not operate at such great pressures as chemical rockets.
Therefore, they tend to be a much safer option when they are
viable [7].
However, due to limitations in thrust capabilities, electric
propulsion cannot be used in every situation. Figure 2
provides that hall thrusters have a specific impulse of 15002000, while monopropellant has a specific impulse of 150225. These are measurements of the change in momentum
the same unit of fuel provides. While it appears that electric
propulsion should have a larger power output than chemical
rockets, this is deceiving. The thrust of electric systems is
much lower than that of chemical systems due to the
limitation on flow of fuel coming out of the thruster.
Because of this, electric thrusters cannot overcome the
earth’s gravity and atmosphere to put a rocket into orbit.
Satellite Station Keeping
Satellite station keeping and deep space travel are the
two main applications of electric propulsion systems with
Hall-Effect thrusters. Many aspects of our daily lives
depend on the continuous and reliable functioning of
satellites. When we watch television, make long distance
phone calls, or locate destinations using the navigation
systems in our cars, we benefit from satellite technology.
Satellites help meteorologists predict the weather, provide
communication and intelligence gathering services for the
military, and allow scientists to view the universe.
Communications, military, and weather satellites must
maintain their place in a geosynchronous orbit to properly
receive and transmit radio signals back to Earth. A satellite
in geosynchronous orbit matches the same speed as the
Earth’s rotation, enabling it to remain in the same spot
relative to a specific area on Earth. Atmospheric drag and
gravitational forces from the Earth, Sun, Moon, and Jupiter
can change the inclination of a satellite’s orbit. The orbit of
a satellite could also change if it collides with orbital debris
or another satellite [13]. To maintain the satellite in its
working position, Hall-Effect thrusters deliver very precise
“impulse bits.” An impulse bit is a small change in
momentum allowing for the fine attitude and orbit control of
a spacecraft [14]. The thrusters typically run for one hour
each day, delivering thrust in the range of 80-100
millinewtons to perform daily North-South and East-West
corrections [15]. The reliability of electrically propelled
satellites using Hall-Effect thrusters is evident in the fact that
these satellites operate consistently while remaining in orbit
for an average period of fifteen years.
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A Future Application: NASA’s Asteroid Redirect
Mission
The SMART-1 Mission
The European Space Agency’s SMART-1 mission was
the first mission using Hall-Effect thrusters outside of the
Earth’s orbit and was also the first European mission to the
moon. On September 27, 2003, the mission’s space probe
was launched on an Arian-5 rocket and used a solar electric
propulsion system with a PPS-1350 Hall-Effect thruster and
a supply of 82 kg of Xenon propellant. The thruster
produced a thrust of 70 millinewtons and a specific impulse
of 1600 seconds [16]. The spacecraft used its ion drive over
14 months to elongate its Earth orbit and was captured by
lunar orbit on November 13, 2004[16]. In addition to testing
the performance of the solar-powered ion drive, the
scientific objectives of the mission were to return data on the
geology and geochemistry of the Moon to help provide
information on how the Earth and Moon were formed and to
determine the presence of ice on the Moon. The mission
was extended from its originally planned six month time
frame by one year because of the successful operation of the
solar electric propulsion system. This extension allowed the
cameras on the space probe to complete a mapping of the
Moon’s surface. After operating for almost 5,000 hours, the
Xenon engine was shut down in September 2006 after
exhausting its fuel supply. At the end of its mission, the
SMART-1 space probe performed a controlled crash into the
Moon on September 3, 2006 [16]. The success of this
mission indicated that electric propulsion systems using
Hall-Effect thrusters were capable of deep space travel.
The Hall-Effect Thruster and the AEHF Satellite
The use of Hall-Effect thrusters played a critical role in
completing the transfer of an Air Force Advanced Extremely
High Frequency (AEHF) military communications satellite
from
geosynchronous
transfer
orbit
(GTO)
to
geosynchronous (GEO) when the satellite’s chemical
engines malfunctioned. On August 14, 2010, a two billion
dollar AEHF satellite was launched via a United Launch
Alliance Atlas 531 rocket [17]. The 13,420 pound satellite
was to be transferred from GTO to GEO using the satellite’s
main propulsion system, a hydrazine apogee engine. The
apogee engine failed due to a propellant line blockage and
hydrazine-fueled reaction engine assembly thrusters were
used to raise the satellite 3,000 miles in orbit [17]. To
complete the satellite’s final transfer to GEO it was
necessary to use the satellite’s Hall-Effect thrusters. The
thrusters, operating at approximately 0.05 pounds of thrust
over a period of a year propelled the satellite into its
assigned orbital slot in October 2001[17]. Even though the
orbital transfer took much longer using the Hall-Effect
thrusters, a two billion dollar satellite was saved due to the
reliable nature of the thruster’s technology.
An electric propulsion system powered by solar arrays
using multiple Hall-Effect thrusters is being developed to
power a robotic spacecraft for NASA’s Asteroid Redirect
Mission (ARM). The ARM will test new technologies that
will redirect asteroids that could collide with Earth and will
provide spaceflight experience needed for a manned mission
to Mars planned after 2030. Large, foldable 50 k-W-class
solar arrays will generate electric power for the propulsion
system consisting of four 10 k-W Hall-Effect thrusters. The
magnetically shielded thrusters will operate in parallel for a
specific impulse of 3,000 seconds. Twelve metric tons of
Xenon will supply the propellant for the thruster [18]. The
electrically propelled system will use ten times less
propellant than a comparable chemical propulsion system.
The first phase of the mission is scheduled to begin in
2020 when the robotic spacecraft will rendezvous with a
near-Earth asteroid and deploy robotic arms to capture a
piece of the asteroid. Through a technique called a gravity
tractor, the combined mass of the spacecraft and the piece of
asteroid exerts a slight gravitational force on the asteroid and
slowly pulls it into a stable lunar orbit. It will take
approximately six years for the ARM spacecraft to move the
asteroid into lunar orbit. The second phase involves the
launch of NASA’s Space Launch System rocket containing
the Orion spacecraft and two astronauts in the mid 2020’s.
Over the 25 day mission the crew will dock with the robotic
spacecraft and conduct spacewalks outside the Orion to
study and collect samples of the boulder [9].
Spacewalks are just one of the many capabilities to be
tested in preparation for a Mars mission. Before and after
docking with the robotic spacecraft the astronauts aboard the
Orion must use a complex set of maneuvers requiring a
critical lunar gravity assist burn. These maneuvers are
comparable to the Mars orbit insertion and departure burns.
Other maneuvers used to intercept the asteroid at a distance
with large time delays will allow the perfection of
techniques needed to transport cargo to Mars [19]. The
successful execution of this maneuver would demonstrate
the utility of solar electrically propelled spacecraft to
position cargo or vehicles for a manned mission to Mars.
ADVANCEMENTS IN HALL-EFFECT
THRUSTER TECHNOLOGY
For solar electrically propelled spacecraft to be able to be
used to travel as far as Mars, advancements must continue to
be researched, tested, and implemented to progress. HallEffect thrusters, as has been previously stated, are limited by
their thrust, efficiency, and lifetime. Several emerging
technologies may improve upon these areas.
Three
innovations in Hall-Effect thruster of nested thrusters, wall-
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less thrusters and magnetic shielding each improve the
effective operation of the thruster.
The first advancement in Hall-Effect thruster technology
is the Nested Hall-Effect thruster. Nested Hall-Effect
thrusters house multiple concentric channels for operation.
As the number of channels increases, the size and mass
increase of the nested thruster is significantly smaller than
multiple single thrusters or larger thrusters. Each channel
can be throttles individually, allowing for fine alterations
and greater efficiency in power consumption. Also, nested
thrusters are scalable so that high power inputs can lead to
much stronger thrusts a thousand times in magnitude
compared to that of standard thrusters [20].
A second advancement comes in the form of the Wallless Hall-Effect thruster. Wall-less thrusters move the area
of ionization and acceleration of ions outside of the thruster
to improve lifetime. While a traditional Hall-Effect thruster
is susceptible to electron sputtering, wall-less thrusters
effectively remove this issue by shifting the anode from the
innermost location of the thruster where the propellant is
emitted to the edge of the outer rim of the thruster. This also
moves the electric field, and, in response, the electrons reach
the anode to be neutralized before entering further into the
channel to deteriorate the wall through bombardment. A
tradeoff for this potential increase in lifetime comes at the
cost of thrust as the exhaust is weakly focused, leading to
inefficiency [21].
The third advancement is the application of Magnetic
Shielding to the Hall-Effect thruster. To try to prevent the
erosion of the channel walls and protect the magnets that
allow for the operation of the thruster, magnetic shielding
alters the shape of the outer rim of the thruster and the
magnetic fields. The magnetic fields are shifted so that
instead of being radial, they are extended from the outside to
curve inside to the center of the thruster in a way so that the
magnetic force on the particles will always direct charged
particles away from the channel walls. This greatly extends
the lifetime of the thruster without significantly affecting
performance [22].
THE ETHICAL IMPLICATIONS OF DEEP
SPACE TRAVEL
Physical and Psychological Consequences of Long Term
Space Flight
Recent advances in electric propulsion and Hall-Effect
thrusters are turning the possibility of manned space flight to
Mars into a reality. However the question exists of whether
astronauts can physically and psychologically tolerate
missions of long durations. A human mission to and from
Mars could last over 500 days, including six to nine months
of transit each way [19]. No astronaut or cosmonaut has
ever lived in space continuously for this amount of time.
The longest consecutive amount of days spent in space was
438 days by Valery Polyakov, a cosmonaut who served
aboard the Mir Space Station from 1923-1995 [23].
Presently American astronaut Scott Kelly has been living at
the International Space Station (ISS) for almost a year and is
scheduled to return home in early March 2016 [23].
The average stay for an astronaut aboard the ISS is six
months. During this time astronauts are exposed to certain
physical hazards and experience behavioral health issues.
Astronauts develop bone demineralization and problems
with their near vision due to microgravity. They also can
suffer from nausea and fatigue caused by acute radiation
exposure during a solar storm. Long term health issues such
as radiation-induced cancer and bone loss resulting in
fractures can occur months or even years after a flight [24].
To minimize bone loss, astronauts perform regular aerobic
and resistive exercises and take Vitamin D supplements.
Visual changes are corrected by wearing glasses or contact
lenses. Radiation levels are monitored through the ISS
sensors. When the levels are elevated the astronauts are
instructed to go to better shielded areas of the ISS.
The psychological health of an astronaut is impacted by
feelings of isolation, confinement, and being separated from
family and friends. In addition, a demanding workload and
lack of sleep undermines the ability to cope with these
feelings, resulting in stress, anxiety, irritability and fatigue
[24]. Interventions used to promote the behavioral health of
astronauts include weekly private two-way audio and video
conferences with their families and access to email and
Internet protocol telephones. Astronauts are also given
“time off” from their work schedule to relax. [25].
Maintaining connections with family decreases the sense of
isolation and scheduled time off gives the crew an
opportunity to rest.
Ethical Issues Related to the Health of Astronauts
The health issues experienced by astronauts in low Earth
orbit on the ISS have been well documented and
preventative measures and treatments for these issues have
been implemented. However, extended journeys may pose
unforeseeable risks and the current health standards in
practice may not adequately address these uncertainties.
Concerns about the safety of manned deep space missions
have been raised by the National Academy of Sciences, a
society of noted scholars, engineers, physicians, and
scientists who advise the federal government on scientific
and technical matters. The National Academy of Sciences
has created a set of ethics regarding health standards for
astronauts on long term missions as a guide for NASA to use
when planning deep space missions.
The six basic tenants of this ethical framework are:
avoiding harm, beneficence, a favorable balance of risk and
benefit, respect for autonomy, fairness, and fidelity [24].
NASA must identify and take action to minimize all known
and potential risks that may harm astronauts. The principle
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of beneficence should be the key determinant for the
justification of a mission. Questions that must be answered
are, “Does the mission have scientific and technical merit
and will it benefit the astronauts as well as society?”
Accordingly, the benefits of any mission should be greater
than the risks. Respect for autonomy addresses the rights of
the astronaut to decide if he or she wants to participate in a
mission based upon current information pertinent to the risks
and benefits of the proposed mission. The principle of
fairness encompasses the equal treatment of participants,
that burdens and benefits should be distributed fairly and
that fair practices be instituted and followed. Finally, the
principle of fidelity charges NASA with the responsibility of
providing lifetime health care for astronauts who face
serious hazards when serving on missions. This set of ethics
enforces the idea that the value of a human life must not be a
secondary concern, superseded by the scientific or
technological importance of a space mission.
HALL-EFFECT THRUSTERS: A WORK IN
PROGRESS
Due to their fuel efficiency and high specific impulse,
electric propulsion systems using Hall-Effect thrusters are
considered a reliable, cost-effective application in the
maintenance of station-keeping for satellites and a legitimate
option to power spacecraft on extended journeys through
space. Manned missions undertaken in space in the past
forty years have been restricted in duration and distance
because of the limitations of chemical rocket propulsion in
providing thrust for an extended period of time. Hall-Effect
thrusters achieve high rates of speed but accomplish this by
operating over a long period of time because of low thrust.
Space vehicles powered by electrical propulsion systems
using Hall-Effect thrusters must be launched into orbit
through chemically propelled rockets to escape the Earth’s
gravity, but once in space where drag does not exist, these
systems can attain velocities well over 100,000 miles per
hour. Engineers are currently working on improvements to
optimize the performance and life of Hall-Effect thrusters
that will power the unmanned spacecraft in NASA’s
Asteroid Redirect Mission in the next decade.
Advancements in the technology of electric propulsion
and Hall-Effect thrusters are ushering in the potential for
manned space travel to Mars, depending on its successful
operation during the Asteroid Redirect Mission. However,
the risks and benefits of sending astronauts into an
environment that has never been explored must be carefully
considered. The potential physical and psychological risks
that will impact crews on lengthy missions must be
addressed using an ethical framework that prioritizes the
health and safety of the astronauts before, during, and after
missions. Only after there is an equitable balance between
the risks and benefits of such a mission will manned deep
space travel be feasible and Robert Goddard’s vision of
using electric propulsion for interplanetary space travel be
realized.
REFERENCES
[1] D. Darling. (2016). “Electric Space Propulsion.”
Encyclopedia
of
Science.
(Online
article).
http://www.daviddarling.info/encyclopedia/E/electricprop.ht
ml
[2] D. Goebel, I. Katz. (2008). Fundamentals of Electric
Propulsion: Ion and Hall Thrusters. Hoboken, NJ: Wiley.
(Print book). pp. 1-442
[3] M. Patterson, J. Sovey. (2013). “History of Electric
Propulsion at NASA Glenn Research Center: 1956 to
Present.” Journal of Aerospace Engineering. (Online
article). DOI: 10.1061/ (ASCE) AS.1943-5525.0000304. pp.
300-316
[4] M. Meyer, L. Johnson, B. Palaszewski, et al. (2012,
April). “In-Space Propulsion Systems Roadmap.” NASA.
(Online
article).
http://www.nasa.gov/pdf/501329main_TA02-ID_rev3-NRCwTASR.pdf
[5] “Fact Sheet-SMART-1.” (2013, March 15). European
Space Agency Science & Technology. (Online article).
http://sci.esa.int/sciencee/www/object/printfriendly.cfm?fobjectid=47367
[6] “About Electric Propulsion.” (2015). Massachusetts
Institute of Technology Space Propulsion Laboratory.
(Online
article).
http://web.mit.edu/aeroastro/labs/spl/aboutElectricPropulsio
n.html
[7] “Electric Propulsion.” (2002, July). European Space
Agency.
(Online
article).
http://www.esa.int/esapub/br/br187/br187.pdf
[8] “Advanced Space Transportation Program Fact Sheet.”
(2008).
NASA.
(Online
article).
http://www.nasa.gov/centers/marshall/news/background/fact
s/astp.html
[9] “NASA Announces Next Steps on Journey to Mar:
Progress on Asteroid Initiative.” (2015, March 25). NASA.
(Online
article).
http://www.nasa.gov/press/2015/march/nasa-announcesnest-steps-on-journey-to mars-progress-on-asteroid-initiative
[10] “Overview of Hall Thrusters.” (2007, October 2). NASA
Glenn Research Center at Lewis Field. (Online article).
http://www.grc.nasa.gov/www/hall/overview-/overview.htm
[11] D. Darling. (2016). “Hall Effect Thruster.”
Encyclopedia
of
Science.
(Online
article).
http://www.daviddarling.info/encyclopedia/H/Halleffectthru
ster.html
[12] E. Choueiri. (2009, February). “New Dawn for Electric
Rockets.”
Scientific
American.
(Online
article).
http://www.uvm.edu/~wgibson/20/Choueiri.pdf
7
Ben Harper
Christian Marble
[13] H. Riebeek. (2009, September 4). “Catalog of Earth
Satellite
Orbits.”
NASA.
(Online
article).
http://earthobservatory.nasa.gov/Features/ObitsCatalog
[14] P. Erichsen. (2006, September). “Introduction to
Spacecraft Propulsion.” The University Centre in Svalbard,
Norway.
(Online
article).
http://fred.unis.no/AGF218/Handout_Erichsen_Propulsion.
pdf.
[15] M. Dudeck, F. Doviel, N. Arcis, S. Zurbach. (2011,
January 24). “Plasma Propulsion for Geostationary Satellites
and Interplanetary Spacecraft.” Romanian Journal of
Physics. (Online article).
http://www.nipne.ro/rjp/2011_56_Suppl/0003_0014.pdf
[16] “SMART-1.” (2006). NASA. (Online article).
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=200
3-043C
[17] “Busek’s Hall Effect Thruster Technology Saves Air
Force AEHF Satellite.” (2015, March 25). Busek Space and
Propulsion
Systems.
(Online
article).
http://www.busek.com/news_201203_aehf.htm
[18] “Asteroid Redirect Mission Reference Concept.”
(2015).
NASA.
(Online
article).
https://www.nasa.gov/pdf/756122main_Asteroid%20Redire
ct%20Mission%20Reference%20Concept%20Description.p
df
[19] E. Mahoney. (2014, June 27). “How Will NASA’s
Asteroid Redirect Mission Help Humans Reach Mars?”
NASA. (Online article). https://www.nasa.gov/content/howwill-nasa-asteroid-redirect-mission-help-humans-reach-mars
[20] R. Florenz, S. Hall, A. Gallimore, et al. (2013). “First
Firing of a 100-kW Nested-channel Hall Thruster.” The 33rd
International Electric Propulsion Conference, George
Washington
University.
(Online
article).
http://erps.spacegrant.org/uploads/images/images/iepc_articl
edownload_1988-2007/2013index/rle6tu40.pdf
[21] S. Mazouffre, S. Tsikata, J. Voudolon. (2014).
“Development and Experimental Characterization of a Wallless Hall Thruster.” Journal of Applied Physics. (Online
article). http://dx.doi.org/10.1063/1.4904965
[22] R. Hofer, D. Goebel, I. Mikellides, I. Katz. (2013).
“Magnetic Shielding of a Laboratory Hall Thruster. II.
Experiments.” Journal of Applied Physics. (Online article).
http://dx.doi.org/10.1063/1.4862314. pp. 1-13
[23] T. Watson. (2015, March 26). “Astronaut Set To Make
History For Longest Stay In Space.” USA Today. (Online
article).
http://www.usatoday.com/story/news/2015/03/25/astronautscott-kelly-space-voyage/70466704/
[24] J. Kahn, C. Liverman, M. McCoy. (2014). Health
Standards for Long Duration and Exploration Spaceflight:
Ethics
Principles,
Responsibilities,
and
Decision
Framework. The National Academies Press. (Ebook).
http://dx.doi.org/10.17226/18576
[25] “International Space Station Medical Monitoring.”
(2015,
August
5).
NASA.
(Online
article).
http://www.nasa.gov/mission_pages/station/research/experi
ments/1025.html#results
ADDITIONAL SOURCES
S. Anthony. (2012, December 28). “NASA’s ‘NEXT’ Ion
Drive Breaks World Record, Will Eventually Power
Interplanetary Missions.” ExtremeTech. (Online article).
http://www.extremetech.com/extreme/144296-nasas-nestion-drive-breaks-world-record-will-eventually-powerinterplanetary-missions
C. Ellzey. (2013, August 31). “How Do Hall Thrusters
Work?”
Engineering
TV.
(Online
video).
http://www.engineeringtv.com/video/How-do-HallThrusters-Work
“Frequently Asked Questions About Ion Propulsion.”
(2003). NASA Jet Propulsion Laboratory. (Online article).
http://nmp.jpl.nasa.gov/ds1/tech/ionpropfaq.html
ACKNOWLEDGMENTS
We would like express our thanks to our Engineering
Composition Writing Instructor, Professor Joshua Zelesnick,
our Section Chair, Professor Adam Balawejder, and our CoChair, Michelle Banas for their input and recommendations
on the writing of this paper.
8