Ion propulsion is an efficient form of spacecraft propulsion that can enable high-speed space travel using small amounts of propellant. It works by ionizing and accelerating propellant with electricity, allowing spacecraft to attain high velocities. Recent NASA missions like Dawn have demonstrated the advantages of ion propulsion, such as reaching high speeds while consuming minimal propellant. This makes ion propulsion potentially more cost-effective than traditional chemical propulsion for deep space missions.

1. Ion Propulsion: The Future of Space Travel
Jacob Benner, Augustana College
Abstract:
Chemical propulsion is typically the main type of propulsion used today. Recently however, ion propulsion technology has been implemented in space missions such as NASA’s Deep Space 1 and Dawn.
These missions, in particular the Dawn mission, have shed a great deal of light on the advantages of ion thruster systems. By using ionized propellant and sending it through a electrode grid, high
velocities can be attained with little propellant. This reduces the cost of the missions which makes ion propulsion an appealing new approach to space travel.
Introduction:
Since the space race of the 1950’s people have been
fascinated with space travel. Because of that, there have
been vast improvements in the field. Despite this there is
still a problem that gets in the way of going deeper into
space, time and distance. Increasing propulsion velocity is
the most effective way to travel deeper into space. Today
most propulsion systems are chemical based. The most
promising propulsion system however, is ion propulsion.
Ion propulsion offers a more efficient system and higher
velocities.
Conclusion:
• Ion propulsion is an efficient way of space travel
• Great velocities achievable
• High specific impulse
• Ion propulsion is cost effective
How Ion Propulsion works:
In a typical ion propulsion system electrons are
generated by the discharge cathode. The electrons flow
out of the cathode and are attracted to the chamber
walls. The walls are charged with a high positive
potential from the ship’s power supply. These electrons
then ionize the propellant (an inert gas, typically xenon)
by electron bombardment. These ions are then
accelerated using two electrodes (ion optics or grids).
There is an upstream grid and a downstream one. The
upstream grid is highly positively charged, whereas the
downstream grid is highly negatively charged. Since
these ions are highly positive they are accelerated
through the grid at high rates of speed. This creates a
stream of ion jets. Since the thrusters exhaust speed is
based on the voltage applied to the electrodes the speed
attainable is very high. Now, because the thruster expels
positive ions an equal amount of negative ions must be
expelled to keep the charge of the beam equal. Because
of this an extra cathode is added called the neutralizer
to release the extra ions.
*This process is seen in Figure 1 below
Figure 2: an ion thrusters operation. Photo courtesy of NASA
Specific Impulse (Isp):
Definition- thrust divided by weight of propellant
per unit time.
Specific impulse gives a effeciency of a propulsion
system. A higher specific impulse suggests a lower
mass of propellant, higher thrust or both. Therefore,
a higher specific impulse is desired. Figure 2 shows
the relationship between the specific impulse and
mass of the propellant for ion thrusters. This data is
assuming two ion thrusters producing a thrust of
25kN. The data shows how specific impulse can be
attained with little propellant showcasing the ion
propulsion systems efficiency.
NASA’s Dawn Spacecraft:
NASA is currently conducting a mission using ion thruster
technology. The spacecraft (Dawn) is expected to venture 3
billion miles to the asteroid Vesta and the dwarf planet Ceres.
Feats of the spacecraft include:
• Surpassing Deep Space 1’s all-time velocity record at 9,600
mph.
• Reached this velocity using only 165 kg of propellant.
• Over the course of the mission Dawn will reach a velocity of
24,000 mph.
• In a year of thruster operation the spacecraft will reach a
speed of 5,500 mph with only the equivalent of 16 gallons of
gas.
Figure 3: Propellant Mass versus Specific impulse. Graph shows three different points off
the earth. From 300km off earths surface more propellant is required to reach needed
Isp than from 2000km off earths surface and even more so from geosyncronous transfer
orbit (42,164km).
Graph courtesy of: “The impact of advanced platform and ion propulsion technologies
on small, low-cost interplanetary spacecraft”
Figure 1: velocity versus time for the Dawn space mission. The slow acceleration of
ion thrusters is evident.
Data from: “NASA Spacecraft Breaks Speed Boost Record”
Cost:
Ion thrusters are not only efficient but also cost effective. We
see this present in the Dawn mission. NASA says this about
the mission “The use of ion propulsion, combined with other
systems that have extensive flight heritage, allows a project
that can yield significant advances in planetary science at an
affordable price”. The affordability of these projects is a major
advantage of using ion propulsion systems.
References:
• Clark, Stephen D., and David G. Fearn. "The impact of advanced platform and ion propulsion
technologies on small, low-cost interplanetary spacecraft." Acta Astronautica 59.8-11 (2006):
899-910. Print.
• "Ion Propulsion." NASA. NASA, n.d. Web. 14 Mar.
2013.<http://www.nasa.gov/centers/glenn/about/fs21grc.html>.
• Chow, Denise. "NASA Spacecraft Breaks Speed Boost Record." Space. N.p., 11 June 2010. Web.
29 Apr. 2013. <http://www.space.com/8579-nasa-spacecraft-breaks-speed-boost-
record.html>.
• Marc, Rayman D., et al. "Dawn:A mission in development for exploration of main belt
asteroids Vesta and Ceres." Acta Astronautica 58 (2006): 605-15. Print.
• "Spacecraft Propulsion." Wikiipedia. N.p., n.d. Web. 6 May 2013.
<http://en.wikipedia.org/wiki/ Spacecraft_propulsion#Electromagnetic_propulsion>.
Engine
Effective
Exhaust
Velocity
(km/s)
Specific
Impulse
(s)
Fuel mass
(kg)
Energy
required
(GJ)
Energy
per kg
of
propellant
minimum
power/thr
ust
Power
generator
mass/thru
st*
Solid Rocket
1 100 190,000 95 500 kJ 0.5 kW/N N/A
Bipropellant
Rocket
5 500 8,200 103 12.6 MJ 2.5 kW/N N/A
Ion Thruster 50 5,000 620 775 1.25 GJ 25 kW/N 25 kg/N
Rocket propulsion vs. Ion Propulsion:
Chemical propulsion, also known as rocket propulsion, is the most
commonly used propulsion method. Below is a table comparing
rocket and ion propulsion in different categories. This data
assumes a mass of 10,000kg and a delta V of 3000m/s. It also
assumes a specific power of 1kW/kg. Ion propulsion has a great
exhaust velocity and specific impulse which are desired. It also has
the lowest fuel mass which means it is most efficient. The
downsides of ion propulsion rather than rocket propulsion is it
requires more energy, power, and mass.
Figure 4: comparison of different propulsion systems.
Table courtesy of: “Space Propulsion”