Will This Be How Mankind Reaches Mars?
The European Space
Agency, in conjunction with the Australian National University,
announced Thursday the two entities have successfully tested a new
design of spacecraft ion engine that dramatically improves
performance over present thrusters -- and could potentially mark a
major step forward in space propulsion capability.
The new experimental engine, called the Dual-Stage 4-Grid (DS4G)
ion thruster, was designed and built under a contract with ESA in
the extremely short time of four months by a dedicated team at the
Australian National University.
Ion engines are a form of electric propulsion. Instead of
chemical combustion, ion engines work by accelerating a beam of
positively charged particles -- ions -- away from the spacecraft
using an electric field.
The technology isn't new. As was reported in Aero-News,
NASA has had success with versions of the ion engine, and ESA is
currently using electric propulsion on its SMART-1 Moon
mission.
However, the new engine is over ten times more fuel efficient
than the one used on SMART-1, according to ESA.
"Using a similar amount of propellant as SMART-1, with the right
power supply, a future spacecraft using our new engine design
wouldn’t just reach the Moon, it would be able to leave the
Solar System entirely," said Dr. Roger Walker of ESA’s
Advanced Concepts Team, Research Fellow in Advanced Propulsion and
Technical Manager of the project.
Traditional ion engines use three closely separated perforated
grids containing thousands of millimeter-sized holes attached to a
chamber containing a reservoir of the charged particles. The first
grid has thousands of volts applied, and the second grid operates
at low voltage. The voltage difference over the gap between the two
grids creates an electric field that acts to simultaneously extract
and accelerate the ions out of the chamber and into space in a
single step. The higher the voltage difference, the faster the ions
are expelled and the greater the fuel efficiency of the thruster --
but if the voltage gets too high (5,000 volts) some ions collide
inside the engine itself, causing the grid to erode.
The DS4G ion engine utilizes a different concept first proposed
in 2001 by David Fearn, a pioneer of ion propulsion in the UK,
which solves this limitation by performing a two-stage process to
decouple the extraction and acceleration of ions using four grids.
In the first stage, the first two grids are closely spaced and both
are operated at very high voltage and a low voltage difference
between the two (3 kV) enables the ions to be safely extracted from
the chamber without hitting the grids. Then, in the second stage,
two more grids are positioned at a greater distance
‘downstream’ and operated at low voltages. The high
voltage difference between the two pairs of grids powerfully
accelerates the extracted ions.
"The success of the DS4G prototype shows what can be achieved
with the passion and drive of a capable and committed team. It was
an incredible experience to work with ESA to transform such an
elegant idea into a record-breaking reality," says Dr. Orson
Sutherland, the engine’s designer and head of the development
team at the ANU.
During November 2005, the DS4G engine was tested for the first
time in ESA’s Electric Propulsion Laboratory at ESTEC in the
Netherlands, with support from Dr Sutherland and ESA test
engineers. The test model achieved voltage differences as high as
30kV, and produced an ion exhaust plume that travelled at 210,000
m/s, over four times faster than state-of-the-art ion engine
designs achieve.
This makes it four times more fuel efficient, and also enables
an engine design which is many times more compact than present
thrusters -- allowing the design to be scaled up in size to operate
at high power and thrust. Due to the very high acceleration, the
ion exhaust plume was very narrow, diverging by only 3 degrees --
five times narrower than present systems -- thereby reducing the
fuel needed to correct the orientation of spacecraft from small
uncertainties in the thrust direction.
Of course, there is still a great deal of work to be done before
the new engine design can fly in space.
"Working with our industrial partners, the next challenge is to
transition this promising new engine design from laboratory
experiment to spacecraft flight model and properly define the new
missions that it will enable", said José Gonzalez del Amo,
Head of Electric Propulsion at ESA.
The flight-suitable engines must then be tested -- and for ion
engines, this is a long process. Since they must operate
continuously in space for tens of thousands of hours providing a
small thrust, ground tests in a vacuum facility must last several
thousand hours to prove their reliability. Only after all this
could the first flight models be launched.
It may be well in the
future, but scientists are already envisioning ion-engine-propelled
trips to the outermost planets, the newly discovered planetoids
beyond Pluto and even further, into the unknown realm of
interstellar space beyond the Solar System.
"This is an ultra-ion engine. It has exceeded the current crop
by many times and opens up a whole new frontier of exploration
possibilities," said Dr. Walker.
Closer to home, these supercharged ion engines could figure
prominently in the human exploration of space. With an adequate
supply of electrical power, a small cluster of larger, high power
versions of the new engine design would provide enough thrust to
propel a crewed spacecraft to Mars and back.