ESA Accelerates Towards A New Space Drive
Helicon reactor in operation. Credits: LPTP, Ecole
Polytechnique.
Paris (ESA) Dec 14, 2005
ESA has confirmed the principle of a new space thruster that may
ultimately give much more thrust than today's electric propulsion
techniques. The concept is an ingenious one, inspired by the
northern and southern aurorae, the glows in the sky that signal
increased solar activity.
"Essentially the concept exploits a natural phenomenon we see
taking place in space, says Dr Roger Walker of ESA's Advanced
Concepts Team.
"When the solar wind, a 'plasma' of electrified gas released by the
Sun, hits the magnetic field of the Earth, it creates a boundary
consisting of two plasma layers. Each layer has differing
electrical properties and this can accelerate some particles of the
solar wind across the boundary, causing them to collide with the
Earth's atmosphere and create the aurora."
In essence, a plasma double layer is the electrostatic equivalent
of a waterfall. Just as water molecules pick up energy as they fall
between the two different heights, so electrically charged
particles pick up energy as they travel through the layers of
different electrical properties.
Researchers Christine Charles and Rod Boswell at the Australian
National University in Canberra, first created plasma double layers
in their laboratory in 2003 and realised their accelerating
properties could enable new spacecraft thrusters. This led the
group to develop a prototype called the Helicon Double Layer
Thruster.
The new ESA study, performed as part of ESA's Ariadna academic
research programme in association with Ecole Polytechnique, Paris,
confirms the Australian findings by showing that under carefully
controlled conditions, the double layer could be formed and remains
stable, allowing the constant acceleration of charged particles in
a beam. The study also confirmed that stable double layers could be
created with different propellant gas mixtures.
"The collaboration has been absolutely excellent, says Dr Pascal
Chabert, of Laboratoire de Physique et Technologie des Plasmas,
Ecole Polytechnique. "It has been a real kick-off for me and has
given me lots of new ideas for plasma propulsion concepts to
investigate with the Advanced Concepts Team. The new direction for
our laboratory had led to a patent on a promising new electric
propulsion device called an Electronegative Plasma Thruster.
To create the double layer, Chabert and colleagues created a hollow
tube around which was wound a radio antenna. Argon gas was
continuously pumped into the tube and the antenna transmitted
helicoidal radio waves of 13 megahertz. This ionised the argon
creating a plasma.
A diverging magnetic field at the end of the tube then forced the
plasma leaving the pipe to expand. This allowed two different
plasmas to be formed, upstream within the tube and downstream, and
so the double layer was created at their boundary. This accelerated
further argon plasma from the tube into a supersonic beam, creating
thrust.
Calculations suggest that a helicon double layer thruster would
take up a little more space than the main electric thruster on
ESA's SMART-1 mission, yet it could potentially deliver many times
more thrust at higher powers of up to 100 kW whilst giving a
similar fuel efficiency.
In the next steps, ESA will now construct a detailed computer
simulation of the plasma in and around the thruster and use the
laboratory results to verify its accuracy, so that the in-space
performance can be fully assessed and larger high power
experimental thrusters can be investigated in the future.
http://www.spacedaily.com/news/rocketscience-05zzzb.html