Helicon double layer thruster
Department of Nuclear Physics and Accelerator Applications
The Helicon Double Layer Thruster (HDLT) is being developed in the Space Plasma, Power and Propulsion Group (led by Professor Christine Charles) at the Research School of Physics at The Australian National University in Canberra, Australia.
Dr Christine Charles has invented the world's first Helicon Double Layer Thruster or HDLT. This new propulsion concept has the potential to propel humans to Mars and beyond and greatly decrease the costs of maintaining satellites and spacecraft in their desired orbits.
What is a plasma?
Plasma is a 'fourth state of matter' in which many of the atoms or molecules are ionized. Plasmas have unique properties compared to the other states of matter i.e solids, liquids, and gases. Most plasmas can be thought of at first as extremely hot gases, but their properties are generally quite different.
Some examples of plasmas include the sun, fluorescent light bulbs and other gas-discharge tubes, very hot flames, much of interplanetary, interstellar, and intergalactic space, the earth's ionosphere and parts of the atmosphere around lightning discharges. Plasmas actually make up nearly 99 per cent of the matter in the universe but are extremely rare on Earth. One of the most spectacular examples of a plasma is the aurora. Known as the Aurora Australis or the Southern Lights this plasma forms as a result of interactions between the Earth's ionosphere and the solar wind.
What is a double layer?
Electric double layers are like cliffs of potential (like a riverwaterfall) and can energise charged particles falling through them. They exist in the plasma environment of the earth and the stars and can cause phenomena as diverse as aurorae, luminous draperies in the polar sky, and electromagnetic radiation from rotating neutron stars called pulsars .
We have discovered such a double layer in our laboratory plasma systems and measured the energy of the highly supersonic ions it has accelerated. The fascinating part is that the double layer is not triggered by forcing two plasmas (independantly generated by grids with separate potentials, much like a man-made dam) to interact, but self generates under certain parameters, much like the riverbed suddenly falling away to create a waterfall. We are optimising this effect to create a very efficient thruster for interplanetary spacecraft.
1. M.A. Raadu, 'The physics of double layers and their role in astrophysics', Physics reports 178, 25-97 (1989)
How does HDLT work?
Our laboratory is internationally recognised as the inventor and prime developer of the helicon source, arguably the most efficient plasma source available. Krypton (but eventually Xenon) gas is injected into a tube, called the source, that is open at one end and terminated at the other and is energised by a radio frequency antenna. Solenoids create an expanding magnetic field that is roughly uniform in the source tube but that expands very rapidly out into space until it is only a few gauss 20cm away from the source. The high density plasma formed in this way is restricted from exiting the source by a non-linear plasma effect known as a current free electric double layer that is located near the exit of the source tube.
This double layer can be thought of as a thin standing shock wave across which there exists a strong electric field gradient. It is this electric field that accelerates ions from the source plasma to very high exhaust velocities creating thrust. Because the double layer is purely the result of plasma density, system and magnetic field geometry, no accelerating grids are required. Also, because there is equal flux of electrons and positive ions from the thruster there is no need for a neutraliser. It is in this sense that the HDLT is a "true" plasma thruster as it ejects equal numbers of both positive ions and negative electrons.
Power is required only for the maintenance of plasma and the creation of the magnetic field. In our current bench top prototype, 250W is sufficient to create several milli-Newtons of thrust. In space the solenoids that generate the 250 Gauss of magnetic field this requires we estimate could be cooled to 200K, reducing the resistance in the coils by a factor of 5 and representing a power consumption of a few 10s of Watts. Relative to other existing systems this constitutes quite a power saving and is well with-in the capabilities of solar panels. The 0.5sccm of feed gas represents a mass consumption of 160 mg/hr, so that a typical 5 hour burn would use 0.8g of propellant.
Satellite station keeping
Though the HDLT has not yet flown in space, several current orbiting satellites use ion thrusters in the same fashion as is envisaged for the HDLT. In response to any change in a satellite's orbital plane an North South Station Keeping (NSSK) maneuver is engaged. For a satellite carrying ion thrusters, this is typically achieved by firing the NSSK thrusters twice a day for around 5 hours. As the satellite ascends through the Earth's equatorial plane on its inclined plane, the North thruster is fired for a period centered around this point of passage. Twelve hours later when the satellite this time descends through the equatorial plane, the South thruster is fired in the same manner and for the same duration. EWSK and attitude control is undertaken in a similar fashion.
In the future, it is increasingly likely that we will see plasma propulsion systems such as the HDLT flying on low earth orbit (LEO) satellites. It is envisaged that such thrusters would be used to transfer the satellites from their drop-off altitude to their operational orbit and maintain proper station keeping. At the end of their useful lifetimes, the plasma thrusters would be used to deorbit the satellites in a controlled fashion so that they burn up harmlessly in the atmosphere.
Artificial satellite's have enabled many scientific advances, but Humanity's imagination has not been satisfied to dwell on the Earth and its very close orbital neighbourhood. Many satellites have been deployed on interplanetary missions and humans have traveled as far as the moon. Though the moon landing is arguably Humanity's greatest engineering achievement, the moon itself has represented the boundary of practical manned missions into the solar system using conventional chemical rockets. The shear quantity of propellant and incredible time scale required to reach even our closest planetary neighbour, Mars, with traditional space technologies has to this day made the dream of crossing interplanetary space prohibitively costly both in financial terms and in potential risk to would-be human travelers. If chemical propulsion is capable of great thrust (on the order of several Mega-Newtons) it also has very low specific impulse a measure of the propellant burn rate efficiency. Maximum velocity is also restricted by low specific impulse making transit time too long for any practical mission with a human payload. If effective manned missions are to be mounted to breach the distance of interplanetary space, a faster and more efficient mode of transport is required. Plasma propulsion can achieve these goals.
It is for the purpose of interplanetary missions that NASA has sought to collaborate with our laboratory. In particular we are currently active with Astronaut F. Chang-Diaz's VASIMR group in the Advanced Space Propulsion Laboratory at Johnson Space Center, Houston. We envisage that the high performance and low risk design of the HDLT will make it a viable candidate for future manned missions to Mars.
The Plasma Research Laboratory at the Australian National University (Australia), the Cooperative Research Center for Satellite Systems and Auspace are also collaborating with the Propulsion and Aerothermodynamics Division at the European Space Agency (ESTEC Holland) on the development and testing of the HDLT prototype. This joint research program is funded by the DEST innovation access grant in Australia.
- Cooperative Research Centre for Satellite Systems
- ESTEC - The European Space Agency's European Space Research & Technology Centre, Holland
- ESTEC EPL - ESTEC's Electric Propulsion Laboratory
- ESA's ACT - ESA's Advanced Concepts Team
- LPTP - Laboratoire de Physique et Technologie des Plasmas (LPTP), Ecole Polytechnique, France
- Advanced Space Propulsion Laboratory at NASA's Johnson Space Centre, Houston
Archive of magazine articles, newspaper and radio reports, online interviews and the like in the local, national and international media regarding the development of the Helicon Double Layer Thruster.
- Revolutionary Thruster Set For Space Launch - ANU Media Release - Apr 22 2009
- ESA accelerates towards a new space thruster - European Space Agency Media Release - Dec 13 2005
- Electric Double Layer is Secret Behind Revolutionary Space Thruster (PDF, 80KB)- ANU Research Highlights Article - 2004
- Australian Space Engine for Satellite Trial - Cooperative Research Centre Association Media Release - Mar 16 2004
- ANU Thruster could take man to Mars - ANU Media Release - Jan 27 2004
- Electric Double Layer is Secret Behind Revolutionary Space Thruster (PDF, 1.2MB)- ANU Research Highlights Poster - 2004
Online newspaper articles
- Aussie hardware thrusts in to space - Technology and Business - April 24 2009
- Aust-made plasma thruster faces space test - ABC News Online - April 22 2009
- Plasma thruster tested for Mars mission - PhysOrg.com- Jan 03 2006
- Australia develops power for inter-planetary travels - The National Business Review, New Zealand - Dec 29 2005
- ESA trials Australian plasma thruster - ABC Regional Online - Dec 29 2005
- Space agency to do more Aussie tests - ninemsn.com - Dec 28 2005
- Space agency to do more Aussie tests - Sydney Morning Herald - Dec 28 2005
- Look Out, Stars, Here We Come - Plasma Engine Passes Test - Free Internet Press - Dec 15 2005
- Here's how space travel can get faster - Daily News & Analysis, India - Dec 15 2005
- New Plasma Thruster Promises Faster Spacecraft - Science a Gogo - Dec 14 2005
- ESA Accelerates Towards A New Space Thruster - Science Daily - Dec 14 2005
- Plasma engine passes initial test - BBC News, UK - Dec 14 2005
- Plasma Engine Could Open Up Space Exploration - Universe Today - Dec 13 2005
- ESA accelerates towards a new space thruster - Innovations Report, Germany - Dec 13 2005
- ANU Space Work's Big Thrust - Canberra Times - Jul 22 2004
- ANU Could Make US Mars Wish Come True - Embassy of Australia in the US - Current News Section - Feb 2004
- Space thrust - The Bulletin - Cutting Edge Developments Section - Feb 04 2004
- ANU thruster attracts attention - The Australian - IT Section - Feb 03 2004
- Thrusters promise a fast trip to Mars - ABC Science News - Jan 30 2004
- Researchers create new plasma thruster - The Universe Today - Jan 29 2004
- Deep space drive: ANU team developing interplanetary engine - The Canberra Times - Jul 1 2003
- Rocket Scientist Has Sights Set On Mars - ANU ScienceWise - Oct 13 2008
- Perfecting Plasma Power - ANU Reporter - Autumn 2004
- Electric Double Layer is Secret Behind Revolutionary Space Thruster (PDF, 100kB) - RSPhysSE Research Highlights - Aug 2004
- Thruster makes waves (PDF, 300kB) - ANU ScienceWise Article - April Edition 2004 (See page 4)
- Our new engine key to Space exploration? - ScienceNews Western Australia - National News Section - Mar 2004
- Plasma thruster could be ticket to Mars - LabOnline.com.au - Latest News Section - Feb 2004
- Electric Double Layer is Secret Behind Revolutionary Space Thruster (PDF, 1.4 MB)- RSPhysSE Annual Report 2003 - Research Highlights (Page 10)
- Charge to the stars - The Engineer - UK Engineering Industry publication - Jul 11 2003
- ANU helps drive Mars missions (PDF, 1.1 MB) - ANU Reporter Article - Volume 34 No. 3 2003 (See page 11)
- ANU's plasma thrusters could be ticket to Mars (PDF, 0.3 MB) - PriceWaterhouseCoopers TECH Watch - Volume 12 No. 30 - Jul 31 2002 (See page 2)
- To Mars and Beyond: The Australian Plasma Thruster (PDF, 1.9 MB) - The Physicist - Volume 39 No. 6 - Nov/Dec 2002
- Plasma-powered rockets (JPEG, 250kB) - CSIRO's The Helix- 2002
- ANU thrusts back into space race (PDF, 2.5MB) - The Canberra Times - Apr 23 2009
- Mars in our grasp (JPEG, 260kB) - The City Chronicle - Feb 03 2004
- ANU thruster attracts attention (JPEG, 150kB) - The Australian - IT Section - Feb 03 2004
- Space travel makes astronauts environmentally aware (JPEG, 290kB) - The Canberra Times - Aug 19 2003
- Deep space drive: ANU team developing interplanetary engine (JPEG, 150kB) - The Canberra Times - Jul 1 2003
- Plasma Thruster Prototype - Universe Today - Includes mp3 download and transcript of interview with Dr Christine Charles - Dec 22 2002
- Space Travel & the Plasma Thruster Project - The World Today - ABC Local Radio - Transcript of interview with Prof Rod Boswell - Jun 18 2002
- Getting off the Planet - The Science Show - Transcript of interview with Prof Rod Boswell - May 18 2002
- ABC's CATALYST - Feature on Helicon Double Layer Thruster Development - August 2 2007
- A follow up story on the progress made in the development of the Helicon Double Layer Thruster (HDLT) featured on ABC's Catalyst Program on Thursday, 2nd of August @ 8pm. For the transcript of the segment visit the story archive of Catalyst. ABC 2 TV's SKYWATCH - The Helicon Double Layer Thruster - March 5 2007
- The Helicon Double Layer Thruster recently featured in a segment on SkyWatch which aired on ABC 2 TV's AustraliaWide program. The segment aired on Monday March 5 and includes an interview with Dr Christine Charles and PhD student, Michael West and footage of the Helicon Double Layer Thruster operating inside a new space simulation vacuum facility. The segment can be viewed online at ABC 2's website. ABC's CATALYST - Feature on Double Layer Discovery & HDLT - August 26 2004
- The story of the helicon double-layer discovery and the development of the helicon double-layer plasma thruster (HDLT) featured on ABC's Catalyst Program on Thursday, 26th of August @ 8pm. For the transcript and streamed video of the segment visit the story archive of Catalyst.
- CANBERRA ABC TV State Television News - 7.17pm Jul 2 2003 ANU researchers from the Plasma Research Laboratory have claimed a breakthrough in space propulsion systems this week, creating a rocket that runs on hydrogen. Dr Christine Charles (the discoverer of the helicon double-layer thruster) believes that a prototype could be developed in a few years. Professor Rod Boswell says it works through charged ions. Interview with Orson Sutherland who says viability depends on making space travel fast.
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