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HDLT Inventors Get Their Thruster Off The Ground With New ESA Study

Helicon reactor in operation. Credits: LPTP, Ecole Polytechnique.
By Nick Merrett
Canberra, Australia (SPX) Jan 5, 2005
The significance of ESA's announcement late last year confirming their validation of the plasma double layer thruster was, in fact, predated by a more auspicious event- the testing of the Australian HDLT prototype in a space simulation chamber in ESTEC (Netherlands) in April 2005.

The new ESA study, performed as part of ESA's Ariadna academic research program, in association with Ecole Polytechnique, in 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.

"They were aiming to reproduce what we did, here, in Canberra, about six years ago in 1999, to validate the concept of the HDLT, to reproduce the current free electric double layer, which is a potential drop, or like a cliff-of-potential, in the plasma, which accelerates the ions", says Dr Christine Charles, inventor of the world's first Helicon Double Layer Thruster and project leader for HDLT at the Plasma Research Laboratory, Research School Of Physical Sciences & Engineering, at the Australian National University.

"In April 2005 we actually brought our own HDLT prototype, which is the first HDLT prototype ever built, which we mounted on the space simulation chamber at ESTEC, in the Netherlands", says Charles, "and we conducted all our tests of the prototype, like thermal properties, gas injection and radio frequency properties of the plasma etc".

"But we didn't measure the thrust because they didn't have the equipment yet - rather the experiments were aimed at measuring the ion beam which corresponds to these accelerated ions from the double layer - so that still needs to be measured on a proper thrust balance in a space simulation chamber, and we don't have this activity in Australia yet".

"But they're interested in having us back this year, says Rod Boswell, head of the Space Plasma ,Power and Propulsion group at the Australian National University. "What we're now trying to do is put together the funding so we can go back to ESTEC and do a proper thrust measurement".

"They have to move their space simulator chamber to a new building, so it's a bit of a transition", says Charles again, "so we have bought back the prototype to Australia, and we're trying to do some measurements of the beam, since you can calculate thrust from measuring the beam velocity and density. However, the proper, official measurement requires the thruster mounted on a thrust balance".

"But we're going to do that", says Boswell, "because we have a new PhD student who actually wants to do the engineering of the thruster, and we're setting up the thruster in a vacuum chamber, so thrust can be measured. We're going to further develop this thruster, here, in Australia, and then, hopefully, take it back across to Europe, and make detailed measurements with ESA this year".

Charles and Boswell, Peter Alexander and Orson Sutherland of the Australian Lab, were in Europe earlier last year (2005), for the five-week testing campaign, in April and May.

"The first thing ESA wanted to know was the verification - is it just an experiment that can be done in Australia? The important thing was to show that it could be done in another lab, and that has been done now, which is what the most recent press release from ESA has been involved with", says Boswell.

"Now that it has been shown that it will occur in other systems, the basic principle of the Helicon Double Layer Thruster has been proven, and we can move on to developing a stronger space-based thruster concept. So we're going to move through on that with our students".

"Now that they're happy that this double layer occurs, their simulation team can start simulating the HDLT thruster: how much power do you need to get that amount of thrust, what type of prototype would you need to have such-and-such mission, all the standard things they do", says Charles.

"It's the first new concept that's come along for some years", says Boswell. "It's very safe. If you want to go to Mars and come back (although some people are quite prepared to go to Mars, and not come back, he jokes), its useful to know that the system you're using is extremely reliable, that's its not going to kark it (Australian term for 'break down') when you're halfway there, or that you have to go out and screw a few more grids in. That is one of the major advantages of the HDLT- it is extremely reliable and simple".

The biggest drawback, currently, to the technology is its low thrust, says Charles. "We have quite a bit of room for improvement, because you have to see that its really early days. The research discovery was made in 1999, then we have the patent around 2001 and 2002, and then more research experiments, so it's a very slow process, but the recent experiments of the past few years have shown that there's a lot of room to improve the thruster".

"The important thing at this point is to look at the difference between a chemical thruster, which is ballistic, and our thruster, which is continuously on", says Boswell. "With a chemical thruster, it's like throwing a ball: you give it a huge impulse and then it follows a trajectory, but you can't change that. Whereas with the plasma thruster, the thrust is a million times less but its on all the time, so you can steer it as you move, and it gradually gets faster and faster and faster.

"The other thing is that, always, it's down. With a ballistic thruster it goes whoosh, bang, and then there's no gravity, but with our thruster there's always gravity- very small, but there's always down, and that is very comforting for people because you know stuff will always go down. Finally, if you allowed years to pass, the thing would get to the speed of light".

Based on calculations done by their colleagues in NASA for VASIMR (the Variable Specific Impulse Magnetoplasma Rocket project, its primary researcher being veteran shuttle astronaut Franklin Chang-Diaz) for a 10 Megawatt mission, Boswell estimates that humans could get to Mars in 3-4 months. "You'd have to leave Earth at the right time, spiral out, and then catch up with Mars as it was passing Earth, which happens once every eleven years; otherwise you'd have to chase it across the other side of the Sun, which will take you up to a year and a half". The simulation was done with a ten ton cargo ship adds Charles.

"What we have shown", says Charles, "is that this double layer effect works with argon, oxygen, hydrogen, xenon and pretty much everything; and we have to show that it works with CO2, because that's the Mars atmosphere. Hence the propellant could be xenon at the beginning from a terrestrial source and en route even human waste. The propellant could be what you find when you get there, or what you collect along the way".

"The final product of all systems is hydrogen", continues Boswell, "because, after all, oxidation reactions - which is where we get power- occur by forming covalent bonds, which is what burning is. Solid mass and urine, which is uric acid, is what the Space Station has trouble getting rid of tons of. They have a Russian system that presses this to get the water out of it, which is what people drink at the ISS. But then you have to get rid of it, and it's got a PH level of 1, which means it's fairly vicious. But in our system you could use that".

This concentrated product must be brought back to Earth, says Charles, since it's not allowed to be thrown into space, and costs a huge amount of money to correctly dispose of. "They're now thinking of ways to limit that, though."

The new ESA study has led Ecole Polytechnique to take out a patent on a promising new electric propulsion device called an Electronegative Plasma Thruster.

"Ecole Polytechnique have been working for a long time with ANU but have been using electronegative gases, like SF6, which forms negative ions and positive ions, and they're very interested in looking at the possibilities of using negative ions to provide a thruster concept- so the physics is completely different", says Boswell.

" We're doing the electropositive area, and they're doing the electronegative, so its not competition, but just the way its been sorted out. We're doing a lot of the computer simulations for their electronegative plasmas. We're working very closely on this. Their proof of concept showing the existence of an electronegative double layer has been shown to work very nicely, so we'll just wait to see if it can produce thrust".

" NASA have asked us to collaborate with them, because VASIMR's got a few different acceleration stages, and at the heart of their plasma rocket they use the helicon technology, which was patented by Australia's ANU a long time ago", says Charles. We help them with our expertise, and we have joint publications. It would be great if they could also have a double layer in the third stage (the magnetic nozzle), that would help their rocket".

"We are mostly scientists, so we're trying to push the science, and we're hoping that ESA or NASA will take it up at some stage, and anything that any scientist can do, will help the whole game".

"In Australia we have such limited funding that we can not just run any expensive experiment, so our experiment is reasonably cheap to run, and to duplicate if we want to, but VASIMR is really very big and costly just to run everyday, so that probably doesn't help them", continues Charles. "But they have very good equipment, very impressive; the development has been really good but maybe it just costs more to run".

With respect to funding in Australia for HDLT development, Charles says: "At the moment there's no funding but we had an absolutely excellent innovation grant from DEST (Department of Education, Science and Training), which is what allowed us to build the first HDLT prototype and to bring it to ESTEC, have the testing campaign, and bring it back. The grant was just for 18 months and it finished a few months ago. Unfortunately, we have nothing at the moment. So, now, we're trying to have students keep the research going, but for the development, you'd need some funding".

"But we're working with Auspace (a wholly owned subsidiary of EADS Astrium)", , on space related experiments, and with CRC Satellite Systems, and CSIRO, and that actually worked really wonderfully - the guys involved in that were terrific", says Boswell. The Cooperative Research Centre for Satellite Systems managed the whole project, but this Australian joint venture has since been dismantled.

"For the future, we're working with ESA on another contract which was a direct result of the HDLT, and in that contract we're using a lot of the technology which was developed during the earlier work we did with the HDLT, for use in deep space missions", says Boswell.

"This is a new contract that was negotiated at the end of our testing campaign at ESA in April, but you will hear a bit more about this in a few weeks time", Charles says.

"This HDLT validation project", for example, says Charles, "was part of the Ariadna program, and we just could not apply for it, because we're in Australia, and it was just for Europe, and it was very frustrating because that had a lot of financial advantages which could have kept us going for a year or two".

"The Rosetta antenna, for example", says Boswell, "that was put in New Norcia, Western Australia, was built by the Canadians, who are in ESA. They can actually bid in programs in ESA. Their entry level is $US20 million and if Australia had done that, then we could have bid for this Rosetta telemetry station, which cost $US25 million.

"We can do this, given that Australia has $AUD11 billion in surplus on the present budget. It's surprising we can't cough up $20 million to get into ESA because that then leverages a factor of three for Australian industry: forget about science- just for Australian industry to get into space, which is worth about $60-70 million, says Boswell.

"If we enter ESA, and put in $20 million, they guarantee 80% of that back, but there's a leverage factor because you can apply for other contracts that you previously weren't able to do, as the Canadians did to build this Rosetta deep space station in Western Australia".

"We could have done that. This is what is keeping us back from a lot of space exploration: the government's unwillingness to actually go into space and to make a small investment to help Australian industry in the long run".

Related Links
Plasma Research Laboratory
ANU - Research School of Physical Sciences and Engineering
Space Plasma ,Power and Propulsion Group
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ESA Accelerates Towards A New Space Thruster
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.

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