Dr Amelia Greig – Plasma Physicist and Lead Researcher of Pocket Rocket

Dr Amelia Greig completed her Bachelor’s in Engineering/Science, Aerospace Engineering and Theoretical Physics in 2011 at University of Adelaide. With a keen passion for plasma physics and propulsion systems, Amelia completed her thesis work on the innovative PocketRocket design – an innovative thruster for Cubesats – at the Australian National University. She’s now pursuing further research in plasma physics at Caltech, and will soon be lecturing at California Polytechnic.

How do you make ideas happen?

I have always had the idealistic approach that if you want something done, you will find a way to do it somehow. I don’t know if I have a defined process to do that, because each case is different. But I guess my first step is usually to find someone to discuss my idea with; to make sure I am not missing something obvious. After that it’s usually a lot of background research, finding out who has done similar things before and where the new idea is different. In my work, experiments are usually always involved, sometimes simulations as well. Finally, these steps are iterated until eventually the end result is reached. Which may or may not be the same as the original idea as things often change along the way!

Can you briefly describe what the Pocket Rocket is and how it works?

The Australian designed Pocket Rocket thruster is an electrothermal plasma micro-thruster for use on micro-satellites like CubeSats. It consists of a small tube, through which an inert gas, argon for example, flows. Radio-frequency power coupled to the gas ionises a small number of the argon atoms, creating a weakly ionised plasma within the tube. Energetic ions within the plasma collide with the inert background gas and the thruster tube walls, creating propellant heating. The higher the temperature of the propellant gas the faster it exits the tube and the more thrust is produced.

What sets the Pocket Rocket apart from other micro-propulsion designs?

The simplest micro-propulsion system is the cold gas thruster, where an inert gas is expelled through a tube with no heating. Because the gas is cold, the thrust produced per mass of propellant is minimal, but the design is very simple and small. The addition of heat to the propellant in Pocket Rocket increases the thrust per mass of propellant over the cold gas thruster, also making it more complex.

Other electrothermal thrusters like Resistojets and Arcjets also use electrical means to heat the propellant gas to high temperatures, which require a lot of power (100s to 1000s of Watts compared to 10s of Watts). So although they will produce more thrust at higher temperatures, the power requirements limit how small of a satellite they can be installed on.

What does your typical day look like?

One of the best parts of being in research is that there isn’t really a typical day. The best kind of day is usually one spent in the lab playing around with the equipment and trying to discover something new. But the day could also be spent in front of a computer trying to get simulations to match the experimental data, or reading through copious amounts of interesting research from other groups. Travel also becomes a big part of life, it could be Australia one day and Russia the next. You definitely never get bored.

Since this was your PhD thesis work, you’re clearly very passionate about plasma physics and propulsion. What drove you to pursue this particular project?

Space exploration has always been a passion of mine, probably from all the Sci-Fi shows I watched with my Dad when I was younger. The propulsion side is interesting to me as it is a crucial component with so many options, and the engineering and design challenges are second to none. The natural progression of my studies led me to electric propulsion, which offers more fuel efficient methods for in-space propulsion. The Space Plasma, Power and Propulsion lab at the ANU, where I did my PhD and worked on the Pocket Rocket project, is a world leading lab in electric propulsion. When I started there, they showed me the Pocket Rocket thruster idea, which at the time was very new, and seemed very interesting. Turns out it is a very interesting project, so I am grateful to be involved.

 Why would a propulsion system be of benefit to CubeSats?

CubeSats offer a simpler, cheaper path into space for Universities and small companies. However, to date most (if not all) CubeSats are launched with no propulsion system on board, which means there is no way to boost the natural orbit decay that occurs. This limits the lifetime of CubeSat missions, as the orbit decays and the satellite burns up in the atmosphere within a year or so. Adding a propulsion system could periodically boost the orbit, increasing the satellite lifetime to decades. A propulsion system would also allow precision formation missions, where a constellation of CubeSats is flown in a specific pattern to cover a wider area.

What are the main challenges associated with designing and constructing propulsion system like this? Were there any particular challenges that you addressed within your thesis work?

Like any space technology development, one of the biggest challenges is creating the space environment within the laboratory. Vacuum chambers fitted with pumps that reduce the pressure inside the chamber to a millionth of a billionth of the standard atmospheric pressure on Earth provide a decent analog to the space environment for design and testing purposes. But this means that the device has to be completely enclosed within the vacuum chamber, and any probes used to analyse the device performance must also pass though into the vacuum chamber.

Has a prototype been built yet? How far off is the Pocket Rocket from being tested in space and what are the limitations there?

In recent years, development of Pocket Rocket has been supported in part by Lockheed Martin, working towards a on-Earth testing prototype. The biggest limitation is funding, as with all new space technology development. Testing on Earth is expensive enough, getting the resources and funds to launch a flight test prototype into space is even worse. Currently, the future development of Pocket Rocket is being done through the Pocket Rocket collective, led by Christine Charles and Rod Boswell at the Australian National University, and supported by researchers at York University in the UK, Stanford University and the California Polytechnic State University in the US, and Tohoku University in Japan.

One of the big draws for cubesats are their low-cost (relative to other space ventures) and use of “Commercial-Off-The-Shelf” components. Can you yet put a price tag or estimate on what a pocket rocket module for a cubesat might be?

The estimated cost of a Pocket Rocket module for CubeSats is not yet known. However, the thruster and all associated components (gas supply, power, etc) fit comfortably inside a single unit (1U) CubeSat. If it were to become available as a Commercial-Off-The-Shelf component, this would make it very easy, as the 1U Pocket Rocket module can simply be attached to the scientific payload containing CubeSat units, eliminating any need to redesign the satellite integration for each separate satellite.

You recently scored a postdoc position at Caltech; do you mind telling us a bit about what sort of work you’ll be getting up to there?

Since completing my PhD last July, I have been over at Caltech as a postdoctoral research scholar working in the Bellan Plasma Lab. While I am still in plasma physics, the work is a sidestep from propulsion, and instead I am working on plasma compression relating to the relatively new field of Magneto-inertial Fusion. Magneto-inertial Fusion is an intermediary between the well known Magnetic Confinement Fusion (the ITER Tokamak or the Wendelstein Stellarator for example), where a hot plasma is confined by magnetic fields while heated to achieve fusion, and Inertial Confinement Fusion where a high powered laser is used to compress a plasma to fusion temperatures and pressures. In Magneto-inertial fusion, a magnetically confined plasma is then compressed by a liquid metal liner or secondary plasma liner, potentially reaching fusion temperatures at lower cost and complexity.

The work at Caltech is very interesting, but I won’t be there much longer. This September I will be starting as an assistant professor at the California Polytechnic State University (Cal Poly), teaching courses in spacecraft propulsion and the space environment, and developing new and novel micro-propulsion ideas like Pocket Rocket.

What role have mentors played?

I have been lucky to have a number of fantastic mentors along the way so far. They have all given great guidance and helped me progress through to where I am by making me realise that if I want to do something, I can. The most influential would have to be Christine Charles from the ANU. She is an incredibly strong and intelligent woman who has fought hard to get to where she is (running a research lab doing world-leading research in plasma physics and electric propulsion!). I have often said that if I could be even half as successful as Christine then I would be happy. It’s a lot to live up to, but also gives me something to work towards.

(You can read our interview with Christine Charles on the QB50 project here!)

Who else do you think is doing really cool stuff in your industry, in Australia, at the moment? What about internationally?

The QB50 project is a great current project. It is a truly international project and involves engineers, academics, technicians, graduate students, even undergraduate students. Australia has three teams,  Adelaide University, University of New South Wales and a joint team between University of Sydney, UNSW and ANU. Although I am not directly involved with any of them at this point, I know many people involved in all three of the teams, and I am very excited about the prospect of seeing Australia back in space very soon.

The Advanced Instrumentation and Technology Centre (AITC) at the ANU is building up to become a very powerful facility both within Australia and internationally. It officially opened in 2014, and has facilities for the assembly, integration and test of space-based instruments and small satellites. The three Australian QB50 satellites were recently tested there, they are part of the Giant Magellan Telescope (GMT) team, are designing adaptive optics for space debris tracking and were part of the Antarctic Broadband project, just to name a few. There is always something interesting going on there.

3 websites (or books) you’d recommend to Ideas Hoist readers?

Wonderful Engineering 

Twitter – I follow a lot of the main aerospace organisations, both Governmental and private, innovative leaders (Elon Musk, Bob Richards, etc), and anyone else who seems interesting. Then you get a nice summary of what is going on that you can pick through as you like.

The Martian (book) – The movie is good, but the book goes into a lot more of the technical details.

Are you interested in commercialising Pocket Rocket? What would the end goal be after a successful flight test?

Commercialisation of Pocket Rocket would be amazing if it were to happen, but given the nature of micro-propulsion at the moment it is probably not a high priority goal right now. A successful flight test is the next major step to prove that the concept works and works well. After that there are a few more ideas with Pocket Rocket to continue working on, which I can’t say too much about sorry –  but Mars is involved!

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