One of the best things about The Australian National University (ANU) Institute for Space is that we get to work with space experts from across ANU and the students who are becoming the next generation of space experts! This week Director Anna Moore asks Vivienne Wells, a fourth-year systems engineering student at ANU, about atmospheric effects of rocket launches.
Vivienne is interested in solar thermal energy and fuel production, agricultural technology, machine learning and signals processing. She is also the ACT representative for the Australian Youth Aerospace Association (AYAA). Here’s what she has to say about sustainable space research:
Making rocket launches more environmentally-friendly
As with any combustion reaction, rocket engines produce greenhouse gases. While the actual rocket launch only makes up a small proportion of the total pollution caused by transportation activities, the nature of launch can cause it to be more harmful than other methods of pollution. This is why it is of so much interest to researchers.
During a rocket launch, the rocket passes through every layer of the atmosphere. In the troposphere, nitrogen oxides and other ozone-depleting by-products of launch, as well as greenhouse gases are mixed in with the other gases to be cycled through the atmosphere. Higher up in the stratosphere, where mixing is not as prevalent, anything emitted during launch stays there for a long time. Depending on the type of fuel used, this can mean that deposited alumina and carbon soot can heat the stratosphere and cause further ozone depletion.
Launches are usually spaced out so that the ozone layer can regenerate before the next launch, but this will become less possible if the vision of regular commercial space flight is achieved. Luckily, scientists and space researchers are looking to tackle these challenges with many exciting possibilities that will help the global space industry move to sustainable launch technologies.
Hydrogen has a lot of potential for cleaner, renewable rocket launches
Most hydrogen is currently produced through natural gas reforming and coal gasification, which are fossil fuel-based sources. However, electrolysis of water has the potential to provide clean hydrogen, especially when combined with renewable electricity such as from solar photovoltaics. Whilst liquid hydrogen is the fuel of choice for the American space program due to its low molecular weight and high specific impulse, the need to store it cryogenically significantly increases the engineering complexity of using hydrogen as a fuel source.
With methane, it may be possible to close the circle of carbon emissions from rockets
Exciting work is also being done on reforming of methane for kerosene rocket fuel. Methane is a by-product of many human activities. It can be turned into synthesis gas – a mixture of hydrogen and carbon monoxide that can be used to make liquid hydrocarbons like highly refined kerosene, called RP-1, for rockets.
By using the methane produced from biomass (from humans or agricultural activities), there can be a virtually closed circle of carbon emissions from rockets. Kerosene produces carbon dioxide in the atmosphere which is absorbed by plants, eaten by animals and contributes to the production of methane, which can then be used to make kerosene again. The process of producing synthesis gas from methane must be done at high temperatures (around 700-900 degrees Celsius), but this can be done using solar energy in a concentrated solar plant.
This emerging technology isn’t quite scalable to commercial applications yet, but there is a lot of work being done to make it so.
Engineers are rising to the challenges of reusable rockets and more efficient engines
Fuels aren’t the only way to conserve resources. We can improve upon many aspects of rockets and their launches to make many areas of space flight more renewable.
Making rockets takes a lot of energy, but it can still be cheaper to launch new rockets every time. Now companies, most famously SpaceX, are looking at reusing rockets. This provides lots of challenges in terms of guaranteeing that the rocket is operational for subsequent launches. Each component of a rocket must be stripped down and examined for damage. However, it also means engineers are challenged to design more durable components that can withstand several trips into space.
Rocket engine efficiency is also the subject of a lot of research and development. Using staged combustion engines increases the efficiency of the fuel used and decreases the carbon emissions of the rocket. However, this is accompanied by higher levels of engineering complexity.
Great news for the future of space
Many of these fuel and engineering challenges are being considered in different ways in land-focussed industries. Today, unlike ten years ago, companies can use their land-based expertise to become part of the space industry in Australia and innovate for people on Earth and machines in the sky. And students who love space can think about their field of study in new ways and also focus on space research.
Studying what you love
For a long time, I felt torn between my two passions of sustainability and space, the two seemingly incompatible industries in Australia. The growth of the space sector in Australia has shown me how many fields overlap and are vital for the growth of each other. I feel so fortunate to be part of the first generation of Australians to have a chance to study what I love and use what I learn to work in the growing Australian space workforce.