Figure 1: Illustration of a possible methane production system on Mars (Source)
For centuries, kerosene (RP-1) and liquid hydrogen were the most popular rocket fuel used by aerospace industries. For instance, Saturn V, the first rocket to send mankind to the moon, used both kerosene and liquid hydrogen. Hydrogen burns more efficiently than kerosene but takes up too much space. Kerosene, while it burns less efficiently, offers benefits in storage inside the rocket. But, there is also another type of rocket fuel, methane. Methane was in an awkward position between kerosene and hydrogen gas. Methane does not burn as efficiently as hydrogen gas, and it is not as space efficient as kerosene. Therefore, for many years, scientists have dismissed the use of methane as a rocket fuel. However, recently, SpaceX, a spacecraft manufacturer aiming to send humans on space adventures, decided to use methane for its Starship’s Raptor rocket engines.
So why are SpaceX engineers suddenly using methane?
Methane excels at accomplishing SpaceX’s vision of reusable rockets. While kerosene is a hydrocarbon composed of a long carbon chain, methane is a hydrocarbon with one single carbon and four hydrogen atoms. Long carbon chains are more difficult to burn completely; therefore, long carbon chains decompose into smaller reactive radicals. The decomposition of long carbon chains results in coking, the production of soot. Carbon soot damages the engine over time by clogging its flow passage. Conversely, methane produces significantly less soot than kerosene, requiring fewer maintenance checks for the rocket engine. In addition, hydrogen weakens and degrades metals due to hydrogen embrittlement, a process where a metal becomes brittle over time as a result of hydrogen diffusing into the metal. This would be a major flaw in SpaceX’s vision of long-term reusable rockets.
However, the most important reason SpaceX finds methane attractive is that it can be extracted from the rich CO2 atmosphere of Mars. Mars’ atmosphere is 95% carbon dioxide—though this may not be very promising for sustaining life on Mars, it has an enormous potential to support the production of methane. Thus, SpaceX has planned a self-sustainable method to produce methane on Mars. By utilizing solar energy generators to create electricity for the electrolysis of carbon dioxide and water, future astronauts can synthesize methane. Both the two necessary reactants, carbon dioxide and hydrogen gas, can be self-sufficiently synthesized on Mars without constant supply from Earth. Scientists can extract CO2 from the atmosphere into pure solid carbon dioxide through cryofreezing, a method of freezing materials at low temperatures. It would be easy to filter out CO2 as it has the highest freezing point among the gasses that make up Mars’ atmosphere. This property of carbon dioxide will allow scientists to separate carbon dioxide from the air as a solid Furthermore, the electrolysis of water collected from Mars’ polar ice caps (2H2O → 2H2 + O2) converts water into oxygen and hydrogen gas. Finally, the extracted hydrogen gas and carbon dioxide will be used to perform the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O) to create methane. Another benefit of methane is that it requires little complex equipment to store and synthesize. For example, methane is pressurized through autogenous pressurization, a process of using the rocket’s own gaseous propellant to pressurize itself. Adding on, the boiling point of liquid methane (-162℃) is close to that of liquid oxygen (-183℃), enabling much of the infrastructure used to liquify and store oxygen to also be used to store methane. These special features of methane provide unique benefits that were not required in previous space programs but perfectly fit SpaceX’s goal of reusable rockets and space travel to Mars.
But how is any of this important to us? As mentioned before, methane synthesis involves capturing CO2 from the atmosphere. Currently, Earth is suffering from the increase in CO2 levels, which plays a big role in global warming and climate change. By utilizing CO2 in the atmosphere, we could potentially reduce the levels of CO2 and mitigate the effects of climate change. Although further development of an efficient method to capture CO2 is required, collecting CO2 to synthesize methane fuel could offer us a method of storing reusable energy and a solution to climate change.
Q & A:
Anna: [Regarding your first paragraph] You mentioned that many scientists have disregarded methane. Why is that so when methane is much easier to store than hydrogen and burns more efficiently than kerosene? Why use kerosene if it doesn’t work as efficiently as methane? Why use hydrogen if it’s not easier to store than methane?
Many engineers preferred the efficient hydrogen gas that allowed the rocket to produce the necessary thrust and kerosine fuel for its minimal fuel tank volume. Meanwhile, methane did not provide much benefits in terms of fuel efficiency or minimal fuel tank volume. Engineers would rather use hydrogen fuel for its fuel efficiency and kerosine for its easier storage. However, methanes unique properties have finally become useful for SpaceX’s mission for a reusable rocket for a trip to Mars. Previously, organizations like NASA built their rockets without such consideration, and therefore did not need the unique benefits of methane. On the other hand, SpaceX will prefer a rocket fuel like methane as it causes less damage to its engines in comparison to hydrogen and kerosine fuel, supporting its ethos of reusable rockets. Moreover, methane could be synthesized on Mars, unlike the two other fuels, which require complex equipments and specific resources on Earth.
Jennah: Is reducing levels of carbon dioxide solely beneficial for us? Are there any potential drawbacks to getting rid of the carbon dioxide from our atmosphere at such a rapid rate (reduction rate assumed according to the article)?
Currently, we lack the technology to efficiently remove carbon dioxide from our atmosphere. According to vox.com, “The IPCC’s low-end estimate for the amount of carbon capture we need by 2100 is 100 gigatons. So we would need more than 800,000 times our current annual direct air capture capacity by 2100 if we’re going to rely on this method alone to limit warming to 1.5 degrees Celsius.” Therefore, it is highly unlikely that our current carbon capture system can reduce carbon dioxide levels at such a rapid rate to cause damage to our environment. However, removing carbon dioxide from our atmosphere at rapid rates, if it were possible, could be dangerous. Firstly, carbon dioxide is an important greenhouse gas that helps Earth trap heat, allowing Earth to maintain an optimal temperature for life on Earth. Moreover, carbon dioxide plays an important role in the carbon cycle, a process that allows our environment to recycle carbon atoms. For example, photosynthesis is a biological process where photosynthetic organisms use carbon dioxide to produce carbohydrates, an important source of energy for photosynthetic organisms. In conclusion, taking away carbon dioxide from our atmosphere at a rapid rate could be harmful to our environment, but our current technology is not capable of capturing carbon dioxide at such rates.
Hannah: One of the causes of climate change is the excess carbon dioxide in our atmosphere. If the Sabatier reaction consumes a lot of carbon dioxide, ideally, isn’t this process beneficial for the environment? Are there negative effects of this process that is harmful to the environment?
Yes, one of the leading causes of climate change is the excess carbon dioxide in our atmosphere. Therefore, performing the Sabatier reaction using the carbon dioxide collected from our atmosphere could be beneficial to our environment. However, removing carbon dioxide in great quantities can have its drawbacks. Carbon dioxide is an important greenhouse that helps Earth trap heat to keep our planet warm. Furthermore, carbon dioxide plays a key role in the carbon cycle, a process that allows Earth to reuse its carbon atoms. For example, photosynthesis is an important step in the carbon cycle. It is the biological process of utilizing carbon dioxide to create carbohydrates, an important source of energy for the photosynthetic organism.
David: So far your article explains the plan of SpaceX and their reasoning for planning to use methane. Did SpaceX make any advancements currently to achieve this plan of using methane? For example, did they build equipment to conduct cryofreezing?
Unfortunately, SpaceX has not announced any advancements in their plan of creating methane fuel on Mars. On December 14th 2021, Elon Musk tweeted that SpaceX is starting a program to take out CO2 from the atmosphere and turn it into rocket fuel. Furthermore, Elon Musk has created a $100 million competition for carbon dioxide removal. However, there is no further insight of progress SpaceX’s progress on achieving their plan of creating methane fuel on Mars. The idea of carbon capture to create methane fuel is a very complex concept and would require more time and effort for a suitable solution.
Fabian: Are there any other aerospace companies that are following SpaceX’s footsteps? How will this decision impact the overall aerospace industry?
Blue Origin’s BE-4 rocket engines also use methane as their rocket fuel. While SpaceX mostly focuses on sending humans on space, Blue Origin’s mission it to send humans to live and work in space in order to conserve resources on Earth. Despite SpaceX and Blue Origin having varying goals, the two aerospace companies can greatly benefit from being competitors. The competition would encourage both companies to compete in developing better rockets, which will allow for faster developments of rockets powered by methane fuel.
John: How exactly does SpaceX’s sustainable method on Mars help us on Earth? Could you provide a better connection between the two planets?
The atmosphere of Mars and that of Earth is very different. While Earth’s atmosphere is 0.1% carbon dioxide, Mars’ atmosphere is 95% carbon dioxide. However, developing a method to capture carbon dioxide from the atmosphere benefits both space travel to Mars and solving climate change. Increasing levels of carbon dioxide in our atmosphere are the largest contributor to climate change. By developing a method to capture CO2 from Mars’ atmosphere and create methane gas on Mars, scientists can utilize this technology on Earth to reduce CO2 levels in order to mitigate the effects of climate change.
Melissa: What are some detailed plans that SpaceX announced about their project?
SpaceX has set a goal to send a human to Mars by 2029. However, there is still a long way to go for a trip to Mars. Recently, SpaceX has been testing its new Raptor 2 methane-fueled rockets and Starships, a reusable spaceship that SpaceX aims to use for future space travels. Elon Musk has announced that the Starship orbital test flight will take around August if everything goes according to plan. If the orbital test flight goes well, SpaceX plans to send humans to the Moon and cargo to Mars. If all of those flights are successful, SpaceX hopes to send humans to Mars.
Works Cited
Anzlowar, Ian. “Making Methane on Mars.” University of California, University of California, 7 Jan. 2021, https://www.universityofcalifornia.edu/news/making-methane-mars.
Gohd, Chelsea. “Future Astronauts Could Make Methane Rocket Fuel on Mars.” Space.com, Space, 8 Jan. 2021, https://www.space.com/future-astronauts-methane-rocket-fuel-mars.
Irfan, Umair. “Sucking CO2 out of the Atmosphere, Explained.” Vox, Vox, 24 Oct. 2018, https://www.vox.com/energy-and-environment/2018/10/24/18001538/climate-change-co2-removal-negative-emissions-cdr-carbon-dioxide.
Mohon, Lee. “NASA Tests Methane Engine Components for next Generation Landers.” NASA, NASA, 28 Oct. 2015, https://www.nasa.gov/centers/marshall/news/releases/2015/nasa-tests-methane-powered-engine-components-for-next-generation-landers.html.
“Why the next Generation of Rockets Will Be Powered by Methane.” Australia's Science Channel, Australia's Science Channel, 3 Sept. 2019, https://australiascience.tv/why-the-next-generation-of-rockets-will-be-powered-by-methane/.
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