January 10, 2021 by Jennifer Sensiba
Zero-emission cars are very good for the environment, and Tesla has made a lot of them. Elon Musk also owns SpaceX, so people naturally mix them up. When someone saw the rocket launch, it was obviously not a zero emission event. As Jerry Lee Lewis said: “Oh my God, the fireball is big!”
Unfortunately, this led some to conclude that all emissions from the rocket launch must offset all emissions saved by Tesla. I have been trying to cover up for a while and dispel this myth*, but have been waiting for a more precise statement about SpaceX’s real plan. Through a recent tweet by Elon Musk, we now know that zero-emission rockets are definitely coming.
By using electric energy to convert CO2 + H2O→CH4 + O2, electric rockets can be realized indirectly. Even for early missions and Earth, this feature will be needed on Mars.
-Elon Musk (@elonmusk) January 7, 2021
First, let us analyze the current emissions of SpaceX. Both existing and mature SpaceX rocket designs use its Merlin engine. Like many other launch companies and government entities, Merlin engines use RP-1 fuel, which is basically an improved version of the fuel used by most jet engines and oil lamps (kerosene). They mix it with liquid oxygen and burn it, which not only releases CO2 and H2O, but also emits many pollutants, such as hydrocarbons, carbon monoxide and nitrogen oxides.
For new rockets like Starship and Super Heavy, SpaceX is using its new Raptor engine. Although there are many ways to make Raptors better than Merlin, one of the biggest differences is that they can burn methane (CH4) instead of RP-1. Methane can burn like RP-1, but its molecule is much simpler than kerosene. When you burn a methane molecule (CH4) with two oxygen molecules (O2), you will only get carbon dioxide and water in the exhaust gas, but no other pollutants.
This alone is a big advantage of using methane, but as Elon Musk pointed out in his tweet, it may make methane rockets cleaner. Exhausting water vapor will not cause much damage to climate change, but all carbon dioxide is still a problem.
By capturing carbon dioxide (CO2) from the atmosphere left by the rocket, you can make up for everything the rocket does. Then you absorb the carbon dioxide, add some water, and then use the Sabatier reaction to put the methane back in place. You can then use methane to power the next rocket.
result? Zero net emissions.
There is a catch, that is: it needs electricity. You need a metal like nickel to act as a catalyst, and you need a lot of electricity to convert carbon dioxide and water into methane. The good news is that it doesn’t matter where the electricity comes from, so solar, hydroelectric, wind or other clean energy can be used. Therefore, if the operation is correct, your emissions are still zero!
You may first see SpaceX use it on Mars. On earth, methane is easily obtained from natural gas. After all, this is the main ingredient. Compared to buying natural gas, using Sabatier to make methane is an expensive process, so it doesn’t make much sense. The current goal is to get the company to enter Mars and establish a colony, which will be an expensive job.
However, there are no natural gas pipelines on Mars. If you want to refuel an interstellar spacecraft, you need to bring a lot of things to Mars, or find a way to make them on Mars. The journey to Mars is long. Even the fastest thing we know, the light takes about 4 to 20 minutes to get there. The long journey and additional launches will make it too expensive to obtain natural gas there.
On the other hand, the atmosphere of Mars is mainly carbon dioxide, and there is a lot of water in the polar ice caps. It is also possible to use solar panels or other power sources on Mars to power the Sabatier reaction, so this is a really good way to provide fuel for returning to Earth and even to other parts of the solar system.
The biggest news from Elon Musk’s tweet is that SpaceX eventually plans to produce fuel on Earth in this way. We also have a lot of carbon dioxide and water here, but in the long run, we cannot bear the burden of continuing to emit more carbon into the atmosphere. Fortunately, not doing this is part of future plans.
*Editor’s note: The emissions from SpaceX rocket launches are actually surprisingly low. For more information on this, see these two articles:
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