Many around the world will be watching with anticipation this Saturday as NASA launches Artemis I, the agency’s first mission to explore the moon since the 1970s.
The spectacle features the world’s most powerful rocket: the Space Launch System (SLS). Standing nearly 100 meters tall and weighing over 2,600 tons, the SLS produces a whopping 8.8 million pounds of thrust – (more than 31 times the thrust of a Boeing 747).
But rocket science and space exploration is not just amazing engineering. Hidden inside, there is a clever chemistry that powers these fantastic feats and sustains our fragile life in space.
The fuel and the spark
To launch a rocket into space, we need a chemical reaction known as combustion. This is where fuels combine with oxygen to produce energy. In turn, this energy provides the thrust (or thrust) needed to propel huge machines like the SLS into Earth’s upper atmosphere and beyond.
Like cars on the road and jet planes in the sky, rockets have engines in which combustion takes place. The SLS has two propulsion systems: four RS-25 main engines (upgraded Space Shuttle engines) and two solid-propellant rocket boosters. And chemistry is what provides a unique fuel mixture for each engine.
The main engines use a mixture of liquid oxygen and liquid hydrogen, while solid rocket boosters, as the name suggests, contain solid fuel – a solid rubber-like material called polybutadiene acrylonitrile. In addition to being a fuel, this material contains fine particles of metallic aluminum as a fuel, with ammonium perchlorate as an oxygen source.
While fuel for solid rocket boosters is easily stored at room temperature, fuels for main engines must be stored at -253℃ for liquid hydrogen and -183℃ for liquid oxygen. That’s why you see sheets of ice shearing off rockets on liftoff – the fuel vessels are so cold that they freeze moisture from the surrounding air.
But there’s another interesting chemistry that happens when we have to ignite the fuel. Depending on the fuel source, rockets can be ignited electrically via a glorified spark plug… or chemically.
If you’ve ever watched a space launch and heard talk of “TEA-TEB ignition,” this refers to triethylaluminum and triethylborane. These two chemicals are pyrophoric, meaning they can ignite spontaneously when exposed to air.
Sustaining life among the stars
Rockets aren’t the only ones powered by chemistry. Life support systems in space rely on chemical processes to keep our astronauts alive and breathing – something we on Earth often take for granted.
We all know the importance of oxygen, but we also exhale carbon dioxide as a toxic waste product when we breathe. So what happens to carbon dioxide in the confined environment of a space capsule like those on the Apollo missions to the moon or the International Space Station (ISS)?
Remember Tom Hanks trying to fit a square peg into a round hole in the movie Apollo 13? These were carbon dioxide scrubbers that NASA used to remove this toxic gas from inside space capsules.
These scrubbers are disposable filters filled with lithium hydroxide (similar to a chemical you might find in drain cleaning fluid) that capture carbon dioxide through simple acid-base chemistry. Although these scrubbers are very effective at removing carbon dioxide and allowing astronauts to breathe comfortably, the filters have a limited capacity. Once saturated, they are no longer effective.
So for extended space missions the use of lithium hydroxide filters is not feasible. Scientists later developed a system that used a reusable carbon dioxide scrubber made with minerals called zeolites. With zeolite, the captured carbon dioxide can be released into space and the filters are then free to capture more gas.
But in 2010, scientists discovered an even better way to manage carbon dioxide by turning this waste product into another essential component of life: water.
From waste to resource
The ISS’s Environmental Control and Life Support System replaces the carbon dioxide scrubbers with the Carbon Dioxide Reduction System, also known as the Sabatier System. It is named after the chemical reaction central to its function, which in turn is named after its discoverer, the 1912 Nobel Prize in Chemistry winner Paul Sabatier.
This system combines carbon dioxide with hydrogen gas to form water and methane. The methane gas is vented into space, and through a process called hydrolysis, the water is split into breathable oxygen and hydrogen gas. The latter is then recycled to transform more carbon dioxide into water.
This process is not only useful for space exploration. Closer to home, chemists are exploring similar systems to potentially address greenhouse gas emissions—although not a panacea, the Sabatier reaction could help us recycle some carbon dioxide here on Earth.
Meanwhile, NASA’s Artemis Moon mission aims to land the first woman and person of color on the moon and establish a long-term human presence on a lunar base. The Sabatier reaction and other little-known chemical processes will be key to humanity’s continued efforts in space.
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