Thread by @Pinboard

Yay, I get to do my rant about the Sabatier reaction in spaaaaace!

Gather round, everyone, and listen to the story of:

CO₂ + 4H₂ →CH₄ + 2H₂O

https://twitter.com/elonmusk/status/1470519292651352070

Everyone loves the Sabatier reaction because it takes carbon dioxide and turns it into something useful: water and methane (aka rocket fuel or natural gas, depending on who you want to raise the funding from). All you need is a hot metal catalyst and some hydrogen.

This reaction (or a family relative) is part of the SpaceX plan for Mars. You fire autonomous robot factories at Mars with a supply of hydrogen, they unfold their huge solar panels, and in a year you've got 250 metric tons of liquid fuel to refuel your rocket with when you land

On Earth, this is a completely unremarkable industrial reaction. The Great Plains Synfuels Plant in North Dakota makes 3,050 tons of methane a day in a continuous process without being Time Person of the Year

NASA long had its eye on the Sabatier reaction, since it could take two gases that were being vented from the space station as waste (hydrogen and carbon dioxide) and turn them into something that was useful and expensive to send up from Earth (water).

The Sabatier plant on ISS produced about a ton of water before finally giving up the ghost. Towards the end of its life it grew finicky and required constant babysitting by astronauts. When it died, the catalyst beds were sent back down to Earth for an autopsy

The autopsy found that the catalyst beds had been poisoned by two chemicals in the ISS atmosphere. One (dimethylsulfoxide) was a component of astronaut urine, the other (polydimethylsiloxane) is a ubiquitous ingredient in packaging, hygiene products, lubricants, you name it.

The postmortem on the ISS Sabatier reactor is worth reading just to see what an absolute diva an unremarkable industrial process can turn into when you try to run it in space. ttu-ir.tdl.org/bitstream/hand…

Now Elon Musk wants to make rocket fuel by the ton on Mars using this reaction, or something like it, in a robot factory. That's a laudable goal! But it illustrates what I call the Mars Fallacy, the idea that something that's hard to do on Earth will somehow be easy to do on Mars

There's a lot of places on Earth where an autonomous, solar-powered plant that produces hundreds of metric tons of methane a year from carbon dioxide and requires zero maintenance would come in handy!

But Musk is doing his thing again where he falls in love with a technology and handwaves past the part where you make it work. Evacuated tunnels! Self-driving car! Suborbital airliner! And everyone goes off after Elon to chase the new squirrel

When evaluating Muskian promises, it helps to look at the experience of others. Are tunnels expensive because engineers are lazy idiots? Is NASA filled with mouthbreathers who can't crack a simple molecule like CO2? Is Big Pedo keeping mini cave rescue submarines off the market?

Or did we give a manchild money to burn in the pursuit of a world taken from a scifi book cover, and in the process surrender our ability to think critically about his pattern of promises that never pan out? Why do we come back every year to this version of the Fyre Festival?