this post was submitted on 08 Oct 2023
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A Boring Dystopia
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You can’t produce methane from CO2 for free. It requires extremely high pressures and then you have to add in as much as energy as you would get out of burning the methane to make methane from scratch.
SpaceX’s launch facility, where they’d likely try this stupid process, is in Texas. Texas gets most of its electricity from burning fossil fuels. So unless spaceX makes a private nuclear reactor on site to power the methane manufacturing plant, they’ll be burning fossil fuels to make electricity so they can turn C02 back into a fossil fuel. That’s not carbon neutral
They'll probably build a solar farm.
But don't get me started on how there no such thing as carbon neutral because it took carbon to build the solar panels, or wind mills, and the person operating the facility had to eat vegetables which required someone to ship them, which required a EV which required power that came from solar but those solar panels which were made from panels produced via solar panels required someone else to clean them which produced co2 making their meals too!
The launch facility they have in Boca Chica is surrounded by wildlife preserves, where are they going to put a solar farm big enough for a usable methane plant?
To put it in perspective, a square meter of solar panel puts out about 200 watts.
At atmospheric pressure, a cubic meter of methane gas contains about 40 million joules of energy.
40 million/200 = 200,000 square meters of solar panels needed to produce a cubic meter of methane.
And that’s assuming the process is 100% efficient. It’s also not counting the energy needed for the pumps to pressurize plant, or the methods they would use to extract or move the carbon dioxide, or cool down the methane.
That 40million joule figure is for gaseous methane, starship needs liquid methane to run, so the methane would need to be cooled with industrial refrigeration to turn it into fuel, which adds even more energy to the equation.
For the amount of fuel Starship needs, the Sabatier process is not feasible if you’re doing it with solar panels and planning on launching more than once a year or so. Not unless they want to pave over a small city with solar panels.
Putting energy back into CO2 to get fuel is not really economically feasible. It’s a useful process for mars for example, because you can drop off the plant and have it trickle fuel into a launch vehicle while you build the base and wait for the crew to arrive.
Boca Chica isn't going to be the main launch center in the future due to things like the wildlife preserve around it. They're going to be restricted at some point. It's a R&D center.
They could also build the solar/wind elsewhere to offset anything, or maybe they could even invest in a SMR. They'll have the cash once those start coming online.
I wouldn't be surprised if they're investing money to optimize the process as well, just like we see new advances in desalination continually making it more efficient. (Edit: e.g https://iopscience.iop.org/article/10.35848/1347-4065/ace831)
Also even in Texas, it isn't going to be coal forever, more and more renewable sources are being added to the grid every year. I'm not trying to say this will be an immediate thing.