Hacker News Reader

Comment by aphextron | Hacker News Reader

> Starship is methane-powered. There are ways to generate methane sustainably (from C02 and water);

It's not about the generation. Burning methane results in a 1:1 emission of CO2 [0]; literally the equivalent of just dumping pure carbon dioxide into the atmosphere.

https://www.quora.com/What-are-the-products-of-methane-burne...

View on HN

That doesn't matter if you made the methane by extracting CO2 from the atmosphere. Then you are just putting the CO2 back from where you got it.

The bad part with burning fossil fuels is that you are putting carbon in the form of CO2 into the air which was previously locked under ground in the form of coal/gas/oil. If you are burning carbon that you extracted from CO2 in the atmosphere, there is no such problem, assuming you didn't use fossil fuels to extract that carbon.

>That doesn't matter if you made the methane by extracting CO2 from the atmosphere. Then you are just putting the CO2 back from where you got it.

It's not that simple. What you're describing is free energy. We're still burning fossil fuels to extract the methane. Maybe that could be powered by renewables one day. But as of now, it is not.

The point is you could do it with renewables without burning fossil fuels. There would be losses in the step between renewables and methane sure, but it doesn't require "free energy".

Indeed, it's more like molecular assembly & disassembly powered by renewables. Here's a good explanation for a well-tested ethanol process:

https://www.sciencemag.org/news/2019/07/former-playwright-ai...

In the process that would likely be used the CO2 would be sourced from the atmosphere.

https://en.wikipedia.org/wiki/Sabatier_reaction

Ya, but that isn't happening. Look at where liquid hydrogen for rockets is sourced. It could be made from water. In reality, it is made from hydrocarbons because that is cheaper. And even if CO2 is pulled from the air, a huge amount of energy is need to compress/store that rocket fuel, energy that could be put to far better uses. Instead of launching a passenger rocket to london, I'd rather divert that energy into shutting a coal-fired powerplant for a week or two. Once all those powerplants are shut, then we should look at passenger rocket services.

I don't doubt you're right for most existing rockets, but I think the main difference here is that SpaceX has every reason to test the hell out of their propellant-producing appliances here on Earth, even if it's not economical at the beginning. They depend on these appliances working perfectly on Mars for the return trip, so they need to be _very_ reliable.

If these vehicles were from anyone besides a company whose explicit goal is to develop an interplanetary colony ship whose duty cycle will require the launch infrastructure on the other planet to convert atmospheric CO2 into methane using solar power, I’d agree — it hasn’t been done, it’s not economical to do it that way yet.

But Musk needs this process to become economical so that Mars can become economical.

(The same tech may, ironically given Tesla, compete with batteries for the energy storage PV calls for).

If that CO2 was taken from the air in the first place, it's a neutral process overall:

Take CO2 from air => Turn it into methane => Put it into rocket => Burn it back into the air

This process requires far more energy than just using it to power normal modes of transportation. There's no free lunch.

Doesn't matter if it is solar.

Reply on news.ycombinator.com