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Dr. Phil Metzger @DrPhiltill
, 8 tweets, 2 min read Read on Twitter
Today, writing software to simulate small spacecraft extracting water from asteroids. It took 2 weeks to develop equations of thermal conductivity as gas pressure increases in the soil. Finally got the code running! Here is gas pressure developing in & around the coring device:
2/ Granular materials like asteroidal or lunar soil are really good thermal insulators, especially when they are in the vacuum of space so there is no air between the grains Pro tip: if you're stranded on the Moon & need to stay cool in the harsh sunlight, bury yourself 1 m deep.
3/ Therefore it is hard to heat the asteroid's soil to get the minerals to release the trapped water. You can apply heat to the soil, but it takes a LONG time for the heat to travel into the soil. This could waste LOTS of energy as you try to get water.
4/ However, because the minerals DO contain water, once you raise the temperature a bit the water starts coming out as vapor (gas), and it fills the spaces between the soil grains. This gas in the soil causes heat to travel in the soil 10x to 100x faster.
5/ So once you start getting water, it becomes a self-reinforcing effect, allowing you to get more water for less and less energy. To figure out exactly how much energy you will need, you have to include this part of the physics in your equations. So that's what I've been doing.
6/ But then I ran into problems. The soil becomes so good at transferring heat that the equations go unstable. The equations include not just heat transfer but also diffusion of gas through the soil into the spacecraft. So it is tricky: coupled partial differential equations.
7/ Solving problems like this require working from Starbucks instead of the office so there will be adequate caffeine. Twiddling the parameters of the software made it stable again, and that produced the pretty picture of gas pressure.
8/ Next step: run various cases with different types of mining devices, different energy levels, etc., and decide if the spacecraft can operate on Ceres using purely solar power or whether it will require Radioisotopic Heater Units to provide enough energy for mining water.
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