"In 2018 a whistleblower told me about a new satellite thruster that used mercury, the poisonous liquid metal, as a propellant, and that it would inevitably fall back to earth when used, thus beginning my Space Lawyer arc. The company that designed it was in the process of selling the tech to big space companies: SpaceX, OneWeb, etc., who were in the planning stages of putting new "megaconstellations" of 10,000s of satellites into orbit. Every one of these satellites has 20-100kg of propellant onboard, which is ionized and expelled over time to do orbital correction and scoot around up there. Mercury is heavy, which means that it gives you a lot of Δ(v) per unit of propellant used, it isn't explosive, you don't have to heat it as much as other fuels to stay liquid, and it's cheap because nobody wants it.

It's also a powerful bioaccumulative neurotoxin!"

https://twitter.com/KevinHBell/status/1508549006863085580