> What about the remaining four orders of magnitude? I've already factored in the 90% -> 99% reduction in my comments.

This thread started with a statement that satellite thrusters are at "first thought ... about 7 orders of magnitude less" than coal power plants, but where did that number come from? Others are noting that some proposed constellation would have emitted more mercury than the US, which contradicts that thought:

https://news.ycombinator.com/item?id=30841820:

> The US emits 52 tonnes/year into the air, apparently. The article claims _hundreds_ of tonnes for one constellation. Which does seem concerning if correct.

https://news.ycombinator.com/item?id=30840666:

> Apollo Constellation Engine designed their propulsion systems for mega constellations to use mercury, which is what got PEER involved in this. Popular Mechanics also reported on their plans. Even if Apollo changed their minds since, that's a pretty significant 'near miss'.

> https://ecfsapi.fcc.gov/file/111998371507/11_19_18_FCC_compl...

> https://www.popularmechanics.com/space/rockets/a25242578/apo...

I have already addressed the question of orders of magnitude but I will try to be more explicit. The emissions from a single specific coal plant is a tiny fraction of total emissions. The emissions from a satellite fleet is a similarly tiny fraction of total emissions. Why should we crack down on one, but not the other? Your argument is a slippery slope that can be applied to any individual source of mercury emissions in that way.

You see coal emissions and satellite emissions as fundamentally different for some reason, but from the perspective of protecting the environment they are not. They are all just mercury emissions.

The solution is not to slice up mercury emissions sources into categories and issue exemptions or special treatment. We should consistently crack down on all sources of emissions, unless there is an actual specific reason to exempt them.

Of course there's a scale below which chasing down a small source of emissions might not be worth it due to costs, but banning mercury use in satellite propulsion is not a very costly use to crack down on. In fact it's already been done.

I appreciate that we both find the issue so passionate.