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.
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.