[dotancohen]

  > coal is moving to 99% scrubbing instead of 90%

Yes, but that resolves only one order of magnitude difference between the coal plant and the satellite constellations. Another two orders of magnitude are accounted for in the increasing size of the megaconstellations.

So even after those issues are addressed, earth-based coal is four orders of magnitude more problematic. Sure, focus on multiple targets. But don't pick a target 1000 times less significant to "diversify focus".

[simonh]

I think even if 1,000 people are getting cancer a year from a particular cause, that doesn't mean we can ignore this other cause that's only killing 1 person a year.

Should we also exclude small coal plants that only emit <1% of global emissions? What other cost effectively preventable emissions of mercury should we allow? Where do we draw the line? We should be consistent, especially since the costs of compliance don't seem to be all that great.

[dotancohen]

I hate to belittle a point, but this group is addressing the cause that is metaphorically killing 1 person per year while ignoring the cause that is killing 1,000 people per year.

In fact, I would go so far as to say that this cause is deflecting energy from any anti-coal movement by offering an new, shiny, space-age target for activists to concentrate on.

[simonh]

I have already addressed that point in this thread. The emissions from coal plants are being addressed with a 10x reduction already in the works. It is not being ignored, at all.

On the contrary, every effort to minimise mercury emissions and highlight their danger is worthwhile and raises awareness. The only reason we are talking about coal emissions now is because of this effort. If anything, consciously choosing not to address this specific issue and applying mercury emissions controls inconsistently would weaken the case for cracking down on other sources of emissions. It would smack of exceptionalism and preferential treatment. If you can carve out an exception for this source, why not others? Why do high tech rich world projects like a satellite fleet get a pass, but not a specific coal plant in a third world country with the same emissions?

[dotancohen]

  > I have already addressed that point in this thread. The emissions from coal
  > plants are being addressed with a 10x reduction already in the works.

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

This is why I feel that such "feel good" efforts, such as focusing on the space industry, actually distract from the coal burning issue. You feel that things are being done to rectify coal, and I'm demonstrating that a 90% reduction in emissions (from 90% to 99% scrubbed) still pollutes four orders of magnitude (10,000 time more, though I accidentally said 1,000 more previously) than the proposed satellite constellations.

[tablespoon]

> 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...

[simonh]

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.

[dotancohen]

I appreciate that we both find the issue so passionate.