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About a week ago, the 18th Space Control Squadron, US Air Force, relayed warning data to the European Space Agency.
The data indicated that there was a non-negligible collision risk between ESA's Aeolus satellite and Starlink44, an active SpaceX satellite, at 11:02 UTC on Monday, 2 September.
As days passed, the probability of collision continued to increase, and by Wednesday, August 28, ESA's Ops team decided to reach out to Starlink to discuss their options. Within a day, the Starlink team informed ESA that they had no plan to take action at that point. By Thursday evening, ESA's probability threshold for conducting an avoidance manoeuvre had been reached, and preparations were made to lift Aeolus 350 meter in orbit. By Sunday evening, chances of a collision had risen to 1 in 1000, and commands were sent to the Aeolus satellite, which triggered a total of 3 thruster burns on Monday morning, half an orbit before the potential collision. About half an hour after the collision prediction time, Aeolus contacted base, and normal measurement operations could continue.
What the SpaceX satellite was doing in ESA's Aeolus orbit is not clear.
ESA has taken the opportunity to point out that, given SpaceX plans to put up 20,000 of those things, handling monitoring and avoidance semi-manually, and by mail, is no longer practical.
(Score: 2) by Immerman on Tuesday September 10 2019, @02:01AM
>Only about half as fast as they should be due to measured emissions.
Right we're pumping water into a pool at 10 gallons/minute, and the pool is filling at 5 gallons/minute. Doesn't matter how complicated any hidden plumbing is, it's a pretty safe bet that the pool wouldn't be filling without our contribution. Also, we have a pretty good idea where the extra CO2 is going - ocean acidification, etc. It's not like the atmosphere is an isolated system.
> The IR window CO2 blocks is not that wide and adding extra CO2 doesn't really do very much over what is already there.
IR isn't blocked, it's scattered - the same way blue light is scattered by the atmosphere so that the sky looks blue while the sun looks yellow, rather than black and white as they look from orbit. And every time a photon scatters off a CO2 molecule it's a 50/50 chance whether it's re-emitted towards space, or back towards Earth. And one of the features of scattering is that the more scatting substance you put in a solution (like the atmosphere), the more slowly scattered light escapes. 100% of the IR will always escape eventually, the question is how many times an average photon worth of energy ends up back on the surface before it finally makes it out of the atmosphere.
As for the scattering band - the IR band CO2 scatters is separate from, and very roughly the same size as, the scattering band for water, which is the only other IR-scattering gas present in significant quantities in the atmosphere. Methane is the next most common, and there's ~200x more CO2 in the atmosphere than methane.
There's ~50x as much water in the atmosophere as CO2. Water undeniably does most of the work: it averages somewhere around 2 to 2.5% (25,000ppm) of the atmosphere. It varies wildly from about 0 to 4%, but is self-regulating in the sense that the warming from increasing the average amount of water in the air by 1%, is never enough to let the air hold a full 1% more water. So the humidity percentage increases, and with it the chance of the water leaving the air as rain or snow.
CO2 in comparison is tiny, now a bit over 400ppm, but that still makes it at least (400ppm/25,400ppm) = 1.6% of the total amount of greenhouse gasses. Not much, how big a difference can it really make? A reasonable guess would be 1.6% of all the greenhouse warming, so how much is that? Well, we can look at the moon for comparison, it's the same distance from the sun as us, but has no atmosphere. The average temperature of the moon at the equator is about -58C [58], as compared to the Earth's average temperature of about 15C. So greenhouse gasses are currently keeping the planet about 73C warmer than "normal" for our orbit. And probably much more - the Moon is quite dark colored and absorbs about 31% more solar energy than the Earth, plus I chose a nice warm place near the equator.
So, there's at least 73C of current greenhouse-gas warming that's keeping our planet from being a frozen ball of ice. Even if we assume that CO2 is no more potent a greenhouse gas than water, 1.6% of 73C is about 1.2C of extra warmth laid directly at its feet.
And CO2 has a crucial difference to water - it doesn't increase humidity. But any warming it does still increases the maximum amount of water the air can hold, and with it how much water needs to be in the air to have the same equilibrium humidity percentage.
How strong is that effect? Well, at around 15C the maximum water content of air changes by about 7% per degree C. So, if CO2 causes 1.2C of heating on its own, then the air will have to carry (7%/C*1.2C=) 8.4% more water to maintain the same humidity So that ~1.6% of the total greenhouse gas of CO2 is potentially responsible for the presence of an extra 8.4% of the water in the atmosphere, for a combined 10% of the total greenhouse warming - or 7.3C of the total estimated warming. And the effect gets more dramatic at higher temperatures - get closer to 20C, and the amount of water required to maintain the same percentage humidity is increasing by 9% per degree C.