I suppose 9,000 tons of stuff burning up in the atmosphere might cause a brief spike in air pollution, but it’d be spread out globally and I suspect would have minimal effect measured against the usual amount of daily air pollution produced.
I am surprised that no one has yet mentioned the reentry of Kosmos 954 that scattered radioactive debris over northern Canada.
No problem; figured it was a simple error. The picture was of the right thing, at any rate. I believe that tank is in a museum now.
A helium tank from a Falcon 9 second stage survived reentry as well, with a very similar-looking photo:
The big objects like the ISS would certainly ruin the day of whatever they landed on, but that’d be highly localized. And of course, it’d be rather likely that wherever they landed wasn’t any place that humans care about.
I thought (perhaps wrongly) that this was not relevant. You often hear that a shattered comet hitting the Earth would do no less damage than an intact one as the amount of energy being put into the atmosphere remains the same.
The first (and to me, most interesting) part of the book Seveneves had a scenario of that sort. It was more than a little inconvenient.
Global thermal effects are a concern when the total inbound mass is very large. At that point, it doesn’t much matter whether it arrives as a single bolus that impacts the surface (resulting in a local heating that takes a bit more time to propagate around the globe), or as a spray of smaller objects that all vaporize in the atmosphere and heat it up directly.
In the case of the total satellite mass, identified by LSLGuy as about 18M pounds, that’s equivalent to a sphere of granite about 60 feet in diameter - roughly the size of the Chelyabinsk meteor. would cause significant local devastation if it arrived as a single bolus - but the thermal effects on the atmosphere would be negligible if it arrived as a bazillion small satellites that completely incinerate in the atmosphere.
You’d get a nice light show, but that’s about it.
Thanks everyone, ignorance fought.
My ignorance is much higher when starting late night GQ threads it seems.
Yep. If you assume that 9000 tons is a dense iron nickel meteorite, it’s 14 m in diameter. Using this calculator, assuming it enters at escape velocity, the maximum impact I get makes a crater about 100 m in diameter. Really bad for the local vicinity, but not Earth-shattering.
Unless of course you’ve got the Illudium Q-36 Explosive Space Modulator.
They didn’t list illudium in the drop-down menu
If you took all 9200 tons of satellites, put them all together into a big lump and sent them through the atmosphere, you’d get a meteor slightly less massive than the Chelyabinsk Meteor. However, that meteor was going 40,000 mph, so its energy (equivalent to 470 kilotons of TNT) was three or four times higher than the satellite blob would be. The meteor broke apart and mostly burned up in the atmosphere.
The Tunguska meteor explosion was about 15 megatons. It didn’t affect anything outside of the local region.A meteor with the energy of the entire satellite constellation falling hits the Earth every 20 years or so. Meteors with energy equivalent to over a kiloton TNT hit the Earth every couple of years.
So… If all our satellites came down at once across the globe, they’d provide some pretty light shows and that’s about it unless you were unlucky enough to be hit by a piece that survived reentry.
I also remember Skylab. IIRC, most of it crashed in the Australian Outback.
I was out looking for it too. I nearly got lucky. I was antipodal to you, but it re-entered about a thousand miles away from me on the next orbit. So I was 90 minutes out. But we drove out to pretty much under the orbital path, at much the same latitude as it fell, so I felt a bit cheated given where it did finally fall.
Another COPV (Composite Overwrapped Pressure Vessel, used for storing helium, etc.) from a Falcon 9 upper stage landed in Washington:
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Whatever makes it back from orbit is liable to have a very high density or very low density. A big chunk of dense metal will make it down, since the reentry heat can only ablate material so quickly. But low-density objects like this COPV will also make it down, because they can shed velocity in the upper atmosphere at relatively low rates. Once it makes it to the thick, lower atmosphere it’s not going so fast (maybe just terminal velocity).
Are these planned to come down like this?
If that tank lands on you, the phrase “terminal velocity” will take on an unwelcome second meaning.
And if it is a computer kiosk from a space station, three meanings!
Not exactly. Normally, the second stage performs a deorbit burn, so that the stage comes down in a depopulated area (namely, the ocean). The stage still comes down in about the same way, but the remaining pieces don’t land on anyone’s head. In this case, the deorbit burn didn’t happen, so the stage came down naturally a few weeks after it launched (that is by design). But it happens unpredictably and in this case it just happened to be over Washington (giving a nice light show).
SpaceX hasn’t said why the deorbit burn didn’t happen. It doesn’t appear to have been anything catastrophic, like the whole stage exploding. My suspicion: because Starlink launches are right at the performance margins of the Falcon 9, there are just a few wisps of propellant left for the deorbit. The burn doesn’t need much, so usually that’s ok. But in any launch there are hundreds of factors that can affect the overall performance, like wind, temperature, performance variation in the engines, mass variation in the stage, mass variation in the payload, etc. All tightly controlled of course, and not so variable to affect the main mission. But sometimes they get unlucky and they’re left with not quite enough propellant for the final burn. Or, possibly, enough to deorbit, but not enough that they can be confident that the engine won’t ingest a bubble of vacuum and explode.
They could leave off a satellite or two to give them margin, but since this is a low orbit they know the stage will come down on its own in a few weeks, so the risk of it becoming permanent space junk is zero. But it does increase the risk of it coming down in an inconvenient place.