Some fun facts about space debris reentries:
(1) A breakup like the one over Seattle happens at about 60 km (~40 miles) up, far above where airplanes fly (more like 10 km).
(1) A breakup like the one over Seattle happens at about 60 km (~40 miles) up, far above where airplanes fly (more like 10 km).
(2) satellites (including space junk like this rocket stage) orbit the Earth at over 7.5 km/s (17000 mph).
3) We could predict this rocket stage would reenter today. But as of yesterday the TIME at which it would reenter was still uncertain by 5 hours.
4) But remember it's going 17000 mph, so a 5 hour time uncertainty means an 85,000 mile (53000 km) location uncertainty. That's more that one entire loop around the Earth. That's why we couldn't tell in advance that it would be the Seattle area that would see the reentry.
Why can't we predict it better? Partly because the headwind that is causing it to spiral in, the Earth's upper atmosphere, has weather - even hundreds of miles up. Solar activity affects its density.
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