It’s funny how I see scary headlines every time an asteroid is due to pass within 10M miles of Earth, but we’ve got a 20-ton Chinese rocket booster about to have an uncontrolled reentry and...crickets. Currently predicted to happen within 36 hrs.

https://spaceflightnow.com/2020/05/09/u-s-military-tracking-large-chinese-rocket-reentry/

Obviously the odds of this landing on your house (or anyone’s house) are extremely small. But it is highly probable that portions of the rocket survive reentry and land SOMEWHERE (hopefully in the ocean) due to the size of the booster—100ft long and 80,0000 lbs

For the same reasons that it is difficult to engineer vehicles that safely survive reentry, it’s difficult to predict when objects like this re-enter. We struggle predicting: 1) timing; 2) where they end up; 3) how much is left of them.

The problem is there are a lot of complex sets of equations (fluid dynamics, heat, material, chemistry) that are all coupled—meaning that the result from one equation feeds into the others, amplifying any error you make.

But when you’re trying to model an object moving at hypersonic reentry velocities (Mach 20+) every 1 minute error in your calculation equals a difference of hundreds of miles!

What’s particularly frustrating about all this is that unlike an asteroid, this situation could have been completely avoided with some different design choices. It’s unbelievably irresponsible engineering, but here we are. So heads up tomorrow?

If you want updates, @AerospaceCorp has a reentry prediction tracker on their site. Current estimate is 6:30P ET/5:30 P CT Monday May 11 but +/- 17hrs! A full orbit only takes ~90 mins. Predicted to land off the east coast of southern Africa.

https://aerospace.org/reentries/cz-5b-rocket-body-id-45601