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China has succeeded in launching the main module of its future space station, Tian He. Cool! The Long March 5B core that launched it is now in an uncontrolled decaying orbit. It's estimated it will make an uncontrolled reentry in a few days. Not so cool.

I've read a couple of articles on this, and what I don't understand is why this is happening. Does this have to do with the design of the 5B, some trade-off that was deemed acceptable so it could complete its missions? Do we know enough about the 5B to say?

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    $\begingroup$ @Slarty that's what I figured, but then when I thought about that it seemed strange. Didn't they design the rocket to have enough margin to be able to handle things like this? It really doesn't take much propellant to slow down an empty stage so it deorbits. Is it that they don't have thrusters that give them the control to turn it around? But that seems odd too. $\endgroup$ – kim holder May 3 at 22:08
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    $\begingroup$ @kimholder Many orbital stages reenter uncontrolled. Usually when operating too close to margins on the launch, or if the launch profile does not grant easy deorbiting. For example, the vast majority of Geosynchronous transfer satellite delivery stages are left to reenter many months later as debris. For example, right now there as 22 of SpaceX's Falcon 9 second stages orbiting Earth, the oldest from 2010 $\endgroup$ – PcMan May 3 at 22:20
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    $\begingroup$ "what I don't understand is why this is happening" What is happening is that they don't care where it comes down. The same thing happened on its launch last year. $\endgroup$ – Organic Marble May 3 at 22:20
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    $\begingroup$ @kimholder simple anti-china sentiment, based on politics not reality. Yes, it is more polite to do reentry in a controlled way. No, its not always possible. And no, it presents virtually zero danger to anyone under the landing path. $\endgroup$ – PcMan May 3 at 22:28
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    $\begingroup$ It does seem like a matter of perspective, I can accept that. It's a very small risk. All the same, it would make a difference to me to know if this is a small omission because it isn't easy to do, or if it is a big omission because it wouldn't have been hard. That's what it comes down to, and hopefully that can be discussed without being too subjective. $\endgroup$ – kim holder May 3 at 22:41
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A controlled reentry comes at a cost. China and SpaceX are apparently betting that the added cost of a controlled reentry vastly outweighs the cost of debris from an uncontrolled reentry resulting in significant damage. Suppose a chunk of debris kills a cow. Nobody will have a cow over this. People will have a cow if a chunk of debris kills a person. But until then, it's a calculated risk.

Perhaps it's a poorly calculated risk, but it is a calculated risk nonetheless. The Ford Pinto case from almost 50 years ago comes to mind. Ford's advertising agency claimed that the "Pinto leaves you with that warm feeling". Sometimes, it left people with a bit too warm of a feeling. When hit from behind at a speed of 25 mph or more, the Pinto's gas tank would, without fail, rupture and the gasoline would burst into flames. People died. Even more people lived but suffered terrible burns. Ford vastly underrated how much a death lawsuit would cost, and didn't account at all for injuries that came close to death. (Lawsuits related to permanent disfiguring damage tend to cost even more than do lawsuits for premature death. Caskets are cheap. Lifetime replacement for permanent loss of income and for permanent payment for pain and suffering are not cheap.) One and a half million Pintos were recalled. All in all, it was a very poorly calculated risk on Ford's part.

We'll have to wait for lawsuits related to death, brain damage, permanent physical disfiguration, or significant property damage by an uncontrolled reentry to see whether China, SpaceX, et al. have made a poorly calculated risk. Or perhaps they have not, and their cold equations will turn out to be correct.

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    $\begingroup$ My use of "the cold equations" is a reference to a 1954 award winning science fiction story that is once again being used as the basis for a movie. Tom Godwin, the author of that short story didn't want to have the innocent girl die. This was 1954, after all; at that time the male hero was always supposed to rescue the innocent girl. John Campbell, the editor of Astounding, did not want the innocent girl to live because he wanted the cold equations to be very cold indeed. $\endgroup$ – David Hammen May 5 at 4:36
  • $\begingroup$ Wasn't there an international treaty detailing legal consequences for when space debris of some country hits somewhere in another country? $\endgroup$ – Gnudiff May 5 at 14:42
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    $\begingroup$ @Gnudiff That's the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, aka the Outer Space Treaty, which dictates that "States shall be responsible for national space activities whether carried out by governmental or non-governmental entities" and that "States shall be liable for damage caused by their space objects". $\endgroup$ – David Hammen May 5 at 15:18
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    $\begingroup$ The Outer Space Treaty does not say that space objects must have a controlled reentry. All that it says is that states are liable for damage caused by their space objects. This means that if a Falcon 9 uncontrolled reentry kills a Canadian cow (or worse), it's the US that has to pay Canada for that cow. It's up to the US government to collect from SpaceX, which they will do. $\endgroup$ – David Hammen May 5 at 15:24
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    $\begingroup$ @Gnudiff Just posted in The Planetary Society's website: This Is What Legally Happens If An Uncontrolled Rocket Damages Something $\endgroup$ – uhoh May 6 at 21:38

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