Tiangong-1 [Potential landing sites for Chinese Space Station]

I read that the Chinese Space Station is out of control and will land somewhere between 42.8 degrees north and south. This includes a lot of land and I wondered what the odds are of it hitting somewhere important like Rome or any number of big cities in the Southern half of North America.

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General Questions Moderator

Do you have any cite that there is significant risk? The analysis that I’ve seen is that it will break up and burn up on reentry, and that only small fragments are likely to reach the surface.

Right. And it’s apparently impossible to determine where it will impactbefore a few hours before it does so.

No cite - just a news article that highlighted the usual landing sites for dead satellites (The Pacific pole of inaccessibility) and mentioned that Tiangong-1 is totally dead and will come to earth somewhere between those two lattitudes.

For a first order WAG …

The land area of Earth is roughly 149E6km[sup]2[/sup]. Of which about 3.50E6km[sup]2[/sup] is urban/suburban on the most generous definition. So about 2.5% of the land is urban/suburban. But the Earth’s surface is 71% water & 29% land. So about 0.6% (roughly 1 part in 200) of the total surface area is urban/suburban. The truly dense urban areas are about 15% of the total urban/suburban, or 0.1% of the earth’s total surface. IOW, 1 part in 1000.

I don’t know the distribution of land by latitude, but I do know the cities are concentrated within the +/- 43 degree latitude band under the station’s orbit. Let’s bump it to 1% (1 part in 100) urban/suburban to account for that, and 1 part in 500 for the dense urban cores.

Overall, we see the basic odds are on the order of 1 in 100 to 1 in 500 for hitting any meaningful concentration of people or buildings.

From the space shuttle Columbia mishap we saw the debris field was pretty large, but not very dense. Here’s a radar image of the Columbia debris field as it was falling. https://en.wikipedia.org/wiki/Space_Shuttle_Columbia_disaster#/media/File:Columbia_debris_detected_by_radar.jpg. For scale, the straight-line distance between Tyler and Alexandria is roughly 195 miles.

The orbiter weighed very roughly 190,000lbs at reentry and that got distributed over an area of roughly 200 x 10 miles = 2000 square miles. So about 95lbs per square mile. Net of course of whatever vaporized in the atmosphere. That area is mostly farmland and small towns. IIRC nobody on the ground was injured by falling debris.

The Tiangong-1 weighs about 18,000 lbs, 1/10th as much as the shuttle. And as a space vehicle, rather than an air & space vehicle it’s more lightly constructed. Which means relatively fewer heavy solid chunks and relatively more light foil-like materials. The implication being that a smaller percentage of it will survive to touchdown and of what does survive, more of it will be fluttering down rather than plummeting down.
In all, IMO the chance of direct harm to any humans as a whole is pretty low. The chance of direct harm to any given human is close enough to zero as to be ignorable. I predict more people worldwide will die of bee stings that day than will die from being hit by a falling space station.

Thank you LSLguy - that was exactly the kind of answer I hoped for.

“I predict more people worldwide will die of bee stings that day than will die from being hit by a falling space station.” Or, indeed - falling out of bed.

Wow, that’s not much of a “space station” - it’s about 1/10 the mass of Skylab, and 2/3 the mass of the Hubble. I guess I don’t need to dig out my old “Skylab is Falling” hard hat…

Yeah. It’s a power, maneuvering, and life support system attached to a habitable compartment the size of a camper van. It’s much more a pathfinder device to test the systems than it is a long term orbiting habitation.

The original plan was to build a much larger station with the lessons learned here. As so often happens in the West, that plan died for lack of budget somewhere along the way.

They had to ensure that one Astronaut slept in the docked Shenzhou otherwise it would get too cramped inside. (Typically the lady Astronaut would do so).

I believe that they still have plans to build a multi-module station ala MIR. Whether it still gets built with 253% debt to GDP and Uncle Xi’s penchant for building infrastructure all over Central/South Asia and Africa, remains to be seen.

Tiangong 1 was the first technology demonstrator for a space station. They already have the Tiangong 2 in operation, which is also considered a technology demonstration. Their first long-term modular space station is supposed to launch in 2019.