Tiangong-1: Chinese space station will crash to Earth within months

[nitpicker]

https://www.theguardian.com/science/2017/oct/13/tiangong-1-chinese-space-station-will-crash-to-earth-within-months

Tiangong-1: Chinese space station will crash to Earth within months

Michael Slezak
Friday 13 October 2017 06.08 BST

An 8.5-tonne Chinese space station has accelerated its out-of-control descent towards Earth and is expected to crash to the surface within a few months. The Tiangong-1 or “Heavenly Palace” lab was launched in 2011 and described as a “potent political symbol” of China, part of an ambitious scientific push to turn China into a space superpower. It was used for both manned and unmanned missions and visited by China’s first female astronaut, Liu Yang, in 2012.

But in 2016, after months of speculation, Chinese officials confirmed they had lost control of the space station and it would crash to Earth in 2017 or 2018. China’s space agency has since notified the UN that it expects Tiangong-1 to come down between October 2017 and April 2018.

Since then the station’s orbit has been steadily decaying. In recent weeks it has dipped into more dense reaches of Earth’s atmosphere and started falling faster. “Now that [its] perigee is below 300km and it is in denser atmosphere, the rate of decay is getting higher,” said Jonathan McDowell, a renowned astrophysicist from Harvard University and a space industry enthusiast. “I expect it will come down a few months from now – late 2017 or early 2018.”
(snip)

Although much of the craft is expected to burn up in the atmosphere, McDowell says some parts might still weigh up to 100kg when they crash into the Earth’s surface. The chance that anyone will be harmed by the debris is considered remote but China told the United Nations “Committee on the Peaceful Uses of Outer Space” in May that it would carefully monitor the craft’s descent and inform the United Nations when it begins its final plunge.
(snip)

[PearliePoo2]

1. "some parts might still weigh up to 100kg when they crash into the Earths surface."

Oh great. Isn't that nice?
So flaming, molten chunks of metal weighing around 220 pounds are going to slam into earth, "who knows where"?
WTF?

[cstanleytech]

2. It will likely impact somewhere in the oceans rather than play out like

it did for poor George on Dead Like Me.

[Nitram]

3. Considering the ratio of ocean to land on the Earth's surface, the odds are that it will end up

in the ocean.

[lastlib]

8. key question, though, is.....

...what is the ratio of ocean to land below its orbit? That might change the probabilities.

[LongTomH]

5. Hardly 'flaming!' By the time these pieces reach the surface of the Earth, air drag will have......

........slowed them to the same "terminal velocity" as anything falling from a high-flying aircraft.

"The downward force of gravity (Fg) equals the restraining force of drag (Fd) plus the buoyancy. The net force on the object then, is zero, and the result is that the velocity of the object remains constant."

[Jim Lane]

6. You're analyzing only the downward velocity caused by gravity.

As of right now, the space station has a forward velocity (tangential to the force of gravity) of thousands of miles per hour. The atmospheric drag will reduce it but there's no mathematical certainty that it will reduce it to zero. At the moment before a fragment reaches the ground, it will be traveling diagonally relative to the Earth's surface. The vertical component of its velocity will, as you say, be the terminal velocity for an object of its shape and density. The horizontal component will, I'm guessing, be considerably greater.

As for "flaming", I don't know whether there will be visible flames, but the fragments will certainly be intensely hot. IIRC, the space shuttle astronauts have to stay inside for quite a while after the shuttle lands. Even its controlled descent through the atmosphere has left it with a surface temperature of thousands of degrees. A 100kg fragment of a space station would start a fire on Earth if it landed on or near combustible material.

[ffr]

4. I'm surprised they don't attempt to stabilize it's orbit with a rescue

Call Elon Musk. His team would probably figure out a way.

[NNadir]

7. It is actually a better idea, despite the small risk, to let defunct orbital objects...

...crash into Earth to prevent collisions. Objects in orbit if hit by an asteroid, or another object left in space, say a wrench lost by a shuttle astronaut, have the momentum of cannon shells.

There is some risk that privileged orbits, particularly geostationary orbits can become so cluttered with debris that no satellite can remain in orbit for very long.

This also applies to orbital paths through which spacecraft must travel to get to those orbits.

https://www.orbitaldebris.jsc.nasa.gov/

Let it crash into Earth. We certainly don't need more interference from that fool Elon Musk.