China confirmed in a press conference, that Tiangong-1, their first space station put into orbit in 2011, will re-enter and burn up in the atmosphere sometime in late 2017. There seems to be some uncertainty in when it will re-enter the atmosphere, which leads one to believe that the station is not under orbital control and that it will come back to Earth in the same manner that Skylab did in 1979.
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First Chinese Space Station Coming Back to Earth
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(Score: 5, Informative) by martyb on Sunday September 25 2016, @12:43PM
Disclaimer: I'm by no means a 'rocket scientist'
When an object falls out of orbit, it does not suddenly stop and drop straight down. An object in orbit has a huge horizontal component that provides an acceleration that matches the acceleration of gravity. Drag from the upper atmosphere gradually bleeds off speed causing it to lose altitude. As the object dips lower, the density of the atmosphere increases which, in turn, increases the drag on the object, which makes it lose even more altitude. Eventually, that altitude loss reaches the point where the object impacts the ground... and it still has a large horizontal component.
Consider that we are starting with an object which makes a lap of the Earth every 90 minutes or so (compare that to your last long-haul flight), that is a huge amount of speed to bleed off.
A slight variation in density at very high elevations can dramatically affect where on earth the formerly orbiting object ultimately lands. (Consider the different trajectories of throwing a baseball in: a vacuum, air at sealevel, and under water.)
So, forecasts as to where it would land are very difficult to predict until the object has dropped quite a ways into the atmosphere and any air density variation is small compared to the average density. In other words, with reduced variability in the calculated amount of drag, a more precise estimate can be made of the final landing location. Even then, instead of an impact point it is more likely to be an expected path or stripe on the Earth.
It is early in the morning as I post this, so any corrections/clarifications by those more knowledgeable in orbital mechanics are welcome!
Wit is intellect, dancing.
(Score: 2) by Dunbal on Sunday September 25 2016, @02:46PM
GO KERBALS!
Nothing wrong with what you said. The object will heat up and start tumbling. The combination of heat and g-forces from the tumbling it will be doing will cause all but the largest and most solid components to break up into small pieces. There might be a few chunks left that could be hazardous if they fell on anyone but good old probability dictates that those will end up falling in the ocean or on empty land. While there are more people and cities than there were in the 1970's when Skylab came down it's still not THAT crowded yet. This is pretty much a non issue but the uncertainty and fear sells news articles and generates hits.
(Score: 5, Informative) by deadstick on Sunday September 25 2016, @03:16PM
To amplify a bit: The trajectory of a deorbiting object can be predicted accurately if we know the shape and mass of the object, because that's enough information to calculate the drag. It works well for an object that's designed to reenter, like a missile or a manned spacecraft. But these objects are also designed to survive the process.
A space station isn't: it's designed to stay up there and it won't reenter in one piece. It will break up in a highly unpredictable manner, with each piece having a different shape and mass and coming down in a different place. Further, even the point at which the disintegration starts is unpredictable, so there's a huge uncertainty in how far along the orbital track pieces will start impacting. Once the disintegration starts, more information starts to emerge, and the center of the impact area can be predicted to some degree of precision -- but this won't happen until well into the last revolution. Basically, you can draw a stripe on the map many hundreds of km long and say most of the debris will come down in it.
Something to worry about? No: nature throws rocks at you every day, and almost always misses. Meteors big enough to get through the atmosphere hit the surface at a rate of dozens per day, worldwide. Estimate the fraction of the Earth's surface that's occupied by human flesh and you're on the way to seeing why human injuries are pretty rare (one in the 20th century, more in the massive Chelyabinsk event of 2013).
I would gladly stand outdoors at the computed impact center...it would be quite a show.
(Score: 0) by Anonymous Coward on Sunday September 25 2016, @04:20PM
Duh
(Score: 0) by Anonymous Coward on Sunday September 25 2016, @01:15PM
Back in 2008 the US shot down a dead spy satellite [wikipedia.org] officially because it might crash into somebody (but there must have been some really good tech on it to warrant the effort). We can do it again.
(Score: 2, Disagree) by Dunbal on Sunday September 25 2016, @02:51PM
No, they shot it down because there were fears that its hydrazine fuel tanks could survive the landing intact, and hydrazine is highly toxic and not something you'd like a) to fall near inhabited land b) on crops or c) into the hands of terrorists. The intercept was to make sure the tank was ruptured.
(Score: 1, Informative) by Anonymous Coward on Sunday September 25 2016, @05:18PM
You can't really "shoot down" something that's in orbit. All you can do it spread it out a bit. Quite a lot, in fact.
(Score: 0) by Anonymous Coward on Sunday September 25 2016, @02:06PM
The universe spat it out.
(Score: 0) by Anonymous Coward on Sunday September 25 2016, @03:22PM
Objects on earth are still in the universe. Materials in the atmosphere are also still in the universe. Keep an eye on your dumb-o-meter, or the universe may spit you out!
(Score: 0) by Anonymous Coward on Sunday September 25 2016, @04:02PM
That means you'd better duck.
(Score: 2) by fishybell on Sunday September 25 2016, @05:02PM
So, free tacos [spaceref.com]?
(Score: 0) by Anonymous Coward on Monday September 26 2016, @08:19AM
.. because they cannot maintain it, it is impossible.
Now that youtube is everywhere, an increasing number of people sees right through the hoax: there IS NO "Chinese Space Station", as there is no "International Space Station". It is all greenscreens, smoke and mirrors, filmed in zero-G aircraft (and ridiculous amounts of hairspray), with the EVAs shot in a pool.