TianGong is Coming Down!

[Mortymoose]

Been following this for the last two days on stuffinspace....


In the last hour she has dropped 10km..... She's coming in baby!

How exciting is this guys?





/Moose rushes out to make his final braai in anticipation of a bus size Chinese lump of radioactive spoils the taste of the steak!

 

[Mortymoose]

I don't get this, One of you Space nutters explain to me, how this Station dropping to earth, and the suddenly climbs 3 Km higher. Why is this, I saw that flick with Sandra Bullock where she climbed into the Chinese Space Station that was plummeting to the earth, it was shaking to pieces, glowing like Fanie's braai before a Lions game, but it never went up, just down...

Please explain before I get to pissed and land up phoning the Chinese Cafe on the corner for a detailed explanation....

 

[Hamish McPanji]

You assume the earth is round. That's where your problem is.

 

[Gordon_R]

Strange category for a science story, but yes it is coming down: http://www.bbc.com/news/science-environment-43557446

Experts tracking China's defunct Tiangong-1 space lab say it could now fall to Earth later than thought.

The analysis had suggested the 10m-long, 8.5-tonne spacecraft would plunge into the Earth's atmosphere between midday Saturday and the afternoon of Sunday (GMT) - and it still could.

But the most recent assessment has extended the estimated window for re-entry.

It now goes out to the late evening of Sunday, 1 April.

The situation remains highly variable.

 

[Gordon_R]

The orbit is not circular, and can only be measured from a few locations on earth each day, so it is very difficult to confirm the details of the reentry.

P.S. There is a Wikipedia page, if you want the whole story: https://en.wikipedia.org/wiki/Tiangong-1

Edit: Even more detailed story: https://www.space.com/40154-chinese-space-station-crash-pacific-ocean-prediction.html

 

[Mortymoose]

I have been following this for the past week, but tracking since Thursday night, expecting it to come down sometime in the next 24 hours, but have also realised, that Tuesday at 19h34 might be more probable.....

 

[Gordon_R]

Every week at least one satellite reenters the earth's atmosphere. Its only media hype that makes this one special.

Video showing how ESA monitor objects in orbit. Nasa has the main tracking networks, but this video is recent and topical: https://www.youtube.com/watch?v=x-nKA9fSFCk

Each year, about 100 tonnes of defunct satellites, uncontrolled spacecraft, spent upper stages and discarded items like instrument covers are dragged down by Earth’s upper atmosphere, ending their lives in flaming arcs across the sky.

And that's not counting all the discarded rocket boosters, which reenter during the first orbit over the ocean.

Edit: If you are really lucky you might see something (ESA ATV Jules Verne) such as this one: https://www.youtube.com/watch?v=OhBw5yaR_SU

 

[Mortymoose]

Every week at least one satellite reenters the earth's atmosphere. Its only media hype that makes this one special.

Aye! Agree, but this one is the size of a school bus, I know it will burn up on reentry and the remains will fall into the ocean (Near Castaway Island) , but it's still amazing tech to be able to "track" this online!

 

[Mortymoose]

Now 14km higher than when I started this post!

 

[Gordon_R]

http://www.bbc.com/news/world-asia-china-43551144

The latest projection from the Esa points to re-entry at 07:25 Beijing time (00:25 GMT) on 2 April, although the window is still "highly variable" - stretching from Sunday afternoon to Monday morning.

Most of the station is likely to burn up in the atmosphere but some debris could survive to hit the surface of the Earth.

The China Manned Space Engineering Office said on social media that falling spacecraft do "not crash into the Earth fiercely like in sci-fi movies, but turn into a splendid (meteor shower)".

 

[genetic]

You assume the earth is round. That's where your problem is.

The orbit is not circular

This.

 

[Gordon_R]

The subject of orbital mechanics and spaceflight is complex (way beyond my expertise), but worth skimming over:
https://en.wikipedia.org/wiki/Orbital_spaceflight and https://en.wikipedia.org/wiki/Orbital_decay and https://en.wikipedia.org/wiki/Atmospheric_entry#Uncontrolled_and_unprotected_reentries

There are a very large number of issues involved in determining an accurate orbit, though most are not relevant to this discussion. The earth is not round, but an oblate spheroid, with mass concentrations under the continents. This overlaps with GPS and mapping, but the exact shape of the earth is a state secret, since this influences the trajectory of intercontinental ballastic missiles. See: https://en.wikipedia.org/wiki/Figure_of_the_Earth

The majority of satellites are not in pefectly circular orbits, but slightly elliptical. Not relevant to this discussion, but over time an orbit will drift, due to tidal influences from the sun and the moon. Almost every spacecraft has small thrusters to periodically boost the altitude, and keep position (in the case of a geostationary satellites).

The atmosphere is never uniform, and there is very little real-time data on the density of the uppermost layers. In this respect reentry is an 'experiment', since the exact outcome cannot be predicted in advance, only by undergoing the process...

 

[The_Librarian]

Maybe it bounced off the atmosphere like a pebble skips on water?

 

[KleinBoontjie]

^That's it, until it looses enough speed

 

[Magnum]

Maybe it bounced off the atmosphere like a pebble skips on water?

How hard and fast do you need to throw a Pebble to skip 14KM? Superman se moses.

 

[Gordon_R]

Maybe it bounced off the atmosphere like a pebble skips on water?

Skipping off the atmosphere mostly applies to objects that exceed orbital velocity (such as meteorites), or have a shape that promotes areodynamic lift (not likely in this case). An interesting example was the Apollo spacecraft, from trans-lunar orbit reentry: https://en.wikipedia.org/wiki/Boost-glide

 

[genetic]

Maybe it bounced off the atmosphere like a pebble skips on water?

Physically not possible. The space station does not orbit at speeds sufficient enough to cause atmospheric reflection.

 

[Gordon_R]

http://www.bbc.com/news/science-environment-43557446

The estimated window of re-entry for the defunct Chinese space lab Tiangong-1 has narrowed sharply.

The timeframe for the fall to Earth now runs from midnight on Sunday to the early hours of Monday (GMT).

Correction: The orbit chart shown was only a schematic.

 

[biometrics]

Oh boy, Cape Town might get it!

 

[Gordon_R]

http://www.bbc.com/news/science-environment-43557446

The estimated window of re-entry for the defunct Chinese space lab Tiangong-1 has narrowed sharply.

The timeframe for the fall to Earth is centred on 01:07 Monday GMT (02:07 BST), plus or minus two hours.

Edit: No further updates will be issued, due to the lack of real-time data: http://blogs.esa.int/rocketscience/2018/04/01/monitoring-almost-complete/

In just a few hours, we’ll be well within the uncertainty window associated with this reentry, and we don’t expect any more forecast updates with any higher accuracy. In other words, we’re at the limit of what we can forecast.

Just over an hour ago, ESA’s space debris team provided their final estimate for reentry, forecasting a window of about four hours between 23:00 UTC on 1 April to 03:00 UTC on 2 April (01:00 CEST on 2 April to 05:00 CEST on 2 April).

“The high speeds of returning satellites mean they can travel thousands of kilometres during that time window, and that makes it very hard to predict a precise location of reentry.”

Edit: That's an understatement! With an orbit period of less than 90 minutes, it covers the 40,000km cicumference of the earth in an hour and a half. This object is moving over 27,000km/h (or 8km/sec)...