Chinese not sure where space station will land

[wolram]

The Chinese are not in control of there space station and do not know where it will land.

Chinese officials are no longer in control of the Tiangong-1 space station. Video provided by Newsy

They say the rocket motors may not burn up on reentry,

https://www.sciencedaily.com/videos/9838fa11cf2e851cdf0c28671ecefd8a.htm

 

[Laurie K]

Here's the tracking path from Satview.
http://www.satview.org/?sat_id=37820U

 

[Imager]

Shades of 1979, can they rename it Skylab II?

 

[fresh_42]

Shades of 1979, can they rename it Skylab II?

Bad idea. Skylab made history by the first time having two nations met in space.
There is nothing even near that can be said of Tiangong.

 

[Gil Lee]

Today (Jan. 8, 2018), China said in the newspaper that they have all satellites under control. In fact, China has been getting these objects from the obit to the Gobi desert as calculated and China has plenty of experience about where to have the orbiting body to be falling. Having the rover soft-landed on the moon surface at the precise location already, and planning to do the same in the far side of the moon, there is no issue for China to control the Earth orbit body. China has the world fastest supercomputer that must be helping to do all space program.

 

[sophiecentaur]

I was thinking that they were mean, not having it fly over UK. Now, I'm not so sure.

 

[Laurie K]

 

[stefan r]

Today (Jan. 8, 2018), China said in the newspaper that they have all satellites under control. In fact, China has been getting these objects from the obit to the Gobi desert as calculated and China has plenty of experience about where to have the orbiting body to be falling. Having the rover soft-landed on the moon surface at the precise location already, and planning to do the same in the far side of the moon, there is no issue for China to control the Earth orbit body. China has the world fastest supercomputer that must be helping to do all space program.

Tiangong1 did not go to the moon. It does not matter how much computer you have. When you lose communication you lose control.

 

[websterling]

Skylab made history by the first time having two nations met in space

A little late to this, but- Skylab was manned by three all American crews in 1973 and 1974. The Apollo–Soyuz Test Project, in July, 1975, was the first meeting of two nations in space.

 

[Gil Lee]

Tiangong1 did not go to the moon. It does not matter how many computers you have. When you lose communication you lose control.

Well, they confirmed in the news that they are all under good control. So, where was this new coming from? Just ask Chinese if you want to know.

 

[rootone]

Gobi desert then, and if it doesn't behave, then somewhere in the west pacific ocean northeast of Australia.

 

[mfb]

China has the world fastest supercomputer that must be helping to do all space program.

Orbital mechanics is something a phone can do today.
To control where something deorbits, you have to be able to fire the thrusters. Where is a confirmation that this can be done?
To estimate where something deorbits if you don't have access to thrusters, you have to model the atmosphere, and the largest uncertainties are from imperfect knowledge of the atmospheric conditions.

 

[websterling]

Orbital mechanics is something a phone can do today.

Forty years ago we were doing it with an 8-bit processor, clocked at 1.77MHz, with 16k of RAM, with code written in BASIC The biggest problem was obtaining fresh elsets.

 

[rootone]

I noticed that right now ( or very recently), it was above here.
https://en.wikipedia.org/wiki/Kerguelen_Islands
I didn't know that existed!

 

[OmCheeto]

View attachment 218128

Good job catching that snapshot image of the re-entry date: May 2nd
Today, two days later, the date has been changed by a month: April 4th

 

[mfb]

Link to the forecast

 

[Laurie K]

Good job catching that snapshot image of the re-entry date: May 2nd
Today, two days later, the date has been changed by a month: April 4th

Physics Forums copies the

file and stores it as a local attachment but other sites keep the external link so refreshing the page updates the forecast image. The reentry dates now seem to range between April and May.

 

[mfb]

The prediction will become much more accurate closer to the actual deorbit date - predicting the density of the upper atmosphere months in advance is not really reliable.

 

[|Glitch|]

Shades of 1979, can they rename it Skylab II?

Australia will be able to open yet another space junk museum.

Skylab's Remains: NASA Space Station Debris in Australia (Photos) - Space.com, May 13, 2013

 

[|Glitch|]

Today (Jan. 8, 2018), China said in the newspaper that they have all satellites under control. In fact, China has been getting these objects from the obit to the Gobi desert as calculated and China has plenty of experience about where to have the orbiting body to be falling. Having the rover soft-landed on the moon surface at the precise location already, and planning to do the same in the far side of the moon, there is no issue for China to control the Earth orbit body. China has the world fastest supercomputer that must be helping to do all space program.

Since China has such a fast computer maybe they can use it to track the thousands of space debris they intentionally created when they crashed two satellites into each other in 2007. They created the mess, now they can clean it up.

 

[OmCheeto]

Getting pretty close!
According to one site: "Tiangong-1 is currently predicted to reenter the Earth’s atmosphere around April 1st, 2018 14:00 UTC ± 16 hours." [http://www.aerospace.org/cords/reentry-predictions/tiangong-1-reentry/]
Quite a bit of uncertainty.
From one of their graphs, the space station is losing about 0.44 km in altitude per orbit. Current altitude is about 189 km.
Orbital period is 88.5 minutes, which means with the uncertainty, it will orbit the Earth about 22 times in those 32 hours.

Northern and southernmost latitudes that have to be worried about debris are 42.8° N & S.

Another site's infographic shows the debris field being 2000 km long. (Which is about half the width of the USA)

 

[mfb]

From the second link:

If you remember the excitement in February around the Space X Falcon 9 Heavy launch, one of the huge reasons for excitement was that those rockets come back down safely, making them re-usable and not another piece of space junk.

First stages never enter orbit, they cannot become space junk even if they are discarded (they typically land in the ocean downrange of the landing site). SpaceX actively deorbits their second stages for missions to low Earth orbits, however - to avoid adding more junk to orbit.

+- 16 hours starts to get some weak prediction for the longitude-dependence. At +- 6 hours we'll get a wide s-shaped band for the reentry prediction, at +- 4 hours large parts of the map can be ruled out.

The most recent re-entry prediction is now April 1, 14:00 UTC, or 51 hours from now.

 

[Laurie K]

51 hours +/- 16 hours is a very conservative estimate. I can remember all the cyclones coming down the Coral sea around the time of the Apollo missions when the S-IVB stage 3's were coming down.

 

[mfb]

April 1, 16:15 +- 9 hours, 38.5 hours from now. It is getting thinner. Western Turkey is out, northern South America and India to Australia are less likely. Some part in the South Pacific has been ruled out as well but no one cares about that.

 

[rootone]

I picked up some chat that the Mediterranean or N Africa region might be likely, but we wait and see

 

[mfb]

aerospace.org updated their prediction, the nominal point is now 23:30 UTC on April 1st (in 27.3 hours), with +- 7 hours uncertainty. Note that this includes times previously not in the given window. With the new prediction Central Asia and maybe South America are the most likely regions, Europe, North Africa or Australia might be hit if the station deorbits a few hours after the mean prediction. North America would only be hit if the station deorbits much faster or much later than expected.

 

[sophiecentaur]

It strikes me that wilfully ignoring the possibility of such a disaster in the initial planning of the space station should be treated as a criminal act. The must have been a time in the station's life when it could have been brought down Smith precision and somewhere safe. This is a potential International Incident; it is not a potential act of god.
But some nations have less regard than others for human life.

 

[mfb]

Who said they ignored it?
Such a risk is present in all space missions. If you think it cannot be accepted then spaceflight would be impossible. Is this really your opinion?

But some nations have less regard than others for human life.

Skylab entered the atmosphere largely uncontrolled as well. Do you consider the US one of these nations?

 

[sophiecentaur]

Risk. That’s an open term. If the demise of Skylab was as badly planned as that of the Chinese station then my comment applies. If no money can be spared for suitable protective measures then a project should not fly.
Those who are in love with space at all cost should perhaps examine the priorities a bit. We tut tut about all the space junk but it is no surprise that it exists. Disposal could be part of any project but that is not a very glamorous phase to plan (at pay) for.

 

[rootone]

Risk. That’s an open term. If the demise of Skylab was as badly planned as that of the Chinese station.

As far as I know the demise of the Chinese station wasn't just due lack of a plan. something unexpected went wrong with comms.

 

[mfb]

Risk. That’s an open term. If the demise of Skylab was as badly planned as that of the Chinese station then my comment applies. If no money can be spared for suitable protective measures then a project should not fly.

What exactly makes you think it was badly planned? You throw around accusations without any basis for them.
Which risk of injury to humans or property damage do you consider acceptable? 1 in a thousand? 1 in a million? 1 in a billion? How does this compare to the risks of Tiangong-1 and Spacelab?

Those who are in love with space at all cost

Do you have an example for this group?

Disposal could be part of any project but that is not a very glamorous phase to plan (at pay) for.

It is part of all projects. But things can fail.

 

[sophiecentaur]

something unexpected went wrong with comms

Skylab entered the atmosphere largely uncontrolled as well.

Comms can be made as fault tolerant as you're prepared to pay for. Both of those craft were built to sustain human passengers so they would both have been built with appropriate ruggedness. But skylab was twenty years earlier and things could / should be better these days.

Do you have an example for this group?

That would involve a personal comment which would not be nice but we all know how the 'space' solution for many problems gets more approval from many members. I appreciate that the Physics of a space project is often more interesting than a boring old Earthbound solution so there is some excuse for that.

I just thought. Why not use space junk as the source of material for the solar sunshade in that other thread?

 

[Laurie K]

On the latest projections (07:11 UTC, April 1) Satview has Tiangong 1 reentering on 2 April at 01:39 UTC and USstratCom has it reentering at 00:15 UTC. Both projections have an altitude of nominal burst of 128km. 15h 23m as I post.

 

[256bits]

Risk. That’s an open term. If the demise of Skylab was as badly planned as that of the Chinese station then my comment applies. If no money can be spared for suitable protective measures then a project should not fly.
Those who are in love with space at all cost should perhaps examine the priorities a bit. We tut tut about all the space junk but it is no surprise that it exists. Disposal could be part of any project but that is not a very glamorous phase to plan (at pay) for.

Does/did either one have a propulsion system capable of a giving the station a controlled deorbit.
probably not,

 

[256bits]

Which risk of injury to humans or property damage do you consider acceptable? 1 in a thousand? 1 in a million? 1 in a billion? How does this compare to the risks of Tiangong-1 and Spacelab?

Around 1 in a trillion for you or me or anyone else to be hit personally by a piece of space junk.
Globally, in the path of reentry, the number of people expected to be hit is 10^-4.