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China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...
9

China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
China's Tiangong-1 space station will crash to Earth within weeks

Experts say it is impossible to plot where module will re-enter the atmosphere, but the chance is higher in parts of Europe, US, Australia and New Zealand


https://www.theguardian.com/science/2018/mar/06/ch...

John R. Baker, P.E. (ret)
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Chicken Little

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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Somehow I like this paragragh:
"The US-funded Aerospace Corporation estimates Tiangong-1 will re-enter the atmosphere during the first week of April, give or take a week. The European Space Agency says the module will come down between 24 March and 19 April."

Yes, technically, there is a slight difference between 'the first week of April, give or take a week', and 'between 24 March and 19 April', but in this context, the difference is not particularly meaningful.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

TenPenny,
Yes, but if it does come down in the first week of April, the Aerospace Corporation will appear to be brilliant with their "more accurate" prediction, whereas if it comes down in the larger window of time they both are actually predicting, they'll be equally as correct as the ESA

Andrew H.
www.mototribology.com

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

In case anyone is curious, here's the output from STK for one orbit of TianGong-1. STK is absolutely free for doing this sort of thing right out of the box. You can pay to do more, but it's pretty awesome as a free tool. Much more fun that some other programs that are free.





TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

The question is, how many big pieces won't burn up on reentry?

Another is how many small space garbage is it collecting, vs how much is it depositing?

Is there a positive here, or is it all negative?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Remind me to carry my umbrella, Wiley Coyote-style.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"Another is how many small space garbage is it collecting, vs how much is it depositing?"

The stuff it is collecting is essentially irrelevant, as they are extremely small. Whatever it winds up generating will virtually all fall back to Earth, since they'll be in too low an orbit to be sustainable. Anything big that it hits will likely result in a spray of particles and objects, and would be a losing proposition.

TTFN (ta ta for now)
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"...it is impossible to [know] where module will re-enter..."

Wiki says: "Orbital inclination: 42.8 degrees"

Anyone north of about 43°N or south of about 43°S is probably safe. At least from this particular risk.

Checks location, confirms 45°N. Phew!

Fairly good odds (50-50) it'll hit the Pacific... ...maybe.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Is it hard to predict because it might start tumbling?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Reportedly, the upper atmosphere moves up and down depending on the Sun's mood and other factors. Effective upper atmospheric height is a very critical factor due to the high order positive feedback, as it rapidly cascades into re-entry. Since 45 minutes is halfway around the world, and the inclined orbit shifts with each pass, it's all a bit semi-random day to day. That's presumably the most influential factor.

Re-entry, start to finish, can cover a couple thousand miles. But once it starts, any drag or tumbling in the atmosphere would be closely followed by almost immediate disintegration into bits, so that tumbling would merely adjust the outcome within a small region. Drag while still in the very wispy upper reaches would be affected by the station's aspect angles relative to the movement; so you'd have a good point there.

Tidbit: The Apollo CM had manoeuvring capabilities during re-entry, so they could be steered to land a few miles from the recovery fleet, if they were skilled and lucky on the day. The CM actually went back up (400,000 feet ?) to cool off, and then fall back down again.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

I remember that back up in the charts, but it did not understand enough to ask (besides who would I ask).

I also assume the orbit is a little out of round, so it would have some high and low points in the orbit.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Not very eccentric. But most of the action will happen at perigee, due to the high order positive feedback.

Quote (Orbital data)

The orbit data is extracted from the following two-line orbital elements,
1 37820U 11053A 18066.28711319 .00173836 22757-4 17260-3 0 9997
2 37820 42.7506 1.1197 0016400 192.5561 300.3591 16.10185824369864
Epoch (UTC): 07 March 2018 06:53:26
Eccentricity: 0.0016400
inclination: 42.7506°
perigee height: 235 km
apogee height: 257 km

right ascension of ascending node: 1.1197°
argument of perigee: 192.5561°
revolutions per day: 16.10185824
mean anomaly at epoch: 300.3591°
orbit number at epoch: 36986


Ref: http://www.heavens-above.com/orbit.aspx?satid=3782...

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Apollo and similar also had a spacecraft that was command to fire braking thrusters to control time, position, and angle of re-entry. The Chinese station is reportedly no longer under ground control, and so is going to re-enter at some random combination of those factors.

For comsats in geostationary orbits, there is a protocol that requires spacecraft to reserve enough fuel for them to be put into parking orbits away from useful slots, to prevent collisions when replacements are sent up. And at least Iridium, if not others, using low orbits, has (had?) planned for de-orbiting fuel reserves, i.e. dropping their spacecraft back into the oceans, to similarly keep their orbit stations clear and also to drop them into less populated areas.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

3
Somewhere on YouTube is an old (1960s) film (now video), about 20-30 minutes in length, where the whole CM re-entry process is explained. It's much more complicated than one might assume.

The Apollo CM had to be steered into a fairly narrow re-entry corridor, to avoid burning up or skipping back out. So the CSM (CM + SM still attached) was steered into the approach corridor (using thrusters) before the SM section was jettisoned. Once the CM was on its own [and in the atmosphere], they could use aerodynamic steering by rotating the CM on its yaw (?) axis, using little thrusters to turn, to have the center of mass above or below the center of pressure. It actually went back up, trading speed for huge altitude gain (for cooling). One benefit of this steering was that it widened the allowable corridor from something like 2°, which was impractically narrow and thus dangerous, to a more reasonable 8° (these numbers from memory, so might be incorrect).

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Great videos! Those old films are so much better at conveying a subject than the quarter-assed PowerPoint presentations that pass as training these days.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Um, well, thanks for the stars, but VE's the one who pointed me towards them, so gave him one from me...

The YouTube channel that hosts those videos does have a bunch of other old training films (from WW2 onwards), and yes, the level of information and use of humor make for good watching.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Mission reports from all Mercury, Gemini, Apollo missions plus many other subjects:
Apogee Books: http://www.cgpublishing.com/

STF

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Oh, and how could I forget, on a thread about a space station with a decaying orbit:
Skylab

STF

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
Not to mention several so-called spy satellites that have come down over the last few years, some of which there were concerns because of the fear some of the larger components would not completely burn-up before reaching the ground.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

When they contain chunks of radioactive materials, it's perhaps best if those chunks don't burn up in the atmosphere.

- Russian satellite Kosmos 954 made a big radioactive mess in Canada's Arctic.

- Apollo 13's LM contained an RTG. Famously the LM was unexpectedly used to get home. But not so unexpectedly that NASA didn't plan for exactly this sort of thing. They put the plutonium core in a cask for safety.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

On the Apollo 13, I remember batteries, Fuel Cells, but why would they need plutonium? Possible battery for something they wanted to leave behind on the moon?

So the takeaway I am getting is, if it lands in your backyard, don't touch it. One should remember that from the old sci-fi movies.


RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

From the 'net, gently edited:

"Apollo 13 carried the SNAP-27 radioisotope thermoelectric generator (RTG) that was supposed to be left on the moon to power experiments. It had been engineered to make it back to Earth intact, just in the event of exactly such an incident (the LM as Lifeboat scenario). [Somebody should get a Nobel Peace Prize that that decision!] The plutonium apparently survived reentry and came to rest with what remained of the lunar module in the Tonga Trench south of Fiji, approximately 6-9 kilometers underwater (exact location is unknown). Extensive monitoring of the atmosphere in the area indicated that no radiation had escaped."

Edit:

See diagrams and pictures here: https://en.wikipedia.org/wiki/Apollo_Lunar_Surface...

"The RTG cask stored the plutonium-238 fuel element. It was located to left of the SEQ bay. The cask was designed to withstand a launch vehicle explosion in the event of an abort or a re-entry into Earth's atmosphere (which is [EXACTLY] what occurred on Apollo 13). The picture shows Edgar Mitchell practicing the removal of the fuel element."

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
It appears that they're refining their prediction as to where the Chinese space station might impact the Earth:

http://www.dailymail.co.uk/news/article-5486985/Lo...

BTW, my wife and I are flying to Detroit on April 10th, which is at the edge of the current impact 'window', and we'll be staying, at least for the first few days, well within the 43 degrees North Latitude limit.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
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The secret of life is not finding someone to live with
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"put the plutonium core in a cask for safety" ... reminds me of
1) "cone of silence" (get smart), and
2) "surround the camp with a ring of steel" (hogan's heroes)

another day in paradise, or is paradise one day closer ?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Huh? What's that?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

:D I saw the news today that this might fall in SE Michigan. We just had a meteor fall locally about a month ago which inspired quite the manhunt and many jokes involving pics of frozen dog turds posted as "meteor for sale."

I cant wait to see what the locals do this time. :D

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
Here's the latest update on the pending reentry of that Chinese space station:

A space station from China is expected to crash into Earth next week

http://wjla.com/news/offbeat/a-space-station-from-...

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

I know that if the satellite (With its upper stages of the assembled missile) is not adjusted once in orbit by additional motor burns, the furthest north and south of the orbit are determined by the latitude of the launch site if the missile is launched due east to take advantage of the earth's rotation. But what orbital dynamics force the actual path to oscillate between its furthest north and south points?

From logic, I can't figure out the forces that would make an orbiting body launched due east to move back across the equator.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Racooke, not clear what you are asking, so I'm probably rambling a bit here:

What causes orbital perturbations? A couple of things - gravity tides from the moon and sun will tend to pull on a spacecraft in a purely equatorial orbit, shifting its orbital plane over time. Also the gravity field of earth is not uniform, there are some significant mass concentrations (google image search for earth gravity map) that perturb spacecraft orbits.

https://en.wikipedia.org/wiki/Orbital_station-keep...

But Tiangong was not in a purely equatorial orbit, it was launched at a latitude some distance above the equator, so it orbits at an angle to the equator. Not all spacecraft are launched due east, necessarily, they are launched and gain velocity in whatever direction you want the final orbit to be in, or whatever vector the rocket engines pushed in, hopefully those were the same. If launched from say, 45 deg. N, earth's rotation only gives you some 70% of the eastward velocity vector that you get at the equator, which is significant, but it's still only a fairly small fraction of the velocity needed for a stable orbit. And remember, the orbit has to be centered on earth's mass, so if you launch :due east" from 45N, you will still end up in an orbit with at least 45 deg. of inclination, your extra east velocity ends up pushing your orbit inclination more northerly. You might need to grab a ball and some rubber bands to help you visualize it, or a good map with "great circle" shipping/flying routes shown on it. In general, the minimum fuel to low orbit puts you in an orbit with an inclination close to the launch latitude.

FWIW, it's not "intuitive", it takes a bit of study and/or practice. Watching my kids figure out Kerbal Space Program was a lot of fun - and I was surprised how quickly they started to figure this stuff out. Now #2 son is off doing some programming to put KSP-type interfaces to work for real spacecraft.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"...forces that would make an orbiting body launched due east to move back across the equator."

It's moving in an orbital plane, it's just that the orbital plane is inclined to the Earth's equator. As you hinted, that's due to the latitude of the launch site (unless actively compensated).

And it's not sync to the Earth, so the equator crossings move around the Earth in longitude.

Basically, put away the map and refer to a globe. It's actually fairly simple referenced to a globe. smile

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

PS: A good example of an orbit that looks insane on a map is the Tundra Orbit, used by Sirius satellite radio. Viewed against a globe, it's just (as expected) an ellipse.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Quote:

Aerospace, a research organization that advises governments on space, predicts the station could hit a variety of cities in the United States including Boston, Detroit, Philadelphia, Des Moines, Milwaukee and Salt Lake City among others.

...among others....stand by adventure fans!

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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Do I have enough time to get a catcher's mitt?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"Catch a falling star and put it in your pocket..."- which assumes you have a Kevlar catcher's mitt and asbestos pockets, but they didn't put that in the song.

Do you realize that if you made a bulletproof catcher's mitt, somebody would feel obligated to try it out?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
Here's the latest update:

Out-of-control Chinese space station 'will crash into Earth over weekend'

The European Space Agency has revised its prediction for when free-falling Tiangong-1 will crash into Earth.


https://www.mirror.co.uk/science/chinas-free-falli...

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Quote:

"At no time will a precise time/location prediction from ESA be possible," it explained in a statement .
I'm going to guess a few seconds before it impacts terra firma they'll have a pretty good idea of when/where... wink

Dan - Owner
http://www.Hi-TecDesigns.com

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
A friend of mine (and fellow MTU graduate), who used to be in charge of the CIA's spy satellite program (at least the building and launching of them), said that a bunch of his fellow, and now retired, co-workers have a betting pool covering if and where debris will impact the Earth. He said they used to do this whenever one of their own 'birds' was coming down although he said that most of their's would "burn in", meaning that they had enough residual fuel on board to control when they actually re-entered the atmosphere although he says that several still ended-up 'skipping' along the top of atmosphere like a flat stone tossed into a lake, thus the betting pools.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"have a betting pool covering if and where debris will impact the Earth"

I'll take $50 on "if". bigsmile

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

I'll put a dollar on: the ocean.

If I need to be more specific, then: the Pacific.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

I lay odds on "surface."

Also - https://xkcd.com/1337/

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

"If" What are the odds of betting against it hitting the earth?

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

2
"...hitting the earth?"

The odds of it hitting the earth are less than 25%.
The odds of it hitting the Earth are essentially 100%.
smile

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Odds of it hitting a Flat Earther?

Steve

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
Here is the link to the real-time satellite tracker which is watching the Tiangong-1 space station:

http://www.satview.org/?sat_id=37820U

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

From John's link - here's the map with the projected "crash" location - east of South America.

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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

(OP)
I suspect that if we check back in a day or two, the forecast of the date and time of the POINT OF REENTRY (as opposed to the "crash location") will have changed.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

This far out, they should include some Error Bars, i.e. Longitude +/- 180°, Latitude +/- 43°N or S.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

This explains why there's even more uncertainty than usual; the station is tumbling:
https://www.space.com/40089-china-space-station-ti...

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Interesting graph for, will it hit anything that matters or anybody

Link

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

As noted, the "predicted re-entry" time and impact point are still varying. Latest prediction is a bit worrisome, though I'm certain my house (shown on map) is a few degrees north of the possible impact zone.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Concerned about your house? Did you drive to work this morning?

Besides, if part of this thing landed in my yard, I believe it would be like winning the lottery. Who wants to buy a used Chinese space station?


RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

I'm more interested in the possible viewing opportunity, thinking of setting up a time lapse or motion-detecting camera to record it, esp. if it comes down at night, on my side of the planet, within several hundred kilometers, and last, if I remember.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Predictions starting to become meaningful. But still subject to small adjustments.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Tiangong-1 comes down over South Pacific

BBC News

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

http://www.satview.org/?sat_id=37820U

11:33 PM, Sunday night. Claims the space station is now down about 7 minutes ago: About midway between the Brazil and West African coast.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

But other reports have it coming to rest in the Pacific, east of Samoa.

RE: China's Tiangong-1 space station: Perhaps not a disaster yet, but keep looking-up just in case...

Darn, and here I was eyeing the various burnt bits of trash alongside Detroit freeways for a Chinese flag.

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