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

[JohnRBaker]

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...pace-station-will-crash-to-earth-within-weeks

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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[JohnRBaker]

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'
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

 

[VEBill]

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.

 

[cranky108]

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.

 

[VEBill]

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_Experiments_Package#Common_elements

"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."

 

[JohnRBaker]

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/art...crash-site-falling-Chinese-space-station.html

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
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

 

[rb1957]

"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 ?

 

[stevenal]

Huh? What's that?

 

[JStephen]

 

[CWB1]

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.

 

[JohnRBaker]

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-china-is-expected-to-crash-into-earth-next-week

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

 

[racookpe1978]

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.

 

[btrueblood]

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-keeping

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.

 

[VEBill]

"...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.

 

[VEBill]

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.

 

[IRstuff]

Tiangong-1 from space looks like this:

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[JAE]

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!

Check out Eng-Tips Forum's Policies here:
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[3DDave]

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

 

[JStephen]

"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?

 

[JohnRBaker]

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-falling-tiangong-1-12237319

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

 

[MacGyverS2000]

"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...

Dan - Owner

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