

Track Europe's falling, 2,000-pound satellite in real-time - joering2
http://www.foxnews.com/science/interactive/2013/11/08/track-europe-falling-2000-pound-satellite-in-real-time/

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lelf
[http://blogs.esa.int/rocketscience/](http://blogs.esa.int/rocketscience/),
[http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/G...](http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_completes_its_mission):

This morning GOCE was at an altitude of around 160 km. As expected, the drag
levels have increased very much, with the average now around 90 mN
(milliNewton).

Re-entry of GOCE into Earth’s atmosphere is predicted to occur during the
night between Sunday and Monday, 10/11 November. Break-up of the spacecraft
will occur at an altitude of approximately 80 km.

Q: Do we expect any of these to reach the surface?

HK: Most of these fragments will completely burn up. A small fraction of the
initial spacecraft mass – about 20% or 200kg – is expected to reach ground,
distributed across dozens of fragments, spread over a sizable re-entry ground
swath.

Q: Is there any risk to anyone on ground?

HK: The risk to the population on ground will be minute. Statistically
speaking, it is 250,000 times more probable to win the jackpot in the German
Lotto than to get hit by a GOCE fragment. In 56 years of space flight, no man-
made space objects that have re-entered into Earth’s atmosphere have ever
caused injury to humans.

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deletes
Hmm.. is that statistic calculated for each individual or for the entire
population. The changes are to hit are very low in either case, but there is
still a large difference mathematically.

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maigret
Let's try to get an order of the probability... Let's say the parts land on
earth with an an angle of more than 45 degrees. I'd take 1 sqm for each human,
understanding the angle would reduce that number. Which makes around 10000
sqkm, counted generously. The earth total surface is around 510 millions sqkm.
So that's one in 51000 chances for any human to be hit (calculated high). So
quite makes sense that no one was impacted yet, but this seems not impossible
as well - of course depending on how many satellites impact earth each year.
Not counting that people are often in buildings, but one impact could kill
more than 1, etc. Personally, I take this number for negligeable still. It
would rather be hard finding anything build by humans killing less people.

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konceptz
Please correct me if I'm wrong but, your calculations don't take into account
the population's distribution over the surface of the earth; most importantly
water masses.

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Arnt
The falling debris doesn't take that into account either, so the calculation
is right (give or take the odd approximation).

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deletes
Original site:
[http://www.n2yo.com/satellite/?s=34602](http://www.n2yo.com/satellite/?s=34602)

The ( ion-driven :) )satellite:
[http://en.wikipedia.org/wiki/Gravity_Field_and_Steady-
State_...](http://en.wikipedia.org/wiki/Gravity_Field_and_Steady-
State_Ocean_Circulation_Explorer)

Current altitude: 159.30

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joering2
perhaps its one of my extensions, but this is what I am getting from n2yo
site:

Connection refused (111) __* Connection refused (111) __ _

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deletes
Same here, the site must be overloaded.

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iM8t
Out of curiosity: will the satellite burn up while falling down or is there a
slight possibility that it could crash in a residential area?

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iamshs
They (ESA) said, there is a possibility of some pieces surviving the burn, and
affecting 20 sq metres of area.

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ratpik
It is dropping altitude faster (40 metres/sec) as it nears the equator and is
moving at almost constant velocity (between 7.89-7.91). Looks like it will
continue to slowly spiral around the earth and crash in the Atlantic
Ocean/N.America based on simple extrapolation. Except that the it is probably
not going to be that simple. Just hit the equator. Alt: 156, Spd: 7.93, Long:
128.8, Lat: 0. Now altitude is increasing again.

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cshimmin
The altitude is rising and falling because the satellite is in an
(approximately) elliptical orbit around Earth. Go play you some Kerbal Space
Program! :)

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mistermann
I'd think there'd be somewhat of a chance that parts could break off during
reentry which might have a much greater chance of hitting a lower terminal
velocity and therefore not burn up, can anyone explain why this doesn't seem
to be the case? Is it that the high velocity in the upper atmosphere causes
much greater heat and destruction than if it was falling through a more dense
atmosphere?

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gibybo
Anyone know what units the altitude and speed are in? I'm guessing km and km/s
but I can't be sure.

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molecule
looks like km/s in the map widget

via [http://www.n2yo.com/?s=34602](http://www.n2yo.com/?s=34602):

    
    
        SPEED [km/s]:	7.93
        SPEED [mi/s]:	4.93

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praseodym
ESA has more information about the reentry:
[http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/G...](http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_completes_its_mission)

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joering2
How come they are unable to know precisely where it will hit? Isn't it "just"
lots of math to go through?

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gibybo
I'm guessing they don't know exactly how the wind currents are going to change
over the course of it's flight.

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joering2
Yes, however winds would apply only to earth atmosphere. Most of its traction
happens above earth atmosphere, right?

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sp332
What would cause drag besides the atmosphere?

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Xophmeister
For the minute-or-two I've been watching, it's actually been going upwards:
from about 166km to 170km.

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klodolph
Play more KSP. You learn pretty quick "just because it's going up, doesn't
mean it's going to stay there."

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bbllee
Yeah, hard bounce off the atmosphere trades angular momentum for radial
velocity and increases eccentricity, meaning next time you hit the atmosphere
is gonna be even worse.

