Comment by lelf | Hacker News Reader

Comment by lelf | Hacker News Reader

http://blogs.esa.int/rocketscience/, http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/G...:

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.

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.

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.

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.

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

Might be worth taking into consideration that an object will break up into multiple pieces during re-entry.

Thought the odds are still against anyone being hit by anything.

Good point! I just found the Nasa has published on this topic: http://www.nasa.gov/pdf/585584main_UARS_Status.pdf

Risk expected is one in 10000, but for every object if I understand it well. And the current one is rather 1/3200, probably because of its size.

> Q: Is there any risk to anyone on ground?

> HK: The risk to the population on ground will be minute. Statistically speaking,

Its nice to see some common sense and statistics to play key role in "preparedness" in this situation.

To the contrary, the "War on Terror" continues with 1/18th of US debt being spent [1], even though the odds of dying due to terrorist attack are minimalist [2].

[1] http://nationalpriorities.org/cost-of/

[2] http://www.washingtonsblog.com/2013/08/president-obama-the-o...

<NSA>The odds of dying in a terrorist attack are minimalist because we spend 1/18 of the US budget to keep you civilians safe! Also, your wife just emailed you to remind you to pick up milk at the store.</NSA>

> The odds of dying in a terrorist attack are minimalist because we spend 1/18 of the US budget

Yes, I agree. Terrorism in US falls under basic "create problem and offer solution" category.

The odds of dying in a terrorist attack would be even smaller, had we never gone to Iraq, never started Afghanistan war and did thousands other things throughout the history of US that got most of the world pissed off, starting from hard core terrorist from Afgan mountains all the way down to the WW2 veterans (american citizens) being pissed off because Gov closed national parks.

So why don't you stop all those shady operations around the world and eventually, as a result, keep that 1/18th of the budget that you so desperately need to spend on "keeping civilians safe" in your/citizens own pockets.

You do realize that I'm not actually from the NSA, don't you?

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