Thanks Kirk.
I was more complaining about the ridiculous precision of the odds they
give and not meaning to suggest mine was a better order of magnitude,
but only that people read this sort of precision and naturally assume
there is some supercomputer and infallible black box behind it if they
start quoting things like 1:3200, when the reality of the situation is
that someone else could defend their same calculation and have it ten
or even a hundred times less in this example. Also those such
probabilities are calculated on limited information. Just look what
happened: NASA: 1:3200 and coming down Friday evening. Oops! Changed
orientation, our probability is bullhonkey (yet the media continues to
quote it), every assumption is changed. The probability is now
1:1,235.141592
It's not an academic exercise; on the met-list it's of general
interest for those interested in meteorites striking people, houses
and even the occasional loveable crater-headed dog.
But very seriously a risk assessment needs to be done when making such
decisions as converting used satellites into projectiles although no
one will agree on a universal level of risk that is "OK", the first
step is to estimate the probability.
In the future it will be inevitable that this haphazard, seat of the
pants crashing, doesn't continue as earth adds hundreds of satellites
each year and we already have 5000 - 6000 up there plus about triple
that amount of debris, if I haven't guessed right. Satellites will
need not only to make it up, but to have a safe plan to decommission
them, like the evolution of safety controls in the auto industry. It
has to happen, though it's going to be a huge mess to sort out
agreements and give credits to poorer nations that haven't created the
current mess and are cash-strapped and then develop their satellite
networks.
The risk assessment of a 1:10,000 of a minor asteroid hitting earth
causes all this commotion... imagine the zoo all this satellite mess
is headed to turn into.
Hopefully we can figure out how to economically remove satellites
safely, or better yet create a cottage industry of salvage
entrepreneurs that can make a go at it and can be paid to remove scrap
as well by the offending parties...
So, when NASA says 1:3200 - it just looks darn foolish and a bit
arrogant, too if not given with further explanation. It's not like
this is a minor detail for scientists. It is everyone's right to know
and no government's right to put innocents at higher risk, although
they do it all the time...
Kindest wishes
Doug
-----Original Message-----
From: Becky and Kirk <[email protected]>
To: Meteorite-list <[email protected]>; MexicoDoug
<[email protected]>
Sent: Sun, Sep 25, 2011 12:47 am
Subject: Re: [meteorite-list] 1 in 3200 odds of human impact (help)
WOW---some pretty good calculations and science there Doug----BRAVO!!
NASA screws up yet again!!
Kirk.....:-)
----- Original Message -----
From: "MexicoDoug" <[email protected]>
To: <[email protected]>
Sent: Saturday, September 24, 2011 11:31 PM
Subject: [meteorite-list] 1 in 3200 odds of human impact (help)
Hi listers
I'm very suspicious of this widely quoted 1 in 3200 that is being
passed
off as a scientific number by NASA.
Not 1:3000, nor between 1:1000 to 1:10,000: but 1:3200.
This foolishly precise assertation, which if you've read "The Little
Prince" you immediately suspect it is overstated due to the author's
calculations 70 years ago there...where a similar calculation is
actually
done ...
Average cross sectional area of a person? (Depends if it is in the
morning
when everyone is praying, I guess, or in the afternoon when everyone
is
running out of work)...let's say:
Cross section per person:18 inches by 18 inches (1.5 x 1.5 sq. feet)
World population: 6.964 X 10^9 living souls
World Area: 196,939,900 sq miles
Calculations:
* Cross section per person = 2.5 sq. feet
* current world population occupies 624.3 square miles
(a wee bit bigger than Guam, and smaller than Singapore)
* people that could fit on Earth's surface: 2,196,000,000,000,000
(2.2
million X 10^9)
* Fraction of Earth's surface that's "people" = 6.96 / (2,196,000)
=
0.00000317
= People occupy *ONLY* 3.2 parts per million (3.2 ppm) of the earth's
surface
So, saving rounding till the end, each piece of UARS actually has a
1/315,457 chance of falling on people (1/0.00000317).
In rounded numbers, that's about 1:320,000 per fragment ==> 26
fragments
approximately 1:12,000 chance.
I guess if you are American you need more space than if you are
Indonesian, and changing it to a 18 inches X 17 inches would change
the
result by 6% ie, if 3200 were right for 18X18 it would now be about
1:3000, and that is one of so many assumptions making the 3200 number
a
total joke of fake scientific confidence. If you gave everyone a
square
yard ((91.4 cm)^2) instead, it would be in the 3000 range.
But here are the defficiencies I think of looking at it this way:
* this looks at the whole world vs. the limited satellite trace. A
true
measurement would do a little calculus along the path considering the
population density and the probability of earlier or later entry
which
could change probabilities by an order of magnitude easily.
* I think what I did would work for 26 darts, but not hunks of
significant
size compared to a person's area unit.
* Finally there is the Sylacauga effect for bouncing material that
will
affect things another factor of 2, 3, 4 who knows...
There must be a half dozen other complicating factors to do this
right.
Does anyone know what has been considered to arrive at the bogusly
precise
3200-1 odds being fed to us?
Love to hear any improvements on the above model (if you can call it
a
model) which I got the 1:12,000 as a streaming (unverified) starting
point
...
Kindest wishes
Doug
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