Re: Blowing up an asteroid

On Aug 22, 10:37 pm, Alain Fournier <alain...@xxxxxxxxxxxx> wrote:
Willie.Moo...@xxxxxxxxx wrote:
On Aug 22, 7:56 am, "Martha Adams" <mh...@xxxxxxxxxxx> wrote:

"Ian Parker" <ianpark...@xxxxxxxxx> wrote in message

news:c295d071-7bd5-4c9a-9c82-ed9b0657cf90@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On 22 Aug, 02:43, Claude Hopper <boobooililili...@xxxxxxxxxxxxxx>
wrote:

Blowing up Apophis or another earth bound asteroid is dangerous
scientists always claim. I don't believe them. 1000 small pieces
would
cause much less damage than a stadium size rock. Also the pieces
would
slow more easily and burn up more than the big rock. Also many pieces
would be blown off course enough to miss the earth. I do not see how
blowing it up would be a bad idea.

Lets look at what Earth Crossers and Aseroids outside the main belt
are and how they came to be where they are. They arose because of
collisions in the main asteroid belt. Earth crossers typically consist
of boulders bound together by a weak gravitational field. Any
explosion of any sort will separate out these boulders.

The secret is to make an EARLY prediction. Lasers to measure distance
are a good idea. Precise orbital calculation to determine whether it
really will hit the Earth or not is a good idea. Now precision
determination involves GTR. Sorry and all that to the disciples of
Deutsce Physik.

You then attempt to give the asteroid a nudge of mm/s. A laser might
be a good way to do this. Destruction of an asteroid should be done
only as a last resort. It WILL break it up into components of low
relative velocity. Mind mm/s will cause most of these to miss if it is
done early. The trich though is accurate calculation.

http://www.rssd.esa.int/SA-general/Projects/GAIA_files/LATEX2HTML/nod....

Physics is Platonic, theories are an objective fact not simply a
matter of opinion. The destruction of New york will be an objective
Platonic fact. General Relativity will have influenced the orbit.

I wonder whether the readership of this group really cares anyway.
Right wingers and anti Semites happen to be those who advocate
Deutsche Physik. You take a look at the Relativity ostings in
sci.physics.

I recall having a posting of mine on the subject hijacked by right
wingers who wanted to discuss intead what I had said about Anthrax.
BTW recent events have completely vindicated me anyway.

http://groups.google.co.uk/group/sci.space.policy/browse_frm/thread/4....

This is why I ask "Who in this group cares anyway?" Nobody brought the
subject back to track

http://news.bbc.co.uk/1/hi/world/americas/7547823.stm

Just shows doesn't it! Beware the woman scorned. A lot of further ***
is going to come out.

- Ian Parker

PS - In view of what people in this group seem really to be interested
in, I was tempted to change the topic title to "Beware the woman
scorned."

Back to the thread: how can anyone say anything about
blowing up an asteroid found on a Terra intersection
orbit, without knowing what the asteroid is made of?
Is it one single solid piece of near-iron?  Is it an
orbiting pile of sand?  Is it a collection of objects
ranging from micron size up to several meters?

And, how *big* is this thing?  As big as a car?  As
a house?  A few/several km dia?  And on what orbit?
If it comes in at orbital velocity reverse direction
as Terra, vs, it comes in at orbital velocity same
direction as Terra?  Big difference!

Further, "blowing up" an asteroid doesn't mean it's
gone and further detail can be neglected.  What if you
change a pile of sand into a cloud of sand, say a
cubic mile of it, and this cloud, now say 5 km dia,
impacts our atmosphere at say 20 miles/sec?  Seems to
me that might make anything local and volcanic, just
about insignificant by comparison, so far as our
weather was concerned.

I think this is a good topic for here, if those who
are posting here can get onto the topic and say
something useful and relevant about it.

Titeotwawki -- mha  [sci.space.policy 2008 Aug 22]- Hide quoted text -

- Show quoted text -

Blowing up an asteroid won't change its center of mass!  You're
turning a bullet into shrapnel.  Changing its course is the only
reasonable thing to do given the amount of energy required..  Changing
course requires producing jets of material - which can be done with
directed nuclear blasts.

http://en.wikipedia.org/wiki/99942_Apophis

The asteroid is 270 meters in diameter masses 2.1e+10 kg and has a
0.52 km/sec escape speed.

The escape velocity is about 0.52 m/s. You inserted a three orders
of magnitude typo there. This brings later a six orders of magnitude
error in your energy calculations.

hmm.. well lets take a look...

http://en.wikipedia.org/wiki/99942_Apophis

According to this source its 0.52 km/hr - so, we're both wrong.

That makes the velocity 1/3,600th and the energy 1/12.96 million - so
you're figure is about 13 times too high in terms of energy and mine
is 13 million times too high!

This correction reduces the total energy from 2.84e+15 Joules to 219
megajoules! That's 53 kg of TNT!

Now, what do you think 53 kg of TNT will do to a 250 meter diameter
rock?

Not much!

Like Martha said it depends on the details of what its made of. If
its a solid rock, it will take a lot more energy than that. I
calculated how much energy it would take to melt a block of ice and
vaporize it..

Say its a colleciton of dust particles, and there's a cave
conveniently located that goes right to the center. So we can climb
down inside the 250 m diameter ball of dust and place our 53 kg charge
of TNT.

Even if its that easy, which it may not be, it will expand the ball at
0.52 km per hour at the surface, and that ball will slow down as it
expands - after a few months it will fill a volume about a quarter
that of the Earth - and then, tidal effects will take over.

Remember, as I've said from the outset - blow up an asteroid and the
center of mass stays the same. The particles - once you get them -
and that may take lots of energy in its own right to break it up - the
particles will expand and the rate of expansion will slow - until the
velocity falls below the forces caused by tides.

the center of gavity stays the same. the asteroid is now a big cloud
of shrapnel about a quarter of the volume of Earth. Still in the same
orbit.

No problem if it hits Earth then right? all the dust motes will
vaporize in the earths atmosphere. what could go wrong?

Well,, all the dust motes will vaporize in the earth's atmosphere ALL
AT ONCE.

That is the 21 milion tons of dust motes will hit the air at about 30
km/sec meaning

E = 1/2 * 2.1e+10 * (30,000 x 30,000) = 9.5e+18 joules

spread over a disk of air about 6,000 km in diameter and 1 km deep. A
volume of air equal to all at once. 282.7 million cubic kiometers of
air, with 10 million million million joules of energy in it all at
once.

At an average density of 1.21 kg per cubic meter - a cubic kilometer
has 1.21 milion tons of air. Now this is a mass of air equal to 34,2
million million tons of air. That's 263 kilojoules per ton of air.
Air has a specific heat capacity of 1 megajoule per degree per ton.
So, it would rise about a quarter degree.

If density varies over the area, temperatres could get much higher
than this. For example, say the asteroid was 1/10th the diameter -
600 km - thatmeans temperatures rise 26 degrees for a period of time
- 1/100th the diameter - 60 km - from 0.25 km - the temperature rises
to 260 degrees for a period of time - enough to boil the oceans over a
60 km diameter region.


Alain Fournier- Hide quoted text -

- Show quoted text -

blowing up the asteroid doesn't change its center of mass.

It makes far more sense to guide it somewhere it won't do any harm -
or better yet - might have some value.
.

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