Small asteroid misses Earth by only four thousand miles

In article ,
Hop David wrote:
... (In practice, you would probably want to limit the apogee
of the resulting elliptical orbit to well below lunar altitude, to make
sure there weren't any unwanted lunar gravity assists...

Elsewhere I opined that apogee should be within Earth's Sphere of
Influence.

Apogee within Earth's SOI is indeed the minimum requirement. In practice
you'd want to be *well* within it, because solar perturbations are
noticeable out near its boundary, and the delta-V difference is slight.

But I hadn't thought of the moon.

Mind you, one or two well-planned lunar gravity assists could be useful as
part of capture maneuvering. But if you don't want to keep making
occasional adjustments to avoid undesired lunar flybys, eventually you'll
want an orbit that doesn't cross the Moon's, and an apogee well below
lunar altitude is the simplest way to arrange that.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"Louis Scheffer" wrote in message
...

In fact, with perfect aim, a huge amount of guts, and a complete disregard
for the environment, you could capture a km size asteroid this way.
Just come on in, plow through atmosphere, then the Pacific ocean at a
shallow angle (hydrobraking?), go back up to the moon, get deflected, and
you've done it all with no fuel. Of course, even in the best case, you
have
deposited a substantial fraction of the full impact energy into the ocean,
so you'll still get monstrous tsunamis, boiling oceans, nuclear winter,
etc., basically as if a slightly smaller asteroid had hit directly.
However
you have captured a great natural resource without using any fuel. A
perfect
project for (a) a mad scientist, or (b) a Republican admistration energy
czar.

Very funny.

Still, you do make the point that bringing NEO's into Earth's orbit might be
perceived as dangerous, even if every possible precaution is taken. It
would give the anti-nuke protestors something new to worry about. It seems
like they're always convinced that every launch or fly-by of the earth by
anything remotely "nuclear" on it is going to result in total destruction of
all life on earth. ;-)

Jeff
--
Remove icky phrase from email address to get a valid address.

In article ,
Carsten Nielsen wrote:
The dominant hazard *is* objects perturbed from the main asteroid belt,
with an important secondary threat from comets (perturbed from the Kuiper
Belt or the Oort Cloud, farther out).

How about the remnants of the K-T event on Yucatan ?
I read that 12 % of the ejecta escaped...

Long gone. The survival time for small objects in an orbit very similar
to Earth's is short, because they'll make frequent (by geological time
standards) close encounters with Earth, which will alter their orbits
rapidly. (Close encounters are much more likely than actual hits.) The
timescale for them to be driven into the Sun or out to Jupiter (and thus
out of the solar system), or, less likely, to hit an inner planet, is
millions of years, not even tens of millions.

Is there not a remarkable
amount of 1.00xx year objects compared with the others on neo ?

Not that I'm aware of, once you allow for observational selection effects.
(The smaller objects are seen only when quite close, and tracked well
enough for orbit determination mostly when making a relatively slow
encounter, which strongly biases the selection toward near-Earth orbits.)

And if the Moon gets rearended, a good part of the ejecta must have
lunar escape speed, but not enough speed to escape Earth thereafter.
That must be how the meteorites identyifyed as moon rock got here.

It doesn't even have to be a rear-end impact, since ejecta go out in a
wide range of directions.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Jeff Findley wrote:


Very funny.

Still, you do make the point that bringing NEO's into Earth's orbit might be
perceived as dangerous, even if every possible precaution is taken. It
would give the anti-nuke protestors something new to worry about. It seems
like they're always convinced that every launch or fly-by of the earth by
anything remotely "nuclear" on it is going to result in total destruction of
all life on earth. ;-)

Jeff

Fear of aerobraking Toutatis isn't quite the same as anti-Cassini
hysteria (at least in my opinion).

--
Hop David
http://clowder.net/hop/index.html

"Hop David" wrote in message
...
snip
Elsewhere I opined that apogee should be within Earth's Sphere of
Influence. But I hadn't thought of the moon.
snip

And just imagine if the calculations are off, we bring this thing into an
orbit that has it collide with the moon just days before the budget for the
project runs out.

BV.

Carsten Nielsen wrote:

How about the remnants of the K-T event on Yucatan ?

I read that 12 % of the ejecta escaped.

Cite? This would be interesting info for the panspermia arguments I
sometimes participate in.

Is there not a remarkable
amount of 1.00xx year objects compared with the others on neo ?

I don't see that. The folks at jpl list four .99 year, seven 1.00 and
eight 1.01 year NEOs. For comparison there are three 1.99, five 2.00 and
six 2.01 year NEOs and four 2.99, six 3.00 and two 3.01 NEOs.


--
Hop David
http://clowder.net/hop/index.html

In article ,
Hop David wrote:
Still, you do make the point that bringing NEO's into Earth's orbit might be
perceived as dangerous, even if every possible precaution is taken. It
would give the anti-nuke protestors something new to worry about...

Fear of aerobraking Toutatis isn't quite the same as anti-Cassini
hysteria (at least in my opinion).

Indeed, fear of aerobraking Toutatis is thoroughly justified. :-) That
asteroid in particular almost certainly isn't one solid piece... and it's
big enough to make one hell of a mess if anything goes wrong.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Hop David wrote in message ...
Jeff Findley wrote:

Fear of aerobraking Toutatis isn't quite the same as anti-Cassini
hysteria (at least in my opinion).

Anyone who is scared of Cassini should be terrified of asteroids. Do
you know that an average asteroid is 0.008 ppm by weight of uranium,
known to be a poisonous and radioactive substance?? Assuming a 10 km
cubical asteroid of density 10, it weighs 10^16 kg, of which 80
*million* kg is uranium!

And it gets even worse. The Earth's crust is 1.4 ppm uranium, on the
average. So if the asteroid vaporizes an equal wieght of crust,
that's 14 BILLION kg of uranium, or more than 2 KG of uranium FOR
EVERY MAN, WOMAN AND CHILD ON EARTH! Do you have any idea of what
would happen if you breathed 2 kg of vaporized uranium?? You'd DIE,
that's what! The government limit for breathing uranium(well, the
Canadian government, but we'll take their word on this) is 0.05
MILLIGRAMS per cubic meter. 2 kg is 40 MILLION times 0.05 mg!!!
You'd be doomed!!! And that's from just the poisonous effects!

But uranium is also *radioactive*. Fortunately, it's not as
radioactive as plutonium 238 (in fact it's about 50,000,000 times less
per weight, since it has a 5 billion year half life instead of 100
years.) Even taking this into account, though, the 14 billion kg of
uranium dust will have the radioactivity of 280 kg of plutonium, or
about NINE Cassinis worth!!! Since the radioactivity from Cassini's
RTGs was enough to kill everyone on Earth if properly spread out (say
evenly divided and then implanted into everyone's pituitary gland, a
likely result of a launch accident), then the radioactivity from an
asteroid impact is enough to KILL EVERONE ON EARTH 9 TIMES OVER!!!!
That's *at least* 9 times as bad as being killed once!

So if you were against Cassini, the time to stand up and be counted is
now! We need to pass a law, right away, forbidding any asteroid
impacts on Earth!! Join our organization, Citizens for Regulation of
Asteroid/Nuclear Katastrophes, today! And if any impact is scheduled
near you, rush immediately to the site and DEMAND that it be stopped
IMMEDIATELY. And don't let them try to talk you out of it with so
called 'rational arguments'. We KNOW this stuff is dangerous!

(Lou Scheffer) wrote:

So if you were against Cassini, the time to stand up and be counted is
now! We need to pass a law, right away, forbidding any asteroid
impacts on Earth!! Join our organization, Citizens for Regulation of
Asteroid/Nuclear Katastrophes, today! And if any impact is scheduled
near you, rush immediately to the site and DEMAND that it be stopped
IMMEDIATELY. And don't let them try to talk you out of it with so
called 'rational arguments'. We KNOW this stuff is dangerous!

Hey... this is NOTHING compared to the number of deaths every year from
dihydromonoxide. You want to talk about a really dangerous chemical,
that's the one!

http://www.gumbopages.com/fridge/dmho.html

--
"I argue very well. Ask any of my remaining friends. I can win an argument
on any topic, against any opponent. People know this, and steer clear of me
at parties. Often, as a sign of their great respect, they don't even invite
me." -Dave Barry

Lou Scheffer wrote:
Fear of aerobraking Toutatis isn't quite the same as anti-Cassini
hysteria (at least in my opinion).


Anyone who is scared of Cassini should be terrified of asteroids. Do
you know that an average asteroid is 0.008 ppm by weight of uranium,
known to be a poisonous and radioactive substance?? Assuming a 10 km
cubical asteroid of density 10, it weighs 10^16 kg, of which 80
*million* kg is uranium!

Let's say a burn is done 2 AU from earth on an asteroid that would
normally miss earth by 4 LD. The goal is to send it skimming along the
upper reaches of earth's atmosphere to shed velocity so we could bring
it into earth orbit.

The course change is about 3/10 of a degree. A .00003830 degree error
would change "aerobraking" to "lithobraking".

This would be reasonable for a 10 meter asteroid. It'd possible to do
last minute course corrections. And if it did hit earth it wouldn't wipe
out a continent.

It would be hard to do last minute course corrections with Toutatis.
Possibly more difficult than correcting MCO's course which, if I read an
earlier post right, was a Martian probe that litho instead of
aerobraked. It would be bad if Toutatis lithobraked.


So if you were against Cassini, the time to stand up and be counted is
now! We need to pass a law, right away, forbidding any asteroid
impacts on Earth!! Join our organization, Citizens for Regulation of
Asteroid/Nuclear Katastrophes, today! And if any impact is scheduled
near you, rush immediately to the site and DEMAND that it be stopped
IMMEDIATELY. And don't let them try to talk you out of it with so
called 'rational arguments'. We KNOW this stuff is dangerous!


Aerobraking a 10 km asteroid is safe because it's only 0.008 ppm by
weight of uranium? And it'd be even more safe if it were 20%
dihydrogenmonoxide?

Sorry, these "rational" arguments don't persuade me.

--
Hop David
http://clowder.net/hop/index.html