Small asteroid misses Earth by only four thousand miles

On 27 Aug 2004 23:47:58 -0700, Lou Scheffer wrote:

/snip

LOL, hilarious ))

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!

Or short, C.R.A.N.K

--
The butler did it.

On Sat, 28 Aug 2004 10:24:32 -0700, Hop David wrote:
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".

Hm... A burn 2 AU away from Earth would be more than susceptible to random
perturbations that would kill your error margin.

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.

I figure you'd need an even smaller margin for error since a 10 meter
asteroid would need to skip going into much denser atmosphere. Otherwise
You'd end up with just another Tunguska blast. And that's not our
intention, is it?

Most definitely you'd need to do some subtle course corrections after the
initial burn. In any case, it would probably be doable as it's not that big
of a mass.

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.

Nope! As I've read (and Henry nicely pointed out), it was aerobraking
alright!

--
The butler did it.

Ugo wrote:
On Sat, 28 Aug 2004 10:24:32 -0700, Hop David wrote:

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".


Hm... A burn 2 AU away from Earth would be more than susceptible to random
perturbations that would kill your error margin.

Just about anything would kill such a narrow error margin. This was
exactly my point.



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.


I figure you'd need an even smaller margin for error since a 10 meter
asteroid would need to skip going into much denser atmosphere. Otherwise
You'd end up with just another Tunguska blast.

Um... No. The Tunguska object was thought to be around a 100 meters. A
10 meter object would cause less damage. Most likely it would burn up
harmlessly in the upper atmosphere.

And that's not our
intention, is it?

Most definitely you'd need to do some subtle course corrections after the
initial burn. In any case, it would probably be doable as it's not that big
of a mass.

Yup. And I said as much.




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.


Nope! As I've read (and Henry nicely pointed out), it was aerobraking
alright!

(rereading Henry's post. . .) He was talking about the advantages of doing
delta vee burns deep in a gravity well. He mentioned MCO's burns were done
quite deep in the Martian gravity well, deep enough were very small
navigation
errors caused it to plunge in Mars atmosphere. I imagine lithobraking
occured shortly after.

The point remains: close to surface navigation errors can lead to impact.


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

Ugo wrote:


Or short, C.R.A.N.K


Mike? Mike Varney? Is that you?

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

On 2004-08-30, Hop David wrote:

Nope! As I've read (and Henry nicely pointed out), it was aerobraking
alright!

(rereading Henry's post. . .) He was talking about the advantages of doing
delta vee burns deep in a gravity well. He mentioned MCO's burns were done
quite deep in the Martian gravity well, deep enough were very small
navigation
errors caused it to plunge in Mars atmosphere. I imagine lithobraking
occured shortly after.

Within an orbit, at least; it's possible that the burn managed to raise
the altitude high enough to manage an orbit rather than just
intersecting, although it would have been a rather short orbital
lifespan...

The point remains: close to surface navigation errors can lead to impact.

Mariner C!

--
-Andrew Gray

On Sun, 29 Aug 2004 23:16:58 -0700, Hop David wrote:

Ugo wrote:


Or short, C.R.A.N.K


Mike? Mike Varney? Is that you?

Errr... Last time I checked... Nope!?

--
The butler did it.

On Sun, 29 Aug 2004 23:14:56 -0700, Hop David wrote:

Ugo wrote:
I figure you'd need an even smaller margin for error since a 10 meter
asteroid would need to skip going into much denser atmosphere. Otherwise
You'd end up with just another Tunguska blast.

Um... No. The Tunguska object was thought to be around a 100 meters. A
10 meter object would cause less damage. Most likely it would burn up
harmlessly in the upper atmosphere.

I thought it was around 50-60 meters, but still, your estimate's better
than mine. Am I right in thinking that a 10 meter object would give a
kiloton range energy yield? If the object were coming in at a very shallow
angle (like approaching the perigee), wouldn't it be able to survive deeper
into the atmosphere, maybe even reaching the ground? Granted, the damage
there would be negligible, but still...

(rereading Henry's post. . .) He was talking about the advantages of doing
delta vee burns deep in a gravity well. He mentioned MCO's burns were done
quite deep in the Martian gravity well, deep enough were very small
navigation
errors caused it to plunge in Mars atmosphere. I imagine lithobraking
occured shortly after.

Hardly. I read the MCO mishap report and the best estimate given of the
actual periapsis altitude was 57 kilometers. The original targeted altitude
was about 220 kilometers and the lowest estimated survivable altitude was
some 80 kilometers. I doubt any actual lithobraking occured, the only thing
reaching the surface would be leftover debris in freefall.

--
The butler did it.

In article ,
Hop David wrote:
(rereading Henry's post. . .) He was talking about the advantages of doing
delta vee burns deep in a gravity well. He mentioned MCO's burns were done
quite deep in the Martian gravity well, deep enough were very small
navigation errors caused it to plunge in Mars atmosphere.

Basically correct, but that should be burn, singular. The advantages of
doing the orbit-insertion burn at the lowest possible altitude caused the
planners to choose an insertion altitude not far above the atmosphere,
which put a premium on accurate navigation.

I imagine lithobraking occured shortly after.

Drastic aerobraking was sufficient to kill MCO, alas. Debris would have
been down to quite low velocities by the time it reached the surface.

(There is some possibility, depending on exactly when attitude control was
lost and when the solar array broke off, that MCO -- somewhat damaged and
minus its solar array -- might have survived its atmosphere pass to make
one orbit of Mars. However, that orbit would have had a perigee so low
that there wouldn't have been a *second* orbit.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Ugo wrote:
On Sun, 29 Aug 2004 23:14:56 -0700, Hop David wrote:


Ugo wrote:

I figure you'd need an even smaller margin for error since a 10 meter
asteroid would need to skip going into much denser atmosphere. Otherwise
You'd end up with just another Tunguska blast.

Um... No. The Tunguska object was thought to be around a 100 meters. A
10 meter object would cause less damage. Most likely it would burn up
harmlessly in the upper atmosphere.


I thought it was around 50-60 meters,

That also sounds like the right ballpark.

but still, your estimate's better
than mine.

Huh? Why's that? I get most of my info from Google or Usenet. I'm
certainly no authority.

Am I right in thinking that a 10 meter object would give a
kiloton range energy yield? If the object were coming in at a very shallow
angle (like approaching the perigee), wouldn't it be able to survive deeper
into the atmosphere, maybe even reaching the ground? Granted, the damage
there would be negligible, but still...

Yes, I believe an object coming in from a small v inf and shedding a lot
of velocity in the less destructive upper atmosphere _would_ have a
better chance of reaching the ground.

Here is an excerpt from "Rain of Iron and Ice" by John S. Lewis:

"... the ability of a body to survive in the atmosphere depends on
whether its crushing strength exceeds the aerodynamic pressure generated
by its passage through the atmosphere. The aerodynamic 'ram' pressure is
proportional to the square of the velocity of the body; slow bodies are
much better able to penetrate than fast ones." (bottom of page 61, top
of page 62).

Some bodies have a much higher crushing strength than others. A
monolithic metallic asteroid has a better chance of penetrating than a
carbonaceous rubble pile.


To be honest the 10 meter ceiling I threw out was a wild ass guess. But
I believe some sort of size ceiling should be set for imports brought
into earth orbit by aerobraking.

But my opinion remains that delta vee savings vs risk looks a lot better
for aerobraking a 10 meter than a 100 meter object.



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

Ugo wrote:
On Sun, 29 Aug 2004 23:16:58 -0700, Hop David wrote:


Ugo wrote:


Or short, C.R.A.N.K


Mike? Mike Varney? Is that you?


Errr... Last time I checked... Nope!?


(sorting newsgroup by Sender...) I notice this is the only recent ssp
thread you've participated in. So I'm guessing you are reading this from
alt.astronomy.

Varney's recent arguments in ssp have consisted of nothing more than
name calling (so far as I've seen).

I sometimes harbor erroneous opinions. I like to believe if someone
gives a clear explanation of why I'm wrong, I quickly change my views.

In fact exactly that has happened earlier in this thread. I believed
asteroid capture was easier further out from earth's gravity well. Henry
Spencer showed me I was wrong and now I have one less wrong opinion.

However if your arguments consist only of this C.R.A.N.K. b.s., you have
no chance of persuading me. I'll just assume you're an obnoxious idiot.

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