----- Original Message ----From: Brice Yokem <[log in to unmask]>

On Thu, 17 Apr 2008 10:14:57 -0700, Craig Lalley <[log in to unmask]> 
wrote:

>Wirt Atmar <[log in to unmask]> wrote:
> [in response to my comment: likening the comment/asteroid and a geosynchronous satellite to a car and a fly hitting the windshield] 
>
>>In contrast, if your car were in space, every fly impact would alter your 
course
>>a bit. Because of the severity of this effect, NASA has studied a number of
>>alternatives to pushing a gazillion tonne asteroid out of the way.

[Tom] I do agree, to a point, that in the [near]zero-friction environment of space that a collision would have more impact [no pun intended], but I still find it hard to believe that the the relative mass and speed of a geosynch satellite would be sufficient to change the trajectory of a comet/asteroid to change the "probability" on the scale that this kid in germany was claiming [what was it, two orders of magnatude? something like 45,000 --> 450 right?]

Lately, I've taken up curling -- shoving 40+ pound rocks around on a sheet of ice -- except for the possibility of a bad ricochet, I'd be willing to have you try to change the trajectory of my throw [so that I'd miss] using nothing more than one shot from a BB gun :)  [of course, that depends on whether I'd have hit or not in the first place, and no fair shooting me in the arm!]

As you inferred by pointing to the other article, however, I could see you managing this with a much larger caliber gun...  (or a significantly higher muzzle velocity than a typical BB gun provides)

>  Off topic as usual.
>
>  I remember seeing a picture awhile back, where a paint chip severly 
damaged the Challenger's windshield (1983), the paint chip hit at about 
18,000mph IIRC.
>
>  I couldn't find the picture, but it documented here
>  http://tinyurl.com/5h6q82
>
>  One scarry quote.
>
>"The paint chip would likely have punctured the spacesuit of an astronaunt 
involved in extravehicular activity".
>

[Brice] I think the space suits are self-sealing, where a paint chip going
fast enough will disintegrate and the resulting hole in the space 
suit will then be sealed up.

[Tom] at that speed, what's to say the paint chip, (or it's disintegrating-particles), would necessarily stop once it reached the astronaut inside the suit?  This is more to the point Wirt is making [and which I agree with] -- even a very tiny mass /can/ have a devastating effect /if/ the speed differential is great enough.  (by this I mean that "in space" you don't really have a any reference point to judge the speed of the paint chip -- it could be stated that the Challenger hit the "stationary" paint chip at 18,000 MPH and be just as accurate of a statement.)  

Of course, having admitted that, I might have to rethink what I said before -- though I still doubt it, I would have to agree that the speed differential between the "stationary" [relative-to-the-earth] satellite and the Haulin' Mass Asteroid would be sufficient enough that anything from a glancing blow to a head-on encounter might cause a significant deflection in the trajectory.

[Brice] My concern is, if the asteroid can come that close, what are the 
chances of it hitting the moon, and what would be the consequences?


[Tom] Hmmm.... sounds like the log-line of next summer's blockbuster movie...(too late to film it for this year...)


ok -- that's enough armchair physics for me :)

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