[ExI] Asteroid on track for possible Mars hit

[Eugen Leitl]

On Sat, Dec 22, 2007 at 12:41:09PM -0800, spike wrote:

> Hmmm, ja, but I don't expect it to be much less than 100kg.  We need a
> spherical plutonium core surrounded by high explosive with a damper shell,
> next to a heavy hydrogen device.  For this application, I expect it to
> exceed 100.

Even a Davy Crocket could be easily carried by a single grunt. 
Modern fusion devices are the size of a large orange/grapefruit.
You wouldn't need a damper shell, you'd want to flash the
facing face of the asteroid/comet into a thin layer of plasma;
preferrably iteratively. I don't know that the lowest payload
would be (and if I knew, it would be classified), but I'd hazard
more like 10 kg, than 100 kg. I'd rather bet on some 10 shots of 
10 kg payload each rather than one 100 kg shot.

> We do, but it would need a combination ground based or space based radar
> with ground guidance, combined with some pretty tricky endgame guidance
> on-board as is done with the THAAD missile.  I expect the entire package to
> be closer to about 400 to 500-ish kg, since you need guidance propulsion,
> attitude control, antennas etc. 

So you'd need guidance onboard. Still, 400 kg is not that much. 
  
> Ja we would need all of 10 km/sec methinks, but I need to do some BOTECs to
> figure out how we would do this.  I think we would need to get as close as
> possible to coming the exact opposite direction of the rock, otherwise I
> don't know if our endgame guidance authority would be sufficient for a hit
> with current technology.  

We don't want a direct hit. We want a detonation some 100-1000 m during flyby,
so we'd get asymmetric ablation and deflection, instead of fragmenting
the sucker into hundreds to thousands of bolides-to-be. That cure might
be way worse than the disease.
 
> I doubt we could get out to the object, match its velocity and attempt a
> soft landing (the required delta V is way too high.)  So the biggest

While not having your background, this is my impression as well.

> technological challenge might be how to detonate the device within the time
> tolerance when the closing speeds might be in access of 20km/sec.  The
> precision needed to do this is tech we don't currently have.  At 20 meters
> per millisecond, if the device detonates 10 milliseconds too early, 200
> meters might be too far away to do much.  A millisecond too late and the
> impact destroys the device without detonating.

You'd need a pearlstring of successive detonations, not a single on-off bet.

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
______________________________________________________________
ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org
8B29F6BE: 099D 78BA 2FD3 B014 B08A  7779 75B0 2443 8B29 F6BE