Author Topic: Preventing asteroid disaster (via laser)  (Read 6366 times)

Offline sandrot

  • Extreme Veteran
  • Full Member
  • ****
  • Posts: 749
  • Motown
  • Liked: 5
  • Likes Given: 5
Re: Preventing asteroid disaster (via laser)
« Reply #20 on: 03/02/2007 04:10 pm »
I'm reading on the PPT that 40 kw are enough to deviate an asteroid if applied over the course of 1 year.
"Paper planes do fly much better than paper spacecrafts."

Offline meiza

  • Expert
  • Senior Member
  • *****
  • Posts: 3068
  • Where Be Dragons
  • Liked: 3
  • Likes Given: 3
Re: Preventing asteroid disaster (via laser)
« Reply #21 on: 03/04/2007 07:55 pm »
TyMoore - 1/3/2007  2:29 AM

You know, maybe something really 'low' tech might work just as well. If a thin mylar sheet were tensily formed into a circular parabolic reflector, say 1km across with a focal length of say 20km--standing off from an asteroid, such a mirror would intercept:

1350 W/m^2 * pi*(500m)^2 = 1.060 GW of solar power at 1 a.u. from the sun.

If the overall optical efficiency was only 60% and could focus onto a spot say 50m across, the effective irradiance on that spot would be about:

0.60*1060MW/(pi*(25m)^2) = 0.324 MW/m^2  or about 240 suns. Going with a higher 'quality' optical system that allows spot size to shrink to 10m across would put the equivalent of 8.10 MW/m^2 or about 6000 suns on the spot.

Knowing absolutely nothing else about the composition of the 'asteroid' I would have to say that even though this is formidable, I don't think it is enough to cause significant volatilization of the surface materials unless they were composed of ice, or were very rich in volatiles. 6000 suns sounds like enough to melt iron and silicates but you'd probably need closer to 50,000 suns worth of irradiance to get a good vapor jet going.

Just a hunch though...

I don't know optics very well but afaik you run into trouble when trying to focus sunlight very tightly, since the sun is not a point source. Something in the vein that the radiation density that the object sees when looking at the mirror can not be higher than that of the surface of the sun. That should enable pretty hot stuff anyway, especially if the mirror is close to the asteroid. Then the mirror fills a large portion of the object's sky and the density need not be high for high wattage.

I wonder about the various asteroid compositions and their volatility. Could perhaps some additive be carried that would lower the boiling point? From a quick google, only iron iodide has a "low" boiling point of 1000 deg Celsius, and iodine is heavy. Carbon and silicon are very different then too...

Offline publiusr

  • Elite Veteran
  • Full Member
  • ****
  • Posts: 1540
  • Liked: 1
  • Likes Given: 2
Re: Preventing asteroid disaster (via laser)
« Reply #22 on: 03/30/2007 07:56 pm »
A powerful space based laser would be good for defense purposes, and might be good for pushing/assisting solar sails; STEADY communication/power transmission TO extra-solar probes; the illumination of objects studied by such such probes, etc.