6 ms·

A very naive question, but could we rotate an asteroid apart? Suppose we continuously hit it with a laser at an angle, so the resulting heat would cause a bunch

A very naive question, but could we rotate an asteroid apart? Suppose we continuously hit it with a laser at an angle, so the resulting heat would cause a bunch of small explosions and impart angular momentum, until it rotated so quickly that it simply tore itself apart.

thereisnospork 8y ago
Probably not - but it is easy enough to deflect an asteroid's trajectory to avoid earth. Over astronomical distances simply heating a portion of the asteroid can provide enough thrust to sufficiently avoid a collision.
- A2017U1 8y ago
  I believe you need enough advance warning and it's actually quite _simple_ as far as these things go. Always surprised how little science there is in this stuff, both detection and diversion it is a real existential threat to humanity given enough time and yet militaries around the world are out there tilting at windmills spending all their cash on outdated bloated acquisition projects to kill each other better in the most peaceful time on Earth.
  - sagartewari01 8y ago
    The reason is probably same as the reason toddlers aren't afraid of guns.
- throwaway5752 8y ago
  Is that easy? To hit the right spot on a 1km target from a n x 10^9 km (presumably from space and lifting the necessary equipment, otherwise include correcting for atmospheric distortion?). Also, wouldn't power / beam dispersion be a big problem?
  - chmod775 8y ago
    It should be significantly easier in space thanks to the lack of an atmosphere that would mess with your beam. I tried to figure out just how accurately we are able to point stuff in space and found out the hubble telescope is able to "lock onto a target without deviating more than 7/1000th of an arcsecond, or about the width of a human hair seen at a distance of 1 mile." [1] That's pretty amazing to me. Though I'm not sure if that would be enough, or whether we can be even more accurate. With a laser beam it might also not be a problem if you're just slightly inaccurate, say only hitting your mark 70% of the time as long as you still manage to heat your target spot up sufficiently. [1]: https://www.nasa.gov/mission_pages/hubble/story/index.html https://www.nasa.gov/mission_pages/hubble/story/index.html
    - throwaway5752 8y ago
      I was more interested in the dispersion aspect of it. I'm not a specialist in this area, but I think a good dispersion rates for a high powered laser is in the area of 0.3 mrad regardless of the medium of transmission. And with that dispersion, targeting an object as far as Jupiter (600M km) would mean the beam would be 180,000km wide when it arrived. Since people smarter than me have floated this as a way of deflecting asteroids, I assume there's some kind of way to focus it over those distances? It seems nontrivial though.
onetimemanytime 8y ago
Hit it with a laser or whatever force far away and 1mm movement over there means that earth is saved and then some.
Someone 8y ago
To be able to hit a specific part of the asteroid, you either have to wait until it is very close, or you would need very good aim. Also, there’s beam divergence (https://en.wikipedia.org/wiki/Beam_divergence https://en.wikipedia.org/wiki/Beam_divergence). That has a theoretical lower limit (http://www.aml.engineering.columbia.edu/ntm/level1/ch02/html/l1c02s02.html http://www.aml.engineering.columbia.edu/ntm/level1/ch02/html...). Reading https://www.reddit.com/r/askscience/comments/1ihca9/how_much_does_a_laser_beam_spread_over_distance/ https://www.reddit.com/r/askscience/comments/1ihca9/how_much..., that limit is about 1:3000, so a laser beam is at least 100 km wide at the earth-moon distance. I guess you would want to start rotating that asteroid way earlier, and that you would want to hit asteroids smaller than that. That makes it practically infeasible (Given infinitely precise aim, you theoretically still would be able to hit it only at one side, by aiming off-target, but that would wasting most of your beam energy) Also, I am not convinced evaporating the surface by heating it from an angle would significantly impart angular momentum.
- 19870213 8y ago
  One of the asteroid redirection ideas is to have a probe with a laser evaporate part of the asteroid, the exhaust would then impart a force to nudge it off course. If caught earlier enough it's sufficient to prevent a collision with Earth.

thereisnospork 8y ago

Probably not - but it is easy enough to deflect an asteroid's trajectory to avoid earth. Over astronomical distances simply heating a portion of the asteroid can provide enough thrust to sufficiently avoid a collision.

A2017U1 8y ago
I believe you need enough advance warning and it's actually quite _simple_ as far as these things go. Always surprised how little science there is in this stuff, both detection and diversion it is a real existential threat to humanity given enough time and yet militaries around the world are out there tilting at windmills spending all their cash on outdated bloated acquisition projects to kill each other better in the most peaceful time on Earth.
- sagartewari01 8y ago
  The reason is probably same as the reason toddlers aren't afraid of guns.
throwaway5752 8y ago
Is that easy? To hit the right spot on a 1km target from a n x 10^9 km (presumably from space and lifting the necessary equipment, otherwise include correcting for atmospheric distortion?). Also, wouldn't power / beam dispersion be a big problem?
- chmod775 8y ago
  It should be significantly easier in space thanks to the lack of an atmosphere that would mess with your beam. I tried to figure out just how accurately we are able to point stuff in space and found out the hubble telescope is able to "lock onto a target without deviating more than 7/1000th of an arcsecond, or about the width of a human hair seen at a distance of 1 mile." [1] That's pretty amazing to me. Though I'm not sure if that would be enough, or whether we can be even more accurate. With a laser beam it might also not be a problem if you're just slightly inaccurate, say only hitting your mark 70% of the time as long as you still manage to heat your target spot up sufficiently. [1]: https://www.nasa.gov/mission_pages/hubble/story/index.html https://www.nasa.gov/mission_pages/hubble/story/index.html
  - throwaway5752 8y ago
    I was more interested in the dispersion aspect of it. I'm not a specialist in this area, but I think a good dispersion rates for a high powered laser is in the area of 0.3 mrad regardless of the medium of transmission. And with that dispersion, targeting an object as far as Jupiter (600M km) would mean the beam would be 180,000km wide when it arrived. Since people smarter than me have floated this as a way of deflecting asteroids, I assume there's some kind of way to focus it over those distances? It seems nontrivial though.

onetimemanytime 8y ago

Hit it with a laser or whatever force far away and 1mm movement over there means that earth is saved and then some.

Someone 8y ago

To be able to hit a specific part of the asteroid, you either have to wait until it is very close, or you would need very good aim. Also, there’s beam divergence (https://en.wikipedia.org/wiki/Beam_divergence https://en.wikipedia.org/wiki/Beam_divergence). That has a theoretical lower limit (http://www.aml.engineering.columbia.edu/ntm/level1/ch02/html/l1c02s02.html http://www.aml.engineering.columbia.edu/ntm/level1/ch02/html...). Reading https://www.reddit.com/r/askscience/comments/1ihca9/how_much_does_a_laser_beam_spread_over_distance/ https://www.reddit.com/r/askscience/comments/1ihca9/how_much..., that limit is about 1:3000, so a laser beam is at least 100 km wide at the earth-moon distance. I guess you would want to start rotating that asteroid way earlier, and that you would want to hit asteroids smaller than that. That makes it practically infeasible (Given infinitely precise aim, you theoretically still would be able to hit it only at one side, by aiming off-target, but that would wasting most of your beam energy) Also, I am not convinced evaporating the surface by heating it from an angle would significantly impart angular momentum.

19870213 8y ago
One of the asteroid redirection ideas is to have a probe with a laser evaporate part of the asteroid, the exhaust would then impart a force to nudge it off course. If caught earlier enough it's sufficient to prevent a collision with Earth.