
Directed Energy Planetary Defense and Relativistic Probes - chr1
http://www.deepspace.ucsb.edu/projects/directed-energy-planetary-defense
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fitzwatermellow
Happened to catch rockstar astrophysicist Neil deGrasse Tyson on Charlie Rose
the other night and the subject of asteroid deflection came up. For small
candidates, vaporization would be ideal. But for larger ones, any attempt at
destroying them may have unwanted consequences. Debris fields, partial
cleaving, etc. Sending a team of human miners with demolition expertise is not
in the cards. So the current vogue in asteroid deflection would be to send
something heavy to intercept the asteroid and deflect it a degree or two using
only gravitational pull! A very clean and elegant solution that would no doubt
make a great simulation or video game ;)

Mission Concepts and Operations for Asteroid Mitigation Involving Multiple
Gravity Tractors

[http://www.ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201...](http://www.ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120013195.pdf)

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mabbo
The point isn't the vaporize them, it's to nudge them ever so slightly.

Consider a comet- you fire one or more lasers to a specific spot on the comet,
causing heat. The heat causes the water to expand, and shoot off from the
comet. Does this destroy the comet? Certainly not much of it. But as that
water vapor shoots away from it, Newtons Third Law comes into play and the
comet, ever so slightly, is pushed in the opposite direction.

You may rightfully say that this would be a very minuscule push, so what good
will it do? Well, if you play Kerbal Space Program you'll quickly learn that
tiny nudges can have huge effects in the long-run, especially on big orbits.
Add a few mm/s to the velocity of a comet two years ahead of time, and it can
make the difference between that comet hitting a planet, or not. It can mean
the comet is ever so slightly closer to Jupiter, causing it to be pulled by
its gravity just a bit more.

~~~
jerf
For the "larger ones" that fitzwatermellow was mentioning, the problem is that
your mental model of a big rock starts breaking down. You'd be closer to think
"big gravel pile sort of iced together, sort of held together by local gravity
because there's nothing else pulling them apart". You shoot a little pulse at
the gravel pile and break a piece off and it may simply fly out into space,
taking almost all the momentum with it and not affecting the bigger body at
all. You apply a big force and you might just send rocks _through_ the pile,
with, again, the rocks going through taking most of the momentum you applied
with them. (Same for landing a booster on it... there may be nowhere you can
boost where the booster doesn't just drill right through and come out the
other side.) Hit it harder and it may simply spread out.

The advantage of the gravity towing approach is that gravity affects the
entire pile equally; it doesn't matter how tenuously the whole thing is held
together. This approach could literally deflect a mountain-sized ball of pure
sandbox-grade sand, completely and correctly. That's not something a lot of
other approaches can say. It's only downside is that it's miserably slow, so
you have to call the problem years in advance.

~~~
Retric
The problem with gravity pull is you first need to mach orbits which takes a
long time or a lot of delta V. From an energy and complexity perspective your
best bet is to impact with a large low mass object like foam or lots of tiny
objects like a cloud of sand. The advantage being just about any orbit that
gets you there works and high relative velocity's are good. The problem is
it's easy to miss.

A solar sail is a solid candidate as you get a large low mass object and
'free' delta V at the same time.

PS: Due to risk of malfunction you likely want to send several ships anyway,
while the miss chance is an issue, the cheaper direct approach lets you take
more chances.

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jlebrech
can this be weaponised to direct asteroids to a particular place on earth?
just asking for a friend.

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JulianMorrison
My guess is no. Reason: steering towards is a smaller target than steering
away. If you can only point a laser from over here, it's hard to steer an
asteroid any way except "thataway" (normal to the most visible surface).

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viggity
unless the asteroid was closer to the sun than the earth, then you could push
it so it hit earth 6 months from when you pushed it.

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LinuxBender
What is our next move when it shoots back?

~~~
simonebrunozzi
LOL!

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JulianMorrison
Welp, it's officially the future once we have planetary defense laser bases.

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Terr_
> DE-STAR or Directed Energy System for Targeting of Asteroids and exploRation

Ugh! "exploRation"?

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executive
Naming it DEath-STAR is probably not the best way to build public support.

~~~
defiblep
Have you _met_ geeks?

> sufficient warning

Well, yes, quite. Wouldn't we be better off making sure we can reliably find
them first?

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privong
> Wouldn't we be better off making sure we can reliably find them first?

People are already are working on that. For example, there's the NEOWISE
project[0], which used the Wide-field Infrared Survey Explorer to look for
potentially dangerous astroids. And there is a ongoing effort for a new space
mission, NEOCAM[1], specifically designed to do this same thing and find more
objects.

[0]
[http://neo.jpl.nasa.gov/programs/neowise.html](http://neo.jpl.nasa.gov/programs/neowise.html)

[1] [https://en.wikipedia.org/wiki/Near-
Earth_Object_Camera](https://en.wikipedia.org/wiki/Near-Earth_Object_Camera)

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bakhy
has anyone checked out the relativistic probes claim? what potential speeds
are we talking about? and, i presume, there are no brakes? :D

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brotaku
Trying to force asteroids away are we?

