[ExI] Mining the Sky SL Talk I gave today

[spike]

> ...On Behalf Of samantha
> ...
> >>
> >> Cool idea, especially if we can manage to do the re-entry 
> without a 
> >> control system and without a thruster...
> 
> So it is not possible to de-orbit an object like an asteroid 
> in such a 
> way as to ensure that it lands in some fixed size deserted area?   I 
> don't see why this would be so... - samantha

It isn't impossible, just very difficult.  It's one of those chaos things: a
very tiny uncartainty in the input makes an enormous uncertainty in the
output.  In the case of an asteroid, the unknowns in the aerodynamics makes
it durn near impossible to guess where it would land.  

Recall that a typical reentry event would have the asteroid tearing thru the
upper atmosphere at a very high velocity on the first pass, scrubbing just
enough velocity to send it into a highly eliptical orbit.  The next pass
scrubs off more velocity, and so on possibly several times, until the
re-entry event.  Without a lot of knowledge of the aerodynamics and mass
properties of the asteroid, we have no good way to even know how many times
it would orbit the earth before re-entry.  There are also uncertainties in
the density of the upper atmosphere.  If it doesn't catch enough air, it
might go into a hyperbolic orbit, never to return, or if so, it could be
centuries from now.

spike