[TML] Solution to the near-c rock question

[Timothy Little]

On Fri, Feb 01, 2008 at 12:58:10PM -0800, Brad Murray wrote:
> 20 tons or so.  Big for a scientific package but not logistically
> impossible.

That wouldn't be enough.  They used as an example Apophis, meaning the
spacecraft can't get closer to the center than about 200 m.  That
means the gravitational acceleration of the asteroid toward the craft
about 3*10^-11 m/s^2.  The article said one year of thrust 10-20 years
before impact.  One year of thrust provides a velocity of approximately
0.001 m/s.  20 years of drift with that speed gives 700 km deflection.

Not enough by an order of magnitude.  A 200-tonne craft might do it,
but not with any margin of safety.  Hovering for 10 years instead of 1
could also do it - and would be more feasible than sending a craft 10
times larger.


- Tim