[TML] Solution to the near-c rock question

[Jerry W Barrington]

On 2/1/08 6:39 PM, "Timothy Little" <tim at little-possums.net> wrote:

> 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.

In that particular case, all they want to do is miss a 2000ft keyhole in
space.  A few 100 km works fine for that.  For the larger case of missing
the Earth itself, yeah, that's probably not enough (unless it was only
barely going to hit).

> 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.

Or keep sending small 1-year craft over and over.  :)