Kent Paul Dolan wrote:
"Malcolm Street" wrote:

All you need to do is get a dinosaur-killer-sized
asteroid into orbit closer than the moon without
risking it hitting the earth.

No, and no. You don't have to start with something
10 km in diameter, 200 m in diameter is a huge good
start for just getting a lot of mass available that
isn't at the bottom of (quite so deep) a gravitational
well, and you don't have to get it physically closer
than the material on the moons surface, just
energetically closer, which any stable Lagrangian
point orbit would suffice to accomplish.

Right, but 200m is still way too big - that's about 8 million tons. For
a first attempt, go for about 20m diameter - about 8,000 tons.

Now that Smart-1 has proved humankind capable of doing
space the slow and steady way, what _are_ the
implications for robotically shipping a "rock" from
the asteroid belt to L5, probably (I have no clue how
to do the math) simpler than diverting something in a
profoundly non-circular solar orbit, like an earth's
orbit transiting asteroid, if one is willing to be
patient.

Forget asteroid belt rocks, there are NEOs which can be captured with
just 169m/s Delta V. Lets assume a Delta V requirement might be 300m/s.
Exhaust velocity might be 30,000 m/s, so you'd need to "burn" 1% of the
asteroid, or 80 tons in a plasma engine. That's why I keep asking
about Oxygen fuelled plasma engines, since oxygen is a fuel that can be
got from most asteroids, or the moon.


And, what constitutes a big enough "rock" to be worth
the effort?

NEOs - 8,000 tons is plenty for starters - it would:

1. Provide shielding for a base for dozens of people.
2. Allow, assuming suitable techniques, the manufacture of a 100 MW
solar array
3. Allow, assuming suitable techniques, a mission to be assembled to
fetch a NEO with a mass of 200,000 tons.