[ExI] De-Orbiting Gold

[BillK]

On Sun, May 20, 2012 at 5:43 PM, Kelly Anderson wrote:
> Ok, so what about a limited version of how they put the mars rovers
> down? heat shield, Air bags, parachutes, that whole gig?  Again, you
> don't have to get it down to 5 Gs, just 200 Gs... so it doesn't have
> to have the full size parachute and so forth... Is that going to be
> terribly expensive? Is the weight of the whole mass what will cause
> the problem?
>
>

I think we have to remember that these recovered asteroids will have
to be small.

Nobody will be allowed to send a large object towards earth with the
intention of aerobraking it into orbit. Safety precautions would have
to assume the worst case scenario that something could go wrong and
the asteroid might dive straight into the atmosphere. Energy = mass x
velocity.  So it would have to be small enough that mistakes would
burn up harmlessly high in the atmosphere.

How small is safe?

I think Spike's 7 meter total diameter is too big. You don't want
anything that makes a crater.  :)

I suspect we are probably considering pretty small asteroids, (maybe
about football size) which might well be suitable for the type of
landing you are describing. But as I think Spike mentioned, you then
have the cost problem of getting your landing equipment up into orbit
and attaching it to a small asteroid for retrieval. So the value of
the package retrieved may not cover the cost of retrieval.

Alternatively, if you have lots of these tiny asteroids in orbit (like
we don't have enough space junk in orbit already!) you could have a
robot shuttle type vehicle which could go up and wander around
scooping up these asteroids and filling up the hold, before re-entry.
A similar type of robot vehicle has already been proposed for cleaning
up space junk in earth orbit.


BillK