These are highly predictable, and well within our technological capability, but they just don't occur that frequently. Great for the occasional probe, but they can't be counted on for a mining colony that is depending on a 100 ton payload supply every six months or so.

Remember, this whole thread is about a business operation on the asteroid belt. We're talking simple, straightforward, cheap, repeatable operations, an industrial effort, not a one-shot-deal scientific triumph. And every move requires a plan B when the inevitable screw-up happens.

We're not there yet, and at our current level of technology, we're not going to be there ever. Now if we achieve a ten or hundredfold increase in exhaust velocity, maybe we could do something.

But although we can't rule out any new tech that doesn't violate physical law, neither can we count on it. Right now, chemical rockets can get us to the outer planets. Ion drives, light sails and fission propulsion could make exploration routine. But industrial exploitation is going to require fusion power, at the very least. And we can't even get that to work here on the ground, much less in a machine that will fit on a spacecraft.

I can't rule out we might get lucky tomorrow, but today, I don't want my pension plan investing in this enterprise.