Donuel,

"You misunderstand, Gravity tractors can delay or speed up asteroids to miss Earth. "

I do understand what you mean, but we do NOT have a deployable gravity tractor at this time, nor in the immediate future.


"Pure research that is not profit driven may enable needed discoveries like deflectors."

Agreed.

"Not even mining the moon of isotopes of Helium is not yet cost effective. Making a buck off space is a Trump mindset that sounds good while pure research is one of the harder things to sell to Congress."

Actually, the water found by a program I was on (Clementine/DSPSE) at the south pole of the moon would be cheaper than launching it from earth for lunar colonies/bases and deep-space missions. The potential yield of even a small asteroid in usable metals would be significant, and would be cheaper IN ORBIT than earth-produced by the launch costs ( hopefully going down, by for now a significant amount).


"I have a mental picture of a dramatic day on Earth when a less than moon sized body struck the pacific area in a trajectory slightly east to west and up from the equator. BAM the collision sent more material up into orbit that the impact body. The heavier elements in the Earth came up as the molten crater filled in."

A theory that is making the rounds- but it would have been 3-5.5 billion years ago, when the earth was a lot hotter.

Mr. Shaw,

http://theweek.com/speedreads/667239/nasa-scientist-warns-earth-due-extinctionlevel-event

I will presume you don't bother with accident insurance, either.

Mr. Red,

"The effort to get to Mars with people is going to be a very expensive venture. The Newtonian reality is the energy needed to get peeps and supplies is never going away. And getting them back needs more energy."

It requires energy, but we have the technology today to do it.

"Solving the problems of bone loss and muscle atrophy are not small projects. Once you get peeps to Mars could they stand up/walk and do anything useful? If the answer was yes it implies yet more bulk (and energy) to get it all there."

Currently, a centripetal force base ( centrifuge , spinning spacecraft, or two linked spacecraft tethered together) is the best we can do- but it can be done. We would only need Mars normal gravity, about 1/3 g. ISS has proven that long duration zero gravity can be withstood by appropriate exercise routines.