Elon Musk says

“If humanity is to become multi-planetary, the fundamental breakthrough that needs to occur in rocketry is a rapidly and completely reusable rocket … achieving it would be on a par with what the Wright brothers did. It’s the fundamental thing that’s necessary for humanity to become a space-faring civilization. America would never have been colonized if ships weren’t reusable.”

More on this...

“We need to take all heavy industry, all polluting industry, and move it into space. And keep Earth as this beautiful gem of a planet that it is.”

“We need unifiers, not vilifiers. When you look out at the planet, there are no borders. There’s nothing. It’s one planet and we share it and it’s fragile.”