The primary means of energy generation is going to solar. It will at least be a plurality, and probably be a slight majority in the long term.

Boeing just took $20 billion and 10 years to improve the efficiency of their planes by 10 percent. That's pretty lame. I have a design in mind for a vertical liftoff supersonic jet that would be a really big improvement.

I'd like to dial it back 5% or 10% and try to have a vacation that's not just e-mail with a view.

In order for us to have a future that's exciting and inspiring, it has to be one where we're a space-bearing civilization.

I realized that a methane-oxygen rocket engine could achieve a specific impulse greater than 380.

I tend to approach things from a physics framework. And physics teaches you to reason from first principles rather than by analogy.

It was obvious to me that we could never colonize Mars without reusability, any more than America would have been colonized if they had to burn the ships after every trip.