When you have a transportation system that the price of propellant is essentially negligible something is very wrong. If you look at any other transportation system, a car, a motorcycle, a train, an oil tanker, an airliner, you name it; about a quarter to a third of the operating cost is buying the propellant.

I have a hunch the most important reason we're going to space is not known now.

A NASA astronaut and a Russian cosmonaut can't be creative. He has to follow a predetermined detailed checklist written by an engineer and if he gets a little creative he'll never fly again.

I don't see anything beneficial about the US spending 100 billion dollars to go back to the moon unless we learn something new that will help us go to the moons of Saturn okay and so we ought to use that to breed new breakthroughs and to test new breakthroughs and to fund it.

At various times over 20 years, I did preliminary designs for aircraft like the Stratolaunch. For that whole time I was encouraging us to do something that almost everyone else felt you could not do.

Testing leads to failure, and failure leads to understanding

Everything looks nonsensical before it works.