The space shuttle was often used as an example of why you shouldn't even attempt to make something reusable. But one failed experiment does not invalidate the greater goal. If that was the case, we'd never have had the light bulb.

The revolutionary breakthrough will come with rockets that are fully and rapidly reusable. We will never conquer Mars unless we do that. It'll be too expensive. The American colonies would never have been pioneered if the ships that crossed the ocean hadn't been reusable.

We have the resources to build room for a trillion humans in this solar system, and when we have a trillion humans, we'll have a thousand Einsteins and a thousand Mozarts. It will be a way more interesting place to live.

Russia does not have in its possession any trustworthy data that supports the existence of nuclear weapons or any weapons of mass destruction in Iraq and we have not received any such information from our partners as yet.

The nuclear approach I'm involved in is called a traveling-wave reactor, which uses waste uranium for fuel. There's a lot of things that have to go right for that dream to come true - many decades of building demo plants, proving the economics are right. But if it does, you could have cheaper energy with no CO2 emissions.

The only enemy is ignorance. Peace, people. Let's get rid of all this nuclear testing.