I am never as clear about any matter as when I have finished writing about it.

Our family was very fond of the University of Iowa. We thought it was a good place to go.

I'm one of the most durable and fervent advocates of space exploration, but my take is that we could do it robotically at far less cost and far greater quantity and quality of results.

I think we need someone in a responsible political position to have the courage to say, 'Let's terminate human spaceflight.'

In a dispassionate comparison of the relative values of human and robotic spaceflight, the only surviving motivation for continuing human spaceflight is the ideology of adventure. But only a tiny number of Earth's six billion inhabitants are direct participants. For the rest of us, the adventure is vicarious and akin to that of watching a science fiction movie. At the end of the day, I ask myself whether the huge national commitment of technical talent to human spaceflight and the ever-present potential for the loss of precious human life are really justifiable.

My position is that it is high time for a calm debate on more fundamental questions. Does human spaceflight continue to serve a compelling cultural purpose and/or our national interest? Or does human spaceflight simply have a life of its own, without a realistic objective that is remotely commensurate with its costs? Or, indeed, is human spaceflight now obsolete?

Certainly one of the most enthralling things about human life is the recognition that we live in what, for practical purposes, is a universe without bounds.