Writing a novel is like trying to solve a very long mathematical equation. Changing anything can change everything else.

First rule in government spending: why build one when you can have two at twice the price?

Since, in the long run, every planetary society will be endangered by impacts from space, every surviving civilization is obliged to become spacefaring — not because of exploratory or romantic zeal, but for the most practical reason imaginable: staying alive.

Scientists constantly get clobbered with the idea that we spent 27 billion dollars on the Apollo programs, and are asked "What more do you want?" We didn't spend it; it was done for political reasons. ... Apollo was a response to the Bay of Pigs fiasco and to the successful orbital flight of Yuri Gagarin. President Kennedy's objective was not to find out the origin of the moon by the end of the decade; rather it was to put a man on the moon and bring him back, and we did that.

.. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the 'Momentary' masters of a 'Fraction' of a 'Dot'

Our children long for realistic maps of the future that they can be proud of. Where are the cartographers of human purpose?

The truth may be puzzling. It may take some work to grapple with. It may be counterintuitive. It may contradict deeply held prejudices. It may not be consonant with what we desperately want to be true. But our preferences do not determine what's true.