Naturally, there's got to be a limit for I don't expect to live forever, but I do intend to hang on as long as possible.

All of a sudden, space isn't friendly. All of a sudden, it's a place where people can die. . . . Many more people are going to die. But we can't explore space if the requirement is that there be no casualties; we can't do anything if the requirement is that there be no casualties.

We're forever teetering on the brink of the unknowable, and trying to understand what can't be understood.

But life is glorious when it is happy; days are carefree when they are happy; the interplay of thought and imagination is far and superior to that of muscle and sinew. Let me tell you, if you don't know it from your own experience, that reading a good book, losing yourself in the interest of words and thoughts, is for some people (me, for instance) an incredible intensity of happiness.

Emotionally I am an atheist. I don't have the evidence to prove that God doesn't exist, but I so strongly suspect he doesn't that I don't want to waste my time.

Isn't it sad that you can tell people that the ozone layer is being depleted, the forests are being cut down, the deserts are advancing steadily, that the greenhouse effect will raise the sea level 200 feet, that overpopulation is choking us, that pollution is killing us, that nuclear war may destroy us - and they yawn and settle back for a comfortable nap. But tell them that the Martians are landing, and they scream and run.

Do not forget that a traitor within our ranks, known to us, can do more harm to the enemy than a loyal man can do good to us.