60,000 kilometres per second may be the practical (!) speed limit for space travel - Isaac Asimov

It all had a beginning in the original cosmic explosion, whatever that was, and it'll all have an end when all the stars run down. Some run down faster than others. Hell, the giants won't last a hundred million years. The sun will last ten billion years and maybe the dwarfs will last two hundred billion for all the good they are. But just give us a trillion years and everything will be dark. Entropy has to increase to maximum, that's all. (Lupov)

You are a practical man, Elijah. You do not moon romantically over Earth's past, despite your healthy interest in it. Nor do you stubbornly embrace the City culture of Earth's present day. We felt that people such as yourself were the ones that could lead Earthmen to the stars once more.

The best way to describe anyone is to give an example of the kind of thing he would do.