He was one cool guy. "IF" you wrote him a well crafted and neatly typed (or written) letter he would answer in kind. Especially if the subject of your letter was a query about some of the science he wrote about. When I was a teenager I wrote him a letter that my science teacher prompted me to write and got an answer. (My teacher made me re-write it several times until he was sure it was free of mistakes)
Sadly I left it at my Mom's house and it got ruined when her basement flooded.
Niven does/did the same. I did send an SASE.
/johnny
We were just discussing the old time pulp editors last night. They mentored the writers and they were accessible to the fans.
I had a 20-minute conversation once with John Campbell. A straightforward sort of guy, witty, well-read, polite.
Those were the days.