[Nate]

I thought it was Douglas Adams. He said they'd attempted to fuel spaceships with monarchy but they weren't very popular with noble families.

I thought it was in Mort.

EDIT: Yup, I was right:



The only things known to go faster than ordinary light is monarchy, according to the philosopher Ly Tin Weedle. He reasoned like this: you can't have more than one king, and tradition demands that there is no gap between kings, so when a king dies the succession must therefore pass to the heir instantaneously. Presumably, he said, there must be some elementary particles -- kingons, or possibly queons -- that do this job, but of course succession sometimes fails if, in mid-flight, they strike an anti-particle, or republicon. His ambitious plans to use his discovery to send messages, involving the careful torturing of a small king in order to modulate the signal, were never fully expanded because, at that point, the bar closed.

-- (Terry Pratchett, Mort)

EDIT AGAIN: I think you're getting confused with the Douglas Adams quote about the spaceship powered by bad news.