Clark was the author of "Ignition! An Informal History of Liquid Rocket Propellants" (Rutgers University Press, 1972), based on his experiences in the field, which he dedicated to his wife Inga. It chronicles the development of liquid rocket fuel technology through both technical explanations of the work scientists performed and also anecdotes about the people involved and the often humorous incidents which took place. Copies of the original edition, now out of print, are rare and sell for over $400. In May 2018 Rutgers University Press began publishing "Ignition! An Informal History of Liquid Rocket Propellants" again.