What Makes Hard Science Fiction "Hard?"

From Author Wars - https://authorwars.com/books/what-makes-hard-science-fiction-hard-999789.html

Overview:

Title: What Makes Hard Science Fiction "Hard?"
Author: David Clayton
Year: 1986
Type: Essays

Editions/Publications:

Unknown. Hard Science Fiction (Unknown, David Clayton, Southern Illinois University Press, ISBN-10: 0809312344, , xvi+284 pages, Hardcover, Non-fiction)