Crack Dust, Black Dust
written by Anne McCaffrey
This title remains unpublished in this form.
A short story
Analog editor John W. Campbell requested "to see dragons fighting Thread", Pern's menace from space, and he also suggested time travel. In response, McCaffrey wrote a short story titled "Crack Dust, Black Dust", which was not separately published, but provided crucial material for the novel Dragonflight.