I started working up a short story idea in 1981 called "The Quanta", which is essentially one of the last chapters of "Forbidden The Stars". Ten years later, I began to outline the novel, finishing the first draft in 1993, but continued tinkering with it for the next two decades, releasing it in 2010.
I'd always had a trilogy in my mind, and I began outlining and writing "Music of the Spheres" April 2011, releasing it December 2011.
I started drafting "Worlds Away" early June 2012.
Basically, the trilogy took 32 years from inception to completion, though the vast bulk of it was written over the past two-and-a-half years.
Thank you for your interest!