He spent some time in radar intercept control and battle management, including tours in Alaska and Korea, but worked mainly as an astronautical engineer, managing satellite operations, engineering, and advanced propulsion research. In the latter capacity, he met and became inspired to write by physicist and author Dr. Robert L. Forward. He retired as a major at the end of 1989 and began submitting stories in 1990, using the "G. David" form of his name for fiction (though lately it has migrated to articles as well) and Gerald D. for technical papers, the intent being to separate the work in computer author searches.

As a writer, his main interest is the future of human exploration and settlement of space, and his stories typically focuses on the dramatic aspects of individual lives within the broad sweep of a plausible human future. Trying to keep up with just what is plausible is a challenge, but he recycles his research for occasional nonfiction articles. He continues to write a few pieces of short fiction eachyear, but is currently concentrating on novels, with three complete books looking for publishers and two more in serious production efforts. The Black Hole Project, a novel in five parts written with C. Sanford Lowe,was published as a series in Analog. in 2006-2007. A collection of linked Mars-related stories was published as an electronic book by ScorpiusDigital in September 2001, with a print version appearing in 2003 (sold out). He is a four-time winner of the AnLab, the Analog reader's award for best story or article of the year, and has also been a Hugo and Nebula awardnominee.