Acronyms are a part of modern life. GPS instead of Global Positioning System; TV instead of television; CSI instead of Crime Scene Investigation, etc. streamline speech. Since the best writing is tight writing, feel free to use them in your story. Remember to define them at first usage, a standard practice in technical writing.

This can be done in a variety of ways. When I was a NASA technical writer the standard format was to write “Global Positioning System (GPS)” but there are others ways that work. Some authors use the acronym initially and include its definition in a footnote. Others would say “Global Positioning System, or GPS.”

An occasional reminder doesn’t hurt, either, especially if you have several in your story. If that’s the case, you might even want to include a list in the beginning or end of the book.