Ask for recommendations from friends or in science fiction reading groups. People who share your preference for clean reads can point you to some great science fiction books. They might know of some under - the - radar authors or books that have a positive, clean message and are still engaging in the science fiction realm.
Online bookstores like Amazon also have filters. You can search for science fiction books and then use the filter options to find those that are appropriate or 'clean'. For example, you can look at the reviews and ratings to see if there are any mentions of inappropriate content. Also, some indie bookstores online might specifically promote clean reads in the science fiction genre.
You can try your local library. Libraries usually have a wide selection of science fiction books, and they are often curated to be suitable for a general audience, which means they are 'clean'. Another option is to look for well - known publishers' websites. Many publishers focus on producing family - friendly or 'clean' content, and their science fiction offerings can be great.