There are several of Andre Norton's books available for free download on Project Gutenberg, including The Time Traders
I enjoyed her books as a teen in the mid 60s.
Trivia:
In the early 70s I’d shop at a used bookstore in Butler Plaza on 436 in the Winter Park area (central Florida). The owner told me that Andre Norton lived in the area and came into the store on occasion. The owner said she (Norton) valued her privacy and would not say any more. I thought it was interesting that an author I liked was so nearby. It would have been nice to have crossed paths and met her.