Something felt awfully familiar about 50 Million Km when I read it. For some reason it reminded me a lot of works by the (in)famous author named IM Dal-Young. I guess it does share a number of themes with series made by the guy. I'm not going to list them here and I'm not going to recommend reading every series by that author either, but if you found 50 Million Km interesting, you might want to give at least The Legend of Maian a try. It's one of IM Dal-Young's better works (most of the others are not that great and\or have some massive flaws).
Yeah, this is one of those gut feel recommendations...