The value of this "act of mining" in the stratosphere is just symbolical, but yeah - all out life consists of symbols and that's a really challenging way of advertising their project.
What I mostly liked in the article you provided is the following: "We even hear word that NASA is researching the possibility of using blockchain technology for communication and navigation in space".
Just imagine how NASA is interested in super-safe blockchain technology. That really could be a prospective product which personally I even would like to invest in.