When reading space exploration related articles, I often come across the use of "former" to classify astronaut's status. NASA even puts "former astronauts" as a separate classification on their pages, describing the status as:
Former astronauts are those who have left NASA, including those who are deceased.
This use of "former" seems a bit awkward to me, especially since NASA doesn't really hold any exclusive rights to the use of the word "astronaut". For example, we usually don't call Ernest Shackleton a "former explorer". Deceased yes, but he was a polar explorer. So my question is:
Is "astronaut" an official title, a job description, or a life achievement? Should we use the word "former", and when would it be appropriate to use it?