The public perception of Black astronauts is best summed up by a line from the TV show "Archer".  That they are so rare they are like unicorns.  The truth is while there have been fewer than our African American share of the population would imply there have been many Black Americans involved in the space program, including astronauts since day one.  Everything big and important done by the United States of America, in peace and war, has been a team effort.  We have never had a diversity problem, but a problem of inclusion.  

This documentary demonstrates what real inclusion looks like.  

Among the current and retired astronauts appearing are former NASA administrator Charles Bolden who describes having grown up in the segregated south.  Going to segregated schools then finding opportunity in the military.  Military service is a common thread for them all.  Indeed, a common thread for most space travelers of any nation to this day. Guy Bluford the first Black astronaut to fly in space says the best way to overcome the challenges one faces is to keep the ultimate goal in mind.  To be patient, hang in there, and don't quit.    This well sums up the message from most of these fine people.  

From what I can tell NASA does a pretty good job of this, without pandering, they simply hire the best people possible for the job, then treat them according to written rules and policies.  Hold them to the same standard, not higher, or lower, than anyone else.   When this is done diversity, equity, and inclusion occur without any loss of quality.  This is simply real fairness in practice. It's easy to do and yet so rare. 
General Advice For Non-Traditional STEM professionals:

This points to qualities to look for in an employer that would apply far beyond the astronaut corps. 

If you are a minority or someone who in any way does not fit the molds of who the public thinks should be a STEM professional* seriously consider government work.  By this I mean anyone who would not look like the picture drawn during a "Draw A Scientist test".  You are not just White, not just Male, not just middle aged or older.  IF you are not all three of those things this advice applies to you.  (To a White male reading this, as you age this will apply less but many leave STEM to do other things before middle age).    

The best source of work for young- mid career STEM professionals are public colleges and universities.  Working adjunct, visiting professor, post doc etc will give you real experience you can build on.  Save up money while you do this, preferably via an investment based government backed pension plan.  Always keep an eye out for a permanent position, or just a better contract position while you do.  The key is to work for places that while you have a contract with them will treat you with fairness.  While teaching expect 5%-10% of the students to have spurious problems and be very loud about it.  Public colleges and universities will be able to dissipate that kind of static much more easily.